2. Complexities of Gene Expression Cells have regulated, complex systems –Not all genes are expressed in every cell –Many genes are not expressed all of the time

3. Gene Regulation Genetic sequences can be expressed in different ways –In different bodies or tissues –Under different conditions –At different times –Accounts for developmental changes –Genetic switches control the expression of specific genes

4. Gene Regulation: Prokaryotes Operon – gene regulation system in which adjacent DNA segments control the expression of a group of genes with closely related functions –Common in bacteria, not in eukaryotes –Ex: lac operon in E. coli used for the digestion of lactose

5. Gene Regulation: Eukaryotes More complex and variable Can occur before transcription and after transcription Operons are rare

6. Gene Regulation: Eukaryotes Transcription factors –Proteins –Interact with RNA polymerases around promoter regions of DNA –Can act as activators (ex: enhancers) or repressors

7. Processing RNA After Transcription Introns – noncoding sequences (do not get translated) Exons – coding sequences RNA Splicing – after transcription, introns are removed. Remaining exons are spliced (rejoined) to form a smaller mRNA molecule for transcription

8. Processing Proteins After Translation After translation, the protein may not go directly into action – may need structure altered –Occurs in many parts such as the Golgi complex Protein sorting – process of getting points to their correct destination; directed by protein sorting signals

9. Roles of Proteins Structure determines function Domains –Parts of the protein that have a specific chemical structure and function –Proteins can have several domains, each with a specific function