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Biology Notes

Digestion and Enzymes
Disease
Spectrum scale, they can range from not harmful (common cold) to severe (AIDS and cholera)
Infectious diseases
Can be passed from person to person but caused by small microorganisms called pathogens
Non-infectious diseases
These are not caused by pathogens – due to genes or lifestyle such as diet, smoking and no exercise
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They can enter our system via:
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Breaks in skin
Digestive system
Reproductive and urinary systems
Gaseous exchange

Digestive System
Breaks down food into small chain molecules that can diffuse into the blood stream via the wall of
the small intestine
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These catabolic reactions include:
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Protein – amino acids
Starch – sugars
Fats – glycerol and fatty acids

Some substances cannot be digested such as cellulose which is egested as faeces along with cells
scraped from the gut lining, enzymes and bacteria
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Macromolecules are made up of smaller molecules called monomers
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Two monomers join together via condensation which is where two –OH groups form a bond to
release water
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Polymers can be broken down into monomers via hydrolysis this is the reversed reaction because a
water group is added
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Glucose, galactose and fructose (6 carbon atoms –
C6H12O6)
Disaccharides – two monosaccharides joined together via condensation
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Biology Notes
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Polysaccharides – many monosaccharide residues joined together
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Glucose + other sugars
Although all monosaccharides have the same molecular formula they have different structures
which makes them different sugars and gives them different properties
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Sucrose is not a reducing sugar but can be heated with acid +
alkali (to keep the same pH) this is because sucrose is split back into fructose and alpha glucose
which are both reducing sugars, now sucrose would give a positive test in Benedict’s solution
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It is made up oif amylose and amylopectin
which are both long chains of glucose
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Test for starch is iodine – if starch is present the iodine will turn blue to black
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Glucose can be passed
straight through the wall of the small intestine because it’s a simple molecule
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Starch  maltose  glucose
Amylase hydrolyses the starch and maltase hydrolyses maltose to glucose which can then be
absorbed into the bloodstream
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The biuret test will test for the presence of protein, if protein is present than the solution will turn
from blue to lilac
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Amino group (– NH2)
Carboxylic acid group (– COOH)
Hydrogen group (– H)
R-group, this differs in each amino acid

Biology Notes
Amino acids join together by condensation to create a peptide bond
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Two amino acids joined together makes a
dipeptide
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Hydrolysis breaks these
molecules back down again
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Different proteins have different shapes
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The sequence of these amino acids are determined by the
genetic coding in the DNA
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Secondary structure of a protein is the way the protein folds
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The structure is held in place by hydrogen bonding and in the
presence of sulphur atoms, disulphide bonding
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This tertiary structure is related to the function of the protein
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If a protein has more than one polypeptide chain it has a quaternary structure
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Enzymes, substrates and products
Enzyme + Biurets = Violet solution: this is the protein test and enzymes are proteins
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Group of amino acids form a pocket
called an active site
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The substrate is broken down into products
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Enzyme-substrate complexes reduce activation energy
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The substrate fits precisely, the
enzyme’s active site is already the right shape
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The
enzyme moulds itself around the substrate
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Increasing the
temperature above the optimum will increase the kinetic energy and break the chemical bonds
holding the structure together
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Biology Notes
pH:
pH = measure of the concentration of H+ ions
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The pH change alters the concentration
of H+ and OH- in the surrounding solution
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A large change means the tertiary
structure changes and the enzyme denatures due to broken bonds
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Competitive inhibitors are complimentary to the active sites of enzymes so they can fit into the
active site and block it
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Non-competitive inhibitors bind to another place on the enzyme that is not the active site
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Low temperatures:
When an enzyme works in a temperature less than the optimum it slows down the rate of the
reaction, therefore increasing the temperature will increase the kinetic energy meaning that more
successful collisions take place and more enzyme-substrate complexes form; the rate of reaction
increases

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