OCR AS Biology- Carbohydrates

OCR AS Biology Revision Notes

Contains: Key Definitions, Diagrams, Explanations and Comparisons

Topics: Structure and Function of Carbohydrates, Condensation and Hydrolysis Reactions

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  • Created on: 14-03-13 14:30
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Carbohydrates
Used for:
-Energy Storage (released form Glucose in respiration)
-Energy Source (such as starch)
-Structure (such as cellulose)
They contain Hydrogen, Carbon and Oxygen molecules.
General formula C(n) H(2)O(n)
The simplest carbohydrates are monosaccharaides:
-3 to 6 Carbon atoms (most common are hexoses such as glucose and fructose)
- Water soluble
-sweet taste
-form crystals
3Carbons: triose sugars
4Carbons:tetrose sugars
5Carbons:pentose sugars
6Carbons:Hexose sugars ( C(6)H(12)O(6) )
Two monosaccharaides join to form a disaccharide in a condensation reaction
2 Alpha Glucose Glycosidic bond formed Maltose molecule

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GLUCOSE
AlphaGlucose
-Six Carbon atoms
-Found naturally in a ring structure
-OH found below plane of ring at first Carbon
BetaGlucose
-Six Carbon atoms
-Identical to alpha glucose with one exception
-The OH is found above the plane of the ring at the first
Carbon
The breaking down of glucose in respiration provides the cell with energy. Animal and plant
enzymes can only `break down' alpha glucose, as B glucose has a different OH and H
arrangement.…read more

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Starch:theenergy-storagepolysaccharideinplants
-A mixture of long, straight amylose chains and branched amylopectin. (a-glucose)
-it is stored in chloroplasts and in membrane-bound starch grains.
-Is broken down to release glucose molecules, which are then respired.
Function: - branched structure allows it to be hydrolysed quickly, and takes up less
storage space.
-Does not dissolve, so stored glucose does not affect cell water potential.
Glycogen:theenergystoragepolysaccharideinanimals
-made up of alpha glucose sub units.…read more

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Both described as energy-storage molecules
Both do not dissolve, so don't affect cell water potential, as glucose stored
freely in a cell would reduce water potential which would have negative
consequences.
They hold glucose in chains which can easily be broken off and hydrolysed for
a quick energy release.
Cellulose:mostabundantstructuralpolysaccharideinnature
-Long linear chain with many beta(1-4) linkages
-Hydrogen bonds form between the B-chains, and are cross linked, forming micro
fibrils.…read more

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Polysaccharides Starch and glycogen Large molecules of
many a-glucose Energy storage.
molecules joined by Starch in plants,
condensation glycogen in animals
reactions. Insoluble and fungi.
in water, and form
grains/granules.
Cellulose Large molecules of
many B-glucose Structural, only
molecules joined by found in plant cell
condensation walls.
reactions. Insoluble
in water, very
strong.…read more

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