Enzyme Past Paper Questions Flashcards
(30 cards)
Describe the induced-fit model of enzyme action and how an enzyme acts
as a catalyst.
Lowers Activation Energy
Substrate binds to active site/enzyme
Enzyme substrate complexes are formed
Active site changes it shape so it is complementary to the shape of the enzyme
Scientists investigated the action of the enzyme ATP synthase. They made
reaction mixtures each containing:
* ATP synthase
* buffer (to control pH)
* substrates.
One of the substrates required in these reaction mixtures is inorganic
phosphate (Pi).
Tick (✓) one box to show which other substrate the scientists must add to
the reaction mixtures to produce ATP.
ADENINE OR
ADENOSINE DIPHOSPHATE OR
GLUCOSE OR
RIBOSE
Adenosine diphosphate
The scientists investigated the effect of concentration of inorganic
phosphate (Pi) on ATP synthase activity.
After 2 minutes, they stopped each reaction and then measured the
concentration of ATP.
The figure below shows the scientists’ results.
Suggest and explain a procedure the scientists could have used to stop
each reaction.
Mark in pairs, 1 and 2 OR 3 and 4 OR 5 and 6
Boil at high temperatures until enzymes denature
Explain the change in ATP concentration with increasing inorganic
phosphate concentration.
increases the number of enzyme substrate complexes as Pi increased
All active sites occupied
A student investigated starch hydrolysis using the enzyme amylase.
During the procedure, the student:
* treated the starch to make it soluble
* prepared 10 cm3 of different concentrations (mg dm−3) of starch
solution
* added an identical concentration of amylase to each starch solution
* measured the time in minutes to completely hydrolyse starch.
He repeated the procedure and calculated the mean time to completely
hydrolyse starch in each concentration of starch solution.
Draw a table the student could use to record all of his results.
You only need to show completed column headings.
Describe the results you would expect the student to obtain.
as starch increases, the time taken to hydrolyse increases
A competitive inhibitor decreases the rate of an enzyme-controlled
reaction.
Explain how.
Inhibitor similar shape to substrate;
Reject same shape
Accept ‘complementary to active site’
Fits/binds to active site;
Prevents/reduces enzyme-substrate complex forming;
When bread becomes stale, the structure of some of the starch is
changed. This changed 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.
Less hydrolysis of starch
To Maltose
So less absorption of glucose
Describe how the structure of a protein depends on the amino acids it
contains.
Structure is determined by position of R group.
Primary is the sequence of amino acids
Secondary is where proteins bend into alpha helix shape and Beta pleated sheets
It is formed by hydrogen bonding
Tertiary is formed from interactions of R groups and hydrogen bonds
creates active sites in enzymes
Figure 2 shows the SGLT1 polypeptide with NH2 at one end and COOH at
the other end.
Describe how amino acids join to form a polypeptide so there is always
NH2 at one end and COOH at the other end.
One amine/NH2 group joins to a carboxyl/COOH group to form a
peptide bond
there is a free amine/NH2 group at one end
and a free carboxyl/COOH group at the other
Explain how the active site of an enzyme causes a high rate of reaction. (induced fit)
Lowers down the activation energy
Induced fit causes the shape of the active site to change shape so it is complementary to the shape of the substrate
More enzyme substrate complexes formed
Other than those stated, give one factor the student would have controlled
in his investigation.
(OSMOSIS OF POTATO)
size of chip
Suggest a change the student could make to his procedure so that 10 cm3
of oxygen would be produced in less than 6 seconds.
(OSMOSIS OF POTATO)
Change the size of potato bigger size
A dipeptide consists of two amino acids joined by a peptide bond.
Dipeptides may differ in the type of amino acids they contain.
Describe two other ways in which all dipeptides are similar and one way in
which they might differ.
A dipeptide has amine group at the end
Has carboyxl group at the end
Difference -> Different R groups
Describe how a non-competitive inhibitor can reduce the rate of an
enzyme-controlled reaction.
Binds to the allosteric site
Active site changes shape no longer complementary to the shape of the substrate so the substrate cant bind
Less enzyme substrate complexes formed
The scientist concluded that pectin is a non-competitive inhibitor of the
lipase enzyme.
Use Figure 1 to explain why the scientist concluded that pectin is a non
competitive inhibitor.
With inhibitor lipid concentration does not increase
Describe how a peptide bond is formed between two amino acids to form a
dipeptide.
Amine group NH2 and Carboxyl group COOH join together by condensation reaction
The secondary structure of a polypeptide is produced by bonds between
amino acids.
Describe how.
Hydrogen bonds
Between amine group and carboxyl group
Forming B pleated sheet and alpha helix structure
Two proteins have the same number and type of amino acids but different
tertiary structures.
Explain why.
Different amino acid sequence
Which forms hydrogen bonds in different places
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how.
REDUCES ACTIVATION ENERGY
DUE TO BENDING BONDS
Lyxose binds to the enzyme.
Suggest a reason for the difference in the results shown in the graph with
and without lyxose.
Binding) alters the tertiary structure of the enzyme ;
Max 1
if lyxose acting as an inhibitor
OR if answer linked to lower rate of reaction
OR if lyxose used an energy source/respiratory
substrate
(This causes) active site to change (shape);
(So) More (successful) E-S complexes form (per minute)
The genetic code is described as degenerate.
WHAT is meant by this
more than one codon codes for a single amino acid
A change from Glu to Lys at amino acid 300 had no effect on the rate of
reaction catalysed by the enzyme. The same change at amino acid 279
significantly reduced the rate of reaction catalysed by the enzyme.
Use all the information and your knowledge of protein structure to suggest
reasons for the differences between the effects of these two changes.
Change at amino acid 300 does not change the shape of the active
Amino acid 279 may have been involved in a (ionic, disulfide or HYDROGEN bond so the shape of the active site changes
The scientist joined DNA molecules together to make tiny cages. The cages are exactly 20
nm long, 20 nm wide and 17 nm deep.
He trapped one GOx molecule and one HRP molecule together in each cage. The GOx
molecule and HRP molecule fill 9% of the cage volume.
The volume of a GOx molecule is eight times larger than an HRP molecule.
Use this information to calculate the volume of a GOx molecule. Give the appropriate unit
with your answer.
Show your working.
544
what can you conclude from Figure 2 about the effect of trapping GOx and HRP inside
cages?
trapping increases enzyme activity
SDs dont develop
