-formed of an amine group (HNH or NH2) and an acidic carboxyl group (COOH).

-These two functional groups are joined together by a carbon atom

-They differ from one another according to the type of molecule attached to the central carbon atom

-The bond between the carbon and nitrogen of adjacent amino acids

-Amino acids linked together by these bonds form a peptide.

-Chains of amino acids longer than about 100 molecules are called proteins.

Fibrous Proteins

(Structural Proteins)

-Formed of long strands

-They are tough, fixed in place, and used to build body structures

-Most abbundant one in the body is collagen, which is found in the skins, tendons, ligaments, and bones.

Globular Proteins

(Functional)

-More rounded molecules that perform specific tasks

-It contains four separate protein strands, each coiled together into a rounded shape. 

-Homeglobin is a complex one that transports oxygen in the bloodstream.

-The fourth class of organic molecule

-play important roles in cell processes such as information storage and the transfer of energy

-Contains 3 building blocks: a simply sugar, a base, and one or more phosphate groups.

-Five bases exist: Adenine, Guanine, Cytosine, Thymine, and Uracil

-Composed of two layers of phospholipis molecules oriented in opposite directions.

-The hydrophilic phosphate heads at either edge of the membrane face the water cytoplasm internall and the watery extracellular fluid externally

-The hydrophobic tails form an internal oily layer that keeps the intracellular and extracellular fluids from mixing with each other

-also contains a substantial amount of cholesterol, another lipid.

-Extend through the full thickness of the membrane.

-Some enable water and water-soluble substances to cross the cell membrane

-Others serve as receptors, binding specific substances that alter cell activity

-Attracted to the inner or outer membrane surface, often to integral proteins

-They serve as anchors, attaching the cell to other cells or extracellular structures

-They may be involved in cell signaling

-Sugary coating formed from carbohydrates projecting out of the membrane

-because it is slippery, it protects the cell from mechanical damage

-acts as a molecular "fingerprint" to distinguish liver cells from kidney cells

-much larger than microvilli and are long hairlike projections

-Serves to brush material and fluid from one point to another