Second Part of Chapter 5 Notes

Lipids--Diverse Hydrophobic Molecules

Unlike the other three major groups of biological molecules, lipids are not polymers. They are grouped together because they are hydrophobic, and this hydrophobic nature is based on their structure. There are many different kinds of lipids, some of which are waxes, oils, fats, and steroids.

Fats are large molecules that are created by dehydration synthesis reactions between smaller molecules. Fats (also called triacylglycerols or triglicerides) are made up of a glycerol molecule and three fatty acid molecules.

Fats differ in the length of their hydrocarbon backbones and also in the presence and positions of the double bonds they contain between carbon atoms.

Saturated fatty acids contain no double bonds, unsaturated fatty acids contain at least one double bond, and polyunsaturated fatty acids contain two or more double bonds.

**a way to remember saturated fatty acids: Single
Saturated
Solid at room temperature

In animals, fats is an important storage molecule. In humans and other mammals, fat is stored in adipose cells (fat cells).

Lipids are a very important part of phospholipids, in which make up cell membranes. Phospholipids have a glycerol backbone and two fatty acid tails; the glycerol head is hydrophilic, and the fatty acid tails are hydrophobic. In forming the cell membrane, they are arranged in a bilayer, with their hydrophobic ends sandwhiched in between the outer portion of the cell membrane and the inner portion. The hydrophilic ends are pointing toward the cytosol and the outer cell environment.

The final type of lipid you will need to be familiar with is steroids. Steroids are made up of four rings that are fused together. One common type of steroid is cholesterol. Cholesterol is an important component of cell membranes. Another example is found in hormones such as estrogen and testosterone.

Protiens--Many Structures, Many Functions

Proteins are a very important component of the cell; in fact, they make uo about 50% of the cell.

Proteins are polymers made up of amino acid monomers.
**every enzyme is a protein, but not every protein is an enzyme

Amino acids are organic molecules that contain a carboxyl group and an amino group, as well as an R group (variable group), that gives each amino acid its adentity and properties. There are twenty amino acids that make up protein molecules. You should be able to recognize from their names that they are amino acids, because most amino acids end in--ine.

In proteins, amino acids are joinde by peptide bonds in a dehydration synthesis reaction. The function of proteins depends on how many amino acids and what type of amino acids are joined together [they are always lined up by amino group (nterminus), carbon skeleton, and carboxyl group(cterminus)].

There are four levels of protein structure. The most basic is the primary structure--the sequence in which the amino acids are joined.

The secondary structure refers to one of two three-dimensional shapes that the prootein can have due to its hydrogen bonding. One shape is a coiled shape called an alpha helix, and the second shape is an accordian shape called a beta pleated sheet.