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Metabolism > Week 1 and week 4 > Flashcards

Week 1 and week 4 Flashcards

0
Q

When are we in negative nitrogen balance?

A

Starvation, muscle wasting.

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1
Q

When are we in positive nitrogen balance?

A

Growth and pregnancy

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2
Q

What is transamination?

A

Transfer of an amino group from an amino acid to either alphaketoglutarate (yielding glutamate and a ketoacid) or oxaloacetate (yielding aspartate and a ketoacid)

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3
Q

What are ALT and AST, and what is their clinical significance?

A

ALT is alanine aminotransferase, converts alanine to glutamate
AST is aspartate aminotransferase, converts glutamate to aspartate
They are present in high concentrations in the liver, high levels in the blood would indicate liver damage

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4
Q

What is the purpose of transamination?

A

Transfer amino group to ketones to produce amino acids that can enter the ornithine cycle

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5
Q

What enzyme is deficient in Phenylketonuria? What reaction does it catalyse?

A

Phenylalanine hydroxylase, which catalyses the reaction from phenylalanine to tyrosine.

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6
Q

What is tyrosine used for?

A

Noradrenaline, adrenaline, dopamine, thyroxine.

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7
Q

What is elevated in PKU?

A

Phenylketones (phenylpyruvate) in blood plasma and urine

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8
Q

What are the effects of elevated plasma phenylpyruvate?

A

Inhibits brain development by inhibiting uptake of pyruvate into mitochondria, interferes with TCA cycle and production of ATP

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9
Q

What is the inheritance pattern of PKU, and what chromosome is the gene that codes for phenylalalanine hydroxylase found on?

A

Autosomal recessive.

Chromosome 12.

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10
Q

What enzyme is deficient in homocystinuria?

A

Cystathionine beta synthase

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11
Q

What reaction does cystathionine beta synthase catalyse?

A

Homocysteine to cystathionine.

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12
Q

What treatment is given for homocystinuria and why?

A

Vitamin B6 is a cofactor for the reaction catalysed by CBS.

Low methionine in diet (homocysteine synthesised from methionine)

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13
Q

What is elevated in homocystinuria?

A

Homocysteine and methionine in plasma

Homocystine in urine

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14
Q

What are the consequences of elevated homocysteine in plasma?

A

Interferes with fibrillin-1, can be mistaken for Marfan’s syndrome.
Associated with increased incidence of cardiovascular disease.
Also affects central nervous system, muscles.

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15
Q

What is the inheritance pattern of homocystinuria, what chromosome is the gene coding for CBS found on?

A

Autosomal recessive.

Chromosome 21.

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16
Q

What important gas signalling molecules are produced by amino acid metabolism?

A

Nitrous oxide - neurotransmitter, vasodilator, inflammatory mediator. From arginine.
Hydrogen sulfide - vasodilator, neuromodulator, cytoprotective. From cysteine.

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17
Q

Explain the clinical significance of creatinine levels.

A

Creatinine phosphate is a breakdown product of creating and creative phosphate and is produced at a constant rate proportional to muscle mass.
High creatinine levels in urine would be indicative of muscle wasting.
Levels of creatinine in blood compared with urine can be diagnostic of kidney damage if unable to excrete.
Marker of dilution of urine.

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18
Q

How is glutamine synthesised?

A

From glutamate and ammonia in cells (requires ATP)

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19
Q

What is the fate of glutamine?

A

Deamination to yield glutamate and ammonia (catalysed by glutaminase) which either enter urea cycle in the liver, or ammonia excreted in kidneys.
Can also be used to synthesise purines and pyrimidines.

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20
Q

What are the toxic effects of hyperammonaemia?

A

High levels of ammonia means alphaketoglutarate is aminated to form glutamate. Depleted alphaketoglutarate inhibits TCA cycle.
Reduces blood pH
Affects neurotransmitter synthesis.

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21
Q

What is the consequence of a defect in the urea cycle:
A. Total absence of an enzyme
B. Partial deficiency of an enzyme

A

Always fatal.
Hyperammonaemia, accumulation of intermediates. Leads to vomiting, lethargy, irritability, mental retardation, seizures, coma, death.

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22
Q

How do you manage defects in the urea cycle?

A

Low protein diet, replace amino acids with keto acids.

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23
Q

Why does reseeding syndrome occur?

A

Enzymes of urea cycle repressed by long term protein deficiency, when proteins consumed ammonia accumulates in blood stream, hyperammonaemia, toxic.

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24
Q

Why is urea a good waste product?

A 
Non toxic.
Metabolically inert
Useful osmotic effect in kidneys
High nitrogen content
Water soluble
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25
Q

What is deamination? Give an example and the enzyme that catalyses it.

A

Removal of amine group. Glutamine - glutamate and ammonia catalysed by glutaminase.

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26
Q

What are the essential amino acids?

A

Threonine valine leucine isoleucine tryptophan lysine methionine phenylalalanine.

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27
Q

Which amino acids become essential under certain conditions?

A

Histidine, cysteine, tyrosine, arginine

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28
Q

What are the energy stores in a 70kg man.

A

100g glycogen in liver
300g glycogen in skeletal muscle
6kg skeletal muscle
15kg triacylglycerols

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29
Q

Describe the structure of glycogen

A

Polymer of glucose consists of alpha 1-4 and alpha 1-6 glycosidic bonds in a ratio of 10:1. The 1-6 bonds make the structure highly branched.

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30
Q

Outline glycogenesis, including the enzymes involved.

A

Glucose + ATP -> glucose 6 phosphate + ADP (hexokinase, glucose as in liver)
Glucose 6-P -> Glucose 1-P (phosphoglucomutase)
Glucose 1-P + UTP + Water -> UDP glucose + 2Pi
Glycogen (n residues) + UDP-glucose -> glycogen (n+1 residues) + UDP (glycogen synthase and branching enzyme)

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31
Q

Describe glycogenolysis, including the enzymes.

A

Glycogen (n+1 residues) + Pi -> glucose 1-phosphate + glycogen (n residues) (glycogen phosphorylase). Debranching enzyme produces free glucose.
Glucose 1-P -> Glucose 6-P (phosphoglucomutase)
Glucose 6-P -> Glucose (glucose 6-phosphatase, only present in the liver)

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32
Q

How is the synthesis and degradation of glycogen regulated?

A

High ATP and low ADP promotes glycogen storage and inhibits glycogenolysis. Low ATP and high ADP stimulates glycogenolysis and inhibits glycogenesis (allosteric control)
They are also regulated hormonally. Insulin promotes dephosphorylation of glycogen synthase and glycogen phosphorylase, which allosterically inhibits phosphorylase and stimulates synthase. Glucagon and adrenaline promote phosphorylation which has the opposite effect. (Covalent modification)

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33
Q

What tissues have an absolute requirement for glucose?

A

Erythrocytes, leukocytes, kidney medulla, lens of the eye.

CNS prefers glucose but can use ketone bodies.

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34
Q

What are the possible consequences of glycogen storage disease? Give an example and the affected enzyme.

A

Affects muscle or liver - may have abnormal glycogen structure.
Excess glycogen storage can lead to tissue damage.
Reduced glycogen storage can lead to poor exercise tolerance, hypoglycaemia.
von Gierke’s disease - glucose 6-phosphatase deficiency.

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35
Q

How many hours after a meal does gluconeogenesis start?

A

8-10 hours.

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36
Q

Where does gluconeogenesis occur?

A

Liver, and to a lesser extent the kidney cortex.

37
Q

Name 6 substrates for gluconeogenesis.

A

Pyruvate, lactate, glycerol, gluconeogenic amino acids which give rise to intermediates of TCA cycle when metabolised, fructose, galactose, oxaloacetate.

38
Q

How are steps 1 and 3 of glycolysis bypassed in gluconeogenesis, and why is this necessary?

A

Step 1 is catalysed by glucose 6-phosphatase. Step 3 is bypassed by fructose 1,6-bisphosphatase. They are thermodynamically spontaneous.
This is necessary because steps 1 and 3 of glycolysis are irreversible.

39
Q

How is stage ten of glycolysis bypassed in gluconeogenesis from pyruvate, and what enzymes catalyse it?

A

Pyruvate to oxaloacetate by pyruvate carboxylase

Oxaloacetate to phosphoenylpyruvate by phosphoenylpyruvate carboxykinase (PEPCK)

40
Q

What is the significance of the reaction catalysed by PEPCK?

A

Catalyses oxaloacetate to pyruvate, which provides the link between the Krebs cycle and gluconeogenesis and allows gluconeogenic amino acids to be used for the synthesis of glucose.

41
Q

How is gluconeogenesis regulated?

A

It is under hormonal control. Insulin decreases the activity of PEPCK and glucagon and cortisol increases the activity of PEPCK, by altering the amount of the enzyme.
Insulin decreases the amount and activity of fructose 1,6-bisphosphatase, and it’s amount and activity are increased by glucagon and cortisol.

42
Q

What is the effect of diabetes on gluconeogenesis?

A

Insulin deficiency means glucagon to insulin ratio is high, gluconeogenesis stimulated. This contributes to hyperglycaemia.

43
Q

What is the function of adipose tissue?

A

Storage of fuel
Insulation
Protection of organs.

44
Q

What hormone promotes storage of triacylglycerols, and what hormones reduce storage of triacylglycerols?

A

Insulin.

Adrenaline, glucagon, growth hormone, cortisol, thyroxine.

45
Q

What is required for fatty acid synthesis, and where does it come from?

A

Acetyl coenzyme A - obtained from proteolytic cleavage of citrate from mitochondria to oxaloacetate and acetyl CoA.
NADPH from pentose phosphate pathway.
ATP from oxidative phosphorylation, glycolysis.

46
Q

What enzymes are involved in fatty acid synthesis, and what reactions do they catalyse? What cofactors are required, if any?

A

Fatty acid synthase complex catalyses the addition of malonyl CoA to the fatty acid chain, and the subsequent loss of CO2.
Acetyl CoA carboxylase catalyses the carboxylation of acetyl CoA to malonyl CoA. This requires biotin (vitamin B7) as a cofactor.

47
Q

Describe how the activity of acetyl CoA carboxylase is regulated. What process does this enzyme control the rate of?

A

It is allosterically inhibited by AMP and activated by citrate.
It is activated by dephosphorylation, promoted by insulin.
It is inhibited by phosphorylation, promoted by glucagon and adrenaline.
Fatty acid synthesis.

48
Q

List six differences between fatty acid synthesis and fatty acid beta oxidation.

A

Oxidation occurs in mitochondria, synthesis occurs in cytoplasm.
Oxidation uses free enzymes, synthesis uses a multienzyme complex.
Oxidation removes two carbons as acetyl CoA, synthesis adds three carbons as malonyl CoA and then loses CO2.
Oxidation produces NADH and FADH2, synthesis uses NADPH.
Oxidation indirectly regulated by availability of fatty acids, synthesis regulated by regulating activity of Acetyl CoA Carboxylase.
In oxidation the intermediates are bound to Acetyl CoA, in synthesis they are bound to carrier proteins in the multi enzyme complex.

49
Q

What is the relationship between joules, calories and kilocalories?

A

1 kilocalorie = 1000 Calories.

1 Calorie = 4.184 Joules

50
Q

What is energy required for in cells?

A 
Osmotic work - kidney
Electrical work - nervous impulses
Mechanical work - muscle contraction
Biosynthesis/anabolism
Active transport, maintenance of concentration gradients and uptake of nutrients.
51
Q

Define exergonic and endergonic.

A

Exergonic: energy released during reaction is greater than energy input.
Endergonic: energy input is greater than energy release.

52
Q

Why must chemical bond energy be used for activities in cells?

A

Human body is isothermal so cannot use energy released as heat.

53
Q

How do reactions that require energy input take place?

A

Coupling with exergonic reactions (usually through the ADP-ATP cycle)

54
Q

What are the three components of daily energy expenditure?

A

Basal metabolism
Voluntary physical activity
Diet induced thermogenesis - energy to process food.

55
Q

What are the main tissues that contribute to the BMR, and in what proportions?

A

Skeletal muscle - 30%
Central nervous system - 20%
Liver - 20%
Heart - 10%

56
Q

What increases BMR?

A

Hyperthyroidism, pregnancy, lactation.

57
Q

What is a rough estimate of BMR in kilojoules in an individual who is not obese?

A

100*weight in kg

58
Q

Why is BMR less for a woman than a man, if they were of the same weight?

A

Women have more adipose tissue, which is less metabolically active.

59
Q

What proportion of the energy from ingested food is used to digest the food?

A

Roughly 10%

60
Q

What is the energy content of fat?

A

37kJ/g

61
Q

What is the energy content of carbohydrate?

A

17kJ/gram

62
Q

What is the energy content of protein?

A

17kJ/gram

63
Q

What is the energy content of alcohol?

A

29kJ/gram

64
Q

What is the recommended proportion of our energy requirements that should come from fat, carbohydrates and proteins?

A

30%, 55%, 15%

Fats should be mostly unsaturated.

65
Q

Why are fats an important part of the diet?

A

High energy content
Absorption of fat soluble vitamins (A, D, E and K)
Unable to synthesise polyunsaturated fatty acids, including linoleic and linolenic acids - part of plasma membranes and needed to synthesise eicosanoids.

66
Q

How much water is lost per day, and how?

A

2.5 litres - 1.5 litres in the urine. 0.4 litres through the lungs, 0.5 litres through the skin, 0.1 litres in faeces.

67
Q 
What proportion of the body weight of:
A child
An adult
An elderly person
An obese person
Is water?
A

70%
50-60%
50%
Less than in an adult.

68
Q

Which vitamins have antioxidant properties?

A

Vitamin C, vitamin E and selenium.

69
Q

How do you calculate BMI?

A

Weight in kg/height in metres^2

70
Q

What might be a better measurement than BMI?

A

Waist to hip ratio.

71
Q

What BMI corresponds to what category?

A

35 = severely obese

72
Q

What are the possible causes of malnutrition?

A

Malabsorption such as coeliac disease or Crohn’s disease.
Eating disorders such as anorexia nervosa, bulimia nervosa.
Reduced availability of food - protein energy malnutrition.

73
Q

What is marasmus?

A

Energy deficiency - muscle weakness, thinning of hair, loss of body fat, diarrhoea, no oedema, anaemia

74
Q

What is kwashiorkor?

A

Protein deficiency - abdominal ascites, muscle wasting, apathy, lethargy, loss of appetite, hepatomegaly, low serum albumin, anaemia.

75
Q

What is homeostasis?

A

The control of the internal environment within set limits and in a dynamic equilibrium.

76
Q

What is the normal reference range for fasting glucose?

A

3.3-6.0 mmol/L

77
Q

What is the reference range for plasma potassium concentration?

A

3.5-5.3 mmol/litre

78
Q

What is the reference range for plasma sodium concentration?

A

133-146mmol/litre

79
Q

What is the reference range for plasma cholesterol concentration, and what is the ideal maximum?

A
  1. 5-6.5mmol/litre

5. 2mmol/litre.

80
Q

What are the three major carrier molecules?

A

FADH2
NADH
NADPH

81
Q

What vitamins are required for the synthesis of carrier molecules?

A

Niacin for nicotinamide

Riboflavin for flavin

82
Q

What can you say about the total concentration of carriers in a cell?

A

Constant - therefore if they are all in reduced (NADH, NADPH, FAD2H) form, no reducing power is available and vice versa.

83
Q

How is Gibbs free energy related to temperature, enthalpy change and entropy change?

A

deltaG=deltaH-T*deltaS

84
Q

What are the standard conditions?

A

Temperature 25 degrees Celsius
Concentration 1M
pH 7.0

85
Q

What is Pi?

A

HPO4-

86
Q

What is the Gibbs free energy of the removal of a phosphate group from ATP or ADP by hydrolysis?

A

-31 kJ/mol

87
Q

What are high energy signals?

A

ATP, NADPH, NADP, FAD2H.

88
Q

What are low energy signals?

A

AMP, ADP, NAD+, NADP+, FAD

89
Q

What other compounds have high energies of hydrolysis?

A

Phosphoenolpyruvate (-62kJ/mol)
1,3 Bisphosphoglycerate (-49kJ/mol)
(Both important for substrate level phosphorylation of ADP in glycolysis)
Creatine Phosphate (-43kJ/mol)

Metabolism (9 decks)

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