SUMMARY QUESTIONS - Biological molecules

Question 1

Large molecules often contain carbon, Explain why

Answer 1

Carbon atoms readily link to one another to form a chain

Question 2

State the general name for a molecule that is made up of many similar repeating units

Answer 2

Polymer

Question 3

Explain why Benedict’s reagent turns red when heated with a reducing sugar

Answer 3

Sugar donates electrons that reduce blue copper (II) sulfate to orange copper (I) oxide

Question 4

Suggest a way, other than comparing colour changes, in which different concentrations of reducing sugar could be estimated

Answer 4

• Dry the precipitate in each sample and weigh it.
• the heavier the precipitate = the more reducing sugar present

Question 5

Explain why it isn’t possible to distinguish between very concentrated samples, even when their concentrations are different

Answer 5

Once all the copper (II) sulfate has been reduced to copper (I) oxide, further amounts of reducing sugar cannot make a difference

Question 6

Identify which one, or more monomer units make up each of the following carbohydrates
A: lactose
B: sucrose
C: starch

Answer 6

A - glucose + galactose
B - glucose + fructose
C - alpha glucose only

Question 7

Glucose (C6H12O6) combines with fructose (C6H12O6) to form the disaccharide sucrose. From your knowledge of how disaccharides are formed, deduce the formula of sucrose

Answer 7

C12H22O11
- because: (C6H12O6) + (C6H12O6) - H20 (form removal of water to form glycosidic bond)

Question 8

To hydrolyse a disaccharide it can be boiled with hydrochloric acid but if hydrolysis is carried out by an enzyme a much lower temp (40’C) is required. Explain why

Answer 8

Enzymes are denatured at higher temps and this prevents them functioning / enzymes lower the activation energy required

Question 9

What will ‘stain blue with iodine solution’

Answer 9

Starch

Question 10

What ‘is known as “animal starch”’

Answer 10

Glycogen

Question 11

What saccharide is found in plants

Answer 11

• alpha and beta glucose
• starch
• cellulose

Question 12

Fill the gap:
Fats and oils make up a group of lipids called (A) which, when hydrolysed, form (B) and fatty acids. A fatty acid with more than one carbon-carbon double bond is described as (C). In phospholipid the number of fatty acids is (D); these are described as (E) because they repel water

Answer 12

A - triglycerides
B - glycerol
C - polyunsaturated
D - two
E - hydrophobic

Question 13

List 2 differences between a triglyceride molecule and a phospholipid molecule

Answer 13

• Triglyceride: 3 fatty acids / no phosphate group / nonpolar
• Phospholipids: 2 fatty acids + 1 phosphate group / hydrophilic ‘head’ and hydrophobic ‘tail’

Question 14

Organisms that move, e.g. animals, and parts of organisms that move, e.g. some plant seeds, use lipids rather than carbohydrates as an energy store. Suggests one reason why

Answer 14

• lipids provide 2x as much energy as carbohydrate when they are oxidised
• if fat is stored, the same amount of energy can be provided for less than half the mass
• therefore its a lighter storage product — a major adv if the organism is motile

Question 15

Name the type of bond that joins amino acids together

Answer 15

Peptide bond

Question 16

State the type of reaction involved in joining amino acids together

Answer 16

Condensation reaction

Question 17

List 4 different components that make up amino acids

Answer 17

• amino group (—NH2)
• carboxyl group (—COOH)
• hydrogen atom (—H)
• R group

Question 18

Define a catalyst

Answer 18

A substance that alters the rate of a chemical reaction without undergoing permanent change

Question 19

Explain why enzymes are effective in tiny quantities

Answer 19

They aren’t used up in the reaction and so can be used repeatedly

Question 20

Outline why changing one of the amino acids that make up the active site could prevent the enzyme from functioning

Answer 20

The changed amino acid may no longer bind to the substrate, which will then not be positioned correctly, if at all, in the active site

Question 21

Explain why changing certain amino acids that aren’t taking part of the active site also prevents the enzyme from functioning

Answer 21

• The changed amino acid may be one that forms hydrogen bonds with other amino acids
• if the new amino acid doesn’t form hydrogen bonds the tertiary structure of the enzyme will change, including the active site, so that the substrate nay no longer fit

Question 22

Explain why enzymes function less well at lower temps

Answer 22

• To function, enzymes must physically collide with their substrate
• lower temps decrease the kinetic energy of both enzyme and substrate molecules, which then move around less quickly
• they hence collide less often and therefore react less frequently

Question 23

Explain how high temps may completely prevent enzymes from functioning

Answer 23

• The heat causes hydrogen and other bonds in the enzyme molecule to break
• The tertiary structure of the enzyme molecule changes, as does the active site
• the substrate no longer fits in the active site

Question 24

Enzymes produced by microorganisms are responsible for spoiling food. using this fact and your knowledge of enzymes, deduce why each of the following procedures are carried out:
A - food is heated to a high temp before being canned
B - Some foods, such as onions, are preserved in vinegar

Answer 24

A - High temps denature the enzymes and so they can’t spoil food
B - Vinegar is very acidic and the very low pH will denature the enzymes and so preserve the food

Question 25

Calculate the pH of a solution that has a hydrogen ion concentration of 0.0001 M

Answer 25

• pH = 4

Question 26

Different conditions affect how enzymes work. Name one that might vary between one organelle and another

Answer 26

• pH / substrate conc. (not temp)

Question 27

Suggest why enzymes are attached to the inner membrane of an organelle ‘in a very precise sequence’

Answer 27

• in a metabolic pathway
• the product of 1 reaction acts as the substrate for the next reaction
• By having the enzymes in appropriate sequence there is a greater chance of each enzyme coming into contact with its substrate than if enzymes are floating freely in the organelle
• this is a more efficient means of producing the Ned product

Question 28

If an end product inhibits enzyme B rather than enzyme A, predict what would be:
A - the initial effect on the concentration of intermediate 1
B- the overall longer term effect on the concentration of the end product

Answer 28

A - it would increase
B - it would be unchanged

Question 29

Suggest one advantage of end-product inhibition being non-competitive rather than competitive. relate your answer to how the two types of inhibition take place

Answer 29

ADV - the level of the end product doesn’t fluctuate with changes in the level of substrate
Explanation:
- Non-competitive inhibition occurs at a site on the enzyme other than active site
- Hence its not affected by the substrate conc.
- therefore changes in level of substrate doesn’t affect the inhibition of the enzyme, nor the normal level of the end product
- If it were competitive, changes in level of substrate would affect end product molecules combining with active site, resulting in fluctuating of the degree of inhibition AND level of end product

Question 30

Distinguish between a competitive and a non-competitive inhibitor

Answer 30

Competitive inhibitors occupy the active site of an enzyme while non-competitive inhibitors attach to the enzyme at a site other than the active site

Question 31

An enzyme-controlled reaction is inhibited by substance X. Suggest a simple way in which you could tell whether substance X is acting as a competitive or a non-competitive inhibitor

Answer 31

• Increase the substrate conc.
• if the degree of inhibition is reduced = competitive inhibitor
• if it stays the same = non-competitive inhibitor