Protein Synthesis

Question 1

What is the process of transcription?

Answer 1

Copies segment of DNA into RNA

Occurs within nucleus in 3 stages

Question 2

What occurs during the first stage of transcription: Initiation?

Answer 2

RNA polymerase binds to promotor region of gene and then separates DNA strands forming a replication bubble
It forms single-stranded template

Question 3

What occurs during the second stage of transcription: Elongation?

Answer 3

An RNA molecule is built out of complementary nucleotides, containing same base pairs except is uses Uracil instead of Thymine
Nucleotides always added to 3’ end

Question 4

What occurs during the third stage of transcription: Termination?

Answer 4

When RNA polymerase transcribes a sequence known as ‘terminator’, it stops. RNA sequence is then ready to be translated into mRNA.

Question 5

Differentiate between replication and transcription.

Answer 5

Replication

• DNA -> DNA
• Starts at replication origins
• Unwinds with helicase
• DNA polymerase
• Proofreads
• Starts with 1 x DNA
• End with 2 x DNA
• Leading and lagging strand

Transcription

• DNA -> RNA
• Starts at promotor region
• Does not need helicase
• RNA polymerase
• No proofreading
• Starts with 1 x DNA
• Ends with same DNA and 1 x RNA
• Coding and template strand

Question 6

What does translation do?

Answer 6

Codons on mRNA form amino acids (forming polypeptide)

Occurs on ribosomes - act as ‘docking station’

Question 7

What occurs during the first stage of translation: Initiation?

Answer 7

Ribosomal subunit attach to 5’ end of mRNA strand which moves along strand until reaches start codon (AUG)
tRNA molecule with anticodon UAC joins to mRNA start codon AUG attaching complementary base pairs (tRNA to mRNA - anticodon to codon)

Question 8

What occurs during the first stage of translation: Elongation?

Answer 8

After start codon attached, another tRNA with complementary anticodon to the codon on mRNA attaches, adds specific amino acid to growing peptide chain 
Ribosomal subunit (includes tRNA and its anticodons) continues to move along mRNA chain until stop codon reached

Question 9

What occurs during the first stage of translation: Termination?

Answer 9

Attachment of amino acids continue until STOP codon reached -> chain is released from ribosome where chain forms a functional protein in cytoplasm or released into ER for other functions