Biological Molecules Exam Questions

Describe a biochemical test to show that a piece of coconut contains lipids.

(Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour;

Scientists are trying to find a way to give the missing enzyme to people with Tay Sachs disease. Suggest why they cannot give the enzyme as a tablet that is swallowed.

(Enzymes are) proteins; Digested / broken down / destroyed (by enzymes / acid);

Tests using monoclonal antibodies are specific (line 7). Use your knowledge of protein structure to explain why.

(Specific) primary structure / order of amino acids; (Specific) tertiary / 3D structure; (So) Only binds to / fits / complementary to one antigen;

A significant increase in temperature above the optimum has an effect on the rate of an enzyme-controlled reaction. Explain why this is so.

(enzyme) increases in kinetic energy; enzyme vibrates and breaks bonds (hydrogen and ionic) changes, tertiary structure of enzyme; active site changes, shape substrate will not fit/no enzyme-substrate complex formed; enzyme denatured; will, decrease rate/stop reaction;

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

(high tensile) strength / strong; is not elastic; flexible insoluble

An important enzyme that is used in respiration is succinate dehydrogenase. Its substrate is succinate, which is converted into fumarate. Malonate acts as a competitive inhibitor, but does not bind permanently to the enzyme. (a) Describe how malonate inhibits the enzyme.

(malonate) same / similar, shape as substrate; binds to active site; for a limited time prevents, formation of ESC / substrate from binding; no / less, product formed;

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.

-- (ice less dense because) molecules spread out; P2 molecules form, crystal structure / lattice / AW; P3 ice forms insulating layer / ions / named ion, polar / charged; -- P6 ions /named ion, attracted to / bind to / interact with, water; S4 (named) organisms / plants / animals, uptake / AW, minerals / named mineral / nutrients; many / stable, (hydrogen) bonds between molecules; -- Many hydrogen bonds between molecules P8 at lot of energy to, force apart molecules / break bonds; ACCEPT heat as alternative to energy P9 high (specific) heat capacity; DO NOT CREDIT latent heat capacity S6 temperature does not change much / small variation in temperature; (gases still soluble)

Describe how the structure of a phospholipid differs from that of a triglyceride.

1 less fatty acid / 2 fatty acid not 3; 2 ester bonds not 3; phosphate; hydrophilic / polar, end / head;

Describe how the concentration of a reducing sugar can be measured using a colorimeter.

1 using, standard / known, concentrations (of reducing sugar); 2 heat with, Benedicts (solution) 3 (use of) same volumes of solutions (each time); 4 (use of) excess Benedicts; 5 changes to, green / yellow / orange / brown / (brick) red; 6 remove precipitate 7 calibrate colorimeter; using water 8 reading of absorbance; 9 less absorbance, of filtrate = more sugar present 10 (obtain) calibration curve; 11 plot absorbance, against (reducing) sugar concentration; 12 use reading of unknown sugar solution and read off graph to find conc.

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

1) disulphide bond; between, cysteine / SH / S (atoms); 2) ionic bonds between, oppositely charged / + and -, R groups; 3) hydrophilic R groups, on outside of molecule / in contact with water (molecules); 4) hydrophobic R groups, on inside of molecule / shielded from water (molecules);

Explain the effect of increasing the concentration of substrate on the rate of reaction; (i) without inhibitor,

1) more substrate, molecules enter active site: 2) more successful collisions between substrate and active site 3) ESCs, formed; 4) At low concentration not all active sites occupied / at high concentration all active sites occupied; 5) active sites filled 6) reaches Vmax; 7) (at high substrate concentration) enzyme concentration limiting;

(b) (i) Aspirin only affects one of the enzymes in this pathway. Use information in lines 5 - 7 to explain why aspirin does not affect the other enzymes.

1. Affects one monomer/amino acid; 2. Not found in all active sites;

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.

1. Covalent peptide bond formed between, amine group (of one amino acid) and carboxyl (of another); 2. H (from amine group) combines with OH (from carboxyl group); 3. in a condensation reaction water, lost

1 (a) Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids.

1. Crush/grind; 2. With ethanol/ alcohol; 3. Then add water/then add to water; 4. Forms emulsion / goes white/cloudy;

(iii) Use the diagram to explain what is meant by an unsaturated fatty acid.

1. Double bonds (present); 2. Some/two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen; 3. In (fatty acid) C/3;

Explain the effect of increasing the concentration of substrate on the rate of reaction; (ii) with inhibitor.

1. Inhibitor can bind to / compete for, active site; 2. (occupies it) for a short time / temporary / reversibly; 3. Fewer active sites available (for substrate) 4. More substrate reduces chance of inhibitor getting in; more ESC formed

(c) Aspirin is an enzyme inhibitor. Explain how aspirin prevents substrate molecules being converted to product molecules.

1. Occupies/blocks/binds to active site; 2. Substrate will not fit / does not bind / no longer complementary to / enzyme-substrate complex not formed

(ii) The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different.

1. Phosphate/ PO4; 2. Instead of one of the fatty acids / and two fatty acids;

Describe the structure of a cellulose molecule and explain how cellulose is adapted for its functions in cells.

1. made from β-glucose; 2. joined by condensation/removing molecule of water/glycosidic bond; 3. 1 : 4 link specified or described; 4. "flipping over" of alternate molecules; 5. hydrogen bonds linking chains/long straight chains; 6. cellulose makes cell walls strong/cellulose fibres are strong; 7. can resist turgor pressure/osmotic pressure/pulling forces; 8. bond difficult to break; 9. resists digestion/action of microorganisms/enzymes;

Explain what is meant by the term semi-conservative replication.

2 molecules / helices, (of DNA) produced;identical (molecules of DNA produced); (each made up of) 1, original / parent / old, strand; 1 new strand; 1 conserved strand.

(b) A triglyceride is one type of lipid. The diagram shows the structure of a triglyceride molecule. (i) A triglyceride molecule is formed by condensation. From how many molecules is this triglyceride formed?

4/four

State what a gene codes for.

A sequence of amino acids - primary structure.

2 (a) Induced fit and lock and key are two models used to explain the action of enzymes. (i) Describe the induced fit model of enzyme action.

Active site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form;

Induced fit and lock and key are two models used to explain the action of enzymes. 2 (a) (i) Describe the induced fit model of enzyme action.

Active site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form;

(ii) Describe one way that the lock and key model is different from the induced fit model.

Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding);

Describe one way that the lock and key model is different from the induced fit model.

Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding);

Gangliosides are lipids found in the cell surface membranes of nerve cells. Hexosaminidase is an enzyme present in blood that breaks down gangliosides. If gangliosides are not broken down, they damage nerve cells. 5 (a) Hexosaminidase only breaks down gangliosides. It does not break down other lipids. Explain why this enzyme only breaks down gangliosides.

Active site; (Complementary / specific) structure / shape; (Only) fits / binds to gangliosides; Forms enzyme-substrate complexes; OR Active site; (Complementary / specific) structure / shape; (Does not) fit / bind with other lipids; Does not form enzyme-substrate complexes;

7 Read the following passage. Use information from the passage and your own knowledge to answer the following questions. 7 (a) Name the monomers that make up the active site of the enzyme (lines 6 - 7).

Amino acid / amino acids;

Explain why triglycerides are not polymers.

Because they do not have a repeating unit in their structure - they are made up of components.

Describe how you would use a biochemical test to show that a solution contained protein.

Biuret / alkali + copper sulphate; Lilac/purple/mauve/violet;

Heating may affect the tertiary structure of a protein. Explain how.

Causes bonds which hold the tertiary structure / named bond to break; protein denatured;

Explain how sulphur containing amino acids help to give keratin molecules their characteristic strength.

Chemical bonds formed between sulphur-containing groups/ R-groups/form disulphide bonds; Stronger bonds; Bind chain(s) to each other;

Explain why 'the longer the voyage, the higher the temperature bananas must be kept at to avoid chilling'.

Chilling caused by time and temperature so if time long, temperature must be higher;

(c) (ii) A triglyceride does not contain sucrose or bond X. Give one other way in which the structure of a triglyceride is different to olestra.

Contains glycerol / three fatty acids / forms three ester bonds;

A triglyceride does not contain sucrose or bond X. Give one other way in which the structure of a triglyceride is different to olestra.

Contains glycerol / three fatty acids / forms three ester bonds;

Explain how DNA structure determines the specific shape of enzymes.

DNA codes for, protein / polypeptide; transcription and translation (or described); enzyme is globular (protein); 3 bases ≡ 1 amino acid; sequence of bases / triplets, determines, sequence of amino acids / primary structure; coiling / α helix / β-pleated sheet / particular secondary structure; folding / bonding, for tertiary structure; 3-D structure is tertiary structure;

Similarities and differences between RNA and DNA.

Differences: - DNA is double-stranded, RNA is single-stranded. - DNA contains a pentose sugar Deoxyribose, RNA contains the pentose sugar Ribose. A pentose is a 5-carbon sugar molecule. - DNA is limited to the nucleus, RNA is made in the nucleus, but can travel outside of it. - DNA has a nitrogenous base called Thymine, but RNA doesn't. Instead, RNA has Uracil. In DNA thymine pairs with adenine, but in RNA uracil pairs with adenine. - There is only one type of DNA but 3 kinds of RNA (messenger, transfer and ribosomal RNA) Similarities: - DNA and RNA are made up of monomers called nucleotides. - DNA and RNA both contain pentose sugars. - DNA and RNA both have 3 nitrogenous bases: Adenine, Cytosine and Guanine. - DNA and RNA both have a phosphate groups in their nucleotides. Sometimes called phosphoric acid. - They both have the base pair of Guanine and Cytosine. - They are both necessary for the cell to produce proteins. - DNA makes mRNA which then is translated into protein.

4 (a) Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?

Double bond(s); (Bonds) between carbon atoms.

What is meant by the term activation energy?

Energy put in to get reaction started.

Give three differences between the structure of glycogen and collagen.

GLYCOGEN carbohydrate / polysaccharide (alpha) glucose (units) identical units glycosidic bond branched non-helical contains C H O COLLAGEN peptide bonds different amino acid units unbranched / linear helical three chains (per molecule) cross links (between chains) contains C H O N

Explain why both glucose and maltose both taste sweet but starch does not.

Glucose and maltose soluble/starch insoluble;

Explain why pure glucose obtained from starch has a dextrose equivalent of 100.

Glucose is a monomer / all (the glycosidic) bonds will be hydrolysed / broken down;

Explain why only a plasma membrane allowed glucose to pass through and not an artificial membrane.

Glucose unable to pass through artificial membrane as not lipid soluble; Glucose transported by proteins; (Proteins) found in plasma membrane / not found in artificial membrane;

Olestra is an artificial lipid. It is made by attaching fatty acids, by condensation, to a sucrose molecule. 4 (c) (i) Name bond X.

Glycosidic;

Explain what causes a phospholipid to be arranged to form a bilayer.

Head hydrophilic/ attracted to water/ polar; Tail hydrophobic/ avoids/ shuns water/ non-polar;

(c) (ii) Explain the result you would expect with the enzyme.

Lactase (enzyme) is a protein; OR Lactase contains peptide bonds.

(c) (i) Describe how you could use the biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose.

Lactase (enzyme) will give purple / lilac colour; OR Lactose (reducing sugar) will not give purple / lilac and will remain blue.

Explain how the structures of fibrous proteins is related to their functions.

Long chains of amino acid; Folding of chain into a coil / folds / helix / pleated sheet; Association of several polypeptide chains together; Formation of fibres / sheets explained; 2 H bonds / Disulphide bonding (In context); Fibres provide strength (and flexibility); Sheets provide flexibility; Example e.g. keratin in hair, collagen in bone; Insoluble because external R-groups are non-polar;

Explain how proteins are suited for their roles as receptor molecules.

Many different sorts of proteins; Different primary structures/sequences of amino acids; Tertiary structure; Shape; allowing formation of receptor/binding site/site into which substance/substrate fits;

Methotrexate is a drug used in the treatment of cancer. It is a competitive inhibitor and affects the enzyme folate reductase. (c) (i) Explain how the drug lowers the rate of reaction controlled by folate reductase.

Methotrexate / drug is a similar shape / structure to substrate; Binds to / fits / is complementary to active site; Less substrate binds / less enzyme-substrate complexes formed

(c) (ii) Methotrexate only affects the rate of the reaction controlled by folate reductase. Explain why this drug does not affect other enzymes.

Methotrexate / drug is only similar shape to specific substrate / only fits this active site; OR Methotrexate / drug is a different shape to other substrates / will not fit other active sites;

Explain what causes the water potential of the banana pulp to decrease as the fruit ripens.

More sugar/solute/soluble substances present; So concentration of water lower/less free water molecules; (Decreases solute potential)

Explain what causes the starch hydrolysis to be slow in chilled bananas.

Process controlled by enzymes; Low temperature/cold means less (kinetic) energy; Fewer collisions/enzyme-substrate complexes formed;

What is the difference between a saturated and unsaturated fatty acid?

Saturated - all valencies of C filled / saturated with hydrogen / all (C-C) single bonds / no double bonds;

The diagram shows the structure of a molecule of PABA. It also shows the structure of a molecule of a drug called sulfanilamide, which can be used to treat bacterial infections. Sulfanilamide prevents bacteria producing folic acid. (b) Use the diagram and your knowledge of enzymes to explain how sulfanilamide prevents bacteria producing folic acid.

Similar structure / shape (to PABA) / both complementary; Competes for / binds to active site / competitive inhibitor; Less PABA binds / less E-S complexes; OR Specific reference to different structure / shape (to PABA); Binds to position other than active site / binds to allosteric site / binds to inhibitor site / non-competitive inhibitor; Changes the active site so substrate cannot bind / less PABA binds / less E-S complexes;

Suggest how you could use a reducing sugar test to compare the amount of reducing sugar in two solutions.

Standardise specific feature / carry out tests the same; e.g. amounts used / time heated / temperature Compare colour / amount of precipitate / time taken to get colour;

Explain why a buffer solution is added to an enzyme containing solution.

To keep pH constant; A change in pH will slow the rate of the reaction / denature the amylase / optimum for reaction;

Describe a test that the student could carry out to discover whether this sample contained a lipid.

add / mix with ethanol; then, add to/ mix with, water; milky emulsion

Describe the test that is used to indicate the presence of a reducing sugar, such as glucose, and state the observation that would be made if glucose was present.

add / use, Benedict's (reagent); heat; (blue to) green / yellow / orange / brown / red (precipitate);

Describe a test that the student could carry out to discover whether the food sample contained protein.

add, copper sulphate (solution) and sodium hydroxide (solution) / biuret (reagent); blue to lilac

Fungi such as Fusarium venenatum are grown in huge batch cultures to manufacture protein for food products. Explain why these cultures are often maintained at the optimum temperature for protein production and not at a temperature above the optimum. (Make clear how the structure and activity of enzymes relates to the effects described.)

at optimum temp - molecules have more kinetic energy; (frequent) collisions between enzyme and substrate molecules; more enzyme-substrate complexes formed; max rate of reaction; at higher temp - molecules have more kinetic energy collisions occur more frequently; molecules vibrate hydrogen bonds, broken; tertiary structure of enzymes altered; active site loses complementary shape; enzymes are denatured; substrate molecule no longer fits active site; reaction stops; fungus destroyed

Hydrolysis of gum arabic releases four different monosaccharides. Describe what happens during the hydrolysis of a polysaccharide molecule.

breaking (glycosidic) bond; glycosidic bond drawn; addition of water / H2O;

Cellulose and collagen are both fibrous molecules. Cellulose, a carbohydrate, is the main component of the .................. .................. in plants. Cellulose is made of chains of many ...... glucose molecules which are joined by 1,4 .............................. bonds. Each glucose molecule is rotated ...............° relative to its neighbour, resulting in a .............................. chain. Adjacent chains are held to one another by .............................. bonds.

cell wall(s); β / beta; glycosidic; 180; straight/linear; hydrogen

The immense biodiversity of the oceans includes: • corals that host symbiotic algae which die if the sea temperature rises by 1°C; • animals like polar bears that use floating ice as a base for sea fishing expeditions; • sessile animals like mussels that feed by filtering food particles from the water and reproduce by releasing gametes into the water; • reef-building animals like corals that form hard calcium carbonate skeletons by extracting mineral ions such as Ca2+ from the water; • seaweeds of different colours which occur in shallow water; • animals like fish that hunt prey using well-developed visual skills; • large animals such as the blue whale; • physically delicate organisms like jellyfish that lose their shape in air. Using examples from the list above, describe and explain how the properties of water make it a suitable environment for these organisms.

coral algae - (high) thermal stability / temperature remains fairly constant; - water has high specific heat capacity; much energy needed to break hydrogen bonds; polar bears - cooling allows maximum number of hydrogen bonds to form; - water molecules spread out to allow this; - water expands as it freezes / ice is less dense than water; seaweeds, fish eyes - water is transparent to light; - photosynthesis possible (in shallow water); - wavelength of light varies with depth; whales, jellyfish - cohesion / water molecules stick to each other; - water not easily compressed; - gives support to large bodies ; - solubility of named gas linked to use in named organism mussels, filter-feeders and sessile animals - water is transport medium for, food particles - (tentacles / appendages / cilia) create currents bringing food;

Describe how you would test an extract of the seed pods for protein.

crush (small amount of) seed pod; add (small volume of) biuret, A / NaOH, and biuret, B positive = colour change from blue to lilac;

State the components of a DNA nucleotide.

deoxyribose (sugar); phosphate (group); (nitrogenous / purine or pyrimidine) base

Describe the structure of a DNA nucleotide. In your answer you should spell the names of the molecules correctly.

deoxyribose sugar; a nitrogenous base; phosphate group;

Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for.

different, sequence of amino acids different protein / different tertiary structure; (product) different function;

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.

double helix; anti-parallel; sugar-phosphate; hydrogen;

Explain the effects of enzyme concentration, substrate concentration and competitive inhibitors on the rate of an enzyme-controlled reaction.

enzyme concentration ~ 1) reaction (rate) increases with increased enzyme; A high / low 2) more active sites available; 3) in excess substrate / as long as enough substrate (molecules available to occupy active site); 4) (as reaction progresses) the rate will decrease as substrate becomes limiting. substrate concentration ~ 1) reaction (rate) increases with increased substrate; A high / low 2) more ESC formed; more successful collisions 3) reaches point where all active sites occupied; 4) no further increase in rate / reaches Vmax and levels off 5) enzyme conc. becomes limiting / unless add more enzyme; competitive inhibitor ~ 1) inhibitor has similar shape to substrate; 2) can occupy, active site; 3) for short time 4) prevents substrate from entering active site; 5) rate determined by relative concentrations; 6) little inhibition if substrate conc bigger than inhibitor conc. 7) effects can be reversed by increasing substrate conc.;

Glucose molecules can be joined by condensation top form a variety of polymers. Describe how the condensation reaction can be catalysed by an enzyme.

enzyme has an active site; with a complementary shape to the substrate molecules; enzyme-substrate complex formed; lowering the (activation) energy for the reaction; glycosidic bond formed/bringing together hydroxyl groups/water molecule removed; products leave the active site; enzyme unchanged;

'Scientists have discovered that certain microorganisms can survive in the Antarctic, completely surrounded by ice.' Suggest how this discovery was useful in the development of certain biological washing powders.

enzymes (of microorganisms) work in low temperatures; enzymes used in stain removal; can be used for cool washes; saves energy;

A covering of lignin protects cellulose from enzyme attack. Use your knowledge of the way in which enzymes work to explain why cellulose-digesting enzymes do nit digest lignin.

enzymes are specific; shape of lignin molecules;

Explain why different enzymes are involved in each stage of the digestion process of cellulose.

enzymes are specific; the substrates, are different shapes; active site and substrate are complementary; so that substrate will fit / formation of ESC;

Describe how the structure of RNA differs from that of DNA.

has ribose; uracil, instead of, thymine single stranded;

The seeds of Acacia species are sometimes eaten by people. Suggest why it might be better for people living in areas where the tree grows to let their cattle feed on the trees and fallen seed pods and then obtain their nutrition from the cattle.

humans eat only the seeds so do not gain, nutrition from, leaves; seeds maybe deficient in (some) essential amino acids; cattle better at digesting, plant matter than humans

Describe how the two nucleotide chains in DNA are bonded together.

hydrogen bonds between bases; complementary base pairing; purine to pyrimidine (A to T and G to C)

Arachidonate reaches the active site of COX through a hydrophobic channel in the surface of the enzyme. Ibuprofen and aspirin are drugs that inhibit the action of the COX enzyme. • Ibuprofen enters and occupies the hydrophobic channel in the surface of the enzyme. • Aspirin reacts with one of the R groups close to the active site of the enzyme. Suggest how each drug inhibits the action of the COX enzyme.

ibuprofen competitive; ibuprofen blocks active site; substrate cannot reach active site; aspirin non-competitive; changes shape (of) / blocks; active site; binds to allosteric site; no ESC formed.

In this question, one mark is available for the quality of written communication. Some of the properties of water are listed below. • boils at 100 °C • freezes at 0 °C • water below 4 °C is less dense than water above 4 °C • excellent solvent • much energy is required to raise the temperature of water • much energy is required to change water into water vapour • high surface tension and cohesion Describe and explain the roles of water in living organisms and as an environment for living organisms. You will gain credit for using information about the properties of water.

liquid at normal temperatures; 2 hydrogen bonding between water molecules; 3 molecules more difficult to separate; 4 ice floats on water / water freezes from top down; 5 insulates water beneath; 6 large bodies of water don't freeze completely / animals can still swim etc.; 7 (change in density with temperature) causes currents to circulate nutrients; 8 solvent for, polar / ionic, substances; 9 solubility of gases in environment; 10 allows reactions to take place; 11 transport medium; 12 e.g. (of substance carried in what); 13 transport medium for, gametes / blood cells; PMT 14 water slow to change temperature; 15 lakes / oceans / large volumes, provide thermally stable environment; 16 internal body temperature changes minimised; 17 used for cooling; 18 e.g. (sweating / panting / transpiration); 19 large amount of energy must be removed for water to freeze; 20 organisms can use surface of water (as habitat); 21 e.g.; (of organism) 22 can form (long / unbroken) columns of water; 23 ref. to vascular tissue / xylem; 24 reactant (photosynthesis); 25 role in, hydrolysis / condensation;

Describe the molecular structure of glycogen.

polymer/polysaccharide; (made of) α-glucose; joined by 1,4 links; glycosidic; (chain is) branched; 1,6 links where branches attach;

Describe how you could compare the reducing sugar content of the leaves with that of the seed pods.

preparation - 1 crush, samples, separately with water; 2 use same mass of each and use same volume of water; 3 filter; method - 4 add benedict's reagent to filtrate; 5 stated volume; 6 same volume added; 7 heat in a water bath 8 for stated time (up to 5 min); analysis - 9 colour change from blue to green / yellow / orange / red; 10 shows increasing concentration of reducing sugar.

Explain what is meant by the primary and secondary structure of a protein.

primary sequence / order, of amino acids (in a polypeptide); secondary coiling / folding, of the, polypeptide / chain of amino acids / peptide chain / primary structure; (α-) helix; (β-) pleated sheet; hydrogen bonds; between amino acids in (same) chain;

Suggest how the substrate changing shape slightly will assist enzyme action.

puts strain on the bonds in the substrate / bonds break more easily; lowers activation energy.

An important enzyme that is used in respiration is succinate dehydrogenase. Its substrate is succinate, which is converted into fumarate. Malonate acts as a competitive inhibitor, but does not bind permanently to the enzyme. Explain what would happen to the reaction if the concentration of succinate was increased relative to the concentration of malonate.

rate increased; greater chance of substrate binding with, active site / enzyme; more, product formed / substrate converted; will reach Vmax

Explain how a non-competitive inhibitor affects the rate of an enzyme-catalysed reaction.

reduces rate; inhibits fits into, allosteric site alters, shape / charge, of active site; so substrate cannot bind to active site / form ESC; will not reach Vmax; increasing substrate concentration has no effect (on the rate);

State three ways in which the structure of DNA differs from that of RNA.

ribose (instead of deoxyribose); uracil replaces thymine; single stranded (instead of double stranded); smaller molecule / different 3-D structure to DNA;

Before a cell divides, the DNA needs to be accurately replicated. Describe how a DNA molecule is replicated.

semi-conservative replication untwist and unzip H bond breaks between complementary base pairs DNA helicase both strands act as template; (aligning of) free (DNA) nucleotides; complementary, base / nucleotide, pairing; C to G and T to A / purine to pyrimidine; hydrogen bonds reform; sugar-phosphate back bone forms; covalent / phosphodiester, bond; DNA polymerase

Explain enzyme specificity.

shape of active site; complementary; correct substrate will, fit; form ESC; any other molecule will not.

Describe the effect of low temperature, such as 5 °C, on enzyme action.

slows, reaction / rate / activity of enzyme; less kinetic energy; molecules moving, slowly few collisions / collisions less likely; few ESC formed / ESC less likely to be formed; reversible / enzyme not denatured / enzyme still works; activation energy lowered;

Collagen has tremendous strength, having about one quarter of the tensile strength of mild steel. Explain how the structure of collagen contributes to its strength.

small (to allow close packing); the small one is, every 3rd amino acid / at every level in the molecule; chains, form a tight coil; held together by hydrogen bonds; molecules form, fibres / bonds with adjacent molecules; A fibril covalent bond between, adjacent molecules; fibres composed of parallel molecules; ends of parallel molecules staggered; prevents line of weakness;

Water is essential for life. It makes up a high proportion of the cytoplasm in a cell. Many different compounds can dissolve in it and it is therefore described as an excellent ..................................... . Water remains in the ....................... state over a wide range of environmental temperatures. As it cools below 4 °C it becomes less ............................. than warmer water. Ice floats on water, forming a layer that ................................... the water beneath with the result that large bodies of water rarely freeze entirely. The ............................... bonds that form between water molecules are responsible for its high ............................................................. , which allows small insects such as pond skaters to move on its surface without sinking.

solvent; liquid; dense; insulates; hydrogen; cohesion;

DNA codes for the structure of polypeptides. State the role of messenger RNA (mRNA).

transfers, the (complementary DNA), code / genetic information out of the nucleus; (transfers it) to the, ribosome for protein synthesis;