Chapter 2 Cell Biology

Cell: The basic, living, structural and functional unit of the body.
- Compartmentalizes chemical reactions.
- Regulates inflow & outflow of substances.
- Uses genetic material (DNA) to direct cellular activities.

Plasma/Cell Membrane
- Described as a "sac" surrounding the cell.
Nucleus
- A type of organelle containing the genetic material of the cell (DNA).
Cytoplasm
- Everything between the membrane and the nucleus.
- Cytosol: The intracellular fluid (liquid part), mostly water, where many chemical reactions occur.
- Organelles: Subcellular structures with specific functions.

Composed of:
two centrioles surrounded by pericentriolar material, playing a key role in organizing microtubules and regulating the cell cycle.
Cytoplasm: The gel-like fluid within the cell that contains organelles, cytoskeleton, and various molecules essential for cellular processes.
- Centrioles: Perpendicular to each other, formed by 9 clusters of 3 microtubules.
- Pericentriolar Material: Area surrounding the centrioles.

Plasma Membrane: Flexible but sturdy barrier.
Lysosome: Contains digestive enzymes for breaking down various substances.
Smooth Endoplasmic Reticulum (ER): Synthesizes lipids and detoxifies.
Peroxisome: Contains enzymes that oxidize organic material and detoxify substances.
Mitochondrion: Generators of ATP for energy.
Flagellum/Cilium: Cellular projections for movement.
Rough Endoplasmic Reticulum: Synthesizes and processes proteins covered with ribosomes.
Ribosom: Site of protein synthesis; can be free or membrane-bound.
Golgi Complex: Key for modifying, sorting, and packaging proteins produced in the rough ER.

Fluid Mosaic Model: Describes the structure as a phospholipid bilayer with proteins embedded.
Protein Channels, Pumps, and Receptors: Act as "gatekeepers" of the cell, regulating substance entry and exit.

Phospholipid Bilayer: Permeable to small nonpolar and uncharged molecules (e.g., O2, CO2).
Integral/Transmembrane Proteins: Act as specific channels for polar and charged particles (ions).
Peripheral Proteins: Attached to the free surface and act as receptors for various stimuli.
Macromolecules: Unable to pass freely; utilize vesicular transport methods such as endocytosis and exocytosis.

Intracellular Fluid (ICF): Fluid within cells (cytosol).
Extracellular Fluid (ECF): Fluid outside cells; includes:
- Interstitial/Intercellular Fluid: Between cells.
- Plasma: Liquid portion of blood.
- Lymph: Fluid found in lymphatic vessels.

Definition: Requires no additional energy from ATP; relies on kinetic energy of molecules.
Types:
1. Diffusion: Movement from high to low concentration until equilibrium is reached.
2. Osmosis: Specific diffusion of water molecules through a semipermeable membrane.
3. Facilitated Diffusion: Uses specific transmembrane proteins (e.g., glucose transport).
4. Filtration: Movement through a membrane influenced by gravity and/or mechanical forces (e.g., blood pressure).

Water molecules diffuse across a semipermeable membrane, generally moving from high to low concentration of water, impacting intracellular fluid volume significantly.

Definition: Must compare two fluid compartments to describe relative solute concentration.
Types of Tonicity:
- Hypertonic: More solute compared to another compartment.
- Hypotonic: Less solute compared to another compartment.
- Isotonic: Same solute concentration in both compartments.
Understanding tonicity is crucial for IV solutions and hydration implications.

Isotonic Solution: No net movement of water; equal concentration inside and outside the cell.
Hypotonic Solution: Water moves into the cell, leading to swelling and potential lysis.
Hypertonic Solution: Water moves out, causing the cell to shrink (crenation).

Definition: Requires energy from ATP to move substances against their concentration gradient.
- Example: Sodium-Potassium Pump (Na+/K+ ATPase) maintains low Na+ and high K+ concentrations within cells.

Endocytosis: Process of bringing substances into the cell by engulfing them in a vesicle.
- Phagocytosis: "Cell eating,” where solids are engulfed, often by white blood cells.
- Pinocytosis: "Cell drinking,” where liquids are engulfed.
- Receptor-Mediated Endocytosis: Specific uptake of substances.
Exocytosis: Releasing substances from the cell using vesicles.

Cytoskeleton: Composed of protein filaments that support cell structure, facilitate movement, and organize chemical reactions.
Ribosomes: Sites of protein synthesis, exist as free or bound to rough ER.
Endoplasmic Reticulum (ER):
- Rough ER: Covered with ribosomes for protein synthesis.
- Smooth ER: Synthesizes lipids and detoxifies.
Golgi Body/Apparatus: Modifies, sorts, and packages proteins.
Lysosomes: Contain enzymes for digestion.
Peroxisomes: Metabolize fatty acids, detoxify substances.
Mitochondria: Double membrane organelles responsible for ATP generation.
Nucleus: Houses the organism’s genetic material (DNA) in the form of chromosomes.

Mitosis: Occurs in somatic cells, resulting in two identical diploid daughter cells (2n).
Meiosis: Occurs in germ cells (reproductive), resulting in four non-identical haploid daughter cells (1n).

Phases:
- Interphase (G1, S, G2)
- G1 Phase: Cell growth, organelle duplication.
- S Phase: DNA replication occurs.
- G2 Phase: Preparation for mitosis.
- Mitotic Phase: Actual division of cell contents into two daughter cells.

Involves the division of the cytoplasm and organelles, typically occurs from late anaphase/early telophase, resulting in two identical daughter cells.

Homeostasis regulates the balance between cell division and death.
- Apoptosis: Programmed cell death involving the activation of suicide enzymes.
- Necrosis: Cell death due to injury or infection.