RNA Polymerase and Promoters

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Questions and Answers

What is a key difference between transcription in eukaryotes and prokaryotes?

The presence of transcription factors

The type of RNA polymerase used

The location of transcription

The complexity of the process (correct)

What is the function of transcription factors in eukaryotic transcription?

To synthesize RNA

To remodel chromatin structure

To translate mRNA

To bind to distinct DNA sequences (correct)

What is the result of chromatin remodeling?

Transcription termination

Decreased gene expression

Altered chromatin structure (correct)

Increased gene expression

What type of chromatin is most actively transcribed genes found in?

Euchromatin Signup and view all the answers

What does RNA polymerase I synthesize?

rRNA precursors Signup and view all the answers

What is the function of RNA polymerase II?

To synthesize mRNA precursors Signup and view all the answers

What is the term for the interconversion of euchromatin and heterochromatin?

Chromatin remodeling Signup and view all the answers

What is a characteristic of RNA polymerases in eukaryotic cells?

Having multiple subunits Signup and view all the answers

What type of RNA is synthesized by RNA polymerase III?

tRNA, 5S rRNA, and some snRNA and snoRNA Signup and view all the answers

What is the function of the CAAT box in gene transcription?

It acts as an enhancer of transcription Signup and view all the answers

What is the effect of α-amanitin on RNA polymerase II?

It inhibits RNA polymerase II Signup and view all the answers

What is the difference between prokaryotic and eukaryotic mRNA?

Prokaryotic mRNA is extensively modified co- and post-transcriptionally Signup and view all the answers

What is the name of the enzyme that synthesizes tRNA, 5S rRNA, and some snRNA and snoRNA?

RNA polymerase III Signup and view all the answers

What is the term for the collection of all primary transcripts synthesized in the nucleus by RNA polymerase II?

Heterogeneous nuclear RNA (hnRNA) Signup and view all the answers

What type of RNA is synthesized by mitochondrial RNA polymerase?

Mitochondrial RNA Signup and view all the answers

What is the term for the process of modifying RNA after transcription?

Post-transcriptional modification Signup and view all the answers

What is the primary function of the 5' cap in eukaryotic mRNA?

To protect the mRNA from degradation Signup and view all the answers

What is the function of polyadenylate polymerase in eukaryotic mRNA processing?

To add a poly-A tail to the mRNA Signup and view all the answers

What is the role of snRNPs in eukaryotic mRNA splicing?

To recognize the splice sites Signup and view all the answers

What type of bond is formed between the 2'-OH group of the adenosine residue and the phosphate at the 5'-end of the intron?

2'→5' phosphodiester bond Signup and view all the answers

What is the estimated percentage of genetic diseases that result from mutations affecting RNA splicing?

15% Signup and view all the answers

What is the function of the branch site in mRNA splicing?

To facilitate the formation of the lariat structure Signup and view all the answers

What is the purpose of the poly-A tail in eukaryotic mRNA?

To increase mRNA stability Signup and view all the answers

What is the outcome of the splicing reaction in eukaryotic mRNA processing?

Removal of introns and joining of exons Signup and view all the answers

Study Notes

Transcription of Eukaryotic Genes

Eukaryotic transcription is more complicated than prokaryotic transcription
Three separate polymerases are involved in eukaryotic transcription: RNA polymerase I, II, and III
Transcription factors (TFs) bind to specific DNA sequences to initiate transcription
Chromatin structure affects transcription; actively transcribed genes are in euchromatin, while inactive genes are in heterochromatin

RNA Polymerases

RNA polymerase I synthesizes precursor rRNA in the nucleolus
RNA polymerase II synthesizes nuclear precursors of mRNA, snoRNA, snRNA, and miRNA
RNA polymerase III synthesizes tRNA, 5S rRNA, and some snRNA and snoRNA

Promoters for RNA Polymerase II

The TATA or Hogness box is a consensus sequence found in some genes transcribed by RNA pol II
The CAAT box is another consensus sequence found in some genes
Enhancers are cis-acting DNA sequences that increase the rate of transcription initiation
RNA polymerase II is inhibited by α-amanitin

Posttranscriptional Modification of RNA

Primary transcripts of eukaryotic RNA and rRNA are modified by cleavage
Eukaryotic mRNA is extensively modified co- and post-transcriptionally

Posttranscriptional Modification of mRNA

The primary transcripts undergo extensive co- and posttranscriptional modification in the nucleus
Modifications include:
- Addition of 5' cap
- Addition of poly-A tail
- Removal of introns

Mechanism of Splicing

Uracil-rich small nuclear RNAs (snRNA) form small nuclear ribonucleoprotein particles (snRNPs) that mediate splicing
snRNPs facilitate removal of introns by forming base pairs with consensus sequences at each end of the introns
The binding of snRNPs brings the sequences of neighboring exons into correct alignment for splicing
The 2'-OH group of an adenosine residue attacks the phosphate at the 5'-end of the intron, forming an unusual 2'→5' phosphodiester bond and creating a "lariat" structure

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Description

This quiz covers the role of RNA polymerase II and III in synthesizing different types of RNA, including small ncRNAs, tRNA, and 5S rRNA. It also explores the promoters for RNA polymerase II, including the TATA box.