Cell Biology Basics

Cell Theory

• The cell, from the Latin "cella" meaning "small room," is the fundamental structural, functional, and biological unit of all known organisms.
• It's the smallest unit of life, often called the "building blocks of life."
• A semi-permeable membrane allows only certain materials to pass through under specific conditions.

Cytoplasm

• The fluid portion of the cell containing the cytoskeleton, organelles, and inclusions.
• Also known as the "soup" of the cell.

Cytoskeleton

• A network of protein filaments (microtubules, microfilaments) providing support and maintaining cell shape.
• Acts as the framework of the cytoplasm, aiding organelle movement.

Nucleus

• A membrane-bound organelle containing the genetic material (DNA) of eukaryotic organisms.
• Maintains cell integrity by facilitating transcription and replication.
• The largest organelle, occupying about a tenth of the cell's volume.

Parts of the Nucleus

• Nuclear Envelope: A membrane separating the nucleus from the cytoplasm.
• Nucleoplasm: A protoplasm composed of water, molecules, and dissolved ions.
• Nucleolus: The site of ribosome biogenesis.

Cytoplasmic Organelles

Endoplasmic Reticulum (ER)

• A network of flattened sacs and tubes extending from the nuclear membrane to the plasma membrane.
• Transports substances and synthesizes lipids, enzymes, and proteins.
• Rough ER: Has ribosomes on its surface.
• Smooth ER: Lacks ribosomes.

Ribosomes

• Sites of protein synthesis.
• Found attached to rough ER or free in the cytosol.
• Produced in the nucleolus.

Golgi Bodies

• Flattened membrane stacks that modify and package proteins and lipids into vesicles.
• A vesicle is a self-contained structure with fluid or gas enclosed by a lipid bilayer.

Mitochondria

• The "powerhouse" of the cell, producing ATP (adenosine triphosphate).

Vacuole

• A single-membrane sac involved in storage, waste release, intracellular digestion, and maintaining hydrostatic pressure.

Lysosomes

• Small, membrane-bound structures containing enzymes for cellular digestion.
• The "garbage disposal" of the cell.

Glycocalyx

• The cell coat on the outer part of animal cells; involved in cell recognition and adhesion.

Plastids (Plant Cells)

• Large, disk-shaped organelles containing pigments.
• Found only in plant cells and some photosynthetic protists.
• Chloroplasts: Contain green pigment.
• Chromoplasts: Contain red, yellow, and orange pigments.
• Leucoplasts: Lack color.

Centrosome

• The main microtubule organizing center.
• Regulates the cell division cycle.

Centriole

• A cylindrical organelle composed mainly of tubulin.
• Found in most eukaryotic cells.
• A centrosome contains a pair of centrioles surrounded by pericentriolar material.

Prokaryotes vs. Eukaryotes

Prokaryotes

• "Before the nucleus."
• Single-celled organisms, the smallest and most metabolically diverse life forms.

Eukaryotes

• Organisms with free-living cells (capable of independent existence) or trillions of cells working together.
• Contain visible organelles and a true nucleus.

Specialized Animal Cells & Adaptations

• Osteoclasts: Dissolve old bone tissue for replacement.
• Chondrocytes: Produce collagen and extracellular matrix for cartilage maintenance.
• Fibroblasts: Secrete collagen for tissue framework.
• Muscle cells: Contract and relax; found in cardiac, skeletal, and smooth muscle.
• Fat cells: Store energy as fat; expand to store more fat; have few mitochondria; act as padding.
• Ciliated cells: Move mucus and other substances; have cilia that beat rhythmically.

Cell Types & Tissues (Animals)

• Cells form tissues, which fulfil similar functions.
• Four basic animal tissue types: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Covers body surfaces (internal and external).
• Functions: protection, absorption, secretion, sensory reception.
• Classified by cell layer number (simple, stratified, pseudostratified) and cell shape (squamous, cuboidal, columnar).

Epithelial Cell Types Based on Shape

• Squamous: Thin, scaly; diffusion, filtration, secretion, protection (kidneys, air sacs, heart lining).
• Cuboidal: Dice-shaped; secretion, absorption (kidney tubules, egg cells, glands).
• Columnar: Taller than wide; absorption, secretion, sensory reception (digestive tubes, gallbladder, uterus).
• Ciliated Columnar: Have cilia; move mucus (nose, uterus).
• Pseudostratified Columnar: False stratification; filtration, absorption, secretion (ducts, trachea).

Connective Tissue

• Connects, binds, supports body parts.
• Highly vascularized; contains cells and a matrix (ground substance and fibers).

Connective Tissue Types

• Bone: Support, protection, leverage, storage, hematopoiesis (osteocytes, hard matrix).
• Hyaline Cartilage: Support, cushioning (chondrocytes, firm matrix).
• Fibrocartilage: Shock absorption (chondrocytes, collagenous matrix).
• Elastic Cartilage: Support (chondrocytes, elastic matrix).
• Areolar Tissue: Holds and conveys tissue fluid; inflammation (mast cells, white blood cells, fibroblasts, macrophages, gel-like matrix).
• Adipose Tissue: Lipid storage (adipocytes, reticular matrix).
• Cartilage Tissue: Support, structure (chondrocytes, rubbery matrix).
• Areolar Tissue: Holds organs (fibroblasts, collagenous, elastic matrix).

Muscle Tissue

• Composed of muscle cells that contract.
• Contains sarcoplasm (cell membrane), sarcolemma (cytoplasm), and nuclei.

Muscle Tissue Types

• Striated/Voluntary/Skeletal: Long, cylindrical; many nuclei, striations (skeletal muscles).
• Striated/Involuntary/Cardiac: Short, branching; few striations, one or two nuclei (heart).
• Non-striated/Involuntary/Smooth: Spindle-shaped; one nucleus, no striations (visceral muscles).

Nervous Tissue

• Contains neurons (conducting cells) and neuroglia (supportive cells).
• Neurons have irritability (respond to stimuli) and conductivity (transmit impulses).
• Neuron parts: cell body (soma) containing the nucleus and processes.