AQA AS Biology Unit 1 3.1.2 Enzymes and The Digestive System

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Preview of AQA AS Biology Unit 1 3.1.2 Enzymes and The Digestive System

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Revision: Unit 1 Biology and Disease 3.1.2 Enzymes and the Digestive System
All carbohydrates contain the elements carbon, hydrogen and oxygen.
The general formula is CH2O.
The units from which all larger carbohydrates are made.
Single sugars, small molecules that dissolve in water and taste sweet.
Glucose is a hexose sugar because it has 6 C atoms (C6H12O6).
There are two forms of glucose, -glucose and -glucose.
Glucose is used in respiration.
It is also used to make other important polysaccharides such as starch, glycogen and cellulose.
Fructose is a hexose monosaccharide.
Glucose and fructose are isomers.
o They have the same number of carbon, hydrogen and oxygen atoms, but they are arranged
Difference in shapes gives the two sugars different properties.
o They are both reducing sugars.
Test Conditions Result
Make sample into solution.
Add a few cm3 of Benedict's Colour change
reagent. to an orange
s reagent
Place in a hot water bath for a red precipitate.
few minutes.
Triose sugars have 3 C atoms.
Pentose sugars have 5 C atoms.
Ribose and Deoxyribose are important pentose sugars.
o They are important components of DNA and RNA.
Properties of Monosaccharides

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Sugars are small molecules.
o They are soluble in water.
o They are easy to transport to different parts of an organism.
o Required for growth and repair of organs as they are the building blocks for other carbohydrates.
Disaccharides form when a condensation reaction joins 2 Monosaccharides.
Two -glucose molecules combine to form the disaccharide maltose.
The bond formed is a Glycosidic bond which is a very
strong covalent bond.
Glucose and Fructose combine to form sucrose.
o A non-reducing sugar.…read more

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It is insoluble so cannot diffuse out of cells and will not exert any osmotic effect.
o It contains many C-C and C-H bonds which are high energy so it is a good energy store.
The main structural component of plant cell walls.
Made up of long chains of -glucose units which form long flat chains.
Individual cellulose chains lie parallel to each other. Hydrogen bonds can form between them.
o This forms a tough, strong and rigid structure.…read more

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Made by adding more amino acids.
Each polypeptide has its own unique sequence of amino acids.
o This is known as the primary structure of the protein.
By changing just one amino acid in a polypeptide chain the complete properties of the molecule can be
The Structure of Proteins
1. Primary Structure
The sequence of amino acids that make up the polypeptide chain.
This sequence determines the way in which the chain can fold.…read more

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Tend to be structural proteins e.g.
Keratin ­ forms hair, horn, nails and the upper layer of skin.
Collagen ­ an important component of skin, bone and tendons.
Fibrin ­ forms the fibres in blood clots.
o Fibrous proteins are insoluble and usually metabolically inactive.
In other proteins, the tertiary structure forms a Globular protein.
o More spherical.
Enzymes and hormones are globular proteins.
o Usually soluble and metabolically active.
4. Quaternary Structure
Two or more polypeptide chains and non-protein groups combine.…read more

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Complex tertiary and often quaternary structure in which polypeptides are folded around each other to form
a roughly spherical or globular shape.
Overall 3D shape of the enzyme is very important, if it is altered; the enzyme cannot bind to its substrate and
so cannot function.
Shape is maintained by hydrogen bonds and ionic forces.
Function of an enzyme can be affected by changes in temperature and pH.
Factors Affecting Enzyme Function
1. Temperature
As the temperature rises the rate of reaction increases.…read more

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Competitive Inhibitors
Compete with normal substrate molecules to occupy the active site.
Inhibitor molecules must be a similar shape and size to the substrate molecule to fit the active site but
cannot be converted into product.
The effect of competitive inhibitors can be reduced by increasing the substrate concentration as more
enzyme-substrate complexes will form and the effect of the inhibitor is effectively diluted.
5. Non-Competitive Inhibitors
The binding of an inhibitor causes a change in the 3D tertiary structure of the enzyme.…read more

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Therefore enzyme-substrate complexes cannot form so the reaction rate is reduced.
The Digestive System
Salivary Glands (3 pairs in the mouth)
Saliva is produced which contains amylase.
Amylase breaks down starch into maltose.
Saliva lubricates the food to make it easier to pass
down the oesophagus.
Saliva also provides a pH of 7 for optimum conditions for amylase to act.
Relatively large circular and longitudinal muscle layer as peristalsis is needed to push food down.
No adaptations for digestion or absorption, only transportation.…read more

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Mucosa is folded into villi with millions of microvilli to increase the surface area for absorption.
Brunner's gland secretes alkali to neutralise HCl from the stomach.
Adapted for digestion and absorption
o Villi with microvilli, also it's very long therefore increased surface area.
o Epithelial cells have many mitochondria to provide energy for active transport.
o Rich blood supply in the villi to remove absorbed molecules away quickly, maintaining a diffusion
gradient.…read more


Iqra Zubair

what grade did you get? :)

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