Macromolecules
February 2, 2000


Starr Text: Ch 3 Front page, 3.2 - 3.3.5, 3.7 - 3.8


The object of opening the mind, as of opening the mouth, is to shut it again on something solid.- Gilbert Keith Chesterton, 1864-1936

Life is woven out of air by light. -Jacob Moleschott, 1822-1893

Outline:

I. Building and breaking down macromolecules
II. Carbohydrates
III. Fats
IV. Proteins
V. Nucleic acids



I. The 4 macromolecules of life see Table 3.1

Cells cannot live by sugar and water alone - they need to put the chemical "building blocks" C, O, H, and N (and others) together to make useful molecules for food and energy that allow them to perform the functions of life.

Cells join together small organic molecules (monomers; building blocks) to form large molecules (polymers) or Macromolecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids

 

 

How do cells build organic compounds?

Chemical reactions assemble monomers into polymers and break polymers back down into monomers:

Dehydration (loss of water)

II. Carbohydrates (sugars, starches, cellulose)

1. Monosaccharides (simple sugars; monomers) = energy for cells

 

 

 

2. Disaccharides (double sugars)

3. Polysaccharides (long chains of sugar polymers) - these sugar polymers are not "sweet" although they are made up up repeating glucose monomers!

       

1-4 linkage of a-glucose (energy reserves used as fuel)
Note that animal cells can't make sugars "from scratch", but can polymerize plant sugars into glycogen
1-4 linkage of b-glucose (plant cell walls are cellulose = "fiber" - almost undigestable)

 

 

 

III. Lipids - Fats, oils, and phospholipids - All are hydrophobic!

1. Triacylglycerides (fats and oils): large molecules, not polymers.

 Saturated (fats) : no double bonds; saturated with hydrogens.  Unsaturated (oils): a double bond ("kink") forms (loss of 2 H) Polyunsaturated (margarine, crisco) - hydrogens are added synthetically
Solid at room temperature - animal fats (bacon, lard, butter)  Liquids at room temperature - olive oil, corn oil, cod liver oil.  Solids at room temperature - liquid oil converted to a solid shortening - margarine (20% H) or semi-solid (13% H) "soft" margarine

 

 

 

 

 

   

 

Major functions of fats and oils

1. Energy storage. Fats are a more compact fuel than starch.

2. Cushions and insulates the body and nerves

 

Perhaps you have wondered (as you ate "Fat Free Pringles")...What in the world is Olestra? Olestra is a synthetic fat with 8 fatty acid tails - it is very big and bulky. Because it is a fat, foods fry up just fine with it with it, but because it is so bulky, the fat-digesting enzymes (lipases) in our intestines cannot break it down...and it passes through unchanged...ooh, yummy.

Only for the truly curious...the Olestra Poetry Page (warning: funny but pretty gross)

 

2. Diacylglycerides (phospholipids): lipid bilayers (the plasma membrane of every cell and the membranes within eukaryotic cells; the boundary between a cell and its environment!!!)

Structure - similar to a triacylglycerol, but has only 2 fatty acid tails, and in addition has a phosphate group = (1 glycerol, 2 fatty acids, and a -PO4)

The -PO4 makes the glycerol "head" water soluble (polar), or hydrophilic.

The long hydrocarbon tail is hydrophobic (nonpolar).

Due to this "amphipathic" nature, phospholipids self assemble into bilayers that shield the tail from water = forming membranes (phospholipid bilayers)

 Sketch a lipid bilayer here: membrane proteins optional...

 

 

 

 

 

IV. Proteins

Cells have thousands of different proteins, each with a specific function. Even so, all proteins are polymers constructed from a set of 20 amino acid monomers linked end-to-end, up to thousands of amino acids long, each in a unique 3-D shape.

There are 20 amino acid monomers: Each has the overall structure shown in Fig 2.24 - molecules with a C bound to an amino group (NH3), a carboxyl group (COO-), a hydroxyl group (OH), and a variable region, the R group (side chain)

1. Functions of proteins - structural (muscle, skin, hair), antibodies, enzymes, hormone receptors, insulin, hemoglobin, neurotransmitters. In addition, proteins are important sources of food

2. Four levels of protein structure - when a protein is synthesized from the instructions provided by a gene, it folds spontaneously into its shape reinforced by chemical bonds. If it doesn't form into the right shape, the protein often does not work!

1° structure - sequence of amino acids specified by a gene
2° structure - folding and coiling due to hydrogen bonds
3° structure - bonding between side chains (R groups) "rivets" parts of proteins together
4° structure - aggregation between 2 or more protein chains
 

3. Diseases caused by proteins that do not form correctly: sickle cell disease, cystic fibrosis, muscular dystrophy

Caution! High temperature, pH, or salt, can unravel or denature a protein (loss of shape) and inactivate it -"you can't unboil an egg"!

 

V. Nucleic Acids (We will just skim over these now; later we will go into more detail...)

The monomer for all nucleic acids is the nucleotide, which has 3 parts:

a. A phosphate group (one or more)
b. A 5-carbon sugar (deoxyribose or ribose)
c. A nitrogen-containing base - Adenine (A), Guanine(G), Cytosine (C), Thymidine (T); (Uracil in RNA)


1. ATP :
the main "energy currency" of all living cells...

2. Nucleotide coenzymes: (NAD+, NADP+, FADH+): Carriers of protons and electrons during cellular respiration and photosynthesis

3. DNA: (Deoxyribonucleic acid)

4. RNA: (Ribonucleic acid)

Objectives:

For each of the 4 macromolecules discussed, make sure you understand in each case:

1. What the monomer is
2. What types of polymers result
3. What the functions of each macromolecule are in cells.

You may want to make one big chart with room for this information as well as for simple sketches.