The micrograph shows a cell viewed
under a transmission electron microscope. A circular nucleus is visible. Which of the following is not part
of the structure of a nucleus? (A) Nuclear envelope, (B) nuclear
pores, (C) nucleoplasm, (D) nuclear cristae, or (E) nucleolus.
In eukaryotic cells, the majority
of the genetic material, or DNA, is contained in the nucleus. The DNA is found in long strands
wrapped around proteins. And together, these structures are
known as chromatin. The nucleus also controls the
expression of DNA and therefore has unique structural features that allow it to
store, replicate, and transfer genetic information.
The nuclear membrane is known as
the nuclear envelope. It is a double membrane that has
special openings called nuclear pores. The pores allow some molecules,
such as ribosomal RNA and subunits of ribosomes, to pass between the cytoplasm of
the cell and the interior of the nucleus. So, we know that answers (A) and
(B) can be ruled out because they both describe structures of the nucleus.
In the interior of the nucleus is a
liquid matrix, called the nucleoplasm. It is similar to the cytoplasm
within the cell. Suspended within the nucleoplasm is
the nucleolus, a dense cluster of proteins and genetic material that produces
ribosomes. Let’s go ahead and eliminate
answers (C) and (E), now that we know that the nucleoplasm and nucleolus are both
structures found within the nucleus.
Cristae are not found in the
nucleus but rather are the folds of the inner membrane of mitochondria. So, the correct answer is (D). Nuclear cristae are not a structure
of the nucleus.