Biochemistry 410 Lecture 7 Vikas

8/10/2019 Biochemistry 410 Lecture 7 Vikas

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Biochemistry 410

Carbohydrates

Vikas Kumar

[email protected]

Bio-Bio Room 321

Office hours 2pm-4pmTue-wed & Fri

mailto:[email protected]

mailto:[email protected]



Overview

• Carbohydrates Nomenclature

• Monosaccharides

• Oligosaccharides

• Polysaccharides



Carbohydrate Nomenclature

Carbohydrates are hydrates of carbonwith the general formula (CH2O)n

Carbohydrates are classified in three groups:

• Monosaccharides (simple sugars) - cannot be broken

down into simpler sugars under mild conditions

• Oligosaccharides (oligo = "a few“) - usually 2 to 10

simple sugar residues

• Polysaccharides - polymers of the simple sugars



Monosaccharides

• Aldoses and ketoses containaldehyde and ketone functions,respectively

• Triose, tetrose, etc. denotesnumber of carbons



Important Aldoses



Important Ketoses

Sometimes named by

Inserting the letter

“ ul “

Tri-ul-ose

Tetr-ul-ose

Pent-ul-ose

Hex-ul-ose



Glucose (an aldose) can cyclize to form a cyclic hemiacetal

Preferred structure

In aqueous solution

Carbonyl carbon

Becomes asymmetricCarbon,

Anomeric

carbon



Fructose (a ketose) can cyclize to form a cyclic hemiketal

Preferred structure

In aqueous solution

Anomeric

carbon



Glycosidic Bonds

• Covalent bond joining carbohydrate

to other group.

• A substance containing glycosidic bond

is a glycoside.

• O, N-glycosidic bonds.

• Dissacharides are the simplest oligo--saccharides (Two monosaccharides

linked by a glycosidic bond).

• Each dissacharide has free anomeric

carbon, and is thus a reducing sugar.

• Sucrose is not a reducing sugar.



DissacharidesKnow the important features

• Be able to identify anomeric carbons and reducing and nonreducing

ends

• Note carefully the nomenclature of links. Be able to recognize

alpha(1,4), beta(1,4) linkages, etc., in structures.



Polyssacharides

Functions: storage, structure, recognition

• Nomenclature for polysaccharides is based on their

composition and structure

• Homopolysaccharide – a polysaccharide that

contains only one kind of monosaccharide• Heteropolysaccharide – a polysaccharide made of

several monosaccharides

• Starch and glycogen are storage molecules• Chitin and cellulose are structural molecules

• Cell surface polysaccharides are recognition

molecules



A plant storage polysaccharide

• Amylose and amylopectin

• Amylose has α(1,4) links, onereducing end

• α(1,6) branches every 12-30residues

Storage polyssacharides

The glucose storage device in animals

• Glycogen constitutes up to 10% ofliver mass and 1-2% of musclemass

• Only difference from amylopectin:even more highly branched

• α(1,6) branches every 8-12residues

Starch Glycogen



Structural polyssacharides

• most abundant natural polymer in

the world• Found in the cell walls of nearly all

plants

• Consists of β(1→4) linkages

• Cotton is almost pure cellulose

Cellulose

Cellulose Chitin

• Found in the exoskeletons of

crustaceans, insects and spiders, and

cell walls of fungi

• It is similar to cellulose, but C-2s are

N-acetylglucosamine

• Cellulose strands are parallel; chitins

can be parallel or antiparallel



Heteropolyssacharides

• Polysaccharides can function as information carriers

• In most cases they are covalently attached to either

protein or lipids called Glycoconjugates:

• Peptidoglycan

• Proteoglycans

• Membrane or secreted protein attached to a GAG

• Cell surface or extracellular matrix

• Glycoproteins• Variable oligosaccharides

• Found in cell and out

•Glycolipids

• Membrane lipids where hydrophilic head groups are oligosaccharides



Peptidoglycan



• May be N-linked or O-linked

• N-linked saccharidesare attached via theamide nitrogens ofasparagine residues

• O-linked saccharidesare attached tohydroxyl groups ofserine, threonine orhydroxylysine

Glycoproteins

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Biochemistry 410 Lecture 7 Vikas