cell part 1 week3

Cell Theory and Definition of Cells

Overview of Cell Theory

• Cell theory is the first unifying theory of biology.

• It consists of three main principles:

  • All living things are made of cells.

  • The cell is the fundamental unit of life.

  • All cells arise from preexisting cells.

What is a Cell?

• A cell is the simplest collection of matter that can be considered alive.

• Cells are generally small, typically ranging from 10 to 100 microns in diameter.

  • Frog egg: approximately 1 millimeter to 0.5 centimeters in diameter.

  • Human oocytes: about 10 to 100 microns in diameter.

Structure of Cells

• All cells possess a few basic structures:

  • Plasma Membrane:

    • Acts as a boundary of the cell made of phospholipids.

    • Semipermeable, allowing selective passage of materials.

  • Cytosol:

    • The aqueous component within the cell that is where organelles are suspended.

  • DNA:

    • Genetic material essential for cell function and reproduction.

  • Ribosomes:

    • Structures that read genetic material to synthesize proteins.

The Plasma Membrane

• The plasma membrane serves as a selective barrier.

  • It is defined by a phospholipid bilayer.

  • Molecules need to cross this barrier to enable cellular interactions.

Molecule Movement and Membrane Proteins

• Types of Molecules that Move Across the Plasma Membrane:

  • Small nonpolar molecules (e.g., O2, CO2) can diffuse freely.

  • Larger and polar molecules (e.g., glucose) need special transport mechanisms.

  • Aquaporins help water molecules move across the membrane more efficiently.

• Functions of Membrane Proteins:

  • Transport large or polar molecules across the membrane.

  • Serve as enzymes that catalyze chemical reactions.

  • Provide structural support through the cytoskeleton.

Cytosol and Cytoplasm

• Cytosol:

  • The fluid part of the cytoplasm, rich in proteins, giving it a gelatinous property.

• Cytoplasm:

  • The combination of cytosol and organelles present within the cell.

Protein Synthesis

• When a gene is expressed,

  • DNA is transcribed into mRNA, which is then translated by ribosomes to produce proteins.

  • Example: Insulin synthesis in pancreatic cells when blood sugar levels are high.

Microscopy and Cell Discovery

• Historical Figures:

  • Robert Hooke: Coined the term "cell" after observing cork.

  • Anton Van Leeuwenhoek: Improved microscopy techniques for studying cells.

  • Matthias Schleiden and Theodor Schwann: Contributed to the development of cell theory.

  • Rudolf Virchow: Proposed that all cells come from pre-existing cells.

Types of Microscopes

• Light Microscopes:

  • Commonly used, require staining for contrast.

• Fluorescent Microscopes:

  • Utilize fluorescent dyes to visualize specific cell structures.

• Electron Microscopes:

  • Offer the highest magnification using electron beams instead of light.

  • Ideal for viewing cellular structures like cilia in detail.

Why Are Cells Small?

• Surface Area to Volume Ratio:

  • Smaller cells have a higher surface area relative to their volume.

  • As cells grow larger, this ratio decreases, leading to inefficiencies in molecular uptake and waste removal.

Importance of Small Cell Size

• Facilitates efficient uptake of necessary molecules (like oxygen).

• Enhances quicker release of waste products.

• Supports maintenance of homeostasis through improved interactions with the external environment.

Types of Cells

• Prokaryotic Cells:

  • Generally smaller and simpler.

  • Lack membrane-bound organelles.

  • Exist as unicellular organisms.

• Eukaryotic Cells:

  • Larger and more complex with membrane-bound organelles, including a nucleus to store DNA.

Next lecture will focus on organelles within eukaryotic cells.