NUCLEIC ACIDS
· Genetic Information
DNA (storage) → RNA (messages/function) → protein (structure/function)
Deoxyribonucleic acid (DNA)
· deoxyribose sugar
· mostly double stranded (double helix)
· has thymine instead of uracil
· very stable
Ribonucleic acid (RNA)
· ribose sugar
· mostly single stranded
· has uracil instead of thymine
· easily degraded
Nucleotides
· Monomer subunit used to build DNA and RNA
· All nucleotides are composed of a:
o phosphate group
o pentose sugar
o nitrogenous base
· DNA and RNA polymers (strands) are built by forming covalent bonds between the 5’-phosphate of one nucleotide and the 3’ carbon of the sugar on the adjacent nucleotide
· Condensation reaction forms a phosphodiester bond
· DNA consists of 2 chains of nucleotides that spiral on an imaginary axis to form a double helix
o Strands run in opposite directions - antiparallel
o (5’ – 3’ coding strand and 3’ – 5’ complementary strand)
o
· The two strands of DNA are held together by H- bonds between the base pairs (nitrogenous bases on adjacent strands)
· There are five different nitrogenous bases, therefore, five different nucleotides
· The nitrogenous bases can be divided into two families, purines and pyrimidines
Purines (double rings)
Pyrimidine (single rings)
· Each base pair consists of one purine and one pyrimidine
o Adenine always bonds with thymine with two H-bonds
o Guanine always bonds with cytosine with three H-bonds
o A=T requires less energy to separate than G=C
· During DNA replication, DNA strands come apart and each acts as a template to synthesize complementary DNA molecules
· Structure of DNA is ideally suited to its function:
o encodes information
o super stable
o replicates easily – anti-parallel
o conservative replication but mutates due to imperfect replication (allows evolution).
ATP – Adenosine triphosphate (ATP)
· Nucleotide that acts as the primary energy-transferring molecule in living organisms
· Also ADP (diphosphate) , AMP (monophosphate)