Nucleic Acids

Nucleic Acids

Nucleic acids are composed of nucleotides, nucleotides are monomers of nucleic acids, components of other molecules (ATP, GTP etc.)

Nucleotides

are composed of a

1. Pentose sugar: ribose/deoxyribose

2. Phosphate

3. Nitrogenous base: adenosine, thymine, guanine, cytosine, uracil

   A nucleoside is almost the same thing but it doesn’t have a phosphate

DNA

A nucleic acid arranged in a double helix with two strands

1. Template (antisense) strand 3’-5’

2. Coding (sense) strand 5’-3’

   DNA has nucleotides composed of Deoxyribose, Phosphate, Nitrogenous Bases A,T,C,G

Polymerisation

Performed by DNA polymerase

Nucleotides are linked by phosphodiester linkages in backbone

Double helix is linked together by hydrogen bonds between nitrogenous bases

Two hydrogen bonds: A-T, A-U

Three hydrogen bonds: C-G

Location in cell for eukaryotes: nucleus, mitochondrial matrix, chloroplast, stroma

Location in cell for prokaryotes: cytosol

Chargaff’s rules

States that in the DNA of any species and organism, the amount of guanine should be equal to the amount of cytosine and the amount of adenine should be equal to the amount of thymine

A stoichiometric ratio of purine and pyrimidine bases should exist

Nitrogenous Bases

Two families of nitrogenous bases:

1. Purines (2 rings) A and G

2. Pyrimidines (1 ring) C,T and U

   Pyrimidine bonds to purine with hydrogen bonds

RNA

Single stranded polymer consisting of a ribose, phosphate, A,U,C or G

mRNA: used in protein synthesis, synthesised with RNA Polymerase II

tRNA: used to transport AA’s for translation synthesised with RNA Polymerase III

rRNA: ribosomal RNA component of ribosomes, synthesised with RNA Polymerase I