NUCLEIC ACIDS

NUCLEOTIDE BUILDING BLOCK

 Nucleoside

 Nucleotide

 DNA sugar

 Nucleoside =

nitrogenous base + sugar.

 Nucleotide =

nucleoside + phosphate.

 DNA sugar =

RNA sugar =

deoxyribose;

ribose.

DNA primary =

base sequence;

DNA secondary =

helix;

higher organization = chromatin/packing.

B-DNA =

A-DNA =

common right-handed form;

Z-DNA =

left-handed.

Unwinding

Helicase separates strands.

Priming

Primase lays RNA primer.

Elongation

DNA polymerase adds nucleotides 5' -> 3'.

Termination –

stop codon: UAG, UGA, UAA

Lagging strand

Okazaki fragments are joined by DNA ligase.

Proofreading

DNA polymerase contributes proofreading functions in the source.

TRANSCRIPTION

 DNA template -> RNA.

 RNA polymerase synthesizes RNA.

 post-transcriptional modifications before protein synthesis.

TRANSLATION

 Ribosome reads mRNA codons and builds a polypeptide.

 Start codon:

 Stop codons

AUG (methionine).

terminate translation;

Codon

Rule

3 nucleotides

AUG

Rule

Methionine/start

Degeneracy

Rule

More than one codon can specify an amino acid.

Reading frame

Rule

Triplet-by-triplet reading of mRNA.

WOBBLE –

the ability of certain anticodon to pair with codons that differ at the third base

WOBBLE HYPOTHESIS –

concept by which a tRNA can recognize more than one codon for a specific AA by allowing movement in the first base of the anticodon

MUTATIONS –

unwanted changes in the DNA sequence

POINT MUTATION –

there is substitution of a single base

Transition –

same chemical class;

purine replaced by purine;

pyrimidine replaced by pyrimidine

Transversion –

different chemical class;

purine is replaced by a pyrimidine base and vice versa

FRAMESHIFT –

due to addition or removal/deletion of bases

Silent –

results to still the same AA •

Missense –

different AA •

Nonsense –

results in stop codon