Unit 1: Biological Molecules

Question 1

Describe DNA Replication (6)

Answer 1

1) DNA Helicase unwinds DNA by breaking hydrogen bonds
2)Both acts as templates
3) Nucleotides line up in complementary pair; Adenine-Thymine and Guanine-Cytosine
4) DNA Polymerase joins nucleotides
5) Forming Phosphodiester bonds
6) Each new DNA molecule consists of one original template strand and one new strand

Question 2

Describe and explain how structure of DNA allows accurate replication (6)

Answer 2

1) Two strands therefore semi-conservative replication
2) Hydrogen bonds holds strand together
3) Hydrogen bonds easily broken, allows strands to separate
4) Bases acts as templates
5) A-T C-G/ Complementary copy
6) DNA is one parent and one new strand

Question 3

Describe how phosphodiester bonds is formed between two nucleotides in a DNA molecule (3)

Answer 3

1) Condensation reaction
2) Between phosphate and deoxyribose sugar
3) Catalysed by DNA polymerase

Question 4

ATP- Uses and properties as an energy source (5)

Answer 4

1) Releases small amount of energy/ little energy lost to heat
2) Releases energy instantaneously
3) Phophorylates other compounds, making them more reactive
4) Can be rapidly re-synthesised
5) Does not leave cells

Question 5

Starch- Relate 3 properties to its function (6)

Answer 5

1) Insoluble
2) Doesn’t affect water potential
3) Helical
4) Compact
5)Large molecule
6) Cannot leave cell

Question 6

What is the test for a reducing sugar? (3)

Answer 6

1) Add excess Benedict’s reagent to test solution
2) Heat mixture
3) If reducing sugar is present, colour change for blue to brick red

Question 7

What is the test for a non-reducing sugar? (3)

Answer 7

1) Heat solution with Benedict’s reagent and no colour change
2) Boil with Hydrochloric Acid and then neutralise with Sodium Hydroxide
3) Re-heat with Benedict’s reagent and colour change from blue to brick red showing non-reducing sugar was initially present

Question 8

What is the test for starch? (2)

Answer 8

1) Add iodine to potassium iodide solution
2) Colour change from brown to blue-black

Question 9

Describe how and ester bond is formed in a phospholipid molecule (2)

Answer 9

1) Condensation reaction
2) Between glycerol and fatty acid

Question 10

What is the test for lipid (2)

Answer 10

1) Mix sample with ethanol, then water
2) White emulsion present

Question 11

What is the test for protein? (2)

Answer 11

1) Add biuret reagent to sample
2) Colour change to lilac

Question 12

ATP- Structure compared with DNA nucleotide (3)

Answer 12

1) ATP has ribose and DNA has deoxyribose
2) ATP has 3 phosphates and DNA nucleotides have one
3) Bases always adenine in ATP and bases vary in DNA nucleotide

Question 13

Talk about the two polymers of starch (2)

Answer 13

1) Amylase- Helical
2)Amylopectin -Branched

Question 14

Talk about glucose (mention galactose)

Answer 14

• Has two isomers: Alpha and Beta
  Alpha- Has H on top of C1
  Beta- Has OH on top of C1

Glucose- H on top of C4
Galactose- OH on top of C4

Question 15

What is Hydrolysis?

Answer 15

Breaking of a chemical bond between 2 molecules, using water

Question 16

What is a condensation reaction?

Answer 16

Creating a chemical bond with removing a molecule of water

Question 17

How are triglycerides formed? (3)

Answer 17

1) One glycerol and three fatty acids
2) Condensation and removal of three molecules go water
3) Ester bonds formed

Question 18

Phospholipids compared with triglycerides (8)

Answer 18

1) Both contain ester bonds
2) Both contain glycerol
3) Fatty acids can be saturated or unsaturated
4)Both insoluble
5) Both contain C H and O but phospholipids also contain P
6) Triglycerides contain 3 fatty acids whereas phospholipids has two fatty acids and a phosphate group
7)Triglycerides are hydrophobic whereas phospholipids has hydrophobic and hydrophilic region
8) Phospholipids form bilayer but triglycerides don’t

Question 19

Protein- Protein Structure (7)

Answer 19

1) Polymer of amino acids
2) Joined by peptide bonds
3) Formed by a condensation reaction
4) Primary structure is order of amino acids
5) Secondary structure is folding of polypeptide chain due to hydrogen bonding forming alpha helices
6) Tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulphide bridges between R groups
7) Quaternary Structure is more than one polypeptide chain

Question 20

Enzyme- Denaturation (5)

Answer 20

1) Heat about optimum breaks hydrogen bonds
2) Causing tertiary structure to unfold
3) Active site changes shape
4) Substrate no longer complementary to active site
5) Fewer Enzyme-Substrate Complexes form

Question 21

Glycogen Structure (3)

Answer 21

1) Polysaccharide of alpha glucose
2) Joined by glycosidic bonds
3) It is a branched structure

Question 22

Enzyme- Increased temperature and reaction rate (4)

Answer 22

1) Particles have more kinetic energy
2) Therefore they move more
3) More collision between substrates and active sites
4) More enzyme- Substrate complexes form

Question 23

Glycogen- Glycogen structure related to function (5)

Answer 23

1) Insoluble, so doesn’t affect water potential
2) Branched/coiled, makes molecules compact
3) Polymer of alpha glucose so provides glucose for respiration
4) Branched, fast enzyme action
5) Large molecule, cant cross cell membrane

Question 24

Water- Properties that make water important for organisms (6)

Answer 24

1) A metabolite in condensation/hydrolysis
2) Solvent so metabolic reactions can occur
3) High heat capacity so buffers changes in temperature
4) Large latent heat of vaporisation so provides a cooling effect
5) Cohesion so supports columns of water
6) Cohesion produces surface tension supporting organisms

Question 25

Enzymes- Comparison of Competitive and non-competitive inhibitors (4)

Answer 25

1) Competitive binds to active site but non-competitive binds to allosteric site 2) Competitive doesn't change shape of active site but non-competitive does 3) With competitive, at high substrate concentration, enzyme still available but with non-competitive, enzyme not available 4) At high substrate concentration, likelihood of ES collisions increases with CI but not possible with N-CI

Question 26

Enzyme- Effects of changing in pH (4)

Answer 26

1) ionic bonds holding tertiary structure break 2) Active site distorts and substrate no longer binds to active site 3) Charges on amino acid in active site affected 4) Fewer ES complexes formed

Question 27

Enzyme, Induced Fit Model (3)

Answer 27

1) Before, active site not complementary to substrate 2) Shape of active site changes as substrate binds and enzyme-substrate complexes form 3) Bending bonds in substrate

Question 28

Describe structure of DNA (5)

Answer 28

1) Polymer of nucleotides 2) Each nucleotides formed from deoxyribose, a phosphate group, and an nitrogenous base 3) Phosphodiester bonds between nucleotides 4) Double helix held by hydrogen bonds 5) Hydrogen bonds between A,T and G-C

Question 29

Glycogen- Glycogen compared with cellulose (4)

Answer 29

1) Cellulose made of beta-glucose and glycogen made of alpha-glucose 2) Cellulose is straight chained and glycogen is branched 3) Cellulose is straight chained and glycogen is coiled 4) Glycogen has 1,4 and 1,6 glycosidic bonds and cellulose has only 1,4 glycosidic bonds