Types and Functions of RNA

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Questions and Answers

What is the function of RNA polymerase during transcription?

Catalyzes phosphodiester bond formation between rNTPs (correct)

Synthesizes RNA in a 3′→5′ direction

Separates the RNA strands after synthesis

Releases ATP for energy during transcription

Which statement correctly describes the transcription bubble?

It involves approximately 8–10 base pairs of DNA

It is created when the DNA strands are separated around the transcription start site (correct)

It is the area where RNA polymerase dissociates from the DNA

It is where the nascent RNA strand is fully synthesized

What denotes the 'downstream' direction in transcription?

The sequence of rNTPs added to the growing RNA strand

The area where RNA synthesis begins

The 5′ end of the RNA strand being synthesized

The direction where RNA polymerase moves during transcription (correct)

What does the term 'upstream' indicate in the context of transcription?

The direction opposite to which RNA polymerase moves Signup and view all the answers

What is the maximum rate of RNA synthesis by RNA polymerase at 37°C?

1000-2000 nucleotides per minute Signup and view all the answers

How many base pairs of DNA are typically separated at the transcription start site?

12–14 base pairs Signup and view all the answers

Which of the following is a characteristic of the elongation complex during RNA synthesis?

It comprises RNA polymerase and the nascent RNA strand Signup and view all the answers

What is the simplest definition of a gene?

A unit of DNA responsible for the synthesis of a single polypeptide chain or functional RNA Signup and view all the answers

What is the primary function of the 5' cap added to nascent RNAs?

To mark the RNA as mRNA precursor and protect it from degradation Signup and view all the answers

Which RNA polymerase is specifically characterized by the presence of the carboxy-terminal repeat (CTD)?

RNA Polymerase II Signup and view all the answers

During the elongation stage, what happens to the RNA structure that forms from termination signals?

It destabilizes the polymerase’s hold on RNA Signup and view all the answers

What are the three major events that occur during the processing of eukaryotic pre-mRNA?

5’ capping, 3’ cleavage and polyadenylation, and RNA splicing Signup and view all the answers

Which component is directly responsible for catalyzing the addition of the 5' cap during transcription?

A dimeric capping enzyme Signup and view all the answers

What effect does 5' capping have on the negative elongation factor (NELF)?

It leads to the release of NELF Signup and view all the answers

Which of the following statements about eukaryotic gene structure is correct?

A gene includes the entire nucleic acid sequence necessary for functional gene product synthesis. Signup and view all the answers

What is indicated by the phosphorylation of the carboxy-terminal repeat (CTD) in RNA polymerase II?

It is associated with elongation and activates capping enzymes. Signup and view all the answers

Which factor is NOT relevant to determining the melting temperature (Tm) of DNA?

Length of the messenger RNA Signup and view all the answers

What type of bond links two amino acids together?

Peptide bond Signup and view all the answers

What is the primary role of RNA Polymerase II in the cell?

Transcription of messenger RNA Signup and view all the answers

Which of the following bonds connects guanine and cytosine in DNA?

Hydrogen bond Signup and view all the answers

Which statement regarding the DNA replication fork is accurate?

It is asymmetrical leading to different replication rates. Signup and view all the answers

What is the role of hnRNP proteins in mRNA processing?

They contribute to RNA splicing or cleavage/polyadenylation. Signup and view all the answers

Which of the following statements accurately describes splicing in eukaryotic cells?

Splicing can occur co-transcriptionally for longer transcripts. Signup and view all the answers

What is the average length of introns found in human genes?

3500 bp Signup and view all the answers

What is a function of SR proteins in the splicing process?

They recognize exonic splicing enhancers. Signup and view all the answers

How does the TATA box influence transcription initiation?

It defines the start site for transcription. Signup and view all the answers

What distinguishes CpG islands from the TATA box in terms of function?

CpG islands are less defined initiation sites compared to the TATA box. Signup and view all the answers

What percentage of single-base mutations that cause human genetic diseases affect exon definition?

15 percent Signup and view all the answers

What occurs immediately following the cleavage and polyadenylation of short transcripts?

Splicing occurs. Signup and view all the answers

What is the primary function of the 5’ cap on mRNA?

To protect the 5’ end from degradation Signup and view all the answers

Which enzymes are involved in the capping of mRNA?

Phosphatase, guanyl transferase, and methyl transferase Signup and view all the answers

How does alternative splicing affect fibronectin production in different cell types?

Fibronectin mRNA varies due to inclusion or exclusion of specific exons. Signup and view all the answers

What is the role of hnRNP proteins in the processing of pre-mRNA?

They increase accessibility and uniformity for interactions with RNA molecules. Signup and view all the answers

Which exons are included in the fibronectin mRNA produced by fibroblasts?

EIIIA and EIIIB exons Signup and view all the answers

What is the importance of the reverse linkage formed during capping of mRNA?

It is essential for cap recognition by ribosomes. Signup and view all the answers

What is the consequence of fibronectin lacking the EIIIA and EIIIB exons in hepatocytes?

It circulates freely in the blood. Signup and view all the answers

What type of complex is formed with RNA molecules during their processing in the nucleus?

Heterogeneous ribonucleoprotein particles (hnRNPs) Signup and view all the answers

What defines CpG islands within DNA?

Regions with high GC content located within 100-1000 bp Signup and view all the answers

Which factor binds first to the TATA box during transcription initiation?

TBP Signup and view all the answers

What is the role of the N-terminal domain of TFIIB?

To help melt the template DNA during initiation Signup and view all the answers

Which RNA Polymerase is primarily responsible for the transcription of tRNA genes?

RNA Polymerase III Signup and view all the answers

What is the function of the helicase activity of TFIIH during transcription initiation?

To melt the DNA and form an open complex Signup and view all the answers

Which component is heavily involved in the formation of the pre-initiation complex?

A combination of general transcription factors and RNA Polymerase II Signup and view all the answers

What happens to general transcription factors after transcription initiation?

They primarily dissociate from the transcription complex Signup and view all the answers

What is the primary function of the cytoskeleton in a eukaryotic cell?

To provide structural support and facilitate movement Signup and view all the answers

Study Notes

RNA Types and Functions

RNA is a type of nucleic acid involved in protein synthesis.
RNA differs from DNA in several key aspects: single-stranded, uses ribose sugar, uracil instead of thymine.
Various types of RNA exist, each with specific functions.

Types of RNA

mRNA (messenger RNA): Carries genetic information from DNA to the ribosomes. Codes for proteins.
rRNA (ribosomal RNA): Forms the core of ribosomes, the complex structures where proteins are made, and catalyzes protein synthesis.
tRNA (transfer RNA): Essential in protein synthesis, acts as an adaptor between mRNA and amino acids.
snRNA (small nuclear RNA): Essential in processing pre-mRNA, vital in splicing.
snoRNA (small nucleolar RNA): Helps in processing and modifying rRNA.
miRNA (microRNA): Regulates gene expression by blocking translation and causing mRNA degradation.
siRNA (small interfering RNA): Silences gene expression via mRNA degradation and compact chromatin structure formation.
piRNA (Piwi-interacting RNA): Protects germ cells from transposable elements.
IncRNA (long noncoding RNA): Regulates diverse cellular processes, including X-chromosome inactivation.

Central Dogma

DNA serves as a blueprint, and its instructions are copied into RNA by a process called transcription.
The instructions in RNA then direct the assembly of amino acids to create protein in a process known as translation.
The process is DNA ↔ RNA ↔ protein.

Gene Definition

A gene is a unit of DNA that contains the instructions for the synthesis of a single polypeptide chain or functional RNA molecule (e.g., tRNA).

RNA Polymerases

Involved in the transcription process.
Eukaryotic cells have three main types of RNA polymerase.
- Their roles in transcription are distinguished by the types of RNA they produce.
Different RNA polymerases produce different types of RNA molecules in eukaryotic cells.

Transcription

RNA polymerase moves along the DNA template strand in a 3' to 5' direction.
The process generates a new RNA strand that is complementary to the template strand in a 5' to 3' direction. (transcription bubble is 1000-2000 nucleotides).
5' capping and 3' cleavage and polyadenylation are post-transcriptional processes that modify mRNA in eukaryotic cells.

RNA Processing

5' capping: Protective structure added to the 5' end of eukaryotic mRNA.
3' cleavage and polyadenylation: Removes the end and adds a poly(A) tail by adding multiple adenine nucleotides to the 3' end of eukaryotic mRNA.
RNA splicing: Removes non-coding introns and joins coding exons together. Splicing is tightly controlled through a complex called a spliceosome.

Alternative Splicing

Different mRNAs may be produced by alternate arrangement of exons during RNA splicing.
Exons are spliced together in a variety of ways.
mRNA diversity is an important process for building a wider array of proteins from one base sequence.

Protein Complexes Associated with Pre-mRNAs

Heterogeneous ribonucleoprotein particles (hnRNPs) are protein complexes containing hnRNA and involved in pre-mRNA processing.
hnRNP proteins include RNA-binding domains that affect accessibility and uniformity of pre-mRNAs, participate in RNA splicing or cleavage/polyadenylation, and export from the nucleus to the cytoplasm.

Transcription Control Regions

Includes promoters, proximal elements, distant enhancers, and silencers.
They can stimulate transcription even when inverted, meaning they can be turned “on” or “off”.
These types of control regions are often cell-type specific making sure proteins build at needed times and places in different cells.

Promoters and Initiation Sites

Promoter sequences are located upstream of the initiation site.
The TATA box and initiators regulate start site selection.
CpG islands are often found in the promoters of mammalian genes where numerous CG sequences appear together.
CpG islands are unique to certain areas of the genome indicating potential initiation regions.
Divergent transcription can start in opposite directions from these islands.

General Transcription Factors

Several proteins are required to initiate transcription by RNA polymerase II. (example: TBP, TAFs)
These factors position RNA polymerase II to the start site leading to initiation.

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Description

This quiz explores the various types of RNA and their specific functions in protein synthesis and gene regulation. It covers the key differences between RNA and DNA, as well as the roles of mRNA, rRNA, tRNA, and other RNA types. Test your understanding of how RNA contributes to cellular processes.