TEST: BIOCHEMISTRY
NAME:
1. Enzymes are used by living organisms to catalyse reactions. Some of these reactions occur in the
cytoplasm of cells. Other reactions take place outside cells, for example the digestion of foods in the
human gut.
(a)
State the name used by biochemists for the chains and cycles of reactions that occur inside cells.
(1)
(b)
Enzymes of digestion in humans are secreted by glands. They have a pH optimum which allows
them to work efficiently in the part of the gut into which they are secreted.
(i)
In the table below, identify the missing enzyme, the two glands, and the pH optimum
Name of
enzyme
amylase
Gland secreting
the enzyme
Substrate
Products
starch
maltose
triglycerides
fatty acids and
glycerol
pH optimum
7
(4)
(ii)
Outline the effect of pH values above and below the optimum on enzyme structure.
(2)
(c)
Enzymes that work inside cells are sometimes affected by non-competitive inhibitors. Explain how
a non-competitive inhibitor affects the activity of an enzyme.
(3)
(Total 10 marks)
2. Outline two examples of the commercial application of named enzymes in biotechnology.
(Total 6 marks)
3. List four functions of proteins, giving an example of each.
(Total 4 marks)
4.
(a)
Define the term active site of an enzyme.
1
(1)
(b)
Outline how enzymes catalyze biochemical reactions.
(2)
(c)
Explain the effect of pH on enzyme activity.
(3)
(d)
State three functions of lipids.
(2)
(Total 8 marks)
(Total 8 marks)
5. To which parts of the deoxyribose molecule do phosphates bind in DNA?
V
CH2 OH
I
O
H
IV
H
H
H
OH
II
OH
H
III
A.
I and V
B.
III and IV
C.
II and III
D.
III and V (1)
(1)
(1)
6. The diagram below shows a channel protein in a membrane. Which parts of the surface of the protein
would be composed of polar amino acids.
A.
I and II only
B. II and III only
C. III and IV only
D. I and IV only
(1)
7. Consider the metabolic pathway shown below.
2
A
1
B
2
C
3
4
D
E
If there is end-product inhibition, which product (B to E) would inhibit which enzyme (1 to 4)?
Product
Enzyme
A.
C
4
B.
B
3
C.
B
4
D.
E
1
(1)
8. Which is not a primary function of protein molecules?
A.
Hormones
B.
Energy storage
C.
Transport
D.
Structure
(1)
9. What can reduce the effect of a competitive inhibitor of an enzyme?
A.
Decrease the temperature at which the reaction takes place.
B.
Increase the temperature at which the reaction takes place.
C.
Increase the substrate concentration.
D.
Add a non-competitive inhibitor.
(1)
1.
(a)
metabolic pathways/metabolic
reactions/metabolism/anabolism and catabolism
(b)
(i)
(ii)
(c)
salivary gland / pancreas;
pH 7.5 ( 0.5);
lipase; (accept lipidase)
pancreas;
ionic bonds / polar bonds broken / disrupted /
charge distribution altered;
ionization of amino / carboxyl groups altered;
conformation / shape of enzyme / active site altered /
tertiary structure altered;
enzyme denatured;
inhibitor binds (to the enzyme) away from the active site /
at allosteric site;
shape / (intramolecular) bonding / conformation of the protein /
enzyme is altered;
shape / properties of active site altered;
substrate no longer fits the active site /
no enzyme-substrate/ES complex formed;
no enzyme activity /
works more slowly (until the inhibitor dissociates);
Award [1 max] if competitive inhibition is described.
1
4
2 max
3 max
[10]
2. the name of the enzyme and the substrate;
3
the name(s) of the product(s);
a statement as to why the application is useful commercially;
Award [3 max] for each example.
e.g. pectinase acts on soluble pectin;
produces smaller, more soluble carbohydrates;
used in fruit juice clarification/improving fruit juice yield;
e.g. DNA endonuclease acts on DNA;
produces DNA fragments;
used in genetic engineering;
e.g. protease acts on insoluble proteins;
produces amino acids;
washing powders – stain removal;
Accept other suitable examples.
[6]
3. Name of function and named protein must both be correct for the mark.
storage – zeatin (in corn seeds) / casein (in milk);
transport – hemoglobin / lipoproteins (in blood);
hormones – insulin / growth hormone / TSH / FSH / LH;
receptors – hormone receptor / neurotransmitter receptor /
receptor in chemoreceptor cell;
movement – actin / myosin;
defence – antibodies / immunoglobin;
enzymes – catalase / RuBP carboxylase;
structure – collagen / keratin / tubulin / fibroin;
electron carriers – cytochromes;
pigments – opsin
active transport – sodium pumps / calcium pumps;
facilitated diffusion – sodium channels / aquaporins;
Mark first four functions only. Allow other named examples.
[4]
4. (a) the site (on the surface of an enzyme) to which substrate(s) bind / the site (on the
enzyme) where it catalyzes a chemical reaction;
(b)
bring substrates close together in active site / in correct orientation;
forms enzyme-substrate complex / substrate(s) bind to active site;
lowers the activation energy for the reaction;
weakens bonds in the substrate;
1
2 max
(c)
enzymes have an optimal pH;
lower activity above and below optimum pH / graph showing this;
too acidic / basic pH can denature enzyme;
change shape of active site / tertiary structure altered;
substrate cannot bind to active site / enzyme-substrate complex cannot form;
hydrogen / ionic bonds in the enzyme / active site are broken / altered;
3 max
(d)
energy storage / source of energy / respiration substrate;
(heat) insulation;
protection (of internal organs);
water proofing / cuticle;
buoyancy;
(structural) component of cell membranes;
electrical insulation by myelin sheath;
(steroid) hormones;
glycolipids acting as receptors;
Three correct [2], one or two correct [1].
2 max
4
Use one tick to mark the first one or two correct answers. Use a second tick to mark the third
correct answer. Mark the first three answers only.
5.
6.
7.
8.
9.
D
A
D
B
C
5