Question

Problem 4 Deaminating agents:

a. Describe how a deaminating agent acts on nitrogenous bases

b. Which two nitrogenous bases can be deaminated?

c. What do each of the named nitrogenous bases above pair with after they have been deaminated?

d. What type of mutations does this mutagen cause (if a substitution, be sure to state if it is a transition or transversion)? How would this agent act on each base pair shown below?

T:A ->

G: C->

A:T ->

C:G ->

e. If a deaminating agent acted on the A shown in the sequence below, what sequence would result after 2 rounds of DNA replication? (You should have 4 sequences of double-stranded DNA!) Put a check by the resulting DNA that has been mutated. Remember that DNA is double stranded and only the TOP strand is written and ONLY the A in the top strand is deaminated below. Also remember in replication EACH strand acts as a template.ATGCT

f. Give an example of a deaminating agent.

Answer 1

• Deamination is the removal of amino acid from the sequence. nitrogenous bases such as thyine, cytosine are replaced by the other nitrogenous bases. This leads to a mutation in the protein sequence.
• Nitrogenous bases that can be deaminated are cytosine which can undergo spontaneous hydrolysis and be converted into uracil. This releases ammonia in the process. Another base that can be deaminated is adenine which is converted into hypoxanthine. This is an imine tautomer of the adenine wich base pair to cytosine in place of thymine. this leads to a mutation in the sequence.
• Deamination of adenine forms hypoxanthine. Whereas the deamination of the cytosine is converted into uracil.