pack 8a Nucleic acids

Question 1

two groups of nitrogen containing bases

Answer 1

purines and pyrimidines. Purines are larger bases than pyrimidines

• Adenine and guanine are purines;
• thymine and cytosine are pyrimidines

Question 2

How the Structure of DNA Relates to Function:

Answer 2

· It is a stable molecule as it is a double helix, and there are many H bonds. It is also strong due to the covalent bonds in the sugar-phosphate backbone.

· Complementary base pairing allows DNA to replicate itself exactly when cells divide. The weak H bonds allow strands to separate in this process.

· It is compact. DNA molecules are long, so contain large amounts of coded information. However the double helix shape allows DNA to fit inside the nucleus of the cell.

· It has a precise genetic code, determined by the sequence of bases, which controls protein synthesis.

Question 3

Semi-conservative Replication

Answer 3

· An enzyme called DNA helicase is required to unwind the DNA double helix, by breaking the weak hydrogen bonds between complementary bases in the polynucleotide strands. This separates the strands.

· Each exposed strand of DNA can now act as a template for the formation of a new strand.

· New DNA nucleotides (present in the nucleus) are attracted to the exposed bases on the template strands, and attach by complementary base pairing. New hydrogen bonds form between the bases.

· The enzyme DNA polymerase joins the new nucleotides together to form a new polynucleotide strand. Phosphodiester bonds are formed between adjacent nucleotides via condensation reactions.

Question 4

what does atp consist of

Answer 4

· The organic base adenine

· Ribose sugar

· Three phosphate groups (ions).

Question 5

Synthesis of ATP

Answer 5

ATP is synthesized by the addition of ADP to an inorganic phosphate, a condensation reaction catalysed by the enzyme ATP synthase. The addition of a phosphate molecule is known as phosphorylation. ATP synthesis requires an input of energy from a metabolic process, and occurs during respiration. Some ATP can also be made in photosynthesis (using light energy).

Question 6

Breakdown of ATP

Answer 6

Useful energy is mainly stored in the phosphate-phosphate bonds of the ATP molecule, between the second and third phosphate groups. This is because the covalent bond linking these phosphate groups is unstable and is easily broken by the enzyme ATP hydrolase in a hydrolysis reaction. When this occurs an inorganic phosphate group is removed, energy is released and ATP becomes ADP

Question 7

what type energy is atp

Answer 7

immediate energy source

Question 8

ATP is much more useful than glucose as an immediate source of energy because:

Answer 8

· The breakdown of ATP to ADP and phosphate is a single reaction, making energy immediately available. The breakdown of glucose is a complex reaction involving several stages.

· ATP is soluble and easily moved around inside cells, but cannot pass through cell membranes.

· The breakdown of a molecule of ATP releases a small amount of energy, ideal for fuelling the energy requiring reactions which occur in the cell. The breakdown of a molecule of glucose may release more energy than is required at one time (inefficient – a lot of the energy would be wasted as heat).