cell biology

1. Introduction to Cells

  • The fundamental unit of life; all living organisms are composed of cells.

  • Cell Theory:

    1. All living organisms are composed of one or more cells.

    2. The cell is the basic unit of structure and function in all organisms.

    3. All cells come from pre-existing cells.

2. Types of Cells
2.1 Prokaryotic Cells

  • Definition: Ancient, simple cells lacking a membrane-bound nucleus and other membrane-bound organelles.

  • Examples: Bacteria and Archaea.

  • Characteristics:

    • Smaller in size (typically 0.10.1 to 55 μm).

    • Genetic material (DNA) is located in a region called the nucleoid.

    • Contain ribosomes for protein synthesis.

    • Often have a cell wall, plasma membrane, cytoplasm, and sometimes flagella or pili.

2.2 Eukaryotic Cells

  • Definition: Complex cells possessing a true nucleus and other membrane-bound organelles.

  • Examples: Animal cells, plant cells, fungi, protists.

  • Characteristics:

    • Larger in size (typically 1010 to 100100 μm).

    • Genetic material (DNA) is housed within the nucleus.

    • Highly compartmentalized with various organelles performing specialized functions.

3. Eukaryotic Organelles and Their Functions

  • Nucleus:

    • Contains the cell's genetic material (DNA) organized into chromosomes.

    • Controls cell growth, metabolism, and reproduction.

    • Nuclear envelope: Double membrane surrounding the nucleus with nuclear pores.

    • Nucleolus: Site of ribosome synthesis.

  • Mitochondria:

    • "Powerhouse" of the cell.

    • Site of cellular respiration, producing ATP (adenosine triphosphate) – the cell's energy currency.

    • Contains its own DNA and ribosomes.

  • Ribosomes:

    • Sites of protein synthesis (translation).

    • Can be free in the cytoplasm or attached to the endoplasmic reticulum.

  • Endoplasmic Reticulum (ER): Network of membranes involved in synthesis, modification, and transport of proteins and lipids.

    • Rough ER (RER):

    • Studded with ribosomes.

    • Involved in the synthesis and folding of proteins destined for secretion or insertion into membranes.

    • Smooth ER (SER):

    • Lacks ribosomes.

    • Involved in lipid synthesis, detoxification of drugs and poisons, and calcium ion storage.

  • Golgi Apparatus (Golgi Complex/Body):

    • Further modifies, sorts, and packages proteins and lipids from the ER into vesicles for transport to other destinations or secretion.

    • Consists of flattened sacs called cisternae.

  • Lysosomes (Animal Cells):

    • Contain hydrolytic enzymes to break down waste materials, cellular debris, and foreign invaders.

    • Responsible for autophagy (recycling cell's own organic material).

  • Peroxisomes:

    • Involved in metabolic processes, breaking down fatty acids and detoxifying harmful substances.

    • Produce hydrogen peroxide (H<em>2O</em>2H<em>2O</em>2) as a byproduct, which they then convert to water and oxygen.

  • Vacuoles:

    • Central Vacuole (Plant Cells): Large, single vacuole that stores water, nutrients, waste products, and maintains turgor pressure.

    • Food Vacuoles: Formed by phagocytosis.

    • Contractile Vacuoles: Pump excess water out of the cell (in some protists).

  • Chloroplasts (Plant Cells & Algae):

    • Sites of photosynthesis, converting light energy into chemical energy (sugars).

    • Contain chlorophyll and have their own DNA and ribosomes.

  • Cell Wall (Plant Cells, Fungi, some Protists):

    • Rigid outer layer providing structural support, protection, and preventing excessive water uptake.

    • Primarily composed of cellulose in plants, chitin in fungi.

  • Plasma Membrane:

    • Selectively permeable barrier regulating the passage of substances into and out of the cell.

    • Composed of a phospholipid bilayer with embedded proteins (fluid mosaic model).

  • Cytoskeleton:

    • Network of protein filaments (microfilaments, intermediate filaments, microtubules) providing structural support, cell shape, and facilitating cell movement and transport within the cell.

4. Cellular Processes

  • Cellular Respiration: Process by which cells break down glucose and other organic molecules to generate ATP.

    • Glycolysis: Occurs in the cytoplasm.

    • Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix.

    • Oxidative Phosphorylation (Electron Transport Chain): Occurs in the inner mitochondrial membrane