Foundations of Biology 2 Weekly Study Guide

Foundations of Biology 2 Weekly Study Guide

Disclaimer

  • This guide is intended to assist you in your studies. It outlines the topics covered and provides basic information.

  • It is not a complete set of notes on every concept that may be on the exam.

Topics Covered

Prokaryotes

  • Morphologically simple but metabolically diverse.

    • Flagella: tail-like structure that aids in locomotion.

    • Photoheterotrophy and Chemoautotrophy: modes of metabolism.

      • Photoheterotrophy: organisms use light energy and organic compounds for growth.

      • Chemoautotrophy: organisms obtain energy from chemical reactions involving inorganic molecules.

    • Horizontal Gene Transfer: mechanism that contributes to genetic diversity (refer back to Week 1).

    • Extremeophiles: organisms thriving in extreme conditions, e.g., environments at 130°C.

    • Hibernation: adaptive strategy for survival in non-favorable environments.

Selective Gene Expression

  • Conserves energy and resources through different regulatory mechanisms.

Pre-transcriptional Regulation

  • Manipulation of Promoters: Enhances or inhibits the ability of RNA polymerase to bind and initiate transcription.

    • Most Efficient: Prevents unnecessary transcription by regulating expression at the promoter level.

Post-transcriptional Regulation (Eukaryotes only)

  • Strategies such as intron/exon splicing and mRNA processing.

    • Mechanisms existing to deactivate mRNA include degradation or inhibition by regulatory proteins.

Post-translational Regulation

  • Mechanisms to catabolize and/or deactivate proteins, which is the speediest method of gene expression control.

Prokaryotic Gene Expression

  • Operons: Group of genes regulated by a single promoter.

    • Function Unit of Prokaryotic Gene Expression.

  • Promoters: Specific sequences (usually at -10 or -35) where RNA polymerase binds, influenced by strength (weak vs. strong) of the promoter affecting the binding efficiency of RNA polymerase.

  • Sigma Factors (Proteins): Facilitate the binding of RNA polymerase to the promoter, essential for the initiation of transcription; without them, transcription cannot occur.

Operators

  • Control the transcription process.

    • Negative Control: Involves a repressor protein binding to the operator; this blocks or reduces the efficiency of transcription—down-regulating transcription.

    • Positive Control: Activator proteins enhance transcription efficiency or activate transcription—upregulating transcription.

LAC Operon

  • Important model for understanding cellular pathways; knowledge crucial for advanced biology studies.

    • Controls lactose metabolism in E. coli, demonstrating both negative (lactose) and positive (glucose) control.

    • Glucose: Preferred energy source; suppresses other operons when available.

    • B-galactosidase (B-gal): Enzyme that breaks down allolactose into glucose; production is regulated by the lac operon.

    • cAMP: Binds to CAP (activator) to enhance RNA polymerase activity on the lac promoter—efficient binding requires cAMP.

Inducible System

  • Default State: Usually OFF, can be switched ON by removing negative regulation or adding positive regulation.

    • In Absence of Lactose: Lac repressor binds to the operator, preventing B-gal production (negative regulation).

    • In Presence of Lactose: Allolactose functions as an inducer, changing the repressor's conformation, allowing de-binding from the operator; transcription of B-gal occurs.

Interactions of Glucose and Lactose

  • Presence of Both: E. coli uses glucose first; lac operon is transcribed at low levels due to high glucose (inhibits cAMP production).

  • Absence of Glucose: Lactose is the primary food source; cAMP assists in increasing lac operon transcription.

TRP Operon

  • Represents a repressible negative control system.

    • Negative Feedback Loop: The product (tryptophan) shuts down the metabolic pathway when abundant.

    • Default State: Tryptophan synthesized when repressor unbound to operator.

    • Accumulation of Tryptophan: Binds to the trp repressor, altering its shape and allowing it to inhibit transcription by binding to the operator.

Eukaryotic Gene Expression

  • Introduction to gene expression regulation examples, including insulin resistance mechanisms in bears.

    • Differential Expression: Controlled by eight proteins across different life stages.

    • PPARG: Transcription factor essential for liver, muscle, and adipose tissue regulation potentially solving insulin resistance issues.

  • Hox Genes: Transcription factors influencing the morphology of bilateral organisms.

Types of Gene Expression Regulation

  1. Pre-transcriptional (e.g., acetylation and methylation).

  2. Transcription (most preferred): Involves promoters, transcription factors, enhancers, and silencers.

  3. Post-transcriptional: Unique to Eukaryotes, utilizes mRNA processing.

  4. Pre-Translation: Prevents or delays the translation of mRNA.

  5. Post-Translation: Involves tagging proteins for degradation or functionally altering them.

Transcriptional Control

  • Most genes are OFF by default, requiring the binding of transcription factors to promoters for activation.

  • General Transcription Factors (TFs): Basal transcription apparatus required for transcription initiation.

Steps of Basal Transcription Apparatus Action:

  1. TFIID: Binds to the promoter (TATAAA sequence).

  2. TFIIB: Ensures proper alignment of TFIID.

  3. TFIIF: Links TFIID to RNA polymerase.

  4. TFIIE/TFIIH: Enhances RNA polymerase performance, assisting in DNA denaturation.

Specific Transcription Factors

  • Regulate specialized cellular processes, necessitating additional regulatory sequences.

  • Distant Control Elements: Can influence transcription through DNA bending; enhancers and silencers involved in regulation.

Study Tips and Practice

  • Distinguish regulated processes: Identify and differentiate pretranscriptional, posttranscriptional, and post-translational modifications.

  • Example questions addressing mechanisms, significance, and consequences of different types of regulation in the context of the lac and trp operons.

Example Fill-in-the-Blanks

  • Allolactose formation is caused by the presence of (lactose). This molecule is an (inducer) that will cause the (repressor) to change its shape and be released from the (operator). This will cause (transcription) to occur. This is an example of (negative regulation).

Review of Scenarios

  • Glucose's influence on lac operon: High levels reduce cAMP, affecting CAP binding and transcription efficiency.

  • Conditions favoring lac operon expression: Lactose present, glucose absent (allows maximal operon activity).