carbohydrates chemistry, lecture for 1st year m b b s . delivered by dr mohammad waseem kausar
TRANSCRIPT
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Dr MUHAMMAD WASEEM KAUSARAssistant professor. Bio-chemistry
I M D C.
Carbohydrates chemistry
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Carbohydrates
– Cell structure:– Cellulose, LPS, chitin
Cellulose in plant cell walls Lipopolysaccharides (LPS) in bacterial cell wall
Chitin in exoskeleton
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The elements which make up carbohydrates are:
•Carbon (C)•Hydrogen (H)•Oxygen (O)Some carbohydrates also contain N and S
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Carbohydrates• commonly known as sugars, Saccharide, hydrates
(H2o) of carbon• ARE ALDEHYDE OR KETONE DERIVATIVES OF
POLYHYDRIC ALCOHOLS or• Are polyhydroxylated compounds with at least 3 carbons, with
potentially active carbonyl group, which may be either aldehyde(CHO) or ketone (CO) group.
• general formula CnH2nOn .but
Many CHO contain H & O not in the same proportionAs in water .e.g deoxyriboseC5H10O4.
• Sources– Plants– animals
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BIOMEDICAL IMPORTANCE • A variety of functions in the cell
– Provides majority of energy(4.1 kilocalories/gm)– Structural component of cell wall.– In animal cells carbohydrates on the exterior surface of the cell
serve a recognition and identification function– Serve as metabolic intermediate(G-6-p)– Component of nucleotides that form DNA , RNA – precursor for synthesis of all the other carbohydrates in the body
e.g. glycogen, galactose, ribose, glycolipids, glycoproteins and proteoglycans.
– For synthesis of FA, cholesterol, amino acids– Carbohydrates derivatives are used as drugs e.g.– Principal sugar in milk, galactose– Strong detoxification agent in body e.g. Glucoronic acid– Play a role in lubrication, cellular intercommunication, and
immunity.– Diseases ssociated with carbohydrate metabolism include Diabetes
mellitus, galactosemia, glycogen storage diseases, and lactose intolerance.
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Carbohydrates Classificationno satisfactory classification. •GENERALLY 1.Simple carbohydrates2.Complex carbohydrates
• On the basis of hydrolysis1.Monosaccharides2.Disaccharides3.Oligosaccharides, 4.Polysaccharides. and .Derived carbohydrates
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MonosaccharidesMonosaccharides
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Monosaccharides -Single Sugar-
•Glucose
The Formula for glucose is
C6 H12 O6
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Glucose
C
C
CH2OH
H OHC
OHH C
HHO
H OH
C OH
D-Glucose
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Fructose
C
C
CH2OH
H OHC
OHH C
HHO
O
CH2OH
D-Fructose
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• These are the basic building blocks of other carbohydrates
• Simple sugars• Can not be further hydrolyzed• Name usually suffix - ose• Empirical formula is CnH2nOn, here “ n” =3 or more• Color less, white, solid crystalline in nature, soluble
in water, sweet taste, insoluble in non-polor solvent• Simplest m/s are two, which are 3 carbon. Trioses
glyceraldehyde & dihydroxyacetone.• Subdivision of m/s1.On the basis of “C” atoms.2.On the basis of functional group.
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Classification of m/s
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1.number of carbons
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2.On the basis of functional group
• Aldoses are monosacchrides with an aldehyde group and many hydroxyl (-OH) groups.
• Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups.
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Some properties of m/s with reference to glucose
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chiral Carbon:
ISOMERS=
2n.
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1. Monosaccharides contain one or more asymmetric C-atoms: get D- and L-forms, where D- and L- designate absolute configuration
2. D-form: -OH group is attached to the right of the asymmetric carbon
3. L-form: -OH group is attached to the left of the asymmetric carbon
4. If there is more than one chiral C-atom: absolute configuration of chiral C furthest away from carbonyl group determines whether D- or L-
Chirality rules.
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Ring formation / Ring structure
An aldose: Glucose
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A ketose: Fructose
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Ring Structure
• Linear known as “Fischer” structure”• Ring know as a “Haworth projection”• Cyclization via intramolecular hemiacetal (hemiketal)
formation• C-1 becomes chiral upon cyclization - anomeric
carbon• Anomeric C contains -OH group which may be or mutarotation
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EPIMERS•Carbohydrate isomers that differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon) Epimers: Isomers differing as a result of variations in configuration of the -OH and -H on carbonatoms 2, 3, and 4 of glucose are known as epimers. . For example, glucose and galactose are C-4 epimers ,their structures differ only in the position of the -OH group at carbon 4
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OPTICAL ACTIVITY
• The presence of asymmetric carbon atoms also confers optical activity on the compound. When a beam of plane-polarized light is passed through a solution of an optical isomer, it will be rotated either to the right, dextrorotatory (+); or to the left, levorotatory (−). The direction of rotation is independent of the stereochemistry of the sugar, so it may be designated D(−), D(+), L(−), or L(+). For example, the naturally occurring formof fructose is the D(−) isomer.