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Biomolecules
Enzymes
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What is an enzyme?
An enzyme is a
protein
that acts as a
catalyst
in
biological
reactions, speeding up the rate of the reaction without being consumed in the process
How do enzymes catalyse reactions?
Lowering
activation energy
Why do enzymes lower activation energy?
Hold together the molecules and reducing repulsion
Putting strains on
substrate
bonds so they are broken more easily
What is the lock and key model?
Specific binding of a
substrate
to an enzyme's
active site
What is the induced fit model?
Active site of enzyme changes shape slightly after substrate has binded to it
What are the properties of enzymes?
Usually
catalyse
one reaction
Tertiary
structure determines shape of
active sites
How can we measure enzyme activity?
How fast the
product
is made
How fast the
substrate
is broken down
What are the factors affecting enzyme activity?
Temperature
pH
Enzyme
concentration
Substrate concentration
How does temperature affect enzyme activity?
Increased kinetic energy for substrate molecules
More collisions with active sites
If temp exceeds optimum enzyme denatures
How does pH affect enzyme activity?
Above and below
optimum
pH the H+ and OH-
ions
disrupt enzyme bonds
Active site
denatures
How does substrate concentration affect enzyme activity?
More
substrates
means more
collisions
with enzymes
Saturation point (all
active sites
are full)
How does enzyme concentration affect enzyme activity?
More enzymes means more collisions with
substrate
Saturation point
when (all substrates have bonded)
What is an enzyme inhibitor?
A substance that decreases its
activity
of an enzyme
What is a competitive inhibitor?
A molecule with a similar shape to the
substrate
that binds to the
enzyme
instead
What is a non-competitive inhibitor?
Molecule that binds to an
enzyme
away from
active site
, changing enzyme structure so
substrate
is unable to bind
What are the 2 ways we can use to measure the rate of an enzyme controlled reaction?
Measure how fast the
product
of the reaction appears
Measure how fast the
substrate
is broken down
Measuring the effect of temperature on product formation (catalase and hydrogen peroxide)
Set up boiling tubes containing same volume and concentration of hydrogen peroxide
Add equal amounts of buffer solution to each boiling tube so pH remains constant
Put boiling tubes in different temp water baths
Use a pipette to add same volume and concentration of catalase to each boiling tube then attach bung and deliver tube
Record how much oxygen is produced in the first minute
Repeat the experiment 3 times at each temp
Calculate mean volume of oxygen produced at each temp
Calculate mean rate of reaction at each temp
Measuring effect of temp on product formation (
catalase
and
hydrogen peroxide
)
Apparatus:
Measuring the effect of enzyme concentration on substrate breakdown (amylase and maltose)
Put a drop of iodine in potassium iodide solution into each well in the spotting tile
Label each well
Mix together a known concentration of amylase and starch in a test tube
Use a pipette to drop the amylase/starch mixture in each well at regular intervals
Observe resulting colour
How fast amylase is working=how long it takes for iodine solution to no longer change colour when starch/amylase mixture is added
Repeat experiment with different amylase concentrations
Repeat experiment 3 times at each amylase concentration
Calculate mean time taken for each amylase concentration
Measuring effect of enzyme concentration on substrate breakdown (amylase and maltose)
Apparatus
:
How do we estimate initial rate of reaction?
Draw a
tangent
at t=0
Calculate the
gradient
of the tangent
Unit
= y-axis unit/x-axis unit
Temperature effect on on rate of enzyme-controlled reactions
Graph:
pH effect on rate of
enzyme-controlled
reaction
Graph:
Substrate
concentration
effect
on rate
of
enzyme-controlled
reactions
Graph:
Enzyme concentration effect on rate of
enzyme-controlled
reactions
Graph:
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