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Unit 1 –Key Area 5 – Proteins and enzymes
1- Describe a chemical reaction in
A substrate is chemically altered into a product
general terms
A catalyst is a substance which speeds up the rate
2- Explain the meaning of the term
(i.e. the speed) of a chemical reaction without being
“catalyst”.
changed or used up.
(i.e. a catalyst is neither a substrate nor a product as
it is unaffected by chemical reactions).
An enzyme is a biological catalyst made up by all living
3-State what an enzyme is.
cells. It speeds up reactions and is left unchanged.
4-Which part of the enzyme binds
The active site. The shape of the active site is
to the substrate?
complementary to that of its specific substrate.
5-Explain the word “specific” as
Each enzyme only works on one substrate because the
applied to enzymes and their
shape of the active site is only complementary to
substrate
that of its specific substrate. E.g. Amylase only breaks
down starch. Enzymes and substrates have matching
shapes like a “lock and key”.
6-Explain why enzymes are required The cell processes necessary for life would happen too
for the functioning of living cells.
slowly without enzymes.
7-Give an example of an enzyme
C-L-A-P
- Catalase: breaks down hydrogen peroxide into water
involved in a degradation reaction.
and oxygen
- Lipase: breaks down fats into fatty acids and glycerol
- Amylase: It breaks down starch into maltose.
- Pepsin: breaks down proteins into polypeptides and
amino acids.
Potato phosphorylase: in potatoes, joins molecules of
8-Give an example of an enzyme
involved in synthesis (building up)
Glucose-1-phosphate to form starch.
Enzymes are proteins.
9-State what type of molecule
enzymes are.
10-Describe the effect of
At low temperatures, enzymes do not work effectively
temperature on enzyme activity
(molecules move too slowly). Enzymes work best at a
temperature called the optimum. Beyond that
temperature, the shape of the enzyme and its active
site change which slows down reaction rate. Above a
certain temperature, an enzyme becomes denaturated,
i.e. it is irreversibly damaged.
11-Describe the effect of a range of Each enzyme has an optimum pH, i.e. a pH at which it
pH on the activity of an enzyme
works most effectively (faster rate of reaction).
Enzyme may work at other pH but the rate of the
chemical reaction that they control is usually not as
fast.
12-Explain the term “optimum” as
The conditions at which enzymes works best are called
optimum conditions: optimum pH and optimum
applied to the activity of enzymes
temperature.
13-Explain what a control is.
A repeat of an experiment to show that the effect
observed is only due to the factor being investigated
(e.g. activity of an enzyme).