2. Protein And Amino Acid Metabolism

Question 1

What are the major and minor nitrogen containing compounds?

Answer 1

Major: amino acids, proteins, purines and pyrimidines
Minor: porphyrins, creatine phosphate, neurotransmitters

Question 2

What is creatinine?

Answer 2

Breakdown product of creatine and creatine phosphate
Produced at constant rate depending on muscle mass
Provides estimate of muscle mass - creatinine urine excretion over 24h proportional to muscle mass

Question 3

What is N equilibrium?

Answer 3

Intake = output
No change in total body protein
Normal state in adult

Question 4

What is positive N balance?

Answer 4

Intake > output
Increase in total body protein
Normal state in growth and pregnancy or in adult recovering from malnutrition

Question 5

What is negative N balance?

Answer 5

Intake < output
Net loss of body protein
Never normal
Causes include trauma, infection or malnutrition

Question 6

Name a glycogenic amino acid and a ketogenic amino acid

Answer 6

Glucogenic - alanine

Ketogenic - lysine

Question 7

Name an amino acid that is both glucogenic and ketogenic

Answer 7

Tyrosine

Question 8

What happens in Cushing’s syndrome?

Answer 8

Excessive breakdown of protein fur to excess cortisol

Weakens skin structure leading to striae formation (stretch marks)

Question 9

What extra amino acids do children and oregano women require in their diet?

Answer 9

Arginine
Tyrosine
Cysteine

Question 10

Where do carbon atoms for non-essential amino acid synthesis come from?

Answer 10

Intermediates of glycolysis
Pentose phosphate pathway
Krebs cycle

Question 11

Why is removal of amino group from amino acid essential?

Answer 11

To allow carbon skeleton of amino acids to be until I see in oxidative metabolism

Question 12

What are the 2 main pathways that facilitate removal of nitrogen form amino acids?

Answer 12

Transamination

Deamination

Question 13

What is transamination?

amino acid 1 + keto acid 2 amino acid 2 + keto acid 1

Answer 13

Transfer of the amine group of an amino acid with the oxygen of a keto acid
Most amino acids are converted to glutamate and some to aspartate

Question 14

What do most aminotransferase enzymes use?

What is the exception?

Answer 14

Alpha-ketoglutarate to funnel amino group to glutamate

Exception: aspartate aminotransferase uses oxaloacetate to funnel amino group to aspartate

Question 15

What do all aminotransferase require?

Answer 15

Coenzyme pyridoxal phosphate which is a derivative of vitamin B6

Question 16

What are ALt and AST and what do they do?

Answer 16

ALT - alanine aminotransferase, converts alanine to glutamate
AST - aspartate aminotransferase, converts glutamate to aspartate

Question 17

What can plasma ALR and AST levels show?

Answer 17

Measures as part of liver function test
Levels particularly high in conditions that cause extensive cellular necrosis such as: viral hepatitis, autoimmune liver disease, toxic injury

Question 18

What is deamination?

Answer 18

Liberates amino group as free ammonia
Mainly occurs in liver and kidney
Also important in deamination of dietary D-amino acids

Question 19

Name the enzymes that can deamination amino acids

Answer 19

Amino acid oxidases
Glutaminase
Glutamate dehydrogenase

Question 20

Describe features of the urea cycle

Answer 20

Occurs in liver
Involves 5 enzymes
Amount of urea cycle enzymes relate to need to dispose of ammonia
High protein diet induce enzyme levels
Low protein diet or starvation represses levels

Question 21

What is refeeding syndrome?

Answer 21

Can occur when nutritional support given to severely malnourished patients
Ammonia toxicity significant factor

Question 22

What defects can occur in the urea cycle?

Answer 22

Autosomal recessive geneticist disorders caused by deficiency of one of enzymes in urea cycle
Mutations cause a atrial loss of enzyme function

Question 23

What can defects in the urea cycle lead to?

Answer 23

Hyperammonaemia

Accumulation/excretion of urea cycle intermediates

Question 24

When do severe urea cycle disorders present?

Answer 24

Show symptoms within 1 day after birth, can lead to death if left untreated

Question 25

What is the management of a patient with a defect in the urea cycle?

Answer 25

Low protein diet

Replace amino acids in diet with keto acids

Question 26

What are the 2 mechanisms utilised for the safe transport of amino acid nitrogen from tissues to the liver for disposal?

Answer 26

Using glutamine and using alanine

Question 27

What is glutamine transport?

Answer 27

Ammonia combined with glutamate to form glutamine
Glutamine transported in blood to liver or kidneys, it’s cleaved by glutaminase to reform glutamate and ammonia
In liver, ammonia fed into urea cycle

Question 28

What is alanine transport?

Answer 28

Amine groups transferred to glutamate by transamination
Pyruvate transaminated by glutamate to form alanine
Alanine transported in blood to liver, converted back to pyruvate by transamination
Amino group fed via glutamate into urea cycle

Question 29

What inborn errors of metabolism can be detected with the heel prick test?

Answer 29

Phenylketonuria
Maple syrup urine disease
Isovaleric acidaemia
Glutaric aciduria
Homocystinuria

Question 30

What is phenylketonuria?

Answer 30

Deficiency in phenylalanine hydroxylase
Autosomal recessive
Accumulation of phenylalanine in tissue, plasma and urine
Phenylketones in urine

Question 31

What is the treatment for phenylketonuria?

Answer 31

Low phenylalanine diet etched with tyrosine

Avoid high protein foods such as meat, milk and eggs

Question 32

What are the symptoms of phenylketonuria?

Answer 32

Sever intellectual disability
Developmental delay
Microcephaly
Seizures

Question 33

What is homocystinuria?

Answer 33

Problem breaking down methionine
Excess homocystine excreted in urine
Autosomal recessive 
Defect in cystathionine beta-synthase
Affects connective tissue, muscles, CNS and CVS

Question 34

What is the treatment for homocystinuria?

Answer 34

Low-methionine diet
Avoid milk, meat, fish, cheese, eggs
Cysteine, vit B6, beanie, B12 and folate supplement

Question 35

What is elevated plasma homocysteine shown to be associated with?

Answer 35

Cardiovascular disease