Practice Questions - Week 6 - Carbohydrates

Question 1

Haworth projection formulas

a) are representations of the cyclic form of sugars

b) can show the distinction between the alpha and beta anomers

c) both of the above

d) neither of the above

Answer 1

c)

Question 2

Which of the following monosaccharides is a ketose?

a) glucose

b) fructose

c) galactose

d) mannose

Answer 2

b)

Question 3

T/F: A hemiacetal is a cyclic structure of a ketose

Answer 3

False

(A hemiacetal is a cyclised aldose structure; a hemiketal is a cyclised ketose)

Question 4

It the open-chain form of a sugar, which carbon becomes the anomeric carbon in the cyclic form?

a) the carbonyl carbon

b) the highest numbered chiral centre

c) the highest numbered carbon

d) it depends on the individual sugar

Answer 4

a) the carbonyl carbon

Question 5

T/F: A furanose is a sugar that contains a five-membered ring as part of its cyclic structure.

Answer 5

True

Question 6

The alpha and beta forms of the same sugar are called

a) epimers

b) diastereoisomers

c) enatiomers

d) anomers

Answer 6

d)

Question 7

Glycosidic linkages between monosaccharide units may vary based on

a) the anomeric form of the cyclic structure, that is the alpha or beta

b) which -OH group is involved

c) both of the above

d) none of the above

Answer 7

c)

Question 8

T/F: Linear polymers are more water-soluble than branched ones

Answer 8

False

(Cellulose is a linear polymer and is less water soluble than branched starch)

Question 9

T/F: Branched polymers have one non-reducing end, and many reducing ends

Answer 9

False

(Branched polymers have several non-reducing ends, one in each branch)

Question 10

Which of the following molecules have the highest degree of alpha[1-6] branching linkages

a) Amylose

b) Amylopectin

c) Starch

d) Glycogen

Answer 10

d)

Question 11

Glycoproteins:

a) are involved in the metabolism of sugars

b) are proteins covalently bound to sugars

c) occur in the bloodstream of diabetics

d) are mainly found in the cytosolic leaflet of the cell membrane

Answer 11

b)

Question 12

When two carbohydrates are epimers:

a) one is a pyranose, the other a furanose.

b) one is an aldose, the other a ketose.

c) they differ in the number of carbons.

d) they differ only in the configuration around one carbon atom.

Answer 12

d)

(Epimers differ only in the configuration around one carbon atom. Please note: the term anomer also refers to monosaccharides that are epimers)

Question 13

Which of the following statements about starch and glycogen is false?

a) Amylose is unbranched; amylopectin and glycogen contain many (α1→ 6) branches.

b) Both are homopolymers of glucose.

c) Both starch and glycogen are stored intracellularly as insoluble granules.

d) Both serve primarily as structural elements in cell walls.

e) Glycogen is more extensively branched than starch.

Answer 13

d)

(Starch and glycogen serve as energy storage. Cellulose is the primary structural carbohydrate in plant cell walls, chitin and glucans in fungi, and peptidoglycans in prokayotes)

Question 14

The preferred energy source of the brain is ________. Why?

fructose

glucose

mannose

glycogen

Answer 14

glucose

(Glucose is virtually the sole fuel for the human brain, except during prolonged starvation. The brain lacks fuel stores and hence requires a continuous supply of glucose. It consumes about 120 g daily, which corresponds to an energy input of about approx. 1760 kJ, accounting for some 60% of the utilization of glucose by the whole body in the resting state)

Question 15

The most abundant organic substance on earth is __________. Why?

cellulose

starch

chitin

sucrose

Answer 15

Cellulose

(Cellulose is the most abundant organic polymer on Earth. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms)

Question 16

Which of following monosaccharide sugars is an anomeric pair? Why?

a) D-glucose and D-fructose

b) D-glucose and L-fructose

c) α-D-glucose and β-D-glucose

d) α-D-glucose and β-L-glucose

Answer 16

c)

(An anomer is an epimer at the hemiacetal/hemiketal carbon (this atom is called the anomeric carbon) in a cyclic saccharide. Two anomers are designated alpha (α) or beta (β). Regardless of the configuration of the starting D-glucose, a solution will gradually move towards being a mixture of approximately 64% β-D-glucopyranoside and 36% of α-D-glucopyranose)

Question 17

Carbohydrates play a wide variety of roles in biology. For each of the following biological functions / roles, select the most appropriate carbohydrate.

Match the following:

Left side:

a. cell-cell communication
b. exoskeleton structure in insects
c. energy storage in animal liver
d. fast energy
e. energy storage in plants
f. cell wall structure in plants

Right side:

1. starch
2. glycogen
3. cellulose
4. chitin
5. proteoglycan
6. glucose

Answer 17