The Chemistry of Life 35
- Proteins have four types of structure based on
bonding:- primary (amino acid sequences),
secondary- (based on hydrogen bonds between
amino acids, causing coiling), tertiary (secondary
folding based on sulfur atoms), and quaternary
(based on spatial relationships between units).
Nucleic Acids
- Deoxyribonucleic acid (DNA) is the genetic material
of the cell found in the nucleus that determines all of
the characteristics and functions of the cell.^
- Ribonucleic acid (RNA) exists in two forms
necessary- for protein synthesis: messenger RNA
and transfer RNA.^
- Nucleic acids are composed of chains of
nucleotides.^
- A nucleotide is a complex combination of a nitrogen
base (purine or pyrimidine), a sugar (deoxyribose), and
a phosphate group.^
- The two purine bases are adenine and guanine. The
three pyrimidine bases are thymine, cytosine, and
uracil (uracil is found in RNA only and is substituted
for thymine).
Adenosine Triphosphate
- ATP is a high-energy molecule that is the fuel that
allows cells to function and maintain themselves.^
- The ATP molecule consists of a ribose sugar,
adenine,- and three phosphate groups. The energy of
the molecule is stored in the second and third
phosphate groups.^
- The breakdown of the glucose molecule and other
nutrients provides the energy to make ATP
molecules.
MOVEMENT OF MATERIALS
INTO AND OUT OF CELLS
Materials move through plasma membranes in three
-different ways: diffusion, osmosis, and active transport.
Diffusion
- Diffusion is the movement of molecules through a
medium from an area of high concentration of those
molecules to an area of low concentration of those
molecules.^
- The random collision of diffusing molecules is
called Brownian movement.
3. Increased temperature accelerates the rate of
diffusing molecules.^ - An example of diffusion in the human body is the
uptake of oxygen by the blood in the lungs and the
release of carbon dioxide gas to the lungs from the
blood.
Osmosis1.^ Osmosis is a special kind of diffusion.^
2. Osmosis is the movement of water molecules through
a selectively permeable membrane, such as a plasma
membrane, from an area of higher concentration of
water molecules (e.g., pure water) to an area of low
concentration of water molecules (e.g., water to
which a solute like salt or sugar has been added).
3. An isotonic solution (e.g., normal saline) is a
solution- in which the salt concentration outside a cell
is the same as that inside a cell. The cell would
neither gain nor lose appreciable amounts of water.
4. A hypotonic solution (e.g., pure distilled water) is a
solution in which the salt concentration inside the
cell is higher than it is outside the cell. The cell
would absorb water in such a solution.^
5. A hypertonic solution (e.g., a 5% salt solution) is one
in which the salt concentration is greater outside the
cell than it is inside the cell. The cell would lose wa-ter
in such a solution.^
6. Active transport is the transportation of materials
against a concentration gradient in opposition to other
factors that would normally keep the material from
entering the cell. This mechanism requires en-ergy in
the form of ATP and is the main mechanism by which
most cells obtain the materials they need for normal
functioning.
pH- pH is the negative logarithm of the hydrogen ion
concentration in a solution: pH 5 2log [H^1 ].^ - If a substance dissociates and forms an excess of H^1
ions when dissolved in water, it is referred to as an
acid. Acids have pH values below 7.^ - A substance that combines with H^1 ions when
dissolved- in water is called a base. Basic solutions
have a pH value above 7.^ - Distilled pure water has a pH value of 7 and is
neutral.