Exam 2 AA metabolism pt 2

Question 1

Name two linear compounds in the proline biosynthetic pathway.

Answer 1

Glutamate, Gultamate semialdehyde

Question 2

What are the functions of hydroxyprolines?

Answer 2

They are important in stabilizing the triple helix of collagen

Question 3

Name the amino acid that is required for selenocysteinyl tRNA synthesis.

Answer 3

Serine (attached to tRNA as Seryl-tRNA)

Question 4

What is the cofactor that is required for the phenylalanine hydroxylase reaction?

Answer 4

Tetrahydrobiopterin (THB)

Question 5

What enzyme deficiency causes phenylketonuria (PKU)?

Answer 5

Phenylalanine hydroxylase

Question 6

Name two disorders of tyrosine metabolism.

Answer 6

Alcaptonuria, Albinism, PKU

Question 7

What enzyme deficiency causes albinism?

Answer 7

tyrosinase

Question 8

Methionine adenosyltransferase catalyzes the synthesis of ______?

Answer 8

S-adenosylmethionine (SAM)

Question 9

What compound is the precursor for cystine synthesis?

Answer 9

Methionine

Question 10

Name a disorder of cystine metabolism.

Answer 10

Homocystinuria

Question 11

Name the oxidized form of homocysteine.

Answer 11

homocystine

Question 12

Name the amino acid precursor for NMP synthesis

Answer 12

Tryptophan

Question 13

Name an enzyme that requires a vitamin B12 derivative as a coenzyme.

Answer 13

Methionine synthase (in converting homocysteine to methionine)

Mutase (converting propionyl CoA to Succinyl CoA)

Question 14

Name the pathway that requires both the derivatives of vitamin B12 and another of vitamin B.

Answer 14

Catabolism of branched chain amino acids (BCAA’s) into succinyl CoA:

Leucine, Valine, Isoleucine are transaminated with vitamin B derivative [Lip. 234, 249]

Successive reactions of oxidative decarboxylation and dehydrogenation can lead to Propionyl CoA [Lip. 249]

Propionyl CoA is isomerized into succinyl CoA with mutase and a vitamin B12 derivative. [Lip. 326]

Additionally, carboxylase reactions require Biotin (another B-complex derivative)

Question 15

Name a disorder of a branched chain amino acid metabolism.

Answer 15

Maple syrup urine disease. (MSUD)

Question 16

Name the amino acid that is required for carnitine biosynthesis.

Answer 16

Lysine

Question 17

Name the amino acids that are required for creatine synthesis.

Answer 17

glycine and arginine

Question 18

Name 4 functional groups that can be added to tetrahydrofolate.

Answer 18

Formyl
Methenyl
Methylene
Methyl

They are attached to the N5 or N10 active centers.

Question 19

Name the amino acid and the vitamin derivative that is required for glycine synthesis.

Answer 19

Serine and THF [Lip. 325]

Question 20

Name the 2 degradative pathways that require tetrahydrofolate.

Answer 20

Histidine → Glutamate [L. 247]

Resynthesis of methionine from homocysteine [L. 249, Venk Amino Acid metabolism lecture 4]

Also involved in the degradation of tryptophan

Question 21

Name two reactions that require tetrahydrobiopterin as a cofactor.

Answer 21

Phenylalanine + O2 → Tyrosine + H2O
(Phenylalanine hydroxylase & THB)

Arginine + O2 + NADPH → NO + Citrulline
(Nitric oxide synthase & THB)

Question 22

24. Describe how homocysteine is converted into methionine

Answer 22

Homocysteine → Methionine

(Vit B12 derivative & Methionine synthase)

Question 23

Lysine is required for synthesis of _______?

Answer 23

carnitine

Question 24

Name the components of folate

Answer 24

Pterin, PABA and Glutamic Acid

Question 25

Name the 2 degradative pathways that require tetrahydrofolate.

Answer 25

Histidine → Glutamate [L. 247]

Resynthesis of methionine from homocysteine [L. 249, Venk Amino Acid metabolism lecture 4]

Also involved in the degradation of tryptophan

Question 26

Name the vitamin derivative that is required for the prolyl hydroxylase reaction.

Answer 26

vitamin c

Question 27

Why is the element selenium is essential?

Answer 27

Selenium is used to synthesize selenocysteine. Selenocysteine is part of
glutathione peroxidase, which is important to prevent oxidative damage.

Question 28

phenylketonutia

Answer 28

Normally, phenylalanine is converted to tyrosine via phenylalanine
hydroxylase. This reaction requires THB (tetrahydrobiopterin).
■ Defect in phenylalanine metabolism due to deficiency of phenylalanine
hydroxylase will lead to phenylketonuria.

Question 29

phenilanaline accumulates and gets excreted as

Answer 29

phenylpyruvate and phenylketone

Question 30

PKU is a defect in ???

Answer 30

phenylalanine metabolism, NOT

tyrosine metabolism.

Question 31

homocystinuria (2nd type)

Answer 31

Deficiency in ​cystathionine beta­synthase

Question 32

alcaptonuria

Answer 32

Normally, during tyrosine metabolism, the intermediate homogentisic acid
gets converted to maleyl acetoacetate via homogentisate oxidase.
■ Deficiency in homogentisate oxidase→ accumulation of homogentisic
acid → homogentisic acid is oxidized into a dark brown polymer →
polymer is deposited in joints → arthritis

Question 33

albinism

Answer 33

Normally, tyrosine is used to synthesize melanin via tyrosinase.
■ Deficiency in tyrosinase → defective melanin production → skin
susceptible to damaging effects of sunlight such as skin cancer.

Question 34

in homocystinyria accumulation of what ??? what forms

Answer 34

accumulation of homocysteine ­­>
● excreted in the urine
● form h​omocysteine thiolactone​­ a very reactive intermediate
that thiolates LDL, which aggregates & forms a​theromas​.**

Question 35

importance of homocysteine

Answer 35

2 homocysteine​can be linked together via disulfide bond to
form ​homocystine (​oxidized form)**
○ causes skeletal abnormalities, thrombosis & mental
retardation

Question 36

**​Homocystinuria​can also manifest if there is a deficiency in:

Answer 36

methionine synthase
● vitamin B12
● N5­CH3­THF deficiency
● In this case, ​homocysteine c​anNOT​be used to reconverted
into ​methionine
● lack of methionine → impaired SAM synthesis and associated
methylations.

Question 37

maple urine disease /defficiency in enzyme

Answer 37

Normally, the catabolism of branched chain amino acids (valine, leucine,
isoleucine)​requires the enzyme BCKA (branched chain keto acid)
dehydrogenase.
■ Deficiency in ​BCKA dehydrogenase​causes the branched chain amino
40

acids to accumulate and in the urine, making urine smells like maple
syrup → maple syrup urine disease
■ Therapy: reduced consumption of branched chain amino acid in the diet.
■ genetic frequency of MSUD worldwide: 1 in 185,000 newborns
■ genetic frequency of MSUD in the inbred Mennonite population of
Lancaster County, PA is ​1 in 175 ***n​ewborns.

Question 38

Histinidemia

Answer 38

Normal metabolism of histidine requires histidase,​which converts
histidine to urocanate. Histidase is highly expressed in skin and liver. In
skin, urocanate is one of the components of sweat. The complete
catabolism of histidine happens only in the liver.
■ Deficiency of histidase → histidine accumulation in blood → histidinemia.
Histidase deficiency can be confirmed using skin biopsies.

Question 39

can folate acid be synthesized by humans

Answer 39

No ­ because humans lack the enzyme that converts PABA into folic acid.

Question 40

What step is inhibited by sulfamethoxazole?

Answer 40

PABA → Folic acid

Question 41

35. Describe in detail, the role of folate in relation to one carbon metabolism.

Answer 41

Folate (folic acid) is used to make THF.
○ THF can act as a carrier of carbon atoms.
○ One carbon metabolism involves the transfer of one­carbon groups such
as ​formyl, methenyl, methylene, or methyl groups​to ​THF ​form formyl­THF,
methenyl­THF, methylene­THF, or methyl­THF.

Question 42

without folic acid whats impaired

Answer 42

impaired synthesis of purine, thymidine, and methionine.

Question 43

36. Describe the biosynthesis of carnitine.

Answer 43

SAM provides methyl (­CH3) groups.

○ Methyl transferase transfers three methyl groups from 3 SAMs to lysine to form
N­trimethyl lysine & 3 homocysteine. Through additional steps, N­trimethyl lysine
is converted to carnitine.

Question 44

What are some organism specific d​ihydrofolate reductase (DHFR) inhibitors?​

Answer 44

Epiroprim (a type of trimethoprim)
○ Pyrimethamine
○ Methotrexate

Question 45

38. Trimethoprim, methotrexate and pyrimethanimine inhibits ____ (specify the organisms).

Answer 45

trimethoprim ­ inhibits bacterial DHFR; does not affect human
○ pyrimethanimine ­ inhibits protozoan (ameoba) DHFR; does not affect human
○ methotrexate ­ inhibits eukaryotic DHFR; affects human