Molecular Cell Biology

Table of Contents:

Section a (the Cell Wall): page 3

Section b (cell membrane): page 4

Section c (endoplasmic reticulum): page 5

Section d (mitochondria): page 6

Section e (chloroplast): page 7

Section f (ribosomes): page 8

Section g (golgi body or the golgi apparatus): page 9-10

Section h (lysozomes): page 11-13

Section i (vacuoles and vesicles): page 14-16

Section j (nucleus and nucleolus): page 17-21

Section k (cytoskeleton): page 22-24

Section f (flagella and cilia): page 25-26

Work Citied page: 27-29

A) Cell Wall

The cell wall protects the plant cell, maintains it shape, and prevents excessive uptake of water. Plant cell walls are much thicker than the plasma membrane, ranging from 0.1 µm to several micrometers. Plant cell walls are made of cellulose fibers in a cementing matrix of other polysaccharides and proteins. This mixture of materials is the basic architectural design found in steel-reinforced concrete and in fiberglass. At cell division in plants, the primary wall is laid down on the middle lamella of the cell plate as a loose mesh of cellulose fibers. This gives an elastic structure that allows cell expansion during growth. Later, the secondary wall grows and acquires greater rigidity and tensile strength. New cellulose fibers are laid down in layers, parallel within each layer, but orientated differently in different layers.

Plant cells walls are an important route for movement of water and mineral salts. Also, cell walls are freely permeable to gases, water, and solutes. They have a mechanism function, allowing the cell to become turgid by osmosis, but preventing bursting. Plant cell walls can be strengthened for extra support by addition of lignin or extra cellulose. Other modifications include the uneven thickening of guard cells, the sieve plates in phloem, and the waterproof coverings of epidermal and cork cells.

[pic]

The cell walls of two adjoining plant cells both have Primary walls and Secondary wall with Middle lamella cementing the two cells. Type of microscope-unknown, Magnification unknown. (http://www.yellowtang.org/images/cell_walls_in_plant_c_ph_784.jpg)

B) Cell Membrane

The cell membrane, or unit membrane, as it is sometimes called, is a flexible, elastic envelope around the cell contents. The membrane is composed of three layers. This “sandwich” has a thin layer of protein on each side with a double layer of lipid (fat) between. Large globular proteins are embedded right in the membrane and these proteins are believed to have channels through which water-soluble materials can be passed. The whole membrane is extremely thin. In spite of this, however, it is very strong and able to withstand wear, bumps, and abrasions.

The plasma membrane functions as a selective barrier that allows sufficient passage of oxygen, nutrients, and wastes to service the entire volume of the cell. For each square micrometer of membrane, only so much of a particular substance can cross per second. Rates of chemical exchange with the extracellular environment might be inadequate to maintain a cell with a very large cytoplasm. The need for a surface sufficiently large to accommodate the volume helps explain the microscopic size of most cells.

[pic]

The cell membrane (above) consists of protein channels, protein molecule, and channel proteins. Type of microscope-unknown, Magnification unknown. (http://library.thinkquest.org/C004535/media/cell_membrane.gif)

C) Endoplasmic reticulum (rough and smooth ER)

The endoplasmic reticulum is a system of double membranes enclosing a narrow space. It is arranged in a network of interconnecting channels throughout much of the cytoplasm. The connecting canals appear to form a link, at some points, with both the membrane of the nucleus and the outer cell membrane. Other connections are made with the