WEEK 5: Amino acid metabolism

Question 1

what are amino acids?

Answer 1

Monomeric units for proteins

Question 2

what is the main source of nitrogen in the body?

Answer 2

dietary protein

Question 3

what compounds contain nitrogen?

Answer 3

haem, creatine, purines and pyrimidines

Question 4

what happens to excess dietary amino acids?

Answer 4

not required for protein synthesis can’t be stored (in mammals) & aren’t excreted so are converted to energy metabolites

Question 5

what are the major metabolic fuels?

Answer 5

glucose and fatty acids

Question 6

what percentage of energy requirements come from amino acids (in humans)?

Answer 6

10-25%

Question 7

what are 2 sources of amino acids in the amino acid pool?

Answer 7

dietary protein digestion and synthesis of non-essential amino acids

Question 8

what are 2 utilisation factors of amino acid pool?

Answer 8

go over slide 5 yellow boxes

Question 9

what are essential amino acids?

Answer 9

cannot be synthesized by the body; obtained via diet

Question 10

what are non-essential amino acids?

Answer 10

can be synthesized by the body

Question 11

what are glucogenic amino acids?

Answer 11

catabolism yields pyruvate or an intermediate of the citric acid cycle

Question 12

what are ketogenic amino acids?

Answer 12

yields acetoacetate, acetyl CoA or acetoacetyl CoA

Question 13

what do glucogenic amino acids produce when broken down?

Answer 13

carbon skeletons broken down to glucose precursors

Question 14

what do ketogenic amino acids produce when broken down?

Answer 14

carbon skeletons broken down to ketone body or fatty acid precursors

Question 15

where is the major site of aa catabolism?

Answer 15

liver

Question 16

what is the first stage of aa catabolism?

Answer 16

Deamination/Transamination– removal and conversion of amino group to ammonia or amino group of aspartate

Question 17

what is the second stage of aa catabolism?

Answer 17

Incorporation of nitrogen from ammonia/aspartate to urea

Question 18

what is the third stage of aa catabolism?

Answer 18

Conversion of amino acid carbon skeletons (a-keto acids) to one of the 7 common metabolic intermediates

Question 19

go over and understand slide 9 diagram

Question 20

what is the name of the enzyme responsible for the removal of the amino group in the initial stages of catabolism?

Answer 20

aminotransferases - these are specific for each amino acid.

Question 21

what does the aminotransferase require as a coenzyme?

Answer 21

pyridoxal phosphate (vitamin B6)

Question 22

slide 11 - just learn the bullet points

Question 23

slide 12 ???

Question 24

what are the 2 isomeric forms that amino acids occur in?

Answer 24

L- or D-

Question 25

which isomeric form of amino acids do animals utilise?

Answer 25

L-AA

Question 26

why are D-AAs broken down?

Answer 26

D-AA’s can interfere with metabolism of L-AA’s

Question 27

what enzyme breaks D-AAs down?

Answer 27

D-amino acid oxidase (D-AAO)

Question 28

Catabolism of glucogenic amino acids produces...(6)

Answer 28

pyruvate oxaloacetate, a-ketoglutarate fumerate or succinyl-CoA.

Question 29

slide 15 - what happens and what enzyme? vit B6 is required )

Question 30

what is aspartate converted to?

Answer 30

oxaloacetate via transamination

Question 31

what enzyme is required to convert aspartate?

Answer 31

Aspartate aminotransferase (AST). requires B6

Question 32

what is asparargine converted to? what enzyme? slide 17

Question 33

how can asparagine be used in the treatment for leukaemia patients?

Question 34

what is required for the urea cycle?

Answer 34

Glutamate and glutamine are required for the Urea Cycle.

Question 35

why is glutamate a special amino acid?

Answer 35

can be formed or degraded by aminotransferases or by glutamate dehydrogenase (mitochondrial enzyme). both reactions are reversible

Question 36

slide 18

Question 37

what is oxidative deamination?

Answer 37

removal of amino group. Oxygen is being put where the ???what group is. also rpoduces NH4+.

Question 38

slide 19 - is nad(p) h a product or needed for reaction?

Question 39

what is glutamine?

Answer 39

Glutamine is a non-toxic, transport form of ammonia from the peripheral tissues (especially important in brain)

Question 40

how is glutamine produced? what does it require?

Answer 40

In peripheral tissues glutamate is converted to glutamine – Glutamine synthetase enzyme. Requires ATP and free ammonia.

Question 41

how is glutamine converted back to glutamate?

Answer 41

by enzyme glutaminase - water is needed and ammonia is released

Question 42

how is a-ketoglutarate produced?

Answer 42

through catabolism of both glutamine and glutamate

Question 43

methionine is cyclic - what does that mean?

Question 44

what is methionine convertd into?

Answer 44

homocysteine

Question 45

what are the 2 "fates" of homocysteine?

Answer 45

1. can be converted back to methionine by methionine synthase. 2. degraded further into cystiene

Question 46

Catabolism of ketogenic amino acids produces...(3)

Answer 46

Acetyl-CoA Acetoacetate Acetoacetyl-CoA

Question 47

what are the 2 ketogenic amino acids?

Answer 47

leucine and lysine. Both are essential

Question 48

what is glucogenesis?

Question 49

what is ketogenesis?

Question 50

what is phenylanine converted to?

Answer 50

tyrosine

Question 51

what is required in the conversion of phenylanine?

Answer 51

phenylalanine hydroxylase

Question 52

what is tyrosine broken down into?

Answer 52

Hydroxyphenylpyruvate

Question 53

what is Hydroxyphenylpyruvate broken down into?

Answer 53

homogentisate

Question 54

what is Phenylketonuria (PKU)?

Answer 54

Autosomal recessive disorder, high levels of Phenylalanine hydroxlase, low levels of tyrosine

Question 55

what occurs if Phenylketonuria (PKU) is left untreated?

Answer 55

If untreated, leads to permanent intellectual disability, seizures, delayed development, behavioural problems, & psychiatric disorders

Question 56

how is Phenylketonuria (PKU) treated?

Answer 56

amino acid restriction via low-protein diet, avoid aspartame, supplementation with Tyrosine, monitor blood

Question 57

what are the branched chain amino acids?

Answer 57

Valine, Leucine, Isoleucine

Question 58

how are Valine, Leucine, Isoleucine broken down first step

Answer 58

transamination

Question 59

how are Valine, Leucine, Isoleucine broken down - second step

Answer 59

oxidative decarboxlyation

Question 60

go over slide 36 third step!! need to know

Question 61

maple syrup urine disease, go over

Question 62

how is MSUD treated?

Question 63

why is ammonia converted?

Answer 63

Ammonia is produced as a result of amino acid degradation and is potentially toxic – required to be converted into a non-toxic form

Question 64

what are amino acids broken down into basically?

Answer 64

NH3 is TOXIC Carbon skeleton

Question 65

what is NH3 detoxified into?

Answer 65

urea in the urea cycle in the liver

Question 66

slide 42

Question 67

where does the breakdown of amino acids occur? double check

Answer 67

muscle, peripheral tissues

Question 68

slide 44

Question 69

what does alanine do?

Answer 69

main ammonia transporter produced in muscle due to the high levels of pyrvuate generated

Question 70

chemical formula of urea contains 2 N atoms. How are they donated?

Answer 70

One of the N atoms of urea is donated by ammonia (GDH & Glutaminase) the second N atom is donated by aspartate

Question 71

What 2 roles does glutamate play in the formation of NH3 for urea cycle?

Answer 71

Transamination: the amino group of an amino acid is transferred to α-ketoglutarate to form glutamate Oxidative deamination by Glutamate dehydrogenase forms free ammonia

Question 72

learn the reaction of the urea cycle, write down steps - slide 48

Question 73

how many enzymatic reactions of urea cycle?

Answer 73

5

Question 74

what are the 5 enzymatic reactions of urea cycle?

Answer 74

2 mitochondria 3 cytosolic

Question 75

what is a rate limiting step of the urea cycle?

Answer 75

the requirement of hydrolysis of 2 ATP

Question 76

go up to slide 54

Question 77

what indicates that the urea cycle needs to be regulated?

Answer 77

Increase in arginine indicates substrate availability i.e. NH3