Chapter 11: Carbohydrates

Question 1

Epimer

Answer 1

Epimers are diastereomers that differ in configuration of only one stereogenic center

Question 2

Anomer

Answer 2

Anomers have a different cyclic configuration only about the anomeric carbon atom and are thus diastomers

The anomeric carbon is the chiral carbon furthest from the most oxidized carbon; the last carbon in a Fischer projection

Question 3

Forming cyclic sugars

Answer 3

Groups on the left of the Fischer projection face up on the Haworth projection

Groups on the right face down

The β-anomer is when the CH₂OH and OH are both oriented up on the Haworth projection

The α-anomer is when the CH₂OH is up but the OH is DOWN

Question 4

Reducing sugars

Answer 4

Can reduce copper ions (Fehling’s solution/Benedict’s reagent) while becoming oxidized

Must contain a hydroxyl group on the anomeric carbon

Question 5

Lactose

Answer 5

Disaccharide sugar composed of a galactose and glucose subunit

Joined by a β-1,4-glycosidic linkage

Is a reducing sugar

Question 6

Sucrose

Answer 6

Disaccharide sugar composed of a glucose and fructose subunit

Joined by an α-1,β-2-glycosidic linkage

Is a non-reducing sugar

Question 7

Maltose

Answer 7

Disaccharide formed from two units of glucose molecules

Joined by an α-1,4-glycosidic bond

Is a reducing sugar

Question 8

Glycosidic bonds

Answer 8

Can be an O-glycosidic bond or an N-glycosidic bond

Can be an α-glycosidic bond or a β-glycosidic bond

• α-glycosidic- oxygen attached to the anomeric carbon is oriented DOWN
• β-glycosidic- oxygen attached to the anomeric carbon is oriented UP

Question 9

Glycoprotein linkages

Answer 9

Carbohydrates in glycoproteins attach to amino acid side chains through either an N‑linkage or an O‑linkage

• N‑linkage- carbohydrates attach to the nitrogen atom of the terminal carboxamide group on asparagine’s side chain
• O‑linkage- carbohydrates attach to the oxygen atom of the terminal hydroxyl group on the side chain of either serine or threonine

Question 10

Answer 10

Glucose

Question 11

Answer 11

Galactose

Question 12

Answer 12

Ribose

Question 13

Answer 13

Mannose

Question 14

Answer 14

Fructose

Question 15

GLUT 2

Answer 15

GLUT 2 (glucose transporter) is a transmembrane carrier protein that facilitates glucose movement across cell membranes down its concentration gradient

Is the principal transporter for transfer of glucose between liver and blood

Unlike GLUT4, it DOES NOT rely on insulin for facilitated diffusion

Question 16

GLUT 4

Answer 16

GLUT 4 (glucose transporter) is an insulin-regulated intermembrane glucose transporter that facilitates the diffusion of circulating glucose down its concentration gradient and into cells

Is the primary glucose transporter found in adipose tissues and striated muscle (skeletal and cardiac)