Module 3.1 Introduction to Cells

Main Parts of a Cell

• Plasma Membrane: The outer boundary of the cell, also called the cell membrane. It regulates the movement of substances into and out of the cell and provides structural support.

• Cytoplasm: The region between the plasma membrane and the nucleus. It contains cytosol (the fluid component) and organelles. Note: Cytoplasm is intracellular, not extracellular.

• Nucleus: The control center of the cell, housing DNA and coordinating activities such as growth, metabolism, and reproduction.

Intracellular vs. Extracellular Fluid

• Intracellular Fluid (ICF): Fluid within the cell, mainly cytosol.

• Extracellular Fluid (ECF): Fluid outside the cell, including interstitial fluid, plasma, and lymph.

Cytoplasm vs. Cytosol

• Cytoplasm: Includes cytosol, organelles, and inclusions.

• Cytosol: The fluid portion of the cytoplasm, where many metabolic reactions occur.

Organelles

• Definition: Specialized structures within the cell that perform specific functions necessary for cell survival.

• Examples: Mitochondria (energy production), ribosomes (protein synthesis), endoplasmic reticulum (protein and lipid processing), Golgi apparatus (modification and packaging), lysosomes (digestion), peroxisomes (detoxification).

Module 3.2 Structure of the Plasma Membrane

Lipid Distribution and Function

• Phospholipids: Form a bilayer, with hydrophilic heads facing outward and hydrophobic tails inward, creating a semi-permeable barrier.

• Cholesterol: Interspersed within the bilayer, stabilizes membrane fluidity and integrity.

Carbohydrates and Proteins in the Plasma Membrane

• Proteins: Integral (span the membrane) and peripheral (attached to the surface). Functions include transport, signaling, and structural support.

• Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids), forming the glycocalyx, which is involved in cell recognition and protection.

Fluid Mosaic Model

• The plasma membrane is described as a fluid mosaic because it is flexible and composed of various molecules that move laterally within the layer.

Module 3.3 Transport across the Plasma Membrane

Passive Transport

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

• Facilitated Diffusion: Movement of solutes via membrane proteins; still passive, no energy required.

• Osmosis: Diffusion of water across a selectively permeable membrane. Water moves toward higher solute concentration.

Tonicity Effects

• Isotonic: No net water movement; cell remains the same size.

• Hypertonic: Water leaves the cell; cell shrinks (crenation).

• Hypotonic: Water enters the cell; cell swells and may burst (lysis).

Active Transport

• Primary Active Transport: Direct use of ATP to move substances against their concentration gradient (e.g., sodium-potassium pump).

• Secondary Active Transport: Uses the energy from the movement of one substance down its gradient to move another substance against its gradient.

Vesicular Transport

• Endocytosis: Uptake of materials via vesicles (includes phagocytosis and pinocytosis).

• Exocytosis: Release of materials from the cell via vesicles.

• Transcytosis: Movement of substances across, into, and out of the cell via vesicles.

Module 3.4 Cytoplasmic Organelles

Structure and Function of Organelles

• Mitochondria: Site of ATP production via cellular respiration.

• Ribosomes: Synthesize proteins; can be free or attached to rough ER.

• Endoplasmic Reticulum (ER): Rough ER (protein synthesis and modification), Smooth ER (lipid synthesis and detoxification).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes for breakdown of waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

Endomembrane System

• Includes the nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles. These organelles work together to modify, package, and transport lipids and proteins.

Module 3.5 The Cytoskeleton

Components of the Cytoskeleton

• Microfilaments: Composed of actin; involved in cell movement and shape.

• Intermediate Filaments: Provide mechanical support and maintain cell integrity.

• Microtubules: Hollow tubes of tubulin; maintain cell shape, enable intracellular transport, and form mitotic spindle.

Centrioles, Cilia, and Flagella

• Centrioles: Organize microtubules during cell division.

• Cilia: Short, hair-like structures for movement of substances across cell surfaces.

• Flagella: Long, whip-like structures for cell movement (e.g., sperm cell).

Role in Cellular Motion

• The cytoskeleton enables cell movement, intracellular transport, and changes in cell shape.

Module 3.6 The Nucleus

Structure and Function

• Nucleus: Surrounded by a double membrane (nuclear envelope) with nuclear pores for material exchange.

• Function: Stores genetic material (DNA) and coordinates cell activities.

Nucleolus

• Structure: Dense region within the nucleus.

• Function: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly.

Module 3.7 Protein Synthesis

Transcription and Translation

• Transcription: DNA is used as a template to synthesize messenger RNA (mRNA) in the nucleus.

• Translation: mRNA is decoded by ribosomes in the cytoplasm to assemble amino acids into a polypeptide (protein).

Module 3.8 The Cell Cycle

Interphase

• Cell grows, performs normal functions, and duplicates DNA in preparation for division.

Stages of the Cell Cycle

• G1 Phase: Cell growth and normal metabolism.

• S Phase: DNA replication.

• G2 Phase: Preparation for mitosis.

• M Phase (Mitosis): Division of the nucleus.

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Mitosis vs. Cytokinesis

• Mitosis: Division of the nucleus and its contents.

• Cytokinesis: Division of the cytoplasm.

DNA Replication

• Process by which DNA makes an exact copy of itself during the S phase.

Module 4.1 Introduction to Tissues

Definition and Levels of Organization

• Histology: The study of tissues.

• Tissues are groups of similar cells performing a common function, fitting between the cellular and organ levels of organization.

Four Major Tissue Types

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Nervous Tissue

Extracellular Matrix (ECM)

• Non-cellular component produced by cells, providing structural and biochemical support.

Cell Junctions

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap Junctions: Allow communication between cells.

Module 4.2 Epithelial Tissues

Classification and Identification

• Classified by cell shape (squamous, cuboidal, columnar) and layers (simple, stratified).

Location and Function

• Simple Squamous: Lining of blood vessels, alveoli; allows diffusion.

• Stratified Squamous: Skin, mouth; protects against abrasion.

• Simple Cuboidal: Kidney tubules; secretion and absorption.

• Simple Columnar: Digestive tract; absorption and secretion.

Glandular Epithelium

• Exocrine Glands: Secrete products into ducts (e.g., sweat glands).

• Endocrine Glands: Secrete hormones directly into the bloodstream.

Module 4.3 Connective Tissues

Cells and Fibers

• Cells: Fibroblasts, adipocytes, macrophages, mast cells, etc.

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

Types and Locations

• Loose Connective Tissue: Under epithelia, around organs.

• Dense Connective Tissue: Tendons, ligaments.

• Cartilage: Joints, ear, nose.

• Bone: Skeleton.

• Blood: Circulatory system.

Functions

• Support, protection, transport, storage, and immune defense.

Module 4.4 Muscle Tissues

Types and Characteristics

• Skeletal Muscle: Striated, voluntary, attached to bones.

• Cardiac Muscle: Striated, involuntary, found in the heart.

• Smooth Muscle: Non-striated, involuntary, found in walls of hollow organs.

Functions

• Movement, posture, heat production, and propulsion of substances.

Module 4.5 Nervous Tissue

Location and Characteristics

• Found in the brain, spinal cord, and nerves.

• Composed of neurons (transmit impulses) and neuroglia (support cells).

Structure and Function

• Neurons: Conduct electrical impulses.

• Neuroglia: Support, protect, and nourish neurons.

Module 4.7 Membranes

Structure and Function

• Membranes are sheets of tissue that cover or line body surfaces.

Types of Membranes

• Serous Membranes: Line body cavities not open to the exterior; secrete serous fluid.

• Synovial Membranes: Line joint cavities; secrete synovial fluid.

• Mucous Membranes: Line cavities open to the exterior; secrete mucus.

• Cutaneous Membrane: The skin; protects the body surface.

Module 4.8 Tissue Repair

Effects of Injury

• Different tissues have varying abilities to repair after injury.

Regeneration

• Replacement of damaged tissue with the same type of cells, restoring normal function.

Fibrosis

• Replacement of damaged tissue with scar tissue (dense connective tissue), which may impair function.