Urgh, way to too detailed stuff we prbly don't have to know

Question 1

As a summary…

List the intermediates of the purine synthesis.

Answer 1

starts w/ PRPP

• PRA → GAR → FGAR → FGAM
• AIR → CAIR → SAICAR → AICAR → FAICAR

ends w/ IMP

Question 2

Which enzyme catalyzes the first reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 2

Gln PRPP amidotransferase
N9 from Gln attached to ribose-5-P
→ 5-phosphoribosyl-amine (PRA)

PRPP + H₂O + Gln → PRA + Glu + PP_i

Question 3

Which enzyme catalyzes the second reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 3

GAR synthetase
C4, 5, 7 from Gly attached to PRA
→ 5’PR-glycinamide (GAR)

PRA + Gly + ATP → ADP + P_i + GAR

Question 4

Which enzyme catalyzes the third reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 4

GAR transformylase
C8 from N¹⁰-formyl H₄F attached to GAR
→ 5’PR-formyl-glycinamide (FGAR)

GAR + N¹⁰-formyl H₄F → FGAR + H₄F

Question 5

Which enzyme catalyzes the fourth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 5

FGAM synthetase
N3 from Gln attached to FGAR
→ 5’PR-formylamidine (FGAM)

FGAR + ATP + H₂O + Gln → FGAM + ADP + P_i + Glu

Question 6

Which enzyme catalyzes the fifth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 6

AIR synthetase
imidazole ring formed in FGAM
→ 5’PR-5-amino-imidazole (AIR)

FGAM + ATP → ADP + P_i + AIR

Question 7

Which enzyme catalyzes the sixth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 7

AIR carboxylase
C6 from CO₂ attached to AIR
→ 5’PR-4-carboxy-5-amino-imidazole (CAIR)

AIR + CO₂ → CAIR

_reversible

Question 8

Which enzyme catalyzes the seventh reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 8

SAICAR synthetase
N1 from Asp (amino group donor) attached to CAIR
→ 5’PR-succinyl-5-aminoimidazole-4-carboxamide (SAICAR)

CAIR + ATP + Asp → ADP + P_i + SAICAR

Question 9

Which enzyme catalyzes the eighth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 9

adenylosuccinase (ASA)
AICAR cleaved, fumarate dissociates
→ 5’PR-5-aminoimidazole-5-carboxamide (AICAR)

SAICAR → fumarate + AICAR

Question 10

Which enzyme catalyzes the ninth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 10

AICAR transformylase
C2 from N¹⁰-formyl H₄F attached to AICAR
→ 5’PR-5-formamidoimidazole-4-carboxamide (FAICAR)

AICAR + N¹⁰-formyl H₄F → FAICAR + H₄F

Question 11

Which enzyme catalyzes the tenth reaction of the de novo synthesis of purines?

Reaction + structures.

Answer 11

IMP cyclohydrolase
FAICAR hydrolyzed
→ inosinemonophosphate (IMP)

FAICAR → IMP + H₂O

Question 12

What happens in the 1^st step of FA synthesis?

Domain of FA synthesis?

Answer 12

MAT (malonyl/acetyltransferase) → charging + acetyltransfer

1. acetyl group from acetyl-CoA transferred to central ACP-SH
2. then transferred to peripheral KS-SH

+ CoA-SH released

Question 13

What happens in the 2^nd step of FA synthesis?

Domain of FA synthesis?

Answer 13

MAT (malonyl/acetyltransferase) → malonyltransfer
malonyl from malonyl-CoA is transferred to central ACP-SH

• CoA-SH formed

Question 14

What happens in the 3^rd step of FA synthesis?

Domain of FA synthesis?

Answer 14

KS (β-ketoacyl-ACP synthase)
→ condensation
acetyl transferred to malonyl on central ACP-SH
→ β-ketobutyryl-ACP + CO₂

_{​NOTE: after this step growing FA always on central -SH}

Question 15

What happens in the 4^th step of FA synthesis?

Domain of FA synthesis?

Answer 15

KR (β-ketoacyl-ACP reductase)
→ 1. reduction
β-ketobutyryl-ACP reduced to β-hydroxybutyryl-ACP

• NADPH/H⁺ used

Question 16

What happens in the 5^th step of FA synthesis?

Domain of FA synthesis?

Answer 16

DH (β-hydroxyl-ACP dehydratase)
→ dehydration
β-hydroxybutyryl-ACP dehydrated to trans-Δ²-butenoyl-ACP

• H₂0 produced

Question 17

What happens in the 6^th step of FA synthesis?

Domain of FA synthesis?

Answer 17

ER (enoyl-ACP reductase)
→ 2. reduction
reduction of trans-Δ²-butenoyl-ACP to butyryl-ACP

• NADPH/H⁺ used

Question 18

What happens in the 7^th step of FA synthesis?

Domain of FA synthesis?

Answer 18

KS (β-ketoacyl-ACP synthase)
→ translocation
butyryl-ACP translocated to peripheral KS-SH

→ next malonyl can be attached to central ACP-SH

Question 19

Why does the β-oxidation of unsaturated FAs differ from that of saturated FAs?

Answer 19

natural FA double bonds in cis conformation

⇒ FA oxidized until Δ³-cis or Δ⁴-cis enoyl-CoA formed,
then eventually converted to intermediate of β-oxidation (Δ²-trans)

Question 20

How is Δ³-cis enoyl-CoA converted back to an intermediate of β-oxidation?

Structures.

Answer 20

Δ³-cis → Δ²-trans enoyl-CoA isomerase
isomerized to Δ²-trans enoyl-CoA

⇒ then continues β-oxidation normally

Question 21

How is Δ⁴-cis enoyl-CoA (product of β-oxidation of unsaturated FA) converted back to an intermediate of β-oxidation?

Structures.

Answer 21

1. acyl-CoA dehydrogenase​
   converted to Δ²-trans Δ⁴-cis dienoyl-CoA (FADH₂ produced)
2. Δ²-trans Δ⁴-cis dienoyl-CoA reductase
   reduced to Δ³-cis enoyl-CoA, NADPH/H⁺ used

⇒ then isomerized to Δ²-trans enoyl-CoA, then continues normal β-oxidation (cf. own card)