BIOL 208 - EXAM 4 Lecture Summary

Flashcards covering Prokaryotic and Eukaryotic Gene Regulation, including operon structures, transcriptional control, epigenetic modifications, and related concepts.

Gene Regulation (Prokaryotic)

Enables bacteria to respond to changing environmental conditions by turning specific genes "on" or "off" as needed; primarily occurs at the level of transcription.

Operon

A stretch of DNA that includes a promoter, operator, and genes coding for functionally related proteins.

Promoter (in Operon)

Binding site for RNA polymerase; in prokaryotes, a single sigma factor typically directs RNA polymerase to the promoter.

Operator (in Operon)

A regulatory DNA sequence located downstream of the promoter that acts as an "on/off" switch by interacting with repressors.

Genes of operon

Genes of operon. A cluster of functionally related genes, code for functionally related proteins.

Regulatory Gene (in Operon)

Gene located upstream of the operon that codes for a repressor or activator protein.

Negative Control (Transcriptional)

Involves repressor proteins that block RNA polymerase (on → off).

Positive Control (Transcriptional)

Involves activator proteins that enhance RNA polymerase binding (off → on).

Trp Operon (Repressible Operon)

Codes for enzymes that synthesize tryptophan; usually "on" but can be turned "off" when tryptophan is abundant.

Trp Repressor

Expressed in inactive form in Trp Operon

Corepressor

Tryptophan, binding to the repressor to activates it in Trp Operon

Lac Operon (Inducible Operon)

Codes for enzymes that degrade lactose; usually "off" but can be turned "on".

Repressor (in Lac Operon)

Made in active form; blocks transcription in Lac Operon

Inducer (in Lac Operon)

Allolactose (lactose present) binds repressor → inactivates it → transcription proceeds in Lac Operon.

Glucose Effect on Lac Operon

Low glucose → high cAMP → cAMP binds CRP activator → promotes transcription

Gene Regulation (Eukaryotic)

Enables cell specialization and allows cells to adapt to internal and external signals by precisely controlling when and where genes are expressed; regulation occurs via transcriptional control and epigenetic modification.

Promoter (Eukaryotic)

Located near the transcription start site of a gene; binds general transcription factors and RNA polymerase II.

Proximal Control Elements

Located near the promoter region; bind specific transcription factors.

Distal Control Elements

Located far from the gene (upstream, downstream, or in introns).

Enhancers

Increase transcription via activator proteins.

Silencers

Decrease transcription via repressor proteins.

DNA-Binding Domain (of Activator Proteins)

Binds to specific sequences such as enhancers.

Activation Domain (of Activator Proteins)

Interacts with general transcription factors and mediator proteins to promote assembly of the transcription initiation complex.

Epigenetic Modification

Heritable regulation of gene expression without changes to the DNA sequence.

Euchromatin

Loosely packed chromatin that is transcriptionally active.

Heterochromatin

Densely packed chromatin that is transcriptionally inactive.

Histone Acetylation

Acetyl groups added to histone tails → chromatin opens → increases transcription.

Histone Deacetylation

Acetyl groups removed → chromatin condenses → decreases transcription.

DNA Methylation

Methyl groups (-CH3) added to cytosines in DNA → reduces transcription: via block transcription factor binding, promote formation of heterochromatin, or recruit repressor proteins.

Epigenetic Inheritance (cell division)

Chromatin modifications are heritable across cell divisions and help cells maintain identity and specialized function in tissues.

Epigenetic Inheritance (transgenerational)

Most epigenetic marks are erased and reset during gamete formation and early embryonic development (epigenetic reprogramming), but some modifications escape this reprogramming, leading to transgenerational epigenetic inheritance.