Cell Structure, Function, and Transport: Study Notes for Anatomy & Physiology

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.

Membrane Protein Type	Location	Function
Integral (Transmembrane) Protein	Span the membrane	Transport, signal transduction
Peripheral Protein	Attached to membrane surface	Support, cell signaling

• 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.