CELL ORGINZATION NOTES
a at plate (squamous)
the form of a structure is op mally suited to perform par cular func ons assigned to that structure
A primary responsibility of each cell is to contribute to homeostasis
The concept of a cell started with microscopic observa ons of dead cork ssue by scien st Robert Hooke in 1665. Hook coined the term "cell" based on the resemblance of the small subdivisions in the cork to the rooms that monks inhabited, called cells.
Despite di erences in structure and func on, all living cells in mul cellular organisms have a surrounding cell membrane
The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipids (a "bilayer"). Cholesterol is also present, which contributes to the uidity of the membrane, and there are various proteins embedded within the membrane that have a variety of func ons.
phospholipid molecule has a phosphate group on one end, called the "head," and two side-by-side chains of fa y acids that make up the lipid tails. The phosphate group is nega vely charged making the head hydrophilic. Phosphate heads are thus a racted to the water molecules of both the extracellular and intracellular environments. lipid tails, on the other hand, are uncharged, or nonpolar, and are hydrophobic. Some lipid tails consist of saturated fa y acids and some contain unsaturated fa y acids
Phospholipids are thus amphipathic molecules. An amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region
The cell membrane consists of two adjacent layers of phospholipids. The lipid tails of one layer face the lipid tails of the other layer, mee ng at the interface of the two layers. The phospholipid heads face outward, one layer exposed to the interior of the cell and one layer exposed to the exterior.
Intracellular uid (ICF) is the uid interior of the cell. Extracellular uid (ECF) is theuid environment outside the enclosure of the cell membrane. Inters al uid (IF) is the term given to extracellular uid not contained within blood vessels.
An important feature of the membrane is that it remains uid; the lipids and proteins in the cell membrane are not rigidly locked in place.
Two di erent types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein.
As its name suggests, an integral protein is a protein that is embedded in the membrane. A channel protein is an example of an integral protein that selec vely allows par cular materials, such as certain ions, to pass into or out of the cell.
Another important group of integral proteins are cell recogni on proteins, which serve to mark a cell's iden ty so that it can be recognized by other cells.
A receptor is a type of recogni on protein that can selec vely bind a speci c molecule outside the cell, and this binding induces a chemical reac on within the cell.
A ligand is the speci c molecule that binds