Cytosol & Organelles

**The Cell** * **Components:** Plasma Membrane, Cytoplasm, Nucleus * **Average adult:** 100 trillion cells, 200 types of cells grouped into 4 types of tissues * **Structure & function:** relative to each cell type **Plasma Membrane** * **Phospholipid bilayer:** selectively permeable, contains cholesterol * **Membrane Proteins act as "gates"** * Integral and Peripheral proteins * **Ion channels:** transport ions across membrane * **Carrier proteins:** change shape, transport molecules * **Receptor proteins:** bind with specific molecules to initiate cell function * **Enzymes:** catalyze metabolic reactions * **Structural proteins:** give & maintain cell shape * **Linking proteins:** attach cells to each other * **Cell identity markers:** used for cell recognition **Passive Transport Across Membrane** * **Does NOT require energy** to move molecules from high to low concentration * **Simple diffusion:** does NOT require a membrane protein * **Facilitated diffusion:** does require a membrane protein **Osmosis & Tonicity** * **Water moves down its own concentration gradient** * Uses channel proteins (aquaporins) * Force associated with water movement = osmotic pressure * Tonicity (osmotic pressure) used to change cell volume * Isotonic vs Hypotonic vs Hypertonic solutions **Active Transport Across Membranes** * **Requires ATP energy** to move molecules from low to high concentration * **Primary:** energy directly used to move molecules * **Secondary:** energy stored in an ion gradient used to move molecules **Vesicular Transport** * **Vesicle:** small sac created by using part of the membrane * **Endocytosis:** materials move INTO the cell * Receptor-mediated, phagocytosis, pinocytosis * **Exocytosis:** materials move OUT of the cell * **Transcytosis:** endo + exocytosis **Cytosol & Organelles** * **Cytoplasm:** Cytosol + organelles + cytoskeleton * **Cytosol:** liquid portion of cytoplasm * **Cytoskeleton:** Protein filaments for structural support * **Organelles:** Specialized structures for specific cell functions * **Centrosomes:** 2 centrioles; organize microtubules for mitosis * **Cilia & Flagella:** Motile membrane projections * **Lysosomes:** Vesicles with digestive enzymes * **Peroxisomes:** Smaller vesicles; detoxification * **Endoplasmic Reticulum:** Series of flattened, membranous sacs * **Rough ER:** Attached ribosomes; protein synthesis, detoxification * **Smooth ER:** No ribosomes; transport, synthesis, detoxification * **Golgi Complex:** 4-8 flattened, membranous sacs * Modify, sort, package proteins for transport * **Mitochondria:** ATP production; 2 membranes, inner membrane structure critical for ATP production; contain their own DNA **Nucleus** * Most cells have 1 * Contains Chromosomes & Nucleoli * Pores in nuclear envelope regulate movement of RNA * Chromosomes: Long, coiled molecules of DNA * Contain cell's hereditary units (genes) * Human cells have 46 chromosomes (23 pairs) **Cell Cycle** * Series of events in which a cell duplicates its contents (interphase) and divides (mitosis) * **Phases of Interphase:** * G1: growth * S: chromosome replication * G2: preparation for mitosis * **S Phase of Interphase:** * One strand of the helix is template for new strand * Semiconservative replication