biomolecules

Question 1

Explain why phenylalanine and tyrosine are classified as amino acids.

Answer 1

both have an
amine / amino / NH2 ;
COOH / carboxyl / carboxylic ;

Question 2

Name the covalent bond between two adjacent amino acids in a chain of amino acids.

Answer 2

peptide (bond / link) ;

Question 3

Name the type of reaction involved in breaking this bond and describe what happens in this reaction.

Answer 3

hydrolysis ;

water / H2O , is , added / used / needed ;

Question 4

Erythrocytes contain haemoglobin, which is a globular protein.Blood vessel walls contain collagen, which is a fibrous protein.
Describe the differences between globular and fibrous proteins using haemoglobin and collagen as examples.
In your answer you should refer to collagen and haemoglobin.

Answer 4

Globular
ball (shaped) / spherical / AW ;
hydrophilic , (R-)groups / regions , on outside (of 3-D
structure) / hydrophobic (R-)groups on inside ;
form H-bonds with water ;
soluble ;
example of globular protein (other than haemoglobin) ;
haemoglobin , carries / transports , oxygen / carbon
dioxide ;
haemoglobin contains , prosthetic group / haem / Fe2+ /
iron ion (to allow oxygen to be carried) ;
(polypeptide chains within) haemoglobin have tertiary
structure (in a ball shape) ;
Fibrous
linear / long (chain) ;
(chains can) form (H) bonds with adjacent , chains
(within a molecule) ;
insoluble / few hydrophilic groups ;
strong / provide strength ;
have structural role ;
collagen has high proportion of glycine , so chains can
lie close together / AW ;
collagen forms , crosslinks / covalent bonds , between
molecules ;
crosslinks / ends of molecules, are staggered to avoid ,
weak points / AW ;
collagen forms part of , tendon / cartilage / ligament /
bone / connective tissue / bronchi / bronchioles /
trachea / skin ;

Question 5

Describe how to do the emulsion test for lipids and how a positive result would be identified.

Answer 5

mix with / add , ethanol / alcohol , and water ;

(goes) cloudy ;

Question 6

How might the lipid content of mycoprotein differ from food that comes from animals?

Answer 6

less (overall , lipid / fat) ;
less / no , saturated (fat / lipid / fatty acids) ;
more unsaturated (fat / lipid / fatty acids) ;

Question 7

Complete the following table to show three other differences in the structures of starch (amylose) and cellulose molecules.

Answer 7

(contains) α / alpha / A /
a ,-glucose
(contains) β / beta / B / b
, -glucose ;
α / alpha / A / a 1-4
glycosidic bonds
β / beta / B / b 1-4
glycosidic bonds ;
all , monomers / AW , in
same orientation
alternate monomers at ,
180° / AW , to each other ;
granular / not fibrous fibrous / not granular ;
H bonds within molecule
/ no (H) bonds (between
molecules)
(H) bonds between
adjacent molecules

Question 8

Which properties of cellulose make it suitable for forming cell walls?

Answer 8

(tensile) strength / strong ;
(H) bonds / links , can form (between adjacent fibrils) ;
insoluble ;

Question 9

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

Answer 9

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

Question 10

Hydrogen bonds allow water to act as a solvent.Why is the ability of water to act as a solvent important for the survival of organisms?

Answer 10

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

Question 11

State one property of collagen that makes it a useful component of blood vessel walls.

Answer 11

strength / toughness / insolubility ;

Question 12

Describe the structure of the collagen molecule.

Answer 12

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 13

State one function of haemoglobin.

Answer 13

transport / AW , of, oxygen / O2 ;

Question 14

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

Answer 14

haemoglobin (has / is):
globular ;
hydrophobic (R) groups on inside / hydrophilic
(R) groups on outside ;
4 , chains / sub-units / polypeptides ;
idea that subunits are (two) different types ;
α / alpha , helix ;
idea that proportion of glycine similar to that ,
of other amino acids / in other proteins ;

Question 15

Identify two differences and two similarities in the structures of triglycerides and phospholipids

Answer 15

triglyceride phospholipid
difference 3 fatty acids 2 fatty acids ;
difference 3 ester bonds 2 ester bonds ;
difference absence of phosphate presence of phosphate ;
similarity (contain) glycerol ;
similarity (contain) fatty acids ;
similarity (contain) ester bonds ;
similarity (contain elements) C,H and O ;

Question 16

Name the test used to identify the presence of lipids.

Answer 16

emulsion (test) ;

Question 17

Describe how you would carry out this test on a food sample.

Answer 17

emulsion test
1 add , ethanol / alcohol , (to sample) ;
2 shake / stir / agitate / mix thoroughly / AW ;
3 add (to) water ;
If candidate is clearly describing Sudan III test
5 mix sample with water ;
6 add Sudan III (stain) ;
7 shake / stir / agitate / mix thoroughly / AW ;
If candidate is describing translucent grease mark test
AWARD one mark only ;

Question 18

State the expected result if lipid is present in the food sample.

Answer 18

(mixture) turns, cloudy / milky / white ;

Question 19

Name the precise group of carbohydrate molecules of which glucose is an example.

Answer 19

monosaccharides

Question 20

State and explain two ways in which the glucose molecule is well suited to its function in living organisms.

Answer 20

soluble so can be (easily) , transported / carried
(around organism) ;
small (molecule) so can , be transported / diffuse ,
across (cell) membranes ;
easily / quickly , respired / oxidised / broken down , to ,
release energy / produce ATP ;
molecules can , join / AW , to produce , (named)
disaccharides / (named) polysaccharides

Question 21

Identify three mistakes made by the student when describing the structure of cellulose.

Answer 21

α-glucose /
β-glucose ;
some / no , 1–6 bonds
or
only 1 –4 bonds ;
condensation / hydrolysis ;
branches / straight chain ;

Question 22

Suggest the name of a molecule that closely matches the student’s description.

Answer 22

glycogen / amylopectin

Question 23

identify the type of carbohydrate molecule of which the carbohydrate agarose is an example.

Answer 23

polysaccharide

Question 24

Suggest two ways in which the reliability of the experiment could be improved.

Answer 24

replicate(s) / repeat(s) ;
more than one sample tested from each tube / sample
each tube twice ;

Question 25

Name the polymer formed from a chain of amino acids.

Answer 25

polypeptide / protein

Question 26

Name the bond that is formed when two amino acids are joined together. Describe the formation of this bond.

Answer 26

``` peptide (bond / link) ; plus any two from ... description of formation between, amine group (of one amino acid) and carboxyl group (of another) ; H (from amine) combines with OH (from carboxyl) ; condensation (reaction) OR water, lost / eliminated / produced / created / AW ; ```

Question 27

Many of the physical properties of water arise as a result of these hydrogen bonds.Describe ways in which the physical properties of water allow organisms to survive over a range of temperatures. In your answer you should make clear links between the properties of water and the survival of organisms.

Answer 27

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 ; P1 transparent ; P2 allows underwater photosynthesis ; D1 idea of high density ; D2 allows flotation / support ; U organisms can still obtain, oxygen / (named) minerals / food / carbon dioxide, from water ;

Question 28

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

Answer 28

protein secondary structure / α-helix / -pleated sheet ; (protein) tertiary structure ; between polypeptide chains in (named) quaternary structure ; (between chains of) cellulose ; (between, strands of / bases in) DNA ;

Question 29

State two roles of cholesterol in living organisms.

Answer 29

regulates fluidity of / stabilises / AW, membranes / phospholipid bilayer ; (converted to) steroid / named steroid, hormone(s) ; waterproofing the skin ; making Vitamin D ; making bile (salts) ;

Question 30

Identify one way in which the molecular structure of cholesterol is similar to the molecular structure of a carbohydrate.

Answer 30

contains C and H and O ; has, OH / hydroxyl, groups ; hex / 6-membered, ring ;

Question 31

Cholesterol is transported in the blood within molecules of low-density lipoprotein (LDL).Name two molecules that combine with cholesterol to form LDLs.

Answer 31

(saturated) lipids / fats / triglycerides ; | protein / polypeptide ;

Question 32

Explain why glycogen makes a good storage molecule.

Answer 32

insoluble ; does not , change / affect , water potential / Ψ , of cell ; can be , broken down / hydrolysed / built up , quickly / easily ; lots of branches for enzymes to attach ; compact ; (therefore) high energy content for mass / energy dense / AW ;

Question 33

When glycogen is hydrolysed, mole A is produced. State the precise name of molecule A State one function of molecule A.

Answer 33

α /alpha , glucose ; respiratory substrate / used for respiration ; source of / releases / provides, energy ; formation of ATP ; conversion into named compound ;

Question 34

Complete the table below to give three differences in the structures of glycogen and cellulose.

Answer 34

``` glycogen cellulose no hydrogen bonding hydrogen bonding α / alpha , glucose β / beta , glucose ; 1,4 and 1,6-glycosidic bonds or 1,6-glycosidic bonds present 1,4-glycosidic bonds (only) or 1,6-glycosidic bonds not present ; branched not branched / linear / straight ; no , fibres / fibrils fibres / fibrils ; granules no granules ; all glucose units in same orientation adjacent glucose units in opposite orientation ```

Question 35

Name the monomers that make up: proteins RNA

Answer 35

``` amino acid(s) ; nucleotide(s) ; ```

Question 36

Describe how a hydrogen bond is formed.

Answer 36

between oxygen and hydrogen (atoms) ; | (between) electronegative / δ-, and electropositive / δ+ ;

Question 37

suggest what would happen to the iodine-amylose complex if the solution was heated to 60 °C

Answer 37

hydrogen / H, bonds break ; helix, lost / unravels / AW ; iodine, released / no longer in complex / AW ;

Question 38

Haemoglobin is a globular protein.Describe the structure of a haemoglobin molecule. In your answer, you should include details of the secondary, tertiary and quaternary structure of the molecule.

Answer 38

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: disulfide / 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 39

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

Answer 39

``` (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 ; ```