We introduced the central dogma of biology by comparing it to Patrick making music tapes to listen to in his car. Patrick used CDs to make tapes. This is analogous to transcription, the DNA-directed synthesis of RNA. DNA and RNA hold the same information, but in different forms. Patrick used the tapes to play music in his car. This is analogous to translation, the RNA-directed synthesis of a protein. The information in the RNA is used to make a functional product, a protein.

The central dogma of biology states that DNA is used to make RNA, which is used to make a protein. The process always goes in this forward direction.

We looked at the structure of RNA and how it differs from DNA. RNA contains ribose sugars and uses uracil bases in place of thymine bases. RNA is generally single-stranded. The main functional difference between DNA and RNA is that DNA is permanent, while RNA is temporary. A cell uses its DNA to make temporary copies of the information as RNA. If the copies are damaged or more are needed, the cell makes more copies. Different cells make different sets of RNA, depending on which proteins they need. No matter what happens to the RNA, the original information is still available in the DNA.

For transcription to begin, RNA polymerase binds to the promoter region of the DNA, with the help of transcription factors. RNA polymerase adds nucleotides one at a time to the 3-prime end of the RNA molecule until it reaches the termination sequence. In eukaryotes, the RNA is processed before it is used to make a protein. The introns are cut out and the exons are glued back together in a process called splicing. To protect the ends of the molecule, a 5-prime GTP-cap and a 3-prime poly-A tail are added to the RNA before it's transported out of the nucleus. The fully processed RNA is called messenger RNA, or mRNA.

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