The Function of Cell Membranes

Cell Membranes

Peer advising group dates – Biology majors

P. Cell-to-cell interactions

Cell identity – One way that cells interact is to express identity whether it is the cell of the organism or the tissue

Cell junctions – attachment or communication. Several types of these talks about surface markers and various other kinds.

  1. Tight junction – when two cells are held tightly to one another to prevent leakage to the cells so no liquid can go between them.
  2. Desmosome – anchoring junction, intermediate filaments on different sides of the skeleton and there are different things in between.  “Cadherin” protein (skin cells, held together tightly)
  3. Adherens junction – anchoring junction, a lot like the previous one (skin and epithelial cells)
  4. Communication – Animals – gap junction. Function is to communicate between cells, create hold between the two. Cells need to communicate, this is how animal do it
  5. Communication – Plants – plasmodesmata (saw in lab?) ) Holes through the cell wall, some membrane connecting the cells, cytoplasm in there, movement of substances within there. Cells sending messages/hormones

Cell Membranes

Membranes – made of proteins(50-60%) and lipids(40-50%). Proteins are slightly more than lipids. Lipids are mostly phospholipids (tube, end is polar, other is nonpolar)Polar end is hydrophilic. Molecules tend to come together in some way, away from the water. “Lipid Bilayer” not only lipids, there are also proteins in the cell membranes (book diagram of phospholipid)

Figure numbers may be off

Lipid bilayer with proteins interdispersed. Some proteins sit on the surface, some go in. Cholesterol molecules as well. Majority of molecules are the phospholipids.

Fluid Mosaic Model – some proteins go in the middle, some are on the outside. Peripheral proteins – integral proteins, span the membrane. Majority of proteins are this kind (span the whole membrane)

Sugar chains are also attached (to establish identity) Some chains are attached to a protein, called a glycoprotein. Sometimes the sugar chains are attached to a lipid (called a glycolipid)

Sugar chains together are called the “glycocalyx” (sugary material that sticks to the outside)

There is an occasional peripheral protein on the inside. Often their function is to attach to the cytoskeleton to maintain stability.

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