Paper 1 - Genetic Information, Variation And Relationships

Question 1

Transcription (making mRNA from DNA)

Answer 1

1. Hydrogen bonds between DNA bases are broken by DNA helicase
2. One strand acts a template
3. Free RNA nucleotides align by complimentary base pairing - adenine with uracil, cytosine with guanine
4. RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds
5. Stops when a stop codon is reached
6. Single strand of pre-mRNA is produced, which can be spliced to produce mRNA

Question 2

Translation (making a polypeptide using mRNA)

Answer 2

1. The mRNA attaches to ribosome
2. The tRNA molecule with complimentary anticodon aligns with the first codon on mRNA
3. The 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. 1st tRNA molecule is released
7. Ribosome moves along the mRNA
8. Cycle repeats forming a polypeptide until a stop codon is reached

Question 3

How a mutation affects a protein

Answer 3

1. Change in DNA base sequence = different sequence of amino acids
2. Different primary structure
3. Different tertiary structure - hydrogen, ionic and disulphide bonds form in different positions
4. Function of protein therefore changes

Question 4

How a mutation affects an enzyme

Answer 4

1. Change in the DNA base sequence = different sequence of amino acids
2. Different primary structure of protein
3. Different tertiary structure - hydrogen, ionic and disulphide bonds form in different positions
4. Active site change shape and is no longer complementary to substrate
5. No enzyme-substrate complexes can form

Question 5

Describe the process of meiosis

Answer 5

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

Anaphase 2 - spindle fibres contract and sister chromatidd are pulled apart to opposite poles

4 haploid daughter cells are produced - not genetically identical

Question 6

Crossing over

Answer 6

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

Question 7

Independent segregation

Answer 7

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

Question 8

Natural selection

Answer 8

1. Variation in population due to mutations
2. Various selection pressures e.g, diseases, competition etc
3. Organisms with an advantageous allele are more likely to survive,reproduce and pass in the advantageous allele to their offspring
4. The frequency of the advantageous allele increases

Question 9

Compare the processes of mitosis and meiosis

Question 10

Explain how aseptic techniques are used to prevent contamination of bacterial cultures

Question 11

Explain the different techniques that can be used to determine evolutionary relationships