Eukaryotic Test 3 Lecture 8

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

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

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

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.