Module 1 Longer Mark EQS

Question 1

Describe how an enzyme, such as pepsin, breaks down a substrate. (5)

Answer 1

substrate / protein , shape is (nearly) complementary to
active site

substrate / protein , enters / fits into , active site (on
enzyme) ;

induced fit / description of induced fit ;

(forms) enzyme-substrate complex / ESC ;

destabilising / straining / AW , of bonds (in substrate) ;
then (forms) enzyme-product complex ;

product(s) / amino acids , leave (active site) ;

Question 2

Describe the formation of a hydrogen bond between two molecules of water and explain why water can form these bonds. (3)

Answer 2

between O and H (of adjacent molecules) ;
between , electropositive / δ+ / delta+ (H), and ,
electronegative / δ- / delta- (O) ;
water molecule , is polar / has charge separation ;

Question 3

Why is the ability of water to act as a solvent important for the survival of organisms? (3)

Answer 3

medium for (metabolic) reactions ; (because) allows (named) ionic compound(s) to separate ;
transport ;
two named transport , systems / media
one example of a transport , medium / system , with a
named example of what is transported ; - blood, xylem, phloem, tissue fluid
(organisms can) absorb / take in , (named) minerals /
ions / (named) gas / food ; -
able to dilute toxic substances ;

Question 4

Describe the structure of the collagen molecule. (6)

Answer 4

peptide bonds , between amino acids / in
polypeptide ;
every 3rd amino acids is , same / glycine ;
coil / twist / spiral / helix ;

left-handed (helix) ;
glycine / small R group , allows closeness /
twisting (of polypeptide chains) ;
three polypeptide chains ;
hydrogen / H , bonds between (polypeptide)
chains ;
no / few, hydrophilic (R) groups on outside (of
molecule) ;
(adjacent molecules joined by) crosslinks ;

crosslinks / ends of molecules , being
staggered ;
fibril ;

Question 5

Describe three other ways in which the structure of haemoglobin differs from that of
collagen. (3)

Answer 5

• globular protein
• hydrophobic R groups are found on the inside, hydrophilic R groups are on the outside
• 4 polypeptide chains –> two alpha, two beta

Question 6

Describe ways in which the physical properties of water allow organisms to survive over
a range of temperatures. (9)

Answer 6

V1 high latent heat of vaporisation / large amount of energy
required to change from liquid to gas / AW ;
V2 evaporation is (efficient) cooling mechanism / AW ;
V3 example of cooling in living organism ;

H1 high specific heat capacity / large amount of energy needed
to, raise / change, temperature ;

H2 (thermally) stable environment for, aquatic /

named aquatic, organisms ;
H3 (aquatic) organisms use less energy on temperature
control ;
H4 (internal) temperature of organisms changes only slowly ;
H5 (biological) reactions / enzymes / metabolism, function(s)
correctly ;

F1 ice, is less dense than water / floats ;
F2 (surface of) ice provides habitat for, organisms / named
organism
I1 water (beneath ice), insulated / remains liquid / doesn’t
freeze ;

I2 (aquatic) organisms, do not freeze / can still swim ;
S1 (effective) solvent ;
S2 medium for reactions / (internal) transport medium / able to
dilute toxic substances
C1 cohesion / adhesion ;
C2 example of cohesion / adhesion, in living organism ;
T1 surface tension ;
T2 habitat for (named) invertebrates ;

Question 7

List three other examples of where hydrogen bonds are found in biological molecules. (3)

Answer 7

protein secondary structure / α-helix / -pleated sheet ;
(protein) tertiary structure ;e.g. between adjacent chains in collagen
between polypeptide chains in (named) quaternary
structure ;

(between chains of) cellulose ;
(between, strands of / bases in) DNA ;
between mRNA and tRNA
binding between enzyme and substrate
(coiling of) amylose
between DNA and mRNA during transcription

Question 8

Describe the structure of a haemoglobin molecule. (7)

Answer 8

sequence / chain, of amino acids ;
(amino acids) joined by peptide bonds ;

secondary
alpha / α, helix ;
small regions of, beta / β, pleated sheet / fold ;
hydrogen / H, bonds ;

tertiary
secondary structure / helix / polypeptide chain, undergoes
further, coiling / folding ;
3 bonds / interactions from: disulphide / ionic / hydrogen /
hydrophobic or hydrophilic ;
hydrophilic R groups on outside (of molecule) / hydrophobic
R groups on inside (of molecule) ;

quaternary
4, polypeptides / subunits ;
2, alpha / α, chains and 2, beta / β, chains ;
1 haem (group) per polypeptide / 4 haems (per molecule) ;
prosthetic group (is) haem, (which) contains Fe2+ ;

Question 9

Describe the ways in which the structure of collagen is similar to the structure of haemoglobin. (4)

Answer 9

(collagen has)
amino acid, chain / sequence ;
peptide bonds ;
helical / helix ;
3 bonds / interactions from: disulfide / ionic / hydrogen /
hydrophobic or hydrophilic ;

quaternary structure ;
more than one polypeptide / subunit ;

Question 10

Describe the structure of a triglyceride molecule. (3)

Answer 10

(one) glycerol / glyceride ;
3 fatty acids ;
ester bond (between glycerol and fatty acid) ;

Question 11

State three roles of lipids in living organisms. (3)

Answer 11

(thermal) insulation ;
energy, store / source / release ;

protection ;
membranes / phospholipid bilayer /

control entry and exit into cells ;

(steroid) hormones / named steroid hormone ;
buoyancy ;
waterproofing ;
source of water (from respiration) ;
(electrical insulation) in myelin / around neurones /

around axons / around dendrons ;

aid, absorption / storage / production, of,

fat soluble / A / D / E / K, vitamins ;

Question 12

Three properties of water that contribute to this stability are as follows:
* the density of water decreases as the temperature falls below 4 °C so ice floats on the
top of the pond
* it acts as a solvent for ions such as nitrates (NO3–)
* a large quantity of energy is required to raise the temperature of water by 1 °C.
Explain how these three properties help organisms survive in the pond.

Answer 12

ice floats
(ice less dense because) molecules spread out ;
molecules form, crystal structure / lattice / AW ;
ice forms insulating layer / clearly described ;
water (below ice), does not freeze / still liquid /

remains water / kept at higher temperature ;

organisms do not freeze ;
animals / organisms, can still, swim / move ;
allows, currents / nutrients, to circulate ;
solubility
ions / named ion, polar / charged ;
ions /named ion, attracted to / bind to / interact with, water;
(named) organisms / plants / animals,
uptake / AW, minerals / named mineral / nutrients ;
correct use of named, mineral / nutrient, in organism

Question 13

Describe how these R groups can interact to determine the tertiary structure of a protein.

Answer 13

some R groups, attract / repel ;
2 disulfide, bridges / bond ;
3 between, cysteine / SH / S (atoms) ;
4 hydrogen / H, bonds ;
5 ionic bonds between, oppositely charged / + and -, R groups ;
6 hydrophilic R groups, on outside of molecule / in contact with
water (molecules) ;
7 hydrophobic R groups,
on inside of molecule / shielded from water (molecules)

Question 14

Describe the structure of a plasma (cell surface) membrane. 3

Answer 14

phospholipid bilayer containing proteins ;
head / hydrophilic region, facing outwards
OR
tail / hydrophobic region, facing inwards ;
ref to intrinsic and extrinsic (glyco)proteins /
described ;

idea of: glycoproteins / glycolipids, sticking out (of
bilayer / membrane);

cholesterol, inside bilayer / between phospholipids

Question 15

Explain the effects of competitive inhibitors on the rate of an enzyme controlled reaction

Answer 15

1 inhibitor has similar shape to substrate;
2 can, fit / occupy, active site;
3 for short time / temporary / reversible;
4 prevents / blocks, substrate from entering active site;
5 rate determined by relative concentrations;
6 little inhibition / rate little reduced,if substrate conc. > inhibitor conc.;ora
7 ref to chance of, substrate / inhibitor, entering active site;
8 effects can be reversed by increasing substrate conc.;