nucleic acids Flashcards
define nucleic acids
large polymeric molecules:
- limited number of repeating units that are covalently linked to form long chains
difference between RNA and DNA
RNA: ribonucleic acid (most abundant, several functions, extremely unstable - hydrolyses quickly)
DNA: deoxyribonucleic acid (storage genetic information)
what is a nucleotide?
- basic components of DNA and RNA
- energy currency (ATP)
- hormone-like functions (cAMP) in regulation of metabolism
- components of coenzymes
what are the main components of nucleotides?
one or more phosphate groups (3’ or 5’), strong acid
- more phosphates can be linked together via phosphoanhydric bonds
ribose or deoxyribose
nitrogenous base (heterocyclic compound with nitrogen with basic properties) linked to C1 atom via beta-N-glycosidic linkage
biological nucleotides
pentose D-ribose
DNA
pentose D-2’-deoxyribose
nucleosides and the work of adenosine
breakdown and synthesis intermediate of nucleotides and nucleic acids
- no phosphate ester (ribose/deoxyribose + base)
- found in metabolism reactions
- ex. adenosine -> neurotransmitter regulating sleep/wake cycle binding to specific neuronal adenosine receptors
- adenosine levels increase during the day and decrease during sleep
- when bound to receptor induces sleep
- antagonist of adenosine: caffeine (natural alkaloid found in plants) binds to receptor without activating it
properties of nitrogenous bases
- planar
- aromatic
- heterocyclic derived from purine/pyrimidine
- acidity: phosphate groups are ionised, first ionisation is strong ad following are less acidic due to charge repulsion (more negative charges)
describe the bond in nitrogenous bases
high energy phosphoanhydric bonds -> hydrolysis releases -31 kJ/mol
- anhydride bonds causes high energy
- ATP reacts with water in presence of Mg+ (acts as catalist) -> free phosphate groups can stabilise the charge by resonance, creating low energy compounds
mechanism of polymerisation
- each nucleotide has free phosphoric acid functional group and 1/2 alcohol functions (-OH)
- acids and alcohols can condense to form esters and release water to create oligonucleotides (many nucleotides linked together)
- delta G-> +25 kJ/mol- unfavourable in aqueous solutions
- can be synthesised through activation of individual nucleotides
oligonucleotides
- linked through phosphodiester bonds between 3’ hydroxyl of nucleotides N and the 5’ phosphate of nucleotide N+1
- 5’ to 3’ polarity of chain -> looking in 5’ to 3’ direction atoms are different than 3’ to 5’ direction
- primary structure: sequence of nucleotides linked by phosphodiester bonds -> sequence nitrogenous bases
- can be synthesised in lab
structure of DNA
winds as double helix (2 chains)
- right handed (due to chirality)
the two chains have opposite polarity -> one is 5’->3’ the other 3’->5’
- backbone is deoxyribose+phosphate groups, outside of molecule (exposed to water since phosphate fives hydrophobic properties)
- bases are inside the structure (shielded from solvent)
- interact through N bonds (A-T, G-C)
- sequence is not restricted (can be changed and adapted to carry genetic information without changing overall structure)
base pairing in DNA
- carry genetic information
- double helix allows for semi-conservative replication
- one filament is template for synthesis of the opposite
- bases inside the helix are paired with specific hydrogen bonding pattern
- A–T (2H bonds)
- G—C (3H bonds)
biological synthesis of DNA
- condensation of 2 nucleotides is disfavoured by the positive free-energy variation between reactants and products
- use of (deoxy)nucleotides triosphates
- anhydrid is used as it is more reactive
- ergonic reaction that releases energy
structure and synthesis of RNA
- pentose
- bases A U G C can be modified after synthesis of nucleic acid
- mostly single-stranded but forms helix structures by pairing different parts of same molecule (fold other making H bonds)
- genetic material for viruses
- high turnover in cells -> easily hydrolysed in process catalysed by ribonuclease
- synthesis in most organisms is catalysed by DNA-dependent RNA polymerase
