Question

Indicate whether each of the following statements is true or false.

a. A single nucleolus always corresponds to a single nucleolus organizer region.
b. The fibrils seen in electron micrographs of nucleoli contain DNA and RNA.
c. The DNA of nuclei carries the cells tRNA genes which are present in the clusters of multiple copies.

Answer 1

a. false

b. true

c. true

Step-by-step explanation:

NORs (Nucleolus organizer regions) are chromosome regions in which ribosomal genes are encoded, while nucleoli (singular = nucleolus) are nuclear territories where ribosomes are produced and assembled. A nucleolus may contain one or more NORs.

Nucleoli are composed of DNA, RNA and proteins arranged around NORs.

The transference RNA (tRNA) genes are known to be spatially associated with the nucleolus as happen, for example, in Saccharomyces cerevisiae.