2. Cellular Metabolism (HT) Flashcards

Question

What is the name of a major study that proposed the link between saturated fatty acid consumption and heart disease?

Answer 1

Seven Countries Study

Answer 2

* Carbohydrate = 4kcal/g * Fat = 9kcal/g * Protein = 4kcal/g * Alcohol = 7kcal/g

Answer 3

No more than 14 units a week for men and women

Answer 4

0.75g/kg/day.

Answer 5

Young and eldery people need more protein than adults.

Answer 6

* Enable the body to produce enzymes, hormones and other substances essential for proper growth and development * The consequences of their absence are severe

Answer 7

Relative risk: * If RR=1 -\> Risk in exposed equal to risk in unexposed (no association) * If RR\>1 -\> Risk in exposed greater than risk in unexposed (positive association) * If RR\<1 -\> Risk in exposed is less than risk in unexposed (negative association)

Answer 8

* The chemical processes that occur within a living organism in order to maintain life. * Purely a means of getting from A to B by the most efficient route.

Answer 9

Reactions can be either: * Catabolic -\> Breaking things down * Anabolic -\> Building things up

Answer 10

* Synthesis of energy * Glycolysis * Fatty acid oxidation (β-oxidation) * Breakdown of glycogen (glycogenolysis) * Breakdown of ketone bodies (ketolysis)

Answer 11

* Synthesis of storage molecules * Glycogen (glycogenesis) * Triglycerides (lipogenesis) * Synthesis of glucose (gluconeogenesis) * Synthesis of ketone bodies (ketogenesis)

Answer 12

* Relatively reduced compounds of carbon -\> Contain high amounts of hydrogen * Therefore, energy is released by oxidation

Answer 13

Quoted from the syllabus: * Partial and complete oxidation to release energy * Trapping of energy as ATP * Coupling of ATP hydrolysis to energy-requiring reactions * CO₂ and water production.

Answer 14

In vitro combustion: * 1 step * Complete conversion to CO₂and H₂O * All of the energy lost as heat and light Biological oxidation: * Controlled process, occuring in steps * Can be complete of partial oxidation (since stepwise) * (Some) Energy trapped in chemically useful form (ATP) * Also yields waste products: CO₂ and H₂O

Answer 15

* If the Gibbs Free Energy (ΔG) is negative, then the reaction can take place spontaneously * If it is not, then the reaction can be coupled to ATP hydrolysis to allow it to happen

Answer 16

ΔG = ΔH - TΔS Where: * ΔG = Gibbs Free Energy (kJ/mol - CHECK THIS) * ΔH = Enthalpy change (kJ/mol) * T = Temperature (K) * ΔS = Entropy change (J/K/mol) If ΔG is negative, then the reaction is spontaneous.

Answer 17

* Glucose * Fatty acids * Amino acids

Answer 18

No, not really.

Answer 19

* Most tissues contain about 6mM ATP * Whole body contains 75g of ATP * Whole body uses 75kg per day

Answer 20

* ADP is much lower because it is a stimulus for ATP synthesis, so ATP is rapidly resynthesised. * This is the main signal driving ATP synthesis, not a decrease in ATP!

Answer 21

ΔG = -30.5 kJ/mol (-7.3 kcal/mol)

Answer 22

* Substrate level phosphorylation * Oxygen independent * e.g. Glycolysis, etc. * 5% total ATP * Oxidative phosphorylation * Oxygen dependent * 95% total ATP

Answer 23

1. Larger macromolecules broken down to smaller ones (e.g. glucose, amino acids) 2. Small molecules degraded to common units (e.g. acetyl-CoA) 3. TCA cycle / Oxidative phosphorylation to complete oxidation to water, carbon dioxide and ATP

Answer 24

* Acetyl-CoA * Many pathways utilise or feed into acetyl-CoA, depending on conditions

Answer 25

Anabolic vs Catabolic: * Fed vs. fasted vs. starvation state * Relaxed vs. fight/flight response * Rest vs. exercise * Healthy vs. disease

Answer 26

* Physiological state (e.g. fed vs. fasted) * Organ (e.g. liver)

Answer 27

* Allosteric (millisecs) * Binding of effector to site away from enzymes active site * Usually intracellular effector * Covalent (secs to mins) * Addition/removal of molecule attached to the enzyme via a chemical bond that shares electrons * Usually in response to extracellular effector * Translocation (secs to mins) * Movement from one cell compartment to another

Answer 28

* Transcription/translation (hrs to days) * Enzyme induction or suppression * Multiple enzymes targeted together

Answer 29

Control of metabolism includes 2 main points of regulation outside the target organ: * Delivery of substrate * Substrate must be supplied from somewhere * This is done via the circulation * Transmembrane movement * Substrate must be taken up selectively * Control of membrane transporters, as well as enzyme regulation

Answer 30

Cori cycle

Answer 31

Greek: * Glycos = sugar (sweet) * Lysis = split

Answer 32

* Glucose is the primary fuel for the brain, RBCs & the renal medulla * Skeletal muscle also uses glucose majorly

Answer 33

* Anaerobic process – allows us to make ATP in the absence of oxygen * Occurs in 3 stages (energy investment / 6C splitting / energy harvest) * Occurs in the cytosol * The fate of the end products depends on the conditions of the cell * Control is mediated by “supply & demand” * Supply in terms of selecting the “best” fuel * Demand in terms of the energy needs of the cell * Glycolysis is a highly conserved pathway that occurs in virtually all cells

Answer 34

It is very hypoxic.

Answer 35

* Transport * Phosphorylation

Answer 36

* GLUT 1-4 transporters (**GLU**cose **T**ransporters) * Facilitated diffusion (Na⁺-independent) * Tissue-specific; all tissues * Specialised functions * SGLT transporters (**S**odium/**GL**ucose-co **T**ransporter) * Secondary active transport -\> Co-transport with sodium * Energy requiring, against concentration gradient * Epithelial cells of intestine, renal tubule, choroid plexus

Answer 37

All tissues.

Answer 38

* Epithelial cells of intestine * Renal tubule * Choroid plexus

Answer 39

* GLUT2 * Insulin-independent * Found in liver, kidney, intestine and pancreatic ß-cell * GLUT4 * Insulin-dependent * Found in muscle and adipose tissue

Answer 40

* Uptake dependent on plasma glucose concentration * In liver and endocrine pancreas * Uses insulin-independent GLUT2 transporters * Uptake dependent on energy needs of tissue and regulated in tissues that can also use non-glucose energy substrate * In peripheral tissues * Uses insulin-dependent GLUT4 transporters

Answer 41

* If Km \<\< physiological [S] – uptake is independent of [S] * If Km ≥ physiological [S] – uptake is highly dependent on [S]

Answer 42

* GLUT2 (insulin-indepedent) * The liver plays a key role in buffering blood glucose concentrations * The presence of GLUT2 – with a high Km (7-20mM) ensures that: * If blood glucose concentration is high – it is taken up into the liver for “storage” * If blood glucose concentration is low – the liver doesn’t take it up – sparing it for organs that need it (i.e. brain, RBC, renal medulla)

Answer 43

* GLUT2 (insulin-independent) * The pancreas plays a key role in regulation of blood glucose concentrations through the production of insulin / glucagon * The presence of GLUT2 – with a high Km (7-20mM) ensures that the pancreas can release insulin when blood glucose is high

Answer 44

* GLUT4 * This is the 'insulin-regulatable' glucose transporter, so it allows glucose uptake to be dependent on insulin levels

Answer 45

1. Glucose priming 2. Splitting of phosphorylated intermediate 3. Oxidoreduction-phosphorylation

Answer 46

* Locks glucose inside cell * Activates glucose * Maintains concentration gradient

Answer 47

* Hexokinase -\> Most tissues * Glucokinase -\> Liver, Pancreatic islets (glucose sensor)

Answer 48

Glucokinase (liver, pancreatic islets): * Co-operative kinetics * High K_m and V_max * This enables sensitivity to glucose concentration (‘glucose sensor’). At low glucose concentrations during fasting, the high Km means that glucose is not unnecessarily converted to glycogen, thereby engendering hypoglycaemia. The high Vmax means that the liver is able to rapidly convert glucose into glycogen after a meal, performing its role as an excess glucose store. * Glucokinase is induced by insulin and inhibited by cortisol, epinephrine, glucagon and growth hormone, helping the liver respond to blood glucose more efficiently. Hexokinase (most tissues): * Michaelis Menten kinetics * Low K_m and V_max * Means that glucose conversion occurs at a relatively high and constant rate, even at low blood glucose concentrations, meaning that glucose uptake into cells can occur due to maintenance of concentration gradients. * Regulation of glucose conversion (and therefore uptake) occurs by allosteric inhibition of hexokinase by G6P, which is a form of negative feedback, so that G6P levels remain constant in skeletal muscle cells.

Answer 49

Glucose-6-phosphate (this is a form of negative feedback).

Answer 50

* Glyceraldehyde 3-phosphate and dihydroxyacetone phosphate * Enzyme: Triose phosphate isomerase (TPI) * Catalytically perfect enzyme * At equilibrium, 96% of triose phosphate is DHAP * TPI deficiency is a rare autosomal recessive disorder -\> Leads to haemolytic anaemia and cardiomyopathy

Answer 51

Glyceraldehyde-3-P + NAD⁺+ P_i → 1,3-bisphosphoglycerate + NADH + H⁺ Of the original energy of glucose: • Energy in 1,3-bisPGA used directly for synthesis of ATP (later) • Energy in NADH used indirectly for synthesis of ATP (also later)

Answer 52

Substrate-level phosphorylation

Answer 53

* Substrate-level phosphorylation refers to the formation of ATP from ADP and a phosphorylated intermediate, rather than from ADP and inorganic phosphate, as is done in oxidative phosphorylation. * It is one of the two ways that respiration generates

Answer 54

* 2 ATP per glucose molecule * This is because 2 ATP is invested near the start, then 2 ATP is produced per 3C molecules generated NOTE: The pyruvate can then continue further through respiration to produce more ATP.

Answer 55

Glycolysis produces 2 ATP, 2 NADH, and 2 pyruvate molecules.

Answer 56

* Pyruvate -\> It depends on the metabolic state of the cell (aerobic or anaerobic) * NADH -\> It needs to get inside the mitochondria to participate in the ETC

Answer 57

* Cori cycle * Cahill (or glucose-alanine) cycle

Answer 58

Glycolysis is regulated by the energy needs of the cell.

Answer 59

Hexokinase is inhibited by its product, G-6-P.

Answer 60

Glucokinase is induced by insulin and inhibited by cortisol, epinephrine, glucagon and growth hormone, helping the liver respond to blood glucose more efficiently.

Answer 61

* Phosphofructokinase-1 (PFK) * It catalyses the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate * This is such an important step because it is: * Irreversible * It consumes energy * It is a committed step (Glycogen synthesis / PPP are other fates for G-6-P)

Answer 62

* Inhibited by: * ATP [IMPORTANT] * Citrate * H⁺ * Activated by: * AMP * Fructose-2,6-bisphosphate [IMPORTANT]

Answer 63

Feed-forward activation by fructose-1,6-bisphosphate.

Answer 64

* Fructose * Sucrose * Lactose * Galactose

Answer 65

* Most cancer cells produce energy from a high rate of glycolysis followed by the conversion of pyruvate to lactate, rather than oxidative phosphorylation in the mitochondria, even in the presence of oxygen * Many different reasons have been proposed for this effect but there are still many questions to be answered

Answer 66

* TCA cycle (Tricarboxylic acid cycle) * Citric acid cycle

Answer 67

* Yes, because oxygen is required in the electron transport chain FURTHER DOWN the pathway (oxidative phosphorylation) in order to regenerate NAD⁺ from NADH. * Without oxygen, NADH accumulates and the cycle cannot continue as it needs NAD⁺to run. Also, glycolysis produces lactic acid instead of pyruvate, which is necessary in the Krebs cycle.

Answer 68

* Glycolysis - Anaerobic * Krebs cycle - Aerobic * Electron transport chain - Aerobic

Answer 69

Mitochondrial matrix

Answer 70

No, it also participates in several important synthetic reactions: * Glucose * Amino acids * Haem

Answer 71

Acetyl-CoA is seen as the main susbstrate. Other intermediates can also feed into the cycle though.

Answer 72

* Different pathways of substrate oxidation converge on a small number of common molecules -\> Acetyl-CoA (which feeds into the Krebs cycle) or one of the Krebs cycle intermediates * This means that not only glucose metabolism feeds into the Krebs cycle (via glycolysis), but also fat oxidationand protein oxidation

Answer 73

After glycolysis, pyruvate is transported into the mitochondria, where it is converted to acetyl-CoA, then enters the Krebs cycle.

Answer 74

* Common intermediates can be completely oxidised to CO₂ and H₂O (allowing full oxidation of fuels) * Common intermediates can be used as starting materials for biosynthetic pathways * Produces NADH (for oxidation and energy yield) * Produces FADH₂ (for oxidation and energy yield) * Produces energy in the form of GTP (-\> ATP)

Answer 75

* NAD⁺/NADH * FAD/FADH₂ * NADP⁺/NADPH

Answer 76

NADH and FADH₂

Answer 77

Oxidising i.e. They accept electrons.

Answer 78

Enzymes that use NAD⁺ and FAD as electron acceptors, respectively.

Answer 79

E’_O = - 0.32 V

Answer 80

E'_o = -0.18V

Answer 81

Coenzymes/Cofactors (NOTE: Cofactors are molecules that assist the function of an eznyme. Coenzymes are a type of cofactor that are organic. CHECK THIS!) In the lecture, NAD⁺is named a coenzyme, while FAD is a cofactor.

Answer 82

XH₂ + NAD⁺ -\> X + NADH + H⁺ This is reversible.

Answer 83

YH₂ + FAD -\> Y + FADH₂ This is reversible.

Answer 84

* NAD+ and NADH should really be considered as substrate/product, rather than a cofactor -\> They are free to diffuse away from the enzyme * FAD and FADH₂ should be considered as a cofactor -\> They are covalently bound to the enzyme and are not free to diffuse to the inner membrane. The enzymes must be physically associated with the membrane for the ETC.

Answer 85

Acetyl-CoA enters the Krebs cycle and goes round it once. However, two acetyl-CoA molecules are produced per molecule of glucose, so if asked to name the products of the Krebs cycle per molecule of glucose, you must double the numbers.

Answer 86

* 3 NADH * 1 FADH₂ * 1 GTP (equivalent of 1 ATP) * 2 CO₂ NOTE: This must be doubled for a molecule of glucose because each glucose molecule produces two acetyl-CoA molecules that enter the Krebs cycle.

Answer 87

NOTE: This must be doubled for a molecule of glucose because each glucose molecule produces two acetyl-CoA molecules that enter the Krebs cycle.

Answer 88

* Fatty acids -\> β-oxidation * Ketone bodies -\> Ketone body oxidation * Amino acids -\> Amino acid degradation * Sugar carbohydrates -\> Glycolysis to pyruvate, then link reaction

Answer 89

No, the pyruvate produced by glycolysis must go through the link reaction to produce acetyl-CoA, which feeds into the Krebs cycle.

Answer 90

The pyruvate dehydrogenase reaction.

Answer 91

Pyruvate dehydrogenase

Answer 92

* It catalyses the conversion of pyruvate (from glycolysis) to acetyl-CoA (which can enter the Krebs cycle) * This is an important step because it is irreversible and therefore commits the glucose to respiration

Answer 93

By a specific H⁺ symport.

Answer 94

No, it is really a complex of 3 enzymes that perform 3 functions: * E₁ - Pyruvate decarboxylase / Pyruvate dehydrogenase * E₂ - Dihydrolipoyl transacetylase * E₃ - Dihydrolipoyl dehydrogenase

Answer 95

* Irreversible / energy costly * Committed steps – “points of no return” * Energy sensing

Answer 96

* There is an inactive and active form * PDH is inactivated by PDH kinase * PDH is activated by PDH phosphatase

Answer 97

* PDH is directly inhibited by NADH and acetyl-CoA * **PDH kinase** phosphorylates PDH to make it inactive * Stimulated by: ATP, NADH and acetyl-CoA * Inhibited by: ADP, pyruvate, CoA-SH and NAD⁺ * Levels upregulated by fasting, high-fat feeding and diabetes * **PDH phosphatase** dephosphorylates PDH to make it active * Inhibited by: Mg²⁺, Ca²⁺ and insulin

Answer 98

* Phosphoryl donor in protein synthesis, gluconeogenesis * Signal transduction * Translocation of proteins into the mitochondrial matrix * Conversion to ATP

Answer 99

* Embedded in inner mitochondrial membrane * Directly linked to the electron transport chain * Only enzyme common to both TCA cycle and ETC

Answer 100

* FAD is hydrogen acceptor because free energy is insufficient to reduce NAD+ * Two electrons from FADH₂ are transferred directly to enzyme Fe-S clusters and then on to ubiquinone (QH₂)

Answer 101

* Catalytically small amounts of cycle intermediates are required to oxidise large amounts of acetyl-CoA * For example, if the cycle is blocked between succinate and oxaloacetate, lots of oxaloacetate is required to react with the acetyl-CoA since it is not regenerated

Answer 102

No, it is related to demand for ATP, not substrate availability.

Answer 103

* Reactions that are used to resynthesise the intermediates of the Krebs cycle * They are important becausethe intermediates of the Krebs cycle are used in biosynthesis, so their anaplerotic reactions help maintain their concentrations

Answer 104

* It catalyses the conversion of pyruvate directly to oxaloacetate * This is an anaplerotic reaction that is used to replenish oxaloacetate when it is depleted (the reaction is triggered by a build-up of acetyl-CoA) * It allows the Krebs cycle to keep happening

Answer 105

It is activated by acetyl-CoA, which builds up when there is a lack of oxaloacetate (so it is a marker for this).

Answer 106

No, it is near constant at 6mM.

Answer 107

Adenylate kinase

Answer 108

* ATP = 6mM * ADP = 10μM * AMP = 5nM

Answer 109

It signals energy distress, resulting in activation of AMP-activated protein kinase (AMPK), which upregulates energy generating pathways and suppresses energy consuming processes within the cell.

Answer 110

* ADP -\> Signals ATP utilisation to mitochondria * AMP -\> Cytoplasmic signal to upregulate glycolysis

Answer 111

* Outer membrane = Relatively permeable * Inner membrane = Highly impermeable

Answer 112

* Electron transport chain * Krebs cycle and PDH * β-oxidation * Ketone body metabolism * Urea cycle

Answer 113

* Substrate-level phosphorylation = 5% total ATP * Oxidative phosphorylation = 95% total ATP

Answer 114

The process of ATP synthesis resulting from the transfer of electrons from NADH and FADH₂ to oxygen by a series of electron carriers.

Answer 115

Metabolism of carbohydrates, fatty acids and amino acids (mostly in the Krebs cycle) produces reduced co-factors (NADH and FADH₂), which can they been oxidised in oxidative phosphorylation to produce ATP.

Answer 116

Electron transport chain -\> A series of electron transporters embedded in the inner mitochondrial membrane .

Answer 117

1) Generation of a proton gradient * Respiration: Oxidises hydrogen carriers, transports electrons, consumes oxygen and produces water * This generates a proton gradient across the mitochondrial inner membrane 2) ATP synthesis * Uses proton gradient across inner mitochondrial membrane * Phosphorylates ADP to ATP

Answer 118

In ATP synthesis, electron transport and ADP phosphorylation are indirectly linked: 1. Movement of electrons drives proton pumping from the matrix to the intermembrane space 2. This creates an electrical and pH gradient across the inner memrbane (proton motive force) 3. Protons then move down their gradient through the phosphorylation apparatus to drive ATP synthesis

Answer 119

No, it is impermeable, which means that extrusion of H⁺creates a pH and electric potential gradient across the membrane.

Answer 120

Indirect coupling of energy release from oxidation of energy substrates to the synthesis of ATP.

Answer 121

It can be thought of as large protein complexes linked by smaller, mobile intermediates. 4 large complexes, each consisting of tens of proteins: * Complex I * Complex II * Complex III * Complex IV Linked by 2 small mobile electron carriers: * Ubiquinone (**Q**) links Complexes I and II onto Complex III * Cytochrome c links Complex III to IV.

Answer 122

* Ubiquinone (symbolised by Q) * Cytochrome (symbolised by Cyt c)

Answer 123

* The ETC features multiple redox centres allowing sequential redox reactions * The redox potential of these reactions **increases** along the ETC * This allows the transfer of electrons from NADH/FADH₂ to O₂ via the ETC

Answer 124

* Starting donor = NADH or FADH₂ * Final acceptor = O₂

Answer 125

* E'_o= +1.14V * This is a large potential difference, which is important because it maintains movement of electrons along the ETC and provides lots of energy for H⁺ pumping

Answer 126

1/2O₂ + NADH + H⁺ -\> H₂O

Answer 127

* They are groups within complexes that allow electron movement through oxidation/reduction reactions along the ETC * Different complexes have different oxidation/reduction centres * Each oxidation/reduction centre has a different affinity for the electrons, so movement continues

Answer 128

* Type of oxidation/reduction centre (e.g. haem) * Protein environment of the complex it is in

Answer 129

* Haem * Iron-sulphur centre * Ubiquinone * Copper

Answer 130

* Iron-sulphur clusters -\> In complexes I, II and III * Haem -\> In complexes III and IV, and in cytochrome c * Copper -\> In complex IV * Ubiquinone

Answer 131

Fe²⁺ ⇌ Fe³⁺+ e^-

Answer 132

Fe²⁺ ⇌ Fe³⁺+ e^-

Answer 133

Cu⁺ ⇌ Cu²⁺+ e^-

Answer 134

NADH -\> Complex I FADH₂ -\> Complex II

Answer 135

No, they both feed into complex III though.

Answer 136

No, complex II does not fully span the membrane, so no proton pumping occurs at complex II.

Answer 137

Co-enzyme Q10 (hence the symbol Q)

Answer 138

Ubiquinone

Answer 139

It is highly hydrophobic.

Answer 140

Note: Ubiquinol is then passed to complex III.

Answer 141

Transports 1 electron from complex III to IV.

Answer 142

* The process itself requires 4 cytochrome c molecules (i.e. 4 e^-), which enable 4 protons to be moved and one O₂ molecule to be reduced * However, each NADH or FADH₂ donates 2 electrons, so 2 NADH or FADH₂ molecules are required to reduce an O₂ molecule * To get round the doubling up situation you often see it referred to as 2 cytochrome c, ½ O₂ and 2 H⁺ pumped

Answer 143

ATP synthase

Answer 144

* F₀ * F₁

Answer 145

It reverses.

Answer 146

* Adenine nucleotide translocase (ANT) * This moves ATP out into the intermembranal space, while moving ADP into the matrix * This discharges the electrochemical gradient (i.e. the proton gradient created by the ETC)

Answer 147

The phosphate pump.

Answer 148

* Discharge of the proton gradient stimulates the electron transport chain * This in turn means that there is more need for susbtrate oxidation (e.g. use of glucose) * This is called "respiratory control" coupling

Answer 149

* Generation of heat * It is important mainly in brown adipose tissue in newborns

Answer 150

* Cells express uncoupling protein 1 (UCP1), also known as thermogenin, which is a membrane protein * It acts in parallel to ATP synthase and uses the same H⁺gradient, except it does not produce ATP * Therefore, it dissipates the gradient without producing ATP, instead resulting in non-shivering heat generation while using up the fuel to maintain the proton gradient

Answer 151

Drugs that uncouple substrate oxidation and ATP generation, leading to less efficient respiration overall.

Answer 152

2,4-dinitrophenol (a.k.a. DNP)

Answer 153

Hormones signal to metabolism in distant tissues: * The whole body's nutritional status (fed vs fasted state) * The whole body's energy needs (fight or flight requires more ATP) Metabolism in distant tissues responds by: * Taking substrate from blood into tissue * Returning substrate from tissue to blood * Diverting substrate within tissue into energy generating pathways

Answer 154

* Insulin * Glucagon * Adrenaline

Answer 155

* Released by β-cells of the pancreas * Stimulated by high blood glucose, certain amino acids and certain fatty acids * Acts on muscle, adipose and other tissues * Signals fed state and tells tissue to store fuel and breakdown glucose

Answer 156

* Released by α-cells of the pancreas * Stimulated by low blood glucose * Acts only on liver * Signals fasted state, so that glucose is released from the liver into the blood

Answer 157

* Released by the adrenal gland * Stimulated by sympathetic innervation * Acts on nearly all tissues, although effect varies between tissues * Signals the fight or flight response + Tells tissues to divert substrates towards making ATP

Answer 158

A diverse group of molecules: * Non-esterified fatty acids (a.k.a. free fatty acids) * Triglycerides (TAG) * Sterols * Phospholipids

Answer 159

* Triglycerides = TAG (this stands for triacylglycerides) * Free fatty acid = NEFA (this stands for non-esterified fatty acid)

Answer 160

1. Source of energy -\> NEFA (free fatty acids) and triglycerides 2. Structural roles -\> Phospholipids and cholesterol 3. Signalling role -\> Phospholipids, prostoglandins and steroid hormones

Answer 161

* Brain * Red blood cells

Answer 162

Advantages: * More energy dense per molecule than glucose * Rapidly mobilised and stored * Ideal for tissues with high energy demand Disadvantages: * Can’t be used by all tissues (brain, red blood cells) * Requires more oxygen to extract the energy than glucose

Answer 163

* They are digested in the lumen of the small intestine * When they have been packed into micelles, they can be taken into intestinal cells * Components are then packed into chylomicrons, which are taken via lymphatics to tissues (including muscle and adipose tissues)

Answer 164

* Bile salts in the small intestine break down large triglyceride droplets into smaller droplets * Lipases from the pancreas can now attack these smaller droplets (they require a large surface area to function) * Lipases break down the triglycerides (TAG) into free fatty acids (NEFA) and glycerol -\> This forms micelles * Micelles can now be taken up into intestinal cells

Answer 165

The microvilli-covered surface of simple cuboidal and simple columnar epithelium found in different parts of the body (e.g. the small intestine).

Answer 166

* Small fat globule composed of protein and lipid. * Chylomicrons are found in the blood and lymphatic fluid where they serve to transport fat from the intestine to the peripheral tissues.

Answer 167

* Micelles containing free fatty acids and glycerol cross the brush border membrane of intestinal cells to release the contents inside * The glycerol and fatty acids are reassembled: * First, they form 2-monoacylglycerol * Then they form 1,2-diacylglycerol * Finally, they the triacylglycerol * In other words, the triglycerides are broken down in the lumen of the intestine, taken across the membrane, and then reassembled in intestinal cells * Triglycerides, cholesterol and phospholipids are then packed into chylomicrons

Answer 168

Chylomicrons are transported in the lymphatic system to peripheral tissues.

Answer 169

* The endothelial cells of the lymphatic system have enzymes on the surface called lipoprotein lipase (LPL) * LPL hydrolyses triglycerides into free fatty acids and glycerol, enabling their uptake into adipose tissue and muscle * LPL is induced and upregulated by insulin

Answer 170

They are recombined with glycerol to form triglycerides for storage.

Answer 171

Hormone-sensitive lipase (HSL)

Answer 172

* LPL = Lipoprotein lipase * HSL = Hormone-sensitive lipase

Answer 173

Bound to albumin protein, as NEFA isn’t water soluble.

Answer 174

* Adipose triglyceride lipase * Hormone sensitive lipase (HSL) * Monoacylglycerol lipase

Answer 175

* The enzyme responsible for lipolysis is hormone-sensitive lipase (HSL). * Stimulated by adrenaline: * Adrenaline increases cAMP * cAMP stimulates PKA * PKA phosphorylates HSL, activating it * Also stimulated by fasting glucagon and thyroxine (thyroid hormone) * Inhibited by insulin: * Insulin stimulates protein phosphatase * Protein phosphatase dephosphorylates HSL, inactivating it

Answer 176

* Fed state (insulin) -\> 0.3 - 0.6 mmol/L * Prolonged exercise -\> 2.0 mmol/L * Stress/trauma -\> 0.8 - 1.8 mmol/L * Fasting -\> 0.5 - 2.0 mmol/L * Under influence of thyroxine -\> 0.6 - 0.8 mmol/L

Answer 177

* Small stores of TAG in cells provide a source of energy if need to suddenly increase oxidative phosphorylation. * TAG stores must be kept low to avoid compromising normal cell function. * If you put too much TAG into non-adipose tissue it can lead to steatosis. i.e. non-alcoholic fatty liver disease and cardiac lipotoxicity in type 2 diabetes. * Example stores in: Heart, renal cortex and skeletal muscle

Answer 178

* It has a very high metabolic demand and it is one of the organs that can use non-glucose substrates for fuel * Therefore, 60-70% of ATP in the heart comes from oxidation of fatty acids * These are supplied as NEFA-albumin, CM-TAG or VLDL-TAG (very low density lipoprotein) * If external (exogenous) fatty acid supply is insufficient, the heart will metabolise its intracellular (endogenous) TAG reserves in addition

Answer 179

Renal cortex: * Able to use various metabolic fuels: * Plasma NEFAs = \>50% * TAG (endogenous) = 40-50% * Amino acids = 5-10% * Glucose = \<1% Renal medulla: * Has poor oxygen supply so there is limited mitochondrial respiration and a more anaerobic metabolic phenotype

Answer 180

* Type I - Slow twitch * Type IIa - Slower fast twitch * Type IIb - Faster fast twitch

Answer 181

* Most oxidative (aerobic) = Type I, Slow twitch * Most glyolytic (anaerobic) = Type IIb, Faster fast twitch

Answer 182

Acetyl-CoA (and reduced co-factors are also produced)

Answer 183

1. Uptake -\> NEFAs cross the cell membrane from the blood into the cell 2. Activation -\> NEFAs converted to fatty acyl CoA 3. Carnitine shuttle 4. β-oxidation

Answer 184

Two mechanisms for fatty acid uptake: * Diffusion across the membrane via a flip-flop mechanism * Transporter-mediated uptake -\> Allows for control

Answer 185

Fatty acid translocase (FAT/CD36) -\> It is a primary transporter

Answer 186

* Intracellular fatty acids are bound to cytoplasmic Fatty Acid Binding Protein (cFABP). * This protein performs a similar role to albumin.

Answer 187

* Activated by adding a co-enzyme A molecule to their structure, which requires ATP. * This produces fatty acyl-CoA * This is catalysed by acyl-CoA synthetase (ACS). * Significance: This traps the fatty acid in the cell and commits it to a metabolic pathway (just like phosphorylation of glucose)

Answer 188

Co-enzyme A

Answer 189

Problems: * Needs to get across highly impermeable mitochondrial inner membrane to be oxidised, but there are no specific transporters for fatty acyl CoA Solution: * Carnitine shuttle * Turn the fatty acyl CoA into a molecule that can be transported * Carnitine (an amino acid derivative) can be transported, and can be conjugated to fatty acids * This is achieved by two enzymes (1 to add the carnitine on and 1 to take it back off) and one transporter (to get it across the inner membrane)

Answer 190

Inner mitochondrial membrane

Answer 191

* Carnitine Palmitoyl Transferase (CPT) 1 -\> Catalyses the conjugation of fatty acyl CoA to carnitine * Carnitine Acyl Translocase (CAT) -\> Inner membrane transporter * Carnitine Palmitoyl Transferase (CPT) 2 -\> Catalyses the reverse reaction of CPT1.

Answer 192

* Once NEFAs (in the form of fatty acyl CoA) have been taken up into mitochondria via the carnitine shuttle, in order to be used in the Krebs cycle and other pathways, they must be converted to acetyl-CoA. * Acetyl-CoA is a 2 carbon molecule, so β-oxidation is a cycle in which 2 carbons are lost from the fatty acid with each loop. * Reduced cofactors are also produced.

Answer 193

All of the oxidation occurs at the beta carbon.

Answer 194

* There are 4 different acyl CoA dehydrogenases (the first enzyme in the cycle) * Each one has a peak activity at a different fatty acid chain length

Answer 195

1. Several acetyl-CoA molecules 2. Several NADH + H⁺ 3. Several FADH₂

Answer 196

* 8 acetyl CoA units * 7 NADH + H⁺ * 7 FADH₂

Answer 197

* Acetyl-CoA goes to the Krebs cycle * Reduced co-factors go to the electron transport chain

Answer 198

The numbers are somewhat disputed. For example, glucose is sometimes quoted as between 36-38 as opposed to 30-32, but this is dependent on the assumed energy yield per redued co-factor.

Answer 199

1. Hormone sensitive lipase: * This changes delivery of fatty acids to peripheral tissues from adipose * Regulation is from an extracellular signal 2. The Carnitine Shuttle * Regulates entry of the fatty acyl CoA into the mitochondria for oxidation * Regulation is intracellular

Answer 200

* Carnitine Palmitoyl Transferase 1 (CPT1) is allosterically inhibited by malonyl CoA * Malonyl CoA is an intermediate in synthesing new fats -\> Through this inhibition it also prevents the breakdown of pre-existing fat and prevents futile cycling

Answer 201

* Systemic carnitine deficiency * Jamaican Vomiting Sickness * Medium Chain Acyl CoA Dehydrogenase deficiency

Answer 202

* Liver -\> Used as a buffer of blood glucose * Muscle -\> Provides a local store of energy for contraction

Answer 203

Glycogenesis and glycogenolysis

Answer 204

As granules in the cytoplasm.

Answer 205

10 to 40nm

Answer 206

α glucose

Answer 207

* Polymer of α glucose * Joined by mostly α-1,4 glycosidic bonds * Every 8-10 residues contain an α-1,6 bond, which allows for branching

Answer 208

* The molecule has one reducing end (start of the chain) and many non-reducing ends (ends of the branches) * The non-reducing ends are the locations of all glucose additions or removals.

Answer 209

It is not a very efficient storage form.

Answer 210

* Liver * Muscle * Most tissues store small amounts of their own use

Answer 211

* Liver -\> 10% of mass is glycogen * Muscle -\> 2% of mass is glycogen However, the total muscle mass is much greater, so muscle stores 200g while liver stores 70g.

Answer 212

In the liver: * Glycogen is converted into glucose-6-phosphate * G6P is converted to glucose, which can then be released to increase blood glucose In the muscle: * Glycogen is converted to glucose-6-phosphate * G6P enters glycolysis to generate ATP for muscle contraction

Answer 213

* We need to be able to maintain a constant blood glucose concentration for the brain, RBC and renal medulla * We need to be able to produce ATP rapidly in the absence of O₂

Answer 214

* Offers up multiple end points for rapid degradation * Increases the solubility meaning that it is easier to store close to the site of utilization

Answer 215

Note: The debranching enzyme is also involved.

Answer 216

* The major enzyme involved in breaking down glycogen is glycogen phosphorylase, which catalyses a phosphorolysis reaction that releases glucose-1-phosphate molecules from the non-reducing ends of glycogen following the attack by a phosphate molecule. * Glycogen phosphorylase is a homodimer enzyme with active sites in clefts, which allows water to be kept from the active site, but also means that the enzyme is subject to steric hinderances at branch points. * As a result, the glycogen must first be “debranched” by a debranching enzyme. This has dual function, with it having both transferase activity (that moves 3 residues from the branch to other non-reducing ends) and glucosidase activity (that hydrolyses alpha-1,6 bonds to remove the final molecule of glucose from the branch). * Glucose-1-phopshate molecules released from the glycogen molecule are then typically converted to glucose-6-phosphate by the aforementioned phosphoglucomutase enzyme. * In muscle, often this is the end of glycogenolysis, because G6P can enter other metabolic pathways, namely glycolysis, which is required in ATP production for contraction. * In the liver, the G6P may be converted back to glucose by glucose phosphatase, which occurs because the glucose phosphatase enzyme is translated at a much higher rate in the liver.

Answer 217

* Involved in glycogenolysis * Phosphorylates glucose monomers on the non-reducing ends of glycogen, releasing glucose 1-phosphate (G1P) * Name: Phosphorolysis

Answer 218

* Water must be excluded from the active site * Glycogen phosphorylase is a homodimer enzyme with active sites in clefts, which allows water to be kept out of the cleft * However, the effect of this is that the enzyme is subject to steric hinderances at branch points. * As a result, the glycogen must first be “debranched” by a debranching enzyme.

Answer 219

* It converts glucose 1-phosphate (G1P) that has been released from glycogen into glucose 6-phosphate (G6P) * In muscle cells, the G6P can directly enter the glycolytic pathway -\> 50% increase in glycolytic ATP production * In the liver, the glucose 6-phosphate is converted to glucose inside the smooth endoplasmic reticulum, ready for release into the blood NOTE: This is a reversible reaction, with the opposite reaction occuring in glycogenesis.

Answer 220

In the liver, glucose phosphatase converts G6P to glucose, ready for release back into the blood.

Answer 221

It is a bifunctional enzyme.

Answer 222

* Transferase -\> Moves 3 residues from the branch to other non-reducing end * Glucosidase -\> Hydrolyses alpha-1,6 bonds to remove the final molecule of glucose from the branch

Answer 223

* First is the conversion of glucose into glucose-6-phophate, which follows the uptake of glucose into liver or muscle cells. This traps the molecule within the cell. This phosphorylation requires ATP hydrolysis and either glucokinase (in the liver and pancreas) or hexokinase (in all cells, including skeletal muscle). * G6P is a metabolite involved in multiple metabolic pathways and therefore a glucose molecule converted to G6P is not yet committed to glycogenesis. The G6P is then converted to glucose-1 phosphate by phosphoglucomutase, which is a reversible reaction. * The first irreversible reaction is the reaction of this G1P with uridine triphosphate (a nucleoside triphosphate) to form UDP-glucose. This is catalysed by UTP-glucose phosphorylase. Pyrophosphate is the other product of this reaction and is later hydrolysed by pyrophosphatase into two phosphate molecules, which drives the reversible reaction preceding this. * UDP-glucose monomers are combined into glycogen initially by glycogenin, which acts as a primer, but after around 8 glucose molecules are in the chain, it is extended by glycogen synthase. * Glycogen synthase forms alpha-1,4 bonds to join the next monomer onto the chain. The process is energy-requiring, in the form of UTP being converted to UDP. * Branching enzyme enables branching by forming alpha-1,6 bonds at intervals of at least 4 residues. This is done by transferring 6 or 7 molecules from one of the non-reducing ends of the glycogen to a point along the chain that was synthesised earlier, as long as this attaches on a branch having at least 11 residues.

Answer 224

* It converts glucose 6-phosphate (G6P) that has been released from glycogen into glucose 1-phosphate (G1P). * This is a reversible reaction (the reverse reaction occurs in glycogenolysis) * This forwards reaction is driven by the cleavage of PPi (pyrophosphatase) by pyrophosphatase (PPi is produced as a by product of the next reaction in glycogenesis)

Answer 225

* It catalyses the reaction of G1P with uridine triphosphate (a nucleoside triphosphate) to form UDP-glucose. * It is the first irreversible reaction in glucogenesis. * Pyrophosphate is the other product of the reaction catalysed by UTPG phosphorylase and is later hydrolysed by pyrophosphatase into two phosphate molecules, which drives the reversible reaction preceding this.

Answer 226

* It is the primer and catalyst that starts the process of forming glycogen from glucose residues in glycogenesis * It is a glycosyltransferase * It is formed of two identical subunits that add glucose units (from UDP-glucose) to one another * Once the chain is 8 residues long, glycogen synthase takes over

Answer 227

* Glycogen synthase forms the α-1,4 linkages to grow the glycogen molecule * It takes over from glycogenin after 8 residues are in the chain * The cost of each limkage is 1 molecule of ATP, in the form of UTP-\>UDP

Answer 228

* 1 ATP is used by hexokinase/glucokinase to phosphorylate glucose upon entering the cell (although this is not strictly part of glycogenesis) * 1 UTP (the equivalent of 1 ATP) is used when forming UDP-glucose. The UDP from this is released when joining UDP-glucose residues by glycogen synthase.

Answer 229

* In glycogenesis, the branching enzyme that forms alpha-1,6 bonds at intervals of at least 4 residues. * This is done by transferring 6 or 7 molecules from one of the non-reducing ends of the glycogen to a point along the chain that was synthesised earlier, as long as the branch has more than 11 residues.

Answer 230

* Glycogenesis -\> Glycogen synthase * Glycogenolysis -\> Glycogen phosphorylase These two enzymes are related because they have reciprocal regulation, which means that the same hormones have opposing effects on them.

Answer 231

* Glycogen synthase is in the inactive state when phosphorylated and in the active state when it is not phosphorylated. * The opposite is true for glycogen phosphorylase. * This means that hormones that lead to phosphorylation can affect both of these enzymes in opposing manners, so that the response to physiological changes can be rapid.

Answer 232

* a = Active * b = Inactive

Answer 233

Occurs through regulation of glycogen synthase, which is in the inactive state when phosphorylated and in the active state when it is not phosphorylated: * Covalent control: * Glucagon + Adrenaline * Increase intracellular cAMP, which stimulates PKA to phosphorylate glycogen synthase (inhibiting it) * Insulin * Activates protein phosphatase-1, which dephosphorylates glycogen synthase (activating it) * Inhibits glycogen synthase kinase (GSK) which will reduce the phosphorylation of glycogen synthase (activating it) * Allosteric control * G6P -\> Activator of glycogen synthase

Answer 234

* Glycogen phosphorylase can be in the hosphorylated “active” state (a) or dephosphorylated “inactive” state (b) * Each of these states can be “relaxed” (R) or “tense” (T) * Phosphorylase a prefers the r state, while phosphorylase b prefers the t state Covalent regulation (i.e. due to hormones) tends to switch between active and inactive state, while allosteric regulation tends to switch between relaxed and tense state.

Answer 235

Occurs through regulation of glycogen phosphorylase, which is in the active state when phosphorylated and in the inactive state when it is not phosphorylated: * Covalent control: * Glucagon (in liver) + Adrenaline (in muscle) * Increase intracellular cAMP, which stimulates PKA to phosphorylate phosphorylase kinase, which will phosphorylate glycogen phosphorylase (activating it) * Insulin * Activates protein phosphatase-1, which dephosphorylates glycogen phosphorylase (inhibiting it) * Allosteric control: * In liver * Glucose -\> Transitions phosphorylase a in the relaxed (R) state to the tense (T) state * Insensitive to AMP/ATP * In muscle * AMP -\> Transitions phosphorylase b in the tense (T) state to the active (R) state * ATP and G6P -\> Inhibit this transition from T to R state

Answer 236

* It is an enzyme that phosphorylases glycogen phosphorylase, causing it to be activated and increasing glucose production * Hormonally, it it is stimulated by glucagon (in liver) and adrenaline (in muscle) -\> These increase intracellular cAMP, which stimulates PKA to phosphorylate phosphorylase kinase * Allosterically, it is activated by calcium: * Calcium binds to the d-subunit – “Calmodulin” * In muscle, the calcium is released in response to muscular contraction * In the liver it is released in response to adrenaline

Answer 237

* A branch from the glycolytic pathway * The purpose is to generate: * NADPH -\> To use in reducing reactions, such as the synthesis of fatty acids * Various different sugars, especially pentoses (5C) for nucleic acid synthesis

Answer 238

* Oxidative phase * Non-oxidative phase

Answer 239

* Hexose monophosphate shunt * 6-phosphogluconate pathway

Answer 240

In the cytosol

Answer 241

No ATP is used or produced.

Answer 242

* Oxidative -\> Irreversible * Non-oxidative -\> Reversible

Answer 243

* Synthesis of 5C sugars -\> These are used in the biosynthesis of: * ATP * CoA * NAD, FAD * RNA, DNA * Synthesis of NADPH: * Antioxidant * Used in lipogenesis

Answer 244

Glucose 6-phosphate (G6P) -\> That's why it is considered a branch of glycolysis, because glycolysis can feed into it (although glycogenolysis and gluconeogenesis can too)

Answer 245

* Glucose 6-phosphate (G6P) enters the irreversible oxidative reactions * The irreversible oxidative pathway ends in ribulose-5-phosphate * Ribulose-5-phosphate enters the reversible non-oxidative interconversions, which produces ribose-5-phosphate and a series of products that could enter glycolysis

Answer 246

* Transketolase : Moves 2 carbon units * Requires thiamine pyrophosphate as a prosthetic group * Similar in structure to E1 subunit of pyruvate dehydrogenase * Transaldolase: Moves 3 carbon units * Forms a Schiff base between the enzyme and one of the sugars * Similar in mechanism to aldolase in glycolysis

Answer 247

It is released as CO₂.

Answer 248

Pentose phosphate is more of an anabolic patehway, while glycolysis is catabolic and aims to generate lots of ATP.

Answer 249

Controlled by glucose-6-phosphate dehydrogenase, which is: * Stimulated by NADP⁺ * Inhibited by NADPH

Answer 250

The reactions are freely reversible and so the flux through them is controlled by the levels of their substrates and products.

Answer 251

* Mode 1 * When there is a need for lots of ribose sugars * e.g. In cells producing RNA * Mode 2 * When there is an equal need for NADPH and ribose sugars * e.g. In rapidly dividing cells (since NADPH is required to make deoxyribose from ribose) * Mode 3 * When there is a need for lots of NADPH * e.g. In cells synthesising fatty acids or experiencing oxidative stress

Answer 252

An imbalance between anti-oxidants and molecules such as peroxides and free radicals that can cause damage to components of the cell, including proteins, lipids and DNA.

Answer 253

* Pentose phopshate pathway produces NADPH * NADPH can be used to reduce glutathione disulfide (oxidised form) into glutathione (reduced form) * Glutathione is an antioxidant that acts by reducing peroxides to water -\> This process regenerates gluthione disulfide, so NADPH must reduce it again

Answer 254

It allows us to store excess carbohydrate and protein energy.

Answer 255

* Chemically they are opposites * But mechanistically the two processes are different * This allows for reciprocal regulation

Answer 256

* Synthesised in the cytosol of the liver * Transported to the adipose tissue for storage as TAG (triglycerides)

Answer 257

* Involves the elongation of a fatty acid chain using malonyl-CoA * Synthesis is powered by ATP & NADH * Occurs mostly in the cytoplasm of liver and lactating mammary gland

Answer 258

No, but they can do the reverse.

Answer 259

* Acetyl-CoA is converted to malonyl-CoA using acetyl-CoA carboxylase * Acetyl-CoA and malonyl-CoA are converted to acetyl-ACP and malonyl-ACP by acetyl transacylase and malonyl transacylase repectively * Acetyl-ACP and malonyl-ACP are the starting substrates for fatty acid synthesis, with an additional malonyl-CoA being incorporated with each turn of the cycle

Answer 260

Acetyl-CoA -\> The rest of the starting substrates can be synthesised from acetyl-CoA

Answer 261

Note the investment of ATP.

Answer 262

ACP (acyl carrier protein)

Answer 263

* Fatty acid synthesis involves reduction: * NADPH * Fatty acid oxidation involves oxidation: * NAD⁺ & FAD

Answer 264

Note that these are both actually cycles. In FAO, the acyl-CoA_n-2 loops back round and enters the cycle again. In FAS, the acyl-ACP_n loops back round and joins with another malonyl-ACP.

Answer 265

* 2 carbons * This is not intuitive because a malonyl-ACP molecule is added with each turn, which is 3 molecules -\> However, 1 carbon is lost as CO₂ as the molecule is incorporated

Answer 266

One ATP molecule is invested to convert each acetyl-CoA molecule to malonyl-CoA.

Answer 267

* 16 carbons * So 7 passes of the fatty acid synthesis cycle are required to make it

Answer 268

8 Acetyl-CoA + 7 ATP + 14 NADPH + 6 H⁺ **-\>** Palmitate + 14 NADP⁺ + 8 CoA + 6 H₂O + 7ADP + 7P_i

Answer 269

* Odd chain length fatty acids -\> Ggenerated through the introduction of propionyl-ACP rather than acetyl-ACP * Longer chain fatty acids -\> Produced by enzymes on the cytoplasmic face of the smooth endoplasmic reticulum * Unsaturated fatty acids -\> ER systems also introduce double bonds to long chain FAs to generate unsaturated FAs

Answer 270

Mammals lack the enzyme to introduce double bonds beyond C-9, so linoleate (18:2 cis-D9,D12) and linolenate(18:3 cis-D9,D12,D15) are considered “essential” fatty acids.

Answer 271

Fatty acid synthase (FAS)

Answer 272

* It is a dimeric enzyme, with each of the monomers being a multi-catalytic polypeptide with many functions. * It is only functional as a dimer. * In total, it has 7 different enzymatic activities and a phosphopantetheine binding domain (Don't need to know the structure or function though!)

Answer 273

* Acetyl-CoA in the mitochondria combines with oxaloacetate (OAA) to form citrate * Citrate is exported into the cytosol by a tricarboxylate transporter * In the cytosol, citrate combines with CoA-SH to form OAA and acetyl-CoA. This is an ATP-requiring reaction and is catalysed by ATP-citrate lyase.

Answer 274

CoA is often referred to in this way when it is not attached to an acetyl group (i.e. in acetyl-CoA).

Answer 275

It is transported back into the mitochondria.

Answer 276

Enzymes: * In fatty acid synthesis, enzymes are joined in a single polypeptide chain (fatty acid synthase, FAS) * In fatty acid oxidation, the enzymes are all seperate Cofactors: * In fatty acid synthesis, the intermediates are linked to ACP (acyl carrier protein) and the reductant is NADPH * In fatty acid oxidation, the intermediates are linked to CoA and th oxidants are NAD⁺ and FAD Subcellular compartments: * Fatty acid synthesis occurs in the cytosol * Fatty acid oxidation takes place in the mitochondria

Answer 277

Acetyl-CoA carboxylase -\> This is the enzyme that converts acetyl-CoA to malonyl-CoA

Answer 278

* Inactive -\> Phosphorylated * Active -\> Not phosphorylated This is a regulation point in fatty acid synthesis.

Answer 279

Allosteric regulation: * **Citrate** -\> Promotes activation of acetyl-CoA carboxylase, activating it * **Long chain fatty acyl-CoA** -\> Inhibits activation of acetyl-CoA carboxylase, inactivating it Covalent regulation (intacellular signals): * **AMP** -\> Stimulates AMPK (AMP-activated protein kinase), which phosphorylates acetyl-CoA carboxylase, inactivating it Covalent regulation (hormonal): * **Insulin** -\> Stimulates protein phosphatase 2A, which dephosphorylates acetyl-CoA carboxylase, activating it * **Glucagon/Adrenaline** -\> Stimulate PKA, which phosphorylates acetyl-CoA carboxylase, inactivating it

Answer 280

* Malonyl-CoA inhibits CPT-1, blocking transfer of FAs into the mitochondria * Hence, this promotes FAS alongside inhibiting FAO

Answer 281

Esterification

Answer 282

* 3 x Fatty acyl-CoA * 1 x Glycerol-3-phosphate

Answer 283

* Can be synthesized from the glycolytic intermediate DHAP -\> Remember – this was part of the glycerol-phosphate shuttle mechanism to get NADH into the mitochondria * Can also be synthesised from glycerol itself

Answer 284

It can be phosphorylated to provide a source of glucose during starvation.

Answer 285

* Exported inside VLDL (very low density lipoprotein) particles -\> These are made of TAGs, cholesterol and proteins, so they are very similar to chylomicrons * VLDL particles are recognised by LPL (lipoprotein lipases) on the surface of endothelial cells in capillaries of muscle and adipose cells -\> LPL hydrolyses these TAGs into FAs and glycerol * In adipose -\> These are taken up and re-esterified into TAGs * In muscle -\> The FAs are taken up for oxidation

Answer 286

Activity and expression increased by: * Insulin (in adipose) * Glucagon and adrenaline (in muscles)

Answer 287

1. GLuconeogenesis 2. Ketogenesis + Ketolysis

Answer 288

* Glycos = sugar * Neo = new * Genesis = synthesis

Answer 289

Pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates.

Answer 290

* Lactate * Glycerol * Amino acids -\> Such as alanine and glutamine * Other sugars

Answer 291

* Liver (predominantly) * Kidney cortex (smaller amount)

Answer 292

There are sections in: * Mitochondria * Cytosol

Answer 293

* Brain = 110g\* * Muscle = 30g * Renal medulla = 30g\* * Red blood cells = 25g\* (\* = cant use fatty acids) * Daily intake of glucose = ~100g * Stored glucogen in the liver can liberate 90g * Blood glucose = 15g This shows the importance of gluconeogenesis in short-term fasting.

Answer 294

12 hours -\> Beyond this, gluconeogenesis is required to make new glucose for glucose-dependne tissues

Answer 295

Mitochondrial

Answer 296

* Mitochondrial -\> It depends (e.g. lactate) * Cytosolic -\> Phosphoenolpyruvate The whole purpose of the mitochondrial reaction is to funnel products into the phosphoenolpyruvate.

Answer 297

* The conversion of phosphoenolpyruvate to pyruvate by pyruvate kinase is an irreversible reaction * The pyruvate is converted to oxaloacetate, but there is no transporter for this in the inner mitochondrial membrane, so OAA is converted to malate for transport before being converted back to OAA and then phosphoenolpyruvate

Answer 298

\* denotes any enzymes that are not present in glycolysis

Answer 299

* Glucose 6-phosphatase is only expressed here. * This is the enzyme required to convert G6P to glucose, prior to release into the blood. * The liver has this enzyme because it is involved in glycogenolysis.

Answer 300

Endoplasmic reticulum

Answer 301

* Supplied by the blood * Converted to pyruvate by lactate dehydrogenase, which requires NAD.

Answer 302

* Supplied by the blood * Converted to pyruvate by alanine aminotransferase, releasing NH₃.

Answer 303

* Supplied from the muscle * It is converted to glutamate, then alpha-ketoglutarate (losing an NH₃ in each reaction) * Alpha-ketoglutarate enters the Krebs cycle and is converted to malate, which is in the gluconeogenesis pathway

Answer 304

* Supplied from the breakdown of triglycerides into glycerol and fatty acids * It is converted to glycerol-3-phosphate, which is in turn converted to dihydroxyacetone phosphate

Answer 305

* Lactate is produced by anaerobically respiring muscle, RBCs and renal medulla * It must be converted so it is exported to the liver * The liver resynthesises glucose via gluconeogenesis, before releasing it back into blood for uptake by tissues (completing the cycle)

Answer 306

Acute: * Allosteric control by metabolites * Covalent modification by hormones Chronic: * Transcriptional control of gluconeogenic genes/enzymes

Answer 307

* Pyruvate carboxylase * Phosphoenolpyruvate carboxykinase * Fructose 1,6-bisphosphatase * Pyruvate kinase (NOTE: This is not directly in gluconeogenesis, but it can short-circuit the process, making it futile)

Answer 308

* It is stimulated by acetyl-CoA

Answer 309

* It is stimulated by glucagon

Answer 310

* It is stimulated by citrate * It is stimulated by glucagon (indirectly by fructose 2,6-bisphosphate)

Answer 311

* It is inhibited by glucagon * This is important because pyruvate kinase reverts phosphoenolpyruvate to pyruvate, essentially making the start of gluconeogenesis redundant

Answer 312

No, gluconeogenesis slows a bit. This is because ketone body metabolism begins.

Answer 313

* There is a cost to prolonged starvation -\> It is that you are using body proteins, so muscle atrophy occurs * Ketone body metabolism takes over instead

Answer 314

* Small 4 carbon molecules that are water soluble * Used as an alternative fuel to power our bodies in times of nutrient deprivation * Cannot get them from the diet, but instead the body makes them during fasting and starvation

Answer 315

Ketogenesis and ketolysis -\> Both are upregulated in fasting and starvation

Answer 316

* Production of ketone bodies * Occurs in the mitochondria in the liver

Answer 317

* Breakdown and utilisation of ketone bodies as a fuel * Occurs in the mitochondria in peripheral tissues (except the liver)

Answer 318

* Brain * Nerve cells

Answer 319

* Not in the liver -\> Because it would be a futile cycle (since that is where ketogenesis occurs) * Not in RBCs -\> Because they do not have mitochondria

Answer 320

It is an **alternative fate for acetyl-CoA** after fatty acids are converted to acetyl-CoA.

Answer 321

Fatty acids that have been released from the adipose tissue and taken to the liver.

Answer 322

* HSL (hormone-sensitive lipase) * This is the enzyme that breaks down TAGs into NEFAs and glycerol * HSL is active in fasting because there is no insulin to inhibit HSL, so NEFAs are released into the blood for uptake by the liver

Answer 323

Ketogenesis essentially follows on from fatty acid oxidation. After uptake of NEFAs, their activation, the carnitine shuttle and finally beta-oxidation, acetyl-CoA molecules are produced. Usually, they would enter an energy-generating pathway through the Krebs cycle, but here the acetyl-CoA is diverted into ketogenesis.

Answer 324

* Acetoacetate * Acetone * β-hydroxybutyrate

Answer 325

Ketogenesis only occurs when gluconeogenesis is also occuring. This is because gluconeogenesis stimulates ketogenesis.

Answer 326

Uptake is proportional to concentration in the blood.

Answer 327

* Liver doesn’t express 3-Ketoacyl CoA Transferase needed for ketolysis * This prevents futile cycling of ketones in the liver

Answer 328

Note: The intermediates are the same as in ketogenesis.

Answer 329

1) It is a glucose-sparing fuel (because the brain can use it instead of glucose) 2) It prevents wasting of muscle in gluconeogenesis

Answer 330

* Many peripheral tissues -\> Muscle, heart, kidney * Brain

Answer 331

In type 1 diabetes, ketosis is uncontrolled: * Causes much higher concentrations of ketone bodies in blood * These keto acids drop the pH * Associated with diabetic ketoacidosis, coma and death * Rapid breathing – Kussmaul breathing * Smell acetone on breath * Acid change that’s dangerous – rather than ketone per se.

Answer 332

* Malate-aspartate shuttle * Glycerol-3-phosphate shuttle The purpose of these is to transport NADH from the cytosol across the inner mitochondrial membrane, which is impermeable to NADH.

Answer 333

Malate-aspartate shuttle: * Liver and cardiac cells * Because it is more efficient Glycerol-3-phosphate shuttle: * Muscle cells * Because it is more rapid and it can work against an NADH concentration gradient

Answer 334

Malate-aspartate shuttle: * NADH is converted to NAD⁺. * Malate is transported out across the mitochondrial membrane. * An equivalent amount of NADH is then formed in the mitochondrial matrix. * It can then enter Complex I. Glycerol-3-phosphate shuttle: * NADH is converted to FADH₂ in the inner mitochondrial membrane * Electrons pass directly to QH₂

Answer 335

* The body typically turns over around 300g of proetin per day * The intake is around 100g per day * The excertion is around 100g per day

Answer 336

The protein intake each day is the same as the excretion, under normal conditions.

Answer 337

No, all protein in the body is functional.

Answer 338

* Excess amino acids are separated into a nitrogen group (for disposal) and a carbon skeleton (for energy generation) * The nitrogen group is transported to the liver and processed via the urea cycle for excretion as urea by the kidneys

Answer 339

* Nitrogen group -\> For excretion (via conversion to urea) * Carbon skeleton -\> For energy generation

Answer 340

* It is transported to the liver * It is processed via the urea cycle for excretion by the kidneys

Answer 341

The carbon skeleton enters the TCA to generate ATP (or other molecules).

Answer 342

* Essential * Non-essential * Semi-essential (i.e. conditionally essential) Note: The same classification does not relate to breakdown of amino acids.

Answer 343

* Via active sodium-linked co-transporters * The sodium gradient for this is generated by an Na⁺/K⁺-ATPase on the opposite membrane

Answer 344

* When older proteins are broken down in the body, they must be replaced. * This concept is called protein turnover, and different types of proteins have very different turnover rates.

Answer 345

* Damaged or incorrectly produced/folded proteins need to be removed * Signalling proteins need to be produced and removed as needed * Enzymes are often up/down regulated as part of regulatory mechanisms

Answer 346

Proteins that need to be broken down are tagged with ubiquitin.

Answer 347

* Proteins that need to be borken down are tagged with ubiquitin * The tagged protein then goes into proteasomes for degradation

Answer 348

Proteasome

Answer 349

* Ubiquitin ligases attach the ubiquitin to the protein * These ligases are made up of three components – E1, E2 & E3: * E1 & E2 -\> Responsible for activating the ubiquitin * E3 -\> Recognises the damaged/misfolded protein, as well as markers of an old protein

Answer 350

* Recognises damaged/misfolded proteins * It can also recognise certain N-terminal residues which signal the “half-life” of the protein

Answer 351

Angelman's syndrome: * Caused by a mutation in ubiquitin ligase * Characterised by severe motor and intellectual disability

Answer 352

* Insulin -\> Anabolic effect: * Stimulates chain initiation (effects on transcription are protein-specific) * Inhibits protein breakdown * Thyroid hormones and glucocorticoids (cortisol) -\> Catabolic effect * Other steroids (anabolic steroids) -\> Anabolic effect

Answer 353

Testosterone

Answer 354

* It must be deaminated * This is because the α-amino group prevents catabolism

Answer 355

The removal of an amino group from an amino acid. It is done so that amino acids can enter catabolic energy-generating pathways (i.e. be oxidised).

Answer 356

Liver (mostly) and kidneys

Answer 357

* Oxidative -\> e.g. Glutamate (done by glutamate dehydrogenase) * Non-oxidative -\> e.g. Serine & threonine: OH in side chain * Hydrolytic -\> e.g. Asparagine & glutamine: N in side chain

Answer 358

* Amino acid -\> α-keto acid + NH₄⁺ * This involves the conversion of NAD(P)⁺ to NAD(P)H + H⁺. * Enzyme: Glutamate dehydrogenase Note: This is a reversible reaction!

Answer 359

* It is lost as ammonium (NH₄⁺) * This can then be incorporated into other compounds or excreted

Answer 360

Only glutamate (thus the enzyme glutamate dehydrogenase).

Answer 361

Glutamate dehydrogenase

Answer 362

Reductive amination

Answer 363

* NAD⁺ used mostly in oxidative deamination * NADPH used mostly in reductive amination (the opposite reaction of deamination)

Answer 364

Glutamate dehydrogenase is able to catalyse both oxidative deamination and reductive amination: * ADP and GDP -\> Stimulate oxidative deamination * ATP and GTP -\> Stimulate reductive amination The rate of each reaction also depends on substrate concentration.

Answer 365

* Ketoacids are organic compounds that contain a carboxylic acid group and a ketone group. * They are the oxidised form of an amino acid.

Answer 366

It is the only amino acid that can undergo oxidative deamination (by glutamate dehydrogenase), so some other amino acids are "funnelled" into it in order to be oxidised.

Answer 367

* The reaction of an amino acid with an α-ketoacid to produce a different amino acid and different α-ketoacid. * Essentially, the amino group is moved from the amino acid to the ketoacid.

Answer 368

Transaminases (a.k.a. aminotransferases)

Answer 369

It funnels other amino acids into glutamate, which can be undergo oxidative deamination. The α-ketoacid can also be used in metabolism.

Answer 370

* Carbon component -\> α-ketoacid, which enters energy metabolism * Nitrogen component -\> Ammonium, which enters the urea cycle

Answer 371

* In transamination, α-ketoglutarate is converted into glutamate (by receiving an amino group from the other amino acid), which can enter oxidative deamination. * This means that the other amino acid is converted to an α-ketoacid that can enter energy metabolism

Answer 372

Catalysed by alanine transaminase: * alanine + α-KG ⇌ pyruvate + glutamate Catalysed by aspartate transaminase: * aspartate + α-KG ⇌ OAA + glutamate

Answer 373

Catalysed by alanine transaminase: alanine + α-KG ⇌ pyruvate + glutamate

Answer 374

Catalysed by aspartate transaminase: aspartate + α-KG ⇌ OAA + glutamate

Answer 375

The co-enzyme of aminotransferases in transamination.

Answer 376

* Pyruvate * It it the product at the end of glycolysis

Answer 377

* Oxaloacetate * Enters the TCA cycle

Answer 378

* 2-oxo-3-methyl valerate * Oxidised in muscle

Answer 379

* 2-oxo-4-methyl valerate * Oxidised in muscle

Answer 380

* 2-oxo-3-methyl butyrate * Oxidised in muscle

Answer 381

* Serine and threonine * Because they have an OH group

Answer 382

Dehydratases (they are called this because dehydration precedes deamination)

Answer 383

* Serine -\> Pyruvate + NH₄⁺ * Enzyme: Serine dehydratase

Answer 384

* Threonine -\> α-ketobutyrate + NH₄⁺ * Enzyme: Threonine dehydratase

Answer 385

* Glutamine and asparagine * This is because they have a nitrogen in their variable group

Answer 386

* Glutamine + H₂O -\> Glutamate + NH₄⁺ * Enzyme: Glutaminase

Answer 387

* Asparagine + H₂O -\> Aspartate + NH₄⁺ * Enzyme: Asparaginase

Answer 388

* Mitochondrial * In liver -\> To generate urea * In kidneys -\> To generate NH₄⁺ for acid-base balance * In neurons -\> To assist in neurotransmission

Answer 389

In the liver.

Answer 390

It is necessary for gluconeogenesis and other energy metabolic pathways.

Answer 391

* 10-11kg of proteins * 5-7kg in muscle

Answer 392

* 90% as urea * 10% as ammonia

Answer 393

It is less toxic.

Answer 394

It is used in acid-base balance.

Answer 395

* Uric acid * It prevents water loss

Answer 396

A cycle of biochemical reactions that produces urea (NH₂)₂CO from ammonia NH₃.

Answer 397

Periportal cells of the liver lobule

Answer 398

CO₂ and NH₄⁺

Answer 399

* The conversion of CO₂ and NH₄⁺ into carbamoyl phosphate * It is catalysed by carbomyl phosphate synthetase-I: * Activated by N-acetylglutamate

Answer 400

2 molecules of ATP

Answer 401

The aspartate that enters the urea cycle (by combining with citrulline) can come from the TCA cycle.

Answer 402

Acute: * The enzymes are upregulated by glucagon and glucocorticoids (i.e. in catabolic conditions) * Carbamoyl phosphate synthetase-I is upregulated by N-acetylglutamate Chronic: * High protein diet induces the enzymes

Answer 403

Hyperammonemia (high levels of ammonium ions in the blood), since ammonium is not cleared from the blood.

Answer 404

* Lethargy and vomiting may be visible a couple of days after birth * Comma and brain damage may follow

Answer 405

* Glucogenic via pyruvate * Glucogenic via TCA cycle intermediates * Ketogenic via acyl-CoA * Mixed

Answer 406

* Glucogenic AAs: * Those that can be degraded into TCA intermediates that can enter glucogenesis via OAA * Ketogenic AAs: * Those can be degraded directly into acetyl-CoA, which is the precursor of ketone bodies * Glucogenic AAs can't form ketones because there is no way to exit the TCA cycle into acetyl-CoA, while ketogenic AAs can't form glucose because the 2 carbons from the acetyl-CoA are lost in the TCA cycle before OAA is formed. * Some AAs are both glucogenic and ketogenic because they can be degraded into both acetyl-CoA and TCA intermediates

Answer 407

* Alanine * Cysteine * Glycine * Serine * Threonine * Tryptophan

Answer 408

Note that threonine can also be converted to pyruvate by threonine dehydrogenase (with the loss of a CO₂), but it can also be converted to succinyl-CoA.

Answer 409

* Phenylalanine * Tyrosine Note that these can also be converted to acetoacetate, meaning they are both glucogenic and ketogenic.

Answer 410

* Asparagine * Aspartate

Answer 411

* Isoleucine * Leucine * Methionine * Threonine * Valine

Answer 412

* Arginine * Glutamine * Glutamate * Histidine * Proline

Answer 413

Acetyl-CoA: * Isoleucine * Leucine * Tryptophan Acetoacetyl-CoA: * Leucine * Lysine * Phenylalanine * Tryptophan * Tyrosine

Answer 414

* They use branched chain amino acids (BCAAs) -\> These are leucine, isoleucine and valine. * They can also use transamination to produce ketoacids that can enter metabolism. The by-product of this is typically glutamate, which is converted to alanine or glutamine, which can be taken to the liver for deamination. [Add notes on this - Check if amino acids are transaminated]

Answer 415

Do it. Involved in transport of ammonia to the liver, similar to the Cahill cycle. https://www.ncbi.nlm.nih.gov/books/NBK22475/

Answer 416

The ammonia is taken to the liver, kidneys and small intestine mostly in the form of glutamine.

Answer 417

BCAA (branched-chain amino acids) [CHECK THIS]

Answer 418

Glutamine is degraded by the intestines by means of the enzyme glutaminase, yielding glutamate and ammonia. Subsequently ammonia is released in the portal vein, and the glutamate is subsequently metabolized by the intestine, mostly to α-ketoglutarate.

2. Cellular Metabolism (HT) Flashcards

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