Thursday, March 08, 2007

Bio 101:5

Okay, it could have been because I was reading this late at night, but I found this chapter to be strangely poetic. Imagine a poet reading these sections in that ultra-slow poetry reading voice.

Chapter 5. Cellular Architecture

1. The cell surface is a selective interface between the cell and the outside environment. It recieves and transmits incoming messages, controls which substances enter and leave the cell, and mediates attachments to and interactions with other cells and extracellular material.

2. The features of a cell's surface identify it as belonging to a particular species, individual, and tissue within that individual. The surface consists of molecules embedded in and extending from the cell membrane. Cell surfaces guide embryonic cells to form tissues and organs. The human leukocyte antigen cell surface markers establish self and are associated with increased risks of developing certain disorders.

3. A biological membrane consists of a phospholipid bilayer embedded with moveable proteins, glycoproteins, and glycolipids, like a fluid mosaic. The percentage and distribution of membrane proteins varies in different cell types. Membrane proteins include receptors, carriers, adhesion molecules, and cell surface proteins establishing self.

4. Osmosis is the simple diffusion of water across the cell membrane or other semipermeable membrane. In osmosis, water is driven to move because the solute concentrations differ on each side of the membrane. Tonicity: Refers to the differences in solute concentration in two compartments separated by an impermeable membrane. Terms describing tonicity (isotonic, hydrotonic, hypertonic) predict whenther cells will swell or shrink when the surroundings change. Several adaptations maintain cell shape in the face of solute concentration changes.

5. Facilitated diffusion: molecules cross a membrane following the concentration gradient with the aid of a carrier protein. In active transport, molecules cross a membrane across the concentration gradient and require a carrier protein and energy from ATP (adenosine triphosphate- the energy molecule in many cases).

6. Exocytosis: Vesicles inside the cell carry substances to the cell membrane, where they fuse with the membrane and release the cargo outside. Endocytosis: Molecules are brought into the cell by a vesicle in the cell membrane. Endosome: An intermediate stage vesicle that shuttles between exocytosis and endocytosis. Endocytosis is more specific when a receptor in the vesicle binds a specific molecule. Within cells, proteins guide vesicles to particular organelles.

7. Intercellular junctions join cells. In animals they include tight junctions, demosomes, and gap junctions. In plants, they include a pectin layer and plasmodesmata.

8. Cytoskeleton: A network of rods and tubes that provides cells with form, support, and the ability to move. Microtubles self-assemble from hollow tublin subunits to become cell flagella, and the spindles that separate one cell into two in cell division. Microtubles have a characteristic 9+2 configuration. Dyenin causes adjacent microtubles to slide, which moves the overall structure. Microfilaments are solid and smaller than microtubles. They are composed of the protein actin and provide contractile motion. Intermediate filaments provide scaffolding.

9. In signal transduction, receptors in the cell membrane recieve input from first messengers (hormones or growth factors) and transmit the messages through a series of membrane proteins. Eventually this signalling activated a second messenger, which stimulates the cell to carry out a specific function.

10. Cellular adhesion molecules enable cells to contact each other in precise steps that carry out a particular function.

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