Basic Organic Compounds in Living Things
I. Carbohydrates:
-- include sugars and complex carbohydrates (starches)
-- contain the elements carbon, hydrogen, and oxygen (the hydrogen is in a 2:1 ratio to
oxygen)
a.) monosaccharides (simple sugars)
-- all have the formula C6 H12 O6
-- all have a single ring structure (glucose is an example)
b.) disaccharides (double sugars)
-- all have the formula C12 H22 O11
-- sucrose (table sugar) is an example
c.) Polysaccharides (formed of three or more simple sugar units)
glycogen -- animal starch stored in the liver and muscles
cellulose -- indigestible in humans -- forms cell walls
starches -- used as energy storage
How are complex carbohydrates formed and broken down?
1.) dehydration synthesis -- combining simple molecules to form a more complex one
with the removal of water
ex. monosaccharide + monosaccharide ----> disaccharide + water
(C6H12O6 + C6H12O6 ----> C12H22O11 + H2O
-- polysaccharides are formed from repeated dehydration syntheses of water
2.) hydrolysis -- the addition of water to a compound to split it into smaller subunits
(also called chemical digestion)
ex. disaccharide + H2O ---> monosaccharide + monosaccharide
C12H22O11 + H2O ---> C6H12O6 + C6H12O6
3. Lipids (Fats) : exs. fats, oils, waxes, steroids
-- lipids chiefly function in energy storage, protection, and insulation
-- contain carbon, hydrogen, and oxygen but the H:O is not in a 2:1 ratio
lipids tend to be large molecules -- an example of a neutral lipid is below
-- neutral lipids are formed from the union of one glycerol molecule and 3 fatty acids
3 fatty acids + glycerol ----> neutral fat (lipid)
-- fats -- found chiefly in animals
-- oils and waxes -- found chiefly in plants
-- oils are liquid at room temperature, waxes are solids
-- lipids along with proteins are key components of cell membranes
-- steroids are special lipids used to build many reproductive hormones and cholesterol
III. Proteins:
-- contain the elements carbon, hydrogen, oxygen, and nitrogen
-- composed of amino acid subunits (below is the structure of an amino acid)
[Major Protein Functions]
1. Growth and repair
2. Energy
3. Buffer -- helps keep body pH constant
dipeptide -- formed from two amino acid subunits
Dehydration synthesis of a dipeptide
amino acid + amino acid ----- dipeptide + water
Hydrolysis of a dipeptide
dipeptide + H2O ---> amino acid + amino acid
polypeptide (protein) -- is composed of three or more amino acids linked by synthesis
reactions
Examples of proteins include insulin, hemoglobin, and enzymes.
** There are an extremely large number of different proteins. The bases for variability
include differences in the number, kinds and sequences of amino acids in the proteins
IV. Nucleic Acids: present in all cells
DNA (deoxyribonucleic acid)
-- contains the genetic code of instructions that direct a cell's behavior through the
synthesis of proteins
-- found in the chromosomes of the nucleus (and a few other organelles)
RNA (ribonucleic acid)
-- directs cellular protein synthesis
-- found in ribosomes & nucleoli
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catalyst: inorganic or organic substance which speeds up the rate of a chemical reaction
without entering the reaction itself
enzymes: organic catalysts made of protein
-- most enzyme names end in -ase
-- enzymes lower the energy needed to start a chemical rx. (activation energy)
-- begin to be destroyed above 45 C. (above this temperature all proteins begin to be
destroyed)
It is thought that, in order for an enzyme to affect the rate of a reaction, the following
events must take place.
1. The enzyme must form a temporary association with the substance or substances
whose reaction rate it affects. These substances are known as substrates.
2. The association between enzyme and substrate is thought to form a close physical
association between the molecules and is called the enzyme-substrate complex.
3. While the enzyme-substrate complex is formed, enzyme action takes place.
4. Upon completion of the reaction, the enzyme and product(s) separate. The enzyme
molecule is now available to form additional complexes.
** Although enzymes may be reused in cells, they eventually are destroyed and new ones
must be synthesized.
Active site: the pockets in an enzyme where the reacting molecules (substrate) fit
(Usually enzyme molecules are much larger than the molecules they interact with.)
(Composition of Enzymes)
-- all enzymes are composed of proteins or proteins attached to other molecules
coenzyme -- non-protein part attached to the main enzyme (usually a vitamin or a
mineral)
[How do enzymes work?]
substrate: molecules upon which an enzyme acts
the enzyme is shaped so that it can only lock up with a specific substrate molecule
enzyme
substrate -------------> product
"Lock and Key Theory"
-- each enzyme is specific for one and
ONLY one substrate (one lock - one key)
-- this theory has many weaknesses, but it
explains some basic things about enzyme
function
[Factors Influencing Rate of Enzyme Action]
1. pH - the optimum (best) in
most living things is close to 7
(neutral) -- high or low pH
levels usually slow enzyme
activity
A few enzymes (such as gastric protease) work best at a pH of about 2.0
2. Temperature strongly influences
enzyme activity
- optimum temperature for
maximum enzyme
function is usually about
35-40 C.
-- reactions proceed
slowly below optimal
temperatures
-- above 45 C. most
enzymes are denatured
(change in their shape so
the enzyme active site no
longer fits with the
substrate and the enzyme
can't function)
3. Concentrations of Enzyme and Substrate
** When there is a fixed amount of enzyme and an excess of substrate molecules -- the
rate of reaction will increase to a point and then level off.
** This leveling off occurs because all of the enzyme is used up and the excess substrate
has nothing to combine with.
-- If more enzyme is available than substrate, a similar rx. rate increase and leveling off
will occur. (The excess enzyme will eventually run out of substrate molecules to react
with.)