Nucleotides and Nucleic acids

Nucleotides and Nucleic acids

Nucleotides are nitrogen containing organic substances wich play a vital role in every espect of an organisms life.Nucleotide molecules occur singly(mononucleotides) or combined in numbers frol two to many thousands(polynucleotides).
Nucleotides are made of three parts:

1. a nuitrogen-containing organic base
2. a five-carbon sugar ( pentose)
3. one or more phosphate groups

ATP is energy to drive reactions.(Adenosine triphosphate or ATP) is a mononucleotide.It is vital because ir the main source of chemical energy. The base is adenine and the sugar is ribose. Attached to the ribose are three phosphate groups.The covalent bond linking the second and third phosphate groups is unstable, and is easily broken by hydrolysis.

When this bond is broken a phosphate group(Pi) is removed, and ATP becomes ADP (adenosibne diphpsphate).Energy is release so it is calle exergonic reaction.This reaction can be reversible because from ADP it can be obtained ATP by resynthesis and the inorganic phosphate by a condensation reaction.(energy for this reaction comes from respiration).

Nucleic acids: DNA

Nucleotides are combined by condensation reactions to form long chains wich are called nucelic acids.DNA plays the key role in inheritance and protein synthesis. The basic structure of DNA seems simple because it is made of only four type of nucleotide.Each DNA nucleotide has a phosphate group, a pentose sugar (deoyribose,and one of four types of base ( all of wich containing nitrogen) adenine, cytosine,guanine or thymine.

DNA FORMS A DOUBLE-HELIX

• The DNA molecule consists of two strands, each of wich is a polynucleotide chain
• Each strand has a helical (spiral) shape, so that DNA has become known as the "double helix"
• The polyunucleotide chains run in opposite directions and are joined by pairs of bases.
• The bases are held together by hydrogen bonds between the hydrogen atoms of a base in one chain and the oxygen and nitrogen atoms of a base in the other chain