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Enzymes (Factors affecting enzyme activity (pH (Small changes of pH slow…
Enzymes
Factors affecting enzyme activity
Temperature
Increase in temperature
Both enzymes and substrates will gain kinetic energy
Move faster
Increase rate of successful collisions
Rate of formation of ES complexes increases
Number of EP complexes per second increases
Molecules vibrate
Can break some weak bonds that hold the tertiary structure of the enzyme's active site together
Active site's shape begins to change
Substrate molecules don't fit as well into the active site
More heat is applied
Active site's shape is changed irreversibly
No longer complementary to the substrate molecule
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Primary structure is not altered
Peptide bonds between amino acids aren't broken
pH
Hydrogen ion is attracted towards negatively charged ions, molecules, or parts of molecules
Hydrogen bonds and ionic forces between amino acids hold the tertiary structure of the active site
Excess hydrogen ions will interfere with the hydrogen bonds and ionic forces
Active site changes
Substrate molecule cannot fit into the active site well
Rate of reaction is lowered
Can alter the charges on the active site of enzyme molecules
More protons will cluster around negatively charged groups
Interferes with the binding of the substrate molecule to the active site
Small changes of pH slow the rate of reaction
Shape of active site is disrupted
If optimum pH is restored
Hydrogen bonds can reform and the active site's shape is restored
Extremes of pH
Enzyme's active site may be permanently changed
Enzyme is denatured
Substrate concentration
Substrate concentration increases
Rate of reaction increases
More ES complexes can form
Substrate concentration is the limiting factor
Maximum rate is reached
Adding more substrate molecules will not increase the rate of reaction
All the enzyme's active sites are occupied
Substrate molecules cannot successfully collide and fit in the active site
Enzyme concentration
Enzyme degradation
Cells degrade old enzyme molecules
Component amino acids
Synthesise new enzyme molecules from amino acids
Advantages
Eliminates abnormally shaped proteins the might accumulate and harm the cell
Regulates metabolism in the cell
Eliminates any superfluous (surplus) enzymes
Increasing enzyme concentration
More active sites become available
More successful collisions between the enzyme and substrate occur
More ES complexes can form
Rate of reaction increases
Enzyme concentration is the limiting factor
Control of metabolic sequences
End-product inhibition
Catalysed reaction has reached completion
Product molecules stay tightly bound to the enzyme
Enzyme cannot form more of the product than the cell needs
Negative feedback
Product of one enzyme-catalysed reaction
Substrate for next enzyme-catalysed reaction in the metabolic pathway
May attach to a part of the first enzyme in the pathway
But not its active site
Binding changes shape of enzyme 1's active site
Prevents pathway from running
Concentration of the product within the cell falls
Molecules will detach from enzyme 1
Active site resumes normal shape
Pathway can run again
Multi-enzyme complexes
Efficient
Metabolic reactions are carried out in particular regions or organelles in cells
Doesn't increase substrate concentration
Enzymes and substrate molecules are kept in the same vicinity
Reduces diffusion time
Mechanism of enzyme action
Lock and key hypothesis
Catabolic
Substrate molecule fits into the enzyme's active site
Temporary hydrogen bonds hold the two together
Enzyme-substrate complex formed
Substrate molecule is broken down into smaller product molecules
Product molecules leave the active site
When a substrate molecule and an enzyme molecule successfully collide
Anabolic
Substrate molecules fit into the active site
Forms an enzyme-substrate complex
Temporary hydrogen bonds form between substrate molecules
Enzyme product complex
Larger product molecule leaves the active site
Induced fit hypothesis
Proposed by Daniel Koshland
Substrate molecules converted to product molecules
enzyme product complex
Product molecules have a slightly different shape from substrate molecule
Detach from the active site
Enzyme molecule can catalyse another reaction
Lock and key hypothesis does not explain how the ES complex is established
Active site is not a rigid fixture
Presence of the substrate molecule in the active site induces a shape change
Gives a good fit
Active site still has a shape complementary to the shape of the substrate molecule
On binding, small changes of shape of the side chains (R-groups) of the amino acids
Gives more precise conformation
Fits substrate molecule exactly
More effective binding to the active site
Substrate molecule fits into the active site
Active site changes shape slightly to mould itself around the substrate molecule
ES complex formed
Non-covalent bonds bind the substrate molecule to the active site
Ionic attractions
Hydrogen bonds
van der Waals forces
Enzymes inhibitors
Competitive inhibitors
Inhibitor molecule has a similar shape to that of the substrate molecule
Competes with the substrate for the enzyme's active site
The competitive inhibitor fits into the active site
Substrate molecule cannot enter
Reduces formation of ES complexes
Reduces number of ES complexes formed
Enzyme-inhibitor complex
Does not affect shape of the active site
Amount of inhibition depends on relative concentration of substrate and inhibitor molecules
More inhibitor molecules
More inhibitors collide with active sites
Effect of inhibition is greater
Increase substrate concentration
Inhibitor is unlikely to collide with active site if enough substrate is added
'Dilutes' effect of inhibitor
Means competitive inhibition can be reversible
Inactivator
When a competitive inhibitor binds irreversibly to the enzyme's active site
Non-competitive inhibitors
The competitor molecule attaches to the part of the enzyme molecule but not the active site
Active site no longer becomes complementary in shape to the substrate molecule
Prevents ES complexes from forming
Disrupts enzyme's tertiary structure
Allosteric site
Maximum rate of reaction is reduced
More inhibitor molecules present
Greater the degree of inhibition
More enzyme molecules are distorted
ES complexes cannot complete the catalytic reaction
Can bind either reversibly or irreversibly