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Metabolism, Endocrinology and Haematology > Session 1 - Alcohol Metabolism, Oxidative Stress and Protein and Amino Acid Metabolism > Flashcards

Session 1 - Alcohol Metabolism, Oxidative Stress and Protein and Amino Acid Metabolism Flashcards

1
Q

What are the 2 steps of alcohol metabolisms and the 2 enzymes involved?

A

Alcohol converted to acetaldehyde by alcohol dehydrogenase, releasing NADH

Acetaldehyde converted to acetate by aldehyde dehydrogenase, releasing NADH

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2
Q

What are 2 ways that metabolism of alcohol can cause damage to the liver?

A

Acetaldehyde is toxic, if accumulated can cause liver damage

Decrease in NAD+/NADH ratio and increased acetyl~coA affects liver metabolism

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3
Q

What are 4 effects of decreased NAD+/NADH ratio on liver cell metabolism?

A

Lactic acidosis - lactate cannot convert to pyruvate and accumulates in blood
Gout - increased lactate reduces kidney’s ability to excrete uric acid
No gluconeogenesis
Hypoglycaemia

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4
Q

What are 2 effects of increased acetyl~CoA?

A

Increased synthesis of fatty acids and ketone bodies, fatty acids converted to triacylglycerols, lack of lipoprotein synthesis prevents transport away from liver and causes fatty liver.

Increased ketone bodies can cause keto-acidosis

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5
Q

What are the 2 enzymes to look for in order to detect liver cell damage?

A

Loss of enzymes like transaminases and gamma glutamic transpeptidases

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6
Q

What drug is to be used to treat chronic alcohol dependence?

A

Disulfiram

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7
Q

How does disulfiram treat chronic alcohol dependence?

A

Inhibits aldehyde dehydrogenase, so acetaldehyde cannot be converted to acetate and accumulates in the blood causing symptoms of hangover

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8
Q

What is a free radical?

A

Any atom, molecule or ion that contains one or more unpaired electrons and is capable of independent existence

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9
Q

How are free radicals formed by the mitochondria?

A

In electron transport chain, some electrons do not reach the end of the chain and prematurely reduces oxygen to form superoxide

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10
Q

What are the 3 reactive oxygen species?

A

Superoxide
Hydrogen peroxide
Hydroxyl radical

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11
Q

What is one other way of forming superoxide radicals?

A

Toxins such as herbicide paraquat

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12
Q

What are 3 types of damages that can be caused by ROS?

A

DNA damage - modifying bases leading to mutations
Protein damage - modifying protein structure, leading to loss of function
Lipids - lipid peroxidation, disrupts lipid structure

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13
Q

What are 3 forms of cellular defenses against oxidative stress?

A

Superoxide dismutase
Catalase
Glutathione
Free radical scavengers

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14
Q

What does superoxide dismutase do?

A

Converts superoxide to hydrogen peroxide and oxygen

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15
Q

What does catalase do?

A

Hydrogen peroxide is broken down to molecular oxygen and water

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16
Q

What is glutathione and its function?

A

Antioxidant to protect against oxidative damage, donates electrons to ROS, catalyze by glutathione peroxidase and selenium and forms disulphide.

Disulphide needs to be reduced back to glutathione by glutathione reductase which catalyze electron transfer back from NADPH to disulphide bond.

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17
Q

What are 2 examples of free radical scavengers?

A

Vitamins C and E

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18
Q

What is the function of free radical scavengers?

A

Reduces ROS damage by donating a hydrogen atom to free radicals in a non enzymatic reaction

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19
Q

How do vitamins E and C work together?

A

Vitamin E is lipid soluble and plays an important role in protecting against lipid peroxidation while C is water soluble antioxidant and plays an important rule in regenerating the reduced form of Vitamin E

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20
Q

What is respiratory burst?

A

Immune cells when stimulated, rapidly produces a release of ROS to destroy micro organism cells

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21
Q

What is respiratory burst produced by?

A

NADPH oxidase

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22
Q

How does NADPH oxidase produce ROS?

A

Transfers electrons from NADPH across the membrane to couple these to molecular oxygen to generate superoxide radicals

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23
Q

What is chronic granulomatus disease?

A

Genetic defect in NADPH oxidase complex causes enhanced susceptibility to bacterial infections

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24
Q

How does oxidative stress cause cataracts in galactosaemia?

A

Increased activity of almost reductase consumes excess NADPH, compromises defenses against ROS damage because disulphide cannot be converted back to glutathione, crystalline protein in lens of eye denatured, forming cataracts

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25
Q

How does oxidative stress cause haemolysis in G6PDH deficiency?

A

Decreased G6PDH activity limits amount of NADPH, and NADPH is needed to reduce GSSG to GSH, lower GSH means less protection against oxidative stress, can cause lipid peroxidation, damaging cell membrane and protein damage which causes Heinz bodies

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26
Q

What is the effect of overdosage of paracetamol?

A

With high levels of paracetamol, toxic metabolite NAPQI accumulates, a strong oxidizing agent conjugates with glutathione and depletes levels of glutathione. NAPQI causes covalent binding in hepatic proteins and resulting oxidative stress results in liver cells destruction and liver failure.

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27
Q

What drug to give for overdose of paracetamol?

A

Acetylcysteine

28
Q

How does acetylcysteine resolve paracetamol overdose?

A

Replenishes glutathione allowing liver to safely metabolism NAPQI

29
Q

What is nitrogen balance?

A

Amount of nitrogen taken into the body equals amount lost

30
Q

What is positive N balance?

A

N intake is greater than loss, during periods of active growth, pregnancy etc

31
Q

What is negative N balance?

A

N intake is less than N loss during starvation, malnutrition and trauma

32
Q

What is protein turnover?

A

Continuous breakdown resynthesis of body proteins

33
Q

How are proteins catabolised and what are the 2 enzymes involved?

A

Proteases and peptidase hydrolyse peptide bonds to release free amino acids

34
Q

What are 2 hormones that stimulates uptake of amino acids into tissues?

A

Insulin and growth hormone

35
Q

What hormone promotes breakdown of muscle proteins?

A

Cortisol

36
Q

What are the 2 steps of catabolism of amino acids?

A
  1. Removal of amino group, converted to urea

2. Remaining C skeletons of amino acids forms acetyl coA or products used for gluconeogenesis

37
Q

What are ketogenic amino acids?

A

Amino acids that produce acetyl coA which can be used for synthesis of ketone bodies

38
Q

What are glucogenic amino acids?

A

Amino acids that produce products that can be used for glucose synthesis by gluconeogenesis

39
Q

Before becoming urea, amino groups are initially transferred to other molecules. What are the 2 ways of doing so?

A

Transamination or deamination

40
Q

What is transaminagion and name the enzyme involved?

A

Using aminotransferase enzymes and alpha-ketoglutarate, glutamate is produced to feed into urea cycle, requires vitamin B6

41
Q

What is an exception that does not use alpha ketoglutarate during transamination?

A

When aspartate aminotransferase is used, o all acetate is used to funnel amino group to aspartate

42
Q

What are 2 key aminotransferase enzymes used to assess liver function?

A

ALT alanine aminotransferase converts alanine to glutamate

AST aspartate aminotransferase converts glutamate to aspartate

43
Q

What is deamination and the 2 enzymes involved?

A

Removing amino group as free NH3 using L and D-amino acids that convert amino acids to keto acids and NH3

44
Q

What is phenylketonuria?

A

Defective phenylalanine hydroxylase abuses phenylalanine to accumulate and undergo other pathways to form phenylketones which is excreted in urine

45
Q

What are 2 ways to diagnose phenylketonuria?

A

Measure blood phenylalanine concentration, >0.1mmol/L

Defection of phenylketones in urine

46
Q

What is the inheritance pattern of phenylketonuria?

A

Autosomal recessive

47
Q

What are 3 ways to treat phenylketonuria?

A

Strictly controlled low phenylalanine diet enriched with tyrosine

Avoid artificial sweeteners

Avoid high protein foods

48
Q

What are 5 symptoms of phenylketonuria?

A 
Severe intellectual disability 
Developmental delay
Microcephaly
Seizures
Hypoppigmentation
49
Q

What is homocystinurias?

A

Defect in cystathionine beta-synthase leads to accumulation of homocysteine and methionine

50
Q

What are 2 ways to detect homocystinuria?

A

Elevated levels of homocysteine and methionine in plasma

Presence of homocystine in urine

51
Q

What is inheritance of homocystinuria?

A

Autosomal recessive

52
Q

What are 2 ways of treating homocystinuria?

A

Low methionine diet

Vit B6 supplement

53
Q

What is creatinine?

A

Breakdown product of creatine and creatine phosphate in muscle

54
Q

What are 2 clinical uses of measuring creatinine?

A

Provides estimate to muscle mass

Indicator of renal function

55
Q

What is hyperammonaemia?

A

High levels of ammonia in blood

56
Q

What are 2 ways of metabolizing ammonia?

A

Glutamine synthesis

Urea synthesis

57
Q

What are the 2 steps of glutamine synthesis?

A

Glutamine synthetase produces glutamine from ammonia and glutamate

Glutaminase releases ammonia and glutamate from glutamine which is disposed in the urine or converted to urea

58
Q

How many enzymes are involved in urea cycle?

A

5

59
Q

What kind of diet induces enzyme levels?

A

High protein

60
Q

What kind of diet represses enzyme levels?

A

Low protein or starvation

61
Q

What is refeeding syndrome?

A

Rapid refeeding of energy rich foods in starved patients will rapidly increase blood sugar and insulin causing metabolism that utilizes electrolytes and cause hypophosphataemia

Too much protein and down regulation of urea cycle causes ammonia toxicity

62
Q

What are 3 risk factors of refeeding syndrome?

A

BMI <16
Unintentional weight loss of >15% in 3-6 months
10 days or more with little or no nutritional intake

63
Q

How to feed patients with malnutrition?

A

5-10kcal/kg/day for a week

64
Q

What are 2 effects of defects in urea cycle?

A

Hyperammonaemia

Accumulation or excretion of urea cycle intermediates

65
Q

What is the biochemical basis of ammonia toxicity?

A

Ammonia is readily diffusible and very toxic to the brain

66
Q

What are 6 symptoms of ammonia toxicity?

A 
Vomiting 
Lethargy 
Irritability
Mental retardation 
Seizures
Coma
67
Q

What are 2 mechanisms of transporting amino acid nitrogen to liver?

A

Ammonia combines with glutamate to form glutamine which is then cleaved by glutaminase to reform glutamate and ammonia, which is fed into urea cycle in liver or excreted in kidney

Amine groups transferred to glutamate by transamination, which then transaminates pyruvate to form alanine, which is transported to liver and then converted back to pyruvate and glutamate, which is fed into urea cycle and pyruvate is used to synthesize glucose

Metabolism, Endocrinology and Haematology (8 decks)

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