Today’s topics:

Carbohydrate chemistry polyhydroxy aldehyde/ketones chirality and optical isomers – diatereomers & enantiomers hemiacetals and anomers – the cyclic forms of sugars acetals and glycosidic bonds – disaccharides to polysaccharides

Allosteric enzymes …….a) Have two distinct folded conformationsb) Have quaternary structurec) Have a sigmoidal v vs. [S] plotd) all of the above

Allosteric enzymes …….a) Can only be turned on one timeb) Can be regulated only to decrease activityc) Require an ‘activating’ enzyme.d) Can have incremental alterations in activity.

CH = O |CH — OH | CH2 — OH

C3H6O3 or…C3(H2O)3

Opposite amino acids, nature typically makes only D carbohydrates.

A carbohydrate is a polyhydroxy aldehyde or ketone and their derivatives (e.g. hemiacetals)Although initially named for having the general formula Cn(H2O)n, this is no longer required for something to be classified a carbohydrate.

Name some carbohydrates.

Carbohydrates you might be familiar with include: sugars (monosaccharides) like glucose, and fructose.

Disaccharides like sucrose, maltose, and lactose ….

Polysaccharides like starch, glycogen, and cellulose.

Monosaccharides3-carbon or triose

4-carbon or tetrose

5-carbon pentose

6-carbon hexose

# optical isomers = 2n

C=O | H - C - OH |HO - C - H | H - C - OH | H - C - OH | CH2 - OH

H

Glucose

C=O | H - C - OH |HO - C - H |HO - C - H | H - C - OH | CH2 - OH

H

Galactose

C6H12O6

Fructose

CH2 - OH | C = O |HO - C - H | H - C - OH | H - C - OH | CH2 - OH

Does glucose exhibit optical isomerism? a) yes b) no How many chiral carbons? a) 1 b) 2 c) 4 d) 6

DiastereomersOptical isomers that are not mirror images of each other.

C=O | H - C - OH |HO - C - H | H - C - OH | H - C - OH | CH2 - OH

H

D- Glucose

EnantiomersOptical isomers that are

mirror images of each other. C=O |HO - C - H | H - C - OH |HO - C - H |HO - C - H | CH2 - OH

H

L- Glucose

All natural sugars are D isomers

Hemiacetals and Hemiketals

C=O | H - C - OH |HO - C - H | H - C - OH | H - C - OH | CH2 - OH

H

D- Glucose b – D - Glucose

a – D - Glucose

Anomers

OOH

OHOH

OH

OH

b – D - Galactose

OOH

OHOH

OHOH

a – D - Glucose

OOH

OHOH

OH

OH

b – D - Glucose

OOH

OH

OHOH

OH

L - Glucose

Anomers – diasteromers that interchange in solution

Enantiomers the optical isomer that is the mirror image

Diastereomers optical isomers that aren’t mirror images

OOH

OHOH

OHOH

a – D - Glucose

OOH

OHOH

OHOH

OOH

OHOH

OH

O

OOH

OH

OHOH

maltose – a – 1,4 glycosidic bond

Lactose (milk sugar)Galactose + Glucose b -1,4

OHOH

O

OH

OHO

OH

HOOH

OHO

Sucrose (Table Sugar)

OH

HO

OH

OOH

O

OH

O

1

2a - 1, b - 2

HO

OH

OH

Common PolysaccharidesChitin

N-acetylglucosamine b-1,6 insect exoskeleton & fungal cell walls

GlycogenGlucose - a-1,4 & a-1,6 Animal glucose storage

Cellulose Glucose - b-1,6 Plant cell walls

StarchAmylose: glucose a-1,4

Amylopectin: glucose a-1,4 & a-1,6

Plant glucose storage

Polysaccharides

Chitin ― insect exoskeleton & fungal cell walls

Glycogen : Animal glucose storage

Cellulose : Plant cell walls

Starch : Plant glucose storage

Starch & glycogen store glucose in plants & animals. They contain mostly a-1,4 glycosidic bonds.

OH HO

OH

OHO

O

OH

OH

OHO

O

OH

OH

OHO

Oetc.

O

OHOH

OH

OHO

O

OH

OH

OHO

O

OH

OH O

Glycogen (& amylopectin of starch)

etc.

O

OHOH

OH

OHO

O

OH

OH

OHO

a-1,6a-1,4

Glycogen (& amylopectin of starch)

a-1,6

a-1,4

etc.Cellulose ― b-1,4 Linkage

OH

OH

OHO O

OH

OH

OHO O

OH

OH

OHO O

GLYCOGEN

Carbohydrate – protein/peptide combinationscarbohydrate groups can be attached to peptides, polypeptide chains or proteins to form …..

Peptido glycans – bacterial cell walls – penicillin antibiotics inhibit construction

Proteoglycans – Protein + glycosaminoglycans - lubricants in connective tissue cartilage = proteoglycan + collagen

Glycoproteins – Proteins with oligosaccharides attached to hydroxyl groups erythropoietin (EPO) – hormone that stimulates RBC production Blood group determinants Even Hemoglobin can be glycosylated – evidence of prolonged hyperglycemia Glycosylation of eye crystallins induce cataracts – connection with diabetes

O – CH2 HOOH

OHOH

OH

Glycoproteins

O H || N - C – CH2 -HO

OH

OHHO

NHC=OCH3

O-linked

N-linked

Ser

Asn

Man Man

Man

GlcNAc

GlcNAc

Asn

N-linked core

Blood Types & Glycosyl Transferases (EC 2.4)

Fuc

Gal

GlcNAc

Gal

Ser

GalNAcFuc

Gal

GlcNAc

Gal

Ser

Fuc

Gal

GlcNAc

Gal

Ser

Gal

O A B

Early stop codon mutation in glycosyltransferase gene results in nonfunctional enzyme

A vs. B glycosyltranferase enzymes differ in sequence in only 4/354 residues.

H-antigenRBC glycoprotein

gene probability Mother Father Type probabilityO 0.68 O O O 0.46A 0.26 A O    B 0.06 O A A 0.42(-) 0.18 A A        B O        O B B 0.09    B B        A B AB 0.03    B A  

What is your blood Type? a) A b) B c) O d) ABe) don’t know

What is your RH factor? a) + b) - c) don’t know

“There are no known natural effects of these differing blood types. People with A, B, AB and O phenotypes do not differ in fitness in any major way that we have been able to detect. This suggests that the complete absence of the enzyme (null mutation) is neutral in the current human population and so is the switch from one form of the enzyme to another. (Suggestions that blood type determines susceptibility to some infections are common in the scientific literature. Most of them have not held up. The best correlation is a possible association between blood type O and susceptibility to cholera. This looks pretty good but the cause-and-effect relationship is still up in the air.) “

Laurence Moran – Professor of Biochemistry – University of Toronto

Flu virus’ gain entry into their host cell by bindingTo (sialic acid) glycoproteinsUsing the hemagglutinin (H).

New viral particles exit by Hydrolyzing the sialic acid offThe host glycoprotein using theirNeuraminidase (N)Tamiflu is a competitive inhibitor of this process.

The H1N1 designation of the flu indicates the type of these two proteins.

Did you get a flu shot?a) Yes b) no