Topic 2: Nucleic Acids

Question 1

Why is water important for life?

Answer 1

• Metabolite used to break down complex molecules via hydrolysis.
• Chemical reactions take place in aqueous medium.
• Raw metabolite in photosynthesis.
• Polar water molecules attract other polar molecules.

Question 2

What is cohesion and adhesion? What does cohesion enable?

Answer 2

Cohesion: water molecules ‘stick together’ by forming hydrogen bonds with other water molecules.

Adhesion: tendency of water molecules to stick to other substances

Cohesion causes surface tension (allows some organisms to walk on water).

Question 3

Why is a high specific heat capacity for water important?

Answer 3

• Acts as a buffer against sudden changes in temperature/
• Provides thermostable aquatic environment but also within fluids of terrestial organisms.
• Minimises temperature fluctuations in cells.
• Provides optimum rate of reactions.
• Prevents enzymes denaturing.

Question 4

What are the five main biological functions that ATP provdes the energy for?

Answer 4

• Activation of molecules: can lower activation energy.
• Metabolic processes: building of macromolecules etc.
• Active transport: allows movement of molecules against conc. gradient.
• Secretion: formation of lysosomes.

Question 5

What are the steps for DNA replication?

Answer 5

1) DNA helicase unwinds parent DNA and breaks hydrogen bonds.
2) Hydrolysis of ATP activates free nucleotides in nucleus.
3) Attach themselves to bases on parent polynucleotide strands by base pairing, forming hydrogen bonds.
4) New DNA molecules built up using 4 activated nucleotides.
5) DNA polymerase catalyses condensation reactions that join nucleotides (phosphodiester bonds).
6) ‘Proof-reading’ enzyme checks for mutations and ‘winding’ enzyme winds daughter polynucleotides.
7) Two daughter DNA molecules genetically identical, contain one old and new polynucleotide.

Question 6

What is semi-conservative replication?

Answer 6

One original strand remains intact and a new complentary strand is formed using the old strand as a template for replication.

Question 7

What 4 conditions must be met for replication?1)

Answer 7

1) A ‘pool’ of the 4 nucleotides must be present.
2) both strands of DNA being copied (template).
3) Enzymes DNA helicase and DNA polymerase must be present.
4) ATP is required.

Question 8

What are the main structure and properties of DNA?

Answer 8

• Stable: passes from generations without changing. Rarely mutates.
• Linked by hydrogen bonds: during DNA replication and protein synthesis, strands can separate easily.
• Huge: stores vast amounts of info.
• Double helix: information slightly protected within the coils.
• Base pairing: DNA can replicate and transfer information as RNA

Question 9

Why is a high latent heat for water important?

Answer 9

Requires a very large energy input to change state

Question 10

What are the properties of water?

Answer 10

• No overall charge
• High specific heat capacity
• Latent heat
• Cohesion
• Adhesion

Question 11

Is ATP an immediate energy source?

Answer 11

Yes

Question 12

What are the monomers of DNA and RNA called? What reaction joins the components of a nucleotide together?-

Answer 12

• Nucleotide.
• Condensation reaction.

Question 13

What are the 4 nitrogenous bases in DNA and RNA?

Answer 13

DNA: Adenine, Thymine, Cytosine, Guanine.

RNA: Adenine, Uracil, Cytosine, Guanine.

Question 14

What molecules are DNA and RNA made from?

Answer 14

• Phosphate group
• Deoxyribose sugar- Nitrogenous base

Question 15

What is DNA made from?

Answer 15

Two polynucleotide molecules that are arranged in a ladder like structure, referred as a double helix.

Question 16

What type of protein is contained in chromosomes?

Answer 16

Histones.