Biology AS AQA Enzymes and the Digestive System

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 12:35
Preview of Biology AS AQA Enzymes and the Digestive System

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Enzymes and the Digestive System
Broken down to smaller pieces e.g. teeth
Provides large surface area for chemical digestion
All digestive enzymes function by hydrolysis: Splitting up of molecules by adding water to the
chemical bonds.
ASSIMILATION: Where molecules are incorporated into body tissues and/or used in bodily
Carbohydrates- Monosaccharides
MONOSACCHARIDE: A single monomer unit
DISACCHARIDE: A pair of monomer units
POLYSACCHARIDE: Several monomer units.
E.g. glucose CHO
Carbohydrates ­ Disaccharides
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose= glucose + galactose
CONDENSATION REACTION: When monosaccharides join and a molecule of water is removed, a
glycosidic bond is formed.
HYRDOLYSIS: When the releasing of monosaccharides occurs as the glycosidic bond is broken by
adding water.
Carbohydrates ­ Polysaccharides
Polysaccharides are monomers, joined by condensation reaction. This reaction forms the glycosidic
bonds needed to join the monomers together.
Polysaccharides are large, insoluble so are good for storage.
E.g. starch found as grains in plants (starch grains in chloroplasts)

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Test for reducing sugars ­ BENEDICT'S TEST
All monosaccharides and some disaccharides are reducing sugars.
Reduction is the chemical reaction involving the gain of electrons.
Reducing sugars can donate electrons to another chemical (Benedict's reagent)
Benedict's is an alkaline solution of copper sulfate.
When sugar is heated, Benedict's forms an insoluble red precipitate. ­ Copper oxide
1. Add Benedict's to the liquid solution
2.…read more

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Test for proteins- BIURET TEST
Biuret test detects peptide links.
1. Add solution with sodium hydroxide solution
2. Add drops of very dilute copper sulfate solution
3. Goes from blue to purple
Different enzymes work at different pHs (so different enzymes at different parts of body)
Amylase produced in the mouth and pancreas hydrolyses the alternate glycosidic bonds of
the starch molecule to produce disaccharide maltose.…read more

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Structure of an Amino Acid
Amino acids are the monomer which combines to make the polymer
Polypeptides form to make proteins.
Contains amino group (-NH), carboxyl group (-COOH), hydrogen atom (-H), R
Formation of a Peptide Bond
Amino acids combine to form dipeptide.
Condensation reaction with removal of water. (Combing ­OH with ­H)
The link becomes the peptide bond
Primary structure of proteins ­ polypeptides
Through a series of condensation reactions, many amino acid monomers can be joined by
polymerisation.…read more

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Have structural functions.
E.g. collagen found in tendons (held together by cross-linkages of adjacent chain amino acids):
Primary- unbranched polypeptide chain
Secondary- tightly wound chain
Tertiary- Twisted into a second helix
Quaternary- 3 polypeptide chains
Carry out metabolic functions.
E.g. enzymes, haemoglobin.
Enzymes as Catalysts
CATALYST: Alter the rate of a chemical reaction without permanently changing themselves.
The energy of the products must be less than that of the substrates.
ACTIVATION ENERGY: Minimal energy required for reactions to occur.…read more

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Induced fit model
Rather than the enzyme being rigid, the enzyme is flexible and changes its shape slightly to fit the
profile of the substrate.
As the enzyme changes its shape, it puts a strain on the substrate molecule which distorts
particular bonds lowering its activation energy enough to break the bond.
Measuring enzyme-catalysed reactions
Measure either:
1. Formation of products
2. Disappearance of substrate
Effect of temperature
A rise in temperature increases the kinetic energy of
molecules.…read more

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Effect of pH
The pH of a solution is a measure of its hydrogen ion concentration.
A change in pH alters the charges on the amino acids that make up the active site. As a result, the
substrate cannot form enzyme substrate complexes.
A change in pH can cause the bonds that maintain the enzyme's tertiary structure to break. The
enzyme changes shape prevents enzyme-substrate complexes forming and hence the enzyme is
denatured.…read more


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