exam question Flashcards
Raffinose is a trisaccharide of three monosaccharides: galactose, glucose
and fructose. The chemical formulae of these monosaccharides are:
* galactose = C6H12O6
* glucose = C6H12O6
* fructose = C6H12O6
Give the number of carbon atoms, hydrogen atoms and oxygen atoms in a
molecule of raffinose.
C = 18, H = 32, O = 16
A biochemical test for reducing sugar produces a negative result with
raffinose solution.
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.
- Heat with acid and neutralise
- Heat with Benedict’s (solution)
- Red precipitate/colour
Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.`
- Cellulose is made up of β-glucose (monomers) and glycogen is
made up of α-glucose (monomers) - Cellulose molecule has straight chain and glycogen is branched
During early pregnancy, the glycogen in the cells lining the uterus is an
important energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer.
- Hydrolysed (to glucose);
- Glucose used in respiration;
Name the type of chemical bond that joins the two monomers to form maltose.
glycosidic bond
Explain how cellulose molecules are adapted for their function in plant
cells.
- Long and straight chains
- Become linked together by many hydrogen bonds to form fibrils
- Provide strength (to cell wall).
Describe how you would test for the presence of a lipid in a liquid sample of
food.
- Add ethanol/alcohol then add water and shake/mix
- White/milky (emulsion)
Scientists investigated the percentages of different types of lipid in plasma
membranes from different types of cell. The table shows some of their results.
The scientists expressed their results as Percentage of lipid in plasma
membrane by mass. Explain how they would find these values.
- Divide mass of each lipid by total mass of all lipids (in that type
of cell); - Multiply answer by 100.
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.
- Boil
- Denatures the enzyme/ATP synthase;
A competitive inhibitor decreases the rate of an enzyme-controlled
reaction.
Explain how
- Inhibitor similar shape to substrate
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 (relative) position of amino acid/R
group/interactions - Primary structure is sequence/order of amino acids
- Secondary structure formed by hydrogen bonding (between amino
acids)
alpha helix/β-pleated sheet - Tertiary structure formed by interactions between R groups
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / - Creates active site in enzymes/ complementary/specific shapes in antibodies/carrier
proteins/receptor (molecules) - Quaternary structure contains >1 polypeptide chain
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 - (So in chain) there is a free amine/NH2 group at one end and a free carboxyl/COOH group at the other
Describe two other ways in which all dipeptides are similar and one way in
which they might differ.
SIMILARITIES
1. Amine/NH2 (group at end)
2. Carboxyl/COOH (group at end)
DIFFERENCES
3. Variable/different R group(s)
Explain how the active site of an enzyme causes a high rate of reaction
- Lowers activation energy
- Induced fit causes active site (of enzyme) to change shape
- (So) enzyme-substrate complex causes bonds to form/break
Two proteins have the same number and type of amino acids but different
tertiary structures.
Explain why
- Different sequence of amino acids
- Forms ionic / hydrogen / disulfide bonds in different places;
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how
- Reduces activation energy;
- Due to bending bonds
the role of the DNA nucleotides
Forms complementary pairs / A – T, G - C
the role of the single-stranded DNA fragments
- Template;
- Determines order of nucleotides/bases;
The arrows in Figure 2 show the directions in which each new DNA strand is
being produced.
Use Figure 1, Figure 2 and your knowledge of enzyme action to explain
why the arrows point in opposite directions.
- (Figure 1 shows) DNA has antiparallel strands / described;
- (Figure 1 shows) shape of the nucleotides is different / nucleotides aligned differently
- Enzymes have active sites with specific shape
- Only substrates with complementary shape /only the 3’ end can bind with active site of enzyme / active site of DNA polymerase
Scientists investigated treatment of a human bladder infection caused by a
species of bacterium. This species of bacterium is often resistant to the
antibiotics currently used for treatment.
They investigated the use of a new antibiotic to treat the bladder infection. The
new antibiotic inhibits the bacterial ATP synthase enzyme.
The new antibiotic is safe to use in humans because it does not inhibit the
ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase
is inhibited.
Human ATP synthase has a different tertiary structure to bacterial ATP synthase, so they are not complementary
ATP is an energy source used in many cell processes.
Give two ways in which ATP is a suitable energy source for cells to use.
- Releases relatively small amount of energy / little energy lost as heats energy instantaneously
- Phosphorylates other compounds, making them more reactive
- Can be rapidly re-synthesised
Explain why it is not possible to determine the identity of the structures
labelled X using an optical microscope.
- Resolution (too) low;
- Because wavelength of light is (too) long;
Describe the role of one named organelle in digesting these bacteria.
- Lysosomes;
- Fuse with vesicle;
- (Releases) hydrolytic enzymes;
