7. DNA, RNA and genes Flashcards
polynucleotide structure
phosphodiester bond has polarity- assymetric
directionality is 5’->3’
any polynucleotide has polarity
DNA double helix
anti parallel chains
bases on inside, sugar and phosphate outside
which forces hold DNA double helix
hydrogen bonding between bp
hydrophobic stacking forces
DNA replication is…
semi conservative
sequence of bases
genetic code
phenotype
expressed information
unit of DNA function
gene
DNA-dependent DNA polymerase
- All four deoxynucleotide triphosphates are needed. (dAMP · dGMP · dTMP · dUMP · dCMP)
- DNA synthesis requires an RNA primer.
why can DNA replication be a target for drugs
- Eukaryotic DNA replication does not require DNA gyrase (inhibitors can be used as anti- bacterial therapy)
- Eukaryotic DNA replication requires topoisomerase enzymes (inhibitors can be used for chemotherapy)
- Bacteria make folic acid.
- Synthesis of tetrahydrofolate essential for DNA replication (anti-cancer)
RNA species in eukaryotic cells
– mRNA – hnRNA – tRNA – rRNA – 7S RNA – snRNA
which RNA species is most abundant in eukaryotic cells
rRNA
RNA in vivo is highly structured
the precursor to mRNA
hnRNA
- contains non-coding intron sequences
- processed after transcription to yield mature mRNA
- introns within hnRNA are removed by splicing
features an mRNA contains
– 5’ cap – 5’ and 3' UTR – Ribosome Binding Site (RBS) or Kozak sequence – Start/initiation codon – Coding sequence/open reading frame (ORF) – Termination/stop codon – poly(A) addition consensus signal – poly(A) tail
5’ cap on eukaryotic mRNA
- Unusual 5’->5’ triphosphate linkage.
- Added post-transcriptionally.
- Important for translation.
UTR=
untranslated region
• Eukaryotic mRNAs carry both 5’ and 3’ UTRs.
• UTRs carry important information affecting translation and mRNA stability.
UTR mutation causes human disease
RBS (shine-dalgarno sequence)
– consensus: AGGAGG
– spacing with respect to AUG critical
– specific to bacterial mRNAs only
Kozak sequence
– consensus: RccRccAUGG
– positions -3 and +4 critical
3’ tail
• Tail added post-transcriptionally.
• Tail is a non-template-directed polymer of A residues known as a poly(A) tail.
• Tail addition requires consensus sequence.
– AAUAAA
How is transcription termination achieved
cleavage of nascent hnRNA
Function of Poly(A) tail
aids if efficient nucleocytoplasmic transport
regulates mRNA stability and translation
