Cells

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Cells Enzymes
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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
Enzyme
Manganese dioxide
Water oxygen
Catalase
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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.

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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
Oxygen water
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The biological catalyst present in the cytoplasm
of plant and animal cells that speeds up the
breakdown of hydrogen peroxide is called CATALASE.
Catalase
Water oxygen
Catalase cannot speed up any other reaction. It
is SPECIFIC to this reaction.
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There are thousands of different enzymes in your
body. Why are there so many different enzymes?
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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.
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MOVIE
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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
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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.
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2.3 Using a Control
Only one variable should be altered in an
investigation, this is said to be the altered
variable.
What was the altered variable in the last
investigation you carried out?
It is important to ensure that all other
potential variables are kept the same in the
investigation, these are called the controlled
variables.
What were the controlled variables in the last
investigation you carried out?
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Enzymes involved in breakdown reactions
Catalase
Hydrogen peroxide
Water Oxygen
Amylase
Starch
Maltose
Lipase
Fatty acids Glycerol
Fat
Pepsin
Amino acids
Protein
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2.4 Synthesis reactions
Glucose is used by leaves as energy source or
transported to root for storage.
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2.4 Synthesis reactions
What is phosphorylase?
Phosphorylase is an enzyme that synthesises
starch.
What is substrate of phosphorylase?
Glucose-1-phosphate
What is the product?
Starch
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2.4 Synthesis reactions
Amylase catalyses the breakdown of starch to
produce maltose. How is starch produced?
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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 Optimum temp
Notes on Denaturation
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2.5 Effect of High Temperature
What happens to the activity of an enzyme at high
temperatures?
Notes on Optimum temp
Notes on Denaturation
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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
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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.
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Enzyme Summary
Enzyme Substrate Product(s) Degradation or synthesis?
Amylase Starch Maltose Degradation
Catalase Hydrogen peroxide Oxygen and water Degradation
Pepsin Protein Amino acids Degradation
Phosphorylase Glucose-1-phosphate Starch Synthesis
Lipase Fat Amino acids Degradation