DNA is an abbreviation for

deoxyribonucleic acid .

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*It is formed in the cells of all living things ,including the human body .

*The DNA is a very long molecule and is found in the nucleus of

cells

DNA consists of three basic components:

A . A sugar (pentose sugar) ~ dexoyribose which is oxygen less of the ribose sugar

B. Phosphate group ~ chemically

reactive

C. Organic nitrogenous base ~ 4types of nitrogenous base, 2 purines and 2 pyrimidines ~ purines consists of adenine (A) and Guanine(G)~ pyrimidines consist of cytomsine(C) and thymine

(T)

In 1962, James Watson (from America) and

Francis Crick (from Britain) discovered the structure of DNA.

They were awarded a Nobel Prize.

(A) The sequence of bases in DNA provides the genetic code to give information to contr

ol the cell activities and is specific to each species.

(B) The complementary relationship of the bases in the DNA molecule enables the DNA to replicate (make an exact copy) so that the same genetic information can be passed to the offspring.

The type of protein and enzyme is characteristic of a species of organism.

Chromosomes are made up of proteins (e.g.histones) and nucleic acid (DNA and RNA). The nucleic acids carry the genetic code or genetic

formation.

Some interesting information about DNA

Genetic engineering is an unnatural insertion of a foreign sequence of genetic codes

in the midst of the orderly sequence of genetic codes of the recipient, developed through millions of years.

Cloning is one aspect of genetic engineering, the

part that allows scientists to use a variety of methods to duplicate copies of already existing organisms or genetic material.

But the term "genetic engineering" is much broader, encompassing a wide range of procedures designed to alter genetic material, not only copying genes, but in some cases, making completely new proteins.

Introduce the mutations of DNA:

(1) Chromosome mutationsinvolve changes in the number of

chromosomes per cell or changes in the gross structure of a chromosome.

These changes are generally observable under the microscope.

(2) Gene mutations involve the chemical changes in an individual gene and they cannot be seen under the microscope.

(1) Induced mutation can be induced artificially to occur at a higher rate by applying mutagenic agents (mutagens ). For example:

(a) Chemical mutagens - nitrous acids, base analogues, mustard gas, ethyl urethane formaldehyde. (b) Physical mutagens - X rays, ultra-violet rays, cosmicrays atomic radiation.

(E) Changes involve in the addition or loss of (E) Changes involve in the addition or loss of one or more chromosomes.one or more chromosomes. 

(a) If change in the addition of one or more chromosomes, mongolism in

man is caused by the presence of one extra piece of the 21st

chromosome in the cell. Such

individuals have abnormalities

of the face, Eye-lids and tongue

are mentally retarded. >>>>>THE END<<<<<