Cell Biology Basics

Study Notes

Cell Biology Study Notes

Cell Definition: The smallest living units in the body, typically 0.1 mm in diameter. Named by Robert Hooke, observed via microscopy.
Cell Function: Building blocks of all plants and animals, derived from pre-existing cells. Responsible for vital physiological functions and maintaining cellular homeostasis.
Organization of Living Things (Hierarchy):
- Atoms work together to form Molecules
- Molecules work together to form Organelles
- Organelles work together to form Cells
- Similar cells form Tissues
- Tissues form Organs
- Organs form Organ Systems
- Organ Systems form an Organism
Fundamental Tissues: Consist of cells and extracellular matrix. Characteristic associations allow for recognition of subtypes. Most organs are composed of a precise combination of multiple tissue types. Histology is dependent on microscopes due to the small size of cells and matrix components.
Cell Membrane Structure: A thin membrane composed primarily of phospholipid and protein layers; less than a millionth of an inch thick with 65-100 Angstroms (Å) thickness. Composed of a double layer of phospholipids with larger proteins embedded.
Cell Membrane Components: Phospholipid bilayer,Peripheral membrane proteins,Integral membrane proteins,Cholesterol,Protein channels,Glycoprotein,Glycolipid,and Cytoskeletal filaments.
Cell Membrane Function:
- Separates the interior of a cell from its extracellular environment.
- Controls passage of substances into and out of the cell.
- Regulates passage of substances into and out of the cell (a highly selective exchange process).
Cell Membrane Permeability Factors:
- Size of molecules (e.g., larger molecules are less permeable, smaller ones like water and amino acids are more permeable).
- Ionic charge (like charges repel).
- Lipid solubility (substances readily dissolved in lipids pass easily).
- Carrier molecules (specialized membrane proteins facilitate transport).
- Pressure differences.
Transport Across Cell Membranes:
- Diffusion: Movement of substances from high to low concentration.
- Simple Diffusion: Substances cross the membrane on their own (e.g., gases, like CO2 and O2).
- Facilitated Diffusion: Movement with help of carrier proteins. Faster than simple diffusion and specific.
- Osmosis: Water movement from high to low water concentration across a membrane.
- Filtration: Movement of substances from high to low pressure.
- Active Transport: Molecules move from low to high concentration; requires energy (ATP).
Endocytosis: A process where cells engulf material with specific receptors for certain substances.
- Phagocytosis: Cells engulfing solid particles.
- Pinocytosis: Cells engulfing liquids.
- Receptor-mediated endocytosis: Cells ingesting molecule that attach to specific receptors.
Exocytosis: A process of removing unwanted materials from inside the cell by packaging it into vesicles and fusing them to the plasma membrane to release the material outside the cell
Cytoplasm: The material within the cell membrane, but outside the nucleus.
Organelles: Specialized structures within the cytoplasm with distinct functions.
Nucleus Structure: A spheroid/oval body near the cell's center, containing DNA (the genetic material). It controls cellular activities.
Ribosomes: Composed of two subunits. Involved in protein synthesis occur at these subunits.
Lysosomes: Membrane-bound organelles contain digestive enzymes; break down cellular waste and foreign materials, including worn-out organelles.
Peroxisomes: Similar in size to lysosomes but have different enzymes. Involved in detoxification, lipid breakdown, and synthesis of certain lipids like cholesterol
Intercellular Junctions: Structures where cells connect; important for adhesion, communication. Includes tight junctions, adherens junctions, desmosomes, gap junctions, and interdigitations between cell membranes.
Cell Surface Specializations:
- Microvilli: Finger-like extensions that increase the surface area for absorption in cells like those in the small intestine.
- Stereocilia: Long, nonmotile extensions that increase surface area for absorption and secretion in cells in the male reproductive tract (epididymis and ductus deferens).
- Cilia and Flagella: Cylindrical motile extensions that facilitate movement of materials along cells surfaces. Flagella move the entire cell (e.g., sperm).