Comprehensive Study Notes: Cell Structure, Genetics, and Tissue Organization in Anatomy & Physiology

Plasma Membrane Structure and Components

Overview of the Plasma Membrane

The plasma membrane is a selectively permeable barrier that surrounds the cell, maintaining the internal environment and mediating communication with the external environment.

• Phospholipid bilayer: Composed of hydrophilic heads and hydrophobic tails, forming the basic structure.

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

• Carbohydrates: Attached to proteins and lipids, forming glycoproteins and glycolipids for cell recognition.

• Cholesterol: Stabilizes membrane fluidity.

Glycocalyx Composition

Definition and Function

The glycocalyx is a carbohydrate-rich layer on the cell surface, important for protection, immunity, and cell recognition.

• Composed of glycoproteins and glycolipids.

• Facilitates cell-cell adhesion and communication.

Fluid Mosaic Model Principles

Key Concepts

The fluid mosaic model describes the dynamic and flexible nature of the plasma membrane.

• Lipids and proteins can move laterally within the layer.

• Membrane is not rigid; components are distributed in a mosaic pattern.

Types of Cell Junctions

Classification and Functions

• Tight junctions: Seal adjacent cells, preventing leakage (e.g., intestinal lining).

• Desmosomes: Provide mechanical strength by anchoring cells together.

• Gap junctions: Allow direct communication between cells via connexons.

Substances that Can Diffuse Directly Through the Plasma Membrane

Selective Permeability

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

• Lipid-soluble substances pass easily.

• Large or charged molecules require transport proteins.

Types and Characteristics of Passive Transport

Mechanisms of Movement

• Simple diffusion: Movement down a concentration gradient without energy input.

• Facilitated diffusion: Uses carrier or channel proteins for transport.

• Osmosis: Diffusion of water across a semipermeable membrane.

Effects of Hypertonic, Hypotonic, and Isotonic Solutions on Cells

Osmotic Balance

• Hypertonic: Higher solute concentration outside; cell shrinks (crenation).

• Hypotonic: Lower solute concentration outside; cell swells and may burst (lysis).

• Isotonic: Equal solute concentration; no net water movement.

Endocytosis Types and Mechanisms

Cellular Uptake Processes

• Phagocytosis: "Cell eating"; engulfment of large particles.

• Pinocytosis: "Cell drinking"; uptake of extracellular fluid.

• Receptor-mediated endocytosis: Specific uptake via receptor binding.

Sodium-Potassium Pump (Transport Type)

Primary Active Transport

• Uses ATP to move 3 Na+ out and 2 K+ into the cell against their gradients.

• Maintains membrane potential and cell volume.

$3\text{Na}^+_{\text{in}} + 2\text{K}^+_{\text{out}} + \text{ATP} \rightarrow 3\text{Na}^+_{\text{out}} + 2\text{K}^+_{\text{in}} + \text{ADP} + \text{P}_i$

Secondary Active Transport Mechanism

Coupled Transport

• Uses energy from the movement of one substance down its gradient to transport another against its gradient.

• Examples: Symport (same direction), antiport (opposite direction).

Cell Signaling: Chemical Signaling, G Protein-Linked Receptor Signaling

Signal Transduction Pathways

• Chemical signaling: Ligands (hormones, neurotransmitters) bind to receptors.

• G protein-coupled receptors (GPCRs): Activate intracellular G proteins, triggering second messenger cascades (e.g., cAMP).

Organization of DNA in the Nucleus

Chromatin Structure

• DNA wraps around histone proteins, forming nucleosomes.

• Chromatin condenses into chromosomes during cell division.

Functions of Types of RNA in Protein Synthesis

Roles of RNA Molecules

• mRNA (messenger RNA): Carries genetic code from DNA to ribosomes.

• tRNA (transfer RNA): Brings amino acids to ribosomes during translation.

• rRNA (ribosomal RNA): Structural and catalytic component of ribosomes.

Definition of Semiconservative DNA Replication

DNA Duplication Mechanism

• Each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.

Lysosome Functions

Cellular Digestion

• Contain hydrolytic enzymes for breaking down waste, pathogens, and cellular debris.

• Involved in autophagy and apoptosis.

Definition of a Gene

Genetic Information Unit

• A gene is a segment of DNA that encodes a functional product, usually a protein.

Enzymes in DNA Replication

Key Enzymes and Their Roles

• Helicase: Unwinds the DNA double helix.

• DNA polymerase: Synthesizes new DNA strands.

• Primase: Synthesizes RNA primers.

• Ligase: Joins Okazaki fragments on the lagging strand.

Transcription vs. Translation

Gene Expression Processes

• Transcription: DNA is copied into mRNA in the nucleus.

• Translation: mRNA is decoded to synthesize proteins at the ribosome.

Base Pairing Rules (mRNA Codon and tRNA Anticodon)

Complementary Base Pairing

• DNA: A-T, C-G

• RNA: A-U, C-G

• Codon (mRNA) pairs with anticodon (tRNA) during translation.

Genetic Code Redundancy

Degeneracy of the Genetic Code

• Multiple codons can code for the same amino acid.

• Provides protection against mutations.

mRNA Processing

Post-Transcriptional Modifications

• 5' capping, 3' poly-A tail addition, and splicing (removal of introns).

Signal Recognition Particle (SRP) Role

Protein Targeting

• SRP directs ribosome-mRNA complexes to the endoplasmic reticulum for protein synthesis.

Genetic Theory of Aging

Role of Genes in Aging

• Suggests that aging is programmed by genetic factors, such as telomere shortening and gene regulation changes.

Endocrine vs. Exocrine Glands

Glandular Classification

Feature	Endocrine Glands	Exocrine Glands
Secretion	Hormones	Enzymes, sweat, mucus
Delivery	Into bloodstream	Via ducts to surface
Examples	Thyroid, pituitary	Salivary, sweat glands

Epithelial Tissue Classifications

Types Based on Layers and Shape

• Simple: Single layer (e.g., simple squamous, cuboidal, columnar).

• Stratified: Multiple layers (e.g., stratified squamous).

• Pseudostratified: Appears layered but is not.

Cell Types in Each Connective Tissue

Major Connective Tissue Cells

• Fibroblasts: Produce fibers and ground substance.

• Adipocytes: Store fat.

• Chondrocytes: Found in cartilage.

• Osteocytes: Found in bone.

• Blood cells: Found in blood tissue.

Connective Tissue Extracellular Matrix Composition

Matrix Components

• Fibers: Collagen (strength), elastic (flexibility), reticular (support).

• Ground substance: Water, proteoglycans, glycoproteins.

Connective Tissue Origin

Embryonic Source

• All connective tissues arise from mesenchyme, an embryonic tissue derived from the mesoderm.

Connective Tissue Fiber Types

Structural Proteins

• Collagen fibers: Strong, resist stretching.

• Elastic fibers: Stretch and recoil.

• Reticular fibers: Form supportive networks.

Epithelial Membranes

Types and Functions

• Mucous membranes: Line body cavities open to the exterior.

• Serous membranes: Line closed body cavities; secrete serous fluid.

• Cutaneous membrane: The skin.

Tissue Repair Stages and Inflammation

Healing Process

• Inflammation: Initial response to injury; increased blood flow and immune activity.

• Organization: Formation of granulation tissue.

• Regeneration/Fibrosis: Replacement of tissue or scar formation.

Germ Layer Origins of Tissues

Embryonic Development

• Ectoderm: Forms nervous tissue and epidermis.

• Mesoderm: Forms muscle, connective tissue, and some epithelial tissues.

• Endoderm: Forms lining of digestive and respiratory tracts.