Cell Structure, Function, and Tissue Organization: Study Guide for Anatomy & Physiology

Cell Structure and Function

The Smallest Living Unit

The cell is the fundamental structural and functional unit of all living organisms, including the human body.

• Definition: A cell is the smallest unit capable of independent life and performing all vital physiological functions.

• Example: Human cells include muscle cells, nerve cells, and epithelial cells.

Cell Theory

Cell theory is a foundational concept in biology that describes the properties of cells.

• Key Points:

  1. All living things are composed of one or more cells.

  2. The cell is the basic unit of structure and function in living organisms.

  3. All cells arise from pre-existing cells.

• Application: Explains growth, development, and reproduction in multicellular organisms.

Cytoplasm

The cytoplasm is the material within a cell, excluding the nucleus, where most cellular activities occur.

• Components: Cytosol (watery part), organelles, and inclusions.

• Cytosol: The aqueous, gel-like component that surrounds organelles; contains dissolved ions, nutrients, and proteins.

• Organelles: Specialized structures such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

Plasma Membrane Composition

The plasma membrane is a selectively permeable barrier that surrounds the cell.

• Main Components:

  • Phospholipid bilayer

  • Proteins (integral and peripheral)

  • Cholesterol

  • Carbohydrates (glycoproteins and glycolipids)

• Function: Regulates entry and exit of substances, cell signaling, and structural support.

Cytoskeleton Properties

The cytoskeleton is a network of protein filaments that provides structural support and facilitates movement within the cell.

• Components: Microfilaments (actin), intermediate filaments, microtubules.

• Functions: Maintains cell shape, enables intracellular transport, and assists in cell division.

Membranous vs. Non-Membranous Organelles

Organelles are specialized structures within cells, classified by the presence or absence of a surrounding membrane.

• Membranous Organelles: Surrounded by lipid bilayers (e.g., mitochondria, endoplasmic reticulum, Golgi apparatus).

• Non-Membranous Organelles: Not surrounded by membranes (e.g., ribosomes, centrioles).

• Comparison: Membranous organelles compartmentalize cellular processes; non-membranous organelles are involved in structural and synthetic functions.

Endoplasmic Reticulum (ER)

The ER is an extensive network of membranes involved in protein and lipid synthesis.

• Rough ER: Studded with ribosomes; synthesizes and processes proteins.

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

• Comparison Table:

Feature	Rough ER	Smooth ER
Ribosomes	Present	Absent
Main Function	Protein synthesis	Lipid synthesis, detoxification
Location	Near nucleus	Throughout cytoplasm

Golgi Apparatus

The Golgi apparatus is a stack of flattened membranes that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Appearance: Series of flattened sacs (cisternae).

• Function: Processes and packages macromolecules.

Mitochondria and ATP Production

Mitochondria are the cell's powerhouses, generating ATP through cellular respiration.

• ATP Production: Occurs primarily in mitochondria via the electron transport chain.

• Cellular Implication: Cells with many mitochondria (e.g., muscle cells) have high energy demands.

Nucleus and Nuclear Membrane

The nucleus is the control center of the cell, containing genetic material (DNA).

• Nuclear Envelope: Double membrane that surrounds the nucleus and regulates transport of molecules.

RNA and Protein Synthesis

RNA molecules play key roles in protein synthesis.

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

• rRNA (ribosomal RNA): Forms the core of ribosomes and catalyzes protein synthesis.

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

• Transcription: DNA is copied into mRNA.

• Translation: mRNA is decoded to synthesize proteins.

DNA to RNA Sequence

Complementary base pairing allows for the transcription of DNA into RNA.

• Example: DNA sequence CAT AAA CGT transcribes to RNA sequence GUA UUU GCA.

Cell Membrane Transport

Transport across the cell membrane can be passive or active.

• Permeability: The ability of the membrane to allow substances to pass through.

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a membrane.

• Active Transport: Movement against a concentration gradient using energy (ATP).

• Passive Transport: Movement along a concentration gradient without energy input.

• Facilitated Transport: Passive movement via membrane proteins.

• Endocytosis: Uptake of materials via vesicles.

• Exocytosis: Release of materials via vesicles.

Osmotic Conditions

Cells respond differently to solutions of varying osmolarity.

Condition	Description	Effect on Red Blood Cells
Hypotonic	Lower solute concentration outside cell	Cell swells and may burst
Isotonic	Equal solute concentration	No net change
Hypertonic	Higher solute concentration outside cell	Cell shrinks

Main Ions in Active Transport

• Sodium (Na+) and Potassium (K+) are the primary ions moved against their concentration gradients by the sodium-potassium pump.

• Equation: $3\,\text{Na}^+_{\text{out}} : 2\,\text{K}^+_{\text{in}}$ per ATP hydrolyzed

Cell Cycle and Division

Main Divisions of the Cell Cycle

The cell cycle consists of two main phases: interphase and mitotic phase.

• Interphase: Cell grows and DNA replicates.

• Mitotic Phase: Cell divides (mitosis and cytokinesis).

• Majority of Time: Cells spend most of their life in interphase.

Mitosis vs. Cytokinesis

• Mitosis: Division of the nucleus and its genetic material.

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

Phases of Mitosis

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at the cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelopes reform.

• Cytokinesis: Cytoplasm divides.

Tissues and Histology

Main Tissue Categories

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Nervous Tissue

Histology

Histology is the study of tissues at the microscopic level.

• Application: Used to diagnose diseases and understand tissue structure.

Epithelium Functions and Cell Shapes

• Functions: Protection, absorption, secretion, filtration.

• Cell Shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

Apical End and Basal Lamina

• Apical End: The surface of the epithelial cell facing the lumen or external environment; cilia and microvilli are found here.

• Basal Lamina: Thin layer anchoring epithelium to underlying connective tissue.

Glandular Cells and Hormones

• Endocrine Glands: Produce hormones released into the bloodstream.

• Exocrine Glands: Release secretions via ducts.

Cell Connections

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap Junctions: Allow communication between cells.

Specialized Tissues

• Transitional Epithelium: Lines the bladder.

• Simple Cuboidal Epithelium: Lines kidney tubules.

• Adipocytes: Fat storage cells.

• Macrophages: Immune cells that engulf pathogens and debris.

Connective Tissue Components

• Tendons: Connect muscle to bone.

• Ligaments: Connect bone to bone.

• Plasma: Liquid component of blood.

• Cartilage in Ear: Elastic cartilage.

• Osseous Tissue: Another name for bone tissue.

Muscle Tissue Types

Type	Structure	Location	Function
Skeletal	Striated, multinucleated	Attached to bones	Voluntary movement
Cardiac	Striated, branched, single nucleus	Heart	Pumps blood
Smooth	Non-striated, single nucleus	Walls of organs	Involuntary movement

Neural Tissue

• Role: Conducts electrical impulses, processes information, and coordinates responses.

• Regeneration: Neural tissue has the least ability to regenerate among the main tissue types.

Additional info: Some content was expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.