2.2 Nucleic Acid

nucleic acid

A polymer consisting of many nucleotide monomers - for storage, transmission and use of genetic information. The two types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

nucleotide

building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one to three phosphate groups

nucleosides

molecules containing pentose sugar and base but no phosphate group

nitrogenous bases

2 forms - pyrimidine (single ring) and purine (2 rings)

pyrimidines = Cytosine, thymine and uracil

purines = adenine and guanine

phosphodiester bond

type of covalent bond that links nucleotides together by connecting the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another via condensation reaction

complementary base pairings

DNA - thymine+adenine, cytosine+guanine

RNA - uracil+adenine, cytosine+guanine

Formed via hydrogen bonds

RNA

contains ribose sugar and bases adenine, uracil, guanine and cytosine - single-stranded; - used in protein synthesis and as genome of some viruses

DNA

a double-stranded helix, contains deoxyribose sugar and bases adenine, cytosine, guanine and thymine - can be replicated and determines the structure of proteins

The 2 strands run in opposite directions = antiparallel

2 ways genetic information is transmitted

DNA replication - polymerisation using an existing strand as a base-pairing template

transcription - certain sequences can be copied by RNA and then used to specify a sequence of amino acids in peptide chain = translation (transcription+translation = gene expression)

genome

complete set of DNA in living organisms

genes

segments of DNA that encode functional products, typically proteins

How does DNA base sequences reveal evolutionary relationships

over long time changes occur in base sequence = closely related species have more similar base sequences than ones more distantly related

nucleoside strand names

DNA: adenine = deoxyadenosine, cytosine = deoxycytidine, guanine=deoxyguanosine, thymine = deoxythymidine

RNA: adenine = adenosine, cytosine = cytidine, guanine = guanosine, uracil = uridine

DNA and RNA direction is often described as 5’ to 3’. What do the “5” and “3” refer to?

refer to the carbon atoms in sugars in nucleic acids. The "5' end has phosphate group attached to the fifth carbon, and 3’ has hydroxyl (-OH) attached to third carbon