Session 1- Protein and amino acid metabolism

Question 1

N equilibrium

Answer 1

intake = output

no change on total body protein

Question 2

Positive N balance

Answer 2

intake > output
increase in total body protein.
normal state in growth and pregnancy or in adult recovering from malnutrition

Question 3

negative N balance

Answer 3

intake < output
net loss of body protein
never normal
causes include trauma, infection and malnutrition

Question 4

name a glucogenic, ketogenic and both amino acid

Answer 4

aspartate
leucine
threonine

Question 5

what is cushings syndrome

Answer 5

caused by excessive breakdown of protein. Weakens skin structure leading to striae formation

Question 6

what is transamination

Answer 6

Process that swaps the amino group (NH2) on an amino acid for a carboxyl group (C=O). This can be done through two enzymes called alanine aminotransferase (ALT) and aspartate aminotransferase (AST).

all aminotransferases require the coenzyme pyridoxal phosphate which is a derivative of vitamin b6

Question 7

what is ALT

Answer 7

alanine aminotransferase- converts alanine to glutamate

Question 8

what is AST

Answer 8

aspartate aminotransferase- converts glutathione to aspartate

Question 9

how is liver function tested

Answer 9

by measuring the levels of AST and ALT which are high in conditions that cause extensive cellular necrosis such as: viral hepatitis, autoimmune liver disease, toxic injury

Question 10

what is deamination

Answer 10

liberates amino acid as free ammonia
mainly occurs in liver and kidney
keto acids can be used for energy
also important in deamination of dietary D-amino acids

Question 11

how is ammonia removed

Answer 11

it is very toxic and must be removed. ultimately converted to urea or excreted directly in urine

at physiological pH ammonia is rapidly converted into ammonium ion

Question 12

what enzymes deaminate amino acids

Answer 12

amino acid oxidases
glutaminase
glutamate dehydrogenase

Question 13

urea

Answer 13

high nitrogen content
non-toxic
extremely water soluble
chemically inert in humans (bacteria can break it down to release NH3)
most urea is excreted in urine via the kidneys
also performs useful osmotic role in kidney tubules

Question 14

urea cycle

Answer 14

occurs in liver and involves 6 enzymes
amount of urea cycle enzymes normally related to need to dispose of ammonia
high protein diet induces enzyme levels
low protein diet or starvation represses levels
cycle is inducible but not regulated

Question 15

refeeding syndrome

Answer 15

can occur when nutritional support given to severely malnourished patients
ammonia toxicity significant factor
refeed @ 5 to 10 kcal/kg/day. Raise gradually to full needs within a week

Question 16

what are risk factors of refeeding syndrome

Answer 16

BMI < 16
Unintentional weight loss >15% in 3- 6 months
10 days or more with little or no nutritional intake

Question 17

what do defects in the urea cycle lead to

Answer 17

hyperammonaemia

accumulation/ excretion of urea cycle intermediates

Question 18

what causes defects in the urea cycle

Answer 18

autosomal recessive genetic disorders caused by deficiency of one of enzymes in the urea cycle

Question 19

symptoms of defects in the urea cycle

Answer 19

vomiting
lethargy
irritability
mental retardation
seizures
coma

Question 20

how do you manage defects in the urea cycle

Answer 20

low protein diet

replace amino acids in diet with keto acids

Question 21

why ammonia toxic

Answer 21

readily diffusible and extremely toxic to brain

blood level needs to be kept low

Question 22

effects of ammonia

Answer 22

interference with amino acid transport and protein synthesis
disruption of cerebral blood flow
pH effects
interference with metabolism of excitatory amino acid neurotransmitters
alteration of blood-brain barrier
interference with TCA cycle reacts with alpha-ketoglutarate to glutamate

Question 23

what are the glutamine mechanisms that are utilised for the safe transport of amino acid nitrogen from tissues for disposal

Answer 23

glutamine- ammonia combined with glutamate to form glutamine which is transported in blood to liver or kidneys where it is cleaved by glutaminase to reform glutamate and ammonia

Question 24

what are the alanine mechanisms that are utilised for the safe transport of amino acid nitrogen from tissues for disposal

Answer 24

alanine- amine groups transferred to glutamate by transamination. Pyruvate then transaminated by glutamate to form alanine. Alanine transported in blood to liver where it is converted back to pyruvate by transamination. Amino group fed via glutamate into urea cycle for disposal as urea whereas pyruvate is used to synthesise glucose which can be fed back into tissues.

Question 25

what is PKU

Answer 25

• phenylketonuria
• most common inborn error of amino acid
• deficiency in phenylalanine hydroxylase
• autosomal recessive. Affected gene is on chromosome 12
• accumulation of phenylalanine in tissue, plasma and urine
• phenylketones in urine
• musty smell

Question 26

how do you treat PKU

Answer 26

strictly controlled low phenylalanine diet enrinched with tyrosine
avoid artificial sweeteners
avoid high protein foods such as meat milk and eggs

Question 27

symptoms of PKU

Answer 27

severe intellectual disability 
developmental delay 
microcephaly
seizures
hypopigmentation 

they can all be avoided with early intervention

Question 28

homocystinurias

Answer 28

problem breaking down methionine
excess homocysteine excreted in urine 
autosomal recessive 
defect in cystathionine beta-synthase 
affects connective tissue, muscles, CNS, CVS

Question 29

how do you treat homocystinuria

Answer 29

low methionine diet
avoid milk, meat, fish, cheese, eggs
nuts, and peanut butter also contain methionine