Understanding Life
Biochemistry |
Objectives for today:
* Identify the Organization of living systems.
All life is dependent on the chemical reactions between molecules.
Life begins with the simplest molecules and builds more and more
complicated chemical interactions.
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 positive. 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 enviornment 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.
The breakdown of complex molecules, like polymers, is called hydrolysis. 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.
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 monosaccharides, 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 monosaccharides.
Two polysaccharides that you will learn about this year are starch and cellulose.
Proteins: compounds composed of carbon, hydrogen, oxygen, and nitrogen.
