Reproduction and Inheritance - Inheritance (Paper 2)

Question 1

what is the structure of a dna molecule?

Answer 1

two strands of complementary base pairs coiled to form a double helix. composed of deoxyribose

Question 2

what are the dna base pairings?

Answer 2

adenine-thymine
cytosine-guanine

Question 3

what is the structure of a rna molecule?

Answer 3

a single-stranded molecule which contains uracil instead of thymine to bind in complementary with adenine. composed of ribose

Question 4

what are the stages of protein synthesis?

Answer 4

transcription and translation

Question 5

what happens during transcription?

Answer 5

• rna polymerase enzyme binds to a region of non-coding DNA in front of a gene
• the two DNA strands unzip and the rna polymerase moves along one of the strands of the DNA
• rna polymerase uses the coding DNA in the gene as a template to make the mrna. base pairing between the DNA and rna ensures the mrna is complementary to the gene
• once made, the mrna molecule moves out of the nucleus and joins with a ribosome in the cytoplasm

Question 6

what happens during translation?

Answer 6

• amino acids are brought to the ribosome by trna
• the order in which the amino acids are brought to the ribosome matches the order of the codons in mrna
• part of the trna’s structure is called an anticodon. it’s complementary to the codon for the amino acid. the pairing of the codon and the anticodon makes sure the amino acids are in the correct order
• amino acids are joined together by the ribosome

Question 7

what is codominance?

Answer 7

pairs of alleles that both affect the phenotype

Question 8

how can a change in dna affect the phenotype?

Answer 8

• for protein synthesis, dna sequences need to be transcribed and translated
• when DNA is changed, base sequence is changed
• so the modified mrna transcript will be translated to code for different amino acids

Question 9

what effect do most genetic mutations have on the phenotype?

Answer 9

most genetic mutations have no effect on the phenotype - they alter the base pair sequence but not the protein
some have a small effect
rarely, they will have a significant effect - also alter the base pair sequence but the altered sequence codes for a different protein

Question 10

what can the chances of mutations be increased by?

Answer 10

ionising radiation (gamma rays, x-rays and uv rays) and chemical mutagens (carcinogens in tobacco)