Enzymes Flashcards
How do you assess the rate of enzymic reactions?
Measure time course for:
-formation of the products of the reaction
-the disappearance of the substance
What happens to the rate when the graph of ‘effect of substrate concentration on rate of reaction’ plateaus?
Constant rate
Why are enzymes less efficient at low temps?
-rate of reaction is slowed down
-due to reduced kinetic energy of the reactant molecules
Describe the effect of temperature on the rate of an enzyme-controlled reaction.
-increase in temp provides molecules with more kinetic energy, resulting in more frequent successful frequent collisions between active sites and substrate molecules
-more enzyme-substrate complexes formed
-this increases rate of reaction up to the optimum temp where rate of reaction is at its maximum
-continuing to increase the temperature causes the tertiary structure of the enzyme to denature as hydrogen and ionic bonds are broken
-rate of reaction decreases as the substrate can’t bind to the altered active site (less e-s complexes formed)
What happens to proteins above 50 degrees?
- denaturation is permanent
- the tertiary structure is irreversibly altered
-substrate can’t bind to the active site
What’s an enzymes optimum pH?
-the rate of reaction is at its maximum
-most enzymes are active over a narrow pH range
How does pH cause denaturation?
-very different pH’s from from the optimum can cause denaturation
-the change in pH alters ionic charges of acidic and basic groups
-hydrogen and ionic bonds are broken altering the tertiary structure and active site
-the substrate can’t bind to the altered active site
What are enzyme inhibitors?
-a number of chemicals can act as enzyme inhibitors
-slowing down the rate of enzyme catalysed reactions
Explain how competitive inhibitors effect rate of reaction.
-the inhibitor has a similar structure to the substrate molecule
-competes with it for the attachment to the active site
-binds to active site and blocks the substrate from doing so
-rate of reaction is reduced as there are fewer enzyme-substrate complexes
How can competitive inhibition be reduced?
Addition of more substrate
Explain an example of a competitive inhibitor and how it’s treated.
-carbon monoxide
-competes with oxygen in haemoglobin
-treated by giving 100% oxygen to the patient to flush out the carbon monoxide
Sketch a graph showing the effect of a competitive inhibitor on rate of reaction compared with no inhibitor present
X= substrate conc
Y=rate of reaction
Explain how non-competitive inhibitors effect rate of reaction.
-the inhibitor is not similar in structure to the substrate
-it binds at another place other than the active site to form an enzyme-inhibitor complex
-alters tertiary structure and shape of the active site
-the substrate can’t attach or substrate binds but no product is formed
-the degree of inhibition is completely dependant on the mount of inhibitor present
Can you reduce the inhibition of non-competitive inhibitors?
-no
-the addition of more substrate wont reduce this inhibition
Draw a graph to show the effect of non-competitive inhibitors on rate of reaction compared with no inhibitor present.
X=substrate conc
Y=rate of reaction
Describe the induced fit model of enzyme action. (2)
- before reaction active site not complementary
- shape of active site changes as substrate binds and e-s complexes form
- distorting bonds in substrate leading to reaction
A quantitative Benedict’s test produces a colour whose intensity depends on the conc of reducing sugar in a solution. A colorimeter can be used to measure the intensity of this colour.
The scientist used quantitative Benedict’s tests to produce a calibration curve of colorimeter against conc of maltose.
Describe how the scientist would have produced the calibration curve curve and used it to obtain the results in figure 4 (sharp increase in conc of maltose then curves round to nearly plateau).
Do not include details of how to perform a Benedict’s tests in your answer. (3)
- use maltose solutions of a known conc and carry out Benedict’s test on each
- use colorimeter to measure colour of each solution and plot a calibration curve
- find conc of sample from calibration curve
Explain how the active site of an enzyme causes a high rate of reaction. (3)
- induced fit causes active site of enzyme to change shape
- so e-s complex causes bonds to form/break
A competitive inhibitor decreases the rate of an enzyme-controlled reaction reaction. Explain how. (3)
- inhibitor has similar shape to substrate
- so fits into active site
- reduces e-s complexes forming
When bread becomes stale, the structure of some of the starch is changed. This changed starch starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could help to reduce weight gain. (3)
- less hydrolysis of starch
- to maltose
- so less absorption of glucose
A scientist investigated the activity of GOx and HRP enzymes when they are:
- trapped inside cages (T)
- not trapped (NT) but free in solution with no cages
Figure 10 shows his result: (relative activity of enzymes in T was 6.5+-2. For NT the relative activity of the enzymes was 1+-2)
What a you conclude from figure 10 about the effect of trapping GOx and HRP inside cages? (3)
- trapping increases enzyme activity
- increase is significant
- bc SD’s dont overlap
Describe how monomers join to form the primary structure of a protein. (3)
- condensation reaction between amino acids
- forming peptide bonds
- creating specific sequence of amino acids
Describe one similarity and one difference between the induced fit model of enzyme action and the lock and key model of enzyme action. (2)
SIMILARITY: substrate binds to active site
DIFFERENCE: active site changes shape but doesn’t in lock and key
State how enzymes help reactions to proceed quickly at lower temps. Do not write about active sites in your answer. (1)
Lower activation energy
