mRNA Structure and Production

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Questions and Answers

What is the function of the 5' untranslated region in mRNA?

Specifies the amino acid sequence of a protein

Plays a role in translation initiation (correct)

Provides stability to the mRNA

Has no specific function

What is the main difference in mRNA production between eukaryotes and bacteria?

The type of gene regulation

The location of transcription

The type of RNA polymerase used

The need for RNA processing in eukaryotes (correct)

What is the function of the 7-methyl guanosine (m7G) cap?

Recruits ribosomes for translation initiation

Specifies the reading frame during translation

Protects the mRNA against degradation (correct)

Induces transcriptional termination

What is the function of the poly(A) tail?

Required for efficient export of the mRNA from the nucleus to the cytoplasm Signup and view all the answers

What is the purpose of RNA processing in eukaryotes?

To modify the pre-mRNA to produce the mature mRNA Signup and view all the answers

What is the characteristic of eukaryotic mRNAs?

They are monocistronic Signup and view all the answers

What is added to the 5' end of the pre-mRNA during co-transcriptional capping?

A guanine nucleotide Signup and view all the answers

What is the consequence of not having a 5' cap?

mRNA degradation Signup and view all the answers

What is the main function of transcription?

To synthesize a single-stranded RNA copy of a DNA segment Signup and view all the answers

What is the name given to the two-step process of DNA → RNA → protein?

Central Dogma Signup and view all the answers

What type of RNA molecule encodes the amino acid sequence of a polypeptide?

mRNA Signup and view all the answers

What is the function of tRNA?

To bring amino acids to ribosomes during translation Signup and view all the answers

What is the function of rRNA?

To make up the ribosomes with ribosomal proteins Signup and view all the answers

What is the function of snRNA?

To form complexes used in eukaryotic RNA processing Signup and view all the answers

How many main types of RNA molecules are there?

4 Signup and view all the answers

What is the processing of translating mRNA into a polypeptide called?

Translation Signup and view all the answers

What is the direction of RNA synthesis during transcription?

5'-to-3' Signup and view all the answers

What is the role of RNA Pol in transcription?

To catalyze the linkage of ribonucleoside triphosphates Signup and view all the answers

What is the template strand in transcription?

The 3'-to-5' DNA strand that is read to make the RNA strand Signup and view all the answers

What is the function of gene regulatory elements?

To regulate transcription Signup and view all the answers

What is the difference between RNA Pol and DNA Pol?

RNA Pol makes one mistake for every 104 nucleotides copied, while DNA Pol makes one mistake for every 107 nucleotides copied Signup and view all the answers

What is the base used in RNA instead of T?

U Signup and view all the answers

What is the function of the nontemplate strand in transcription?

It is the strand that is not read to make the RNA strand Signup and view all the answers

How many different RNA Pols are involved in transcribing the genes for four main types of RNAs in eukaryotes?

Three Signup and view all the answers

What is the role of general transcription factors (GTFs) in transcription initiation?

To position RNA Pol II correctly at the promoter Signup and view all the answers

What is the function of the TATA-binding protein (TBP)?

To recognize and bind to the TATA box sequence Signup and view all the answers

Where is the TATA box sequence typically located in eukaryotic promoters?

25 nucleotides away from the transcription start site Signup and view all the answers

What is the function of TFIID in transcription initiation?

To recognize and bind to the TATA box sequence Signup and view all the answers

What is the step that follows the formation of the preinitiation complex in transcription?

Initiation Signup and view all the answers

What is the purpose of the general transcription factor TFIIB?

To aid in the binding of RNA Pol II Signup and view all the answers

What is the function of RNA Pol II in transcription?

To synthesize the RNA molecule Signup and view all the answers

What is the primary role of GTFs in transcription initiation?

To position RNA Pol II correctly at the promoter Signup and view all the answers

Which RNA polymerase is responsible for synthesizing 28S, 18S, and 5.8S rRNA molecules?

RNA Pol I Signup and view all the answers

What is the main function of the core promoter (CP) elements?

To specify the start site of transcription Signup and view all the answers

What is the consensus sequence of the Inr element?

5'-TATAAAA-3' Signup and view all the answers

Where are the promoter-proximal elements (PPEs) typically located?

Upstream of the transcription initiation site Signup and view all the answers

What is the function of the TATA box?

To specify the start site of transcription Signup and view all the answers

Which RNA polymerase is responsible for synthesizing mRNAs and some snRNAs?

RNA Pol II Signup and view all the answers

What is the purpose of the CAAT box and GC box?

To enhance transcription initiation Signup and view all the answers

Where is RNA Pol I located?

Nucleolus Signup and view all the answers

Study Notes

Structure of mRNA

A 5' untranslated region (leader sequence) is present at the 5' end of the mRNA.
The protein-coding sequence specifies the amino acid sequence of a protein during translation.
A 3' untranslated region (trailer sequence) is present at the 3' end of the mRNA.

mRNA Production in Eukaryotes

The RNA transcript (pre-mRNA) is modified in the nucleus by RNA processing to produce the mature mRNA.
The mRNA must migrate from the nucleus to the cytoplasm.
mRNA is always transcribed completely and then processed before it is translated.
Eukaryotic mRNAs are typically monocistronic, meaning they contain the amino acid-coding information from just one gene.

Modification of mRNA in Eukaryotes

5' Capping

A capping enzyme adds a guanine nucleotide (most commonly, 7-methyl guanosine (m7G)) to the 5' end of the pre-mRNA.
The 5' cap remains throughout the lifetime of the mRNA and plays a crucial role in protecting the mRNA against degradation by exonucleases.
The 5' cap is also important for the binding of the ribosome as an initial step of translation.

3' Modification

A poly(A) tail is added to the 3' end of the pre-mRNA.
The poly(A) tail is required for efficient export of the mRNA from the nucleus to the cytoplasm.

Transcription and Translation

Transcription is the synthesis of a single-stranded RNA copy of a segment of DNA.
Translation is the conversion of the mRNA base-sequence information into the amino acid sequence of a polypeptide.

Gene Expression - The Central Dogma

The central dogma is the two-step process of DNA → RNA → protein (transcription followed by translation).
In transcription, only one of the two DNA strands is transcribed into RNA.

Types of RNA Molecules

There are four main types of RNA molecules: mRNA, rRNA, tRNA, and snRNA.
Each type of RNA is encoded by its own type of gene, but only mRNA is translated.

The Transcription Process

Gene regulatory elements are sequence elements associated with each gene that are involved in regulating transcription.
The enzyme RNA polymerase (RNA Pol) catalyzes the process of transcription.
The DNA double helix unwinds for a short region next to the gene before transcription begins.
RNA is synthesized in the 5'-to-3' direction.
The 3'-to-5' DNA strand that is read to make the RNA strand is called the template strand.
The 5'-to-3' DNA strand complementary to the template strand is called the non-template strand.

RNA Polymerase

RNA polymerase is responsible for the synthesis of RNA from DNA.
RNA polymerase catalyzes the linkage of ribonucleoside triphosphates (ATP, GTP, CTP, and UTP) to form a complementary RNA strand.
RNA polymerase can start an RNA chain without a primer.
RNA polymerase makes about one mistake for every 10^4 nucleotides copied into RNA.

Transcription in Eukaryotes

Three different RNA polymerases (RNA Pol I, RNA Pol II, and RNA Pol III) transcribe the genes for four main types of RNAs.
RNA Pol I is located in the nucleolus and synthesizes the RNAs found in ribosomes.
RNA Pol II is located in the nucleoplasm and synthesizes mRNAs and some snRNAs.
RNA Pol III is located in the nucleoplasm and synthesizes tRNAs, 5S rRNA, and the snRNAs not made by RNA Pol II.

Promoters and Enhancers

Promoters of protein-coding genes encompass about 200 base pairs upstream of the transcription initiation site and contain various sequence elements.
The core promoter is the set of cis-acting sequence elements needed for the transcription machinery to start RNA synthesis at the correct site.
The promoter-proximal elements (PPEs) are upstream from the TATA box and are involved in the regulation of transcription.

Steps in Transcription

Promoter recognition
Preinitiation complex formation
Initiation
Elongation
Termination

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Description

This quiz covers the components of mRNA, including the 5' untranslated region, protein-coding sequence, and 3' untranslated region, as well as differences in mRNA production between bacteria and eukaryotes.