Topic 1 - Biological Molecules + Enzymes

Question 1

What is the test for reducing sugars? How does it work?

Answer 1

Benedict’s Test
1) Add food sample into test tube.
2) Add Benedict’s reagent into it.
3) Heat mixture in water bath for 5 minutes.
4) Positive result = green, yellow, orange, red.

Question 2

Which disaccharide does alpha glucose and galactose make?

Answer 2

Lactose

Question 3

What disaccharide does alpha glucose and alpha glucose make?

Answer 3

Maltose

Question 4

What disaccharide does alpha glucose and fructose make?

Answer 4

Sucrose

Question 5

How is a disaccharide formed?

Answer 5

When monosaccharides join, a molecule of water is removed (condensation reaction). The bond formed is a glycosidic bond.

Question 6

What is the test for non-reducing sugars? How does it work?

Answer 6

Benedict’s Test
1) Add dilute hydrochloric acid and leave in water bath for 5 minutes
2) Add sodium hydrogencarbonate solution to neutralise acid.
3) Add Benedict’s reagent and place back in water bath for 5 minutes.
4) Positive result = green, yellow, orange, red

Question 7

The polymer Glycogen:
Monomer it is made from
Structure
Role
Why its role is suited for its structure.

Answer 7

• Alpha glucose
• 1-4 and 1-6 glycosidic bonds, highly branched.
• Storage.
• Insoluble (does not diffuse out of cells), compact, more rapidly broken down to form glucose.

Question 8

The polymer Cellulose:
Monomer it is made from
structure
role
why its role is suited for its structure.

Answer 8

• Beta glucose.
• 1-4 glycosidic bonds, unbranched, microfibril chains.
• Keeping structure of plant cell walls stable.
• Hydrogen bonds form crosslinks between adjacent chains which strengthens it, high tensile strength of fibres maintain shape and rigidity.

Question 9

The polymer Starch:
Monomer it is made from
structure
role
why its role is suited for its structure

Answer 9

• Alpha glucose.
• 1-4 and 1-6 glycosidic bonds, branched, coil shape held together by hydrogen bonds.
• Energy storage.
• Insoluble (doesn’t affect water potential, water not drawn into cells by osmosis). Compact, when hydrolysed forms alpha glucose which is easily transported and used in respiration.

Question 10

What is the test for starch? How does it work?

Answer 10

1) Place sample in test tube.
2) Add few drops of iodine solution.
3) Positive result = blue-black colour.

Question 11

What are the main roles of lipids?

Answer 11

• Energy source (provide twice as many calories as carbohydrates + proteins).
• Waterproofing (waxy cuticle).
• Insulation.
• Protection (delicate organs have fat around them).

Question 12

What is a triglyceride? What is the main features of them?

Answer 12

Composed of 1 glycerol molecule and 3 fatty acids that join via 3 condensation reactions. The bond that joins them is an ester bond.
- Low mass to energy ratio (good storage).
- Insoluble in water.
- High ratio of hydrogen to oxygen atoms (release water when oxidised).
- High ratio of energy-storing carbon-hydrogen bonds to carbon atoms (excellent source of energy).

Question 13

Do saturated fatty acids have single carbon bonds or double?

Answer 13

Single.

Question 14

Do unsaturated fatty acids have single carbon bonds or double?

Answer 14

Double.

Question 15

What is a phospholipid? What are its main features?

Answer 15

One fatty acid replaced by a phosphate molecule.
- Hydrophilic ‘head’ (likes water, not fat).
- Hydrophobic ‘tail’ (hates water, mixes with fat).
- Bipolar layer (hydrophilic head faces outwards, hydrophobic tails face towards the centre).

Question 16

What is the test for lipids? How does it work?

Answer 16

Emulsion test.
1) Add sample to test tube.
2) Add ethanol and shake vigorously.
3) Add distilled water and shake gently.
4) Positive result = milky-white emulsion.

Question 17

What is a protein? What are the 3 major parts of them?

Answer 17

Three dimensional molecules whose monomers are the 20 different amino acids found in nature.

Consists of: Amine group, R group, and a Carboxyl group.

Question 18

How are dipeptides formed?

Answer 18

Amino acids become linked by a new peptide bond between carbon atom of one amino acid and the nitrogen atom of the other. Formed by the removal of water (hydrolysis reaction).

Question 19

What is the primary structure of protein responsible for?

Answer 19

Polymerisation forms polypeptides - determines the protein’s shape and function. Sequence of amino acids.

Question 20

What is the secondary structure of a protein responsible for?

Answer 20

Long polypeptide chain twisted into a 3D shape - alpha helix or beta pleated sheets.

Question 21

What is the tertiary structure of a protein responsible for? What bonds does it contain?

Answer 21

Structure gives complex, specific 3D structure of each protein.
- Disulfide bridges (fairly strong).
- Ionic bonds (weak, formed between carboxyl and amino groups).
- Hydrogen bonds (weak and easily broken, but numerous).

Question 22

What is the quaternary structure of a protein responsible for?

Answer 22

More than one polypeptide group. May also contain non-protein groups.

Question 23

What is the test for proteins? How does it work?

Answer 23

Biuret test.
1) Place sample in test tube.
2) Add sodium hydroxide (room temp).
3) Add few drops of dilute copper(II) sulfate solution and mix gently.
4) Positive result = violet/purple.

Question 24

What are the main properties of enzymes?

Answer 24

• Biological catalysts.
• Globular proteins at tertiary level.
• Effective in small amounts.
• Most reactions are reversible.
• Most denatured by extreme pH and temperature.

Question 25

What are the 3 conditions required for a chemical reaction to occur?

Answer 25

• Substrate collide with enzyme with sufficient kinetic energy.
• Energy of products lower than substrates.
• Initial boost of energy required (activation energy).

Question 26

What is the structure of an enzyme?

Answer 26

• They are a protein.
• Bonds such as hydrogen bonds maintain the shape.
• Single polypeptide chain of 50 amino acids form the enzyme.
• Amino acids not forming part of the active site.
• 2 of 6 amino acids bind to substrate.

Question 27

What is the Lock & Key Model? Are there any advantages or disadvantages?

Answer 27

A substrate will only fit into an active site of a specific enzyme. The shape of the substrate is the exact shape as the active site.

• Enzyme was considered to be a rigid structure, but scientists observed that other molecules could combine to enzymes at sites other than the active. This model is no longer accurate.

Question 28

What is the Induced Fit Model? Any advantages / disadvantages?

Answer 28

Active site forms the enzyme, and the substrate interacts with it. The substrate is complementary to the active site and the active site will change its shape to bind to the substrate forming enzyme-substrate complexes.

+ The model is now more widely accepted after the discovery of an enzyme being flexible (active site moulds to shape of substrate).

Question 29

What are the main factors affecting enzyme action?

Answer 29

• Temperature.
• pH
• Enzyme concentration
• Substrate concentration

Question 30

What is a competitive inhibitor?

Answer 30

They fill the active site of the enzyme instead of the substrate. The substrate can no longer use the active site and enzyme-substrate complexes can’t be formed.

Question 31

What is a non-competitive inhibitor?

Answer 31

These bind to the enzyme in places other than its active site. This changes the shape of the enzyme which ends up changing the shape of the active site. The substrate is no longer complementary to the active site and enzyme-substrate complexes can no longer form.