key concept 14.2 Information Flows from Genes to Proteins

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As we discussed in Chapter 13 and Key Concept 14.1, DNA is the hereditary material and codes for proteins and RNAs. In the remainder of this chapter we will focus on the processes that occur when a protein-coding gene is expressed. We briefly outlined gene expression in Key Concept 4.1. To review, this process occurs in two major steps:

  1. During transcription, the information in a DNA sequence (a gene) is copied into a complementary RNA sequence.

  2. During translation, this RNA sequence is used to create the amino acid sequence of a polypeptide.

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Francis Crick and James Watson, who deciphered the structure of DNA, first proposed this model for gene expression. They took the concept further by suggesting that gene expression can go in only one direction: DNA can be used to create a protein, but a protein can never be used to create DNA. At the time, Crick called this “the central dogma of molecular biology.”

focus your learning

  • Gene expression involves the processes of transcription and translation.

  • Some virus genomes are composed of single-strand RNA, which is used to direct DNA synthesis by reverse transcription when the virus infects a host cell.