Chapter 8 - Carbohydrates

Question 1

Functions

Answer 1

Energy storage: central metabolite in most organisms

Structural materials: repetitive structure and hydrogen bonding

Nucleic acid components: provides a scaffold for other groups

Protein & Lipid Glycolysation: huge variation and 3D structure

Question 2

Basic chemical composition

General formula for simple sugars

Elements

Answer 2

polyhydroxy aldehydes and ketones

(CH2O)n

C, H, O, (some N, S, and P)

Question 3

Sugar classification

Answer 3

By carbonyl group (aldehyde or ketose)

By size: monomers -> disaccharides -> oligiosaccharides (2-20) -> polysaccharides

By configuration of specific chiral carbon: D vs. L monosaccharides

Question 4

Mos common monosaccharide features

Answer 4

very water soluble

linear, unbranched, carbon backbone connected by single bods

only carbonyl and terminal carbons are not chiral, many stereoisomers

Question 5

D vs. L classification

Answer 5

based on the configuration of the chiral carbon farthest from the most oxidized carbon (C=O)

Question 6

only achiral carbon

Answer 6

Dihydroxyacetone

Question 7

Diasteromers

Answer 7

differ in 1 or more chiral centers

Question 8

Epimers

Answer 8

differ at only 1 carbon

D-Glucose and D-Galactose

Question 9

Alcohols and carbonyls react

Answer 9

form hemiacetal/ketal linkages

freely reversible at pH 7

Question 10

Pentoses and hexoses

Answer 10

form rings by internal hemiacetal/ketal formation

Question 11

Cyclization Reaction

Answer 11

C=O electrophile reacts with nucleophilic -OH

(furanose (5-membered ring) & Pyranose (6 embered ring)

Question 12

Anomeric Carbon

Answer 12

used to be aldehyde

the most oxideized

new chiral carbon at C1

Question 13

Alpha and Beta anomers

Answer 13

Can interact

*can attack from top or bottom = two configurations (beta and alpha)

Question 14

Cyclic Monosaccharides Mutarotate

Answer 14

spontaneous, reversible ring opening/closing in solution

interconversion results in 2 configurations at C1 -> alpha and beta anomers

Question 15

Glucose composition in solution

Answer 15

based on stability

64% beta, 36% alpha pyranose

small amount of furanose and open forms

Question 16

Monosaccharides: many conformations (conformers)

Answer 16

most atom centers are tetrahedral; single bonds allow rotation

cyclic structures sample many conformations - most common are chair and boat

Chair is the most stable form becaus it has the lowest steric hindrance in ring -> all bulky groups in equatorial position

(twisiting common to relieve steric strain between substituents)

Question 17

Challenges of Representing Carbohydrates with Multiple Forms

Answer 17

Besides the fact that they’re a pain in the ass to draw, Fisher: 2D representation

Haworth: better represents chiral center

*number from C1 on left to right

Question 18

Conformers possible for other sugars

Answer 18

affects larger macromolecular structures

Sugar puckers in B vs A DNA

Question 19

Monosaccharide Derivatives and types of modifications

Answer 19

oxidation; reduction; deoxy sugars; group modification (amino, phosphate, n-acetyl)

Question 20

Sugar Alcohols

Answer 20

Reduce aldehyde group

both found in lipids

Question 21

Oxidation of Aldehyde

Answer 21

sugar acids - ring formation only if C1 aldehyde intact; component of many polysaccharides

*still forms pyranose ring?

Question 22

Vitamin C

Answer 22

Derived fro glucuronate (sugar acid)

acts as a reduction agent and antioxidant

Primates and guinea pigs lost the enzyme for a step in the conversion to ascorbic acid (no problem, abudant in diet)