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Lecture 32: Transcription (Types of RNA: (ribosomal (rRNA): translation,…
Lecture 32: Transcription
Eukaryotes: mRNA manufactured inside nucleus; translation occurs in cytoplasm
Prokaryotes: Everything in cytoplasm
Transcription and Translation occur simulatenously
Differences between RNA and DNA
SIngle stranded
Many different types w/ different functions
Ribose instead of deoxyribose, uracil instead of thymine
Synthesized from discrete regions of the genome
Types of RNA:
ribosomal (rRNA): translation
small nuclear (snRNA): splicing
transfer (tRNA): translation
micro (miRNA): regulatory
messenger (mRNA): protein coding
long noncoding (lncRNA): regulatory
Just in Archaea:
RNA Transcription
Begins at promoter (determines template strand & transcription orientation), ends at terminator in prokaryotes, poly-A in eukaryotes
Pre-mRNA is before introns are removed
Regulators of transcription:
RNA polymerases (I-III)
General (core) transcription factors
Mediator complex
Cell- and tissue-specific transcription factors
RNA polymerase II initiation
TATA box at beginning of promoter
TATA-binding protein & other general transcription factors help polymerase find promoter
Activators bind to enhancers
DNA-binding protein causes strand to bend
Activators bind to group of mediator proteins, which binds to bundle of transcription factors
Primary mRNA modification
5' UTR
Protein-coding Region
5' cap (triphosphate with modified guanine at end)
This cap needed for mRNA export from nucleus & ribosome binding (recognition signal for initiation of translation)
3' UTR (Polyadenylation Signal) (AAUAAA)
In order of 5' to 3':
Start Codon- only needed for translation
Stop codon- only needed for translation
50-250 A's at 3' end (Poly-A tail)
Important for nuclear export, increases mRNA stability & aids in translation initiation
3 Ways pre-mRNA is modified:
Addition of 5' cap
Addition of 3' tail
RNA Splicing (removal of introns)
In bacteria, only 1 RNA polymerase
RNA Polymerase I
rRNA
RNA Polymerase III
tRNA, snRNA
RNA Polymerase II
mRNA, snRNA, miRNA, lncRNA
Eukaryotic mRNA splicing
Spliceosome, which contains snRNAs, cut out introns
Template Strand is used to make mRNA; Coding strand is complimentary
Housekeeping Gene: Products are needed at all times, so transcription is continuous
Sigma factors mediate promoter recognition