Carbohydrates + questions

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CARBOHYDRATES
Most carbohydrates are large, complex molecules composed of long chains of monosaccharaides. Single monosaccharaides are
also carbohydrates.
Glucose is a hexose sugar- a monosaccharaide with six carbon atoms in each molecule.
EXAMINERS TIPS
1. Make sure you recognise and draw the abbreviated (simple) forms of alpha and beta glucose.
2. Remember that there are two products of a condensation reaction-the larger molecule produced as a result of
bonding two smaller molecules, and a water molecule. Don't forget to write down the water molecule produced.
FUNCTION
It it is a `substrate'.
It is a store of energy.
Their further bonds after glycosidic bonds include hydrogen bonds.
Helps form glycoproteins.
Helps form mucus.
The monomers of carbohydrates are simple sugars
(monosaccharaides).
They have similar characteristics: sweet, soluble, end in `ose' and most
are in 5-6 membered rings. They all are in Cn(H2O)n structure.
Most are C6H12O6 and several are C6H10O5.
Glucose can occur in two forms called isomers. The position of the H
and OH groups on C1 are swapped. Beta glucose is similar; however, on
one of the chains the OH and H are swapped.
DISACCHARIDES
This is two monosaccharaides joined by a glycosidic bond in a
condensation reaction. E.g. sucrose (glucose +fructose). A hydrogen on
one monosaccharide bonds to a hydroxyl (OH) group on the other,
releasing a molecule of water.
ALPHA AND BETA GLUCOSE
Their isomers make a difference.
The alpha glucose molecules are joined by an alpha 1-4 glycosidic bond.
The beta glucose molecules are joined by a beta 1-4 glycosidic bond.
A B;' `eta 1-4 glycosidic bond flips one of the glucose residues by 180 degrees.

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POLYSACCHARIDES
AMYLOSE
It is coiled in a spiral-straight unbranched helix and this is due to the angles of the glycosidic bonds. This makes it
compact and so easy for storage.
It is the main molecule of starch.
It is insoluble and so doesn't affect water potential or reactions.
It is metabolically inactive.
It is joined by alpha 1-4 glycosidic bonds.
Amylose is storage of energy.
GLYCOGEN
Has short branched chains of alpha glucose, this is useful as there are more sites for enzymes to digest.…read more

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QUESTIONS
1. Draw the structure of an alpha glucose molecule.
2. What is a disaccharide?
3. What is the function of glycogen?
4. Describe, with the aid of a diagram, how glycosidic bonds are formed and broken in living organisms. (7 marks)
5. Describe how the structure of starch makes it suited to its function. (6 marks)
6. Define the following terms: monosaccharide, disaccharide, polysaccharide and glycosidic bond.
7. Explain why starch and glycogen are good stores of energy.
8.…read more

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