Enzymes Flashcards
Describe the ‘lock and key’
Substrate is complimentary in shape to the enzyme’s active site.
Substrate fits into the active site exactly forming an enzyme-substrate complex (ESC).
induced fit model’ of enzymes.
Substrate is similar in shape to the active site (not exactly the same).
Fits into the active site.
Active site changes shape, binding to substrate so it is now complementary.
Forms an E-S complex.
Substrate bonds are put under strain / stress.
Explain how enzymes act as biological catalysts, speeding up biochemical reactions.
Substrate is similar in shape to the active site (not complementary).
Fits into the active site.
Active site changes shape, binding to the substrate
Enzyme-substrate complex (ESC) is formed
Induced fit model.
Activation energy for reaction is lowered (reaction more likely to occur).
Substrate bonds are put under strain / stress.
Substrate changes into product.
Product released from active site and enzyme returns to original shape.
Enzyme is unused in the reaction.
explain a typical ‘product-time’ graph.
Reaction is fastest at start as there is more substrate and a higher frequency / more ESCs can form.
Reaction slows as substrate is being converted to product, so ESCs forming less often / fewer.
Eventually all the substrate has been converted to product (reaction stopped / plateau)..
Explain how substrate concentration affects rate of an enzyme catalysed reaction.
At lower concentrations not all the enzymes’ active sites are occupied.
Increasing substrate concentration increases the frequency of “successful collisions” / ESCs form more rapidly, producing product faster.
At high substrate concentration all the active sites are fully occupied so the rate is at its maximum / V max
Explain how enzyme concentration affects rate of an enzyme catalysed reaction.
Increasing the concentration of enzyme increases the rate of reaction.
Proportional.
More active sites become available so more ESCs can form at any point forming product faster.
Explain how temperature affects rate of an enzyme catalysed reaction.
Increasing the temperature from low UP TO THE OPTIMUM increases the kinetic energy of the substrates.
higher frequency of successful collision / ESCs form more rapidly.
Product is produced faster.
Increasing temperature ABOVE THE OPTIMUM rapidly decreases the rate.
The heat denatures the enzymes.
The bonds in the tertiary structure break so the active site is destroyed and cannot bind to substrate.
Explain how ph affects rate of an enzyme catalysed reaction.
Changing the pH from the optimum causes disruption of the tertiary structure of the enzyme.
Tertiary bonds are distorted so is the shape of the active site.
Fewer ESCs can form.
Extreme pHs will denature the enzyme completely.
What is protein denaturation
Heat / changes in pH can break the R-group interactions within the enzymes.
The tertiary structure of the polypeptides is disrupted.
Hydrogen bonding, hydrophobic / ionic interaction, disulphide bonds are broken.
Polypeptide structure unfolds.
The active site is destroyed.
Substrate molecules can no longer bind / cannot form enzyme-substrate complexes.
Irreversible .
What does “controlling key variables” mean when conducting enzyme experiments
IF you are changing a factor (independent variable) e.g. substrate concentration, then ALL OTHER factors that can affect enzyme rate must be kept “the same” i.e. temperature, enzyme concentration, pH
What is meant by “the control”
A “control” is where you remove what is responsible for the change you observe.
So with enzymes you would have a separate tube where the enzyme has been boiled (denatured).
This can then be compared..
Detail the effect of competitive inhibitors.
Are similar in shape to the substrate.
They fit into the enzyme’s active site.
They block the active site and prevent the substrate binding / prevent ESC formation.
Increasing substrate concentration can dilute a competitive inhibitor effect.
Detail the effect of non-competitive inhibitors.
Bind to a site OTHER THAN the active site.
Enzyme’s active site changes shape.
Prevents substrate binding / prevents ESC.
Increasing substrate concentration CANNOT dilute a non-competitive inhibitor effect!
