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 helicase, DNA polymerase, DNA ligase

Answer 7

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

Question 8

DNA replication

Answer 8

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 9

3 parts of the genetic code

Answer 9

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 10

Nucleotide vs Nucleoside

Answer 10

Nucleotide- has a nitrogenous base, deoxyribose sugar and phosphate

Nucleoside- does not have a phosphate

Question 11

Phosphorylation

Answer 11

The addition of a phosphate group

Question 12

Energy uses

Answer 12

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

Question 13

Structure of ATP

Answer 13

Adenine — Ribose |
|
3 phosphates

Question 14

Translation

Answer 14

1. mRNA attaches to a ribosome
2. The first mRNA codon binds to a tRNA molecule with a complementary anticodon
3. The tRNA is bound to an amino acid specific to its anticodon
4. A second tRNA (carrying another amino acid) binds the tk adjacent mRNA codon
5. A peptide bind forms between the amino acids
6. The ribosome continues along the mRNA molecule, from codon to codon
7. Amino acids are bonded together in a polypeptide chain until a stop codon is reached
8. The polypeptide is released

Question 15

Transcription

Answer 15

1. DNA helicase unwinds and unzips DNA
2. RNA nucleotides bind to complementary DNA bases in the template strand (antisense)
3. RNA polymerase joins rna nucleotides together with phosphodiester bonds
4. A stop codon causes rna polymerase to detach
5. The mRNA molecule detaches from the DNA and leaves the nucleus