DNA

Question 1

the 6 stages of transcription

Answer 1

1. DNA helicase unwinds double helix, breaking H bonds
2. one DNA strand acts as template
3. free nucleotides attracted to exposed bases
4. join by base pairing rule
   Adenine- Uracil, Cytosine - Guanine
5. RNA polymerase joins nucleotides forming phosphodiester bonds by condensation
6. pre-mRNA spliced to remove introns

Question 2

what is transcription

Answer 2

copying base sequence of gene onto base sequence of mRNA molecule

Question 3

what is translation

Answer 3

how polypeptide is made

Question 4

what are the 7 stages of translation

Answer 4

1. mRNA binds to ribsome
2. at two points
3. ribosome finds START codon
4. tRNA complementary anticodons bind with codon from mRNA
5. ribosome catalyses formation of peptide bonds between amino acids by condensation reaction using energy from ATP
6. tRNA released as ribosome moves along
7. ribosome releases polypeptide into RER when STOP codon reached

Question 5

what is the definition of a gene mutation

Answer 5

a spontaneous change in a base that results in the formation of a new allele

Question 6

what is a base deletetion/ addition mutation

Answer 6

lost/ gain of a DNA nucleotide base
may cause a frameshift
different amino acids so different polypetide chain/ protein synthesised

Question 7

what is a substitution mutation

Answer 7

• point mutation of one DNA nucleotide base
• may cause a change in a amino acid, change to structure and folding of protein
• new codon may code for same amino acid so no change in protein, genetic code is degenerate