ap bio gene expression

Development and Gene Regulation

• Cells in multicellular organisms need to communicate and differentiate to avoid being a single giant block.

• Specific genes are activated or silenced during development leading to different tissue types which form organs.

• Hox Genes:

  • These genes are crucial for correct development patterns, acting as transcription factors.

  • Example: The fruit fly with a leg growing from its head due to improper Hox gene activation location.

Gene Expression Mechanisms

• Morphogenesis refers to the physical traits developed from gene expression.

• Prokaryotes and eukaryotes regulate gene expression differently, with eukaryotes requiring more complex systems due to multicellularity.

• DNA Packaging:

  • DNA is wrapped around histone proteins forming nucleosomes (string-bead structure).

  • The tightness of the nucleosomes affects RNA polymerase's ability to bind and transcribe.

  • Euchromatin (loose packing): transcription can occur.

  • Heterochromatin (tight packing): transcription cannot occur.

Environmental Influence on Gene Expression

• Environmental factors influence gene expression without mutating the DNA.

• Changes in the phenotypic expression arise from alterations to nucleosome packing.

• Acetyl Groups:

  • Adding acetyl groups loosens chromatin, encouraging transcription.

• Methyl Groups:

  • Adding methyl groups tightens chromatin, silencing genes.

• Example: Identical twins can exhibit different traits due to lifestyle and environmental exposure, despite having identical DNA.

Regulatory Sequences in Eukaryotic Cells

• Eukaryotic gene regulation involves promoters and enhancers:

  • Promoter Region: Where RNA polymerase typically binds to start transcription.

  • Enhancers: Can be located far from the promoter and facilitate transcription by binding activators.

• Enhancers work through mediator proteins that assist in attracting RNA polymerase for transcription.

Transcription Factors and Their Roles

• Activator Proteins: Bind to enhancers to initiate transcription.

• Repressor Proteins (Silencers): Prevent gene expression by blocking RNA polymerase from binding.

• DNA Bending Proteins: Aid the activators in connecting to the transcription complex, ensuring proper transcription initiation.

• The effectiveness of transcription largely depends on the availability and amount of transcription factors.

Alternative RNA Splicing

• Post-transcriptional modification where RNA can be cut and spliced in different ways.

• This process generates various protein products from a single gene.

• MicroRNA (miRNA):

  • Can inhibit translation and cause messenger RNA to degrade, acting as another level of regulation.

Eukaryotic vs Prokaryotic Gene Regulation

• Prokaryotes operate with simpler mechanisms such as operons controlled by inducers and repressors to manage gene expression.

• Eukaryotic cells utilize enhancers, specific transcription factors, and epigenetics, allowing nuanced control over gene expression.

• Epigenetics:

  • Changes gene expression without altering the underlying DNA sequence, influencing phenotype through histone modifications and nucleosome organization.

Classroom Activities

• Aimed at understanding developmental patterns and their influence on gene expression.

• Hands-on experiences with pipettes in lab settings to help solidify practical applications.

• Important dates for upcoming exams and lab events are being communicated to prepare adequately.