Cell Structure and Function

Mitochondrion and Cell Structures

  • Mitochondrion: Organelles responsible for energy production through oxidative metabolism.

  • Smooth Endoplasmic Reticulum: System of internal membranes that aids in the manufacture of carbohydrates and lipids.

  • Cytoskeleton: Network that supports organelles and cell shape, plays a role in cell motion.

    • Microtubule: Tube of protein molecules in centrioles, cilia, and flagella.

    • Intermediate Filament: Intertwined protein fibers providing support and strength.

    • Actin Filament: Twisted protein fibers responsible for cell movement.

  • Nuclear Pore: Opening embedded with proteins that regulates passage into and out of the nucleus.

  • Ribosome: Small complexes of RNA and protein synthesizing proteins.

  • Golgi Body: Collects, packages, and distributes molecules manufactured in the cell.

  • Cell Membrane: Lipid bilayer regulating entry and exit of substances, protecting and supporting the cell.

Cell Types

  • Animal Cells: Contain lysosomes, microvilli, and various organelles including nucleus and ribosomes.

  • Plant Cells: Contain cell wall, chloroplasts, and a large central vacuole.

Historical Background

Early Scientists in Cell Theory

  • Anton van Leeuwenhoek (1600s): First to observe living organisms in water through a microscope.

  • Robert Hooke (1600s): Used a light microscope on plant tissues; coined the term "cells" for chamber-like structures observed.

  • Matthias Schleiden (1800s): Concluded that all plants are made of cells.

  • Theodor Schwann (1800s): Concluded that all animals are made of cells.

  • Rudolf Virchow (1800s): Declared that new cells arise only from pre-existing cells (cell division).

The Cell Theory

  1. All living things are composed of cells.

  2. Cells are the basic unit of structure and function in living organisms.

  3. New cells are produced from existing cells.

Microscopy and Cell Study

  • Microscope Overview: Enlarges images using lenses; modern microscopes are superior to early versions.

    • Light Microscope: Allows light to pass through specimens using two lenses (objective and ocular).

    • Issues with Light Microscope: Cells are often nearly transparent; chemical stains or dyes are used for visibility.

  • Electron Microscopes:

    • Types:

    • Transmission Electron Microscope (TEM): Can study structures as small as 1 billionth of a meter; requires ultrathin slices of specimens.

    • Scanning Electron Microscope (SEM): Scans surfaces to acquire 3D images.

Classification of Cells

  • Prokaryotic Cells:

    • Generally smaller and simpler, lack a nucleus.

    • Conduct all activities of living things, primarily single-celled organisms.

    • Example: Bacteria.

  • Eukaryotic Cells:

    • Larger and more complex, contain a nucleus and various organelles.

    • Can be single-celled (e.g., protists) or multicellular (e.g., plants and animals).

Cell Structure Overview

  • Eukaryotic Cells contain a nucleus with DNA and specialized structures (organelles).

  • Cytoplasm: Fluid portion of the cell containing organelles and cytosol (mixture of filaments, molecules, and water).

  • Nucleus: Control center, contains nearly all DNA.

    • Nucleolus: Site for ribosome production.

    • Nuclear Envelope/Pore: Double membrane with openings regulating nucleic transport.

Organelles Supporting Cell Functions

  • Vacuoles: Storage structures for water, salts, and organic molecules.

  • Lysosomes: Filled with enzymes for breaking down large molecules and worn out organelles.

  • Cytoskeleton: Provides cell shape and movement.

  • Centrioles: Organize cell division in animal cells.

Protein Synthesis and Transport

  1. Ribosomes: Produce proteins by interpreting coded instructions from DNA.

  2. Endoplasmic Reticulum (ER):

    • Smooth ER: Synthesizes lipids.

    • Rough ER: Studded with ribosomes, site of protein synthesis.

  3. Golgi Apparatus: Modifies, sorts, and packages proteins for storage or secretion.

Energy-Related Organelles

  • Chloroplasts: Capture sunlight energy for photosynthesis in plant cells; contain chlorophyll.

  • Mitochondria: Sites for ATP production through oxidative metabolism.

Cell Membranes and Transport

  • Cell Membrane Structure: Lipid bilayer with embedded proteins, selectively permeable.

    • Phospholipids: Composed of two fatty acid chains and a phosphate group.

  • Selectivity and Transport: Passive transport (no energy) vs. active transport (requires energy).

Types of Transport Mechanisms

  1. Passive Transport:

    • Substances move based on concentration gradients without energy.

    • Simple Diffusion: Direct passage through membranes.

    • Facilitated Diffusion: Requires transport proteins.

  2. Active Transport:

    • Movement against a concentration gradient, requiring energy and carrier proteins.

    • Endocytosis: Cellular intake process for material.

    • Exocytosis: Secretion of materials from cells.

Homeostasis in Cells

  • Definition: Maintaining constant internal conditions necessary for survival.

  • Unicellular Organisms: Must grow, respond to the environment, transform energy, and reproduce.

  • Multicellular Organisms: Exhibit specialization, where cells differentiate for specific functions.

Specialized Animal Cells Examples

  • Red Blood Cells: Transport oxygen via hemoglobin.

  • Pancreatic Cells: Produce digestive enzymes.

  • Skeletal Muscle Cells: Utilize an enhanced cytoskeleton for movement.

Levels of Biological Organization

  • Cells → Tissues → Organs → Organ Systems → Organisms: Structure and function resolution leading to multicellular life.

  • Tissues: Groups of similar cells sharing a common function.

  • Organs: Composed of multiple tissue types working collaboratively.

  • Organ Systems: Groups of organs combining efforts for broader functions.

Cellular Communication

  • Cells communicate through chemical signals affecting activity pace or functionality; e.g., hormones influencing cellular operations.