NAM Flashcards
(301 cards)
1
Q
What are catabolic pathways?
A
Where food molecules are broken down into small building blocks for biosynthesis. They produce useful forms of energy and heat in this process. These pathways mainly occur in the cytosol.
2
Q
What are anabolic pathways?
A
When small molecules are made into larger molecules that form cells. This process requires energy. These pathways mainly occur in the mitochondria.
3
Q
What is the definition of metabolism?
A
A series of enzyme reactions within cells for converting fuel molecules into ‘useful energy’ as well as the enzyme reactions of synthesis/breakdown/interconversion of essential biomolecules.
4
Q
What is the equation for conversion of glucose to CO2 and what pathways act together to do this?
A
C6H12O6 + 6O2 -> 6CO2 + 6H2O + 30ATP
Glycolysis and TCA cycle act together.
5
Q
Why do mitochondria have a double membrane?
A
- In order to maintain a gradient.
- In order to have organised protein complexes than can channel electrons.
6
Q
Why are fatty acids bound to proteins in the body? Which proteins do they bind to?
A
- Free fatty acids are not good for you so they bind to proteins.
- In the blood they bind to albumin and in the cells they bind to fatty acid binding protein.
7
Q
What are the three components of ATP?
A
1) Phosphate
2) Sugar
3) Nucleotide base adenine
8
Q
In which pH range is ATP chemically stable?
A
pH 6-9
9
Q
What is the formula for ATP hydrolysis?
A
ATP + H2O -> ADP + Pi + H+
10
Q
What are the functions of ATP?
A
- Used directly in cell motility and contraction.
- Used in Na/K pumps, active transport systems and metabolic control.
- Used in metabolism and to add Pi to metabolic intermediates.
11
Q
What are endergonic and exergonic reactions?
A
Endergonic = when energy is absorbed in a reaction.
Exergonic = when energy is released in a reaction.
12
Q
How can the rate of an enzyme reaction be regulated?
A
- By altering the availability of the substrate to the cell.
- Increasing the amount of enzyme present in the cell by increasing the rate of transcription.
- Interconversion of active and inactive forms of key enzymes.
13
Q
What do metabolic reactions require?
A
- Fuel molecules
- Enzyme catalysts
- Cofactors
14
Q
For what does ATP act as a cofactor for?
A
Kinase enzymes
15
Q
How much energy is released in the breakdown of ATP?
A
31 kJ of energy per mol of ATP
16
Q
What are UTP, CTP and GTP cofactors for?
A
- UTP = drives the synthesis of complex sugars.
- GTP = drives the synthesis of proteins.
- CTP = involved in lipid synthesis.
17
Q
What are oxidation and reduction?
A
- When a substance is being oxidised, it is losing its electrons to something else i.e. losing a hydrogen atom which is made up of a H+ and an electron.
- When a substance is reduced, it is gaining electrons i.e. a hydrogen atom.
These tend to happen together as redox reactions, one substance steals electrons from the other.
18
Q
What type of reaction is going from a double bond to a single bond?
A
Reduction reaction. This is because you add hydrogen atoms to compensate for the lost bond.
19
Q
Why is a more reduced molecule better at producing ATP than a less reduced one?
A
Because being more reduced means that the molecule contains more electrons that it can give away. These electrons then go into the electron transport chain where ATP is make. More electrons means more ATP.
20
Q
What type of cell relies entirely on anaerobic metabolism and why?
A
Red blood cells because they do not contain any mitochondria.
21
Q
Why is glucose dangerous when it is not controlled?
A
It is a highly reactive molecule that can react with proteins. This is what happens in diabetes with high blood glucose. The ring structure of glucose is caused when it reacts with itself.
22
Q
What are the Fischer and Haworth projections of glucose?
A
- Fisher = D-glucose linear form.
- Haworth = D-glucopyranose ring form.
23
Q
What are the three sources of glucose for glycolysis?
A
- Sugars and starch from diet.
- Breakdown of stored glycogen from the liver.
- Recycled glucose from lactic acid, amino acids or glycerol.
24
Q
What is the summary, location and function of glycolysis?
A
Summary = glucose C6 -> 2x pyruvate C3.
Location = cytosol.
Function = energy trapping by formation of ATP. Is also forms some intermediates for fat and amino acid synthesis.
25
Is glycolysis an oxidation or reduction reaction?
Oxidation
26
What are the four stages of glycolysis?
1) Activation
2) Splitting of 6C sugar in half
3) Oxidation
4) Synthesis of ATP
27
Describe the three reactions that occur during the activation stage of glycolysis.
- Glucose is converted to glucose 6-phosphate with the help of ATP and hexokinase/glucokinase. Addition of a phosphate. This reaction is irreversible.
- Glucose 6-phosphate is converted to fructose 6-phosphate by phosphoglucose isomerase.
- Fructose 6-phosphate is converted to fructose 1, 6 biphosphate by phosphofructokinase. Addition of a second phosphate from ATP. This reaction is irreversible.
28
What are the products of the activation stage of glycolysis?
2ADP and one fructose 1, 6 biphosphate.
29
What happens during the splitting stage of glycolysis?
Fructoses 1, 6 biphosphate is split into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate by aldolase.
These products are more stable than their fructose origin.
30
What is the role of triose phosphate isomerase in the splitting stage of glycolysis?
It ensures that you can make glyceraldehyde 3-phosphate from dihydroxyacetone phosphate (the products of splitting) and vice versa. This ensures the correct products are formed so the rest of the pathway can go in the right direction.
31
Describe the oxidation step of glycolysis.
Glyceraldehyde 3-phosphate goes to 1, 3-biphosphoglycerate with the help of glyceraldehyde 3-phosphate dehydrogenase. NAD+ and Pi are also converted to NADH and H+ simultaneously. The Pi is given to the molecule forming a biphosphate.
32
What does NAD stand for?
Nicotinamide Adenine Dinucleotide
33
What do you need to make NADH and H+ from NAD+?
H+ and two electrons.
34
Describe the ATP synthesis stage of glycolysis.
- 1, 3-biphosphoglycerate is coverted to 3-phosphoglycerate with the help of phosphoglycerate kinase. This reaction produces one ATP.
- 3-phosphoglycerate is converted to 2-phosphoglycerate with the help of phosphoglycerate mutase.
- 2-phosphoglycerate is converted to phosphoenol pyruvate with the help of enolase. This reaction produces one water molecule.
- Phosphoenol pyruvate is converted to pyruvate with the help of pyruvate kinase. This reaction produces an ATP. This reaction is irreversible.
35
What are the final products of the ATP synthesis stage of glycolysis?
Pyruvate and four ATP molecules because this reaction is happening twice.
36
What is the net yield of ATP from glycolysis?
2 ATP because the early activation stage uses up two ATP.
37
What happens to pyruvate in anaerobic glycolysis?
Pyruvate is converted to lactate in order to convert the cofactor NADH back to NAD+ so it can be re-used for more glycolysis. This reaction is catalysed by lactate dehydrogenase.
pyruvate + NADH + H+ → NAD+ + lactate
38
What happens to pyruvate in microorganisms?
It is converted to ethanol.
39
What happens to pyruvate when there is excess calorie intake?
It is converted to acetyl CoA which is converted to fatty acids for storage.
40
Why is glycolysis a major source of ATP in the brain?
Because the cells in the brain are incapable of using fat as fuels.
41
How can you increase the rate of glycolysis?
- Intense muscle workout and exercise.
- After a high carbohydrate meal (high insulin levels).
- AMP increasing the activity of phosphofructokinase.
42
How can you decrease the rate of glycolysis?
- By entering a fasting state with high levels of circulating glucagon.
- Feedback inhibition acting on the reaction of fructose 6-phosphate to fructose 1, 6-biphosphate. There is allosteric control of the enzyme phosphofructokinase by ATP and citrate.
43
What happens in the TCA cycle?
Oxidation of acetyl CoA to carbon dioxide and water along with the production of ATP.
44
How many different molecules are used in the TCA cycle?
8, therefore 8 reactions.
45
What is the most vital molecule for the continuation of the TCA cycle?
Oxaloacetate
46
What is the link reaction?
A reaction that links glycolysis to the TCA cycle: pyruvate + CoA -> acetyl CoA and CO2 catalysed by pyruvate dehydrogenase. One NADH is formed.
47
What are the cofactors for the link reaction?
- Thiamin pyrophosphate
- Lipoic acid
- FAD
- Coenzyme A
- NAD+
48
Describe reaction 1 in the TCA cycle.
Oxaloacetate + Acetyl CoA -> Citrate catalysed by citrate synthase.
This is a condensation reaction.
49
Describe reaction 2 in the TCA cycle.
Citrate -> Isocitrate catalysed by aconitase.
This is an isomerisation reaction.
50
Describe reaction 3 in the TCA cycle.
Isocitrate -> α-ketoglutarate catalysed by isocitrate dehydrogenase.
One CO2 is lost in this reaction and one NADH is formed making this reaction an oxidation.
51
Describe reaction 4 in the TCA cycle.
α-ketoglutarate -> succinyl CoA catalysed by ketoglutarate dehydrogenase.
One CO2 is lost and one NADH is formed making this an oxidation reaction.
52
Describe reaction 5 in the TCA cycle.
Succinyl CoA -> succinate catalysed by succinate thiokinase.
One GTP is formed and one CoA is lost.
53
Describe reaction 6 in the TCA cycle.
Succinate -> fumarate catalysed by succinate dehydrogenase.
One FADH2 is formed from FAD.
54
Describe reaction 7 in the TCA cycle.
Fumarate -> malate catalysed by fumarase.
One H2O is consumed in this reaction.
55
Describe reaction 8 in the TCA cycle.
Malate -> oxaloacetate catalysed by malate dehydrogenase.
One NADH is formed making this reaction an oxidation reaction.
56
What does FAD stand for?
Flavin adenine dinucleotide
57
How does the reoxidation of NADH to NAD+ occur?
By transfer of 2H to the carriers of the cytochrome chain (electron transport chain).
58
Where is the electron transport chain found?
In the inner mitochondrial membrane (the matrix).
59
What are the products of the reduction of one NADH?
One H2O and three ATP.
60
What is the overall energy yield of the electron transport chain?
3 x NADH = 2.5
1 x FADH2 = 1.5
1 x GTP
Makes 10 ATP
61
What are the three enzyme steps that are highly exergonic and irreversible in the TCA cycle?
- Citrate synthase (reaction 1)
- Isocitrate dehydrogenase (reaction 3)
- Ketoglutarate dehydrogenase (reaction 4)
62
What can also happen to oxaloacetate and α-ketoglutarate?
They can leave the TCA cycle and undergo transamination to form aspartate and glutamate respectively.
63
Apart from aspartate, what can oxaloacetate also be used to form?
Phosphoenol pyruvate catalysed by PEP carboxylase. This can then be used to make glucose.
64
What can citrate be used to form outside the TCA cycle?
Fatty acids and sterols.
65
What can malate be used to form outside the TCA cycle?
Pyruvate catalysed by malic enzyme.
66
The longer fatty acids are, what consistency do they have?
Longer is more solid, shorter is more liquid.
67
What is a fatty acid?
A hydrocarbon chain ending in =O, -OH
68
What are the biological functions of lipids?
- Components of cell membranes (phospholipids and cholesterol)
- Precursors to hormones
- Long term fuels (triglycerides)
69
What is a triglyceride fat?
Three fatty acids joined together by one glycerol group.
70
How are stored triglyceride fats broken down in adipose tissue?
1) Lipase (activated by adrenaline and glucose) cleaves off one fatty acid to form DAG (diacylglycerol).
2) Lipase cleaves off another fatty acid to form MAG (monoacylglycerol).
3) Lipase works once more to separate the final fatty acid from the glycerol.
71
Where do fatty acids and glycerol go when they are broken down by lipase?
- Glycerol diffuses in the blood to all tissues.
| - Free fatty acids travel in plasma bound to albumin and act as fuel for muscle, heart and liver.
72
What are the two ways in which glycerol can be metabolised?
- In most tissues it enters the glycolysis pathway.
| - In the liver and in starvation, it enters the glycolysis pathway but it converted to glucose by gluconeogenesis.
73
Where do all the reactions for fatty acid metabolism occur?
Within the mitochondrial matrix.
74
How are long-chain fatty acids activated?
With activating enzyme (cytosol), energy from one ATP and CoA reacting with the fatty acid to form a fatty acyl-CoA.
75
How is fatty acyl-CoA transported through the outer and inner mitochondrial membranes into the mitochondria?
CoA is cleaved off and carnitine is added forming long-chain acylcarnitine which is transported through the CPT1 channel in the outer membrane.
It then passes through CACT in the inner membrane.
76
What happens to long-chain acylcarnitine when it is within the mitochondrial matrix?
It goes back to fatty acyl-CoA with the help of CPT2 (carnitine is removed).
77
How many reactions are required for fatty acid metabolism (beta oxidation pathway?
Four
78
What are the key features of the four reactions in fatty acid metabolism?
1) Removal of two H atoms in the form of FADH2.
2) Addition of water.
3) Removal of two H atoms in the form of NADH and H+.
4) Removal of a 2C unit in the form of Acetyl CoA.
79
What happens to the fatty acyl-CoA when it has finished its first beta oxidation pathway?
It comes out two carbons shorter than it started. It then re-enters the cycle and keeps losing carbons.
80
How much product will one 16C fatty acid produce?
8x Acetyl CoA and 7x NADH and FADH2.
81
What is the ATP yield from the 8 Acetyl CoA that is produced by fatty acid metabolism of a 16C carbon?
The 8 acetyl CoA goes into the TCA cycle and forms 80 ATP.
The 7 NADH and FADH2 enters the electron transport chain and produces 28 ATP.
80 + 28 -2 = 106
82
What happens to fatty acids with an odd number of carbons?
The chain is elongated using hydrogen carbonate and ATP forming a methylmalonyl CoA. Vitamin B12 is then used to form succinyl CoA which can enter the TCA cycle.
83
What regulates the lipase enzyme?
Adrenaline and glucagon.
84
What are the three points of regulation of fatty acid metabolism?
1) The release of fatty acids from adipose tissue.
2) The rate of entry of fatty acids into mitochondria via the carnitine shuttle.
3) The rate of reoxidation of cofactors NADH and FAHD2 by cytochrome/respiratory chain.
85
Under what circumstances would you see AMP in muscles?
When the demand for energy is high but the supply is low. ADP is converted to AMP instead of ATP to ADP.
86
What is the difference between hexokinase an glucokinase?
They both catalyse the same reaction (glucose to glucose-6-phosphate) but hexokinase is more general, glucokinase being used specifically for glucose. It has a high Km for glucose so it only works in the liver when glucose levels are high. This is the opposite for hexokinase.
87
What glucose transporter is found on muscle cells?
GLUT4 - it is insulin-dependent.
88
How do you make UDP glucose?
By combining glucose-6-phosphate and UTP catalysed by transferase.
89
How is a glycogen molecule formed?
UDP-glucose is added to a protein primer called glycogenin. This is catalysed by glycogen synthase and involves the loss of UDP. This continues with multiple UDP-glucose molecules until you have a massive branched molecule.
90
What enzyme catalyses the branching of glycogen?
Branching enzyme
91
How is glycogen synthase regulated?
By phosphorylation by protein kinase and ATP. When it is phosphorylated, it is inactive.
92
What dephosphorylates and consequently activates glycogen synthase?
Protein phosphatase
93
What catalyses glycogen breakdown?
Glycogen phosphorylase
94
What is the role of the debranching enzyme?
It removes glucose units from the branched regions allowing glycogen phosphorylase to attack the straight chain regions.
95
What happens to glucose when it is released from the glycogen molecule?
It is released as glucose-1-phosphate. Mutase enzyme converts it to glucose-6-phosphate where it is then converted to glucose by glucose-6-phosphatase in the liver only.
96
Why is muscle unable to provide glucose into the bloodstream for metabolism?
It does not have glucose-6-phosphatase so it is unable to make glucose. Instead, glucose-6-phosphate goes straight into glycolysis for energy.
97
How is glycogen phosphorylase regulated?
It is active when it is phosphorylated by protein kinase.
It is inactive when dephosphorylated by protein phosphatase.
98
How is protein kinase activated?
- A first messenger activates a G-protein coupled receptor.
- The receptor activates adenylyl cyclase increasing the amount of cAMP inside the cell.
- cAMP then causes inactive cAMP-dependent protein kinase to become active.
- cAMP-dependent protein kinase then catalyses the reaction protein + ATP -> protein kinase + ADP.
99
What is the effect of insulin on glycogen enzymes?
- Glycogen synthase becomes dephosphorylated and active.
| - Glycogen phosphorylase becomes dephosphorylated and inactive.
100
What is the effect of adrenaline and glucagon on glycogen enzymes?
- Glycogen synthase is phosphorylated and inactive.
| - Glycogen phosphorylase is dephosphorylated and active.
101
What happens when glucose levels are high in the liver?
Glucose binds to glycogen phosphorylase and inactivates it.
102
What happens to glycogen phosphorylase in muscle during contraction?
- Ca is released into the sarcoplasmic reticulum.
- Ca binds to the calmodulin domain of glycogen phosphorylase kinase activating the enzyme.
- This in turn activates glycogen phosphorylase causing glycogen to be degraded providing energy for the contracting muscle.
103
What are the effects of AMP and ATP on glycogen phosphorylase?
- AMP is an allosteric activator of the enzyme.
| - ATP is an allosteric inhibitor.
104
What is von Gierke's disease?
A glycogen storage disease affecting glucose-6-phosphatase. Causes enlarged liver and hypoglycaemia.
105
What is Pompe's disease?
A glycogen storage disease affecting lysosomal glycosidase causing muscle weakness and cardiac failure.
106
What is McArdle's disease?
A glycogen storage disease affecting glycogen phosphorylase causing exercise intolerance.
107
What is a condition associated with high levels of uric acid?
Gout
108
How much protein is it recommended for a person to eat per day?
0.75g of protein per kg of body weight.
109
What happens when a person takes in more protein then they require?
The surplus amino acids are rapidly catabolised and the nitrogen is excreted as urea in the urine. Very high intake can cause kidney damage.
110
What should the nitrogen balance be in normal healthy adults?
The intake should be equal to the amount excreted i.e. the rate of protein synthesis is equal to the rate of degradation.
111
What is the pathway of degradation for most cellular proteins?
They are recognised as old and damaged and are removed by the ubiquitin breakdown system.
112
What is the pathway of degradation for foreign exogenous proteins?
They are taken into vesicles by endocytosis or autophagocytosis where the vesicles fuse with the lysosome. Here, proteolytic enzymes degrade the proteins into amino acids.
113
What is transamination?
Where an amino acid reacts with a keto acid to form a different amino acid and different keto acid - their amine groups have swapped.
114
What is oxidative deamination?
Amino acid + H2O + coenzyme -> Keto acid + ammonia + coenzyme-2H
Degradation of amino acids.
115
What is transdeamination?
Where there is a transfer of an amine group from one compound to another (transamination) but also the loss of the amine group in the form of ammonia (deamination). Both of these steps are found within the same reaction.
116
What is the fate of keto acids after amination reactions?
They enter the TCA cycle as pyruvate or other citric acid components and are used as a source of ATP.
In starvation, the carbon skeletons 13 amino acids can be converted to glucose by the liver. These amino acids are classified as glucogenic.
117
What are ketogenic amino acids?
AAs that can only be degraded into acetyl CoA. This then goes into the TCA cycle or forms fat. These AAs are leucine and lysine.
118
What are the roles of the liver in nitrogen metabolism?
- Removal of amino acids, glucose and fats from the portal blood supply.
- Absorbs amino acids used for synthesis of cellular proteins.
- Synthesises plasma proteins.
- Synthesises haem, purines and pyrimidines for DNA.
- Undergoes transdeamination to degrade excess AAs.
- Converts ammonia to urea for excretion.
119
How are amino groups transported in the bloodstream and why?
As glutamine because it is more efficient as it can carry two amino groups.
120
What happens to glutamine in the liver?
It is converted to glutamate where one ammonia is released.
121
What are the four amino acids associated with the inter-organ transport of nitrogen?
- Alanine
- Glutamate
- Glutamine
- Aspartate
122
What are the four end products of nitrogen metabolism?
- Urea = protein breakdown
- Creatinine = creatine phosphate breakdown
- Uric acid = DNA and RNA breakdown
- Ammonium = control of body pH
123
Describe the urea cycle (ornithine cycle).
- NH4+ + CO2 + 2ATP -> carbamoyl phosphate + 2ADP
- Carbamoyl phosphate + ornithine -> citrulline
- Citrulline + aspartate -> argininosuccinate
- Argininosuccinate -> arginine + fumarate (lost)
- Arginine -> ornithine + Urea (lost)
124
What are the symptoms of ammonia poisoning?
Cerebral oedema, coma and death
125
What is hyperammonaemia and what is it caused by?
The impaired conversion of ammonia to urea.
Caused by liver failure and genetic defects.
126
What is the average fasting glucose concentration for adults?
4.4 - 5mM
127
What are the roles of glucose aside from producing energy?
- Source of pentose sugars for synthetic reactions (nucleotides, DNA)
- Source of carbon for other sugars and glucoconjugates
128
What are the advantages of glucose as a metabolic fuel?
- Water soluble (does not require a carrier in circulation)
- Can cross the BBB
- Can be oxidised anaerobically
129
What are the disadvantages of glucose as a metabolic fuel?
- Low yield of ATP compared to fatty acids
- Osmotically active (upsets the osmolarity of blood in high concentrations)
- Can cause damage in high concentrations
130
What is the function of glucose in adipose tissue?
The production of glycerol phosphate to be used as a tag.
131
What is the pentose phosphate pathway?
Working in parallel to glycolysis, it generates NADPH and pentoses as well as ribose 5-phosphate.
132
Why does the liver carry out glycogen synthesis and gluconeogenesis?
To provide glucose storage/glucose for other tissues, not itself.
133
What is gluconeogenesis?
In conditions of carbohydrate deprivation, glucose is synthesised from non-carbohydrate sources in the liver including lactate and glycerol but NOT fatty acids.
It works by bypassing the irreversible reactions in glycolysis by using different enzymes.
134
What are the two factors that regulate glyconeogenesis?
1) Motabolism of substrates: glycerol from fat breakdown and amino acids from muscle protein breakdown.
2) Activation of enzymes needed for gluconeogenesis.
135
What are the key enzymes needed for gluconeogenesis?
- Glucose-6-phosphatase
- Fructose-1,6-biphosphatase
- Phosphoenolpyruvate carboxykinase (PEPCK)
- Pyruvate carboxylase
- Pyruvate kinase
136
What is the Cori cycle?
Also called the lactic acid cycle, is a metabolic pathway in which lactate produced by muscles goes to the liver to be converted to glucose, which then returns to muscles to be converted back into lactate.
137
What is the glucose-alanine cycle?
Also called the Cahill cycle, is a series of reactions where amino groups and carbons from muscle are transported to the liver in the form of alanine. Nitrogen (in the form of NH2) is removed from alanine and enters the urea cycle and the remaining pyruvate is used to make glucose which returns to the muscle.
138
What hormones regulate glucose levels?
Insulin, glucagon and adrenaline
139
What are the differences between insulin and glucagon?
Insulin = anabolic hormone that promotes synthesis and storage.
Glucagon = catabolic hormone that promotes degradation of glycogen.
140
What hormone completely stops the action of insulin?
Adrenaline
141
What are the metabolic effects of insulin on the liver?
- Inhibits glyconeogenesis
- Activates glycogen synthesis
- Increases fatty acid synthesis and lipid assembly
- Increases amino acid uptake and protein synthesis
142
What are the metabolic effects of insulin on muscle?
- Increase glucose uptake via GLUT4
- Increases amino acid uptake and protein synthesis
- Activates glycogen synthesis
143
What are the metabolic effects of glucagon?
- Increase blood glucose by increasing glycogenolysis and gluconeogenesis.
- Increase in circulating fatty acids and ketone bodies.
- Decrease in plasma amino acids (by increasing uptake in the liver for gluconeogenesis).
144
What are macronutrients?
Large molecules we eat including lipids, carbohydrates, proteins and alcohol.
145
What are micronutrients?
These include vitamins and essential minerals, amino acids and fatty acids. You only need a tiny amount of these per day but need to be consumed.
146
How is the body's requirement for a nutrient calculated?
By looking at:
- The intake of a nutrient in groups of people with no deficiency and those with deficiency.
- By looking at intakes that would cure clinical deficiency.
- By using intakes that are associated with a marker of nutritional adequacy (enzyme saturation, tissue concentration).
147
What is EAR?
The estimated average requirement.
148
What is RNI and LRNI?
RNI = Reference Nutrient Intake = two standard deviations above the EAR which is sufficient of a nutrient to meet the needs of most of the population.
LRNI = Lower RNI = two standard deviations below the EAR which means that nutrient intakes below this level are almost certainly inadequate for most individuals.
149
How does sugar, fruit and vegetable consumption change over the social classes?
Sugar = increases from classes I to V
Fruit and vegetables = decreases from classes I to V
150
What are the risks for cardiovascular disease?
- High blood cholesterol
- Hypertension
- Smoking
- Inactivity
- Obesity
151
Which ethnic group has a higher incidence of strokes, diabetes and hypertension?
British of South Asian origin - salt features predominantly in traditional diets.
152
What is the average weight and fat percentage of a newborn baby?
3.4kg
14% fat
153
How is body composition measured?
- Body density
- Body water
- Total body potassium
- Methyl histidine or creatinine excretion
- Skinfold measurements
- Mid-arm circumference
154
What is bioelectrical impedance and how does it work?
This is used to calculate the body fat percentage.
Electrical signal is sent through the body. It travels more quickly in lean tissue (has a higher %age of water so conducts faster) and lower through fat. The information from the signals is used to work out body fat %age.
155
What is air displacement plethysmography?
Where you measure the volume of a chamber with and without a subject. From the subject's weight and volume you can calculate body density and fat and free fat mass.
156
When oxygen consumption is proportional to energy expenditure, what does one litre of oxygen equal?
1 litre oxygen = 20 kjoules energy
157
How do you measure basal metabolic rate?
kj/hour/kg of body weight
158
What is diet-induced thermogenesis?
When you get warmer after eating food. This is amplified if you ingest high protein.
159
What does energy requirement depend on?
- Basal metabolic rate
- Diet induced thermogenesis
- Physical activity
- Environmental temperature
- Growth, pregnancy, lactation
- Age
160
When do you measure basal metabolic rate?
12 hours after food or exercise.
161
What are the roles of leptin and insulin in satiety?
Leptin = signals the state of the fat stores - the plasma concentration of leptin reflects the size of these fat stores.
Insulin = signals the fullness of carbohydrate stores.
They inhibit hunger pathways and stimulate satiety pathways by acting on the hypothalamus.
162
What are examples of hunger signals?
- Neuropeptide Y
| - Ghrelin
163
What suppresses appetite?
POMC neurons, PPY3-36
164
What tissues release signalling molecules associated with hunger and satiety?
- Stomach (ghrelin)
- Intestine (PPY3-36)
- Adipocytes (leptin)
- Pancreas (insulin)
165
Where are the signals for hunger and satiety integrated?
In the arcuate nucleus of the hypothalamus.
166
What happens when a person needs food?
The stomach released ghrelin which stimulated NPY/AgRP producing neurons in the hypothalamus. NPY and AgRP then stimulate hunger. AgRP also blocks the action of melanocortin peptides.
167
What happens when a person has eaten enough?
1) PYY3-36, leptin and insulin inhibit the action of NPY/AgRP producing neurons in the hypothalalmus.
2) Leptin and insulin also stimulate POMC neurons in the hypothalamus which releases melanocortin peptides that inhibit hunger.
168
Where do short-term signals for satiety come from and why are they needed?
They come from the GI tract, hepatic portal vein and the liver.
They bring about the feeling of satiety through the vagus nerve and the circulation, because the action via the hypothalamus is too slow.
169
What do you see in obesity in terms of leptin?
You see leptin resistance and in rare cases leptin deficiency.
170
How do you calculate BMI?
weight/height^2
171
What happens to metabolic rate as a person gets larger?
It increases.
172
What are the endocrinological causes of obesity?
- Adrenal hyperactivity
| - Hypothyroidism
173
Is there a viral connection to obesity?
Potentially. AD36 antibodies were found in a higher number of obese subjects than lean. The effect/cause of these antibodies is unknown.
174
What are the risk factors for obesity?
- Low education level
- Chronic disease
- Little physical activity
- Heavy alcohol consumption
- Getting married
- Giving up smoking
175
What is the FTO gene?
Fat mass and obesity-associated protein (nicknamed fatso gene). It was found that people with one copy of this gene were on average 1.5kg heavier and people with two copies were 3kg heavier.
176
Other than the obvious, what diseases are associated with obesity?
- Respiratory problems
- Gall stones
- Reduced fertility in men
- Polycystic ovarian syndrome
- Breast, endometrial, colon and prostate cancer
177
Why do high protein diets work best?
They are easier to follow because the satiety value of protein is higher compared to carbohydrate or fat.
178
What are some pharmacological therapies for obesity?
- Sibutramine increases the concentration of serotonin and tends to reduce appetite (not licensed in the UK).
- Orlistat decreases fat absorption.
- Leptin has a modest effect at high doses but obese have leptin resistance.
179
What is the average daily intake of fat in the UK?
88g
40% of total energy intake, mainly triacylglycerols.
180
Give examples of two essential fatty acids.
1) Linoleic acid
2) Linolenic acid
(omega 3)
181
What is the recommended daily intake of the essential fatty acids?
2-5g/day
182
Which country has the highest number of deaths from CV disease?
Russian Federation
183
What are the risk factors for cardiovascular disease?
- Genetic susceptibility
- Smoking
- Sedentary lifestyle
- High blood pressure
- High serum cholesterol (LDL)
- Obesity
- Diabetes
- Trans fat intake ?
184
What is the effect of eating more saturated fats in the diet?
Increase in LDL and total cholesterol.
185
Which cancers seem to be associated with lifestyle choices? (Namely high fat intake)
Breast
Colon
Pancreas
Prostate
186
Do we actually need carbohydrates?
Not in theory but intake of carbohydrates has a protein-sparing effect (prevents our muscles being metabolised).
187
What is inositol?
It is a sugar alcohol present in fibre as hexaphosphate (phytic acid) which interferes with the absorption of iron and calcium.
188
What is the most common disaccharide that we eat?
Sucrose
189
What is important to remember about sucrose?
It is the frequency of consumption that is more important that the actual amount. A lollipop is the worst for your teeth.
190
What is the most common polysaccharide that we eat?
Starch
191
What diseases are related to a low intake of fibre?
Constipation
Diverticular disease
Appendicitis
Cancer of the colon
192
What are essential amino acids needed for in the body?
- Synthesis of new protein
- Catecholamines
- Thyroid hormones
- Neurotransmitters
- Haem
- Glutathione
193
What has been discovered in women with a high protein diet?
Bone demineralistion.
194
How much protein do newborn babies need?
2.4g/kg/day
195
What are the consequences of protein-energy malnutrition?
- Growth failure (low height for age).
- Marasmus (significantly reduced body weight compared to age).
- Kwashiorkor (lack of protein in diet associated with oedema).
- Marasmic kwashiorkor (combination of above).
196
How much does a child have to weigh to be classified as marasmic?
<60% of expected weight for their age.
197
What are the symptoms of Kwashiorkor?
- Severe oedema (painless, pitting)
- Liver enlargement and fat infiltration
- Changes in colour and texture of hair
- Dermatitis
- Permanent mental retardation (very severe cases)
198
What happens when you try to treat masamus vs. Kwashiorkor infants?
Because of the damage to the intestinal mucosa, it is difficult to treat masamus babies. Start with ORS and build up food.
Kwashiorkor infants will start getting better straight away.
199
What is the most likely cause of Kwashiorkor?
General food deficiency with added deficiency of antioxidant nutrients not being able to cope with the added oxidative stress of infection (infection increases protein requirement).
200
What makes up oral rehydration solution?
8 tsp sugar
1 tsp salt
1 litre boiled water
201
What is a vitamin?
A complex organic substance required in the diet in small amounts whose absence leads to a deficiency disease.
202
What are the water soluble vitamins?
B and C.
They are not stored extensively, are needed regularly are generally not toxic in excess.
203
What are the fat soluble vitamins?
A, D, E, K
They are stored, not absorbed or excreted easily and may be toxic in excess (A and D).
204
What do all B vitamins act as?
Co-enzymes in metabolic pathways.
205
What is thiamin?
Vitamin B1
206
What happens when you have an extreme untreated thiamin deficiency?
First Wernicke's encephalopathy (ataxia and disorientation) and then when it becomes more severe Korsakoff's psychosis (loss of memory) which is irreversible.
This many be linked to alcoholism.
207
Where will you find thiamin?
In most foods with the exception of white polished rice, sugar, fat, anti-thaimin foods and processed foods.
208
What foods are anti-thiamin foods?
Raw fish (contains thiaminases) and coffee and tea (contains anti-thiamin factors).
209
What is the role of thiamin in the body?
Its active form is thiamin pyrophosphate (TPP) which is a cofactor for the reaction pyruvate -> acetyl CoA.
210
What happens in a thiamin deficiency?
Accumulation of lactate in muscles.
Beri-beri.
211
Why does alcoholism lead to a deficiency in thiamin?
The transport of thamin from the intestine into the blood is inhibited as well as the enzyme that converts thiamin to TPP.
212
How does liver cirrhosis affect vitamin levels?
Storage and transport of fat soluble vitamins is impaired.
213
What is riboflavin?
Vitamin B2
214
Why is a riboflavin deficiency so rare?
Because it is usually associated with proteins.
215
What are the functions of riboflavin?
They help form FAD and FMN for use in redox reactions.
216
What is niacin?
Nicotinic acid or nicotinamide. These are vitamers.
217
What are vitamers?
A molecule with a different structural form as a vitamin but with the same function e.g. vitamin A1 works the same as vitamin A.
218
What are the functions of niacin?
They help form NAD and NADP for use in redox reactions.
219
Why do people on high protein diets have no requirement for niacin?
Because the liver can synthesise niacin from the amino acid tryptophan.
220
What is pallegra?
Niacin deficiency. Causes dermatitis, diarrhoea and dementia.
221
What is pyridoxine?
Vitamin B6
222
What is the function to pridoxine?
Its active form is pyridoxal phosphate which is essential for amino acid metabolism and haem synthesis.
223
What are the differences between primary and secondary vitamin deficiency?
Primary = when you're not ingesting enough.
Secondary = when you are given enough but it is not being used due to antagonists being present. Drugs can cause this.
224
What disease can cause pyridoxine deficiency?
TB due to the treatment isoniazid which combines with pyridoxal phosphate rendering it unavailable.
225
What has pyridoxine been used to treat?
- Seizures
- Down's syndrome
- Autism
- PMS
226
What is the function of vitamin B12?
It is a carrier of methyl groups in mammalian metabolism.
227
What is the function of folate (vitamin B9)?
It is a carrier of 1C units which aids reactions including synthesis of purine and pyrimidines and amino acid metabolism.
228
What does vitamin B12 need in order for it to be absorbed?
It needs to bind to intrinsic factor in the stomach.
229
What is the most common cause of pernicious anaemia?
Lack of intrinsic factor meaning vitamin B12 cannot be absorbed.
230
Where is folate found?
Green vegetables, liver and whole grains.
231
How are folate and vitamin B12 linked?
They are both involved in the conversion of homocysteine to methionine.
232
How does methotrexate work?
It blocks the enzyme DHF reductase which is responsible for converting dihydrofolate to tetrahydrofolate. This blocks the synthesis of pyrimidines and purines and therefore DNA.
233
What is megaloblastic anaemia?
Where you have large immature erythrocytes. They cannot mature because you do not have enough B12 and folate to produce tetrahydrofolate and therefore purines and pyrimidines and therefore DNA.
234
Why do you need both folate and B12 for methionine synthesis?
Folate is responsible for the production of MeTHF (methyl tetrahydrofolate), but you need B12 to utilise MeTHF in the synthesis of methionine and then the consequent recycling of tetrahydrofolate. Without B12, the folate is trapped as MeTHF so it cannot be used to carry out its other functions including the synthesis of purine, pyrimidines and other amino acids.
235
Why do you have neurological problems in B12 and/or folate deficiency?
You have inadequate myelin synthesis.
236
What causes vitamin B12 deficiency?
Inadequate intake or inadequate absorption due to a range of GI problems.
237
What causes folate deficiency?
Malabsorption, drugs and ethanol.
238
Why is folate essential during pregnancy?
It prevents neural tube defects when folic acid is taken.
239
What is hyperhomocysteinaemia and what has it been linked to?
Where you have abnormally high levels of homocysteine in the blood caused by a B12 deficiency.
Linked to CVD.
240
What is the link between folate, B6 and B12 and Alzheimer's?
Patients on high levels of supplements saw a reduction in the rate of brain shrinkage.
241
What is the function of pantothenic acid (vitamin B5)?
It is a component of co-enzyme A (CoASH) in the metabolism and transfer of carbon chains e.g. fatty acid oxidation.
242
What are the sources of biotin (vitamin B7)?
Peanuts, chocolate, egg yolk.
Also sufficient quantities provided by intestinal bacteria.
243
What is the most common cause of biotin deficiency?
Long-term antibiotic therapy resulting in sterilisation of the abdominal tract.
244
What is the function of biotin?
Biotin is a cofactor responsible for carbon dioxide transfer in several carboxylase enzymes including pyruvate carboxylase and acetyl CoA carboxylase.
245
What is vitamin C?
Ascorbic acid
246
What are the functions of vitamin C?
- It is an antioxidant nutrient.
- Vital for hydroxylation of proline and lysine in collagen formation.
- Reduces dietary Fe in the stomach so it can be absorbed.
247
What are the features of scurvy?
- Because a well-fed human has a 6 month store of vitamin C, signs appear after three months without it.
- Causes impaired wound healing, haemorrhages and anaemia.
248
Why do smokers need twice the normal intake of vitamin C?
The turnover of ascorbic acid is greatly increased by smoking.
249
What are the risks or megadoses of vitamin C?
- Kidney stones (oxalate is a major metabolite)
- Diarrhoea
- Systemic conditioning (get used to high amounts so have risk of deficiency when doses are lowered).
250
What are the fat soluble vitamins?
K, D, E and A
251
What are the sources of vitamin A?
- Retinol
- Animal liver
- Fish liver oils
- Whole milk
- Egg yolk
- Green/yellow/orange fruit and veg
252
What are the three active forms of vitamin A?
1) Retinoic acid = acts as a hormone similar to steroid hormones and helps cell growth.
2) Retinal = involved in vision.
3) β carotene = antioxidant
253
How does retinal aid vision?
At low light intensity, retinal participates in conversion of light energy to impulses in the optic nerve in the rod cells of the retina.
254
How is vitamin A transported and stored?
1) From the gut to the liver in chylomicrons
| 2) From the liver to tissues bound to a specific retinol binding protein and pre-albumin.
255
What happens when synthesis of retinol binding protein is disrupted?
Vitamin A cannot be transported to tissues. This leads to night blindness followed by progressive keratinisation of the cornea (xerophthalmia), keratomalacia and irreversible blindness.
256
What happens when you take too much vitamin A?
- Dermatitis
- Hair loss
- Mucous membrane defects
- Hepatic dysfunction
- Thinning
- Fracture of long bones
257
Why should pregnant women make sure they do not consume too much vitamin A?
High doses are known to cause birth defects.
258
What are the sources of vitamin E?
- Vegetable oils (especially wheat germ oils)
- Nuts
- Green vegetables
259
What is vitamin E?
A member of the family of tocopherols and is an antioxidant.
260
What are the functions of vitamin E?
- Prevents oxidation of unsaturated/polyunsaturated fatty acids in cell membranes and circulating lipoproteins as they are susceptible to attack by free radicals. Their destruction disrupts membrane structure and cell integrity.
261
Describe vitamin E deficiency.
- In animals it is known to cause sterility and muscular dystrophy.
- Virtually unknown in humans except premature low birth weight infants.
262
What is vitamin D3 and what is its function?
Cholecalciferol
Binds to intracellular receptors that eventually interact with DNA.
263
What is vitamin D2 and where is it found?
Ergocalciferol
It is derviced from ergosterols found widely in plants, fungi and moulds.
264
What is the main function of vitamin D?
Acts to maintain correct levels of calcium and phosphate in the blood so that proper mineralisation of bone is achieved.
265
What is seen in vitamin D deficiency?
Rickets in children = matrix of bones is not mineralised so you have bending of long bones.
Osteomalacia in adults = decalcification of long bones.
266
What happens in excessive consumption of vitamin D?
- Hypercalcaemia
- GI tract disturbances
- Calcification of soft tissues (heart, lungs, kidneys)
- Fatal when severe
10 time RNI produces toxicity (100µg).
267
What are the sources of vitamin K?
- Green leafy vegetables (best)
- Milk (small amounts)
- Meat
- Eggs
- Cereals
- Gut flora (considerable amount)
268
Why do infants have a marginal vitamin K deficiency?
- Human milk has a low vitamin K content
- Does not cross the placenta efficiently
- Neonatal gut is sterile
Some affected babies develop intracranial haemorrhages.
269
What happens in vitamin K deficiency?
Blood clotting is defective (increased blood clotting). Usually seen in long-term antibiotic therapy.
270
What is the long-term reserve of fat called?
Triacylglycerol (TAG)
271
Where does fatty acid synthesis occur in humans?
Liver
272
What is the first step in fatty acid synthesis?
Acetyl CoA to malonyl CoA catalysed by acetyl CoA carboxylase. This enzyme is activated by insulin.
273
What provides NADPH for fatty acid synthesis?
Hexose monophosphate shunt.
274
What is fatty acid synthetase?
Two long enzymes with a number of different active sites. This means the fatty acid just moves along the enzyme and is not lost during synthesis.
275
What do you need to make TAG?
Glycerol phosphate
Three fatty acids
The phosphate is removed when TAG is complete.
276
What happens to TAG when it reaches the blood?
Apoproteins (proteins that do not function on their own) and other lipids (phospholipids and cholesterol) attach to the TAG to form a complex called VLDL.
277
What is the structure of VLDLs?
They have an inner core of TAGs and cholesterol esters surrounded by an outer shell of a single layer of phospholipids with cholesterol and apoproteins.
278
What are the roles of the apoproteins that are found in VLDLs?
- Structural role
- Recognise by receptors (if the VLDL is destined to go inside a cell)
- Activates certain enzymes in lipid metabolism.
279
What are the four classes of lipoproteins?
- Chylomicrons = largest and carries mainly dietary TAGs and fat soluble vitamins
- VLDLs = carries exogenous TAG
- LDLs = carries cholesterol to tissues
- HDLs = carries cholesterol from tissues to the liver
280
What do chylomicrons receive from HDLs when they enter the circulation from the liver?
Two apoproteins called C-II and E.
281
What do you need to do to chylomicrons before their cargo can be stored in adipocytes?
- Remove TAG from the complex and hydrolyse it to form fatty acids.
- Fatty acids are taken into the adipocyte and re-esterified to TAG.
282
What enzyme is used to hydrolyse TAG?
Lipoprotein lipase
283
Why is glycerol sent back to the liver to be re-used when TAG is hydrolysed for adipocyte storage?
Because there is no glycerol kinase in adipocytes.
284
What is a chylomicron remnant?
A chylomicron that has lost some of its TAG.
285
What two factors are able to activate lipoprotein lipase?
Insulin
Apo C-II
286
What happens when the chylomicron remnant reaches the liver?
The apoprotein E is recognised by the Apo-E receptor on the liver and it is taken up and recycled.
287
What is the apoprotein used in endogenous fat?
B-100
288
What is IDL?
Intermediate density lipoprotein. This is what is formed after VLDLs have TAGs removed.
289
What happens to IDL?
It splits to form HDL (carrying apo C-II and E) and LDL (carrying mainly cholesterol and some TAG and apo B-100). The LDL then goes into peripheral tissue or to the liver guided by the B-100 and B-100 receptors on both the tissues and liver.
290
How does HDL take up cholesterol?
It esterifies the cholesterol to cholesterol ester which is neutral (not polar) so it can be stored in the centre of the HDL complex.
291
What is used to esterify cholesterol?
The enzyme LCAT. This is activated by apo A-1.
292
What apoprotein is found on HDL?
Apo A-1
293
What happens when LDL reaches the cells?
- LDL is recognised by B-100 receptors on the cell surface and binds. These receptors are then endocytosed into the cell.
- The receptors and the LDLs end up in lysosomes and the cholesterol escapes and levels build in the cell.
- Cholesterol then goes to the cell nucleus and inhibits the synthesis of enzymes that synthesise cholesterol.
294
How is cholesterol synthesised?
Acetyl CoA + Acetoacetyl CoA -> HMG-CoA -> mevalonate (catalysed by HMG-CoA reductase).
Mevalonate -> cholesterol
295
How do statins inhibit cholesterol synthesis?
They inhibit HMG CoA reductase as it is the rate limiting step.
296
What is familial hypercholesterolaemia?
Deficiecy of LDL receptor B-100.
This is a hyperlipidaemia disease.
297
What is lipoprotein A and what is high concentrations of lipoprotein A in the plasma associated with?
LDL plus apoprotein A.
An increased risk of coronary heart disease.
It has a similar structure to plasminogen so slows down the breakdown of blood clots by competing with plasminogen.
298
What is atherosclerosis?
A plaque in the blood vessels which is a complex structure involving inflammation and proliferation of smooth muscle in the artery wall. It contains connective tissue and a pool of cholesterol rich lipid.
299
What is the start of an atherosclerotic plaque?
A fatty streak which is an accumulation of foam cells.
300
What are foam cells?
Macrophages filled with lipid, mainly cholesterol.
301
What happens if the levels of LDL are high?
It continues circulating in the system and becomes modified (oxidised). This form is not recognised by the normal B-100 receptor so is instead taken up by scavenger receptors in macrophages.
These receptors are not downregulated and the result is the accumulation of cholesterol.
