III. CHAPTER 3 – BIOCHEMISTRY
A. Section 1 – Water
1. Polarity
a. The electrical layout of a water molecule is unevenly
distributed due to the deeper charge of the Oxygen atom.
b. The region that the two hydrogen atoms are located has a slight
positive bias.
c. Polar – refers to the dipole-dipole intermolecular forces
between the slightly positive ends of one molecule to the
negative end of another or the same molecule.
1. Water shares hydrogen atoms unevenly; hence, the
presence of only two hydrogen atoms leaves one side of
the atom predominantly negative. In Methane
hydrogen atoms are distributed evenly, hence the
compound is non-polar.
d. The polar nature of Water makes it a prime candidate for the
dissolution of other polar substances, such as sugars, proteins,
and ionic compounds.
2. Hydrogen Bonding
a. Hydrogen Bond – the type of attraction that holds two water
molecules together. A hydrogen bond has energy comparable
to that of a weak covalent bond, but is easily breakable.
b. Attractive forces:
1. Cohesion – the attractive force between particles of the
same kind. Cohesive forces resulting from water’s
hydrogen bond cause water to act as if it has a “skin”
due to surface tension.
2. Adhesion – the attractive force between unlike
substances. Water droplets, for example, stick to
cobwebs and blades of grass.
i. Capillarity is the ability of a substance to draw
another substance into it.
c. The temperature of water does not experience any significant
change until after hydrogen bonds have fallen apart.
d. Temperature moderation – water molecules can absorb a lot of
energy before its temperature changes.
12
B. Section 2 – Carbon Compounds
1. Organic compounds – compounds containing carbon atoms that are
covalently bonded to other carbon atoms and to other elements as well.
2. Carbon Bonding
a. Carbon’s tendency to bond with itself and other elements
results in an enormous variety of organic compounds, hence
the term carbon-based life form.
b. A single Carbon atom can form up to four covalent bonds with
other atoms, as it has four valence electrons.
3. Functional groups – clusters of atoms that influence the properties of
the molecules they are part of. For example, the hydroxyl group.
a. Alcohol – an organic compound with a hydroxyl attached to
one of its carbon atoms.
1. Ethanol causes cell death in the liver and brain.
2. Methanol is wood alcohol, and causes blindness or
death.
3. Glycerol is needed by humans to assemble some
molecules.
b. Because hydroxyl is polar, alcohol has the ability to form
hydrogen bonds with other molecules.
4. Large Carbon Molecules
a. Forms of Carbon molecules:
1. Monomers are smaller, simpler molecules built up
from Carbon. They can bond with one another to form
more complex compounds.
2. Polymers consist of repeated, linked units. They may
be identical or related to each other.
3. Macromolecules are larger, more complex polymers.
b. Condensation reaction (“dehydration synthesis”) – a chemical
reaction in which two molecules combine to form one single
molecule.
c. Hydrolysis – the process by which some large molecules, such
as polymers, break down. Hydrolysis is a reversal of a
condensation reaction.
1. The addition of water to some complex molecules can
cause them to break down the bonds that hold them
together.
d. Adenosine Triphosphate (ATP) – the universal energy
“currency” for all living things. ATP contains a large amount
of energy in its overall structure.
1. Three linked Phosphate groups (PO4
-) are attached to
one another by covalent bonds. When these bonds
break, more energy is released than was require
breaking them.
C. Section 3 – Molecules Of Life
13
1. Carbohydrates – organic compounds composed of carbon, hydrogen,
and oxygen in a ration of about 2 hydrogen atoms to 1 oxygen. They
are the most abundant of the four biomolecules.
a. Monosaccharides – are the most basic unit of carbohydrates
(monomers). They are simple sugars.
1. General Formula = (CH2O)n
2. The most common monosaccharides are glucose,
fructose, and galactose
i. Glucose is the main energy source for cells.
ii. Fructose is found in fruits and is the sweetest
monosaccharide.
iii. Galactose is found in milk and is usually
combined with the other two.
3. Isomer – compounds with the same molecular formula
but different structural formulae.
b. Disaccharide – two monosaccharides combined through a
condensation reaction. Sucrose is a disaccharide.
c. Polysaccharide – a complex molecule composed of three or
more monosaccharides. Glycogen is a polysaccharide.
1. Starch and Cellulose are other polysaccharides.
2. Animals such as cows can digest cellulose because of
the presence of microscopic organisms inside.
2. Proteins – organic compounds composed mainly of carbon, hydrogen,
nitrogen, and oxygen. The two types are structural proteins and
enzymes.
a. Amino acids – the monomer building blocks of proteins. There
are 20 amino acids.
b. Dipeptide – a molecule consisting of two amino acids joined by
a single peptide bond. Peptide bonds form through
condensation reactions.
c. Polypeptide – short polymers formed from the linking, in a
defined order, of amino acids.
d. Substrate – a molecule upon which an enzyme acts.
e. Enzyme – organic molecules that act as catalysts. Enzymes
work by adding pressure to bonds (twisting), reducing the
amount of activation energy needed.
f. Proteins change shape with shifts in the environment. For
example, the proteins in an egg reshape when fried.
3. Lipids – large, nonpolar organic molecules that do not dissolve in
water. Lipids have a higher ratio of carbon to hydrogen atoms than
carbohydrates. They store more energy than C – O bonds.
a. Fatty acids – unbranched carbon chains that make up most
lipids. Fatty acids have a COOH group on one end.
b. Reaction to Water
14
1. Hydrophilic substances are “water-loving” and tend to
stay close to and form hydrogen bonds with water
molecules.
2. Hydrophobic substances do not interact with water
and are repelled by it. Nonpolar substances, or groups,
are generally hydrophobic.
c. Complex Lipids
1. Triglyceride – composed of three molecules of fatty
acids joined to one molecule of the alcohol glycerol.
i. Saturated Fatty Acids have high melting
points, and are therefore solid at room temp.
ii. Unsaturated Fatty Acids are liquid at room
temp.
2. Phospholipids – have two fatty acids joined by a
molecule of glycerol.
3. Wax – consists of a long fatty-acid chain joined to a
long alcohol chain. They are highly waterproof and can
serve as structural lipids.
4. Steroids – four fused carbon rings with various
functional groups attached. Cholesterol is a steroid.
4. Nucleic acids – very large and important complex organic molecules
that store information within cells.
a. Forms of Nucleic Acids
1. Deoxyribonucleic Acid (DNA) - nucleic acid that
contains the genetic instructions used in the
development and functioning of all known living
organisms.
2. Ribonucleic Acid (RNA) – stores and transfers
information that is essential for the manufacturing of
proteins.
b. Nucleotides – linked monomers composing both DNA and
RNA. DNA and RNA themselves are polymers. They are
composed of three primary parts:
1. A Nitrogen-containing “base”,
2. A 5 Carbon sugar,
3. And a Phosphate group.