BSC1010C: General Biology 1 - Cell Structure (Module 4 - Part 2)

BSC1010C: General Biology 1 - Cell Structure (Module 4 - Part 2)

Learning Objectives - Part 2: Eukaryotic Cells

  • Describe the structure and function of nuclear transport.
  • Describe the structure and function of the endomembrane system.
  • Compare the roles of microfilaments, intermediate filaments, and microtubules, and describe the structure and function of the cytoskeleton.
  • Compare and contrast cilia and flagella.

Introduction to Cell Structure

  • Life's properties emerge from the collaboration of internal structures within a cell.
  • Understanding cells involves:
    • Examining the parts of the cell (prokaryotic and eukaryotic structures).
    • Examining how these parts fit into a whole.
    • Looking closer at nuclear transport, the endomembrane system, and the dynamic cytoskeleton.

Putting the Parts into a Whole: Cytology and Cell Fractionation

Cytology

  • Definition: The study of cells.
  • Method: Combines microscopy and biochemical analysis.
  • Structure-Function Correlation: The structure of each cell component correlates with its function.
    • Size and Number of Organelles: Varied based on cell's specialized function.
      • Fat cells: Rounded, globular structures optimized for lipid storage.
      • Cardiac muscle cells: Long and tapered for contractile function.
    • Variation of organelle content also correlates with specialized function.

Cell Fractionation

  • Purpose: To take cells apart and separate organelles from each other based on size and density.
  • Method: Uses cell lysis (breaking open cells) and differential centrifugation.
  • Centrifugation:
    • Separates cellular and molecular components.
    • Separates components by size and density, often using gradients.
    • Ultracentrifuges: Can spin at speeds up to 130,000 ext{ rpm} and generate forces of 1,000,000 imes ext{G}, allowing separation of smaller cellular particles.

The Dynamic Cell

  • Research Techniques: Differential centrifugation and fluorescent tags are used to isolate cell components and analyze chemical composition.
  • Cellular Activity Examples:
    • Body's cells use approximately 10 ext{ million ATP} molecules per second.
    • Cellular enzymes can catalyze over 25,000 reactions per second.
    • Each membrane phospholipid can travel the breadth of its organelle or cell in under a minute.
    • Hundreds of trillions of mitochondria are completely replaced about every 10 days.

Cell Systems I: Nuclear Transport

Nucleus

  • Information Center: The primary information center of eukaryotic cells.
  • Genetic Information: Genetic information in DNA is decoded and processed here.
  • RNA Production: Large suites of enzymes interact to produce RNA messages.
  • Nucleolus Function: Functions as the site of ribosome assembly.
    • Ribosomal RNA (rRNA) binds proteins to form ribosomes.
    • Messenger RNA (mRNA) carries information to synthesize proteins.

Structure and Function of the Nuclear Envelope

  • Separation: Separates the nucleus from the rest of the cell (cytosol).
  • Nuclear Pore Complexes: Perforated with openings called nuclear pore complexes.
    • Connects the inside of the nucleus with the cytosol.
    • Consists of about 30 different proteins.
  • Inbound Traffic: A typical cell imports over 500 molecules through 2000-5000 nuclear pores every second.
    • Nucleoside triphosphates.
    • Proteins responsible for copying DNA.
    • Proteins responsible for synthesizing RNAs.
    • Proteins needed for assembling ribosomes.

How Do Molecules Enter the Nucleus?

  • Selective Import: Import of large molecules into the nucleus is highly selective.
  • Nuclear Pores as Gates: Nuclear pores serve as dynamic gates to control passage through the envelope.
  • Nuclear Localization Signal (NLS): Nuclear proteins contain a nuclear localization signal (NLS).
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