1.8- FACTORS AFFECTING ENZYME ACTION Flashcards
For an enzyme to work it must…? (2)
come into physical contact with its substrate
have an active site which fits the substrate
To measure the progress of an enzyme-catalysed reaction what do we measure?
its time-course
What is the time-course?
how long it takes for a particular event to run its course
What two changes are most frequently measured?
formation of products
disappearance of substrate
What enzyme-catalysed reaction graphs explain?
at first there’s a lot of substrate but no product
very easy for substrate molecules to come into contact with empty active site
all enzyme active sites filled at any given moment and substrate rapidly broken down into its products
amount of substrate decrease as it’s broken down, resulting in increase in amount of product
becomes more difficult for substrate molecules to come into contact with enzyme molecules as there are fewer substrate molecules and product molecules ‘get in the way’ of substrate molecules and prevent them reaching an active site
so takes longer for substrate molecules to be broken down by enzyme and so its rate of disappearance slows and consequently rate of formation of products slows down
rate of reaction continues to slow until there’s so little substrate that any further decrease in its concentration cannot be measures
What does a rise in temperature increase?
the kinetic energy of molecules
What happens as the kinetic energy of molecules are increased?
molecules move around more rapidly and collide with each other more often
What happens in an enzyme-catalysed reaction when there’s a rise in temp?
enzyme and substrate molecules come together more often in a given time
more effective collisions resulting in more enzyme-substrate complexes being formed and so ROR increases
What does the rise in temp also begin to cause?
hydrogen and other bonds in enzyme molecule to break
What happens when the hydrogen and other bonds break in the enzyme?
enzyme, including the active site, changing shape
what starts to happen when the enzyme changes shape?
substrate fits less easily into this changed active site, slowing ROR
For many human enzymes what is the temperature that enzymes begin to change shape?
45°c
At around what temperature does the enzyme stop working altogether?
60°c
Why does the enzyme stop working altogether?
enzyme is so disrupted- denatured
What is the definition of denaturation?
permanent change and, once it has occurred, enzyme does not function again
Is the optimum temp the same for all enzymes?
no differs from enzyme to enzyme
What is the approximate optimum temp for most enzymes in the human body?
40°c
What temperature has our body evolved to be?
37°c
Why may have our bodies evolved to be 37°c? (3)
although higher body temp would increase metabolic rate slightly, offset by additional energy (food) needed to maintain higher temp
other proteins may be denatured at higher temps
any further increase during illness might denature enzymes
What is the normal body temp of many birds?
40°c
Why do many birds have a normal body temp of 40°c?
they have a high metabolic rate for high energy requirement of flight
What is the pH of a solution?
measure of its hydrogen ion concentration
What is the formula for the pH of a solution?
pH = -log(small 10) (H^+)
What does an increase or decrease in pH do?
reduce rate of enzyme action
What happens when the change in pH is more extreme?
enzyme become denatured
How does pH affect how an enzyme work? (2)
alters the charges on amino acids that make up active site- so substrate can no longer become attached to active site- enzyme-substrate complex cannot be formed
depending on how significant change in pH is, may cause bonds maintaining enzyme’s tertiary structure to break- active site changes shape
What is the arrangement of the active site partly determined by?
hydrogen and ionic bonds between -NH2 and -COOH group of polypeptides that make up enzyme
What does the H+ ions do to this bonding?
affect the bonding, causing active site to change shape
Are the fluctuations in pH inside an organism usually large or small?
usually small
As the fluctuation in pH in an organism in usually small, what does this mean?
they’re far more likely to reduce enzyme’s activity than to denature it
How are enzymes not used up in a reaction?
once an active site acted on its substrate it’s free to repeat procedure on another substrate molecule
What must there be so that an increase in amount of enzyme leads to proportionate increase in ROR?
excess of substrate
What will happen if the substrate is limiting and increase in enzyme concentration?
no effect on ROR
Why is there no effect on ROR when the substrate is limiting an d the enzyme conc. is increased?
available substrate already being used as rapidly as it can be by existing enzyme molecules
What happens to ROR when conc. of enzyme fixed and substrate conc. slowly increased?
ROR increases in proportion to conc. of substrate
Why does ROR increase when conc. of enzyme fixed and substrate conc. slowly increased?
because , at low substrate concentrations, enzyme molecules have only limited number of substrate molecules to collide with, and so active sites of enzymes not working to full capacity.
What happens when more substrate is added?
active sites gradually become filled, until point where all of them working as fast as they can
ROR at its max
What happens when EVEN MORE substrate added?
no effect on ROR
