Bellizzi biochem lecture 15 monosaccharides

monosaccharides are

polyhydroxy aldehydes and ketones with many chiral centers

cyclic form of pentose

furanose

cyclic form of hexose

pyranose

empirical formula of carbohydrates

C(H2O)

monosaccharides are a linear chain with

3 or more carbon atoms

each carbon in monosaccharide chain has one______ attached

oxygen

each monosaccharide has exactly one

C=O bond at C1 or C2

monosaccharides can be linked together by glycosidic linkages to form

disaccharides, oligosaccharides, polysaccharides

biologic roles of carbohydrates

metabolic energy storage and transfer, molecular fingerprint/ bar code, mechanical/ structural components

glucose

primary fuel for all cells

disaccharides and polysaccharides can be used for

long term energy storage

oligosaccharides attached to proteins and lipids(glycoproteins/glycolipids)..

have signaling properties

glycolproteins/glycolipids can specifically function in

sub cellular localization of proteins, cell surface recognition, antigens, blood types

examples of carbohydrates that aid in stability

cellulose, chitin, glycosaminoglycans

most abundant molecule in biosphere

glucose

glucose can be stored as

disaccharides and polysaccharides

oxidizing C in glucose to CO2 releases

> 2000kj/mol

in humans, blood glucose comes from

breakdown of disaccharides/ polysaccharides or synthesis of glucose from metabolic intermediates and amino acids derived from cellular and muscle protein

excess glucose can be used to synthesize fat but

fat cannot be converted to glucose

glycolysis

10 enzyme pathway used by all living cells

in glycolysis glucose is converted into

2pyruvate

in glycolysis net synthesis of ATP is

2

how many electrons are transferred to NADH in glycolysis

4

glycans

glucose polysaccharides

starch and glycogen function in

energy storage

glucose can be converted into ribose for

DNA/ RNA synthesis

in glucose production in all cells, C3 intermediates can be used to synthesize

glucose and other hexoses as well as amino acids and lipids

in animal cells glucose production, C3 intermediates can only be obtained from

degradation of glucose or certain amino acids and other metabolic intermediates (aka things must be broken down to create glucose)

plant cells dont need

to break things down to form glucose

plant cells capture solar photons and generate

ATP and NADPH(photophosphroylation)

plant cells convert CO2 and H2O to C3 intermediates using

the ATP and NADPH produced by photophosphorylation

carbon assimilation reactions in plants do not

require light (dark reactions)

the simplest carbohydrates are

trioses

glyceraldehyde

has a chiral center

dihydroxyacetone

no chiral centers

absolute configuration based on priority

R/S

configuration based on similarity to D or L glyceraldehyde

D/L

all monosaccharides in which the chiral center farthest away form the carbonyl has the same configuration of

D-glyceraldehyde are D-monosaccharides

consitiutional isomers

different bonds in different places

stereoisomers

same bonding groups but oriented in different directions

enantiomers

mirror image, all chiral centers inverted

diastereomers

not all chiral centers are inverted

epimers

diastereomers that have exactly one chiral center inverted

configuration of almost all naturally occurring monosaccharides

D

exceptions to most naturally occurring monosaccharides being D

L-arabinose, L-rhamnose, L-fucose

acetal

hemiacetal

is alcohol (nucleophile) and carbonyl (electrophile) are part of the same molecule

intramolecular hemiacetal formation leading to cyclic monosaccharide occurs

pentoses and hexoses are predominantly found in

cyclic forms

when a monosaccharide cyclized, the carbonyl carbon becomes

a hemiacetal

the hemiacetal carbon in cyclic monosaccharide is known as

anomeric carbon

anomeric carbon in aldoses

C1

anomeric carbon in ketoses

C2

configuration of anomeric carbon change

sp2 (planar) to sp3 (tetrahedral)

D-glucopyranose has ___ anomie's

2

beta D-glucopyranose has C1 OH on

same side of ring as C6

alpha D-glucopyranose has C1 OH on

opposite side of ring as C6

5 and 6 membered rings are the

most stable

aldohexoses can form

both 5 and 6 membered rings

6 membered ring results from

attack of C5 hydroxyl on C1 carbonyl

5 membered ring results from

attack of C4 hydroxyl on C1 carbonyl

most stable/dominant cyclic form of aldohexoses

6 carbon ring

ketohexoses can only form

5 membered rings

5 membered ring from ketohexose results from

attack of C5 hydroxyl on C2 carbonyl

aldopentoses can also form

5 membered rings from C4 attack on C1

Mutarotation

spontaneous interconversion of anomie's in aqueous solution (rapid ring opening and cyclization

at equilibrium D- glucopyranose is about

67% beta and 33% alpha with only traces of linear and furanose forms

beta D-glucopyranose predominates because

chair conformation more stable,

aldoses can be oxidized to

carboxycylic acids

fehling's reagent

Copper (II) sulphate and 2,3-dihydroxybutandioate ions in strong alkali combined and a complex is formed (Fehling's reagent)

oxidation of aldose at C1 converts it to

corresponding aldonic acid

glucose and other aldoses are called

reducing sugars

reducing sugars have a

free aldehyde that can undergo oxidation