Molecular Biology: RNA Transcription & Processing

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Questions and Answers

What is the direction of RNA polymerase synthesizing the mRNA strand?

Both directions simultaneously

3' → 5'

It can synthesize in either direction

5' → 3' (correct)

Which DNA strand is used for mRNA transcription?

Coding DNA strand

Both DNA strands are used

Either DNA strand can be used

Template DNA strand (correct)

What is the pentose sugar found in RNA?

Fructose

Deoxyribose

Ribose (correct)

Glucose

What replaces Thymine in DNA when it comes to RNA?

Uracil Signup and view all the answers

What is the typical structure of RNA?

Single-stranded Signup and view all the answers

What type of bond links the ribose and the phosphate in RNA?

3' → 5' phosphodiester bond Signup and view all the answers

What happens to most newly transcribed RNA molecules in eukaryotes?

They undergo various alterations to yield the mature product Signup and view all the answers

What is the term for the process in which RNA molecules undergo alterations to yield the mature product?

RNA Processing Signup and view all the answers

What is the main objective of RNA transcription?

To create a copy of a DNA strand Signup and view all the answers

What is the direction of the flow of genetic information in the Central Dogma?

From DNA to RNA to protein Signup and view all the answers

Where does the synthesis of an mRNA molecule take place?

In the nucleus Signup and view all the answers

What is the role of RNA polymerase in mRNA transcription?

To catalyze the transcription of a DNA strand into an RNA molecule Signup and view all the answers

What is the outcome of the elongation stage of mRNA transcription?

The formation of a 3'→5' phosphodiester linkage Signup and view all the answers

How many stages are involved in the process of mRNA transcription?

4 stages Signup and view all the answers

What is the function of the promoter in mRNA transcription?

To bind RNA polymerase to the DNA strand Signup and view all the answers

What happens to the mRNA molecule after it is synthesized?

It passes into the cytoplasm and then onto the ribosomes Signup and view all the answers

What is the term used to describe the collective molecular events that allow primary transcripts to become functional mature RNA?

RNA processing Signup and view all the answers

Where is mRNA produced and processed in a cell?

Nucleus Signup and view all the answers

What is the function of the 5'-capping of mRNA?

Protection from 5' to 3' exonuclease cleavage Signup and view all the answers

What is the purpose of the poly(A) tail in mRNA?

mRNA stability Signup and view all the answers

What is the enzyme responsible for adding the poly(A) tail to mRNA?

Poly(A) polymerase Signup and view all the answers

What is the process by which introns are removed from pre-mRNA?

Splicing Signup and view all the answers

What is the term used to describe the direct product of gene transcription from DNA?

pre-mRNA Signup and view all the answers

What is the purpose of the 5'-capping of mRNA during translation?

Recruits initiation factors Signup and view all the answers

What is the function of RNase in RNA processing?

Cleavage of pre-mRNA Signup and view all the answers

What is the molecular weight range of pre-mRNAs?

> 10^7 Signup and view all the answers

What is the process called when pre-mRNA is cut to remove introns and splice/join the exons together?

Splicing Signup and view all the answers

What is the typical signal that marks the boundaries of introns?

GT - AG rule Signup and view all the answers

What is the process that enables a single mRNA to direct the synthesis of different protein variants?

Alternative splicing Signup and view all the answers

What is the process that alters the nucleotide sequence of the primary transcript?

RNA editing Signup and view all the answers

What is the function of ApoB-100 in the liver?

Formation of VLDL Signup and view all the answers

What is the modification that occurs in the mRNA of ApoB-48 in the intestine?

The C of the CAA codon is changed to U Signup and view all the answers

Where does pre-mRNA splicing take place?

In the nucleus Signup and view all the answers

What is the result of removing an incorrect number of nucleotides during pre-mRNA splicing?

The code for the protein is destroyed Signup and view all the answers

What is the difference between ApoB-100 and ApoB-48?

ApoB-100 is involved in the transport of cholesterol, while ApoB-48 is involved in the absorption of lipids from the intestine Signup and view all the answers

What is the result of alternative splicing?

A single mRNA directs the synthesis of multiple protein variants Signup and view all the answers

Study Notes

mRNA Transcription and Processing

The central dogma is the flow of genetic information from DNA to RNA to protein, a one-way street.
Transcription is the process of synthesizing an RNA molecule from a DNA template, and it occurs in three stages: binding, initiation, and elongation.
The mRNA molecule is synthesized in the nucleus during transcription, and it passes into the cytoplasm where it serves as a template for protein biosynthesis.
RNA polymerase is the enzyme that catalyzes mRNA transcription, and it reads the template DNA strand in the 3' → 5' direction.
The 3' → 5' template DNA strand is used for mRNA transcription, and the coding DNA strand moves in the 5' → 3' direction.

mRNA Structure

RNA is more abundant than DNA and has several important differences, including:
- Pentose sugar in RNA is ribose, whereas in DNA it is deoxyribose.
- In RNA, Uracil replaces Thymine in DNA.
- RNA is usually single-stranded, whereas DNA is double-stranded.
RNA primary structure consists of A, C, G, and U linked by 3' → 5' phosphodiester bonds between the ribose and the phosphate (backbone).

RNA Processing

RNA processing is a collective term used to describe the molecular events that allow the primary transcripts to become the functional mature RNA.
These events include cleavage, splicing, editing, and other reactions carried out by RNA-cleaving ribonucleases (RNases).
In eukaryotes, most newly transcribed RNA molecules (primary transcripts) undergo various alterations to yield the mature product.
mRNA is produced and processed in the nucleus and then exported to the cytoplasm as a template for protein biosynthesis.

mRNA Processing Steps

5'-capping and methylation: the 5' end of the mRNA is capped with a 7-methylguanosine, which is linked to the first nucleotide of the RNA via a 5' → 5' triphosphate linkage.
3'-cleavage and polyadenylation: a long chain of AMP residues (poly(A) tail) is added to the 3' end of the mRNA.
Splicing and introns' removal: non-coding regions (introns) are removed, and coding regions (exons) are joined together.
Editing: the RNA sequence is altered after transcription, either by changing residues, deleting residues, or inserting residues at specific sites.

Alternative Splicing

Alternative splicing is a process that enables a single mRNA to direct the synthesis of different protein variants (isoforms).
This occurs by rearranging the pattern of introns and exons that are joined by splicing.

mRNA Editing

mRNA editing is a process that alters the nucleotide sequence of the primary transcript after transcription.
This can occur by changing residues, deleting residues, or inserting residues at specific sites.
Example: Apolipoprotein B, where the codon 2153 is modified in the mRNA, causing a chain termination and resulting in a shortened version of the protein.

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Description

This lecture covers the main steps of RNA transcription, mRNA sequence deduction from DNA templates, and mRNA processing steps. Learn about the differences between RNA and DNA.