My notes and thoughts from Biology 111, for Friday, September 12, 2008. The entire series can be found here.
There are four main classes of organic compounds in living things that Bio 111 is going to cover.
- Carbohydrates* —> C, H, O
- Lipids —> C, H, O (sometimes N & P)
- Proteins* —> C, H, O, N, S
- Nucleic Acids* —> C, H, O, N, P
* Carbohydrates, Proteins, and Nucleic Acids are Macromolecules, meaning “really honkin’ big”.
1. Carbohydrates – Sugars – all “ose” endings mean “sugar”.
They have a C:H:O ratio of 1:2:1, so the basic carbohydrate formula would be CH2O
a) monosaccharides –> “one sugar” – these are the simple sugars, and contain between 3 – 7 C atoms in them.
(Lecture continues below the fold)
We’re going to stick with the hexose group for a bit, because it’s pretty common, and useful to illustrate several things in biology.
Because of the interchangeability of parts, a compound with the formula C6H12O6 (for instance) can actually wind up being arranged in more than one way. When compounds are arranged differently but share a molecular formula, they are called isomers (“same part”). Glucose, Fructose, and Galactose are three simple sugars, all hexose sugars, but have their atoms arranged differently. They are isomers that organisms use for energy.
Each of these hexose isomers have 7 C-H bonds (they are hydrocarbons, and remember that C-H bonds are nonpolar covalent bonds, having a great deal of potential energy)
Monosaccharides often rearrange themselves a little bit from the structural diagrams to the right, and fold in on themselves to make a hexagonal shape. There are illustrations of the process in the textbook.
b) Disaccharides –> “two sugars” – these are simply two sugars linked by a covalent bond.
Since all the bonding places are taken up by atoms in the monosaccarides, a place needs to be make for the link between the two simple sugars. This is accomplished by a dehydration synthesis, also known as a condensation reaction.
The OH– at a place on one sugar will be attracted to the H+ on another sugar. They will each leave their parent sugar molecule and combine to form a water molecule, leaving an unpaired electron in the valence shell of one Carbon in each of the sugar molecules.
This is where the hook-up occurs.
When a galactose and a glucose combine, the resulting disaccharide is called lactose and is found in milk.
When two glucose molecules combine, the resulting disaccharide is called maltose, and is used in brewing.
We can’t use disaccharides for energy, so our bodies add water back into the disaccharide, in a reverse process known as hydrolysis. This breaks the disaccharide back into two monosaccharides, something our body can use for energy.
c) Polysaccharides –> “many sugars” – many monosaccharides linked by covalent bonds. These are macromolecules, and can be hundreds to thousands of monosaccharides linked together.
Polymer –> “many parts” –> large molecule made of many small and similar molecules.
Monomer –> “one part” –> one of the small molecules.
Some polymers of glucose are used by organisms to store energy, some to do other things, like build structure.
Plants use starch for energy storage.
Animals use glycogen for energy storage.
Plants use cellulose for structure.
An emergent property of these polymers is that they are not water soluble. This is the means by which they store the energy inside cells (otherwise they would just dissolve inside the cell which is mostly water).
They are stuck inside the cell until needed, much like a school bus brought in pieces into a classroom and then assembled. In order for the organism to use the energy stored therein, the polymer must first be broken down by hydrolysis.
In order to digest cellulose, water and cellulase are needed. Animals don’t make cellulase in their bodies, and so can’t digest cellulose. Hearkening back to the termite lab, remember that termites subsist on a diet of wood. Wood is made of cellulose. How do they do that? They depend on little microorganisms to digest the cellulose for them.
Breakdown of any -ose (sugar) is facilitated by a corresponding -ase. Breakdown of lactose needs lactase, etc.
2. Lipids –> Of our four classes with which we began this lecture, lipids are the only ones that are not macromolecules.
It’s a diverse class that includes fats and oils, steroids, and phospholipids. Fats and oils are long chains, while steroids are ring structured.
This class is made of mostly C and H, with just a little O. Fats and oils are nonpolar molecules, and so are not water soluble.
Fats and oils = triglyceride –> 1 glycol + 3 fatty acids. The difference between fats and oils is density, and I’ll have lovely little drawings of them for you in the next lecture.
From whence came the art:
The first image is of our textbook, Biology, Eighth Edition, by Campbell & Reese et al.
Other images by me and are licensed under the Creative Commons Attribution- NonCommercial- Share Alike 3.0 License.