Nucleic acids

Question 1

In a eukaryotic cell, transcription results in a molecule of pre-mRNA that is modified to produce mRNA. In a prokaryotic cell transcription produces mRNA directly. Explain this difference. [2]

Answer 1

DNA has introns which are non coding regions of DNA, which have to be removed from pre-mRNA;

Question 2

Give two differences between the structure of mRNA and the structure of tRNA. [3]

Answer 2

mRNA Has more nucleotides than tRNA (mRNA is longer);
mRNA is a straight molecule but tRNA is a folded molecule/clover-leaf shaped molecule;
mRNA contains no paired bases/hydrogen bonds but tRNA has some paired bases/hydrogen bonds;

Question 3

two ways DNA and RNA nucleotides differ? [2]

Answer 3

DNA has thymine and RNA has uracil;
DNA has deoxyribose sugar and RNA has ribose sugar;

Question 4

Describe how one amino acid is added to a polypeptide that is being formed at a
ribosome during translation.

Answer 4

1. tRNA brings specific amino acid (to ribosome);
2. Anticodon (on tRNA) binds to codon (on
   mRNA);
3. Amino acids join by condensation reaction
   (using ATP)
   OR
   Amino acids join to form a peptide bond (using
   ATP);