Biology Of Cell BB1725

Page 1: Gene Expression - Layers of Control

• 7 Layers of Control to Form a Protein from DNA:

  1. Transcriptional Control

  2. RNA Processing

  3. Transport and Localization

  4. Translational Control

  5. RNA Degradation: RNA is broken down to stop certain protein productions.

  6. Protein Degradation: Proteins are broken down for amino acids to be reused.

  7. Protein Activation: Activates proteins to regulate activity.

• Differential Gene Expression: Allows for different cell types to form despite identical DNA content.

  • Certain genes play key roles; for example, RNA genes/Atpase are vital in all cells, while others are tissue-specific.

  • Some genes are regulated by time (developmental and cyclonic stages).

Page 2: Transcriptional Control

• Transcription Factors:

  • Bind to promoters to guide RNA Polymerase II.

  • Trans-acting Factors: Recognize and bind cis-acting elements.

  • Inducible Transcription Factors: Respond to signals (e.g., hormones).

• Alternative Promoters: Regions where transcription begins, producing variations of proteins.

• Epigenetic Control: Affects DNA function without altering base sequences.

  • Heterochromatin: Inactive chromatin.

  • Euchromatin: Active and transcribable chromatin.

  • Histone Modifications:

    • Acetylation - activates transcription by loosening DNA.

    • Methylation - silences transcription.

    • Produces pre-mRNA that undergoes further processing.

Page 3: mRNA Processing and Regulation

• RNA Processing:

  • Alternative Splicing: Produces tissue-specific protein isoforms.

    • Negative Control: Repressors inhibit splicing.

    • Positive Control: Activators enhance splicing.

  • Alternative Polyadenylation: Different sites for adding poly-A tails.

• mRNA Editing: Includes deamination and modification to create stop codons, affecting transcript stability.

Page 4: Translational Control and Protein Function

• Transport and Localization: mRNA is sent to the ER or ribosome based on 3' UTR.

• Translation: mRNA longevity is influenced by cis-acting regulatory sequences targeted by miRNAs.

• RNA Degradation: mRNA is rapidly degraded to control protein production, including through 5' cap removal and 3' degradation.

• Protein Degradation:

  • Ubiquitin-Proteasome Pathway: Tags proteins for degradation.

  • Activities that reveal enzyme-binding sites:

    • Phosphorylation and cleavage affect protein function.

Page 5: Post-Translational Control

• Protein Activity Regulation

  • Cleavage: Removal of amino acids can activate proteins.

  • Inhibitors: Restrict protein activity, while binding can activate proteins (e.g., RhoA protein in actin polymerization).

Page 6: Cell Differentiation and Development

• Somatic Cells: All cell types except gametes.

• Haploid Cells: Gametes (egg and sperm), which combine to form a zygote.

• Model Organisms: Used to study development due to ease of handling and observable features.

  • Example: Xenopus laevis - produces many eggs, easy to observe and manipulate.

• Oocyte Development: Influenced by embryo's surface properties; sperm entry alters developmental orientation.

Page 7: Developmental Processes

• Blastula Formation: Sperm migration leads to a blastula with a potential for gastrulation (tissue layer development).

• Gastrulation: Rearrangement of cells into three germ layers: ectoderm (skin), mesoderm (muscle), and endoderm (internal organs).

Page 8: Human vs. Xenopus Development

• Comparison: Zebrafish and human embryonic development, differences in complexity and stages.

• Cell Fate Determination: Based on an organism's position in the blastula.

Page 9: Cell Cycle Overview

• Hypertrophy: Cell size increase.

• Phases of Cell Cycle:

  • Interphase: Majority of the cycle spent here; includes G1, S (DNA synthesis), and G2.

  • M-phase: Cell division; segregates chromosomes.

• Control: Cells progress through the cycle only when conditions are favorable.

Page 10: Cell Cycle Regulation and Mitosis

• Quiescence: Resting state where cells do not divide.

• Cyclins and CDKs: Key regulators that control progression through the cell cycle.

  • Types of Cyclins for G, S, and M phases, which activate associated CDKs.

Page 11: Mitosis Phases

• Mitosis: Division of somatic cells, detailed phases include Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.

• Cytokinesis: Occurs at the end of mitosis, resulting in two daughter cells.

Page 12: Meiosis Overview

• Purpose: Division of germ cells to produce haploid gametes.

• Meiosis I and II: Both phases involved in reducing chromosome number and generating genetic diversity through recombination.

Page 13: Gender Differences in Meiosis

• Male vs Female Meiosis: Males produce four viable gametes, females produce one egg and polar bodies.

Page 14: Membrane Structure and Function

• Types of Cellular Membranes: Plasma membrane surrounds cells; organelles also have lipid bilayers.

  • Phospholipid Bilayer: Fundamental structure that allows selective permeability.

Page 15: Membrane Proteins

• Functions of Membrane Proteins: Include transport, signaling, and structural roles.

• Glycocalyx: Carbohydrate layer that aids in cell adhesion and protection.

Page 16: Membrane Transport Mechanisms

• Transport Methods:

  • Carrier Proteins: Bind solutes to transport across membranes.

  • Ion Channels: Facilitate ion movement, regulating cellular ion concentrations.

• Types of Transport: Uniport, symport, and antiport systems.

Page 17: Introduction to Organelles

• Importance of Compartmentalization: Eukaryotic cells are organized into distinct compartments, each with specific functions.

Page 18: Protein Traffic within Cells

• Types of Protein Transport: Gated transport between the nucleus and cytosol, transmembrane transport to organelles, and vesicular transport.

Page 19: Mitochondria's Role

• Function: Energy production, with outer and inner membranes housing distinct functions and the Krebs cycle occurring in the matrix.

Page 20: Cytoskeleton Structure and Function

• Components of Cytoskeleton: Actin filaments, microtubules, and intermediate filaments contribute to cell shape, movement, and intracellular transport.