3. Nucleic acids, ATP and Water

Question 1

What is a Nucleotide made up of

Answer 1

Phosphate group
Nitrogen-containing organic base
Pentose sugar

Question 2

What is the pentose sugar in DNA

Answer 2

deoxyribose sugar

Question 3

What are the 4 organic bases in DNA

Answer 3

Adenine
Thymine
Cytosine
Guanine

Question 4

what are the 4 organic bases in RNA

Answer 4

Adenine
Uracil
Cytosine
Guanine

Question 5

What is the sugar in RNA

Answer 5

Ribose

Question 6

How are Polynucleotides formed

Answer 6

A condensation reaction
forms a phosphodiester bond between the phosphate group of one nucleotide to the pentose sugar in the next nucleotide

Question 7

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use

Answer 7

1. Releases relatively small amount of energy/ little energy is lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from/ does not leave cells;

Question 8

Give 2 ways in which the hydrolysis of ATP is used in cells (2)

Answer 8

1. Phosphorlylates other compounds and makes them more reactive;
2. Provides energy for (named process) – protein synthesis/active transport/glycolysis/semi-conservitive replication

Question 9

Describe how ATP is resynthesized in cells (2)

Answer 9

1. ADP + Pi
2. By ATP synthase
3. In respiration

Question 10

Give two properties of water that are important in biology. Explain the importance of each property you identify. (4)

Answer 10

1. Polar (molecules);
2. Dissolves charged particles/acts as a (universal) solvent;
   OR
3. A metabolite;
4. Involved in metabolic/cell reaction/condensation/hydrolysis;
   OR
5. Water molecules stick together/cohesion between water molecules;
6. Provides surface tension/prevents columns of water breaking;
   OR
7. High (specific) heat capacity;
8. Reduces fluctuations in temperature (of water bodies);
   OR
9. High (latent) heat of evaporation;
10. Evaporation of small amount of water cools organisms;

Question 11

Suggest why water becomes lighter as it expands. (2)

Answer 11

1. Density = mass ÷ volume;
2. Ice has same mass of water but greater volume;

Question 12

Suggest one biological advantage of this property of water. (2)

Answer 12

1. Ice is colder than water;
2. (Being lighter than water) ice floats on water;
3. Reduces freezing of water (below ice);

Question 13

Scientists looking for extra-terrestrial life are looking for planets with evidence of free water. Explain why water is considered so important for life to occur. (6)

Answer 13

1. Life (thought to have) evolved in water;
2. Water provides support (for bodies of organisms);
3. Water a major component of cytoplasm;
4. Water is a universal solvent/metabolic reactions occur in aqueous solution;
5. Water is a metabolite/a reactant in many cell reactions;
6. Water stabilises (external) temperature;
7. Water important in cooling/stabilising internal temperature (of organisms);

Question 14

In DNA, what is the function of Sugar-phosphate backbone and double helix structure

Answer 14

Provides strength and stability
Protects bases and hydrogen bonding between bases

Question 15

In DNA, what is the function of it being a Long molecule

Answer 15

Can store a lot of information

Question 16

In DNA, what is the function of it being a helix structure

Answer 16

Compact

Question 17

In DNA, what is the function of it having a base sequence

Answer 17

Codes for amino acids and therefore proteins

Question 18

In DNA, what is the function of it having Complementary base pairing – A-T and C-G

Answer 18

Allows accurate replication

Question 19

In DNA, what is the function of it being Double stranded

Answer 19

Allows semi-conservative replication, as each strand can act as a template

Question 20

In DNA, what is the function of it having Hydrogen bonds between bases which are weak

Answer 20

Allows unzipping and separating of strands for replication

Question 21

In DNA, what is the function of it having Many hydrogen bonds in the whole molecule

Answer 21

Strong and stable molecule

Question 22

How does semi-conservative replication occur?

Answer 22

The enzyme DNA Helicase attaches and moves along the DNA molecule, unwinding the DNA and breaking hydrogen bonds between complementary bases.

The two strands start to separate

New individual DNA nucleotides are attracted to exposed complementary bases on template strands and base pairing occurs

The enzyme DNA polymerase now joins the new nucleotides together through a condensation reaction forming phosphodiester bonds between adjacent nucleotides

Semi-conservative replication ensures that each new DNA molecule contains an original and a new strand and is identical to the original DNA.

Question 23

What did Watson and Crick come up with

Answer 23

Semi-conservative DNA replication