Explain how a cell's DNA nucleotide sequences control cellular functions, outlining the process of RNA transcription.
The genes encoded by a cell's DNA nucleotide sequences control cellular functions by directing the synthesis of enzymes, which, in turn, facilitate all cellular reactions. Typically, one gene controls the synthesis of one protein. Because DNA does not move out of the nucleus and because proteins, including enzymes, are synthesized in ribosomes in the cytoplasm, the translation of a gene's nucleotide sequence into a protein's amino acid sequence must be accomplished by an intermediary messenger, mRNA. From the nucleus, mRNA moves through a pore in the nuclear membrane to the ribosomes where is acts as the template for the synthesis of polypeptide chains. Messenger RNA, rRNA, and tRNA are all produced via a process called transcription, which is very similar to the process of DNA replication. Transcription begins when the two DNA strands uncouple. Unlike in DNA replication, in transcription, only one of the two DNA strands is transcribed. An enzyme, RNA polymerase, brings ribonucleotides to the DNA template, thus the deoxyribonucleotides of the DNA determine the order of the ribonucleotides of the RNA.
