DNA and RNA

Introduction

The discovery of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) had profound effects on molecular biology, medicine, and living standards.   DNA is the building block of the life because it contains the information the cell requires to synthesize protein and to replicate itself; that is, it is the repository for the information that is required for any cell to function.   It has a double-helix structure with 4 nucleotide bases: Adenine (A), Guanine (G), Thymine (T) and Cytosine(C).   A DNA molecule has a sequence of these bases, such as, ATTGCTGAAGGTGCGG.   Each base has its complementary base, which means in the double helical structure of DNA, A will have T as its complementary and G will have C.   The DNA is broken down into bits and is tightly wound into coils, which are called chromosomes; humans have 23 pairs of chromosomes. These chromosomes are further broken down into smaller pieces of code called genes.   The 23 pairs of chromosomes consist of about 70,000 working genes, each with a function (other "junk" genes have no apparent function).   Determining the arrangement of the bases is called DNA sequencing.   A typical sequence would look be, ATTTGCTGACCTG. ^{Bio n.p.}

Determining the gene's functionality and position of the gene in the chromosome is called gene mapping.   A change in the genetic code it is called a mutation.   The gene's sequence is a chemical language that instructs cell to manufacture a particular protein.   An intermediate language, encoded in the sequence of Ribonucleic Acid (RNA), translates a gene's message into a protein's amino acid sequence.   It is the protein that determines the trait.   RNA is somewhat similar to DNA in that they both are nucleic acids of nitrogen-containing bases joined by sugar-phosphate backbone.   However, structural and functional differences distinguish RNA from DNA.   Structurally, RNA is single-stranded where as DNA is double stranded.   DNA has Thymine, where as RNA has Uracil.   RNA nucleotides include sugar ribose, rather than the Deoxyribose that is part of DNA.   Functionally, DNA maintains the protein-encoding information, whereas RNA uses the information to enable the cell to synthesize the particular protein. ^{Bio n.p.}

Transcription is the process of making an RNA strand from a DNA template, and the RNA molecule that is made is called transcript.   In the synthesis of proteins, there are three types of RNA that participate and play different roles:

a. Messenger RNA (mRNA), which carries the genetic information from DNA and is used as a template for protein synthesis.

b. Ribosomal RNA (rRNA), which is a major constituent of the cellular particles called ribosomes on which protein synthesis actually takes place.

c. A set of transfer RNA (tRNA) molecules, each of which incorporates a particular amino acid subunit into the growing protein when it recognizes a specific group of three adjacent bases in the mRNA.

DNA maintains genetic information in the nucleus.   RNA takes that information into the cytoplasm, where the cell uses it to construct specific proteins.   RNA synthesis is transcription, while protein synthesis is translation. ^{Bio n.p.}

To 1899

In the late nineteenth century, a German biochemist found the nucleic acids, long-chain polymers of nucleotides, were made up of sugar, phosphoric acid, and several nitrogen-containing bases. Later it was found that the sugar in nucleic acid can be ribose or deoxyribose, giving two forms: RNA and DNA. ^{PBS n.p.}

1900-1909

1910-1919

1920-1929

1930-1939

1940-1949

In 1943, an American chemist, Oswald Avery, proved that DNA carries genetic information.   He suggested DNA might actually be the gene.   Most people at the time thought the gene would be protein, not nucleic acid, but by the late 1940s, DNA was largely accepted as the genetic molecule.   Scientists still needed to figure out this molecule's structure to be sure, and to understand how it worked. ^{PBS n.p.}

In 1948, an American chemist, Linus Pauling, discovered that many proteins take the shape of an alpha helix, spiraled like a spring coil. ^{PBS n.p.}

1950-1959

In 1950, biochemist Erwin Chargaff found that the arrangement of nitrogen bases in DNA varied widely, but the amount of certain bases always occurred in a one-to-one ratio. ^{PBS n.p.}

James Watson, Francis Crick, and Maurice Wilkins, using the x-ray diffraction photographs of Rosalind Franklin, discovered the structure of DNA in 1953.

1960-1969

1970-1979

1980-1989

1990-1999