Eukaryotic Test 3 Lecture 8
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Messenger RNAs (mRNAs): RNAs that include mucleotic code info for polypeptide synthesis
Ribosomal RNAs (rRNA): RNA components of ribosomes
Transfer RNAs (tRNAS): RNAs that translate the info in the mRNA nucleotide code into AA order of a polypeptide
Other RNAs: snRNA, snoRNA, siRNA, miRNA
DNA-dependent RNA polymerase (RNA polymerases): Enzymes responsible for transcription in both pro- & eukaryotic
Template: DNA strand whose sequence is complementary to RNA molecule synthesized from it
Promoter: the site on DNA to which an RNA polymerase molecule binds prior to initiating transcription
Transcription factors: Proteins that are required to help RNA polymerases to recognize promoters
Transcription in Prokaryotes
A single type of RNA polymerase composed of 5 subunits that are tightly associated to form a core enzyme
Core enzyme can attach to random sites in the DNA to synthesize RNA
Sigma factor: Accessory polypeptide that increases core enzyme's affinity for promoter sites and decreases its affinity for DNA
Complete Enzyme (holoenzyme): Associates w/DNA at proper sites and initiates RNA synthesis
Once 10-12 nt are incorporated into a growing transcript, enzyme will be transformed into a transcriptional elongation complex, followed by release of sigma factor
Transcription and RNA processing in eukaryotic cells
RNA Polymerase I: Synthesizes larger ribosomal RNAs
RNA Polymerase II: Synthesizes mRNA and most small nuclear RNAs
RNA Pol. III: synthesizes various low-molecular-weight RNAs including TRANSFER RNAS
More than 80% of RNA in most cells consists of rRNA
rRNAs and dozens of ribosomal proteins form ribosomes.
Nucleoli Function in producing ribosomes
Bulk of nucleolus is composed of ribosomal subunits that give nucleolus a granular appearance
- Fc: Contains rDNA
- dFC: Contains nascent pre-RNA transcripts and associated proteins
- GC: Contains ribosomal subunits in various stages of assembly
Modifications of pre-RNAs (19)
100's of methyl gropus are addeds to ribose groups and 95+ Uridine residues are chemically convereted to pseudouridine by the time pre-RNA is 1st cleaved.
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