DNA, ATP, water and inorganic ions

Question 1

Describe the structure of DNA

Answer 1

. Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds;
. Long/large molecule so can store lots of information;
. Helix/coiled so compact;
. Base sequence allows information to be stored/ base sequence codes for amino acids/protein;
. Double stranded so replication can occur semi-conservatively/ strands can act as templates;
. Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made;
. (Weak) hydrogen bonds for replication/unzipping/strand separation;
. Many weak hydrogen bonds so stable/strong molecule;

Question 2

Describe Semi-conservative replication.

Answer 2

. Strands separate / H-bonds break;
. DNA helicase (involved);
. Both strands/each strand act(s) as (a) template(s);
. (Free) nucleotides attach;
. Complementary/specific base pairing due to H bonds forming between bases/ Adenine to Thymine and Guanine to Cytosine;
. DNA polymerase joins nucleotides (on new strand) forming phosphodiester bonds by condensation;
. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;

Question 3

Describe the role of DNA polymerase in the semi-conservative replication of DNA.

Answer 3

. Joins (adjacent DNA) nucleotides;
. (Catalyses) condensation (reactions);
. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);

Question 4

Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.

Answer 4

Crick and Watson

Question 5

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.

Answer 5

. Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
. Two strands, so both can act as templates;
. Complementary base pairing allows accurate replication;

Question 6

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 6

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

Question 7

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

Answer 7

. Phosphorylates other compounds and makes them more reactive;
. Provides energy for (named process) - protein synthesis/active transport/semi-conservative replication

Question 8

Describe how ATP is resynthesised in cells (2)

Answer 8

. ADP + Pi;
. By ATP synthase
. In respiration

Question 9

ATP is a nucleotide derivative. Contrast the structure of ATP and a nucleotide found in DNA.

Answer 9

. ATP has ribose whereas DNA nucleotide has deoxyribose;
. ATP has 3 phosphate (groups) whereas DNA nucleotide has 1 phosphate (group);
. ATP base always adenine whereas DNA nucleotide base can be different/varies;

Question 10

Describe how an enzyme can be phosphorylated.

Answer 10

. Attachment/association of (inorganic) phosphate (to the enzyme);
. (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;

Question 11

Explain five properties that make water important for organisms.

Answer 11

. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
. High heat capacity so buffers changes in temperature;
. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
. Cohesion (between water molecules) so supports columns of water (in plants);
. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;

Question 12

Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

Answer 12

Iron ions
. Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen;

Sodium ions
. Co-transport of glucose/amino acids (into cells);
. (Because) sodium moved out by active transport/Na – K pump;
. Creates a sodium concentration/diffusion gradient;
. Affects osmosis/water potential;

Phosphate ions
. Affects osmosis/water potential;
. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
. Used in/to produce ATP;
. Phosphorylates other compounds (usually) making them more reactive;
. Hydrophilic/water soluble part of phospholipid bilayer/membrane