A nucleoside is a nitrogen base and a pentose sugar. Most anti-cancer drugs are nucleoside analogs. A nucleotide is a nucleoside plus phosphate joined at pentose sugar; nucleotides are the building blocks of RNA and DNA. Also, nucleotides serve as the medium of energy exchange inside the cell, most commonly in the form of ATP or Adenosine Triphosphate. ATP is a ribose nucleotide which stores energy from catabolic metabolism in this high energy phosphate bonds.

Deoxyribonucleic acids are polynucleotide chains formed by joining together deoxyribose nucleotides with phosphodiester bonds between the 5'-hydroxyl and the 3'-hydroxyl groups on adjacent deoxyriboses. By convention, the sequence of DNA is written from the free 5' end of the molecule to the free 3'-hydroxyl end. DNA encodes instructions which comprise the genetic code. Ribose is converted to deoxyribose by the enzyme ribonucleotide reductase. This enzyme insures that the amount of Adenine will be equivalent to Thymine, and Guanine equivalent to Cytosine. The following are the characteristics of the structure of a DNA:

• It has a Double Helix, except in some viruses like Parvoviruses which is single.
• It has 2 anti parallel polynucleotide chains one strand running 5'-3', held together by complementary base pairing.
• It is contained in the cytoplasm of prokaryotes.
• It is contained in the nucleus of eukaryotes.
• The middle of the helix is held together by hydrogen bonds.
• It is mildly acidic.
• Mitochondria have their own DNA.
• Has 3' to 5' phosphodiester bonds which hook the nucleotides together.
• Most of its proteins bind in the major grooves and not the minor grooves.

There are three types of Double Helix. A "B" form helix is a right-handed helix with 10.5 base pairs per turn. An "A" form helix is a right-handed helix with 11 base pairs per turn and is formed by dehydrating the "B" form helix. A "Z" form helix is a left-handed helix with 12 pairs per turn occurs in small sections of Deoxyribonucleic Acid. It has an alternating anti- and syn - glycosidic bond conformation.

Ribonucleic acids contain ribose nucleotides and the nitrogen base Uracil instead of Thymine. It is involved with carrying out the instructions encoded for by DNA. The pentose phosphate pathway makes ribose. The 2' Hydroxyl group can be ionized; therefore, Ribonucleic Acid is less stable than the Deoxyribonucleic Acid.

Nitrogen bases form complementary base pairs by hydrogen bonding between one purine and one pyrimidine. Base pairing can hold 2 different polynucleotides together. The sum of the purines is equal to the pyrimidines. The Charkof's Rule is Adenine = Thymidine and Guanine = Cytosine, so as long as you know one of the values, you can calculate the other three. In humans, 30% is Adenine and 30% is therefore Thymidine. Twenty percent is Guanine and 20% is therefore Cytosine, for a total of 100% of bases. Guanine only pairs with cytosine bonded by three hydrogen bonds. Adenine pairs with a thymine from DNA, or a uracil from RNA bonded by two hydrogen bonds. The more G-C bonds between the two strands of double stranded DNA, the more they are stabilized. This will increase the melting point at which the two strands will separate.

Nucleases are enzymes which hydrolyze phosphodiester bonds. An Exonuclease cleaves nucleotides from the end of a polynucleotide chain. An Endonuclease breaks polynucleotide by cleaving at nucleotides inside of the chain. There are also the so called Restriction Endonucleases. These are enzymes, produced by bacteria and viruses, which recognize and cleave at short specific sequences of a polynucleotide called palindromes. These enzymes are used in genetic engineering. They are bacterial defense mechanisims used to fend off an invading DNA. They protect by the process of methylation.

A Palindrome is a short series of nucleotides which has the same sequence as its complementary strand and is read from 5' to 3'. It can be read the same in either direction like this example: 5'-GAATTC-3' " 3'-CTTAAG-5'. These series of nucleotides reads the same in the 5' to 3' direction, GAATTC. An EcoR I restriction site can allow cleavage and re-alignment with other genes to clone and express genes.

The nucleic acids are one the smallest particles inside our bodies. These are also the most important components of a living organism. Thanks to Molecular biology, these very important structures can be studied and enables us to discover more about these nucleic acids.

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