Chapter 3 Cells

The Cell Theory States: Cells are the building blocks of all plants and animals Cells are produced by the division of preexisting cells Cells are the smallest units that perform all vital physiological functions Each cell maintains homeostasis at the cellular level Homeostasis at higher levels reflects combined, coordinated action of many cells

Figure 3.2 The Anatomy of a Representative Model Cell

Cell membrane functions include: Physical isolation Regulation of exchange with the environment Sensitivity to the environment Structural support

Figure 3.3 The Cell Membrane The cell membrane is a phospholipid bilayer with proteins, lipids and carbohydrates. Figure 3.3

Membrane Lipids: Phospholipids: composed of glycerol and fatty acid tails linked by a phosphate group. Acts as a selective physical barrier between cell and extracellular environment Cholesterol and other lipids are also part of the membrane structure.

Membrane Proteins Include: Anchoring proteins: attach to other structures to stabilize cell position Recognition proteins: Identifies cell as “self”, nonself, normal, or abnormal Receptor proteins: trigger changes in cell activity based materials in extracellualr environment that bind to them Carrier proteins: bind and transport materials across cell membrane Channel proteins: pores in cell membrane which allows solutes to diffuse in and out of cell Enzymes: catalyze reactions in and out of cell.

Cell Membrane Proteins

Diffusion Movement of a substance from an area of high concentration to low Continues until concentration gradient is eliminated

Figure 3.4 Diffusion

Figure 3.5 Diffusion across the Cell Membrane

Osmosis Diffusion of water across a semipermeable membrane in response to solute differences Osmosis occurs across a selectively permeable membrane that is permeable to water but NOT freely permeable to solutes In osmosis, water flows across a membrane toward the solution that has the HIGHER concentration of SOLUTES because that is where the concentration of WATER molecules is LOWER

Osmotic Pressure OP = the force of water into a solution as a result of different solute concentrations. Isotonic = no net gain or loss of water Hypotonic = net gain of water into cell Hemolysis (swelling or bursting of cell) Hypertonic = net water flow out of cell Crenation (shrinking of cell)

Figure 3.7 Osmotic flow across a cell membrane (RBC)

Transport Mechanisms Carrier mediated transport Proteins bind and transport specific ions or organic molecules and transport them across the cell membrane Cotransport: 2 substances move together Counter-transport: 2 substances move in opposite directions Passive Transport: no ATP required Active Transport: ATP dependent

Carrier Mediated Transport Facilitated diffusion (passive) Compounds to be transported bind to a receptor site on a carrier protein Not totally dependent on concentration of solutes Active transport (active) Consumes ATP Independent of concentration gradients Types of active transport include Ion pumps Exchange pumps

Facilitated Diffusion Figure 3.8

The Sodium Potassium Exchange Pump Figure 3.9

Vesicular transport Material moves into or out of cells in membranous sacs Endocytosis is movement of materials into the cell Receptor-mediated endocytosis (coated vesicles) Pinocytosis: cell drinking Phagocytosis: cell eating (pseudopodia) Exocytosis is ejection of materials from the cell Hormones Mucus Waste products

Figure 3.10 Receptor-Mediated Endocytosis

Figure 3.11 Pinocytosis and Phagocytosis

Cell Division Cell division is the reproduction of cells Apoptosis is the genetically controlled death of cells Mitosis is the nuclear division of somatic cells Meiosis produces sex cells

Interphase Most somatic cells spend the majority of their lives in this phase Interphase includes G1 S G2

Mitosis, or nuclear division, has four phases Prophase Metaphase Anaphase Telophase During cytokinesis, the cytoplasm divides and cell division ends

The Cell Life Cycle

Interphase, Mitosis, and Cytokinesis

Interphase, Mitosis, and Cytokinesis

Mitotic rate and cancer Generally, the longer the life expectancy of the cell, the slower the mitotic rate Stem cells undergo frequent mitoses Growth factors can stimulate cell division Abnormal cell division produces tumors (neoplasms) Benign Malignant (invasive, and cancerous) Spread via metastasis Oncogenes

Cell Differentiation Process of specialization Results from inactivation of particular genes Produces populations of cells with limited capabilities Differentiated cells form tissues