Proteins

Question 1

Creatinine as a clinical marker

Answer 1

Indicator of renal function as it is excreted by kidneys.
Usually produced at constant rate depending on muscle mass - unless muscle is wasting.
Also provides an estimate of muscle mass.

Question 2

Nitrogen balance

Answer 2

Equilibrium -> intake = output
(Normal state in adult)

Positive balance -> intake > output
(Increase in protein - normal in growth or pregnancy, or recovery from malnutrition)

Negative balance -> intake < output
(Net loss of protein - never normal. Caused by trauma, infection, malnutrition)

Question 3

Protein turnover

Answer 3

The replacement of older proteins as they are broken down by the cell.

Question 4

Example of a glucogenic a.a, a ketogenic a.a, and one that is both

Answer 4

G - glycine

K - tyrosine

B - lysine

Question 5

Hormones that affect utilisation of protein reserves?

Answer 5

Insulin and growth hormone - increase protein synthesis; decrease protein degradation

Glucocorticocoids (cortisol) - decrease protein synthesis; increase protein degradation

Question 6

Disease caused by excess cortisol?

Answer 6

Cushing’s syndrome

Question 7

9 essential a.a

Answer 7

Isoleucine, lysine, threonine, histidine, leucine, methionine, phenylalanine, tryptophan, valine

Eg if learned, this huge list may prove truly valubale

Question 8

Non-essential a.a

Answer 8

Those that the body can synthesise

Question 9

Alanine aminotransferase (ALT)

Answer 9

Catalyses interconversion of alanine and alpha-ketogluterate to pyruvate and glutamate.

ALT levels measured as part of liver function test.

Question 10

Aspartate aminotransferase (AST)

Answer 10

Catalyses interconversion of aspartate and alpha-ketoglutarate to glutamate and oxaloacetate.

ALT levels used as part of liver function test.

Question 11

Basic reaction of aminotransferases

Answer 11

Amino acid + alpha-ketoglutarate -> keto acid + glutamate

Eg alanine + alpha=ketoglutarate -> keto acid + pyruvate

Question 12

Deamination

Answer 12

Liberates amino groups as free ammonia, mainly occurs in liver and kidney - ammonia needs to be removed very quickly - toxic.

Question 13

Urea

Answer 13

Non-toxic compound produced from protein metabolism.

High nitrogen content; water soluble; chemically inert.

Excreted via urine.

Osmotic role in kidney tubules.

Question 14

Urea cycle

Answer 14

Occurs in liver, involves 5 enzymes.

Question 15

Refeeding syndrome

Answer 15

Occurs when nutritional support given to severely malnourished patients.

Electrolyte abnormalities eg hypophosphataemia

Ammonia toxicity due to urea cycle down regulation.

Refeed at 5 - 10 kcal/kg/day.

Question 16

Defects in urea cycle

Answer 16

Autosomal recessive genetic disorders caused by deficiency in one of the enzymes in cycle - don’t need to know specific enzymes.

Leads to hyperammonaemia, accumulation/excretion of urea cycle intermediates.

Question 17

Treat urea cycle deficiency

Answer 17

Low protein diet; replace a.a in diet with keto acids.

Question 18

Effects of ammonia toxicity

Answer 18

Extremely toxic to brain.
Levels need to be 25-40 micro mol/L

Toxic effects:
- alkaline pH
- disruption of cerebral blood flow
- interference with TCA cycle

Question 19

Clinical problems if a.a metabolism

Answer 19

Heel prick test;

Phenylketonuria (PKU)
Maple syrup urine disease
Homocystinuria

Question 20

PKU

Symptoms

Answer 20

Deficiency in phenylalanine hydroxylase
Autosomal recessive
Accum. of phenylalanine in urine, tissue and urine
Phenylketones in urine - musty smell

Severe intellectual disability; developmental delay; microcephaly; seizures; hypopigmentation

Question 21

Homocystinuria
Treatment?

Answer 21

Problem breaking down methionine
Accum. of homocysteine and its metabolites
Excess homocysteine excreted in urine
Autosomal recessive
Defect in cystathionine beta-synthase
Affects connective tissue, muscles, CNS, CVS

Treat with vit B6 supplements for life. Because cystathionine beta-synthase requires this.