.[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
| "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 |
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[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) |
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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.)