Cell Structure, Function, and Transport

Basic Processes of Cells

Cells carry out essential life processes that maintain homeostasis and support the organism's survival. Understanding these processes is fundamental to Anatomy & Physiology.

• Cell Metabolism: The sum of all chemical reactions occurring within a cell, including both anabolic (building up) and catabolic (breaking down) pathways.

• Anabolic Reaction: Chemical reactions that synthesize complex molecules from simpler ones, requiring energy input.

• Catabolic Reaction: Chemical reactions that break down complex molecules into simpler ones, releasing energy.

• Oxidation-Reduction Reaction: Reactions involving the transfer of electrons between molecules, crucial for energy production.

• Transport of Substances: Movement of molecules into, out of, and within cells.

• Communication: Cells communicate via chemical signals and receptors to coordinate activities.

• Cell Reproduction: The process by which cells divide to produce new cells, essential for growth and repair.

• Cell Division: Includes mitosis and cytokinesis, resulting in two daughter cells.

Animal Cell Structure

Animal cells are complex structures with specialized components, each performing distinct functions.

• Plasma Membrane: The outer boundary of the cell, regulating entry and exit of substances.

• Cytoplasm: The jelly-like substance within the cell, containing organelles and cytosol.

• Cytosol: The fluid portion of the cytoplasm.

• Organelles: Specialized structures within the cell, each with specific functions (e.g., mitochondria, ribosomes).

• Cytoskeleton: A network of protein filaments providing structural support and facilitating movement.

• Nucleus: The control center of the cell, containing genetic material (DNA).

Plasma Membrane

The plasma membrane is a selectively permeable barrier that separates the intracellular and extracellular environments.

• Intracellular Space: The area within the cell membrane.

• Extracellular Space: The area outside the cell membrane.

• Intracellular Fluid (Cytosol): Fluid inside the cell.

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

• Phospholipid Bilayer: The fundamental structure of the membrane, composed of two layers of phospholipids with hydrophilic heads and hydrophobic tails.

• Fluid Mosaic Model: Describes the membrane as a dynamic structure with proteins floating in or on the fluid lipid bilayer.

• Channel: Protein that allows specific molecules to pass through the membrane.

• Carrier: Protein that binds and transports substances across the membrane.

• Receptor: Protein that binds signaling molecules and initiates cellular responses.

• Enzyme: Protein that catalyzes chemical reactions.

• Substrate: The molecule upon which an enzyme acts.

• Product: The result of an enzymatic reaction.

• Selective Permeability: The membrane allows some substances to pass while restricting others.

Passive Transport

Passive transport involves the movement of substances across the membrane without energy input, driven by concentration gradients.

• Diffusion: Movement of molecules from an area of higher concentration to lower concentration.

• Concentration Gradient: The difference in concentration of a substance across a space.

• Facilitated Diffusion: Diffusion of molecules across the membrane via specific transport proteins.

• Channel-mediated Diffusion: Movement through protein channels.

• Carrier-mediated Diffusion: Movement via carrier proteins.

• Uniporter: Transports one type of molecule.

• Symporter: Transports two molecules in the same direction.

• Antiporter: Transports two molecules in opposite directions.

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

• Aquaporin: Channel protein specifically for water transport.

• Tonicity: The ability of a solution to cause a cell to gain or lose water.

• Hypertonic Solution: Higher solute concentration outside the cell; cell shrinks.

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

• Hypotonic Solution: Lower solute concentration outside; cell swells.

Active Transport

Active transport requires energy (usually ATP) to move substances against their concentration gradients.

• Primary Active Transport: Direct use of ATP to transport molecules (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.

• Pump: Protein that moves substances against their gradient using energy.

• Vesicular Transport: Movement of large particles or fluids via vesicles.

• Endocytosis: Uptake of materials into the cell by vesicle formation.

• Phagocytosis: "Cell eating"; engulfing large particles.

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

• Receptor-mediated Endocytosis: Specific uptake of molecules after binding to receptors.

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

• Transcytosis: Transport of substances across a cell by vesicle formation.

Cellular Organelles

Organelles are specialized structures within cells, each with unique functions essential for cell survival and activity.

• Mitochondrion: The "powerhouse" of the cell, site of ATP production.

• Outer Mitochondrial Membrane: Encloses the organelle.

• Intermembrane Space: Space between inner and outer membranes.

• Inner Mitochondrial Membrane: Contains proteins for ATP synthesis.

• Cristae: Folds of the inner membrane, increasing surface area.

• Matrix: Fluid inside the mitochondrion containing enzymes.

• Ribosome: Site of protein synthesis; can be free or bound to endoplasmic reticulum.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes proteins.

• Smooth Endoplasmic Reticulum (SER): Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

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

Cell Surface Structures

Some cells possess specialized surface structures that aid in movement or absorption.

• Microvilli: Finger-like projections that increase surface area for absorption.

• Cilia: Hair-like structures that move substances across the cell surface.

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

Nucleus and DNA

The nucleus houses genetic material and controls cellular activities through gene expression.

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Nuclear Pore: Openings in the nuclear envelope allowing exchange of materials.

• Nucleoplasm: Fluid inside the nucleus.

• Nucleolus: Site of ribosome synthesis within the nucleus.

• Chromatin: DNA-protein complex; condenses to form chromosomes during cell division.

• Chromosome: Condensed form of chromatin, visible during mitosis.

• Sister Chromatids: Identical copies of a chromosome, joined at the centromere.

• Centromere: Region where sister chromatids are joined.

Protein Synthesis

Protein synthesis is the process by which cells build proteins, essential for structure and function.

• Transcription: Synthesis of messenger RNA (mRNA) from DNA template in the nucleus.

• Translation: Assembly of proteins at ribosomes using mRNA as a template.

• Gene: Segment of DNA coding for a specific protein.

• Deoxyribonucleic Acid (DNA): Genetic material storing instructions for protein synthesis.

• Ribonucleic Acid (RNA): Includes mRNA, tRNA, and rRNA; involved in protein synthesis.

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

Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide.

• Interphase: Period of cell growth and DNA replication; includes G1, S, and G2 phases.

• G1 Phase: Cell grows and performs normal functions.

• S Phase: DNA replication occurs.

• G2 Phase: Preparation for mitosis.

• Mitosis: Division of the nucleus into two genetically identical daughter nuclei.

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

• G0 Phase: Resting phase where cells exit the cycle and do not divide.

Example: The sodium-potassium pump is a classic example of primary active transport, moving 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradients, using ATP.

Additional info: The above notes expand on the provided outline with academic context, definitions, and examples to ensure a comprehensive understanding suitable for college-level Anatomy & Physiology students.