Cells & Enzymes
Present in
all living cells
Made of protein
Converts substrates
into products
Enzymes
Biological catalysts
Increase the rate of
chemical reactions
Remain unchanged
by chemical reaction
METABOLISM
This term really means two things:
ANABOLISM and CATABOLISM
ANABOLISM
“ TO BUILD” molecules as in the biosynthesis of polymers..
We ingest food digest to monomers and THEN via ANABOLISM we make larger molecules
Catabolism …then is to..
“TO BREAK APART “
Example: Glycogen, (starch) stored in the liver when needed for energy, is
converted to glucose ( monomers).
So during catabolism large molecules are broken into smaller molecules.
Chemical Reactions
A chemical reaction takes place when one or substances is chemically changed into one or
more different substances.
Chemical reactions take place in cells all the time.
Catalyst
Product
Substrate
Enzyme
Manganese
dioxide
Hydrogen
peroxide
Water + oxygen
Catalase
Enzymes and Chemical Reactions
Enzymes can speed reactions by lowering the
chemical reaction
amount of energy needed for a
Catalysts
A catalyst is a substance which speeds up a chemical reaction, without itself being
changed by the reaction.
When a catalyst is present, less energy is needed to get the chemical reaction started.
When a catalyst is present, the speed of the chemical reaction is faster.
3. Although a catalyst helps a chemical reaction to happen, it is unchanged at the end of
the reaction.
Biological Catalysts
The biological catalyst present in the cytoplasm of plant and animal cells that speeds up
the breakdown of hydrogen peroxide is called CATALASE.
Hydrogen
peroxide
REACTANTS
catalase
Oxygen + water
enzyme
PRODUCTS
2.2 Nature of Enzymes
The biological catalyst present in the cytoplasm of plant and animal cells that speeds up
the breakdown of hydrogen peroxide is called CATALASE.
Catalase
Hydrogen
peroxide
Water + oxygen
Catalase cannot speed up any other reaction. It is SPECIFIC to this reaction.
One Enzyme – One Reaction
There are thousands of different enzymes in your body.
Why are there so many different enzymes?
Each enzyme has its own unique protein structure and shape, which is designed to match
or COMPLEMENT its substrate.
Lock & Key Hypothesis
An enzyme only acts on one type of substance, or substrate.
Therefore, the enzyme is said to be SPECIFIC to its one substrate.
The shape of the active site (binding site) of the enzyme, matches the shape of the substrate. Allowing the two molecules to bind
during the chemical reaction.
This theory of enzyme action is called the ‘lock-and-key’ hypothesis.
MOVIE
Different enzymes for different jobs
Enzymes involved in breakdown reactions
Enzyme and substrate separate
Enzyme-substrate complex
Enzyme and products separate
Enzymes involved in synthesis reactions
Enzyme and substrates separate
Enzyme-substrates complex
Enzyme and product separate
2.3 Using a Control
Why is it necessary to include a control experiment in an investigation?
A control is an experiment that allows a comparison within an investigation in order to
ensure that the conclusions drawn from the results are valid.
Enzymes involved in breakdown reactions
Hydrogen peroxide
Starch
Fat
Catalase
Amylase
Lipase
Pepsin
Protein
Water + Oxygen
Fatty acids + Glycerol
Amino acids
2.5 Effect of High Temperature
Optimum conditions are the conditions at which an enzymes works best
Rate of reactions may be affected by temperature and pH
Notes on Denaturation
Notes on Optimum temp
2.5 Effect of High Temperature
What happens to the activity of an enzyme at high temperatures?
Notes on Denaturation
Effect of pH on enzymes
When the pH changes outwith optimal conditions, the shape of the active site of the enzyme alters and the
enzyme is denatured.
Movie
Effect of pH on enzyme activity
Most enzymes work best at a pH close to neutral (pH7), but there are some exceptions. Pepsin, an
enzyme found in the stomach, has an optimum pH of 2.
Enzyme Summary
Enzyme
Substrate
Product(s)
Amylase
Starch
Maltose
Catalase
Hydrogen peroxide
Oxygen and water
Pepsin
Protein
Amino acids
Phosphorylase
Glucose-1phosphate
Starch
Lipase
Fat
Fatty acids
Degradation or
synthesis?
s