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OCR AS/A Level Biology Exam Questions > module 2.2: biological molecules > Flashcards

module 2.2: biological molecules Flashcards

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1
Q

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

A

peptide (bond / link)

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2
Q

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

A
  • hydrolysis
  • water / H2O , is , added / used / needed
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3
Q

describe how an enzyme, such as pepsin, breaks down a substrate

A
  • 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)
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4
Q

identify three errors the student made in the preparation of his table before he recorded his results.

A
  • no units for , 2nd column / egg white
  • amount (rather than volume / in 4th column)
  • incorrect unit / m , in final / time , column
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5
Q

identify a change the student could make to his procedure that would increase the
validity of the investigation

A
  • equal volume in each tube
  • add buffer / control pH
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6
Q

state the term that best describes the purpose of tube 6

A

control

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7
Q

another student suggested that he should repeat the investigation at least twice. how would this have improved the investigation

A
  • improve reliability
  • assess, variability / spread of results
  • allows calculation of mean
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8
Q

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

A
  • mix with / add , ethanol / alcohol , and water
  • (goes) cloudy
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9
Q

lipids form an essential part of a balanced diet. some food, such as mycoprotein, is produced by microorganisms. how might the lipid content of mycoprotein differ from food that comes from animals?

A
  • less (overall , lipid / fat)
  • less / no , saturated (fat / lipid / fatty acids)
  • more unsaturated (fat / lipid / fatty acids)
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10
Q

select the letters of the features that describe the primary level of protein structure.

A

B and D

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11
Q

select the letter or letters of the feature(s) found in the secondary level of protein structure that are not present in the primary structure

A

A and E

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12
Q

select the letter or letters of the feature(s) that are found in the tertiary level of protein structure that are not present in the primary and secondary structures

A

F and G

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13
Q

select the letter or letters of the feature(s) found only in the quaternary level of protein structure

A

C

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14
Q

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

A
  • between O and H (of adjacent molecules)
  • 2 between , electropositive / δ+ / delta+ (H), and , electronegative / δ- / delta- (O)
  • water molecule , is polar / has charge separation
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15
Q

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

A
  • medium for (metabolic) reactions (because) allows (named) ionic compound(s) to
    separate
  • transport ( eg. xylem and phloem)
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16
Q

amino acids form part of the structure of proteins. state the name given to the sequence of amino acids in a protein molecule

A

primary structure

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17
Q

draw the general structure of an amino acid molecule in the space below

A
  • NH2 at one end
  • COOH at opposite end
  • C in centre (of a single amino acid) bonded (separately) to one R and one H
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18
Q

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

A
  • strength / toughness / insolubility
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19
Q

describe the structure of the collagen molecule

A
  • 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) - insoluble
  • (adjacent molecules joined by) crosslinks
  • crosslinks / ends of molecules , being
    staggered
  • fibril
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20
Q

state one function of haemoglobin

A

transport , of, oxygen / O2

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21
Q

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

A
  • 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
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22
Q

name the polymer formed from a chain of amino acids

A

polypeptide/ protein

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23
Q

name the bond that is formed when two amino acids are joined together. describe the
formation of this bond.
name of bond ………………………
description of formation ………………………

A
  • peptide (bond / link)
  • 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 /
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24
Q

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

A
  • high latent heat of vaporisation / large amount of energy. evaporation is (efficient) cooling mechanism. eg. sweating
  • high specific heat capacity / large amount of energy needed to, raise / change, temperature which creates a(thermally) stable environment for, aquatic / named aquatic, organisms
    (aquatic) organisms use less energy on temperature control
    (internal) temperature of organisms changes only slowly so (biological) reactions / enzymes / metabolism, function(s) correctly
  • ice, is less dense than water / floats and the (surface of) ice provides habitat for, organisms / named organism
  • water (beneath ice), insulated / remains liquid / doesn’t freeze so (aquatic) organisms, do not freeze / can still swim
  • (effective) solvent so medium for reactions / (internal) transport medium / able to dilute toxic substances ;
  • cohesion / adhesion. example of cohesion / adhesion, in living organism ; C2 e.g. transpiration stream / apoplast movement
  • surface tension which creates a habitat for (named) invertebrates
  • transparent allows underwater photosynthesis
  • idea of high density which allows flotation / support ;
  • organisms can still obtain, oxygen / (named) minerals / food / carbon dioxide, from water
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25
Q

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

A
  • protein secondary structure / α-helix / beta -pleated sheet
  • (protein) tertiary structure
  • between polypeptide chains in (named) quaternary structure
  • (between chains of) cellulose
  • (between, strands of / bases in) DNA
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26
Q

state two roles of cholesterol in living organisms

A
  • regulates fluidity of / stabilises, membranes / phospholipid bilayer
  • (converted to) steroid / named steroid, hormone(s)
  • waterproofing the skin
  • making Vitamin D
  • making bile (salts)
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27
Q

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

A
  • contains C and H and O
  • has, OH / hydroxyl, groups
  • hex / 6-membered, ring
28
Q

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

A
  • (saturated) lipids / fats / triglycerides
  • protein / polypeptide
29
Q

LDL and a similar molecule, high density lipoprotein (HDL), carry cholesterol in the blood. LDL and HDL affect the formation of atheromas in the arteries.
describe the different ways in which LDLs and HDLs affect the formation of atheromas.

A

LDL
- (carry cholesterol) from liver to, tissues / cells
- receptors on (tissue) cells
- raise / AW, blood cholesterol
- increase / cause, deposition of, fats / lipids / triglycerides / cholesterol,
in artery wall / under endothelium
- form, plaques / atheromas
HDL
- (carry cholesterol) from, tissues / body / blood, to liver
- receptors on, hepatocytes / liver cells
- lower / reduce / decrease, (blood) cholesterol
- reduce deposition, of fats / lipids / triglycerides / cholesterol
- decrease, formation / risk, of, plaques / atheromas

30
Q

suggest why diets with a high red meat content are associated with high blood
cholesterol

A
  • (red) meat contains (large amounts of) saturated, fat / fatty acids
  • (meat / saturated fat) associated with / leads to, increased / large
    amounts of, LDLs
31
Q

name a disease, other than atherosclerosis, for which high blood cholesterol is a risk factor

A
  • (type 2) diabetes
  • angina / coronary heart disease / CHD / stroke / hypertension / high
    blood pressure / obesity
32
Q

molecule E shown in Fig. 3.1 is part of the carbohydrate molecule glycogen.
explain why glycogen makes a good storage molecule

A
  • 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
33
Q

what is the function of alpha glucose

A

respiratory substrate / used for respiration ;
source of / releases / provides, energy ;
formation of ATP ;
conversion into named compound (eg. . starch / cellulose / polysaccharide /
disaccharide / glycogen / protein / lipid / sucrose / maltose / fructose / fat

34
Q

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

A

GLYCOGEN
- alpha glucose
- 1,4 and 1,6 glycosidic bonds
- hydrogen bonding
- no fibres
- granules
- not branched
- adjacent glucose units in opposite orientation
CELLULOSE
- beta glucose
- 1, 4 glycosidic bonds
- no hydrogen bonding
- fibres
- no granules
- adjacent glucose units in same orientation

35
Q

haemoglobin is a globular protein.
describe the structure of a haemoglobin molecule

A
  • 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+
36
Q

describe the ways in which the structure of collagen is similar to the structure of haemoglobin

A

(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

37
Q

triglycerides are a type of lipid found in milk.
describe the structure of a triglyceride molecule

A
  • (one) glycerol / glyceride
  • 3 fatty acids
  • ester bond (between glycerol and fatty acid)
38
Q

state three roles of lipids in living organisms

A
  • (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
39
Q

human populations with diets high in animal fats have a lower life expectancy than those with
diets high in vegetable oils. suggest one difference between lipids from animals and those from plants

A
  • saturated
  • (fatty acids have) no / fewer, double bonds
  • solid at room temperature
40
Q

suggest two medical conditions that may be associated with increased blood cholesterol
levels

A
  • coronary heart disease / CHD / cardio-vascular diseases / heart attack / cardiac arrest / myocardial infarction / MI / angina
  • atherosclerosis / atheroma
  • stroke
  • Type 2 diabetes
41
Q

a balanced diet is one which provides an adequate intake of energy and nutrients for the
maintenance of our body. if energy intake exceeds energy usage over a period of time, an
individual can become ……….…………………………. .
the deficiency disease anaemia can be caused by a lack of the mineral ……….…………………………. in the diet. as a result of this deficiency, the body is unable to produce sufficient amounts of the protein ……….…………………………. in red blood cells

A
  • obese
  • iron
  • haemoglobin
42
Q

ponds provide a very stable environment for aquatic organisms. 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.

A

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
ALSO
- 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 / , minerals / named mineral / nutrients
- correct use of named, mineral / nutrient, in organism (eg. nitrates for amino acids / protein /
nucleic acid / phosphate for ATP / phospholipids/ plasma membrane / magnesium for chlorophyll
TEMPERATURE STABILITY
- many / stable, (hydrogen) bonds between molecules
- at lot of energy to, force apart molecules / break bonds
- high (specific) heat capacity
- temperature does not change much / small variation in temperature
- effect of temperature on , enzymes / metabolic rate
- gases remain soluble

43
Q

the primary structure of a protein consists of a chain of amino acids. describe how a second amino acid would bond to cysteine in forming the primary structure of a protein

A
  • peptide bond
  • between, amine / J group (of one amino acid) and carboxyl / L group (of another)
  • H (from amine group ) combines with OH (from carboxyl group)
  • condensation reaction OR water, lost / eliminated / produced / created
  • covalent
44
Q

each amino acid has a different R group.
describe how these R groups can interact to determine the tertiary structure of a protein

A
  • some R groups, attract / repel
  • disulfide, bridges / bond
  • between, cysteine / SH / S (atoms)
  • hydrogen / H, bonds
  • ionic bonds between, oppositely charged / + and -, R groups
  • hydrophilic R groups, on outside of molecule / in contact with water (molecules)
  • hydrophobic R groups, on inside of molecule / shielded from water (molecules)
45
Q

complete the table below to give three differences between the structure of glycogen
and collagen

A

G - carbohydrate / polysaccharide
C- protein / polypeptide
G - (alpha) glucose (units)
C - amino acid (units)
G -identical units
C - different amino acid units
G - glycosidic, bonds / links
C - peptide, bonds / links
G - branched
C - linear / unbranched
G - non-helical
C - helical
G - one chain (per molecule)
C - three chains (per molecule)
G - no cross links
C -cross links (between chains)
G - contains C H O
C - contains C H O N

46
Q

collagen is found in the ligaments which hold bones together at joints. state two properties of collagen that make it suitable for this purpose

A
  • (high tensile) strength / strong
  • does not stretch / is not elastic
  • insoluble
  • flexible
47
Q

DNA is found in the nucleus. The molecule is twisted into a …………………………….
………………… in which each of the strands are …………………………………. . it has two
……………………………………… backbones attached to one another by complementary bases. these bases pair in the centre of the molecule by means of …………………………… bonds

A
  • double helix
  • anti-parallel
  • sugar-phosphate
  • hydrogen
48
Q

Complete the table below to show three ways in which the structure of DNA differs from that of RNA.

A

NUMBER OF STRANDS
DNA: 2
RNA: 1
BASES PRESENT
DNA: adenine, Thymine, guanine and cytosine
RNA: adenine, Uracil, guanine and cytosine
SUGAR PRESENT
DNA: deoxyribose
RNA: ribose

49
Q

state the role of messenger RNA (mRNA)

A
  • carries / transfers, the (complementary DNA) , code / genetic information / copy of gene
  • out of the nucleus
  • (transfers it) to the, ribosome / RER / site of translation
  • for, protein / polypeptide, synthesis
50
Q

The activity of an enzyme can be measured by testing for the concentration of its product at regular intervals. describe how the concentration of a reducing sugar can be measured using a colorimeter

A
  • using , standard / known , concentrations (of reducing sugar)
  • heat with , Benedicts (solution) / CuSO4 + NaOH
  • (use of) same volumes of solutions (each time)
  • (use of) excess Benedicts
  • changes to , green / yellow / orange / brown / (brick) red
  • remove precipitate / obtain filtrate
  • calibrate / zero , colorimeter
  • using , a blank / water / unreacted Benedicts
  • use (red) filter
  • reading of , transmission / absorbance
  • more transmission / less absorbance , of filtrate
    = more sugar present
  • (obtain) calibration curve
  • plotting , transmission / absorbance , against (reducing) sugar concentration
  • use reading of unknown sugar solution and read off graph to find conc
51
Q

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

A

GLOBULAR
- ball (shaped) / spherical
- 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) (eg. hormone / antibody /
channel / carrier)
- 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
- collagen forms , crosslinks / covalent bonds , between molecules
- crosslinks / ends of molecules, are staggered to avoid , weak points
- collagen forms part of , tendon / cartilage / ligament / bone / connective tissue / bronchi / bronchioles / trachea / skin

52
Q

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

A

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

53
Q

which properties of cellulose make it suitable for forming cell walls

A
  • (tensile) strength / strong
  • (H) bonds / links , can form (between adjacent fibrils)
  • insoluble
54
Q

state the colour of iodine solution in the presence of starch

A

blue - black

55
Q

hydrogen bonds hold the amylose molecule in its helical shape. describe how a hydrogen bond is formed

A
  • between oxygen and hydrogen (atoms)
  • (between) electronegative / δ-, and electropositive / δ+
56
Q

using the information in Fig. 2.1, suggest what would happen to the iodine-amylose complex if the solution was heated to 60 °C

A
  • hydrogen / H, bonds break
  • helix, lost / unravels / AW
  • iodine, released / no longer in complex
57
Q

describe how she could measure the change in concentration of maltose (reducing sugar) as
the reaction proceeds

A
  • take samples at a range of times
  • same volumes (of solutions) added / removed (each time)
  • heat with, Benedict’s (solution) / CuSO4 and NaOH
  • (use of ) excess Benedict’s
  • changes to, green / yellow / orange / brown / (brick) red
  • remove precipitate / obtain filtrate
  • colorimeter
  • calibrate / zero, using, a blank / water / (unreacted) Benedict’s
  • use (red / orange) filter
  • reading of, transmission / absorbance OR mass of precipitate
  • more transmission / less absorbance, of filtrate, OR greater mass ppt, = more maltose present
  • using, standard / known, concentrations (of maltose)
  • (obtain) calibration curve
  • plot, transmission / absorbance / mass of ppt, against (reducing sugar) concentration
  • use graph to read off concentration of maltose
58
Q

complete the following statement:
a sequence of DNA nucleotides that codes for a protein is a ………………….

A

gene

59
Q

suggest why DNA is not able to leave the nucleus

A
  • too big to / does not, fit through pore (in nuclear envelope)
60
Q

explain why the mRNA molecule is shorter than a DNA molecule

A
  • idea that only copies one, gene / section / part , (of DNA)
  • idea that DNA comprises many, genes / alleles
61
Q

the Roman Emperor Claudius was poisoned by his wife Agrippina when she gave him
death cap fungus to eat. the death cap fungus contains α-amanitin.
suggest how the toxin α-amanitin may lead to the death of an organism

A
  • inhibits production of mRNA / mRNA not produced ;
  • prevents protein synthesis
  • specific named protein / (vital) process, that may be affected (eg. respiration / photosynthesis / haemoglobin / cytochrome C oxidase
62
Q

state the meaning of the term primary structure

A

sequence / order, of amino acids

63
Q

when proteins are heated to a high temperature, their tertiary structure is disrupted. explain how this occurs

A
  • increased kinetic energy
  • (any part of protein molecule) vibrates
  • hydrophilic / hydrophobic / hydrogen / ionic, bonds / interactions, break
  • change in, 3D shape / conformation (of protein)
  • denatures
64
Q
  • titin is a fibrous protein. pepsin is a globular protein. compare the properties and functions of fibrous proteins and globular proteins in the human body
A

FIBROUS PROTEINS
Properties:
* insoluble
* elongated / long / rods / filaments / ropes / strands
* strong / tough
* flexible
Functions:
* for structure
* collagen in, bone / cartilage / connective tissue / tendons / ligaments / skin / blood vessels
* fibrin + role described
* for protection
* keratin in, skin / hair / nails
* to give, elasticity / elastic properties
* elastin in, (named) blood vessels / alveoli / cartilage
* for, contraction / mechanical movement
* actin / myosin, in muscle
* microtubules in, cilia / flagella / spindle / cytoskeleton
GLOBULAR PROTEINS
Properties:
* soluble
* spherical / ball-shaped
* have, 3D / tertiary / 3o, shape / structure
* specific / complementary (to another molecule)
* ref. conjugated / contain prosthetic group
* temperature / pH, sensitive
* hydrophilic on outside
Functions:
* enzymes / metabolic role / to catalyse reaction(s) / to lower activation energy
* named enzyme + its specific role described
* hormones / receptors / for cell signalling
* named hormone / insulin + role described
* opsonin / antitoxin / agglutinin + role described
* fibrinogen in blood clotting
* to transport substances across cell membranes
* carrier / channel / pump + role described
* to transport substances in blood
* haemoglobin + role described e.g. carry oxygen
* to, package / organise DNA

65
Q

tubulin is a globular protein that can polymerise to form the cell cytoskeleton. one example of this is the formation of microtubules, which form the spindle fibres to move chromatids during mitosis and meiosis. describe three other cellular functions of the cytoskeleton

A
  • mechanical strength (to cells) ✓
  • cell, support / stability / maintains shape ✓
  • movement of (named), molecules / vesicles / organelles within cell OR holding organelles in position ✓
  • formation / movement, of, cilia /
    flagella ✓
  • cell movement / endocytosis / exocytosis / phagocytosis / cytokinesis / described ✓

OCR AS/A Level Biology Exam Questions (13 decks)

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