Metabolism Flashcards
0
Q
What is the approximate energy requirement for the average 70kg man and 58kg woman?
A
12,000kj and 9,500kj
1
Q
What are the 3 main daily expenditures of energy?
A
Basal metabolic rate, voluntary physical activity and digestion
2
Q
What are the essential components of diet?
A
Fats, proteins, carbohydrates, water, fibre and vitamins/minerals
3
Q
Why are fats essential?
A
Useful energy source (2.2x carbohydrate), needed to absorb fat soluble vitamins and certain fatty acids are essential (such as structural membranes)
4
Q
Why are proteins essential?
A
Needed to help synthesise N containing compounds such as nucleotides. Needed as a source of essential amino acids the body can’t produce
5
Q
Why are carbohydrates essential?
A
Main energy source
6
Q
Why is fibre essential?
A
Bowel function
7
Q
What are the fat soluble vitamins?
A
A, D, E and K
8
Q
Outline the differences between Marasmus and Kwashiorkor and how these differences have arisen
A
Kwashiorkor would have a distended belly. This is because there is no protein in the diet so water moves into tissue fluid by osmosis.
9
Q
What symptoms would you see in protein and energy deficiency?
A
Emaciated appearance, anaemia, lethargic, dry/brittle hair and diarrhoea
10
Q
What is the formula to calculate BMI?
A
Weight(kg) / height (m) ^2
11
Q
What are the ranges for the BMI categories?
A
35=severely obese
12
Q
Define obesity and explain how it occurs
A
Excess body fat to the extent it may have an adverse effect on health. BMI > 30. Caused by energy intake being greater than expenditure
13
Q
What conditions may occur as a result of obesity?
A
Hypertension, heart disease, stroke, type 2 diabetes, osteoarthritis, some cancers and gall bladder disease
14
Q
Define homeostasis
A
Maintaining a relatively stable internal environment. A dynamic equilibrium
15
Q
Why is homeostasis important?
A
Failure leads to disease
16
Q
Define cell metabolism
A
A highly integrated network of chemical reactions
17
Q
What are the functions of cell metabolism?
A
Energy, building block materials, organic precursors and reducing power
18
Q
Describe the origins and fates of cell nutrients
A
Cell nutrients come from: diet, synthesis and stores
Cell nutrients end up being: degraded to release energy, turned into something else or stored
19
Q
Contrast catabolism and anabolism
A
Catabolism: large–>small, oxidative, release energy, produce useful intermediates
Anabolism: small–>large, reductive, use intermediates and energy to synthesise important cell components
20
Q
Why do cells need a constant supply of energy?
A
To carry out their function
21
Q
What is the role of ATP?
A
ATP is an energy carrier. When it is hydrolysed to release the phosphate group it produces energy.
22
Q
Why does the body need creatine phosphate?
A
Creatine phosphate is formed by taking a phosphate group from ATP and acting as an energy store for tissues that need instant supplies of energy like skeletal muscle
23
Q
What is the role of H-carrier molecules?
A
To carry the reducing power generated in catabolism to anabolic pathways
24
Explain the role of high and low energy signals and give examples of each
Catabolic pathways are activated by low energy signals such as: ADP, NAD+, FAD and NADP+
Anabolic pathways are activated by high energy signals such as: ATP, NADH, NADPH and FAD2H
25
What is the basic chemical structure of a carbohydrate?
(CH2O)n. Contain an aldehyde or ketone group and many OH bonds
26
What are the common types of monosaccharide?
3-9C atoms. Commonest is triose, pentose and hexose. Either get aldose (CHO) or ketose (C=O)
27
What are some important physio-chemical properties of sugars?
Hydrophilic and partially oxidised (need less oxygen for full oxygenation than fatty acids)
28
How are disaccharides formed and what are the 3 main types?
A condensation reaction between 2 monosaccharides releases water and forms an O-glycosidic bond. Lactose (glucose and galactose) sucrose (glucose and fructose) and maltose (glucose and glucose)
29
Describe the structure of glycogen
A highly branched polymer of glucose. Joined by alpha 1-4 and 1-6 bonds.
30
Describe the structure of cellulose and why it's important
Made up of beta 1-4 bonds to form long chains. Humans don't have necessary enzymes to break these bonds so helps with digestion
31
Describe how dietary polysaccharides are initially digested
Polysaccharides are broken down to smaller polysaccharides (dextrins) or into glucose or maltose by glycosidase enzymes in the saliva (amylase) and duodenum (pancreatic amylase)
32
How are disaccharides digested and absorbed?
There are glycosidase enzymes (lactase, glycoamylase, sucrase and isomaltase) on the epithelial brush border of the duodenum and jejunum. This releases the monosaccharides which are absorbed
33
Which tissues have an absolute requirement for glucose?
WBCs, RBCs, kidney medulla and lens of the eye
34
Outline glycolysis
Uses 2 ATP to start and produces 4 meaning a net production of 2 moles. Turns NAD+ into NADH which is reducing power. Produces useful building blocks for anabolism. No loss of CO2
35
Which steps in glycolysis are irreversible and what enzyme catalyses them?
Steps 1, 3 and 10. The enzymes are: hexokinase (glucokinase in liver), Phosphofructokinase and pyruvate kinase respectively
36
What is the reaction for the last step of lactic acid production?
Pyruvate + NADH + H+ --> lactate + NAD+
| Catalysed by lactate dehydrogenase
37
Why is anaerobic respiration needed?
Produce more NAD+ so glycolysis can continue. When there isn't enough or any oxygen some ATP is still produced. Some cells (RBCs) can only use the glycolytic and this is the only way glycolysis can continue
38
What happens to lactic acid after its production?
Heart muscle will convert back to pyruvate and oxidise to CO2. Liver will convert it to glucose
39
How can lactose intolerance arise?
Low activity of enzyme lactase
40
Explain the clinical condition galactosaemia
Occurs due to defective enzyme galactokinase (rare and less harmful) or galactose 1 phosphate uridyl transferase (more common and serious as you get build up of galactose 1 phosphate as well which is toxic). Galactose is converted to galacticol which depletes NADPH levels so disulphide bonds form in eye (cataracts)
41
Why is the pentose phosphate pathway important in some tissues?
Produces NADPH which is used in RBCs to stop disulphide bonds and therefore Heinz bodies forming and in adipose/liver for lipid synthesis. Produces ribose sugars for nucleotides which is useful for rapidly dividing tissues
42
Outline the pentose phosphate pathway
Glucose 6 phosphate and NADP+ are converted to a C5 sugar and NADPH by the enzyme glucose 6 phosphate dehydrogenase. The reverse is a complex series of steps that converts leftover C5 into sugars that enter glycolysis
43
Explain the clinical condition glucose 6 phosphate dehydrogenase deficiency
A deficiency of G6PD means there will be less NADPH. This could lead to the formation of Heinz bodies or cataracts
44
What does pyruvate dehydrogenase do in metabolism?
Convert pyruvate into acetyl CoA which can enter TCA cycle. CO2 is lost. Irreversible
45
What are the control mechanisms of PDH?
Acetyl CoA allosteric inhibitor. ATP/NADH inhibit and ADP activates. Insulin promotes as well
46
What are the products of the TCA cycle?
3NADH, 1 GTP, 1 FAD2H, 2CO2 and C6/C5/C4 intermediates that can be used to make non essential amino acids, fatty acids or haem molecules.
47
How is the TCA cycle regulated?
One of the irreversible steps is catalysed by isocitrate dehydrogenase which is allosteric ally regulated by the ATP/ADP ratio or NADH/NAD+ ratio
48
What will have happened to the glucose and its products by the end of the TCA cycle?
All C-C bonds broken and oxidised to CO2. All C-H bonds broken and H atoms transferred to NAD+ and FAD. The energy from breaking these bonds has produced 4 ATP and chemical bond energy of the electrons
49
Outline oxidative phosphorylation
Electrons released from NADH and FAD2H and pass down electron carriers to oxygen. This releases energy which pumps proton into the inter membrane space. This builds a p.m.f. They can't get back across the inner membrane except through ATPase which then drives the synthesis of ATP
50
Which gives more energy, FAD2H or NADH?
NADH has more and uses 3 proton translocation complexes as opposed to FAD2H's 2. 2 NADH gives 5 ATP whereas 2 FAD2H gives 3.
51
How are ATP synthesis and electron transport coupled?
Tightly. If ATP concentration is high then ADP concentration is low so synthesis of ATP stops due to lack of substrate. This means H+ builds up so no more can be pumped across so no more electrons are transported.
52
Name two substances that uncouple electron transport and ATP synthesis and explain how this occurs
Dinitrophenol and dinitrocresol. They make the inner membrane more permeable to protons so they diffuse back across and don't drive ATPase. Generates heat
53
What are UCPs and what is their function? Give a specific example
Uncoupling proteins. They uncouple so that the pmf is used to generate heat instead. UCP1 or thermogenin is useful in non shivering thermogenesis and is found in brown adipose tissue
54
Compare and contrast oxidative phosphorylation and substrate level phosphorylation
Oxidative: requires membrane associated complexes, needs oxygen, energy coupling is an indirect result of the generation and utilisation of p.m.f, major process for energy production
Substrate: needs cystolic enzymes, limited function without oxygen, energy coupling is a direct result of formation of hydrolysis bond, is a minor process for energy production.
55
What are the 3 main classes of lipids and the subgroups within those?
Fatty acid derivatives (fatty acids, triacylglyerols, phospholipids), hydroxy methyl glutaric acid derivatives (ketones, cholesterol/cholesterol esters) and fat soluble vitamins (A, D, E and K)
56
What is the first step in metabolising TAGs?
In the small intestine they are hydrolysed by pancreatic lipase to release glycerol and fatty acids
57
How is glycerol metabolised?
Travels to the liver where it is turned into glycerol phosphate (enzyme: glycerol kinase) and then into DHAP which enters glycolysis. This turns one ATP into ADP and one NAD+ into NADH
58
How are fatty acids metabolised?
First they are activated by binding them to CoA. This means they can't cross the mitochondrial membrane so a carnitine shuttle is required. Then undergo beta oxidation, a cyclic reaction that each time removes 2 carbons from the fatty acid as acetyl CoA and converts 1 FAD and NAD+ to FAD2H and NADH + H+
59
What are the 3 ketone bodies formed by the body?
Acetone, acetoacetate and beta hydroxybutyrate
60
How are the levels of ketones regulated?
HMG CoA can be converted into ketones (lyase) or cholesterol (reductase). These enzymes are controlled by the glucagon/insulin ratio. Low glucose activates lyase.
61
Why are ketones important and how are they metabolised?
Because all tissues containing mitochondria can use ketones (including the CNS). They are converted to acetyl CoA which enters the TCA cycle
62
Describe the central role of acetyl CoA
Acetyl CoA can be produced by sugars, fatty acids, some amino acids, ketones and alcohol. It enters the TCA cycle. It is also used in the synthesis of fatty acids.
63
What are the major energy stores in the average 70kg man?
TAGs, 15kg, 600,000kj
Glycogen, 0.4kg, 4,000kj
Muscle protein 6kg, 100,000kj
64
Outline glycogenesis
Glucose to glucose 6 phosphate (hexokinase) to glucose 1 phosphate (phosphoglucomutase) to UDP glucose to an extra residue on glycogen (branching enzyme, glycogen synthase)
65
Outline glycogenolysis
Glycogen loses a residue to make glucose 1 phosphate (debranching enzyme and glycogen phosphorylase) which turns to glucose 6 phosphate (phosphoglucomutase) which is used in glycolysis in the muscle or is converted to glucose (glucose 6 phosphatase) in the liver
66
What is the difference in muscle and liver glycogen?
Muscle glycogen only produces glucose for the muscle. Liver is a store of glucose for the whole body
67
What are the clinical consequences of a glycogen storage disease?
Too much/little glycogen - tissue damage, exercise intolerance, hypoglycaemia. Abnormal glycogen structure. Usually affects liver or muscles
68
What are some possible substrates for gluconeogenesis?
Pyruvate, lactate, glycerol, some amino acids.
69
How can pyruvate generate glucose as some of the steps in glycolysis were irreversible?
Bypass irreversible steps. Step 1 and 3 bypassed by thermo dynamically spontaneous reactions (glucose 6 phosphatase and fructose 1,6 bisphosphatase) step 10 bypassed using ATP (PEPCK or pyruvate carboxylase)
70
How is gluconeogenesis regulated?
PEPCK and fructose 1, 6 phosphatase under hormonal control. Insulin decreases, glucagon and cortisol increase.
71
How is the storage of TAGs regulated?
Hormonally. Storage promoted by insulin and inhibited by glucagon, adrenaline, cortisol, growth hormone, thyroxine.
72
Outline fatty acid synthesis (lipogenesis)
Acetyl CoA is converted to Malonyl CoA by acetyl CoA carboxylase. This C2 unit is added to the chain in cyclic reactions using fatty acid synthase. NADPH and ATP are turned to NADP+ and ADP
73
How is lipogenesis regulated?
Acetyl CoA carboxylase is allosterically regulated by citrate (activate) and AMP (inhibit) and also regulated hormonally by insulin (activate) and glucagon/adrenaline (inhibit)
74
Outline amino acid catabolism
Remove NH2 group by transamination or deamination and excrete it in the form of urea. The remaining carbon skeleton is converted into a substrate such as pyruvate or acetyl CoA which is used to make glucose or ketones
75
Describe transamination
The amino acid reacts with alpha ketoglutarate to produce glutamate (which can be deaminated or used) and a useful metabolic intermediate (alanine = pyruvate ALT) (aspartate = oxaloacetate AST)
76
Describe deamination
Convert amino acid to keto acid and NH3 by L/D amino acid oxidases. E.g. Glutaminase converts glutamine to glutamate and NH3. Glutamate dehydrogenase converts glutamate to alpha ketoglutarate and NH4+
77
Describe the clinical condition phenylketonuria
Normally phenylalanine is converted to tyrosine by phenylalanine dehydrogenase which in PKU patients is defective. Therefore phenylalanine buil up and other pathways occur producing phenyl pyruvate. Detected by phenylketones in urine or high phenylalanine concentration in blood. Treat with low phenylalanine diet
78
Describe the condition homocystinuria
Homocysteine is normally converted to cysteine using CBS enzyme. If defective homocysteine builds up and is also converted to methionine. High levels damages connective tissue, CNS, CVS and muscle. Similar symptoms to Marfans syndrome
79
What is the clinical relevance of creatinine levels in urine?
Creatinine is produced my muscles at a constant rate (unless muscle wasting) so provides a good measure of muscle mass or to work out how concentrated urine is with other hormones
80
What are the problems with hyperammonaemia and why might this be?
Affects the CNS with blurred vision, slurred speech, coma and death. Possibly because uses alpha ketoglutarate which inhibits TCA cycle. Also affects pH and neurotransmitters
81
Outline ammonia detoxification
Converted to urea (ornithine cycle) or glutamine to be transported to the liver before it is converted back
82
How is urea synthesis regulated?
Not controlled by feedback but is inducible - enzyme activity rate is increased by high protein diet. If on a low protein diet have to slowly increase protein levels or hyperammonaemia
83
What might happen if one of the enzymes in the urea cycle is defective?
Hyperammonaemia or build up of intermediate. Could lead to mental retardation, comas, death, vomiting and lethargy. Treat with low protein or keto acids to use up ammonia
84
How are lipids transported?
98% bound to lipoproteins and 2% to albumin (FAs)
85
What are the different classes of lipoproteins and what do they transport?
Chylomicrons - TAGs from diet to tissue
VLDL - TAGs from liver to tissue
LDL - cholesterol from liver to tissue
HDL - cholesterol from tissue to liver
86
What makes the protein part of a lipoprotein and what does it do?
Apoproteins. Structurally have hydrophilic and hydrophobic parts to interact with lipid and blood. Functionally will bind to different cell surface receptors or react with different enzymes
87
How are the contents of chylomicrons and VLDLs removed? How is lipoprotein stability maintained?
Lipoprotein lipase is secreted by capillaries in muscle tissue or adipose. This breaks down the TAG in the centre to FAs which enter the cell before being stored as a TAG. Stability is restored by converting surface cholesterol to core cholesterol ester by LCAT
88
How are LDLs metabolised?
Cells requiring cholesterol express LDL receptors. This binds to apoprotein B100 on LDL surface and it is endocytosed in. It is then digested by lysosomes releasing free cholesterol. This is used or stored by the cell and also inhibits cholesterol and LDL receptor synthesis
89
Give some examples of hyperlipoproteinaemias
Familial hyperlipoproteinaemia or Type 2a - defective LDL receptor leads to lots of LDLs in blood and has risk of coronary artery disease
Type 1 - defective lipoprotein lipase leads to chylomicrons in fasting plasma. Harmless
90
How can hyperlipoproteinaemia be treated?
Change in diet/lifestyle - exercise, eating less cholesterol and saturated fat
Drugs - statins - reduce activity of reductase enzyme therefore inhibiting cholesterol synthesis
91
How are superoxide radicals produced?
The electrons from the electron transport chain are prematurely released reducing oxygen into (O2)-
92
How are superoxide radicals broken down?
SOD combines superoxide radicals to H2O2. Catalase then breaks down to H2O and O2
93
What other ROS are there?
OH produced due to ionising radiation. Chemicals form them as well. Can't be broken down. NO which also forms ONOO another free radical
94
What defenses are there against ROS?
Glutathione (GSH) is the primary line of defence which when it is oxidised forms GSSG which is recycled by NADPH (catalysed by glutathione reductase and glutathione peroxidase) other defences - antioxidant vitamins, minerals, flavenoids.
95
What is an oxidative burst and why is it useful?
Enzyme NADPH oxidase produces a rapid release of ROS. This destroys cell and nearby fungal/bacterial cells
96
What are some conditions that occur due to ROS
Cancer - ROS damages DNA
Emphysema - lung damaged by ROS
Type 1 diabetes - ROS destroys beta cells
Alzheimer's - protein damage and misfolding by ROS
97
Define pharmacodynamics and pharmacokinetics
Pharmacodynamics is what the drug does to the body
| Pharmacokinetics is what the body does to the drug
98
What does pharmacokinetics cover?
ADME
Absorption, distribution, metabolism, elimination
Of a drug
99
What happens in phase 1 of a drugs metabolism?
A reactive group is exposed which can take part in phase 2 metabolism. This is usually the result of an oxidation, reduction or hydrolysis reaction. Needs CYP enzyme and NADPH. Not all drugs undergo phase 1
100
What happens in phase 2 of drug metabolism?
Reactive intermediate from phase 1 is conjugated with a polar molecule to make the drug water soluble. Common conjugates are glucoronic acid (byproduct of metabolism), sulphate ions and GSH. Need enzymes and UDPGA
101
What is the first pass effect?
Many drugs pass through the liver which contains most enzymes required for drug metabolism leading to the drug being extensively metabolised
102
What is the importance of the cytochrome P450 system?
Isoform CYP3 A4 accounts for 55% of drug metabolism. Cofactor is NADPH. There is polymorphisms in this system in humans hence why drugs affect people different amounts
103
Why is their variation in drug metabolism?
Genetic factors - level of expression of metabolic enzymes
| Environmental factors - enzyme inhibitors and activators (cranberry juice, alcohol)
104
How is paracetamol metabolised in toxic and non toxic doses?
Under normal conditions undergoes phase 2 metabolism with glucuronide or sulphate. If too much has been taken then the pathway is saturated and there's a build up of NAPQI. This damages the liver and uses up antioxidants.
105
How is alcohol metabolised?
Alcohol --> Acetaldehyde --> Acetic acid --> Acetyl CoA
(Alcohol dehydrogenase) (Aldehyde dehydrogenase)
Requires NAD+ which turns produces NADH and ATP
106
Why is it bad that this process uses NAD+ and produces NADH?
A low NAD/NADH ratio inhibits the conversion of lactate to pyruvate and glycerol metabolism. Leads to hypoglycaemia. Stops acetyl CoA being oxidised so fatty acids and ketones are produced. Not enough lipoproteins to carry fatty acids to get fatty liver. Keto-acidosis.
107
What might you see in a patient with decreased liver function?
Jaundice, increased clotting time, oedema, fatty liver and hyperammonaemia
