Nucleic Acids

Nucleotides are the monomers (single unit) for Nucleic acids (many units of nucleotides).

They contain the elements: Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorus.

A Nucleotide is made up of:

• A pentose monosaccharide
• A phosphate group (inorganic molecule, negative charge)
• A nitrogenous base

Nucletides are joined together by condensation reactions forming polynucleotides. They can be broken using hydrolysis reactions. 

The third carbon bonds to a phosphate group of another nucleotide which is on the fifth caron of the pentose sugar. These bonds are called phosphodiester bonds.

the polynucleotide forms a sugar backbone with one base attached to each pentose ring.

DNA uses doexyribose as the sugar in its nucleotides, nucleotides can have 4 different bases.The different bases are categorised into Purines and Pyrimidines.

Purines are larger and contain double carbon ring structures. Bases A and G are purines.Pyrimidines are smaller and contain single carbon ring structures. Bases C and T and pyrimidines.it is easy to remeber as purines is the large group but has a shorter name.

The DNA double helix is made up of two polynucleotide strands, the strands are joined together by hydrogen bonds between bases. The two strands run in opposite directions (one facing up and one facing down) they are refered to as antiparallel.

The A and T bases form 2 hydrogen bonds whilst C and T form 3 so A will only bond to T and C will only bond to G. this is called complementary base pairing. this ensures a small and large base always pair so the helix is parallel.

The sequence of bases carry genetic info in a code form. the sequence codes for amino acids to make diffrent proteins.

DNA is a long molecule that is too large to leave the nuclues. so to copy and transfer information a short section of the DNA that codes for a gene into a short mRNA molecule.

RNA nucleotides have a ribose sugar for the pentose ring and the base T is replaced with U but U still forms 2 hydrogen bonds and is a small single carbon ring just like T.

the RNA polymers are small enough to leave the nucleus and travel to ribosomes to be used in protein synthesis. After protein synthesis, RNA polymers are hydrolysed and the RNA nucleotides can be reused.

• double helix unwinds
• DNA helicase begins to seperate the two strands at their bases by braking the hydrogen bonds
• whilst the splitting of the strand continues activated, free nucleotides are attracted to their complementay bases
• when nucleotides are lined up they are joined together using DNA polymerase to form new hydrogen bonds
• all the nucleotides are joined to form a polynucleotide chain using DNA polymerase

Two identical DNA strands have been formed and each molecule of DNA is composed of the originl strand and a new strand. hence the name, semiconservative replication.