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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
Which amino acid degradation process is reversible?
Transamination
26
What is an important component of aminotransferases and what does it do?
Tightly bound prosthetic group derived from vitamin B6 Acts as a carrier of the amino group
27
What is the prosthetic group of aminotransferases?
Pyridoxal phosphate / pyridoxamine phosphate
28
What is the main function of transamination?
Synthesis of non-essential amino acids
29
What ketoacid can you use to form alanine?
Pyruvate
30
What is a ketoacid?
Molecule with a carboxylic acid group and a ketone group
31
What ketoacid can you use to form aspartate?
Oxaloacetate
32
What ketoacid can you use to form glutamate?
a-ketoglutarate
33
What is oxidative deamination?
Release of amino group as NH3 or NH4+ (if with zwitter ion)
34
What is the only amino acid humans can deaminate?
Glutamate
35
What enzyme is present in the human body for deamination?
Glutamate dehydrogenase
36
What is the reaction of deamination of glutamate?
L-glutamate + water + NAD(P)+ --> a-ketoglutarate + ammonia + NAD(P)H + H+
37
What can happen to ketoacids? (2)
Metabolised in TCA cycle to provide a source of ATP In starvation, C-skeletons of 13 amino acids can be converted to glucose
38
What does glucogenic mean?
Describes an amino acid which can be converted to glucose
39
What does ketogenic mean?
Describes an amino acid which cannot be converted to glucose
40
Give an example of a ketogenic amino acid
Leucine Lysine
41
Give an example of an amino acid which is both glucogenic and ketogenic
Phenylalanine Isoleucine Tyrosine Threonine Tryptophan
42
Where does the liver take amino acids, glucose and fats from?
Portal blood supply
43
What are amino acids used to synthesise in the liver normally? (4)
Cellular proteins Plasma proteins Haem Purines and pyrimidines
44
By what process are amino acids degraded in the liver?
Transdeamination
45
Where is urea excreted?
Kidneys
46
Where can the amino group of amino acids be converted to urea?
Liver
47
What is the main amino acid used to transport 'ammonia' to the liver?
Glutamine
48
Why is glutamine a good transporter of ammonia?
Carries 2 amino groups Safe carrier
49
Which enzyme is used in the conversion of glutamine to glutamate?
Glutaminase
50
Which enzyme is used in the conversion of glutamate to glutamine?
Glutamine synthase/synthetase
51
What type of reaction is the conversion of glutamine to glutamate?
Hydrolysis
52
What are the five reactions of the urea cycle?
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
Where are amino groups added in the urea cycle and via what?
Step 1 - NH4+ from glutamine Step 3 - L-aspartate
54
What enzyme catalyses the reaction: CO2 + NH4+ --> carbamoyl phosphate
Carbamoyl phosphate synthase I
55
What enzyme catalyses the reaction: Carbamoyl phosphate + L-ornithine --> L-citrulline
Ornithine transcarbamoylase
56
What enzyme catalyses the reaction: L-citrulline + L-aspartate --> argininosuccinate
Argininosuccinate synthase
57
What enzyme catalyses the reaction: Argininosuccinate --> L-arginine + fumarate
Argininosuccinase
58
What enzyme catalyses the reaction: L-arginine --> L-ornithine + urea
Arginase
59
What is the structure of urea?
NH2 -- CO -- NH2
60
The breakdown of what compound produces urea?
Amino acids
61
The breakdown of what compound produces creatinine?
Creatine phosphate
62
The breakdown of what compound produces uric acid?
Nucleic acids
63
What causes hyperammonaemia?
Impaired conversion of NH3 to urea due to: Liver failure Genetic defects in catalytic activity of any enzyme in the urea cycle
64
Give an example of a genetic defect which can result in hyperammonaemia
Ornithine transcarbamoylase deficiency X-linked

BMS07 (7 decks)

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