molecular interactions in cell events
TRANSCRIPT
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Molecular Interactions in Cell
Events
Advanced Higher Biology
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Catalysis
Speed up chemical reactions between a
million to a trillion times
Carbonic anhydrase is said to convert 36
million molecules per minute
Enzymes can only speed up a chemical
reaction that could take place anyway
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Case Study: Hydrolysis of Maltose
This reaction can happen
without an enzyme if:
-Maltose and water molecule
collide at the right speed to
provide sufficient energy
-water molecule has to be in
the correct orientation
-water molecule hits the
glycosidic bond at just the
right angle
All this isnt impossible but will
occur infrequently.
Enzymes makes sure this
happens more frequently!
O
HH
Hydrolysis of
maltose
Hydrolysis breaks the 1,4 glycosidic bond
Addition of water provides atoms lost in the
dehydration reaction
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Proteases
Proteases
hydrolyse peptide
bonds
Liberate amino
acids
Digestive system
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ATPases
Hydrolyse ATP into ADP and Pi.
Energy released is used to power a particularreaction
OR
Provide a phosphate to phosphorylate aparticular moelcule
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Nucleases
Nuclease enzymes also take part in a hydrolysis
reaction
Break phosphodiester bonds in RNA and DNA to
separate nucleotides form one another
Endonucleases (restriction enzymes) recogniseand cut at particular base sequences
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Kinases
Add phosphates to molecules
P
hosphate is negative so it will change theshape of the enzyme
Phosphorylation may activate or deactivate(depends on enzyme)
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Specificity of enzyme activity
related to induced fit
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Induced Fit Theory
A change in the conformation of an
enzyme in response to substrate binding
that renders the enzyme catalytically
active.
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1. Active site lined with many amino acid R groups
2. Charged groups in active site complement charged
groups on substrate3. Bind in correct position
4. Enzyme structure altered
5. Enzyme folds round substrate bringing catalytic Rgroups of enzyme closer to substrate reactive groups
6. Enzyme flexes putting substrate under stress andcomplex goes through several unstable intermediateforms (transitional state)
7. Bonds are made and broken and electrons are movedwith catalytic R groups acting as go-between
8. Enzyme-substrate complex formed
9. Product diffuses away and enzyme returns to originalshape
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Inhibition of enzymes
Decrease rate of reaction
1. Competitive
2. Non-competitive
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Competitive Inhibitors
Reaction
Rate
No inhibitor
Low
Vmax
High
Competitive inhibitor
Low HighSubstrate
Concentration
Low concentration of substrate relative to inhibitor = inhibitor will enter active
site first
As substrate concentration increases reaction rate increases as more chance
substrate will enter first
At very high substrate concentrations Vmax will be reached as inhibitor willhardly ever enter first
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Case Study: Succinate Dehydrogenase
Inhibition is
reversible as
malonate issmaller so can
come out of
active site.
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Case Study:
Sulphonamide
Binds permanently to bacterial enzyme
Enzyme is the start of the folic acidsynthesis pathway
Bacterium unable to make folic acid and
dies Humans not affected as do not synthesise
our own folic acid
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Non-competitive inhibition
No inhibitor
Low
VmaxHigh
Non-competitive
inhibitor
Low HighSubstrate
Concentration
Enzyme is non-functional when non-competitive inhibitor is present
Substrate cannot enter active site as the shape of the cleft has changed
Inhibitor lowers enzyme concentration so Vmax also lower
Reaction
Rate
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Summary of Inhibition
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Allosteric effects
Allosteric enzymes have at least 2 binding sites
Small molecules can bind far from the active site
an so affect active site shape-enzyme r-groups reshuffle and make newbonds
Shifting of amino acids result in smalladjustments throughout the rest of the enzymeincluding conformation of the active site
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Positive Modulators (activators)
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Negative Modulator (inhibitor)
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Summary of Allosteric Enzymes
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What to do now
Read p66 Covalent Modification to p67
Role of end-product inhibition in control of
metabolic pathways and make notes
You will be doing a practical next week
based on the information above