A. A Generalized Cell
1. A human cell consists of three major parts
a. Plasma membrane
b. Cytoplasm which includes the cytosol and organelles
c. Nucleus (is technically an organelle but is described separately)
B. Plasma Membrane
1. Every cell is enclosed by a thin barrier called the plasma (cell) membrane which
has two major roles:
a. it separates the internal cellular components from the external environment
b. it regulates the movements of substances into and out of the cell.
2. The fluid mosaic model describes the structure of the plasma membrane.
3. The major chemical components are lipids and proteins.
4. The membrane lipids include:
a. phospholipids, which form a bilayer that is the basic framework of the
plasma membrane
b. cholesterol molecules, which strengthen the membrane
c. glycolipids, which perform functions on the membrane’s outer surface.
5. The membrane proteins include:
a. integral proteins, primarily transmembrane proteins (many of these are
glycoproteins) and lipid-linked proteins
b. peripheral proteins, which are located on the inner and outer surfaces of
the phospholipid bilayer; the carbohydrate portions of the glycolipids and
glycoproteins form a cell surface coat called the glycocalyx.
6. Membrane proteins perform a variety of important functions:
a. some proteins form ion channels through which specific substances may
pass into or out of the cell
b. some proteins are transporters (carrier proteins) that carry specific
substances across the membrane
c. some proteins are receptors for extracellular signalling molecules called
ligands
d. some proteins are enzymes
e. some glycoproteins and glycolipids are cell identity markers involved in
recognition of other cells
f. some proteins serve as linkers which anchor membrane proteins of
neighboring cells to each other or to filaments inside and outside the cell.
7. Due to its chemistry and structure, the plasma membrane has selective
permeability
that selectively regulates the passage of specific substances into and out of the
cell.
8. The various fluids that substances move to or from include:
a. intracellular fluid (ICF) or cytosol
b. extracellular fluid (ECF), which includes:
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