Gastrointestinal biochem (Heck)

Question 1

what is the role of glutamine

Answer 1

seen in fasting state when amino acids release from protein breakdown

delivers ammonia to the kidney - urine

one of 2 main carriers of nitrogen

found in somatic ells and liver

glutamate can accept a second nitrogen to become glutamine

In liver
Reaction used to prevent any ammonia that escaped urea production from leaving liver
In somatic cells
Glutamine released into circulation to go to liver
Glutamine used to produce ammonia for urea cycle

Question 2

what is the role of alanine

and what is the alanine/glucose cycle that takes place in muscle

Answer 2

transporting AA”s for nitrogen use to the liver

In muscle, glucose is metabolized via glycolysis
Produces pyruvate
Pyruvate is transaminated by glutamate to form alanine
Alanine is exported and used as one of two main nitrogen carriers in the blood
Travels to the liver

Question 3

what is the role of glutamate

what does it do in the liver

Answer 3

carries 2 nitrogens

1) (Makes ammonium (NH4+) which enters the urea cycle

2) one in aspartate —>
glutamate can also be broken down into an alpha-keto-glutarate and aspartate

aspartate can enter the urea cycle

in the liver, glutamate accepts another nitrogen forming glutamine

Question 4

hyperammonemia is caused by what in adults

Answer 4

liver failure

Question 5

what are the toxic effects of ammonia

Answer 5

Brain swelling due to osmotic imbalance
High ammonia and glutamate in astrocytes
Initiates glutamine synthetase and inhibits glutaminase
Glutaminase converts glutamine back to glutamate. Doing this will elevate glutamine, lower glutamate  can’t use glutamate as neurotransmitter (loss of function of glutamatergic neurons)

decrease in glutamate concentration (which is an excitatory neurotransmitter)

Question 6

what is transamination

Answer 6

removing the nitrogen from an amino acid–> transferring it to alpha-ketogluatarate to produce glutamate

the amino acid then becomes its corresponding alpha keto acid

Question 7

glutamate dehydrogenase

Answer 7

production of ammonia

glutamate is deaminated by glutamate dehdyrogenase

Question 8

briefly explain the urea cycle

Answer 8

nitrogne enters as ammonium ion or aspartate

in mitochondria:
-ammonium is used to form carbamoyl phosphate (CP)

• CP reacts with ornithine to produce citrulline
• citrulline is transported to cytosol

In cytosol:
Aspartate reacts with citrulline
-arginine is generated and arginine is cleaved to release urea and regenerate ornithine

Question 9

what does it mean if you have a buildup of orotate

Answer 9

it means that ornithine transcarbabmoylase is deficient (normally takes ornithine and combines with carbamoyl phosphate)

excess carbamoyl phosphate enters the pathway for pyrimidine biosynthesis –> creates the intermediate orate or orotic acid (elevation in the urine is indicative of urea cycle defect)

Question 10

autosomal recessive deficiency

presents with cardiovascular disease:
-DVT, Thromboembolism, Stroke-infarction

Dislocation of the lens

Mental retardation

Marfanoid habitus- long limbs *waddling gait

Answer 10

homocystinuria

Question 11

what is the pathophysiology of homocystinuria

Answer 11

deficiency in cystathione B-synthase (which normally converts homocysteine to cystathione) —-> which eventually creates succinyl CoA for TCA cycle

without the enzyme homocysteine builds up and is converted to methionine by Vitamin B12 and folate (so you have elevated methionine)

you have low cysteine b/c its made from homocysteine

elevated homocysteine

Question 12

in contrast to homocystinuria, how would Vitamin B12 or folate deficiency present

Answer 12

you would have low serum methionine levels and high homocysteine

b/c normally B12 Methylates homocysteine to methionine

Question 13

what are the two ketogenic AA’s (amino acids that are broken down to make ketone bodies)

Answer 13

lysine

leucine

Question 14

when does positive nitrogen balance occur

Answer 14

nitrogen balance occurs during growth

Amount incorporated exceeds the amount excreted

Examples: adolescents, infants, after surgical procedure (repairing tissue)

Question 15

when does negative nitrogen balance occur

Answer 15

malnutrition

Question 16

Reduction in the total number of calories in an infant’s diet

child’s weight falls below 60% for normal sex, height and age

significant loss of body fat and muscle occurs due to catabolism of fats and protein, an adaptive strategy to use lipids and amino acids as energy sources

Answer 16

marasmus

Question 17

A protein-energy malnutrition (PEM)

Protein deprivation with adequate caloric intake

Loss of albumin  osmotic imbalance, water moves out of circulation and into the tissue  edema

normal or nearly normal body weight and height for age
Often, the child has been weaned too early and subsequently fed a low-protein, high-carbohydrate diet

Answer 17

kwashiorkor

Question 18

what is the outcome of insufficient essential amino acid intake

Answer 18

decreased protein synthesis

Hypoalbuminemia
Albumin makes up 55-60% of the total serum protein.
Albumin plays important roles in buffering and maintaining osmotic pressure, “pull” of water

Hypopigmentation

Question 19

what is the role of Vitamin B6 (pyridoxal phosphate) in terms of AA’s

Answer 19

Key coenzyme for amino acid metabolism

Required for transamination reactions

Enzyme bound pyridoxal phosphate
Reacts with an amino acid
Acquires the amino group and releases a-ketoacid
Reacts with another a-ketoacid
Releases the amino group to produce an amino acid
Pyridoxal phosphate regenerated

Question 20

alcohol is converted to what in the liver

how does alcohol processing relate to glucose processing

Answer 20

acetaldehyde then to acetate and this requires NAD+

if there is too much alcohol processing going on, you deplete stores of NAD+ which you also need for gluconeogenesis

too much NADH will reverse gluconeogenesis = bad

this all leads to alcoholic hypoglycemia b/c you can’t make sugar

Question 21

what are the 3 main precursors for gluconeogenisis

Answer 21

Lactate (from anaerobic glycolysis)
Oxidized to pyruvate by lactate dehydrogenase

Alanine (from muscle)
Converted to pyruvate by alanine aminotransferase

Glycerol-3-phosphate (from FA’s)
Oxidized to DHAP by glycerol-3-phosphate dehydrogenase