Cellular Organization, Membrane Physiology, and Tissue Types: Study Notes for Anatomy & Physiology

General Organization of the Cell

Plasma Membrane

The plasma membrane is the outer boundary of the cell, composed primarily of a phospholipid bilayer. It serves as a selective barrier and is essential for maintaining cellular integrity and communication.

• Physical Barrier: Encloses the cell and separates cytoplasm from extracellular fluid.

• Selectivity/Permeability: Determines which substances enter or exit the cell.

• Sensing the Environment: Contains proteins that act as sensors to relay messages to the cell interior.

• Cell Recognition: Cell surface carbohydrates (glycocalyx) allow cells to recognize each other.

Cytoplasm

The cytoplasm consists of water and gel-like inclusions and organelles.

• Cytosol: Fluid component of the cell, contains enzymes, DNA/RNA, ions, and nutrients.

• Nucleus: Contains genetic material and controls cellular activities.

Major Organelles: Structure and Function

Mitochondria

Mitochondria are sausage-shaped organelles with a double membrane. They are the site of ATP production and are often called the "powerhouse" of the cell.

• Function: ATP synthesis via cellular respiration.

• Structure: Inner membrane folds (cristae) increase surface area for energy production.

Endoplasmic Reticulum (ER)

• Rough ER: Studded with ribosomes; synthesizes proteins for export.

• Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

Ribosomes

Ribosomes are small complexes of RNA and protein that synthesize proteins. They may be free in the cytosol or attached to the rough ER.

Golgi Apparatus

The Golgi apparatus modifies, packages, and transports proteins and lipids.

Lysosomes

Lysosomes are vesicles containing digestive enzymes. They break down waste and cellular debris.

Cytoskeleton

The cytoskeleton provides structural support and helps maintain cell shape.

• Microfilaments: Actin filaments; cell movement.

• Microtubules: Tubulin; cell organization and movement of organelles.

• Intermediate filaments: Provide tensile strength.

Cell Extensions

• Microvilli: Fingerlike projections that increase surface area for absorption.

• Cilia: Hairlike extensions that move substances across the cell surface.

• Flagella: Long extensions for cell movement (e.g., sperm).

Cell Membrane Structure and Permeability

Phospholipid Bilayer

The cell membrane consists of two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward.

• Proteins: Integral and peripheral proteins serve as channels, carriers, and receptors.

• Glycocalyx: Carbohydrate-rich area for cell recognition.

Membrane Proteins

• Integral proteins: Span the membrane; function as channels or carriers.

• Peripheral proteins: Attached to the membrane surface; function in signaling.

Resting Membrane Potential

The resting membrane potential is the voltage difference across the cell membrane, typically -70 mV, due to ion distribution (mainly K+ and Na+).

Gradients and Types of Diffusion

Types of Gradients

• Concentration Gradient: Difference in solute concentration between two areas.

• Electrical Gradient: Difference in charge across a membrane.

• Pressure Gradient: Difference in pressure between two areas.

Types of Diffusion

• Simple Diffusion: Movement of molecules from high to low concentration without energy input.

• Facilitated Diffusion: Movement via protein channels; no energy required.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Solution Tonicity

• Hypertonic: Higher solute concentration.

• Hypotonic: Lower solute concentration.

• Isotonic: Equal solute concentration.

Types of Membrane Channels

• Leak Channels: Always open; allow ions to flow by simple diffusion.

• Gated Channels: Open in response to specific stimuli (e.g., voltage, ligand, mechanical).

Vesicular Transport

• Exocytosis: Vesicles fuse with the membrane to release contents outside the cell.

• Endocytosis: Cell engulfs substances into vesicles.

• Phagocytosis: "Cell eating"; cell engulfs large particles.

• Pinocytosis: "Cell drinking"; cell engulfs extracellular fluid.

Cell Cycle and Mitosis

Phases of the Cell Cycle

• Interphase: Cell growth and DNA synthesis.

• G1 Phase: Growth and metabolism.

• S Phase: DNA replication.

• G2 Phase: Preparation for mitosis.

• M Phase: Mitosis and cytokinesis.

Mitosis Stages

• Prophase: Chromatin condenses, nuclear envelope dissolves.

• Metaphase: Chromosomes align at the cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelopes reform.

• Cytokinesis: Division of cytoplasm.

Difference Between Mitosis and Meiosis

• Mitosis: Produces two identical daughter cells; for growth and repair.

• Meiosis: Produces gametes; for sexual reproduction.

Protein Synthesis

Genetic Code and Steps

• Codons: Triplets of nucleotides in mRNA that code for amino acids.

• Transcription: DNA sequence is copied into mRNA.

• Translation: mRNA is decoded by ribosomes to build proteins.

• tRNA: Transfers amino acids to the ribosome.

Cellular Autophagy and Apoptosis

• Autophagy: Cells digest their own components for recycling.

• Apoptosis: Programmed cell death; removes damaged or unnecessary cells.

Cellular Metabolism and ATP

ATP: The Energy Currency

Adenosine triphosphate (ATP) stores and provides energy for cellular processes.

• Aerobic Respiration: Requires oxygen; produces up to 32-34 ATP per glucose.

• Anaerobic Respiration: Does not require oxygen; produces 2 ATP per glucose.

Key Equations:

• Glycolysis: $\text{Glucose} \rightarrow 2 \text{Pyruvate} + 2 \text{ATP}$

• Krebs Cycle: $\text{Acetyl-CoA} \rightarrow 2 \text{ATP} + 6 \text{NADH} + 2 \text{FADH}_2$

• Electron Transport Chain: $\text{NADH} + \text{FADH}_2 \rightarrow 28-32 \text{ATP}$

Tissue Types

Muscle Tissue

• Function: Movement and support.

• Types: Skeletal, cardiac, smooth.

Connective Tissue

• Function: Supports, binds, and connects other tissues.

• Examples: Bone, cartilage, blood, adipose.

Epithelial Tissue

• Function: Covers surfaces, lines cavities, forms glands.

• Characteristics: Cell junctions, polarity, avascularity.

Nervous Tissue

• Function: Communication and control.

• Components: Neurons and neuroglia.

Cell Communication and Signaling

• Paracrine: Signals affect nearby cells.

• Autocrine: Signals affect the same cell that released them.

• Juxtacrine: Signals require direct cell-to-cell contact.

• Endocrine: Signals travel through the bloodstream to distant cells.

Tissue Repair

• Inflammation: Damaged tissue releases chemicals; blood supply increases.

• Organization: Blood clot replaced with granulation tissue; fibroblasts produce collagen.

• Regeneration and Fibrosis: Epithelium regenerates; scar tissue may form.

Summary Table: Types of Cell Transport

Type	Energy Required?	Direction	Example
Simple Diffusion	No	High to Low	Oxygen, CO2
Facilitated Diffusion	No	High to Low	Glucose via carrier protein
Osmosis	No	High to Low (water)	Water movement
Active Transport	Yes	Low to High	Na+/K+ pump
Vesicular Transport	Yes	Varies	Endocytosis, exocytosis

Additional info:

• Some details on cell signaling and tissue repair were expanded for clarity.

• Equations for cellular respiration were added for academic completeness.