IMAT 2018 Q40 [Healthy Humans]

Which of the following statements about a neurone in a healthy human is/are correct?

  1. Transport across its cell membrane can occur by exocytosis.
  2. It contains the gene that codes for insulin.
  3. It contains circular DNA.

A. 1, 2 and 3
B. 1 and 3 only
C. 1 and 2 only
D. 2 and 3 only
E. 1 only

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1. Transport across its cell membrane can occur by exocytosis.

Notice the language ‘may’. Is there a case that a neurone, which is a cell, would have a need for exocytosis (which is a process in which secretory vessels fuse with the plasma membrane in order to release certain contents from the cell)? Yes, of course, neurones secrete neurotransmitters via exocytosis when they want to activate cells across a synapse. Therefore 1 is correct.

2. It contains the gene that codes for insulin.

One of the most important universal rules is that all cells contain all genes! Not all genes are expressed, however, all cells (with few exceptions ex. red blood cells - have no nucleus when mature) contain all genes. Therefore 2 is correct because even if the gene that codes for insulin is not expressed in neurones, the gene will still be present.

3. It contains circular DNA.

Where can we find circular DNA? We can find it in bacteria, chloroplasts, and in mitochondria. Since neurones are aerobic and contain mitochondria (they carry out cellular respiration to produce energy for themselves therefore they must have mitochondria), they have circular DNA. 3 is also correct.

\fcolorbox{red}{grey!30}{Therefore $1, 2,$ and $3$ are correct so the answer is A.}