AQA AS Biology Unit 1 3.1.2 Enzymes and The Digestive System

I made these revision notes using my class notes, the AQA AS Biology textbook and the specification. 

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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…

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o 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.…

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o 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…

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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…

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oTend 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…

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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…

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4. 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…

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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…

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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…


Iqra Zubair


what grade did you get? :)

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