Chapter 17: Amino Acid Metabolism

Question 1

Amino acids released from proteins go through deamination or transamination produce C skeletons that the liver can convert to what products?

Answer 1

glucose (glucogenic amino acids)
acetyl CoA,
ketone bodies (ketogenic)

Question 2

Amino groups released by deamination form which ion?

Answer 2

ammonium ion (NH4+)

Question 3

How do most tissues add excess amino acids to blood?

Answer 3

*add excess nitrogen to the blood as glutamine by attaching ammonia to the y-carboxyl group of glutamate

Question 4

How is lactulose used to treat hyperammonemia?

Answer 4

lactulose is metabolized to lactic acid in GI by bacteria

lactic acid in turn converts ammonia (NH3) to ammonium (NH4+) interfering with absorption and treating hyperammonemia

Question 5

Be able to draw out a diagram for amino group removal for elimination as urea and ammonia.

Answer 5

Refer to diagram

Question 6

What is the enzyme that capture nitrogen and in turn converts glutamate to glutamine to be released out into the circulation?

Answer 6

glutamine synthetase

Question 7

What is the purpose of glutaminase in the kidney?

Answer 7

an enzyme that deaminates glutamine arriving in the blood and eliminates the amino group as ammonium ion in the urine.

Question 8

What is another name for aminotransferases?

Answer 8

transaminases

Question 9

What is the function of transaminases? Compare to deaminases?

Answer 9

unlike deaminases, do not release the amino groups

This class of enzymes transfers the amino group from one carbon skeleton (an amino acid) to another (usually a-ketoglutarate, a citric acid cycle intermediate)

Question 10

What vitamin mediates the transfer of an amino group from one carbon skeleton (an amino acid) to another (usually a-ketoglutarate)

Answer 10

Pyridoxal P Vitamin B6

Question 11

How are aminotransferases named? ALT stands for? AST stands for?

Answer 11

according to the amino acid donating the amino group to a-ketoglutarate.

ALT alanine aminotransferase (formerly GPT)
AST aspartate aminotransferase, (formerly GOT)

Question 12

What organs are the aminotransferases usually found?

Answer 12

liver and muscle

Question 13

The reactions catalyzed by aminotransferases are reversible or irreversible?

Answer 13

reversible and play several roles in metabolism

Question 14

A portion of the glutamate formed in the muscle may be aminated by glutamine synthetase (as in other tissue or the amino group can be transferred to what metabolic product to make alanine?

Answer 14

pyruvate

Question 15

What is the purpose of glutamate dehydrogenase?

Answer 15

enzyme found in many tissues where it catalyzes the reversible oxidative deamination of the amino acid gluatamate

Question 16

How many nitrogens does urea contain?

Answer 16

2 nitrogens

Question 17

N-acetylglutamate is only produced in what conditions?

Answer 17

when amino acids are present

Question 18

Draw out the urea cycle.

Answer 18

Refer to diagram

Question 19

Carbamoyl phosphate synthetase and ornithine transcarbamoylase are enzymes found where in the cell?

Answer 19

mitochondrial enzymes

Question 20

The product urea is formed in the mitochondria or the cytoplasm of the liver?

Answer 20

the cytoplasm

Question 21

Compare and contrast ammonia levels in carbamoyl phosphate synthetase deficiency and ornithine transcarbamoylase deficiency. (Ammonia levels, glutamine levels, BUN, orotic acid, inheritance pattern, brain abnormalities, symptoms.

Answer 21

Refer to chart

Question 22

How can genetic deficiencies of urea synthesis be treated?

Answer 22

with a low protein diet and administration of sodium benzoate or phenylpyruvate to provide an alternative route for capturing and excreting excess nitrogen

Question 23

Be able to create a diagram on genetic deficiencies of amino acid metabolism associated disorders and symptomology.

Answer 23

Question 24

Another name for phenylketonuria?

Answer 24

phenylalanine hydroxylase deficiency

Question 25

What is something people may add to a meal/drink that is strictly avoided in phenylketonurics?

Answer 25

aspartame (N-aspartylphenylalanine methyl ester) which is an artificial sweetener

Question 26

Symptoms of PKU? What may their diet be low in as a treatment?

Answer 26

* intellectual disability * musty odor * microcephaly * pale skin and white blonde hair (hypopigmentation) low levels of phenylalanine (restricted) still needed because it is essential amino acid

Question 27

The neurotoxic effects of PKU occur because of a high level of what in the blood?

Answer 27

high levels of phenylalanine and not the phenylketones from which the name is derived

Question 28

What is treatment for PKU?

Answer 28

lifelong semi synthetic diet with restricted amounts of phenylalanine (small quantities are necessary because it is an essential amino acid)

Question 29

Is PKU an example of allelic heterogeneity? Explain

Answer 29

yes because there are >100 known mutations in the gene for phenylalanine hydroxylase causing PKU

Question 30

What is albinism?

Answer 30

group of conditions in which the normal conversion of tyrosine to melanin is altered. Most severe form is a deficiency of tyrosinase

Question 31

Another name for homogentisate oxidase deficiency?

Answer 31

alkaptonuria

Question 32

Explain the cause for dark urine in homogentisate oxidase deficiency.

Answer 32

accumulation of homogentisic acid in the blood causes it excretion in urine, after which it gradually darkens upon exposure to air

Question 33

Ochronosis?

Answer 33

bluish-black discoloration of certain tissues, such as the ear cartilage and the ocular tissue

Question 34

Why can ochronosis be seen in alkaptonuria?

Answer 34

Because the homogentisic acid in the blood accumulates in cartilage and may be seen in the sclera of the eye, in ear cartilage and patients develop arthritis in adulthood

Question 35

Another name for Maple Syrup Urine disease.

Answer 35

Branched-chain ketoacid dehydrogenase Deficiency

Question 36

How is branched chain ketoacid dehydrogenase an enzyme similar to a-ketoglutarate dehydrogenase?

Answer 36

needs all 5 cofactors/coenzymes: thiamine, lipoic acid, CoA, FAD, NAD+

Question 37

What does branched chain ketoacid dehydrogenase metabolize?

Answer 37

branched chain ketoacids produced from their cognate amino acids, valine, leucine, and isoleucine

Question 38

Explain the progression of MSUD.

Answer 38

In the first few days of life, infants are normal, after which they become progressively lethargic, lose weight, and have alternating episodes of hypertonia and hypotonia and urine develops charcteristic odor of maple syrup

Question 39

What are the amino acids metabolized through the propionic acid pathway?

Answer 39

valine methionine isoleucine threonine

Question 40

Deficiency in propionyl-CoA carboxylase and methylmalonyl CoA mutase results in what condition?

Answer 40

neonatal ketoacidosis from failure to metabolize ketoacids produced from the 4 amino acids: valine, methionine, isoleucine, and threonine

Question 41

Propionyl CoA carboxylase deficiency involves an accumulation of what products?

Answer 41

propionic acid, methyl citrate, and hydroxypropionic acid

Question 42

Methylmalonyl CoA mutase deficiency will lead to an accumulation of which products?

Answer 42

accumulation of methylmalonic acid

Question 43

How do you treat propionyl CoA carboxylase deficiency?

Answer 43

a diet low in protein or a semisynthetic diet with low amounts of valine, methionine, isoleucine, and threonine

Question 44

How do you treat methylmalonyl CoA mutase deficiency?

Answer 44

a diet low in protein or a semisynthetic diet with low amounts of valine, methionine, isoleucine, and threonine

Question 45

What is the difference between homocysteine and homocystine?

Answer 45

homocystine is a disulfide dimer of homocysteine

Question 46

Treatment for homocystinemia/homocystinuria?

Answer 46

treating the symptoms and a diet low in methionine

Question 47

What is the major enzyme deficiency producing homocystinemia?

Answer 47

that of cystathionine synthase deficiency

Question 48

Difference between subluxation of the lens in Maarfans vs homocystinemia?

Answer 48

In Marfaan subluxation of the lens is upward and outward; In cystathionine syndrome subluxation of the lens is downward and inward

Question 49

If left untreated those with cystathionine synthase deficiency usually succumb to what?

Answer 49

MI, stroke, or pulmonary embolism

Question 50

When a biochemical reaction requires a methyl group (methylation) what is usually the methyl donor?

Answer 50

SAM S-adenosylmethionine is generally the methyl donor

Question 51

If 1 carbon unit in another oxidation state is required (methylelene, methenyl, formyl) what is required?

Answer 51

THF tetrahydrofolate typically serves as the donor

Question 52

Tetrahydrobiopterin (BH4) is a coenzyme for which enzymes? How is it regenerated?

Answer 52

tyrosine hydroxylase, phenylalanine hydroxylase, and tryptophan hydroxylase (serotonin synthesis) and is regenerated by the dihydropteridine reductase

Question 53

Parkinson's disease is caused by loss of dopaminergic neurons in what part of the brain?

Answer 53

substantia nigra

Question 54

What are important pathways requiring SAM?

Answer 54

include synthesis of epinephrine and of the 7 methylguanine cap on eukaryotic mRNA

Question 55

Homocysteine methyl transferase requires what coenzymes/vitamins to convert homocysteine to methionine?

Answer 55

B12 N5-methyl THF

Question 56

What are important pathways requiring THF?

Answer 56

synthesis of all purines and thymidine which are used for DNA and RNA synthesis during cell growth and division

Question 57

How is additional folate stored in the body?

Answer 57

in the highly reduced N5-methyl-THF form

Question 58

What is the only enzyme that uses N5 methyl THF? What enzyme does the vitamin require?

Answer 58

homocysteine methyltransferase which requires B12