4.2: DNA and protein synthesis

Question 1

What is the structure of RNA?

Answer 1

• ribose sugar
• nitrogenous base
• phosphate
• adenine, guanine, cytosine and uracil

Question 2

Describe mRNA (6)

Answer 2

• single stranded polynucleotide chain
• Complementary copy of a gene from the template DNA strand
• Shorter
• No hydrogen bonds
• No introns
• codons

Question 3

Describe transcription (6)

Answer 3

1) DNA helices breaks hydrogen bonds to separate strands
2) Only one DNA strand acts as a template
3) RNA nucleotides are attracted to exposed bases
4) Base pairing: adenine to uracil and guanine to cytosine
5) RNA polymerase joins adjacent nucleotides forming phosphodiester bonds through condensation reactions
6) Pre-mRNA spliced to remove introns

Question 4

Describe translation (7)

Answer 4

1) mRNA binds to ribosome
2) Ribosome finds start codon
3) Two binding sites on each ribosome
4) tRNA with complementary anticodons binds to mRNA codon
5) Formation of peptide bond between amino acid using energy from ATP
6) tRNA released as ribosome moves along
7) Ribosome releases polypeptide into RER when the STOP codon is reached

Question 5

Describe tRNA (5)

Answer 5

• Single stranded
• Clover leaf structure
• Hydrogen bonds
• Amino acid binding site
• Anticodon