transcription and translation

Question 1

what does transcription produce and where does it occur?

Answer 1

• produces mRNA
• occurs in nucleus

Question 2

outline the process of transcription

Answer 2

• RNA polymerase binds to promoter sequence on the gene
• section of DNA uncoils due to helicase breaking hydrogen bonds between base pairs, creating a replication fork
• antisense strand is used as a template by RNA polymerase to make the mRNA molecule
• free nucleotides line up to their complementary base pair and are joined by phosphodiester bonds forming between adjacent nucleotides

Question 3

what happens after a strand of mRNA is transcribed?

Answer 3

• RNA polymerase detaches at terminator region
• H-bonds reform and DNA rewinds
• splicing removes introns from pre-mRNA in eukaryotic cells
• mRNA moves out of nucleus via nuclear pore and attaches to a ribosome in the cytoplasm

Question 4

what does translation produce and where does it occur?

Answer 4

• produces proteins
• occurs in cytoplasm on ribosomes (made up of protein and rRNA)

Question 5

outline the process of translation

Answer 5

• ribosome moves along the mRNA until ‘start’ codon is reached
• molecules of tRNA from the cytoplasm each have a triplet of unpaired bases at one end
• tRNA anticodon attaches to complementary start codon (AUG)
• second tRNA then brings the next complementary anticodon
• condensation reactions between amino acids on tRNA form peptide bonds (this requires energy from ATP hydrolysis)
• empty tRNA move away, next two tRNA moves in and process repeats until ‘stop’ codon is reached and final polypeptide is formed

Question 6

what is the start codon?

Answer 6

• AUG in RNA
• ATG in DNA
• also known as methionine