The pH value of chemical compounds in living things naturally fluctuates
during metabolism. Metabolismis a collection of chemical reactions occurring
in a living organism. Sometimes the chemical compound is more acidic than
alkaline and vice versa. Any drastic sway in the acid-base balance could have a
devastating effect. A chemical compound called a buffer is used to prevent harm-
ful swings in the acid-base balance. Abufferreleases hydrogen ions or binds
hydrogen ions to stabilize the pH. A weak acid or base does not easily separate
(ionization).
ORGANIC COMPOUNDS
An organic compound is a compound whose chemical elements include carbon.
Carbon plays an import role in living things because compounds that contain it
build many different organic compounds, each having different structures and
functions. The large size of most carbon-containing molecules and the fact that
they don’t dissolve easily in water makes them useful in building body structures.
Organic compounds also store energy required by an organism for metabolism.
Carbon can combine with other atoms because carbon has four electrons in
its outer shell. This leaves room for four additional electrons from other atoms
to bond to the carbon atom in a biological reaction (Fig. 2-8). Carbon also has
low electronegativity and lacks polarity when a bond is formed.
A carbon atom commonly combines with other carbon atoms to form a car-
bon chain. There are two forms of carbon chains. These are straight carbon
chains and ring carbon chains. Fig. 2-9 shows how this is used to illustrate fruc-
tose. Carbon chains are the basic form for many organic compounds.
Organic compounds come in many sizes—small to large. Many, but not all,
large organic compounds are called polymers. A polymer is made up of small
molecules called monomers. A monomer is another name for subunit. Monomers
are bonded together to form a polymer in a process called dehydration synthe-
sis,which removes water molecules from the compound.
CHAPTER 2 Chemical Elements of Microorganisms^39
C
Fig. 2-8. The lines indicate a single bond with other atoms.