heart attack

Topics: Carbohydrate, Glucose, Polysaccharide Pages: 17 (1299 words) Published: November 2, 2014
Carbohydrates & Glycobiology

Dr. Jeelan Moghraby
B.Sc., D.Phil
Assistant Professor
Email: moghrabyj@ksau-hs.edu.sa
Lecture 13 & 14

BIOC211

2013

Objectives


Describe the structure of carbohydrates
 Classify the types of carbohydrates
 Recognise different types of glycoconjugates and
their role

Dr. Jeelan Moghraby

Introduction

Carbohydrates


Most abundant organic molecule in nature
 Empirical formula (CH2O)n
 Originally produced from CO2 and H2O during
photosynthesis
 Sugars and polymers of sugars; range of size

Dr. Jeelan Moghraby



Extensive roles of carbohydrates:







Energy source
Energy storage
Structural components
Cellular recognition

Found linked to proteins and lipids; key roles in
mediation interactions

Dr. Jeelan Moghraby

Carbohydrate Structure

Monosaccharide



Simplest carbohydrate
Classified after the number of carbon atoms

Common
Monosaccharides
Trioses

Glyceraldyhyde,
dihydroxyacetone

Pentoses

Ribose, ribulose

Hexoses

Glucose, galactose, mannose,
fructose

Dr. Jeelan Moghraby




Termed according to location of oxidized functional
group; aldose if aldehyde, and ketose if ketone
Ketose named after the equivalent aldose; with
addition of ‘ul’

Dr. Jeelan Moghraby

Monosaccharides are Chiral




Stereoisomers around asymmetric carbon
Enantiomers are isomers that are mirror images of
each other; D- and L-isomers
Most carbohydrates are in the D-form

Dr. Jeelan Moghraby






Monosaccharides with multiple asymmetric carbons can also
exist as diastereoisomers; not mirror images of each other
Number of possible steroisomers = 2n (n = number of chiral C) Diasteroisomers have different physical properties
D- and L-configuration based on asymmetric carbon furthest
from aldehyde or ketone group

One less chiral centre than aldoses

Dr. Jeelan Moghraby

D-Aldoses containing 3-6 Carbon Atoms


Asymmetrical centre (red) furthest from aldehyde group

Biochemistry. 5th ed. Berg JM et al.
W H Freeman; 2002.

Dr. Jeelan Moghraby

D-Ketoses containing 3-6 Carbon Atoms


Asymmetrical centre (red) furthest from keto group

Biochemistry. 5th ed. Berg JM et al.
W H Freeman; 2002.

Dr. Jeelan Moghraby



Monosaccharides that differ in configuration at only
one asymmetric centre are called epimers

Dr. Jeelan Moghraby

Fisher Projections


Often used for representation of carbohydrates
 Provides clear view of stereochemistry
 Horizontal bonds are in front, while vertical bonds
point behind plane

Dr. Jeelan Moghraby

Cyclization of Monosaccharides




Most pentoses and hexoses exist in a ring or cyclic
form
Aldehyde group (C) reacts with alcohol (OH) to form
hemiacetal
Ketone group reacts with alcohol (OH) group to form
hemiketal

Voet Biochemistry 3e © 2004 John Wiley & Sons, Inc.

Dr. Jeelan Moghraby

Cyclization Reactions of Hexoses



Cyclization results in furanose and pyranose rings
Carbonyl carbon atom becomes chiral; anomeric
carbon

Intramolecular hemiacetal

Intramolecular hemiketal

Dr. Jeelan Moghraby
Voet Biochemistry 3e © 2004 John Wiley & Sons, Inc.

Haworth Projections



Visualisation of stereochemistry
Asymmetry at anomeric carbon results in – and –
forms called anomers

-form: -OH group attached
to anomeric C below plane of
ring; trans to CH2OH
 -form: -OH group attached
to anomeric C above plane
of ring; cis to CH2OH


Dr. Jeelan Moghraby

Reducing Sugars


Act as reducing agents
 Ring form is in equilibrium with open chain form
 Free aldehyde group can react with oxidising agents
 Glucose reacts with Cu2+, reducing it to Cu+, and
itself being oxidized to gluconic acid

Dr. Jeelan Moghraby
Biochemistry. 5th ed. Berg JM et al.
W H Freeman; 2002.

Test for Reducing Sugars





Colorimetric detection of...
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