Gene Regulation in Eukaryotic Cells

Gene regulation is complex

• Regulation, and therefore, expression of a gene is complex.

• Regulation of these genes require all of these to interact together– Regulatory genes– Regulatory proteins– Transcription factors

Transcription Factors

• Transcription factors (proteins) bind to specific DNA sequences and/or other regulatory proteins

• Some of the these transcription factors are activators, some are repressors

Many things must occur for a gene to be expressed

• Combination of transcription factors binding to specific DNA sequences at any one time determines how much transcription occurs or doesn’t occur

Some genes are continuously expressed

• Some genes are always turned “on,” which means they are always expressed (transcription, translation…)– Ribosomal genes– Glycolysis genes

What if we share similar genes with other organisms?

• Gene regulation leads to some phenotypic differences between organisms with similar genes– Arm bones in humans and front leg bones of

dogs– Since we have similar bone structure, this

suggests• Common ancestry• Similar DNA sequences

Transcription factor binding in eukaryotes; influences

• The interactions of transcription factors with one another or with DNA can be influenced by signals– From within the cell– From outside the cell

• Signals are integrated at the promoter

DNA-level Regulation

• Enhancer regions and activator proteins

• Acetylation of histones

• Methylation of C’s on DNA

Stimulationof transcriptionby an enhancer

Transcription-level Regualation

• Alternative splicing– Varies in different tissues (skin vs. liver vs.

lung)

• RNAi (2006 Nobel Prize in medicine)

– siRNA and miRNA• 20-ish nucleotides long

– Then use of RISC and Dicer• Dicer is the enzyme that breaks apart ds RNA

Alternative Splicing

RNAi

Post-Translational Regulation of Expression

• Modifications of protein – Phosphorylation

• Targeting specific proteins to be degraded at a certain time

Importance of gene regulation

• The amount and time of gene expression can be regulated at any one of several steps between the DNA and the final functional gene product

Importance of gene regulation

• Gene regulation results in differential gene expression.

• This leads to cell specialization.