Bio A- Biochemistry
The Wonderful World of Organic Molecules!!
Believe it or not, the subject of chemistry can be broken down into two major categories: Organic
and inorganic. Organic molecules are compounds that are made up of carbon and hydrogen
atoms. Inorganic chemistry deals with compounds that do not have carbons and hydrogen’s. In
biology, the organic compounds that we are going to deal with will also have oxygen, nitrogen,
phosphorus, and sulfur atoms (Remember CHNOPS !?!)
Of our CHNOPS atoms, Carbon is the most important building block of our organic molecules
Carbon likes to form covalent bonds with other atoms. The valence shell of a carbon atom allows it
to form 4 covalent bonds at a time. In living things, carbon will covalently bond to the rest of our
CHNOPS. In addition, carbon also likes to form covalent bonds with other carbon atoms. This
allows for numerous amounts of carbon chains in one single molecule.
So far, we have used lewis dot structures to illustrate the number of valence electrons an atom
has. When we draw covalent bonds, we use one single dash to represent the sharing of 2 electrons
Methane’s chemical structure is composed of one carbon atom covalently bonded to four
hydrogen atoms. The hydrogen atoms share their one valence electron with carbon. Carbon also
shares one of its 4 valence electrons with each hydrogen atom.
Bio A- Biochemistry
Because of carbon and hydrogen’s valence structure, these two elements can covalently bond to
create long (sometimes really, really long) chains of carbons and hyrdrogens.
We call these compounds hydrocarbons. Hydrocarbons serve as the skeleton for our biological
organic compounds. Other elements from CHNOPS will branch off of hydrocarbon skeletons.
So…what about the rest of CHNOPS anyway?
Oxygen
Nitrogen
Phosphorus
Sulfur
Atoms form covalent bonds in order to fill their outermost orbit (or valence shell). For instance,
oxygen has six valence electrons and needs two more to fill its shell. Since oxygen needs two more
electrons, it is going to be able to form two covalent bonds. Nitrogen has five valence electrons,
and will then be able to form three covalent bonds to fill its outer shell (and so on)
Bio A- Biochemistry
For example…
How many covalent bonds do you see?
Circle the covalent bonds between carbon and other atoms.
How many covalent bonds can you see between nitrogen and other atoms?
What do you think the two dots above the nitrogen atom represent?
Ethane is an organic compound with the chemical formula C2H6. Thinking about how these
atoms form covalent bonds, what do you think this molecule might look like?
Bio A- Biochemistry
Questions:
1. How does carbon’s structure relate to its ability to form covalent bonds?
2. Carbon’s structure allows it to form a large number of different molecules. Why do you think this is
important in the world of biology?
3. In your own words, what do we mean when we refer to molecules as organic?
4. What atoms are going to be present in biological organic molecules?
5. In your own words, why are hydrocarbons important?