carbohydrates b.3
DESCRIPTION
Carbohydrates B.3. Introduction. most abundant class of biological molecules range from simple sugars (glucose) to complex carbohydrates (starch) major functions: (B.3.4) energy source: glucose converted into ATP energy storage/reserves: glycogen precursor for molecules such as DNA. - PowerPoint PPT PresentationTRANSCRIPT
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Carbohydrates B.3
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Introduction
• most abundant class of biological molecules
• range from simple sugars (glucose) to complex carbohydrates (starch)
• major functions: (B.3.4)
– energy source: glucose converted into ATP– energy storage/reserves: glycogen– precursor for molecules such as DNA
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Monosaccharides (B.3.1 and 2)
• simplest sugars (single sugars)– empirical formula is (CH2O)– contain a ketone, C=O (fructose) or aldehyde,
H-C=O (glucose) – contain at least two hydroxyl groups (-OH)
• can be straight chains or cyclic form• two common monosaccharides
– both C6H12O6
• glucose• fructose
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Glucose
both on same side of ring
on different sides of ring
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H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OH
H
H
OH
-D-glucose -D-glucose
23
4
5
6
1 1
6
5
4
3 2
H
CHO
C OH
C HHO
C OHH
C OHH
CH2OH
1
5
2
3
4
6
D-glucose (linear form)
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Condensation of monosaccharides to form disaccharides and polysaccharides (B.3.3 and B.3.5)
• example of a typical condensation reaction
A-OH + B-OH ===> H2O + A-O-B
(2 monosaccharides => water + 1 disaccharide)
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• requires enzymes• the hydroxyl (-OH) of two monomers are brought
together and the H of one and the OH of the other come together to make H2O
• the remaining O from one of the monomers bonds the two together in a bond called a glycosidic linkage
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Hydrolysis
• the reverse of condensation
• the decomposition of a substance by the insertion of water molecules between certain of its bonds.
• food is digested by hydrolysis
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Disaccharides• double sugar (contains 2 monosaccharides)• three common disaccharides:
1. sucrose - common table sugar glucose + fructose
2. lactose - major sugar in milkglucose + galactose
3. maltose - product of starch digestion glucose + glucose
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+
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Polysaccharides (3 types)
• longer chains of simple sugars made of glucose• serve principally as food storage and structural
molecules in plants• 3 Types of Polysaccharides
1. Starches (plants)– polymers of glucose molecules
– serve as storage depots of glucose
– two forms
• amylose- water soluble, straight chains, thousands of glucoses
• amylopectin- insoluble, branched chains, up to millions of glucoses
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glucose polymer with
(14) linkages, and
branches formed by (16) linkages
glucose polymer
with only (14) linkages.
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2. Glycogen (animals)• a short-term storage
polysaccharide for animals
• highly branched glucose units put together that are broken down to meet energy demands of the body
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3. Cellulose (plants)• most abundant polysaccharide on Earth• the major structural material of which plants are made
(wood and plant fibers)• insoluble and has great tensile strength because the
hydroxyls (-OH) are reversed on successive glucoses compared to other polysaccharides
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• plant cell walls are among the strongest of biological structures
• most organisms can’t break cellulose down into simple sugars because they don’t have the enzyme cellulase which is necessary to hydrolyze the glycosidic linkages
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Dietary fiber B.3.6-7
• dietary fiber is plant material that we ingest but are not able to digest
• passes through the gut relatively intact, as we do not possess cellulase enzymes capable of hydrolysing it– bacteria in our gut can digest it somewhat– example: cellulose
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• importance in our diet– helps “bulk” move through the large intestine
more eaisly• prevent constipation and diverticulosis (bulges in
the colon at weak places leading to pain)
• may prevent irritable bowel syndrome (IBS)
• may prevent hemorrhoids
– may cause a “full feeling” and therefore decrease chance of obesity
– may help prevent Crohn’s desease