Basic Biology
Everyone’s uniqueness and individuality depends on the interaction of the many chemical
structures found inside our cells. To make genetic engineering possible, scientists need to learn
about such things as chromosomes, genes, and DNA (deoxyribonucleic acid). Along with the
DNA, the genes and inheritance of the living organism needs to be known and understood in
order to modify the current DNA. One more factor that is important in genetic engineering is the
function of enzymes.
DNA
Discovery
In 1869, the first discovery of chemical DNA occurred. However, the use of DNA in genetic
inheritance was not suggested until 1943. After much experimentation with model building,
James Watson and Francis Crick found the structure of DNA to be a double-helix polymer in
1953, meaning two strands of DNA wound on each other creating a spiral.
DNA Structure
Each and every DNA molecule is made up of thousands of
nucleotides. A nucleotide has three parts:



A five-carbon sugar, deoxyribose
Phosphate
A nitrogen base (ex. adenine, thymine, guanine, or cytosine)
Since there are four different nitrogen bases, there are four types of DNA nucleotides. The
nucleotides are arranged and known by the DNA model made by James Watson and Francis
Crick. The order of the bases in a strand of DNA determines the genetic code. This genetic code
is found to be the same in most species and any differences are rare.
DNA molecules have patterns that are constant and may act as the guide of the new duplicated
DNA molecules. Each segment in DNA is a code for the cell’s making of a specific protein,
which is called a gene. Each person’s DNA contains 80,000 to 100,000 genes.
Chromosomes are what the dense protein-DNA complexes are called when DNA is organized
inside a cell. There are two types of cells. One being the eukaryotes and the other is prokaryotes.
In eukaryotes, the membrane-bound cell nucleus holds the chromosomes with DNA attached to
the protein core. While in prokaryotes, the DNA contains the chromosomes because prokaryotic
cells do not enclose single chromosomes into a nuclear membrane. However, some prokaryotes
and few eukaryotes have plasmids. Plasmids are extrachromosomal DNA, which are
independent, self-replicating genetic material. These useful plasmids have been a help in
recombinant DNA technology to study gene expression.
Genes and Inheritance
Genes
A gene is the basic unit of heredity. It is made up of a certain sequence
of DNA or RNA. Genes occupy a fixed position on a chromosome. What genes do to help the
body is by directing the synthesis, formation of chemical compounds, of proteins. In a species,
the genes control the kind of enzymes it produces.
Heredity
Heredity is the passing on of gene factors from one generation to the next. These gene factors are
also known as traits. The passing of traits determines certain characteristics the receiving plant or
animal inherits. The chromosomes in the nucleus of cells break down into smaller units called
genes. Genes contain the hereditary “code.” Every species of plants and animals carry a certain
number chromosomes, which travel in pairs.
There are some traits that are inherited no matter who the plants and animals received it from.
However, there are certain traits in plants and animals that could affect the way it functions or
grows. The possible characteristics plants could inherit can affect their physical and metabolic
processes. On the other hand, animals can inherit behavior, mental, and physical traits.
On the down side, heredity is the cause of many human diseases and disorders. A single defect in
a gene can cause a problem and a disorder characteristic can spread. Other problems can be from
a defective gene in sex chromosomes, structural defects in the number of chromosomes being
more or less than normal, and interaction of genes with drugs, radiation, vitamin deficiency, or
viruses.
In 1866, Austrian monk Gregor Mendel had came up with basic laws of heredity after his
crossbreeding experiments with pea plants. His work became the foundation of modern genetics.
The basic laws of heredity are:




Heredity factors do not mix but remain segregated
Some factors are dominant and others are recessive
A species of the parental generation pass on half of its hereditary factors to each offspring
Different offspring of the same parents receive different sets of hereditary factors
Enzymes
Introduction
the digestive tract, which uses enzymes to help break down food
An enzyme is a protein that is developed by the body to increase a certain chemical reaction in
the body. The breaking down or building up of molecules is in the power of enzymes. Enzymes
act on molecules that are called substrates. A substrate is a surface on which an organism grows
or is attached. Along with that, enzymes are catalysts, which is a substance that verifies and
increases the rate of a reaction without being changed itself in the process. There are many types
of enzymes and to identify them simply, they are categorized into six groups based on their
functions. The categories are:
 Hydrolases - spilt their substrates with the aid of water
 Lyases - spilt their substrates without aid
 Transferases - transfer chemical groups between different molecules
 Isomerases - rearrange the molecules of their substrates
 Oxidoreductases - transfer hydrogen ions
 Ligases(synthetases) - help release energy
Uses
Both animals and plants have enzymes to help them live. In animals, enzymes are used to help
with the digestion system. The enzymes break the foods down into smaller pieces so that the
body can easily absorb them. The uses of enzymes in plants are in the process of photosynthesis.
These enzymes help plants receive their food from the sunlight. Since enzymes specialize in
digestion, the oxidation of the individual cell of a plant or animal releases energy from the
digested food. With this process, enzymes are also helping plants and animals obtain energy.
Discoveries
Later on in the 1980s, it was discovered that enzymes could be replaced with RNA (ribonucleic
acid) molecules or antibodies. These two replacements were unassociated with enzymes, but
could be generated to act like one.
The 1989 Nobel Prize for chemistry was awarded to Americans Sidney Altman and Thomas R.
Cech for discovery of ribozymes being able to cut and merge themselves. Ribozymes are
catalytic RNA molecules.
Researchers in California uncovered an imposter enzyme and named them abzymes. These
abzymes are antibodies that act like enzymes and are able to increase reactions in the human
body.
Another discovery of enzymes that took place in a Canadian biotechnology firm in 1988
consisted of secluding two new enzymes of the cyclodextrin glycosyltransferase kind. The
researchers at the firm concluded that the enzymes are able to remain constant at very high
temperatures.
Sources:






Bleifeld, Maurice. How to Prepare for the SAT II Biology E/M. Hauppauge, New York:
Barron's Educational Series, 2002.
"Chromosome." Encyclopædia Britannica. 2004. Encyclopædia Britannica Online. 28
July 2004 < http://search.eb.com/eb/article?eu=84635>.
"DNA." Encyclopædia Britannica. 2004. Encyclopædia Britannica Online.
19 July 2004 < http://search.eb.com/eb/article?eu=31232>.
“DNA.” WebMD. 2004. MSN Health. 19 July 2004 <
http://content.health.msn.com/hw/health_guide_atoz/std120898.asp?navbar=hw4439>.
"Enzyme." Britannica Student Encyclopedia. 2004. Encyclopædia Britannica Online. 29
July 2004 < http://search.eb.com/ebi/article?eu=296056>.
Farabee, M.J. "Introduction: The Nature of Science and Biology." On-Line Biology
Book. 2002. Estrella Mountain Community Coll. 28 July 2004
<http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookintro.html>.


"Gene." Encyclopædia Britannica. 2004. Encyclopædia Britannica Online.
29 July 2004 < http://search.eb.com/eb/article?eu=37053>.
"Heredity." Britannica Student Encyclopedia. 2004. Encyclopædia Britannica Online.
28 July 2004 < http://search.eb.com/ebi/article?eu=296772>.
Image Sources:




http://www.eufic.org/gb/heal/img/food08_img03.gif
http://www.chadevans.co.uk/gcsebiology/images/imagesm2/XY%20+%20XX%20genes.
gif
http://www.alzheimers.org/unraveling/images/large/DNA-HIGH.jpg
http://www.creationfoundation.co.uk/genes.gif