· Cells are the basic unit of life
o All living things are composed of one or more cells
o Viruses are an exception. We will consider them later and discuss whether they are alive.

· Two basic kinds of cell
o Prokaryotic - primitive cells, do not contain any internal membrane surrounded structures.
· Bacteria
o Eukaryotic - more advanced cells, do contain internal membrane bound structures
· Fungi, Protists, Plants, Animals

· Cells must have a membrane that separates inside the cell from outside the cell
o Membranes are composed of a class of fats called phospholipids composed of two parts.
§ Fatty Acid - long hydrocarbon tail, no oxygens, very hydrophobic (greasy)
§ polar head group that contains phosphate - very polar, hydrophilic

· Phospholipids naturally form a bilayer membrane. The hydrophobic tails congregate together and the polar head groups interact with water on outside and inside of cells.
o Prokaryotic cells only have an outer membrane
o Eukaryotic cells have internal membrane surrounded compartments = organelles.

· Size comparison = organ (collection of various tissues) è tissue (collection of various cell types) è individual cells (collections of structures and organelles) è organelles (collections of molecules)

· Eukaryotic cell = many different organelles that each carry out their own functions
o Nucleus = location of DNA (genetic information), control center of the cell
o Endoplasmic Reticulum = where some kinds of proteins are synthesized
o Golgi apparatus = where some kinds of proteins have sugars added to them
o Lysosome = where old proteins are degraded
o Mitochondria = where energy molecules are synthesized

· Proteins - three major roles in the cell
o enzymes = carry out chemical reactions
o structural = hold up the structure of the cell
o membrane proteins = extend through or are attached to cell membranes

· Membrane Proteins - often have sugars attached to their outer surface
o receptors - usually extend from one side of membrane to the other
§ bind and respond to very specific chemical signals (communication)
§ cause the cell to react in a very specific way
o carriers - move larger molecules from one side of membrane to the other

· Enzymes = each enzyme carries out a very specific reaction
o enzyme + substrate è enzyme + product
o The enzyme has a region of its structure called the active site. The reaction occurs at the active site. Sometimes inhibitors can bind the enzyme at the active site and prevent the substrate from binding. (drugs)