Transcript Molecular Interactions in Cell events

Molecular Interactions in Cell
events
(i)
(ii)
(iii)
Catalysis
The Sodium-Potassium Pump
Cell Signalling
What caused this?
That’s clever
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Bombardier Beetles
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Oxygen gas formed
during break down of
H2O2 forces out water
and other chemicals
Reaction releases a lot of
heat so the water comes
out as steam
A reminder of their importance
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Catalase breaks down 5 million molecules of
H2O2 per minute at 0oC, to protect cells.
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It would take 300 years to break down the
same number of molecules using iron as a
catalyst
Chemical Reactions
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Synthesis (anabolic)
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Condensation reactions
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Removal of water to form a bond
Degradation (catabolic)
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Hydrolysis reactions
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Addition of water to break a bond
Enzymes
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Proteases
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Nucleases
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Hydrolyse peptide bonds
break down proteins into amino acids
Hydrolyse phosphodiester bonds
Break down nucleic acids into nucleotides
ATPases
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Hydrolyse ATP
Break ATP into ADP and Pi with the release of
energy
Enzymes continued….
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Kinases
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Catalyse the transfer of a phosphate group onto a
molecule such as a carbohydrate or a protein
Specificity of enzymes
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Compare the two diagrams
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Think about your knowledge of proteins tertiary structure?
Why do you think the induced fit model is favoured?
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Specificity of enzymes
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Induced-fit model
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When substrate combines with the enzyme it
causes a change in shape of the active site
The change in shape results in an optimal fit for
the substrate-enzyme interaction
Once the product diffuses away, the enzyme
returns to its original shape
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What analogy could be applied to this model?
What do the following have in common?
 Arsenic
 Cyanide
 Nerve
 DDT
Gases
 Tabun
 Sarin
 Mercury
 Lead
 Cadmium
Cyanide
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Cyanide is found is a gas (sometimes liquid)
Used / found in
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House fires
Apricot stones
Suicide pills
Gas chambers (both US and Nazi Germany)
Stock piled by US and Soviet Union in 50’s and 60’s
Mining
Photography
Electroplating
Cyanide
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Binds to iron atom in the enzyme cytochrome
C oxidase
This changes the shape of the enzyme
Knowing how this works has important
applications for
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Detection of poisoning
Treatment
Control of enzyme activity - Inhibitors
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Competitive Inhibitors
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Decrease the rate of reaction
Inhibitor is similar in structure and electrical
charge to substrate
It binds to the active site
An increase in the substrate can result in an
increase of product formation (inhibitor is out
competed)
Competitive inhibition can be reversible or
irreversible (depending on mechanism of binding)
Inhibitors cont..
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Competitive inhibitors cont…
Inhibitors cont…
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Non-competitive inhibitors
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Decrease the rate of reaction
Inhibitors have no similarity to the substrate
Inhibitor binds to part of the enzyme (other than
the active site) distorting the shape of the enzyme
Increase in substrate concentration does not
increase product formation
Can also be reversible
Inhibitors cont…
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Non-competitive inhibition cont….
Control of enzymes – Enzyme modulators
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Allosteric enzymes
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Allosteric enzymes have at least one other binding
site than the active site (called an allosteric site)
Allosteric enzymes have 2 forms – active and
inactive
When a substance binds to an allosteric site it
changes the shape of the active site.
Positive modulation
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The modulator changes the active site so the enzyme
becomes active (substrate fits)
Positive modulators are activators
Enzyme modulators cont…
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Allosteric enzymes cont…
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Negative modulation
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The modulator changes the active site so the enzyme
becomes inactive
Negative modulators are inhibitors
Enzyme modulators cont….
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Allosteric enzymes cont…
Control of enzymes – Covalent
modifications
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Addition, modification or removal of a variety of
chemical groups
Changes the shape of the enzyme
Phosphorylation and dephosphorylation
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Kinase enzymes add phosphate
Phosphatase enzymes remove phosphate
Some enzymes are activated by phosphorylation,
others are inactivated (and vice versa for
dephosphorylation)
Covalent modifications cont…
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Proteolytic cleavage
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Conversion of an inactive enzyme to an active one
Example Trypsinogen – Trypsin
Trypsinogen is synthesised in the Pancreas
Activation occurs when trypsinogen has amino acids
removed in the duodenum by another protease enzyme
This changes the trypsinogen into the active form trypsin
Trypsin then helps to activate more trypsinogen molecules
Back to cyanide
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What type of inhibition is demonstrated by
cyanide in the inhibition of cytochrome
oxidase?
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Enzyme inhibition is often how drugs work –
targeting enzymes specific to other
organisms, not humans
Control of metabolic pathways
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End product inhibition
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Chemical reactions are normally organised into
metabolic pathways with enzymes controlling
each chemical reaction
The end-product can act as a negative modulator,
binding to the first enzyme preventing the
metabolic pathway from proceeding because
intermediary substrates are not produced
This is a process of negative feedback
Learning Activities
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Read and take notes from DART pg 61-68
Scholar 6.3 and 6.4
Check out http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter8/animations.ht
ml#
Find examples for each type of enzyme control
Use flash cards to remember the enzymes and their reactions
Draw posters of each type of enzyme control
Use the information on ‘end-product inhibition in respiration’ to
demonstrate the principle of negative feedback
‘Enzymes’ worksheet
‘Enzyme cofactors and inhibitors’ worksheets
Advanced Higher Biology Questions