Chapter 4- Carbohydrate Structure and Function

Question 1

monosaccharides

Answer 1

trioses- 3 carbons
tetroses- 4 carbons
pentoses- 5 carbons
hexoses- 6 carbons

Question 2

aldoses

Answer 2

carbohydrates that contain an aldehyde group as their most oxidized functional group

Question 3

ketoses

Answer 3

carbohydrates that contain a ketone group as their most oxidized functional group

Question 4

simplest aldose sugar

Answer 4

glyceraldehyde (aka. aldotriose)

Question 5

which carbon is typically the most oxidized

Answer 5

the carbonyl carbon (attached to the doublebonded O)

Question 6

glycosidic linkages

Answer 6

sugars acting as substituents (typically aldehyde carbon)

Question 7

dihydroxyacetone

Answer 7

simplest ketone sugar (ketose). carbonyl carbon is most oxidized (carbonyl carbon is usually C2)

Question 8

stereoisomers

Answer 8

optical isomers. compounds that have the same chemical formula (only differ from one another in terms of spatial arrangement)

Question 9

enantiomers

Answer 9

same molecular formula
nonsuperimposable
mirror images of each other.

any molecule that contains chiral carbons and no internal planes of symmetry.

Question 10

number of stereoisomers with common backbone

Answer 10

2^n (n = number of chiral carbons in the molecule)

Question 11

fisher projection

Answer 11

horizontal lines (wedges)-- out of page (right side pointing down)
vertical lines (dashed)-- into page

Question 12

diastereomers

Answer 12

same molecular formula
nonsuperimposable
not mirror images

Question 13

epimers

Answer 13

subtype of diastereomers that differ in configuration at exactly one chiral center (ex: D-ribose and D-arabinose)

Question 14

most common electrophile

Answer 14

carbonyl group (C doublebonded to O)

Question 15

pyranose and furanose rings

Answer 15

pyranose- 6C rings
furanose- 5C rings

rings are typically hemiacetals or hemiketals

Question 16

what happens when you expose a hemiacetal ring to water?

Answer 16

they will spontaneously cycle b/w open and closed form

Question 17

mutarotation

Answer 17

interconversion between anomers of a compound (ex: a and B conformations)

spontaneous change of configuration about C-1 and occurs more rapidly when the reaction is catalyzed with an acid or base.

Question 18

reactions that monosaccharides can undergo and why

Answer 18

b/c they contain alcohols and either aldehydes or ketones they can undergo….

1. oxidation/reduction
2. esterfication
3. nucleophilic attack (creating glycosides- sugar bound to another functional group)

Question 19

aldonic acid

Answer 19

the aldehyde group of a monosaccharide is oxidized to a carboxylic acid. this oxidized aldose (reducing agent) is called an aldonic acid.

Question 20

reducing sugars

Answer 20

any monosaccharide with a hemiacetal ring

Question 21

lactone

Answer 21

cyclic ester. when aldose being oxidized is in ring formation then the oxidation yields a lactone. (ex: vitamin C)

Question 22

how to detect the presence of reducing sugars?

Answer 22

Tollen’s reagent: uses Ag(NH3)2+ as oxidizing agent. so aldehydes reduce Ag+ to metallic silver
Benedict’s reagent: aldehyde group of an aldose is readily oxidized by Cu(OH)2, indicated by a red precipitate of Cu2O

*note: ketose sugars are also reducing sugars and give positive test results for these.

Question 23

Tautomerization

Answer 23

rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.

Question 24

enol

Answer 24

compound with a double bond and an alcohol group

Question 25

alditol

Answer 25

formed when the aldehyde group of an aldose is reduced to an alcohol

Question 26

deoxy sugar

Answer 26

contains a hydrogen that replaces a hydroxyl group on the sugar (most well known is the deoxyribose which is the carbohydrate found in DNA)

Question 27

esterfication

Answer 27

carbohydrates have hydroxyl groups which can react with carboxylic acids and their derivatives to form esters. (most important reaction in body is the phosphorylation of glucose to form a phosphate ester, this uses hexokinase or glucokinase as an enzyme)

Question 28

acetals/ ketals

Answer 28

formed when hemiacetals (hemiketals) react with alcohols under acidic conditions, resulting C-O bonds are called glycosidic bonds and the acetals (ketals) formed are glycosides –dehydration reaction

Question 29

furanosides and pyranosides

Answer 29

glycosides derived from furanose and pyranose rings, respectively – dehydration reaction

Question 30

esterfication vs. glycoside formation

Answer 30

esterfication- reaction by which a hydroxyl group reacts with either a carboxylic acid or a derivative to form an ester
glycoside formation- reaction b/w alcohol and hemiacetal (or hemiketal) group on a sugar to yield an alkoxy group.

Question 31

how are carbohydrates usually metabolized

Answer 31

oxidized, so they can reduce electron carriers for oxidative phosphorylation

Question 32

what is a complex carbohydrate

Answer 32

all carbohydrates with at least 2 sugar molecules linked together.

Question 33

3 important polysaccharides

Answer 33

All made of D-glucose monosaccharide

1. Cellulose (main structural component of plants, we cant digest it so it works as fiber for us- drawing water into the gut)
2. Starches (linked a-D-glucose monomers, digestible by humans)
3. Glycogen (carbohydrate storage unit in animals, highly branched-making it more soluble)

Question 34

amylose and amylopectin

Answer 34

amylose: plants store starch as this, broken down by B-amylase to yield maltose
amylopectin: starts the same as amylose, but also has a branch of a-1,6 glycosidic bonds.

a-amylase– cleaves randomly along the chain to yield shorter polysaccharide chains

Question 35

glycogen phosphorylase

Answer 35

functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it

Question 36

enantiomerization

Answer 36

aka racemization. the formation of a mirror-image or optically inverted form of a compound.

Question 37

anomerization

Answer 37

ring closure of a monosaccharide, creating an anomeric carbon