Exam 2 Study Guide - Carbohydrates

Question 1

Basic structure of a monosaccharide.

Answer 1

• aldehydes or ketones with at least two hydroxyl groups (CH2On)
• unbranched carbon chains with single bonds linking all carbon atoms…one carbon atoms is double-bonded to an oxygen atom to form a carbonyl group, all other carbon atoms are bonded to hydroxyl groups (OH).

Question 2

Understand the difference between aldose and ketose sugars.

Answer 2

• aldose: carbonyl group is at an end of the carbon chain
• ketose: carbonyl group is at any other position

Question 3

Epimers.

Answer 3

two sugars that differ by only one chiral carbon

Question 4

Stereoisomers – Understand the difference between the α and β.

Answer 4

α Stereoisomer: OH on the carbonyl carbon is opposite CH2OH
β Stereoisomer: OH on the carbonyl carbon is on the same side as CH2OH

Question 5

Disaccharides: Define, know the basic examples.

Answer 5

2 monosaccharides covalently bonded (Ex. Lactose, sucrose, trehalose)

Question 6

O-glycosidic bond.

Answer 6

covalent linkage joining two monosaccharides (formed when a hydroxyl group of one sugar molecule reacts with the anomeric carbon of the other)…readily hydrolyzed by acid

Question 7

Distinguish reducing vs nonreducing sugars.

Answer 7

• Reducing: have an anomeric carbon available for additional bonds
• Non-reducing: anomeric carbon is occupied (Ex. Sucrose and trehalose)

Question 8

Homopolysaccharide vs heteropolysaccharide.

Answer 8

• Homopolysaccharide: single monomeric sugar species
• Heteropolysaccharides: two or more types of monomers

Question 9

Starch: Where is it found?

Answer 9

Plant storage of glucose (stored in granules in the cell)

Question 10

Starch: Composition and structure

Answer 10

Composed of 2 polymers [amylose…(a1-4 bond) and amylopectin (a1-4 bond unbranched regions; a1-6 bond branched regions)]…chains of D-glucose

Question 11

Glycogen: Where is it found?

Answer 11

Animal storage of glucose (abundant in liver and skeletal muscle)

Question 12

Glycogen: Composition and structure

Answer 12

• Similar to starch (a1-4 bond unbranched regions; a1-6 bond branched regions)…more compact than starch (branches every 8-12 monomers)

Question 13

Both starch and glycogen form a (Blank).

Answer 13

coiled helix

Question 14

Cellulose: Where is it found?

Answer 14

Cell wall of plants

Question 15

Cellulose: Composition and structure

Answer 15

• Linear polysaccharide of D-glucose; beta conformation (B1-4 glycosidic bond)
• OH groups form hydrogen bonds with a chain or between neighboring chains

Question 16

Why can’t many organisms digest cellulose?

Answer 16

Humans cannot digest cellulose because we don’t have digestive enzymes (no cellulase or bacteria in our gut) that are able to break apart (hydrolyze) the B1-4 glycosidic bonds that hold the monosaccharides in cellulose together. Since we are not able to break cellulose down, it can act as fiber which helps moves food through our digestive tract.

Question 17

Chitin: Where is it found?

Answer 17

Exoskeleton of arthropods

Question 18

Chitin: Composition and structure

Answer 18

Linear chain of N-acetylglucosamine (B1-4 linkage)…more hydrophobic than cellulose

Question 19

Peptidoglycans: Where is it found?

Answer 19

Bacterial cell wall

Question 20

Peptidoglycans: Structure

Answer 20

Heteropolymer of alternating (B1-4) linked N-acetylglucosamine and N-acetylmuramic acid residues…cross-linked by short peptides

Question 21

Describe in general the composition of the extracellular matrix

Answer 21

Complex of carbohydrate and proteins outside of animal cells that connect cells together and provide a substrate for the cells to grow (network of heteropolysaccharides and fibrous proteins)

Question 22

Dihydroxyacetone is a ketotriose. Explain what this means.

Answer 22

Dihydroxyacetone is a ketotriose because the carbonyl group is at any other position, besides the end of the carbon chain and it is composed of three carbons.

Question 23

What molecule is released when 2 monosaccharides are bonded together to form a disaccharide?

Answer 23

H2O