Organic chemistry and Biological chemistry for Health Sciences
59-191
Lecture 5
Blood cells circulating in the bloodstream behave as dialyzing membrane. Within each
red blood cell is an aqueous fluid with dissolved and colloidally dispersed substances.
Hemolysis:
When red cells are placed in pure water, dialysis occurs to bring fluid into the cell
because the fluid inside the red cell is more concentrated than the surrounding liquid.
Enough fluid moves in to make the cell burst open, the rupturing of red cells is called
hemolysis, and we say that the cell hemolyze.
Crenation:
When red cells are put into a solution with an osmolarity greater than their own fluid,
dialysis occurs in the opposite direction-out of cell and into the solution. Cells lose fluid
volume, and shrivel and shrink. This process is called crenation.
In some medical conditions, body fluids need replacement or nutrients have to be given
by intravenous drip. The osmolarity of the solution being added should match that of the
fluid inside the red cells otherwise, hemolysis or crenation will occur.
Isotonic solution:
Two solutions of equal osmolarity are called isotonic solutions.
Hypotonic solution:
If one solution has a lower osmotic pressure than the other, the first is said to be
hypotonic with respect to the second. A hypotonic solution has lower osmolarity than the
one to which it is compared.
Red cells will hemolyze if placed in a hypotonic environment, including pure water.
Hypertonic solution:
A hypertonic solution is one with a higher osmotic pressure than another.
F. ex. 0.14 M NaCl is hypertonic with respect to 0.10 M NaCl
Red cells will undergo crenation when they are in a hypertonic solution
0.9% (w/w) NaCl solution is called physiological saline solution. It is isotonic with
respect to the fluid inside a red blood cell.
Any solution to be added in any large quantity into the bloodstream has to be isotonic
with respect to the blood cells.
Organic compounds:
Made of carbon atom covalently bonded to each other and to atoms of other non-metals,
like hydrogen, oxygen, nitrogen, sulfur and the halogens
All others are inorganic compounds
Structural features of organic compounds:
Carbon is unique as an element because its atoms can bond to each other successfully
many times and still form equally strong bonds to atoms of other nonmetals.
F.example
Polyethylene- hundreds of carbon atoms covalently joined in succession. Each carbon
atom binds enough hydrogen atoms to fill out its full complement of four bonds.
The sequence of the heavier atoms, here the carbon atoms, is called skeleton of the
molecule, and it holds hydrogen atom.
Carbon skeleton can be two different types

Straight chain

Branched chain
Straight chain:
One carbon follows another like pearls in a single strand necklace, with no additional
carbons joined to the skeleton in the intermediate points
Example:
Pentane
Branched chain:
Chain with at least one carbon atom joined to the skeleton between the ends of the main
chain, like a charm hung on a bracelet.
Example
2-methyl pentane
Structural formula of an organic compound does not show the actual bond angles of
carbon. So it does not show you the actual geometry of the compound. It is normally
understood.
Molecular geometry is properly shown by ball and stick model.
Still we can use the
structural formula but we have to keep in mind that it is not the real geometry of the
molecule.
Geometry of the molecule is as important as any other feature of its structure. You will
realize that when you will study biochemistry, particularly the way the enzymes work.
Two clusters of atoms held by single bond can rotate freely with respect to each other
about the bond.
So the molecule like pentane containing only single bonds is quite flexible.
There are few ways the carbon skeleton of the pentane can be flexed. The differently
twisted forms of molecules are called conformations.
So samples of liquid or gaseous pentane is actually the mixture of different
conformations of pentane.
Generally one conformation is present in a relatively high concentration, the
conformation that corresponds to the most stable arrangement of the electron cloud
(electron clouds of the various parts of the molecule stay as far apart as they can within
the molecule)
Condensed structure:
To simplify the structural formula of carbon chain compounds condensed structure can be
used. All hydrogen atoms held by carbon atom can be grouped beside its symbol. If it
holds three hydrogen we can write CH3, if two we can write CH2 and so on.
Single bond in the horizontal line can be omitted but not the one that is not.
If the molecule contains atoms other than H, no problem arise in writing the condensed
structure.
Every oxygen or sulfur carrying no charge must have two bonds, every nitrogen must
have three and every halogen atom must have just one covalent bond.
Carbon carbon double and triple bonds are usually included in the condensed structure.
Carbon oxygen double bonds are sometimes condensed.
Sometimes two or three identical groups that are attached to the same carbon are grouped
inside a set of parentheses.