February 2, 2000
Starr Text: Ch 3 Front page, 3.2 - 3.3.5, 3.7 - 3.8
Life is woven out of air by light. -Jacob Moleschott, 1822-1893
I. Building and breaking down macromolecules
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 reactions remove water from molecules to join monomers into polymers polymers
- Hydrolysis reactions break down polymers back down to monomers - bonds are broken by the addition of water
- Both types of reaction require energy and enzymes
Dehydration (loss of water)
- Hydrolysis (splitting with water)
II. Carbohydrates (sugars, starches, cellulose)
- Made from water and CO2 by plants during photosynthesis (Ch 6)
- Bread, cereal, potatoes, fruits, vegetables, and pasta = are made mostly of carbohydrates
- General Structure: CH2O
1. Monosaccharides (simple sugars; monomers) = energy for cells
- Glucose: C6H12O6 - (grape sugar, corn sugar, dextrose)
- Fructose: C6H12O6 - (honey)
- Galactose: C6H12O6 - (part of milk sugar)
2. Disaccharides (double sugars)
- Maltose = glucose - glucose (brewing beer)
- Lactose = glucose - galactose (milk sugar)
- Sucrose = glucose - fructose (table sugar)
3. Polysaccharides (long chains of sugar polymers) - these sugar polymers are not "sweet" although they are made up up repeating glucose monomers!
- Storage polymers: starch (plants); glycogen (animals) = energy storage
- 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
- Structural polymers: cellulose (plants), chitin (insects, fungi) = structural support
- 1-4 linkage of b-glucose (plant cell walls are cellulose = "fiber" - almost undigestable)
- Once we have eaten, monosaccharides, disaccharides and starches are converted to the monomer glucose, our bodys preferred fuel, and circulate through the blood (reserves are stored as glycogen). Disorders of blood glucose (diabetes, hypoglycemia) are very serious! Cellulose in breads, cereals, veggies is not digestable, and passes through our digestive systems as "fiber"
- Why is it better to eat "complex carbohydrates" (poly-saccharides) over "simple" or "refined carbohydrates" (mono- and disaccharides)?
III. Lipids - Fats, oils, and phospholipids - All are hydrophobic!
1. Triacylglycerides (fats and oils): large molecules, not polymers.
- Made from 1 glycerol + 3 fatty acid tails = triacylglycerol
- Vary in length and location of double bonds in tail
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...
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!
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)
For each of the 4 macromolecules discussed, make sure you understand in each case:
1. What the monomer is
You may want to make one big chart with room for this information as well as for simple sketches.