AS1 Chapter 1 - Molecules Flashcards

Question

Name three monosaccharides

Answer 1

Glucose Fructose Galactose

Answer 2

Maltose Sucrose Lactose

Answer 3

Cellulose Starch Glycogen

Answer 4

Isomers are substances which share the same molecular formula, but have different structural formulae.

Answer 5

In B-glucose the hydrogen and hydroxyl group (-OH) groups at carbon 1 are reversed.

Answer 6

a-glucose + a-glucose

Answer 7

Starch and glycogen

Answer 8

a-glucose + fructose

Answer 9

a-glucose + galactose

Answer 10

(C6H10O5)n

Answer 11

Amylose (20%) | Amylopectin (80%)

Answer 12

The branches may occur as often as one branch every ten a-glucose monomers.

Answer 13

Alpha 1-6 glycosidic bonds

Answer 14

1. The molecules of both amylose and amylopectin are very compact (aided by the coiled configuration due to hydrogen bonds), therefore they contain a rich store of glucose in a small space. 2. As it is insoluble it will not affect the water relations of the cell - if significant quantities of carbohydrate were stored as glucose this would cause a lot of water to enter by osmosis. 3. Being a large molecule it can be retained in the cell and will not easily pass through the cell membrane. 4. The branching nature of amylopectin creates many terminal ends that are easily hydrolysed. This aids in the rapid enzymatic breakdown of starch into its constituent glucose molecules at times of high respiratory demand.

Answer 15

Starch is stored as solid grains in plant chloroplasts.

Answer 16

Glycogen is found as small granules in animals (liver and muscle cells) and fungal cells.

Answer 17

Structurally, glycogen is very similar to amylopectin, being formed of chains of a-glucose monomers. Glycogen also has a-1,4 glycosidic and a-1,6 glycosidic bonds but the chains are more branched and shorter than the amylopectin chains.

Answer 18

1. All of the chains in glycogen are branched. 2. The branches are shorter and more common. Therefore it has proportionally more terminal ends for enzymatic action and faster hydrolysis.

Answer 19

``` Carbon Hydrogen Oxygen Nitrogen Sometimes sulfur ```

Answer 20

Amino group attached to the alpha carbon Carboxyl group attached to the alpha carbon Hydrogen atom attached to the alpha carbon Varying R-group attached to the alpha carbon

Answer 21

Peptide bonds

Answer 22

Condensation reactions Water

Answer 23

The amino group of one amino acid and the carboxylic group of another amino acid together form a peptide bond with the release of water.

Answer 24

Polypeptide

Answer 25

The primary structure of a polypeptide (protein) is the sequence of the amino acids in the polypeptide chain.

Answer 26

The amino acids in a polypeptide contain -NH and -C=O groups on either side of each peptide bond. The O of the -C=O group has a negative charge, whereas the H of the -NH group has a positive charge. This enables the formation of hydrogen bonds, which in turn cause generalised secondary structures to be formed.

Answer 27

* a-helix - In the a-helix the hydrogen bonds are formed between amino acids occurring at regular intervals in the sequence. The bonds twist the chain of amino acids into a spiral or helical shape. Small sections (or the entire polypeptide) can be held in an a-helix shape by the hydrogen bonds involved. * B-pleated sheets - These are more rigid and less flexible configurations than the a-helix. They are formed by sections of the polypeptide chain, oriented in opposite (anti-parallel) directions, lying adjacent to each other. Hydrogen bonds form between the C=O and NH groups.

Answer 28

Tertiary structure - This involves the further folding of the secondary structure. This additional folding gives each protein it’s unique 3-D shape and is a consequence of the range of bonds formed between the R-groups of amino acids in the chain.

Answer 29

* Hydrogen bonds form between R-groups in the chain. * Ionic bonds are formed between amino and carboxyl groups in some of the amino acid R-groups. * Disulfide bonds (bridges) are covalent bonds formed between R-groups of sulfur-containing amino acids. * Hydrophobic interactions involving amino acids with hydrophobic R-groups, which tend to take up positions within the molecule surrounded by other parts of the polypeptide.

Answer 30

Some proteins consist of two or more polypeptides bonded together (largely by disulfide bonds). Some quaternary proteins contain non-protein components (prosthetic groups) that are integral in their function.

Answer 31

Glycoprotein - Important in membrane structure Haemoglobin - Consists of four polypeptide chains (two each of two different polypeptides). Each chain is attached to an iron-rich haem group, which is an essential part of the molecule in the transport of oxygen.

Answer 32

Fibrous and globular Fibrous proteins - consist of polypeptides arranged in chains that form fibres or sheets. The parallel chains are linked by cross-bridges to form very strong and stable molecules. Fibrous proteins are invariably structural in function. Globular proteins - have a metabolic role and include enzymes and antibodies. The ability of protein to form very specific 3-D shapes is crucial to their role as enzymes and antibodies.

Answer 33

Collagen - Each collagen molecule consists of three identical polypeptides wound round each other and held together by hydrogen bonds. Collagen is found in tendons that link muscle to bone. Obviously, it is very important that it is a very strong molecule and one that does not stretch when tension is applied.

Answer 34

Haemoglobin

Answer 35

Prion are a particular type of protein found in mammals and some other animal groups. They are found in the nervous system and it is thought they are involved in synaptic transmission.

Answer 36

1. The normal prion protein present (PrP) can 'spontaneously' adopt the PrPsc form. 2. Mutations in the DNA that codes for the prion protein. Therefore the disease-causing form can be passed from parent to offspring. 3. Through eating contaminated food that contains the disease-causing form.

Answer 37

PrP or PrPc

Answer 38

Disease-causing prion proteins have a higher proportion of B-pleated sheets (compared to a-helices).

Answer 39

* Scrapie that affects sheep. * Bovine spongiform encephalopathy (BSE) or 'mad cow disease', normally cattle are affected through eating contaminated food products. * Variant Creutzfeldt-Jakob Disease (vCJD), a human version of BSE that is normally acquired through eating contaminated beef products containing the PrPsc form.

Answer 40

If the disease-causing form is present in an individual, it acts as a template causing other prion proteins to convert to the disease-causing form. Once the disease-causing form is present in an organism, it leads to a chain reaction causing the number of other disease-causing prions to increase, ie the prion protein progressively becomes misfolded and changes from the PrP to the PrPsc form.

Answer 41

The nucleotide

Answer 42

1. A pentose (5 carbon) sugar 2. An inorganic phosphate group 3. An organic nitrogenous base

Answer 43

Condensation reactions

Answer 44

Phosphoester (in one nucleotide) Phosphodiester (in a nucleic acid strand, polynucleotide)

Answer 45

A polynucleotide (nucleic acid)

Answer 46

Condensation

Answer 47

5' end = Free phosphate | 3' end = Free sugar

Answer 48

Deoxyribonucleic acid Ribonucleic acid

Answer 49

DNA consists of two anti-parallel strands with the two strands being held together by hydrogen bonds between adjacent bases.

Answer 50

Adenine Thymine Guanine Cytosine

Answer 51

A double helix

Answer 52

1. Messenger RNA (mRNA) 2. Transfer RNA (tRNA) 3. Ribosomal RNA (rRNA)

Answer 53

1. Deoxyribose/ ribose 2. Double stranded/ mainly single stranded 3. Longer molecule/ relatively shorter 4. Thymine / Uracil 5. Chemically very stable/ chemically less stable 6. Permanent/ exists for short periods of time 7. Ratio of adenine to thymine and guanine to cytosine is constant/ ratio of adenine to uracil and guanine and cytosine varies.

Answer 54

RNA is involved in protein synthesis.

Answer 55

Carries the code from the DNA in the nucleus (the DNA remains protected in the nucleus) to a ribosome in the cytoplasm where protein synthesis takes place.

Answer 56

Carries the amino acids to the mRNA/ribosome where protein synthesis takes place. It is a single chain folded into a 'clover leaf' shape. There are as many different types of tRNA as there are amino acids. Their structure is similar except for the part that links with the appropriate amino acid and the part that links with the mRNA.

Answer 57

Ribosomal RNA is made in the nucleolus and forms over half the mass of each ribosome.

Answer 58

Condensation reactions

Answer 59

* Components of nucleic acids (ribose and deoxyribose) | * ATP (ribose)

Answer 60

Hydrolysis reactions

Answer 61

Triglycerides (fats and oils) Phospholipids Waxes Steroids

Answer 62

Triglycerides are condensation products of glycerol and fatty acids.

Answer 63

Three molecules of fatty acids | One molecule of glycerol

Answer 64

Condensation reactions

Answer 65

Ester bonds

Answer 66

Saturated and unsaturated

Answer 67

Saturated fatty acids contain the maximum number of hydrogen atoms. Also, the carbon atoms are linked by C-C single bonds.

Answer 68

Unsaturated fatty acids have at least one C=C double bond in the chain.

Answer 69

Monounsaturated | Polyunsaturated

Answer 70

Triglycerides

Answer 71

* Fats are solid at room temperature * Fats are formed from saturated fatty acids or longer chains * Oils are liquid at room temperature * Oils are formed unsaturated fatty acids or shorter chains

Answer 72

Phospholipids are similar to triglycerides, except that one of the fatty acids molecules is replaced by a phosphate group.

Answer 73

The fatty acid molecules repel water and are insoluble in water, forming hydrophobic 'tails', whereas the phosphate gives the glycerol part ('head') of the molecule hydrophobic properties and it is soluble in water. Phospholipids are polar molecules.

Answer 74

``` 1. Subunits: DNA - Deoxyribonucleotides (contain deoxyribose and thymine) RNA - Ribonucleotides (contain ribose and uracil) 2. Length: DNA - Very long RNA - Relatively short 3. Strands: DNA - Double stranded RNA - Single stranded 4. Base pairing: DNA - A with T and G with C RNA - No base pairing ```

Answer 75

1. Triglycerides are an excellent energy store as they release more energy per unit of mass than carbohydrate. Oils act as energy stores in plant seeds. 2. Fats are important for insulation and are stored in a layer below the body surface in many animals. 3. Many body organs are protected by a layer of fat. 4. Buoyancy 5. Waterproofing

Answer 76

b) It consists of beta glucose monomers which join together to make straight chains. Beta 1-4 glycosidic bonds form. Hydrogen bonds form cross-links between adjacent chains.

Answer 77

Semi-conservative mechanism

Answer 78

The sequence of events in DNA replication is as follows: 1. The enzyme DNA helicase breaks the hydrogen bonds holding the base pairs together and 'unzips' part of the DNA double helix, revealing two strands. 2. The enzyme DNA polymerase moves along each strand, which acts as a template for the synthesis of a new strand. 3. DNA polymerase catalyses the joining of free deoxyribonucleotides to each of the exposed original strands, according to base pairing rules, so that new complementary strands form. 4. The process of unzipping and joining new nucleotides continues along the whole length of the DNA molecule. Each DNA molecule formed is identical to the other and to the original DNA (and contains one strand of the original).

Answer 79

The Meselson and Stahl Experiment

Answer 80

Meselson and Stahl cultured bacteria in heavy isotopes of nitrogen (15N). The bacteria were then transferred to a medium containing the lighter (normal) 14N. Key stages were: * Bacteria growing in 14N (before transfer to 15N). * Bacteria growing in 15N (many generations after transfer from 14N). * One generation after transfer back to 14N. * Two generations after transfer back to 14N. Density-gradient centrifugation was used to separate the bacterial DNA following sampling at the stages listed above. DNA containing the lighter 14N accumulated in a zone near the top of the centrifuge tube, whereas DNA consisting of 'heavy' 15N formed a zone near the bottom of the centrifuge tube. Explanation of Meselson and Stahl's results: • After one generation - The intermediate position of the DNA can be explained by all the DNA consisting of one strand that has bases containing 15N and one strand having bases containing 14N. • After two generations - About half the DNA consisted of 'mixed' DNA of both 14N and 15N but the other half was DNA that only contained 14N.

Answer 81

Water | Nucleotide

Answer 82

Water | Nucleic acid

Answer 83

Benedict's test When a reducing sugar is mixed with Benedict's reagent and heated in a hot water bath, the blue reagent will change the through the sequence blue-green-yellow-orange to form a brick red precipitate.

Answer 84

A reducing sugar is one which can donate electrons (or reduce) Benedict's reagent.

Answer 85

All monosaccharides | Maltose

Answer 86

A non-reducing sugar can be identified through giving a negative Benedict's test result initially, but if hydrolysed into its constituent monosaccharides with dilute hydrochloric acid (and subsequently neutralised with, for example, sodium hydrogen carbonate), it gives a positive result.

Answer 87

1. Benedict's Test = Reducing sugar (and non-reducing sugar if test is modified). 2. Glucose-Specific Tests = Clinistix test identifies the presence of glucose. 3. Iodine Test = Detects the presence of starch.

Answer 88

Clinistix/diastix test | The Clinistix strip is dipped in the test solution and if glucose is present, it will change colour.

Answer 89

Iodine Test - Starch changes the colour of iodine from yellow- brown to blue- black.

Answer 90

Biuret Test - Add potassium/sodium hydroxide to the test sample then add a few drops of copper sulfate solution. Positive test = Blue ---> Mauve/lilac

Answer 91

Procedure: 1. Weigh 5g of white chocolate and 5g of onion. Grind each into a paste (add equal volumes of water if necessary). 2. Add the chocolate and onion separately to equal volumes of Benedict's reagent (eg 5cm^3) in two boiling tubes. 3. Heat the boiling tubes in the same beaker which acts as a water bath. 4. Compare the colours of the Benedict's reagent in the two boiling tubes after the same length of time or when there is no further colour change. 5. Weigh another 5g of white chocolate and 5g of onion, and grind each into a paste (add equal volumes of water if necessary). 6. Heat with hydrochloric acid in a water bath. 7. Neutralise with sodium hydrogencarbonate. 8. Redo the Benedict's test. Comment: 1. Measuring mass is more accurate than volume as it can be difficult to cut to an exact size. Also a top-pan balance can measure mass to one or two decimal places making it very precise. White chocolate will mask the colour of Benedict's reagent much less than brown chocolate. 2. Equal volumes of Benedict's reagent as a controlled variable. 3. Ensures that each boiling tube is heated at the same temperature for the same time. 4. This indicates the relative amounts of reducing sugar in white chocolate and onion. 6. This hydrolyses any non-reducing sugar present. 8. Comparison with tubes from the first Benedict's test will indicate if non-reducing sugar is present. Note 1: this procedure allows comparison of both reducing and non-reducing sugar between the two foods. Note 2: if both the chocolate and the onion contain enough sugar to make the Benedict's solution turn brick red, you can measure the time taken to turn brick red. Note 3: you could use a colorimeter to more accurately compare the colour changes. If doing so you would need to filter the solutions to remove the precipitate.

Answer 92

Any two from: • Solvent should be placed in sealed chromatography jar/container beforehand (to allow vapour to saturate jar). • Avoid touching chromatography paper with bare hands. • All marks on chromatography paper should be in pencil. • Solutions under investigation should not be placed too close together/ too close to the edge of chromatography paper/ samples are same distance from bottom (starting from same point) • Solutions should be concentrated by repeated application in the same position. • Chromatography paper should not touch the sides of the jar/ container.

Answer 93

1. The chromatography paper is cut to fit the tank/vessel used to hold it in a vertical position. 2. The paper (chromatogram) should be long enough to allow attachment to the lid of the apparatus and to drop to just above the base of the tank. 3. A horizontal line should be drawn in pencil a few centimetres above the base of the chromatogram. It is important for the line to be drawn in a position that will lie above the solvent when the chromatogram is placed in the solvent. 4. The solution(s) containing amino acids to be tested need to be 'spotted' on the pencil line. Each solution is added to a pre-determined position by a micro-pipette. After adding a drop of the solution it is then dried before the process is repeated. This allows the solution to be concentrated. 5. It is important to ensure that the concentrated spot forms as small an area as possible. This can be aided by ensuring that the spot is dry before adding additional drops of solution. In addition, it is important to avoid contamination of the chromatogram. Only hold the chromatogram at the edges and avoid setting it on laboratory benches that could be contaminated with a range of chemicals. Before placing the prepared chromatogram in the tank, the solvent should be added and the lid placed on top to allow the atmosphere to become saturated.

Answer 94

The chromatogram is carefully suspended into the solvent and attached to the lid of the tank. It is important to ensure that: * The line (and concentrated spot(s)) do not make contact with the solvent. * The chromatogram is securely attached. * The chromatogram is not suspended at an angle - if at an angle the solvent cannot 'run' the length of the chromatogram. As the solvent 'runs' up the chromatogram, it carries the amino acids, although they will not be visible at this stage. The 'run' of the solvent should be stopped when it is well up the chromatogram but before it reaches the top.

Answer 95

The chromatogram should then be dried. Before the solvent is dry, it is important to mark the 'solvent front' on the chromatogram with a pencil. As amino acids are colourless on the chromatogram, it should be sprayed with ninhydrin in a fume cupboard (this is necessary as ninhydrin can be harmful if breathed in). Following staining, the chromatogram should be re-dried (with a hairdryer or in an oven) and the amino acids will appear as purple spots (proline is an exception as it appears yellow). The spots should be encircled with a pencil as they subsequently fade.

Answer 96

The Rf value is the distance moved by a solute divided by the distance moved by the solvent front.

Answer 97

a)(ii) Any three from: • individual collagen chains show α-helix polypeptide chains/secondary structure helix present in chains/functional collagen comprised of three polypeptide chains; • held by hydrogen bonds; • three chains twisted around each other; • very strong/does not stretch with tension/insoluble; [3]

Answer 98

Q2 a) Has one or more carbon-carbon double bonds/ contains double bonds between carbon atoms. [1]

Answer 99

b)ii) One fatty acid chain replaced with a phosphate group. [1]

Answer 100

Q2 c)i) Synthesis; Condensation | Breakdown; Hydrolysis [2]

Answer 101

``` Q2 c)ii) Any two from: • Energy store/ respiratory substance • Insulation • Buoyancy • Organ protection • Waterproofing [2] ```

Answer 102

Calcium; Calcium Pectate | Magnesium; Chlorophyll [2]

Answer 103

a) Any four from: • Make sure the chromatography paper is only handled at the edges/ use gloves when handling the chromatography paper/ cut paper to fit the chromatography jar. • Draw a line a set distance from the bottom of the chromatography paper, above the solvent level. • In pencil. • Ensure adequate spacing between each spot. • Make a concentrated spot for each amino acid/ spot each amino acid three times.

Answer 104

b)ii) A different solvent was used to run this chromatogram/ other appropriate response. [1]

Answer 105

Q2 a) Any two from: • Solvent should be placed in sealed chromatography jar/container beforehand (to allow vapour to saturate jar). • Avoid touching chromatography paper with bare hands. • All marks on chromatography paper should be in pencil. • Solutions under investigation should not be placed too close together/ too close to the edge of chromatography paper/ samples are same distance from bottom (starting from same point). • Solutions should be concentrated by repeated application in the same position. • Chromatography paper should not touch the sides of the jar/ container. [2]

Answer 106

Q7c)i) Caption = Scatter diagram showing the relationship between mass and Rf of amino acids; Appropriate scaling; Axes labelled including units; Corrects plotting of points (not joined by lines), i.e. Do not connect points with straight lines. Do not draw a line of best fit either, it is only a scatter diagram. [4]

Answer 107

Q7 c)ii) Positive correlation between mass and Rf/ the amino acids with the larger mass travel further up the chromatogram; Larger amino acids are more soluble in the solvent used; [2]

Answer 108

Q2 b) Bonding properties/ solubility/ polarity/ identity/ pH/ formation of secondary, tertiary or quaternary structure. [1]

Answer 109

Q4 a)i) Conjugated proteins; | Structure consists of a polypeptide combined with a non-protein group/ sugar/carbohydrate residue; [2]

Answer 110

Q6 b) Glycogen is hydrolysed rapidly/provides rapid energy source; Animals move so therefore cannot be too massive/heavy/movement is not restricted by mass/ same amount of energy is stored in a smaller mass; [2]

Answer 111

Q6 c) Appropriate safety precaution explained; Any four from: • Add dilute (1M) hydrochloric acid to sample • Heat in a water bath • Neutralise with dilute sodium hydrogencarbonate/sodium hydroxide • Add Benedict's reagent and heat again in a water bath • (Green/yellow)/ brick red precipitate indicates presence of reducing sugar [5]

Answer 112

Q4 a) Any four from: • DNA is unzipped by breaking of hydrogen bonds • this is catalysed by DNA helicase • each strand acts as a template/semi-conservative mechanism • free nucleotides are attracted to their complementary bases/base pairing occurs, A with T and C with G • (phosphodiester) bonds form between the deoxyribose and the phosphate of adjacent nucleotides • catalysed by DNA polymerase [4]

Answer 113

Q4 c)i) Drug A: prevents the DNA being unzipped (due to cross linkage); Drug B: prevents addition of further nucleotides to the spine (due to three phosphates instead of one); [2]

Answer 114

Q5 a)i) Glycosidic; [1]

Answer 115

Q5 a)ii) Carbohydrate Function Location in cell Starch energy store/ storage of glucose chloroplasts/ cytoplasm Cellulose provide support/ strength/rigidity cell walls [4]

Answer 116

Q5 (b) (i) Disaccharides; [1] (ii) Hydrolysis; [1] (iii) Glucose and fructose; [1]

Answer 117

Q5 c) • Erlose has one more monomer than sucrose/consists of three monosaccharides (rings)/is a trisaccharide; • Erlose consists of two glucose plus a fructose/a glucose molecule has been added to the sucrose; [2]

Answer 118

``` Q1 Nucleotides condensation antiparallel hydrogen complementary histones [5] ```

Answer 119

Q2 b) Distance to solvent front = 74 mm, distance to middle of spot = 37 mm; Rf = 37/74 = 0.5 [consequential to values above]; [2] c) Fructose Glucose Maltose Sucrose [3]

Answer 120

Q2 d) Alpha-glucose; [1]

Answer 121

Q6 a) A large molecule/molecule consisting of subunits; including carbon (and hydrogen)/originating in living organisms; [2]

Answer 122

Q6 b)i) Amino acid; [1] | ii) Peptide; [1]

Answer 123

Answer 124

Q5 a)ii) A: glucose; B: protein; C: fructose/galactose/maltose/lactose/other mono- or disaccharide (except sucrose); D: starch; [4]

Answer 125

Q5 a)iii) Mix a small amount of the test solution with an equal volume of Benedict’s reagent and heat; [1]

Answer 126

Q5 b) Sucrose; a non-reducing disaccharide/sugar which hydrolyses into glucose and fructose (reducing sugars); [2]

Answer 127

Q6 a)i) C, H, O, N (not S); [1]

Answer 128

Q6 a)ii) The protein consists of two or more polypeptide chains; [1]

Answer 129

Q6 b)i) Mucin; | keratin/collagen; mucin/trypsin; trypsin; [4]

Answer 130

Q6 b)ii) The keratin is produced in cells, not within the hair/ amino acids are obtained from the diet, rather than applied to the body/other appropriate response; [1]

Answer 131

Q6 e) Research groups working in different parts of the world can study the findings of other teams easily/may be of use to teams working on different areas of biology (or by example)/other appropriate response; [1]

Answer 132

Q2 a) Similarities Any two from: • both contain only carbon, hydrogen and oxygen • both are produced by condensation reactions/are broken down by hydrolysis reactions • both may be used as energy storage/release energy during respiration [both contain/produce energy is not acceptable] • both are insoluble/have no osmotic effect Differences Any two from: • polysaccharides are carbohydrates (starch, glycogen and cellulose) while triglycerides are lipids (fats and oils) • polysaccharides are made from monosaccharides (glucose) while triglycerides contain glycerol and fatty acids • polysaccharides are polymers/many monomers, triglycerides are not • polysaccharides contain glycosidic bonds, while triglycerides contain ester bonds • fats contain much less oxygen than polysaccharides • fats contain more energy per gram than polysaccharides • triglycerides are hydrophobic, polysaccharides are not

Answer 133

Q2 b) Iodine (for starch) and Clinistix (for glucose); [1]

Answer 134

Q5 a)i) Secondary structure: helices evident in polypeptide chains; Quaternary structure: three (more than one) polypeptide chains present; [2] ii) The arrangement of polypeptide chains/triple helix provides (tensile) strength [must relate structure to strength]; [1] b) Hydrophobic amino acids found in interior/at Y; orientated away from cytoplasm/extracellular fluid/because water present to exterior; [2]

Answer 135

Q7 a) A: hydrogen bond; B: phosphodiester bond/covalent; [2]

Answer 136

Q7 b) In a new DNA molecule, one strand is conserved from the parent molecule; while the other strand is newly synthesised (from free nucleotides); [2]

Answer 137

Q7 c)i) (Nitrogenous/organic)bases; [1]

Answer 138

Q7 c)ii) Following one generation: one intermediate band drawn; Following two generations: two bands drawn – one intermediate and one light; [2] iii) In each molecule of DNA, one strand contains heavy nitrogen (15 N)/is the parental strand, while the other contains light nitrogen (14 N)/is the new strand; [1]

Answer 139

Q1 Reducing sugars/minimum of two appropriate examples; diploid; (poly)unsaturated; reverse transcriptase; [Out of 4]

Answer 140

Q5 b) Branched/has 1–6 bonds; produces many terminal ends/aids hydrolysis/makes molecule more compact; or Large molecule; (insoluble) so exerts no osmotic effect/does not pass through the cell membrane; [2]

Answer 141

Answer 142

Q8 a)ii) Any two from • ionic bonds • hydrogen bonds • disulphide bonds/bridges • hydrophobic interactions [2]

Answer 143

Q8 b)i) Any four from • add solvent to the chromatography vessel and allow it to saturate the atmosphere • draw a base line in pencil towards the bottom of the chromatography paper • add a spot of the amino acid solution to the base line, allow it to dry and re-apply the solution to make a concentrated spot • lower the paper into the vessel, ensuring the base line is above the level of the solvent • allow sufficient time for the solvent to rise up the paper but not reach the top/ensure chromatography paper does not touch side of vessel • remove the paper and mark the solvent front • handle the paper using gloves/tongs/avoid touching the paper/ touching only sides or top [4]

Answer 144

Q8 b)ii) Avoid breathing vapour/wear gloves/carry out procedure in a fume cupboard; [1]

Answer 145

Q8 c) Distance moved by spot 3cm, distance moved by solvent 6cm; Rf value 3 ÷ 6 = 0.5 [consequential to answer above]; X corresponds to asparagine [consequential to R f value calculated]; [3]

Answer 146

Q2 a)i) Blue to purple/lilac; [1] ii) Benedict’s (reagent); [1]

Answer 147

Q2 b) A: protein; B: glucose; C: sucrose/non-reducing sugar; D: fructose/maltose/lactose/galactose/reducing sugar other than glucose; [4]

Answer 148

Q3 a)i) Correct pairing of bases; new strand antiparallel to existing strand; [2]

Answer 149

Q3 a)ii) Cytosine = guanine = 21%; Adenine and thymine both = (100 – 42) ÷ 2 = 29%; [2]

Answer 150

Q6 c) Calcium: to make calcium pectate (for cell walls)/middle lamella; Magnesium: to make chlorophyll; [2]

Answer 151

Q7 a)i) Condensation (reaction); [1] | ii) 1:3; [1]

Answer 152

Q8 Thirteen points, with a maximum of seven from each section Similarities and differences in structure: • all three have (1,4) glycosidic links/formed by condensation reactions • starch and glycogen contain alpha-glucose • there are two components of starch, amylose and amylopectin • in amylose the long chain of monomers is wound into a helix • amylopectin is branched due to additional 1,6 (glycosidic) links • glycogen is similar to amylopectin but more branched • cellulose is composed of beta-glucose • and forms straight chains (because every second glucose is ‘upside-down’) • parallel chains are held together by hydrogen bonds/cross linkage Role and distribution: • starch and glycogen are both glucose/energy stores • starch is found in chloroplasts/storage tissue (e.g. seeds/roots/tubers) • glycogen is found in muscle/liver cells/fungi • the helix/branching makes the molecules more compact (for storage) • glycogen/amylopectin are more readily hydrolysed due to more terminal ends (for enzymes to work on) • starch/glycogen are insoluble so exert no osmotic effect/cannot leach out of the cell • cellulose offers tensile strength to plant cell walls • layers of cellulose are arranged at varying angles to each other, which adds to the tensile strength

Answer 153

Q3 A: Cellulose; | B: starch; C: sucrose; D: maltose; E: glucose; [5]

Answer 154

Q5 a) Nucleotide; [Accept deoxyribose nucleotide, but NOT ribonucleotide] [1] b)i) One intermediate band after one generation; two bands, one light and one intermediate after two generations; [2] (ii) Semi-conservative replication of the DNA/each (heavy) strand acts as a template; produces DNA with one heavy chain and one light chain; [2] [allow by means of a diagram] [Note: Diagrams may not be accepted on the current specification]

Answer 155

Q7 a) Any three from • more glucose is absorbed by living intestinal cells than arabinose • similar amounts of glucose and arabinose are absorbed by cyanide-treated cells • treatment with cyanide causes a (significant) reduction in the rate of absorption of glucose • similar treatment with cyanide does not affect the rate of arabinose absorption [3]

Answer 156

Q7 b) Arabinose; as the rate remains the same in the intestinal cells treated with cyanide; suggesting that ATP/respiration is not needed for arabinose absorption/it is a passive process [NOT energy for ATP]; [3]

Answer 157

Q7 c) Glycogen; Any three from • contains alpha-glucose molecules • joined by condensation reactions/glycosidic bonds • both 1–4 and 1–6 bonds are present • 1–4 bonds create the straight chains/1–6 bonds create branching [4]

Answer 158

Q3 a) Amino acids; condensation; peptide; genes/DNA/mRNA; [4]

Answer 159

Q3 b) Any four from • hydrogen bonds (between the amino acids) leads to twisting/folding of the chain/secondary structure • and can take the form of an alpha-helix or a beta-pleated sheet • a protein will then fold further onto itself to form a tertiary structure/ tertiary structure represented by a globular shape • this involves H bonds, ionic bonds, disulfide bonds and hydrophobic interactions (between the R groups of the individual amino acids) [any two] • in some proteins, a quaternary structure forms between two or more polypeptide chains • this involves mainly disulfide bonds between the individual chains [4]

Answer 160

Q3 c) Blue to mauve/lilac; [1]

Answer 161

Q7 a) Hydrolysis; [1]

Answer 162

Q8 a) Any eight points Nucleic acids (common features): • nucleic acids are chains of nucleotides • (a nucleotide) consists of a pentose sugar, a phosphate and a nitrogenous (organic) base/purine and pyrimidine [or by diagram] • the sugars and phosphates are joined to form the spine [or by diagram] • by phosphodiester/condensation/covalent bonds DNA and RNA (comparisons): • in DNA the pentose sugar is deoxyribose, while in RNA it is ribose • DNA is a double chain/double helix, while RNA is single stranded • hydrogen bonds between the bases form the double chain (in DNA) • in DNA the bases are adenine, thymine, cytosine and guanine • in DNA adenine (A) always pairs with thymine (T), while cytosine (C) pairs with guanine (G)/a purine binds to a pyrimidine • in DNA the two strands run anti-parallel to each other • a DNA molecule is much longer than an RNA molecule (allow converse) • in RNA thymine is replaced by uracil • there are three forms of RNA – ribosomal, messenger and transfer [8]

Answer 163

Q8 b) Any five points • DNA replication is said to be semi-conservative, because each new molecule contains one old strand and one new strand • the two sides of the DNA molecule are “unzipped” from one end • by DNA helicase • each strand acts as a template for the formation of new strands • free nucleotides enter opposite their complementary bases (A opposite T and C opposite G) • DNA polymerase catalyses the joining up of the nucleotides • by condensation reactions [5]

Answer 164

Q3 A: polysaccharides/starch/glycogen/cellulose/amylose/amylopectin; B: triglycerides/lipids/fats/oils; C: proteins/polypeptides; D: phospholipid; E: nucleic acids/DNA/RNA; [5]

Answer 165

Q2 a)i) Prion; Protein; [2] ii) BSE/Scrapie; [1]

Answer 166

Q2 b)i) Eating prion-rich food/spontaneous transformation from normal to disease-causing prion/inherited genetic mutation; [1]

Answer 167

Q2 b)ii) Changes to secondary structure, forming more B-pleated sheets, leading to the replication of disease-causing prions/conversion of enough normal to disease-causing prions to cause symptoms; [1]

Answer 168

Q2 c) Contain DNA/RNA/nucleic acids; [1]

Answer 169

Q4 a) Condensation reaction; | Glycosidic bond; [1]

Answer 170

Q4 b) Structure: Made from a-glucose monomers; Starch is comprised of two polymers while glycogen is comprised of only one polymer/glycogen is more highly branched than starch; Function: Storage polymers/store glucose for energy; Glucose is more readily released from glycogen than starch; [4]

Answer 171

Q4 c) Provides support/structural polymer; | Long, parallel unbranched chains/fibrils joined by hydrogen bonds; [2]

Answer 172

Q6 c)i) [1] Organism Percentage of bases in organism’s DNA/% Adenine Guanine Cytosine Thymine E. coli 24 26 24 ii) Sequence of bases are different; [1]

Answer 173

Q6 d)i) Each new DNA molecule contains one template strand and one new DNA strand. [1]

Answer 174

Q6 d)ii) DNA helicase; Breaks the hydrogen bonds between strands; DNA polymerase; Joins the nucleotides of new strand together; [4]

Answer 175

Q6 e)i) The second diagram should show an intermediate (hybrid) band of DNA in the middle of the test tube and a light band of DNA situated at the top of the test tube. [1] ii) The light band (top one) will be thicker (while the hybrid band (intermediate) will stay the same); All new DNA produced will consist of two light (14N) strands (while the amount of hybrid (14N/15N) DNA will remain the same); [2]