Nucleic Acids

Question 1

What is a nucleotide

Answer 1

Monomers of nucleic acids (DNA and RNA)

Made up of:
- phosphate group (always the same)
- pentose sugar (deoxyribose in DNA , ribose in RNA)
- nitrogenous base (DNA= A T C G. RNA= A U C G )

Question 2

How many hydrogen bonds hold base pairs together

Answer 2

G-C has 3 hydrogen bonds
A-T has 2 hydrogen bonds

• purines and pyrimidines always pair together (complementary base pairs)

Question 3

How are nucleotides joined in condensation reactions

Answer 3

Covalent bonds

Question 4

What are purines

Answer 4

Adenine and Guanine
- purines are larger than Pyrimidines

Question 5

What are Pyrimidines

Answer 5

Cytosine, Thymine and uracil (RNA)
- Pyrimidines are smaller than purines

Question 6

Why do purines always bond with pyrimidines

Answer 6

• their structure
• where they can form hydrogen bonds
• to remain parallel (never have 2 large molecules and 2 small molecules)

Question 7

DNA replication

Answer 7

1. Double helix unwinds
2. DNA unzipped when the enzyme and the H bonds between base pairs
3. Both stands act as a template for free DNA nucleotides to align and synthesis new strands and the complementary base pairs (C-G, A-T)
4. Hydrogen bonds between bases reform
5. DNA polymerase joins the sugar phosphate backbones together in the new strands with covalent bonds
6. The molecules twist back into a double helix
   There are now 2 identical DNA molecules

Question 8

DNA helicase, DNA polymerase, DNA ligase

Answer 8

DNA helicase- unzips DNA helix
DNA polymerase- catalyses the joining of nucleotides
DNA ligase- sticks DNA fragments together

Question 9

Process of DNA replication

Answer 9

1. DNA helicase unwinds the DNA and forms a replication fork
   - helicase unwinds and unzips
   - breaks hydrogen bonds
2. Each strand acts as a template
   - free nucleotides pair with the complementary exposed nucleotides
3. DNA polymerase catalyses the joining together of nucleotides
   - hydrogen bonds reform
4. Hydrogen bonds form down the middle
   - this is semi conserved DNA (one old strand, one new strand)

Question 10

3 parts of the genetic code

Answer 10

Triplet- the bases on DNA form triplet codons consisting of 3 nucleotide bases

Non overlapping- each base will only code for one amino acid in one triplet codon

Degenerate- each amino acid can be coded for by multiple codons

Question 11

Nucleotide vs Nucleoside

Answer 11

Nucleotide- has a nitrogenous base, deoxyribose sugar and phosphate

Nucleoside- does not have a phosphate

Question 12

Phosphorylation

Answer 12

The addition of a phosphate group

Question 13

Energy uses

Answer 13

• muscle contraction
• memory formation
• transmission of nerve impulses
• cell division
• active transport
• translocation
• photosynthesis

Question 14

Structure of ATP

Answer 14

Adenine — Ribose |
|
3 phosphates

Question 15

Protein synthesis:Transcription

Answer 15

1. DNA helicase breaks hydrogen bonds between complementary bases, unzips DNA
2. RNA polymerase attaches free nucleotides to complementary bases on the DNA (mRNA - T replaced by U)
3. RNA polymerase continues making strand of mRNA until it reaches the stop codon

Question 16

Protein synthesis:Translation

Answer 16

1. mRNA binds to small subunit of the ribosome at its start codon
2. mRNA leaves nucleus through the nuclear pores
3. tRNA with complementary anticodon binds to mRNA start codon
4. tRNA carries the amino acid
5. Another tRNA with anticodon and carrying corresponding amino acid binds to the next codon
6. The first amino acid is transferred to the amino acid on the second tRNA by the formation of a peptide bond
7. This is catalysed by the enzyme peptidtyl transferase
8. Ribose then moves along the mRNA, releasing the first tRNA
9. The second tRNA becomes the first and this continues until it reaches the stop codon