Chapter 3

Cells

• 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

The Cell Theory States:

Figure 3.2 The Anatomy of a Representative Model Cell

Figure 3.2

• Physical isolation• Regulation of

exchange with the environment

• Sensitivity to the environment

• Structural support

Cell membrane functions include:

• The cell membrane is a phospholipid bilayer with proteins, lipids and carbohydrates.

Figure 3.3 The Cell Membrane

Figure 3.3

• 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 Lipids:

• 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.

Membrane Proteins Include:

Cell Membrane Proteins

• Movement of a substance from an area of high concentration to low

• Continues until concentration gradient is eliminated

Diffusion

Figure 3.4 Diffusion

Figure 3.5 Diffusion across the Cell Membrane

• 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

Osmosis

• 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)

Osmotic Pressure

Figure 3.7 Osmotic flow across a cell membrane (RBC)

• 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

Transport Mechanisms

• 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

Carrier Mediated Transport

Facilitated Diffusion

Figure 3.8

Figure 3.9

The Sodium Potassium Exchange Pump

• 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

Vesicular transport

Figure 3.10 Receptor-Mediated Endocytosis

Figure 3.10

Figure 3.11 Pinocytosis and Phagocytosis

• 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

Cell Division

• Most somatic cells spend the majority of their lives in this phase

• Interphase includes– G1– S – G2

Interphase

• Prophase• Metaphase• Anaphase• Telophase

Mitosis, or nuclear division, has four phases

During cytokinesis, the cytoplasm divides and cell division ends

The Cell Life Cycle

Interphase, Mitosis, and Cytokinesis

Interphase, Mitosis, and Cytokinesis

• 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

Mitotic rate and cancer

• Process of specialization• Results from

inactivation of particular genes

• Produces populations of cells with limited capabilities

• Differentiated cells form tissues

Cell Differentiation