Wednesday, January 20 th, 1999
Announcements:

Lecture notes:

Lipids are almost completely composed of Carbon and Hydrogen and are therefore non-polar (hydrophobic).

Functions: storage and transport of energy (triglycerides)
membranes (phospholipids and cholesterol)
protective coats (waxes)
steroid hormones (testosterone and estrogen)
pigments

Triglycerides are three fatty acids linked to glycerol. Glycerol is a 3C alcohol. A fatty acid is a long chain unbranched hydrocarbon with a COOH (carboxylic acid) on the end. See figures 2.20 and 2.21 in the book.

• We store fat as triglycerides
• The fat we eat is in the form of triglycerides
• The reaction linking glycerol to a fatty acid is a condensation.
  1 fatty acid linked to glycerol is a monoglyceride
  2 fatty acid linked to glycerol is a diglyceride
  2 fatty acid linked to glycerol is a triglyceride

A saturated fatty acid has all single bonds between the carbon atoms. These molecules can pack very tightly.

A monounsaturated fatty acid has one double bond somewhere in the chain of carbons.

A polyunsaturated fatty acid has more than 1 double bond in its structure.

A double bond makes a kink in the molecule and the molecules cannot pack as closely as saturated fatty acids. This is why fats with a high proportion of saturated fatty acids are solid at room temperature and why oils with high proportions of mono- or polyunsaturated fats are liquid at room temperature.

Phospholipids: are important in membranes of cells. They are made of glycerol, 2 fatty acids, a phosphate and another hydrophilic (water loving) molecule.

Waxes: are a "condensation" of an alcohol and a fatty acid and are used for coating and waterproofing.

Steroids: are more complex lipids, which do not contain fatty acids.

Important members of this class include sex hormones, cholesterol (which is found in animal membranes), bile acids, phytosterols (found in plant membranes), vitamin D.

The basic building block molecules of Nucleic Acids are called nucleotides. They have:
1. A 5-carbon-sugar: deoxyribose in DNA and ribose in RNA (S)
2. A phosphate group (P)
3. A nitrogen containing base (B)

Nucleotides have 3 functions in the body:
1. Nucleotide phosphates. Example: ATP, and energy carrier, and cyclic AMP, a chemical messenger
2. Nucleotide coenzymes: involved in transport of protons and electrons in metabolism. Example: NADH, FAD
3. Nucleic acids: chains or nucleotides, either single stranded or double stranded. Involved in storage, transmission and
translation of the genetic message.

• The reason DNA and RNA are called Nucleic Acids is that they are acidic at pH7.

A DNA nucleotide contains:
1. The 5 carbon sugar deoxyribose
2. A phosphate group
3. One of four bases.
a. adenine A
b. guanine G
c. cytosine C
d. thymine T

Important details: The 4 bases are not present in equal amounts. Amounts are different for each species. Human DNA has 3 x 10⁹ base pairs.

In every species the amount of G (guanine) equals the amount of C (cytosine) and the amount of A (adenine) equals the amount of T (thymine).

Interesting detail: You have 800 times more DNA that the E.coli bacterium
Newts have 30 times more DNA than you do.
Beans have 30 times more DNA than you do.

DNA is a double helix - a circular stairway with the sides being composed of a sugar-phosphate "backbone" and the rungs of the stairway being the base pairs G-C of A-T.

1. DNA unwinds a portion of itself.
2. Enzymes direct "grabbing and hooking up" of the complementary base on to the "old strand" (condensation)
3. There is a proofreading function to correct mistakes. (1 mistake for every 100 million base pairs)
4. 1%-10% of DNA is involved in coding for and regulating genes.
5. Replication is semiconservative. 1 old and 1 new strand in each.

• all processes are directed and regulated by enzymes
• All DNA for all living organism is made of the same building blocks

RNA: Ribonucleic Acid is made up of: 1. a sugar - ribose (5C)
2. a phosphate
3. One of four bases:
adenine A
uracil (this replaces thymine in RNA) U
guanine G
cytosine C

RNA is usually single stranded. The base pair: G-C and A-U (instead of T)

Differences between RNA and DNA: DNA is usually double stranded, RNA is usually single stranded. RNA uses uracil instead of thymine. In DNA the sugar is deoxyribose, in RNA the sugar is ribose.

DNA is the "genetic code" for all the information needed to DO THINGS in the cell and to pass this information to succeeding generations. It is located in the nucleus of cells (IN the nucleoid region of bacteria).

How is this code used to "get the message out"?

The message sent out in mRNA (messenger RNA). It is transcribed from the DNA gene template for the protein needed.

How does the mRNA (which is a chain of nucleotides) get "translated" into a protein (which is a chain of amino acids)???

Problem: There are 4 bases (A,C,G,U) in mRNA
There are 20 amino acids.

Solution: If nature used 2 bases for the code, there would only be 16 different codes. (4²).
If nature used 3 bases for the code, there would be 64 possible codes (43) (plenty).

A gene is a piece of DNA that codes for a particular trait in an organism. Mostly proteins.