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MCAT Question A Day - 3/15/14 - Answer!

Eukaryotic chromosomes consist of DNA in association with histone proteins. This association enables the genetic material to remain either tightly coiled, condensed, and visible as distinct chromosomes (only during mitosis), or loose and unwound as chromatin (during the rest of the cell cycle). DNA remains uncoiled during most of a cell’s life so that

A.  exposed nucleotides can efficiently provide phosphate groups for ATP production.
B.  the larger surface area covered by the chromatin acts as a more efficient osmotic attractant.
C.  transcription can take place when necessary.
D.  ER channels cannot penetrate the nucleus.

The correct answer is (C). A fundamental understanding of the relationship between genes and cell function is required. The uncoiled DNA exposes the nucleotide sequence of the gene so that it can be transcribed and translated into the gene product: a protein (or protein subunit). Since different parts of the genome are constantly being activated (depending on the needs of the cell and the needs of the organism), the chromosomes must constantly have their active genes exposed (uncoiled).

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