Page 406 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Naturally Occurring Polymers—Animals 369

and act as master switches in activating other genes necessary in our learning/memory process. The
CREB gene is on chromosome 2. A related and essential gene that helps CREB perform is found on
chromosome 16 and is given the name CREBBP.
Another essential “learning gene,” related to alpha-integrin (integrins are proteins with two
unlike units called alpha and beta that are anchored to the plasma membrane; they act as molecular
adhesives and also as receptors and signal transducers), is also found on chromosome 16. This gene,
called the volado (means in Chilean “forgetful”) gene, appears to be a player in memory and it is
not involved in the cyclic AMP sequence. The volado gene codes for one of the subunits of alpha-
integrin. The volado gene appears to act to tighten connections between neurons as we learn.
We are aware of certain drugs that interfere with the activity of integrins by interfering with a
process called long-term potentiation (LTP), which is an essential part of creating a memory. In the
base of our brain is a part called the hippocampus (Greek for seahorse). A part of the hippocampus
is called the Ammon’s horn (named for the Egyptian god associated with the ram). The Ammon’s
horn has a large number of pyramidal-shaped neurons that assemble the inputs of secondary neu-

rons. Single inputs appear not to “fire” these neurons but when two or more inputs arrive at the same

time the neuron fires. Once fired, it is easier to again fire when one of the two original inputs arrive.

Thus, in a real sense memories are made in the hippocampus. In relation to the human genome, the
brain is much more complex, and it is controlled by a matrix of activities, including our genome. It
operates on a three-dimensional network rather than a one or two dimension somewhat fl at chromo-

some face. So artificial intelligence has a long way to go to mimic our brain.
It is then a group of genes found on several chromosomes that give us the ability to learn and
retain information and we are just beginning to discover the genome elements responsible for this
wonderful ability.

NH
2
N
N
N
O N
(10.12)
HO P O
O
O
OH
Cyclic AMP

Only vertebrates show an immune response. If foreign objects, called antigens, gain entry into
our bloodstream, a molecular level protection system, called the immune response, goes into action.
This response involves production of proteins capable of recognizing and destroying the antigen.
It is normally mounted by certain white blood cells called the “B” and “T” cell lymphocytes and
macrophages. B cells are called that because they mature in the bone marrow, and T cells mature
in the thymus gland. Antibodies which “recognize” and bind antigens are immunoglobulin proteins
secreted from B cells. Because the antigens can be quite varied from the protein inserted from an
insect bite, to pollen, and so on the number of proteins that can “recognize” and bind this variety
of invaders must be quite large. Nature’s answer to creating such a great host of antibodies is found
in the organization of the immunoglobulin genes that are scattered among multiple gene segments
in germline cells (sperm and eggs). During our development and the formation of B lymphocytes,
these segments are brought together and assembled by DNA rearrangement (genetic recombination)
into complete genes. DNA rearrangement, or gene reorganization, provides a mechanism for cre-
ating a variety of protein isoforms from a limited number of genes. DNA rearrangement occurs in
only a few genes, those encoding the antigen-binding proteins of the immune response—the T cell

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