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BMS07 > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

What can be synthesised from amino acids? (4)

A

Proteins

Creatine

Purines and pyrimidines

Blood glucose (fasting + starvation)

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2
Q

What are the possible waste products of nitrogen-based compounds? (4)

A

Urea

Ammonia

Creatinine

Uric acid

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3
Q

What is the average protein turnover in an adult?

A

400-500g/day

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4
Q

How long is the half-life of most proteins?

A

Several days

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5
Q

How long is the half-life of some structural proteins?

A

Years

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6
Q

How long is the half-life of hormones and digestive enzymes?

A

Minutes

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7
Q

What is the amino acid pool?

A

Free amino acids in low concentrations inside cells or in blood stream

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8
Q

Why do we need protein in our diet?

A

No storage form of protein (other than body muscle)

Replace lost amino acids

Allow for tissue repair

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9
Q

What is the recommended protein intake for an adult?

A

50-70g (~1g/kg of body weight) = amount wasted/day (not recycled)

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10
Q

What types of organisms can synthesise all 20 amino acids?

A

Plants

Microorganisms

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11
Q

How many of the 20 amino acids can humans synthesise?

A

10

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12
Q

What are the essential amino acids?

A 
F (phenylalanine)
L (leucine)
I (isoleucine)
T (threonine)
W (tryptophan)
K (lysine)
V (valine)
M (methionine)

H (histidine)
R (arginine)

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13
Q

When is histidine essential?

A

During growth

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14
Q

When does arginine become essential?

A

When/if something goes wrong in the urea cycle

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15
Q

What is nitrogen balance?

A

Nitrogen intake (diet) = nitrogen excretion

Rate of synthesis of N-containing compounds = rate of degradation of these compounds

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16
Q

What is positive nitrogen balance?

A

Nitrogen intake > nitrogen excretion

Synthesis exceeds rate of degradation

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17
Q

When does positive nitrogen balance occur? (5)

A

Normal growth in children

Body building

Pregnancy

In convalescence after serious illness

After immobilisation after an accident

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18
Q

What is negative nitrogen balance?

A

Nitrogen intake < nitrogen excretion

Rate of degradation exceeds rate of synthesis

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19
Q

When does negative nitrogen balance occur?

A

Starvation

Serious illness

Late stages of some cancers

Injury and trauma

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20
Q

How are most old/damaged cellular proteins degraded?

A

Removed by ubiquitin breakdown system to give a mixture of amino acids

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21
Q

How are foreign/’exogenous’ (to the cell) proteins degraded?

A

Taken into vesicles by endocytosis or autophagocytosis

Vesicles fuse with lysosomes

Proteolytic enzymes degrade proteins

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22
Q

What are the two processes by which amino acids can be degraded?

A

Transamination

Oxidative deamination

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23
Q

What is transamination?

A

Transfer of amino group to an acceptor molecule

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24
Q

What type of enzyme catalyses transamination?

A

Aminotransferases

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25
Q

Which amino acid degradation process is reversible?

A

Transamination

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26
Q

What is an important component of aminotransferases and what does it do?

A

Tightly bound prosthetic group derived from vitamin B6

Acts as a carrier of the amino group

27
Q

What is the prosthetic group of aminotransferases?

A

Pyridoxal phosphate / pyridoxamine phosphate

28
Q

What is the main function of transamination?

A

Synthesis of non-essential amino acids

29
Q

What ketoacid can you use to form alanine?

A

Pyruvate

30
Q

What is a ketoacid?

A

Molecule with a carboxylic acid group and a ketone group

31
Q

What ketoacid can you use to form aspartate?

A

Oxaloacetate

32
Q

What ketoacid can you use to form glutamate?

A

a-ketoglutarate

33
Q

What is oxidative deamination?

A

Release of amino group as NH3 or NH4+ (if with zwitter ion)

34
Q

What is the only amino acid humans can deaminate?

A

Glutamate

35
Q

What enzyme is present in the human body for deamination?

A

Glutamate dehydrogenase

36
Q

What is the reaction of deamination of glutamate?

A

L-glutamate + water + NAD(P)+ –> a-ketoglutarate + ammonia + NAD(P)H + H+

37
Q

What can happen to ketoacids? (2)

A

Metabolised in TCA cycle to provide a source of ATP

In starvation, C-skeletons of 13 amino acids can be converted to glucose

38
Q

What does glucogenic mean?

A

Describes an amino acid which can be converted to glucose

39
Q

What does ketogenic mean?

A

Describes an amino acid which cannot be converted to glucose

40
Q

Give an example of a ketogenic amino acid

A

Leucine

Lysine

41
Q

Give an example of an amino acid which is both glucogenic and ketogenic

A

Phenylalanine

Isoleucine

Tyrosine

Threonine

Tryptophan

42
Q

Where does the liver take amino acids, glucose and fats from?

A

Portal blood supply

43
Q

What are amino acids used to synthesise in the liver normally? (4)

A

Cellular proteins

Plasma proteins

Haem

Purines and pyrimidines

44
Q

By what process are amino acids degraded in the liver?

A

Transdeamination

45
Q

Where is urea excreted?

A

Kidneys

46
Q

Where can the amino group of amino acids be converted to urea?

A

Liver

47
Q

What is the main amino acid used to transport ‘ammonia’ to the liver?

A

Glutamine

48
Q

Why is glutamine a good transporter of ammonia?

A

Carries 2 amino groups

Safe carrier

49
Q

Which enzyme is used in the conversion of glutamine to glutamate?

A

Glutaminase

50
Q

Which enzyme is used in the conversion of glutamate to glutamine?

A

Glutamine synthase/synthetase

51
Q

What type of reaction is the conversion of glutamine to glutamate?

A

Hydrolysis

52
Q

What are the five reactions of the urea cycle?

A
  1. Carbon dioxide + NH4+ –> carbamoyl phosphate*
  2. Carbamoyl phosphate + L-ornithine –> L-citrulline
  3. L-citrulline + L-aspartate –> argininosuccinate*
  4. Argininosuccinate –> L-arginine + fumarate
  5. L-arginine –> L-ornithine + urea
53
Q

Where are amino groups added in the urea cycle and via what?

A

Step 1 - NH4+ from glutamine

Step 3 - L-aspartate

54
Q

What enzyme catalyses the reaction:

CO2 + NH4+ –> carbamoyl phosphate

A

Carbamoyl phosphate synthase I

55
Q

What enzyme catalyses the reaction:

Carbamoyl phosphate + L-ornithine –> L-citrulline

A

Ornithine transcarbamoylase

56
Q

What enzyme catalyses the reaction:

L-citrulline + L-aspartate –> argininosuccinate

A

Argininosuccinate synthase

57
Q

What enzyme catalyses the reaction:

Argininosuccinate –> L-arginine + fumarate

A

Argininosuccinase

58
Q

What enzyme catalyses the reaction:

L-arginine –> L-ornithine + urea

A

Arginase

59
Q

What is the structure of urea?

A

NH2 – CO – NH2

60
Q

The breakdown of what compound produces urea?

A

Amino acids

61
Q

The breakdown of what compound produces creatinine?

A

Creatine phosphate

62
Q

The breakdown of what compound produces uric acid?

A

Nucleic acids

63
Q

What causes hyperammonaemia?

A

Impaired conversion of NH3 to urea due to:

Liver failure

Genetic defects in catalytic activity of any enzyme in the urea cycle

64
Q

Give an example of a genetic defect which can result in hyperammonaemia

A

Ornithine transcarbamoylase deficiency

X-linked

BMS07 (7 decks)

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