Unit 1 Section 2: Understanding life: part c
Biochemistry: the chemistry of life.
Section
2 - Understanding life: Part c
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What one element is found in all organic molecules? |
The chemical reactions of all living things take
place in an aqueous solution. This makes water indispensable to life.
The shape of the water molecule causes one side of the molecule to be slightly
positively charged and the other side to be negatively charged. A molecule with
an uneven charge pattern is known as a polar molecule. Even though the
total charge of the subatomic particles within a polar molecule is balanced,
the shape of the molecule causes one area to be slightly positive while another
area is slightly negative. Water is a polar molecule because the two
hydrogen atoms are slightly to one side of the molecule. In the diagram above,
the oxygen atom in each water molecule is red and the two hydrogen atoms are
blue. The red side of the molecule is slightly negative and the blue side is
slightly positive. You can see in the diagram how the positive side of one
molecule aligns with the negative side of another. The polar nature of water
makes it very effective in dissolving other substances. It is these aqueous
(water) solutions that life depends on.
Water must gain or lose a relatively
large amount of energy for its temperature to change. As heat is added to
water, most of the energy is used to break the polar bonds holding water
molecules to each other. Only after these bonds have been broken can the
individual molecules begin to move faster, increasing the temperature. This characteristic of water helps living things maintain
homeostasis - a stable level of internal conditions.
All living things need energy to
survive. Energy is defined as the ability to do work or cause change.
Within any living system, it is the free energy that is important. Free
energy is available to fuel the cell processes of living things. All living things
need a constant flow of energy into and through their systems. Many of the
chemical reactions that transfer energy in living things involve the transfer
of electrons. Reactions that transfer electrons between atoms are known as
oxidation-reduction reactions - redox reactions. These reactions occur most
easily in the polar environment of a water solution.
Organic compounds contain carbon
atoms that are covalently bonded to other carbon atoms and other
elements like hydrogen, oxygen, and nitrogen. Carbon
atoms are special for two reasons. First, carbon atoms easily bond with
other carbon atoms. This is not the case with most atoms. Because of this,
carbon is able to form "chains" of its atoms. Second, small clusters
of atoms combined with carbon, known as monomers, have the ability to link in
repeating units called polymers. Large polymers are known as macromolecules. It
is these macromolecules that make the complexity of life possible.
Dehydration synthesis & Hydrolysis reactions (Practice these reactions on paper: side 1 
& side 2
pdf version 1
& 2
In the formation or joining of two
organic compounds a reaction takes place called dehydration synthesis (condensation reaction) which bonds the two
organic molecules and releases H2O. The opposite of this reaction is
called hydrolysis, the breakdown of complex molecules, like
polymers, by adding H2O. Take a look at these sites
for animations 
and a
short video clip.
The most energy efficient molecule in living things is adenosine triphosphate, ATP. When this molecule is broken down, large amounts of energy are freed for cell processes. There are two other forms called ADP, adenosine diphosphate and AMP, adenosine monophosphate.
ATP Molecule
Groups of organic compounds:
Carbohydrates: compounds
composed of carbon, hydrogen, and oxygen.
Types of carbohydrates:
- Monosaccharide - a simple sugar with the general formula CH2O.
One monosaccharide that you will learn more about when we study
plants is glucose. The chemical formula for glucose is C6H12O6. Notice
that the subscripts in the formula for glucose can be reduced to the general
formula for monosaccharide’s, CH2O.
- Disaccharide - a double sugar composed of two simple sugars. Sucrose,
common table sugar, is a combination of glucose and fructose.
- Polysaccharide - a complex molecule composed of three or more monosaccharide’s.
Two polysaccharides that you will learn about this year are starch and cellulose.
