Homework 9

Question 1

Initiation of glycogen biosynthesis begins with the isomerization of glucose-6-phosphate to glucose-1-phosphate by the enzyme _________.

phosphorylase

phosphoglucomutase

hydrolase

dehydrogenase

none of the above

Answer 1

phosphoglucomutase

Question 2

Glucose monomer can only be transferred to a growing glycogen polymer, if it is in the _________ form.

UTP-glucose

UDP-glucose

UMP-glucose

glucose-1-phosphate

glucose-6-phosphate

Answer 2

UDP-glucose

Question 3

The enzyme that cleaves the branches during glycogen breakdown is _________.

glycogen synthase

glycogen phosphorylase

glycogen debranching enzyme

glycogen cleavage enzyme

none of the above

Answer 3

glycogen debranching enzyme

Question 4

During glycogenolysis, glycogen phosphorylase releases glucose molecules by a _________ reaction whereas the glycogen debranching enzyme liberates the one glucose unit at the branch point by a _________ reaction.

phosphorylation, hydrolysis

hydrolysis, hydrolysis

phosphorylation, phosphorylation

hydrolysis, phosphorylation

Answer 4

phosphorylation, hydrolysis

Question 5

What enzymes perform each of the glycogenesis functions described below?

1. initiates glycogenesis by adding the first few glucose residues _____________
2. performs the majority of glucose incorporation during glycogenesis ______________
3. breaks off short chains of glycogen and reattaches them to form branches __________________

Answer 5

1. Glycogenin
2. Glycogen synthase
3. Branching enzyme

Question 6

Pentose phosphate pathway is the primary means by which _________.

reducing equivalents such as NADPH can be produced

reducing equivalents such as NADH and monosaccharides such as ribose can be produced

reducing equivalents such as NADPH and monosaccharides such as ribose can be produced

monosaccharides such as ribose can be produced

Answer 6

reducing equivalents such as NADPH and monosaccharides such as ribose can be produced

Question 7

The committed (rate-limiting) step in the pentose phosphate pathway involves _________.

a reduction reaction

an epimerization reaction

a dehydrogenation (oxidation) reaction

an isomerization reaction

Answer 7

a dehydrogenation (oxidation) reaction

Question 8

During the pentose phosphate pathway reaction, the following reactions involving various sugar rearrangements are possible EXCEPT _________.

C5 + C4 → C6 + C3

C7 + C3 → C6 + C4

C5 + C5 → C7 + C3

C5 + C5 → C6 + C4

Answer 8

C5 + C5 → C6 + C4

Question 9

The pentose phosphate pathway is divided into two phases, oxidative and nonoxidative. What are the respective functions of these two phases?

to generate energy for nucleotide biosynthesis; to provide monosaccharides for nucleotide biosynthesis

to generate reducing equivalents for the other pathways in the cell; to generate ribose from other monosaccharides

to generate ribose from other monosaccharides; to generate reducing equivalents for other pathways in the cell

to provide monosaccharides for nucleotide biosynthesis; to generate energy for nucleotide biosynthesis

to provide monosaccharides for amino acid biosynthesis; to generate reducing equivalents for other pathways in the cell

Answer 9

to generate reducing equivalents for the other pathways in the cell; to generate ribose from other monosaccharides

Question 10

In bacterial cell walls _________.

monosaccharides form crosslinks between peptides

peptides form crosslinks between polysaccharides

oligosaccharides form crosslinks between proteins

none of the above exists

Answer 10

peptides form crosslinks between polysaccharides