Download Key - UCSB CLAS

Chem 109C - CLAS – Ch 24 - Key
1. What role do cofactors play? Give 2 examples of cofactors. Cofactors are molecules or metal ions that work with
enzymes in biochemical reactions – examples include NAD+, FAD, TPP, biotin, PLP, lipoate, and CoASH
2. Niacin is required to make the coenzymes NAD+, NADP+, NADH and NADPH which are necessary for redox
reactions on functional groups that contain oxygen. The coenzymes NAD+and NADH are used in catabolic
pathways as opposed to the coenzymes NADP+ and NADPH are used in anabolic pathways.
3. Predict the products and provide the mechanisms for the following reactions:
a.
O
O
-
O
O
-
NAD+
O
O
-
O
O
OH
-
O
b.
O
O
O
-
+
NH3
O
NADPH
H+
HO
-
+
NH3
O
4. Vitamin B2 is required to make the coenzymes FAD, FADH2, FMN, and FMNH2 which are necessary for redox
reactions in mostly compounds without the element oxygen.
5. Predict the products and provide the mechanism for the first 3 reactions:
a.
O
O
-
FAD
-
O
O
SH
S S
SH
b.
O
O
O
FAD
-
O
NH2
-
NH
c.
O
O
-
O
-
O
d.
NADH + H+ + FAD
FAD
O
O
-
O
-
O
NAD+ + FADH2
active site for FAD and FMN
6. The coenzyme TPP is derived from the vitamin B1. TPP is required for decarboxylation and acyl transfer reactions
on the substrate pyruvate.
7. Predict the products and provide the mechanism for the following:
a.
O
-
TPP
O
O
H+
+
H
O
CO 2
b.
O
O
O
-
O
+
-
H+
O
O
OH
O + CO 2
TPP
O
O
8. How many enzymes and coenzymes are involved in the pyruvate dehydrogenase system?
O
-
O
O
+
pyruvate
dehydrogenase
CoASH
system
O
SCoA
+
CO 2
3 enzymes and 5 coenzymes – 1) TPP 2) lipoate (enzyme bound) 3) CoASH 4) FAD (enzyme bound) and 5) NAD+
9. The coenzyme biotin a.k.a. vitamin H is used for carboxylation reactions on alpha carbon substrates. Biotin is
accompanied by two other cofactors ATP and Mg2+. Biotin is bound to its enzyme via a(n) amide linkage to a
lysine residue. Bicarbonate is the source of carbon dioxide.
10. Predict the product and provide the mechanism:
O
-
O
O
+
HCO 3
-
biotin
ATP
Mg2+
O
-
O
O
O
-
+
ADP + HPO 4
2-
O
11. The coenzyme PLP a.k.a. vitamin B6 is used for the following 5 reactions: decarboxylation, racemization,
transamination, α,β bond cleavage and α,β elimination All of these reactions take place on amino acids. PLP is
bound to its enzyme via a(n) imine linkage to a lysine residue. All 5 reactions start with a transamination step in
the mechanism.
12. Provide the mechanism for the decarboxylation and transamination of alanine.
Decarboxylation overall reaction ⇒
decarboxylation mechanism ⇒
transamination overall reaction ⇒
transamination mechanism ⇒