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GB > 14. Post-Absorption Processing of Proteins > Flashcards

14. Post-Absorption Processing of Proteins Flashcards

1
Q

What biologically active compounds are amino acids precursors for?

A 
Haem
Nucleic acids
Hormones
Neurotransmitters
Biologically-active peptides
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2
Q

What determines the half life of a protein?

A

N-terminal residue

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3
Q

Which amino-acid sequences are rapidly degraded?

A

Proline
Glutamic acid
Serine
Threonine

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4
Q

What two ways are proteins degraded?

A

Ubiquitin-proteasome system

Lysosomal enzymes

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5
Q

What does the concentration of amino acids in circulation between meals depend on?

A

Utilisation by tissues

Release following protein degradation

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6
Q

How is alanine used in hepatic gluconeogenesis?

A

Alanine is made in muscle by the transamination of pyruvate

Liver coverts the carbon skeleton of alanine to glucose

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7
Q

What does it mean for an amino acid to be glucogenic?

A

Its breakdown yields TCA cycle intermediates

Used to make glucose: gluconeogenesis

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8
Q

What does it mean for an amino acid to be ketogenic?

A

Breakdown yields acetoacetate or acetyl-CoA

Ketogenesis

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9
Q

Which amino acids are glucogenic?

A 
Alanine
Arginine
Asparagine
Aspartate
Cysteine
Glutamate
Glutamine
Glycine
Proline
Serine
Histidine
Methionine
Threonine
Valine
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10
Q

Which amino acids are both glucogenic and ketogenic?

A

Tyrosine
Isoleucine
Phenylalanine
Tryptophan

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11
Q

Which amino acids are ketogenic?

A

Leucine

Lysine

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12
Q

Which amino acids are formed from essential amino acids?

A

Cysteine
Tyrosine
Hydroxylysine

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13
Q

Which enzymes play a role in forming amino acids from amphibolic intermediates?

A

Transaminases
Glutamine synthetase
Glutamate dehydrogenase

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14
Q

What reaction does phenylalanine undergo to make metabolic intermediates?

A

Enzyme: phenylalanine hydroxylase
Produces tyrosine
Tyrosine converted to fumarate or acetoacetate

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15
Q

Which disorder is caused by a deficiency of phenylalanine hydroxylase?

A

Phenylketonuria

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16
Q

How is glutamine synthesised?

A

Glutamate converted to glutamine by glutamine synthetase

Reaction is useful for storing free ammonia in a non-toxic form

17
Q

What coenzyme is used by transaminases?

A

Vitamin B6

18
Q

What is the mostly widely used ‘donor-acceptor’ transaminase couple?

A

Glutamate

a-ketoglutarate

19
Q

Which amino acids use the glutamate - a-keoglutarate pair as part of their degradation?

A 
Aspartic acid
Asparagine
Arginine
Isoleucine
Leucine
Lysine
Tryptophan
Tyrosine
Valine
20
Q

Which enzyme converts alanine and a-ketoglutarate to pyruvate and glutamate?

A

ALT

21
Q

Which enzyme converts oxaloacetate and glutamate to aspartate and a-ketoglutarate?

A

AST

22
Q

What reaction does ALT catalyse?

A

Alanine and a-ketoglutarate
to
Pyruvate and glutamate

23
Q

What reaction does AST catalyse?

A

Oxaloacetate and glutamate
to
Aspartate and a-ketoglutarate

24
Q

What are the two steps in disposal of amino acids?

A

Transamination

Oxidative deamination

25
Q

What are the two steps in synthesis of amino acids?

A

Reductive amination

Transamination

26
Q

Where does the urea cycle take place?

A

Liver

27
Q

How is amino nitrogen transported in circulation?

A

Alanine (made from pyruvate in muscle)

Glutamine (made from glutamate in most tissues)

28
Q

What is free ammonia produced in the body by?

A

Breakdown of purines and pyrimidines
Breakdown of amines and monoamines
Breakdown of glutamine
Bacterial digestion of urea

29
Q

Where do the two amino groups on urea come from?

A

Carbamoyl phosphate

Aspartate

30
Q

How much energy is required to produce urea?

A

3 ATP molecules per molecule of urea

31
Q

What are normal levels of free ammonia in blood serum?

A

5-50mmol/L

32
Q

What is acquired hyperammonaemia caused by?

A

Liver disease or failure

33
Q

What is hereditary hyperammonaemia caused by?

A

Inherited urea cycle defect

34
Q

What are the effects of hyperammonaemia?

A

CNS toxicity
Tremors, slurred speech, vomiting, cerebral oedema
Coma, death

35
Q

What is the most common urea cycle disorder in humans?

A

Ornithine transcarbamylase deficiency

36
Q

What is the function of ornithine transcarbamylase?

A

Converts carbamoyl phosphate and ornithine into citrulline

37
Q

What are the symptoms of an OTC deficiency?

A 
Hyperammonaemia
Vomiting
Refusal to eat
Progressive lethargy
Coma

GB (15 decks)

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