Nucleic Acids

DNA - Deoxyribonucleic Acid

Nucleobases:

Thymine

Cytosine

Adenine

Guanine

RNA - Ribonucleic Acid

Nucleobases:

Cytosine

Guanine

Adenine

Uracil

Nucleotides and Nucleic acids

Nucleic acids contain the elements carbon, hydrogen, oxygen, nitrogen and phosphorus. They are large polymers formed from many nucleotides (the monomers) linked together in a chain.

Each individual nucleotide is made up of three components, a pentose monosaccharide (sugar), containing five carbon atoms. A phosphate group, an inorganic molecule that is acid and negatively charged. A nitrogenous base - a comple organic molecule containing one or two carbon rings in its structure as well as nitrogen.

Nucleotides are linked together by condensation reactions to form a polymer called polynucleotide.

Purines and Pyrimidines

Pyrimidines- The smaller bases, which contain single carbon ring structures - Thymine and Cytosine

Purines- The larger bases, which contain double carbon ring structures - Adenine and Guanine

The Double Helix

- Varies in length from a few nucleotides to millions of nucleotides.

-Made up of two strands of polynucleotides coiled into a helix, kown as the DNA double helix

-The two strands of the double helix are held together by hydrogen bonds between the bases, like steps on a ladder.

-Each strand has a phosphate group at one end and a hydroxyl group at the other.

-Two parallel strands are arranged so that they run in opposite directions, this is known as them being antiparralel.

Base Pairing Rules

Adenine and Thymine always bond together and form two hydrogen bonds.

Guanine and Cytosine always bond together and form three hydrogen bonds.

This is known as complimentary base pairing.

This rule means the smalller pyrimadine base always bonds to the larger purine base. This arrangement maintains the distance between the DNA backbones.

Ribonucleic Acid (RNA)

- Plays an essential role in the transfer of infomation from DNA to the proteins that make up the enzymes and tissues in the body.

- RNA is needed bacause DNA is too long to leave the nucleus.

- A  short section of DNA corresponding to a single gene is transcribed onto a similarly short messenger RNA (mRNA)

- Each individual mRNA is therefore much shorter than the whole chromosome of DNA. It is a polymer composed of many nucleotide monomers.

- RNA - Ribose pentose sugar           - DNA - Deoxyribose pentose sugar

- In RNA the thymine base is replaced with Uracil, like Thymine, Uracil is a pyrimadine that forms two hydrogen bonds with adenine. Therefore the base pairing rules still apply when RNA nucleotides bind to DNA to make copies of the particular part of DNA 

Ribonucleic Acid (RNA) - Continued

- RNA nucleotides form polymers in the same way as DNA nucleotides - by the formation of phosphodiester bonds in condensation reactions.

- Thr RNA polymers are then small enough to leave the nucleus and travel to the ribosomes, where they become a centeral part of protein synthesis.

- After protein synthesis the RNA molecules are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.