proteins and carbs

Question 1

Answer 1

Carbon + hydrogen and oxygen in 2: 1 ratio/same proportions as in water;

Question 2

Explain why sucrose will produce a positive result with Benedict’s test only after it has been boiled with a dilute acid.

Answer 2

Needs to be hydrolysed/glycosidic bond broken;

Product is a reducing sugar/glucose/fructose/monosaccharide;

Frees aldehyde/carbonyl/ketone group;

Question 3

Explain how proteins are suited for their roles as receptor molecules

Answer 3

many different sorts of proteins;

Different primary structures/sequences of amino acids;

Tertiary structure;

Shape;

allowing formation of receptor/binding site/site into whichsubstance/substrate fits;

Question 4

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

Answer 4

Glucose and maltose soluble/starch insoluble;

Question 5

Saccharin, cyclamates and sucrose are chemically different but they all taste sweet. Suggest why.

Answer 5

Have similar molecular shape/structure / similarly positionedchemical groups;

so bind to/fit receptors;

Question 6

Suggest oneadvantage of immobilising the lactase used in thisreaction.

Answer 6

Doesn’t contaminate product/stays in reactor at finish/re-use/allows continuous reaction;

Question 7

In terms of your knowledge of the way in which enzymes work, explain why it is necessary to pass the milk through the reactor several times to reduce the amount of lactose sufficiently.

Answer 7

At low temperatures/9°C;

Relatively little kinetic energy/molecules only moving slowly;

Fewer collisions with enzyme;

Slower rate of reaction/takes longer for lactose to be reduced/somesubstrate goes through unchanged;

or

Enzyme concentration limiting;

Substrate in excess;

Saturation of active sites/all occupied;

Some substrate goes through unchanged;

Question 8

Explain the change in the rate of reaction with time.

Answer 8

Fewer substrate/lactose molecules/lactose concentration falls;

Therefore less chance of collision with enzyme/forming enzymesubstrate complex;

Question 9

Suggest why the reaction is stopped at the time shown on the graph.

Answer 9

Economic reason such as

low levels of lactose not harmful/would take too much time/high cost involved in removing all lactose;

Question 10

Use the graph to explain what is meant by the term activation energy.

Answer 10

Energy put in to get reaction started(Look for idea of getting started);

Question 11

Describe a biochemical test which could be used to show that reducing sugars were produced in the first stage of this process.

Answer 11

Benedict’s / Fehling’s reagent and heat;

orange / red / brown / yellow / green;

Question 12

Acid could have been used in place of the a-amylase in the first stage of this process. Suggest why:

(i) acid could have been used
(ii) acid was not used.

Answer 12

(i) Acid hydrolyses starch / breaks glycosidic bond;
(ii) Not specific / forms by–products / alters pH / corrosive;

Question 13

In the laboratory, the optimal conditions for bacterial a-amylase are a pH of 7 and a temperature of 80°C.In terms of your knowledge of the way in which enzymes work, explain why the rate of reaction would change if:

(i) the temperature fell by 10°C
(ii) the pH changed substantially.

Answer 13

(i)Molecules would have less (kinetic) energy;

move slower;

fewer collisions / fewer E–S complexes form;

(ii)Change in pH alters charge / shape;

distorts active site / tertiary structure of enzyme / denatures enzyme;substrate will no longer fit active site;

Question 14

Suggest two reasons why a test for glucose in urine based on glucose oxidase and peroxidase might be preferred to one using Benedict’s reagent.

Answer 14

Gives quantitative result/level of glucose/concentration of glucose;

specific (to glucose) / Benedicts not specific;

more sensitive / accurate / precise;

Question 15

Name part A

Answer 15

Glycerol / glyceride;

Question 16

With reference to named parts of the diagram, explain the difference between the terms:(i)triglyceride and phospholipid

(ii)saturated and unsaturated.

Answer 16

(i)Phospholipid has (one) phosphate / Phosphoric acid;

replacingfatty acid;

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

fatty acid 1 is saturated/fatty acids 2 and 3 are unsaturated;

Question 17

Starch is an important storage substance in plants. Give two features of starch molecules and explain how each enables starch to act as an efficient storage substance.

Answer 17

coiled shape / compact / branched allows large amount to be packedin small space;

Insoluble so not “washed away” / does not affect water potential /osmosis;

Made of glucose / readily broken down for respiration/ energy release /ATP production ORmany free ends / branched so readily broken down;

Question 18

Describe a chemical test that would enable you to show that glucose syrup contained reducing sugar.

Answer 18

Benedict’s reagent / test and heat;

Green / yellow / orange / red colour,

Question 19

Suggest how you could use this test (benedicts) to compare the amount of reducing sugar in two solutions.

Answer 19

Standardisespecific feature / carry out tests the same;

e.g. amounts used / time heated / temperature

Compare colour / amount of precipitate / time taken to get colour;

Question 20

What are the “same four chemical elements” found in all amino acids

Answer 20

Carbon, hydrogen, oxygen, nitrogen / CHON;

Question 21

Explain why “unlike triglycerides, proteins are polymers”

Answer 21

Proteins made up of many monomers / amino acids;

Tryglyceride made of glycerol and fatty acids / few smaller molecules/not joined in chain;

Question 22

Glycogen is also a polymer. Explain how many different sorts of protein can be produced but only one sort of glycogen.

Answer 22

Different sorts of amino acids;

Only one sort of glucose;

Question 23

Explain what causes molecules of a particular protein always to fold into the same shape.

Answer 23

Protein has primary structure / amino acid sequence;

Therefore bonds always form in same position;

Question 24

Describe how molecular shape is important in explaining the way in which enzymes may be affected by inhibitors.

Answer 24

1Active site (of enzyme) has particular shape;

2(Into which) substrate molecule fits / binds;

3Appropriate reference linking induced fit and shape;

4(Competitive inhibitor) has similar shape to substrate;

5Also fits active sites;6Prevents substrate access;

7(Non-competitive inhibitor) fits at site other than active site;

8Distorting shape of active site / enzyme;

6Prevents substrate access; (award once only)

9Two types identified as competitive and non-competitive;

Question 25

Chitin is a nitrogen-containing polysaccharide. Name one chemical element present in a phospholipid which would not be present in chitin.

Answer 25

Phosphorus / P;

Question 26

An artificial membrane was made. It consisted only of a bilayer of phospholipid molecules. In an investigation, the permeability of this artificial membrane was compared with the permeability of a plasma membrane from a cell. Explain why:

(i) both membranes allowed lipid soluble molecules to pass through
(ii) only the plasma membrane allowed glucose to pass through.

Answer 26

(i) Both membranes contain phospholipid / lipid (bilayer);
(ii) Glucose unable to pass through artificial membrane as not lipid soluble;

Glucose transportedby proteins;

(Proteins) found in plasma membrane /not found in artificial membrane;

Question 27

(i) Give the formula of the chemical group at position X on the molecule
(ii) Give one piece of evidence from the diagram that this molecule is made up from three amino acids

Answer 27

(i) NH2;
(ii) Two peptide bonds / reference to specific feature such as C=O / R groupsappearing three times;

Question 28

The molecular formula of fructose is C6H12O6. What is the molecular formula of sucrose?

Answer 28

C12;

H22O11;

Question 29

The bacteria in the intestine are prokaryotic cells. The epithelial cells which line the small intestine are eukaryotic cells. Describe the ways in which prokaryotic cells and eukaryotic cells differ

Answer 29

1Prokaryotic cells do not have a nucleus / have genetic materialin cytoplasm;

2DNA in loop / ring;

3Not associated with proteins / do not have chromosomes /chromatin / do not divide by mitosis;

4Smaller ribosomes;

5No membrane-boundorganelles;

6Such as mitochondria / lysosomes / endoplasmic reticulum /Golgi / chloroplasts;

7Prokaryotic cells may have mesosomes;

8Prokaryotic cells smaller;

9May be enclosed by capsule;

Question 30

(i) Use the information in the first paragraph to explain why glucagon will only bind to one particular type of receptor molecule
(ii) Suggest why glucagon is able to bind to liver cells but not to cells in other parts of the body.

Answer 30

(i)The receptor / glucagon will have a particular shape / tertiary structure;

The other will fit / bind because of its shape;

(ii)Cells in other parts of the body do not have these receptors /Liver cells have these receptors;

Question 31

Explain how the amino acids from which proteins are built differ in structure from each other.

Answer 31

Side chains / R-groups are different;

Question 32

Amylase is an enzyme, found in saliva, which breaks down starch. It works best at a pH of 8. Explain why amylase does not function in the stomach where the pH isapproximately 3.

Answer 32

Tertiary structure changes / enzyme denatured / bonds broken;

Will affect active site (of enzyme);

Starch cannot bind / fit / form enzyme-substrate complex;

Question 33

When a suspension of mitochondria is prepared from liver, the tissue is ground in a buffer solution, then centrifuged. Explain why a buffer solution is used.

Answer 33

Keeps pH constant;

So proteins / enzymes in mitochondria not denatured / affected;

Question 34

Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells.

Answer 34

1 Some proteins pass right through membrane;

2 Some proteins associated with one layer;

3 Involved in facilitated diffusion;

4 Involved in active transport;

5 Proteins act as carriers;

6 Carrier changes shape / position;

7 Proteins form channels / pores;

8 Protein allows passage of water soluble molecules /charged particles / correct named example;

Question 35

Explain what causes the secondary structure to differ in length from the primary structure.

Answer 35

(Polypeptide is) coiled / folded;

Question 36

(ii) Explain what is meant by the tertiary structure of a protein
(iii) Heating may affect the tertiary structure of a protein. Explain how.

Answer 36

(ii)Way in which whole molecule is folded / globular shape / folding of secondary structure / further folding /Do not accept 3D shape if not further explained. Structure held by ionic / disulphide bonds;

reject hydrogenbonds / peptide bonds only

(iii)Causes bonds which hold the tertiary structure / named bond;

To break;

Shape no longer maintained / protein denatured;

Question 37

How many amino acid fragments will be produced from this polypeptide if it is incubated with a mixture of trypsin and V8protease?

Answer 37

5;

Question 38

Explain why trypsin and chymotrypsin break peptide bonds between different amino acids.

Answer 38

Substrates / active sites with shapes;

Active site / substrate with complementary (shape);

Fitting / binding /forming E-S complex;3

Question 39

Describe how phospholipid molecules are arranged in a plasma membrane.

Answer 39

Bilayer / two molecules thick;

“Heads” / hydrophilic parts outwards / “Tails” / hydrophobicparts inward;

Question 40

Suggest why an LDL will only attach to certain areas on the plasma membrane of a cell

(c)Name the process by which the LDL enters the cell.

Answer 40

(b) Only parts of membrane with receptors / molecules into which surface proteins will fit / recognition / binding sites;
(c) Endocytosis / phagocytosis / pinocytosis;

Question 41

(i) Name organelle A
(ii) Explain how this organelle is involved in the release of cholesterol from the vesicle.

Answer 41

(i) Lysosome;
(ii) Enzymes;

Digests / breaks down / hydrolyses (other molecules);

Reject ‘cholesterol’.2

Question 42

Suggest how two molecules can have the same formula but a different structure.

Answer 42

Atoms / named atoms arranged differently / isomers;

Question 43

How many molecules are produced when a triglyceride molecule is completely hydrolysed?

Answer 43

4;

Question 44

(i) Describe how the control group of caterpillars should have been treated
(ii) In caterpillars, glutamate is a non-essential amino acid. Explain the evidence from Figure 1 which supports this.

Answer 44

(i)Exactly the same way as the experimental group;

But fed on a complete diet/all amino acids present;

(ii)Similar number of caterpillars survive as in control/most/high percentageof caterpillars survive when no glutamate in diet;

Therefore must be synthesised/made from something else;

Question 45

Which tissue, present in the wall of the intestine, mixes the contents of the intestine in a live animal?

Answer 45

Muscle;

Question 46

Explain why the enzyme which converts phenylalanine into tyrosine is called phenylalanine hydroxylase.

Answer 46

Add hydroxyl /OH group (to phenylalanine);

Question 47

Phenylketonuria is a genetic disease in which the enzyme phenylalanine hydroxylase (PAH) is missing. If untreated, phenylketonuria causes damage to the growing brain. Suggest and explain one other sign or symptom of phenylketonuria.

Answer 47

Fair skin/hair/eyes blue/not brown;

Will not produce tyrosine;

No melanin/skin pigment;

OR

Small size/lower rate of metabolism;

No/less thryoxine/thyroid hormone produced;

Controls metabolic rate/important in growth of young children;

OR

Less adrenaline/nor adrenaline;

Affects synapses;

Additional detail as to how;