Paper 2 - Protein Synthesis

Question 1

Transcription

Answer 1

1. DNA helicase breaks hydrogen bonds between the DNA bases, separating the 2 strands.
2. 1 DNA strand acts as a template
3. Free RNA nucleotides align by complementary base pairing
4. RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds.
5. Ends when a stop codon is reached
6. A single stand of pre-mRNA that is spliced to produce mRNA

Question 2

Translation

Answer 2

1. MRNA attaches to ribosome
2. TRNA molecule with complimentary anticodon binds with the 1st codon on mRNA
3. The first tRNA is carrying a specific amino acid.
4. 2nd tRNA molecule joins in the same way
5. 2 amino acids join by peptide bonds in a condensation reaction using ATP
6. First tRNA molecule is released
7. Ribosome moves along the mRNA
8. Cycle reacts forming a polypeptide until a stop codon on mRNA is reached

Question 3

How a mutation affects a protein

Answer 3

• Change in DNA base sequence = different sequence of amino acids
• Different primary structure
• Different tertiary structure as hydrogen, disulphide and ionic bonds from in different places
• Function of protein changes

Question 4

How a mutation affects an enzyme

Answer 4

• Changes in DNA base sequence = different sequence of amino acids
• Different primary structure
• Different tertiary structure as hydrogen, disulphide and ionic bonds form in different places
• Active site changes shape = no longer complementary to substrate
• No enzyme-substrate complexes can form

Question 5

Meiosis 1

Answer 5

1. Prophase - DNA condenses, chromosomes become visible and homologous pairs of chromosomes form bivalents so crossing over can occur.
2. Metaphase - homologous chromosomes line up in pairs on the equator, independent segregation occurs and spindle fibres attach too centromeres.
3. Anaphase - spindle fibres contact and pull apart homologous pairs of chromosomes to opposite poles.
4. Telophase - nuclear membrane forms around each group of chromosomes and cytokinesis occurs.

Question 6

Meiosis 2

Answer 6

Anaphase - spindle fibres contact and sister chromatids are pulled apart to opposite poles.

4 haploid daughter cells are produced but are not genetically identical

Question 7

Crossing over

Answer 7

1. Prophase 1 - homologous pairs of chromosomes form a bivalent
2. Chromatids of each pair become wrapped around each other - chiasmata
3. Tension on areas causes sections of each chromatid to break off and swap with the chromatid of the homologous partner.
4. New combinations of alleles are formed = genetic variation in gametes

Question 8

Independent segregation

Answer 8

1. Metaphase 1- pairs of homologous chromosomes line up on equator
2. Chromosomes line up in a random order so orientation of the homologous pairs is random.
3. Separation in anaphase 1 = different combinations of maternal and paternal chromosomes in gametes.