Rats are given cytidine that is 14C-labeled at both its base and ribose components. Their DNA is

Question:

Rats are given cytidine that is 14C-labeled at both its base and ribose components. Their DNA is then extracted and degraded with nucleases. Describe the labeling pattern of the recovered deoxycytidylate residues if deoxycytidylate production in the cell followed a pathway in which
(a) Intact CDP is reduced to dCDP, and
(b) CDP is broken down to cytosine and ribose before reduction.