EPOB 1210 Lecture 14, 1996
THE CELL part 3 and Membranes

This has been the 878th visit to this site since Sept. 27, 1996.

Word roots:

Glyc (G) = sweet, sugar
Olig (G) = few (as in oligosaccharide)

The CYTOSKELETON = network of fibers in cells for support and movement.

3 main types of fibers: (see Table 7.2)
1. Microtubules
2. Microfilaments
3. Intermediate Filaments

MICROTUBULES:
Hollow fibers about 25 nanometers in diameter.
Made from globular proteins called TUBULIN
(Table 7.2, 27653)

Functions:

1. Cellular support, often radiate from center of the cell

2. Tracks for movement of organelles (Fig. 7.21)

3. Separate chromosomes during cell division

4. CELL MOTILITY

CILIA AND FLAGELLA = locomotor organelles containing microtubules (don't confuse with prokaryotic flagella)

Propel some Protists (Kingdom Protista) & animal sperm cells

Move fluid past stationary cells (ciliated cells in our trachea and lungs).

Movement:

(see FIG. 7.23)
Cilia (singular cilium): work like oars
Flagella (sing. flagellum): undulate

VIDEO 38127 and 35058 Ciliates and Flagellates

Ultrastructure of Cilia and Flagella.

= extensions of the plasma membrane with a core of microtubules

(FIG. 7.24)
9 + 2 pattern

"DYNEIN WALKING" causes the flagellum or cilia to bend as one side "walks" one direction and the opposite side "walks" the other direction.

(Fig. 7.25 and 7.21)

MICROFILAMENTS = Rods about 7 nm in diameter see table 7.2 (27653)

Muscle contraction (next semester)
Changes in cell shape (Fig. 7.27)
Cytoplasmic streaming (Fig. 7.27)

CELL SURFACE
Most cells have coats outside of the plasma membrane.
Cell walls: we have already discussed plants, fungi and bacteria.

Show fig. 7.28 connections between mature plant cells
Plasmodesmata (sing. = plasmodesma) allow free passage of water and small molecules between cells
(animals have similar connections between cells)

Cell surface (cont.)
Animals have an EXTRACELLULAR MATRIX (ECM) consisting of mostly secreted glycoproteins such as COLLAGEN (=1/2 of all proteins in humans). Collagen is embedded in a matric of other glycoproteins called proteoglycans.

(See Figure 7.29)
CHAPTER 8
MEMBRANE STRUCTURE and FUNCTION
PLASMA MEMBRANE = around 8 nm thick,
controls chemical traffic in & out of cell
therefore is selectively permeable.

Scientists predicted the structure of membranes long before they were visualized.
Model until 1972 was a sandwich

(see Fig. 8.2)
FLUID MOSAIC MODEL: (see Fig. 8.2) Lipid bilayer with proteins immersed in it
Membranes are fluid i.e. molecules move around in them (laterally), lipids move faster than proteins
see Fig. 8.3 and 8.4
Membrane function is dependent on fluidity.
Cold tolerant orgs. have more unsaturated fats in their tails to prevent close packing (=increases fluidity at cold temps.) Fig. 8.3b

Chloresterol increases fluidity at cold temps. but decreases it at body temp. (by restricting movement of phosholipids) Fig. 8.3c

MEMBRANES are bifacial
Carbohydrates are external
Inside (cisternal space or lumen) of ER and GOLGI = outside of plasma membrane
see fig. 8.7
MEMBRANE PROTEINS see Fig. 8.5 (animal cell's plasma membrane)
INTEGRAL protein (have large hydrophobic regions)
PERIPHERAL protein

Functions of membrane proteins FIG. 8.6
1. Transport (more later)
2. Enzymes
3. Receptors
4. Junctions
5. Cell-to-Cell recognition: Based on the fact that each cell type and organism has specific oligosaccharrides (< 15 monomers) associated with its membranes. (glycoproteins and glycolipds, see Fig. 8.5)
= basis of immune system recognition of foreign cells.
example of Salmonella
6. Attachment to cytoskeleton and ECM