Chapter 6 Flashcards
How to define transcription
The process of using the information in DNA to make any type of RNA
Ambisense genome
the genome (ssDNA or ssRNA) is partly plus sense and partly minus sense
Enhancer
a short DNA sequence that binds transcrition facto -> increase the frequency of transcription initiation
Promoter
A specific DNA sequence upstream of a gene -> promote recognition of transcriptional start site by RNA polymerase
Transcription factors
Proteins that bind to enhancer and TATA box (in promoter) to control transcription
Virus-encoded transcriptases
carried in virion or translated before transcription DdRp dsRdRp ssRdRp RdDp (not RNA Pol)
RNA processing
posttranscriptional modification of RNA precursor in nucleus (only in eukaryotes)
- Capping
- Polyadenylation
- Splicing
Capping
Cap: 7-methyl guanosine triphosphate 3 functions i. Protect mRNA from 5’ exonucleases ii. Aid mRNA transport to cytoplasm iii. Promote translation (recruit
Polyadenylation
Most mRNA of eukaryotes and their viruses have poly-A tail
Poly-A tail
30-200 adenine nucleotide
Added to 3’ end
Protect mRNA from 3’ exonucleases
Promote initiation of translation
Splicing
Remove intron-> join exons
“split gene” contains exon and intron
Alternative Splicing
Slice in different ways to produce >1 mRNA
Translation of monocistronic mRNA
Cap acts as the binding site Initiation complex forms "Ribosomal scanning" occurs Anticodon in tRNA reached AUG 60S subunit binds to 40s subunit
IRES
Internal Ribosome Entry Site
Leaky Scanning
Ribosome “overlooks” the start codon of ORF1
translation begins at the start of ORF 2
The 2 ORFs in different reading frames -> 2 unrelated proteins
