Genetic information - PROTEIN SYNTHESIS

Question 1

What is the proteome of a cell? (PPQ)

Answer 1

The full range of proteins that the genome of a cell is able to produce

Question 2

Definition of a genome (PPQ)

Answer 2

All of the DNA of an organism

Question 3

Describe the process of transcription

Answer 3

• DNA helicase breaks the hydrogen bonds between complementary bases in a section of coding DNA
• The antisense strand can then be read and the mRNA strand synthesised by RNA polymerase

Question 4

What are the structural differences between tRNA and mRNA? [5]

Answer 4

• tRNA are all the same length/mRNA are different lengths
• mRNA has codons/tRNA has anticodons
• tRNA has an amino acid binding site/mRNA doesn’t
• mRNA is linear/tRNA is clover shape
• tRNA has hydrogen bonds/mRNA doesn’t

Question 5

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide. (PPQ)[5]

Answer 5

• mRNA attaches to ribosome
• Ribosome finds the start codon (always AUG - codes for MET)
• Corresponding tRNA and anticodon (UAC) lines up with the codon on the mRNA
• Ribosome moves along to next codon
• Process is repeated and peptide bond form
• Amino acids join to form a polypeptide

Question 6

What is splicing and why is it necessary?

Answer 6

• Eukaryotic DNA contains both introns and exons
• Hence the pre-mRNA is ‘spliced’ to remove the introns and join the remaining exons
• This creates mature mRNA
• Splicing does not occur in prokaryotes as the DNA only has exons

Question 7

If the triplet on DNA is CGT what will the tRNA anticodon be?

Answer 7

CGU

Question 8

Give the two types of molecule from which a ribosome is made (PPQ)

Answer 8

Ribosomal protein and rRNA

Question 9

How does RNA polymerase synthesise the mRNA strand? (HIGHER)

Answer 9

• Attaches the DNA strand to the promoter site
• Activator and supressor sequences that regulate gene expression are found on some of these promoter sites
• RNA polymerase works in the 5’-3’ direction
• Builds mRNA strand by adding free RNA nucleotides to the exposed DNA strand using complimentary base pairing rule

Question 10

What is the role of RNA polymerase in transcription? (PPQ)

Answer 10

• Catalyses the formation of phosphodiester bonds to form a sugar phosphate backbone

Question 11

Name the organelle involved in translation

Answer 11

Ribosome

Question 12

Describe the role of the ribosome in the production of a polypeptide?

Answer 12

• mRNA binds to the ribosome
• two codons can fit in the ribosome
• allows tRNA with anticodons to bind with mRNA
• formation of peptide bonds/amino acids

Question 13

What is the role of peptidyl transferase? (HIGHER)

Answer 13

Catalyses the formation of peptide bonds between amino acids