5.5--Gene Expression and Regulation

• Gene expression is the process by which the nucleotide sequence of a gene is transcribed to make an mRNA molecule
• information flows from DNA to RNA to proteins
• Gene regulation and expression occur differently in prokaryotic and eukaryotic cells
• In prokaryotes, genes are organized into operons
• Promoter: segment of DNA that promotes RNA polymerase to locate the starting point of transcription
• Operator: segment of DNA that turns genes on and off. Either increases or blocks transcription.
• In eukaryotes, genes are controlled by various promoters.
• Most genes have a nucleotide promoter sequence known as TATA box.
• Eukaryotes have enhancers that speed up transcription.
• Eukaryotes have" silencers that slow down transcription.
• In the presence of the correct transcription factor, transcription begins.
• In prokaryotes, gene regulation mainly takes place in transcription.
• In eukaryotes, gene regulation may occur during transcription, post-transcription, during translation, and post-translation.