Amino Acid Metabolism

Question 1

Definition of turnover

Answer 1

Continual renewal/replacement of protein

Question 2

Definition of amino acid pool

Answer 2

Mixing and exchange with other free AA distributed throughout the body

Question 3

Definition of oxidative deamination

Answer 3

Generates a ketoacids and other oxidized products from amine containing compounds in the liver

Question 4

Definition of transamination

Answer 4

Transfer of an amino group from 1 molecule to another, especially from an amino acid to a ketoacid

Question 5

Definition of glucogenic

Answer 5

Amino acids that can be converted into glucose through gluconeogenesis

Question 6

Definition of ketogenic

Answer 6

Production of ketone bodies from amino acids through ketogenesis

Question 7

Definition of ornithine

Answer 7

Cyle of biochemical reactions that produce urea from ammonia

Question 8

Definition of hyperammonaemia

Answer 8

Excess of ammonia in the blood, can lead to brain injury and death

Question 9

Function of amino acids

Answer 9

Build

• protein
• NT synth
• creatine
• carnitine
• haem
• purine, pyramidine

Source of blood glucose

Question 10

Protein turnover 300-400g/day

Difference in half lives of structural proteins and enzymes

Answer 10

Variable

• Structural; proteins => HL of years
• Enzymes, hormones => HL of minutes

Question 11

Describe the amino acid pool

Answer 11

Mixture of AA in the cell, blood, extracellular fluid
Consists of
-turnover of body protein
-intake of dietary protein
-synthesis of non essential AA

Question 12

Protein requirements (50-70g/day)

Answer 12

Cannot be stored so excess removed as urea

Question 13

Name the 10 essential AA

Answer 13

Valine
Methionine
Histidine
Lysine
Phenylalanine
Leucine
Isoleucine
Threonine
Tryptophan
Arginine

Question 14

Describe the nitrogen balance

Answer 14

N intake = N excretion

Rate of body protein synthesis = rate of protein degredation

Question 15

Positive nitrogen balance

When would this occur

Answer 15

During normal growth in children
In convalescence after serious illness
After immobilization after an accident
In pregnancy

Question 16

Negative nitrogen balance
When would this occur
Why is this bad?

Answer 16

In starvation
During serious illness
Late stages of some cancers
In injury and trauma

Must be corrected and not be prolonged, otherwise there will be irreversible loss of body tissue and death

Question 17

Pathways of amino acid degredation in most cellular proteins

Answer 17

Ubiquitin system => 20 AA

Question 18

Pathways of amino acid degradation in foreign or exogenous proteins

Answer 18

Old/damaged sub cellular organelles
Taken into vesicles by endocytosis/autophagocytosis, vesicles fuse with lysosomes
Proteolytic enzymes degrade proteins => AA
Starvation and hormones, cortisol increases rates of protein breakdown in muscle

Question 19

Oxidative deamination general formula
Where does this occur
What is the most important AA in deamination

Answer 19

AA + NAD+ + H2O <=AADH=> ketoacid + NH4+ + NADH

Only occurs in the liver mitochondria
Glutamate is the only AA with an active DH

Glutamate + NAD+ + H2O <=GDH=> Oxoglutarate + NADH + NH4+

Question 20

Transamination general formula
Where does this occur
What can happen after transamination

Answer 20

Amino acid 1 + Ketoacid 2 <=amino transaminase=> Amino acid 2 + Ketoacid 1

Takes place in cytoplasm of all tissues
AA transported to liver as glutamate => deamination

AA + oxoglutarate <=> keto acid + glutamate

Question 21

What are the 2 types of oxoacid that can arise

Why are there 2 outcomes

Answer 21

Metabolised by TCA

• if from a glucogenic AA => glucose in the liver via pyruvate/oxaloacetate
• if from a ketogenic AA => fat/KB from ACoA

Reaction of pyruvate => ACoA is irreversible

Question 22

What are the 2 ketogenic AA

What are the 4 ketogenic/glucogenic AA

Answer 22

Ketogenic

• Leucine
• Lysine

Keto and glucogenic

• Threonine
• Phenylalanine
• Tryptophan
• Isoleucine

Question 23

What are the 4 most important amino acids in nitrogen transport

Answer 23

Alanine
Aspartate
Glutamine
Glutamate

Question 24

Why is alanine important in nitrogen transport

Answer 24

Alanine + a ketoglutarate <=ALT=> Pyruvate + Glutamate
Glutamate can take part in oxidative deamination

Alanine transported via blood => liver in gluconeogenesis

Question 25

Why is aspartate important in nitrogen transport

Answer 25

Aspartate + a ketoglutarate <=AST=> Oxaloacetate + Glutamate
Glutamate can take part in oxidative deamination

Involved in urea cycle

Question 26

Why is glutamine important in nitrogen transport

Answer 26

Carry 2NH3 => liver => urea

Deliver NH4+ => kidney for pH regulation
Formed from glutamate

Question 27

Why is glutamate important in nitrogen transport

Answer 27

To liver => deamination

Converted to glutamine for safe NH3 excretion

Question 28

Glutamine metabolism
Glutamine => Glutamate
Glutamate => Glutamine

Answer 28

Glutamine =glutaminase + H2O=> glutamic acid + NH3

Glutamic acid =glutamine synthase + ATP + NH3=> Glutamine + ADP + Pi

Question 29

The urea cycle

Location?
Location of each reaction?

Answer 29

IN THE LIVER

MITOCHONDRIA NH4+ + CO2 + 2ATP =Carbomoyl phosphate synthase=> carbomoyl phosphate + 2 ADP + Pi

MITOCHONDRIA Carbonyl phosphate + Ornithine =Ornithine transcarbomoylase=> Citrulline

CYTOSOL Citrulline + Aspartate =Argininosuccinic acid synthase=> Arginosuccinate

CYTOSOL Arginosuccinate =Argininosuccinase=> Arginine + Fumarate (lost)

CYTOSOL Arginine =Arginase=> Ornithine + urea (lost)

Question 30

End products of nitrogen metabolism
Protein
Creatine phosphate
DNA, RNA
pH control

Answer 30

Protein => urea
Creatine phosphate => creatinine
DNA, RNA => uric acid
pH control => ammonia

Question 31

What happens in the impaired conversion of NH3 => urea
Causes?
Symptoms
Prognosis

Answer 31

Hyperammonaemia

Due to

• reduction in catalytic activity of urea cycle enzymes
• liver failure (viral hepatitis, ischaemia, cirrhosis)

Neurotoxic, involves cell death

Leads to cerebral oedema, coma, death