Outline April 21 st and 23 rd , 2010 Carbohydrate basics Aldoses - - PDF document

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MBioS 303 Spring 2010

April 21st and 23rd, 2010 Biochemistry Recitation Outline

Carbohydrate basics Aldoses vs. ketoses L and D configurations and anomers Glycosidic bonds, disaccharides Polysaccharides Storage: amylose and amylopectin (glycogen, starch) Structural: cellulose, chitin NAD(P), FAD(H)

Carbohydrate Basics Types of Carbohydrates

Aldoses vs. Ketoses Aldose sugars have an aldehyde group at the C1 position

Biochemistry, 5th Ed.

4/25/2010 2 Types of Carbohydrates

Aldoses vs. Ketoses Ketose sugars have a ketone group at any other position

Biochemistry, 5th Ed.

Carbohydrate Stereochemistry

Sugars can be in L or D configuration Classified based on the chiral carbon farthest from

carbonyl group

L or D designation referenced to that in glyceraldehyde

If the hydroxyl group at the farthest chiral carbon is on the left

side in the Fischer projection, the sugar is in the L configuration

If the hydroxyl group at the farthest chiral carbon is on the right

side in the Fischer projection, the sugar is in the D configuration

Carbohydrate Stereochemistry

L-Glucose

HO CHO CH2OH

D-Glucose

OH CHO CH2OH

What is the carbon numbering system?

Carbohydrate Ring Formation

(1) What type of sugar is glucose – an aldose or a ketose? (2) When forming a ring structure, what hydroxyl group acts as the nucleophile, and what carbon does it attack? How do you know what side of the ring the substituents will be on?

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L and D Configurations, Ring Structures

L-Glucose

HO CHO CH2OH

D-Glucose

OH CHO CH2OH

O OH H H H O H OH H OH H CH2OH D-Glucose O OH OH CH2OH OH H H OH H H H L-Glucose

Anomeric Carbons

How do you distinguish the

• anomer from the β-anomer?

Glycosidic Bonds

O-glycosidic bond: formed when hydroxyl on one

sugar reacts with anomeric carbon on another sugar

O-glycosidic bond

Glycosidic Bonds: Disaccharides

What is unique about the structure of sucrose?

4/25/2010 4 Polysaccharides

Polymers of monosaccharides Linked by glycosidic bonds

Amylose: A Storage Polysaccharide

Amylose: Unbranched polymer of

glucose monosaccharides

α14 linkages One component of

starch in plants ?

Amylose: An Energy Storage Polysaccharide

Amylose: Unbranched polymer of

glucose monosaccharides

α14 linkages One component of

starch in plants

α14 linkages cause

bending resulting in

• verall helical structure

Amylopectin: An Energy Storage Polysaccharide

Amylopectin: Branched polymer of glucose monosaccharides

Branching approximately every 24-30 residues

α14 linkages within one strand, α16 branch points Second component of starch in plants

Why might branching be useful?

? ?

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Glycogen: An Energy Storage Polysaccharide

Similar to amylopectin Branched polymer of glucose

monosaccharides

Branching approximately every 8-

12 residues α14 linkages within one

strand, α16 branch points

Energy storage in animals

(mainly in liver cells)

http://en.wikipedia.org/wiki/Image:Glycogen.png

? ?

Amylopection versus Glycogen

The Cell: A Molecular Approach, 2nd Ed.

Cellulose: A Structural Polysaccharide

Unbranched polymer of glucose monosaccharides Found in plant cell walls β14 linkages

Neighboring monosaccharides flipped 180⁰ relative to each

• ther

Water insoluble – why?? What effect do the β14 glycosidic bonds have on the structure of cellulose?

?

Cellulose: A Structural Polysaccharide

Forms sheets Stabilized by (1) hydrogen bonds, and (2) van der Waals

interactions

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Cellulose: A Structural Polysaccharide

Most organisms

cannot digest cellulose

No enzyme to break

the β14 glycosidic bonds

This is what our

“dietary fiber” is made up of

http://en.wikipedia.org/wiki/Image:CH_cow_2.jpg

Storage vs. Structural Polysaccharides

The Cell: A Molecular Approach, 2nd Ed.

Chitin: A Structural Polysaccharide

Unbranched polymer of N-acetyl-D-glucosamine

monomers

Found in many insect and arthropod exoskeletons,

fungi cell walls, etc.

β14 linkages Confer properties similar to those of cellulose

?

Nucleotides

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ADENINE RIBOSE PHOSPHATES N-glycosidic bond

Electron Carriers NAD(P)+, FAD

NAD(P)+ and FAD are electron carriers

Can donate or accept electrons, depending on their oxidation

state

This means they undergo redox reactions!

Electron donors can give electrons away, electron

acceptors can accept additional electrons

Notation is important!!

NAD(P)+ and FAD: they are in the oxidized state (can accept

electrons)

NAD(P)H and FADH2 are indicating that they are in the

reduced state (can donate electrons)

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NIACIN

Deficiency leads to Pellagra

FAD, FADH2

RIBOFLAVIN

NAD+ compared to FAD QUIZ TIME!