Metabolic fate of Amino Acids

Question 1

what are the 9 essential amino acids

Answer 1

PVT TIM HLL

Question 2

What makes up an amino group

Answer 2

alpha carbon, R group, carboxyl group, amino group, hydrogen

Question 3

what goes into an amino acid pool

Answer 3

Body proteins (turnover), dietary proteins (after digestion), Synthesis in the liver (non-essential only)

Question 4

what comes out of an amino acid pool

Answer 4

anabolism and catabolism

Question 5

what is produced in anabolism

Answer 5

1. Endogenous proteins e.g. enzymes, hormones, milk, muscle
2. Other nitrogenous compounds e.g. neurotransmitters

Question 6

what is produced in catabolism

Answer 6

1. alpha-keto acid (glucose, ketone bodies, CO2, H20, energy)
2. urea

Question 7

what process produces carbohydrates

Answer 7

glycolysis

Question 8

what process produces protein

Answer 8

AA catabolism

Question 9

what process produces fat

Answer 9

fatty acid oxidation

Question 10

what is it called when Input to the amino acid pool should match its output

Answer 10

nitrogen balance

Question 11

What is the purpose of amino acid degradation?

Answer 11

1. to supply energy
2. to supply intermediates for the synthesis of other important compounds
3. to remove amino acids that in excess amounts could be toxic / harmful

Question 12

where does amino acid degradation take place

Answer 12

in the liver and is a 2-stage process

Question 13

what occurs in stage 1

Answer 13

the α-amino nitrogen must be removed (via transamination and oxidative deamination reactions) – amino group eventually ends up as urea

Question 14

what occurs in stage 2

Answer 14

remaining carbon skeletons are then shuttled into central metabolic pathways (eg. Citric acid cycle)

Question 15

what is Transamination

Answer 15

the transfer of an amino group firstly to a keto acid to form new amino acids

Question 16

what is Aspartate transaminase (AST)

Answer 16

AST catalyses the interconversion of aspartate and α-ketoglutarate to oxaloacetate and glutamate

AST is a commonly used as a clinical diagnostic test for liver function

Question 17

what is Alanine transaminase (ALT)

Answer 17

Alanine transaminase (ALT) catalyses the interconversion of alanine and α- ketoglutarate to pyruvate and glutamate

ALT useful for screening for liver-associated problem

Question 18

what is Oxidative deamination

Answer 18

NAD+ is reduced to NADH and the amino acid is deaminated (amino group removed)

Question 19

what happens to the ammonia

Answer 19

Transamination and oxidative deamination generate large amounts of ammonium ion
* Ammonium ions are extremely toxic and the body must be able to get rid of it
* Ammonium ions can be detoxified in the liver by their conversion to urea
* Urea cycle enables this process → urea excreted in the urine

Question 20

who came up with the cyclic pathway

Answer 20

Krebs and Henseleit in 1932

Question 21

what is the equation for the urea cycle

Answer 21

CO2 + NH4+ + 3ATP + aspartate + 2H2O —–> urea+2ADP+2Pi +AMP+PPi +fumarate+5H+

• Irreversible reaction
• requires in total 4 ATPs to form a single molecule of urea
• Cost of detoxification of ammonia is surprisingly HIGH!

Question 22

what can The carbon skeleton of amino acids after deamination be used for

Answer 22

used in biosynthetic pathways or can be further degraded to produce energy

Question 23

what are ketogenic amino acids

Answer 23

amino acids metabolised to acetoacetate or acetyl CoA > > ketone body formation

Question 24

what are Glucogenic amino acids

Answer 24

amino acids metabolised to pyruvate or TCA intermediates > > gluconeogenesis