Nutrition and Metabolism Flashcards
(103 cards)
1
Q
At what pH is ATP stable?
A
pH 6-9
2
Q
What are the differences in function between ATP, UTP and GTP?
A
ATP: pumps, transporters, contractile events and movement
UTP: synthesis of complex sugars
GTP: protein synthesis
3
Q
In glycolysis, what are the steps that use/produce ATP and which step produces NADH + H+?
A
Use ATP:
- Hexokinase/glucokinase: glucose –> glucose-6-phosphate
- Phosphofructokinase: Fructose-6-phosphate to fructose 1,6-bisphosphate
Produce ATP:
- Phosphoglycerate kinase: 1,3-bisphosphoglycerate to 3 phosphoglycerate
- Pyruvate kinase: phosphoenolpyruvate to pyruvate
Produce NADH + H+:
1. Glyceraldehyde 3-phosphate dehydrogenase: G3P –> 1,3-bisphosphoglycerate
4
Q
Which reactions represent activation in glycolysis?
A
- Hexokinase
- Phosphoglucose isomerase
- Phosphofructokinase
5
Q
Which reaction splits the 6C sugar in glycolysis?
A
- Aldolase
6
Q
Which reaction represents oxidation in glycolysis?
A
- glyceraldehyde-3-phosphate dehydrogenase
7
Q
What are the ATP synthesis stages in glycolysis?
A
- Phosphoglycerate kinase*
- Phosphoglycerate mutase
- Enolase
- Pyruvate kinase*
8
Q
What is the reaction catalysed by lactate dehydrogenase?
A
In muscle:
Pyruvate + NADH H+ –> L-lactate + NAD+
In liver: opposite
9
Q
How is phosphofructokinase controlled allosterically?
A
ATP and citrate inhibit, AMP activates
10
Q
What is the link reaction?
A
Conversion of pyruvate to acetyl CoA (pyruvate dehydrogenase, CoA, NAD+)
Cofactors: thiamine pyrophosphate, lipoic acid
11
Q
What type of bonds does CoA form with carboxylic acids?
A
Thioester bonds
12
Q
What is the condensation reaction of the Krebs cycle?
A
Citrate synthase:
Acetyl CoA + oxaloacetate –> citrate
13
Q
What is the isomerisation reaction of the Krebs cycle?
A
Aconitase:
Citrate –> isocitrate
14
Q
When is the first loss of CO2 in the Krebs cycle?
A
Isocitrate dehydrogenase:
Isocitrate + NAD+ –> alpha-ketoglutarate + NADH H+
15
Q
When is the second loss of CO2 in the Krebs cycle?
A
Ketoglutarate dehydrogenase:
alpha-ketoglutarate + NAD+ –> succinyl CoA + NADH H+
16
Q
When does production of GTP occur in the Krebs cycle?
A
Succinate thiokinase:
succinyl CoA + GDP –> succinate + GTP + CoA
17
Q
When does production of FADH2 happen in the Krebs cycle?
A
Succinate dehydrogenase:
Succinate + FAD –> Fumarate + FADH2
18
Q
What is the enzyme that converts fumarate to malate?
A
Fumarase
19
Q
When does the third production of NADH H+ in the Krebs cycle occur?
A
Malate dehydrogenase:
Malate + NAD+ –> oxaloacetate + NADH H+
20
Q
How many molecules of ATP does the TCA cycle produce?
A
10
21
Q
Which enzyme steps in the Krebs cycle are irreversible and what inhibits or stimulates these?
A
- Citrate synthetase: NADH and succinyl CoA inhibit
- Isocitrate dehydrogenase: NADH inhibits, ADP stimulates
- Ketoglutarate dehydrogenase: NADH and succinyl CoA inhibit
22
Q
What are the biosynthetic roles of the TCA cycle?
A
Transaminations:
1. Oxaloacetate –> aspartate
2. Alpha-ketoglutarate –> glutamate
Phosphoenolpyruvate production: by PEP carboxylase from oxaloacetate
Citrate –> FAs
Malate –> pyruvate (malic enzyme –> production of NADPH H+)
23
Q
What is the activation step of long chain fatty acids?
A
Fatty acid + ATP + CoA –> acyl CoA + AMP + PPi
24
Q
How are fatty acids transported into the mitochondria?
A
Carnitine palmitoyl-transferase I:
Fatty acyl CoA + carnitine –> CoA + fatty acid-carnitine
Translocase: transports through inner mm
Carnitine palmitoyl-transferase II: opposite reaction
25
What is the first step of beta oxidation?
Acyl-CoA dehydrogenase:
| fatty acyl-CoA + FAD --> enoyl CoA + FADH2
26
What is the second step of b-oxi?
Enoyl CoA hydratase:
| enoyl CoA + H2O --> 3-L-hydroxyacyl CoA
27
What is the third step of b-oxi?
3-L-hydroxyacyl CoA dehydrogenase:
| 3-L-HA CoA + NAD+ --> beta-ketoacyl CoA + NADH H+
28
How does the removal of 2C unit in b-oxi happen?
beta-ketoacyl CoA thiolase:
| beta-ketoacyl CoA + CoASH --> fatty acyl CoA + acetyl CoA
29
What do odd-chain fatty acids require?
Enzyme requiring cobalamin (VitB12)
30
What activates lipase enzyme?
Adrenaline and glucagon
31
What are the first stages of glycogen synthesis from glucose?
1. Hexokinase (muscle), glucokinase (liver) --> glucose-6-phosphate
2. Phosphoglucomutase --> glucose-1-phosphate
32
How is UDP glucose formed?
Transferase:
| Glucose-1-phosphate + UTP --> UDP glucose + PPi
33
Which enzyme adds glucose to protein primer (glycogenin)?
Glycogen synthase
34
How is glycogen synthase regulated?
Protein kinase phosphorylates and inactivates glycogen synthase
Protein phosphatase dephosphorylates and activates glycogen synthase
35
Which enzymes are required to degrade glycogen?
Glycogen phosphorylase and debranching enzyme
36
Which enzyme converts glucose-6-phosphate to glucose?
Glucose phosphatase (only present in liver)
37
How is glycogen phosphorylase regulated?
Protein phosphatase deactivates
| Protein kinase activates
38
Which enzyme converts cAMP to AMP?
Phosphodiesterase
39
What stimulates protein kinase?
Adrenaline and glucagon
40
What stimulates protein phosphatase
insulin
41
What are other control mechanisms in the liver and muscle?
Liver: high glucose --> glucose binds to glycogen phosphorylase and inactivates it
Muscle: high calcium concentrations --> calcium binds to calmodulin domain on glycogen phosphorylase kinase and activates it
Prolonged exercise: AMP activates glycogen phosphorylase --> no need for hormonal interaction (ATP is an inhibitor)
42
What is von Gierke's disease?
Defective glucose-6-phosphatase
43
What is Pompe's disease?
Defective lysosomal glycosidase
44
What is McArdle's disease?
Defective glycogen phosphorylase
45
How are most cellular proteins and foreign exogenous proteins broken down?
Most cellular proteins: ubiquitin pathway
Foreign exogenous proteins: taken into vesicles by endocytosis, or autophagocytosis, vesicle fuses with lysosome --> proteolytic enzymes degrade protein
46
What are the two pathways responsible for amino acid degradation?
Transamination: produces non essential aa
Amino acid 1 + keto acid 2 keto acid 1 + amino acid 2
Oxidative deamination: only glutamate by glutamate dehydrogenase
Amino acid + H2O + NADP+ --> keto acid + ammonia + NADPH H+
47
What do all aminotransferases require?
vitamin B6
48
Which are the ketogenic amino acids?
Leucine and lysine
49
Which aa are both ketogenic and glucogenic?
phenylalanine, tyrosine, tryptophan and isoleucine
50
How are amino groups transported in the blood?
As glutamine
51
How is glutamine converted to glutamate and vice versa?
Glutaminase: glutamine --> glutamate
| Glutamine synthetase: glutamate + ATP + NH3 --> glutamine
52
Where do the nitrogens in urea come from?
One from glutamate and one from aspartate
53
What is the physiologically normal glucose concentration?
3. 9-6.2 mM
| 4. 4-5.0 mM average fasting
54
Which are the irreversible reactions in glycolysis and how are they bypassed?
1. Hexokinase --> glucose-6-phosphatase
2. Phosphofructokinase --> fructose-1,6-bisphosphatase
3. Pyruvate kinase --> pyruvate carboxylase + PEP carboxylase
55
What is the estimated average requirement (EAR)?
mean of bell curve; the notional mean requirement of a nutrient
56
What is the reference nutrient intake (RNI)?
two standard deviations above the EAR: sufficient of a nutrient to meet the needs of most of the population
57
What is the lower reference nutrient intake (LRNI)?
2 sd below EAR: intake of a nutrient below this level are almost certainly inadequate for most individuals
58
What are the Vitamin C values for EAR, RNI and LRNI?
EAR: 25 mg
RNI: 40 mg
LRNI: 10 mg
59
What do energy requirements depend on?
Basal metabolic rate, diet induced thermogenesis, physical activity, environmental T, growth, pregnancy and lactation, age
60
What are the functions of leptin and insulin?
Satiety signals; act on hypothalamus to inhibit hunger pathways and stimulate satiety pathways
61
What do pro-opiomelanocortin (POMC) related peptides (PYY 3-36) do?
Suppress appetite; secreted by the intestine
62
Where are satiety and hunger signals integrated?
Arcuate nucleus of hypothalamus
63
What stimulates/inhibits NPY/AgRP producing neurons and POMC neurons?
```
NPY/AgRP producing neurons:
1. Inhibited by: PPY 3-36, leptin and insulin
2. Stimulated by: ghrelin
POMC neurons:
1. Stimulated by: leptin, insulin
```
64
What is the formula for BMI?
wt/ht^2
65
What does orlistat do?
Decreases fat absorption
66
Define kwashiorkor, marasmus and marasmic kwashiorkor?
Kwashiorkor: 60-80% of expected weight for age + oedema (changes in colour and texture of hair, dermatitis)
Marasmus: less than 60% of weight and no oedema
Marasmic kwashiorkor: less than 60% + oedema
67
Which are the water soluble vitamins and which are the fat soluble ones?
Water soluble: B and C
| Fat soluble: A, D, E and K
68
What is beri-beri?
Deficiency of thiamin (B1)
69
What is Wernicke-Korsakoff syndrome due to?
Thiamin deficiency, associated with alcoholism
70
Where can you find thiaminases?
Raw fish
71
What is the biochemical role of thiamin?
Thiamin pyrophosphate coenzyme in pyruvate dehydrogenase
72
What is the function of riboflavin?
B2; functions as FAD and FMN in redox reactions
| Deficiency: rare except in alcoholics
73
What is the function of niacin and what is its deficiency?
B3
| NAD and NADP in redox reactions; pellagra, dermatitis, diarrhoea, dementia
74
What is the importance of vitamin B12 and folate?
Needed for purine, pyrimidine and amino acid synthesis
| Pernicious anemia: deficiency in intrinsic factor --> no B12 absorption (secondary deficiency)
75
What is the function of biotin?
B7; prosthetic group for carboxylations (pyruvate --> oxaloacetate; acetyl CoA --> malonyl CoA)
Rare unless eating raw eggs or long term antibiotic treatment
76
What is the function of vitamin C?
Collagen formation (hydroxylation of lysine and proline); reduction of dietary Fe for absorption
77
What is the function of vitamin A?
Control of protein synthesis and in scotopic vision (low light intensity)
78
What is the function of vitamin E?
Includes family of tocopherols --> antioxidants; prevents oxidation of PUFA and apoB in LDL
79
What is the function of vitamin D?
Cholecalciferol (D3), ergocalciferol (D2); act to mantain correct levels of calcium and phosphate in the blood so that proper mineralisation of the bone is achieved
Deficiency: rickets (children), osteomalacia (adults)
80
What are deficiencies associated with vitamin K?
Defective blood clotting in long term antibiotic therapy
| Haemorrhagic disease in newborns due to poor placental transfer
81
What is the rate limiting step of fatty acid synthesis and what is it activated by?
Acetyl CoA carboxylase (activated by insulin):
| Acetyl CoA + ATP + CO2 --> malonyl CoA + ADP + Pi
82
What does malonyl CoA inhibit?
Carnitine transferase
83
Which pathway is source to NADPH?
Hexose monophosphate shunt
84
What is the structure of lipoproteins?
Inner core: triglycerides and cholesterol esters
| Outer shell: single layer of phospholipids, cholesterol an apoproteins
85
Which apoproteins are present on chylomicrons?
Apo B-48, apo C-II and apoE
86
Which apoproteins are present on VLDLs?
Apo B100, apo C-II and apoE
87
Where are the B100 receptors situated?
Peripheral tissue and liver
88
What is the function of apo C-II?
Activate lipoprotein lipase
89
Where is HDL synthesised and how does it work?
Synthesised in gut and liver; has apo A-1 --> activates LPC and LCAT these provide acids for esterification of cholesterol from phospholipids
90
How is cholesterol synthesised?
Acetyl CoA + acetoacetyl CoA --> HMG-CoA
HMG CoA + HMG-CoA reductase --> mevalonate I (rate limiting step)
Mevalonate I --> cholesterol
*Statins inhibit HMG-CoA reductase
91
What is familial hypercholesterolaemia caused by?
Deficiency in B100 receptors
92
Which are the essential minerals?
sodium, magnesium, potassium and calcium
93
What are the concentrations of sodium and potassium inside and outside the cell?
Inside: Na 12 mM, K 140 mM
Outside: Na 140 mM, K 5 mM
94
What is the function of magnesium?
Cofactor complex (ATP) and enzyme complex
95
Which are the essential 'trace' minerals?
Mn, Fe, Co, Cu, Zn, Mo
96
Where is iron stored and how is it transported?
Stored in ferritin, transported by transferrin
97
How is iron uptaken into cells?
receptor mediated endocytosis (DMT1)
98
Which proteins are important for Zn haemostasis?
ZIP: zinc import proteins
ZNT: zinc export proteins
MT: methallothioneins (zinc transport)
MTF1: zinc sensor
99
What stimulates and inhibits insulin secretion?
Stimulation by: high glucose and aa concentrations, secretin, glucagon
Inhibition by: adrenaline
100
How do increased concentrations of glucose and aa lead to insulin secretion?
ATP production --> K+ channels close --> calcium channels open --> insulin is secreted
101
What are the intracellular effects of insulin?
Tyrosine receptor activation --> Akt protein kinase activation which leads to:
1. Expression of GLUT4 receptors
2. Inactivation of glycogen synthase kinase through phosphorylation --> active glycogen synthase
3. Activation of phosphodiesterase (cAMP --> AMP) --> PKA is inhibited --> hormone sensitive lipase is inhibited --> TAG is stored
4. Activation of Ras and MAPK --> gene expression
102
Which compounds act as ketone bodies?
Acetoacetate and beta-hydroxybutyrate
103
What is the action of ketone bodies on the pancreas?
Stimulates release of insulin --> limits muscle proteolysis and adipose tissue lipolysis --> muscle tissue is preserved
