Carbohydrates

Question 1

Aldoses & Ketoses

Answer 1

sugars with aldehydes and ketones as their most oxidized group, respectively

Question 2

what is nomenclature of all sugars based on?

Answer 2

D- and L- forms of glyceraldehyde

Question 3

D- and L- sugars

Answer 3

D-sugars have highest-numbered numbered chiral carbon with -OH group on the right (in Fischer projection)

L-sugars have highest-numbered chiral carbon with -OH group on the left

Question 4

D- and L-forms of the same sugar are:

Answer 4

enantiomers

Question 5

Diastereomers

Answer 5

nonsuperimposable configurations of molecules with similar connectivity that differ at at least 1 (but not all) chiral carbons

Question 6

Epimers

Answer 6

diastereomers that differ at exactly one chiral carbon

Question 7

Anomers

Answer 7

subtype of epimers that differ at one chiral carbon

Question 8

anomeric carbon

Answer 8

the new chiral center formed in a sugar which has undergone a ring sugar to become a cyclic sugar; it was the carbon containing the carbonyl in the straight chain form

Question 9

alpha-anomers

Answer 9

-OH on the anomeric carbon is trans to the free -CH2OH group

Question 10

beta-anomers

Answer 10

-OH on the anomeric carbon is cis to the free -CH2OH group

Question 11

what are the three main reactions that monosaccharides can undergo?

Answer 11

• redox
• esterification
• glycoside formation

Question 12

aldoses can be oxidized to (a)___ and reduced to (b) ___

Answer 12

(a) aldonic acids

(b) alditols

Question 13

reducing sugar

Answer 13

any sugar containing a free aldehyde or ketone group that is capable of acting as a reducing agent (thus all monosaccharides are reducing sugars)

Question 14

two standard reagents used to test reducing sugars

Answer 14

oxidizing agents: Tollen’s reagent & Benedict’s reagent

Question 15

Tollen’s reagent positive test

Answer 15

Ag(NH3)2+ used as oxidizing agent

aldehydes reduce Ag+ to metallic silver in positive test

Question 16

Benedict’s reagent positive test

Answer 16

aldose that is oxidized yields a red precipitate of Cu2O

Question 17

Enol

Answer 17

a compound with a double bond and alcohol group

Question 18

alditol

Answer 18

an aldehyde group of an aldose that has been reduced to an alcohol

Question 19

deoxy sugar

Answer 19

sugar in which a hydroxyl group is replaced with a hydrogen

Question 20

esterification reaction

Answer 20

reaction between sugar and -CO2H to form an ester

Question 21

mutarotation

Answer 21

interconversion between alpha and beta anomer with the straight chain form as an intermediate
sugar must be a reducing sugar to undergo mutarotation

Question 22

glycosidic bond

Answer 22

covalent bond that links a sugar or cabohydrate to another molecule via the anomeric carbon

Question 23

glucose-alpha-1,2-fructose

Answer 23

sucrose

Question 24

galactose-beta-1,4-glucose

Answer 24

lactose

Question 25

glucose-alpha-1,4-glucose

Answer 25

maltose

Question 26

cellulose

Answer 26

main structural component for plant cell walls
main source of fiber in the human diet

beta-D-glucose molecules linked via beta-1,4-glycosidic bonds

Question 27

starch

Answer 27

main energy storage form in plants

• amylose: alpha-1,4 glycosidic bonds
• amylopectin: alpha-1,4 bond and alpha-1,6 branches every ~25 glucose residues

Question 28

beta-amylase

Answer 28

cleaves amylose at the nonreducing end of the polymer (end with the acetal) to yield maltose

Question 29

alpha-amylase

Answer 29

cleaves randomly along amylose chain to yield shorter polysaccharide chains, maltose, and glucose

Question 30

debranching enzyme

Answer 30

used to cleave amylopectin due to its highly branched nature

Question 31

glycogen

Answer 31

main energy storage for animals

• alpha-1,4 chain
• alpha-1,6 branches every ~10 glucose residues

Question 32

glycogen phosphorylase

Answer 32

cleaves glucose at the nonreducing end of a glycogen branch and phosphorylates it to produce glucose-1-phosphate which plays an important role in metabolism

Question 33

which form of starch is more soluble in solution and why?

Answer 33

amylopectin is more soluble in solution than amylose because of its branched structure which decreases intermolecular bonding between polysaccharide polymers and increases interaction with the surrounding solution

Question 34

what characteristic of glycogen optimizes its energy efficiency in the body and how?

Answer 34

the highly branched structure increases glycogen’s energy efficiency because it makes glycogen more soluble in solution, thereby allowing more glucose to be stored in the body. Additionally its branching pattern allows enzymes to cleave glucose from glycogen