Question

Where on the DNA polymerase I molecule do the 5'—>3' exonuclease, 3'—>5' exonuclease and DNA polymerase activities reside?

a. all of them on the same domain
b. the two exonucleases on one domain and the polymerase activity on another domain
c. the 5'—>3' exonuclease and polymerase activities on 1 domain and the 3'—>5' exonuclease on another
d. the 3'—>5' exonuclease and polymerase activities on 1 domain and the 5'—>3' exonuclease on another
e. each enzyme activity on a different domain

Answer 1

The 3'—5' exonuclease and polymerase activities of DNA polymerase I are on one domain, and the 5'—3' exonuclease is on a separate domain. The correct answer is 'd'.

Step-by-step explanation:

The activities of 5'—3' exonuclease, 3'—5' exonuclease, and DNA polymerase within DNA polymerase I are located on different domains. The 5'—3' exonuclease activity, which is responsible for removing the RNA primer at the terminal end, can be separated from the enzyme by mild protease treatment. This removed domain has the 5'—3' exonuclease activity, while the remaining larger fragment, known as the Klenow fragment, houses the polymerization and proofreading activity associated with the 3'—5' exonuclease function.

Therefore, the correct answer to the student's question is 'd', the 3'—5' exonuclease and polymerase activities reside on one domain, and the 5'—3' exonuclease on another domain. The correct answer is 'd'.