8.4 & 8.5 Transcription and Translation

Question 1

What are the two stages of protein synthesis?

Answer 1

• transcription
• translation

Question 2

What is transcription and where does it happen?

Answer 2

• an mRNA copy of a gene is made from DNA
• takes place in the nucleus for EUKARYOTIC cells

Question 3

Describe the process of transcription in eukaryotic cells (6)

Answer 3

1.RNA polymerase attaches to DNA double helix at the end of the gene
2. DNA helicase breaks hydrogen bonds between two strands
3. One strand is used as a template to make the mRNA molecule
4. Free nucleotides line up by complementary base pairing
5. RNA polymerase forms phosphodiester bonds between the bases
6. Sequence reaches end and stop codon causes mRNA to stop being made it detaches from the nucleus

Question 4

What happens to pre-mRNA in eukaryotic cells?

Answer 4

• pre-mRNA is then spliced to remove the introns leaving just a strand of exons.
• moves out of the nucleus through a pore
• attaches to a ribosome in the cytoplasm

Question 5

Describe the process of transcription in prokaryotes

Answer 5

• mRNA is produced directly from the DNA w
• no splicing as prokaryotes don’t have introns

Question 6

Describe the process of translation (6)

Answer 6

1. mRNA attaches itself to the ribosome and tRNA molecules carry amino acids to it
2. ATP provides energy needed for the bond between amino acid and tRNA
3. Complementary tRNA anticodon attaches to the first codon on mRNA by specific base pairing
4. Second amino tRNA molecule attaches in the same way
5. Amino acids are joined by a peptide bond and tRNA molecule moves away
6. This process continues to produce a polypeptide chain
7. Stop cocoons causes polypeptide chain to move away = translation is complete