Biology Chapter on mRNA Processing and Translation

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Questions and Answers

What is the main function of RNA primase during DNA replication?

To add an RNA primer for DNA polymerase (correct)

To seal Okazaki fragments together

To add nucleotides to the growing DNA strand

To unwind the DNA double helix

Which enzyme is responsible for unzipping the DNA double helix during replication?

Topoisomerase

Helicase (correct)

DNA ligase

RNA primase

What characterizes an operon in bacterial gene regulation?

Genes that are transcribed only in response to stress

Individual genes each have their own promoter

A collection of unrelated genes within a single mRNA

A cluster of genes that share a common promoter (correct)

Which of the following correctly describes the direction of DNA replication?

5' to 3' Signup and view all the answers

What role does DNA ligase play in DNA replication?

It seals the gaps between Okazaki fragments Signup and view all the answers

What is true about the mRNA produced from an operon?

It can code for multiple proteins Signup and view all the answers

What is the role of the operator in an operon?

To control the activation of transcription Signup and view all the answers

Which component is directly responsible for synthesizing mRNA during transcription?

RNA polymerase Signup and view all the answers

What is the function of a corepressor in prokaryotic gene regulation?

To keep the repressor protein attached to the operator Signup and view all the answers

During which stage of gene expression does splicing occur?

mRNA processing Signup and view all the answers

In eukaryotes, which level of regulation involves the degradation of mRNA?

mRNA degradation Signup and view all the answers

What is the primary purpose of mRNA during protein synthesis?

To serve as a template for protein production Signup and view all the answers

Which of these processes is NOT a level of regulation in eukaryotic gene expression?

Gene duplication Signup and view all the answers

What triggers the repressor protein to detach from the operator in the lac operon?

The presence of an inducer, such as lactose Signup and view all the answers

What is the purpose of the cap added to the 5' end of mRNA?

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

What does splicing specifically involve?

Joining exons together Signup and view all the answers

What is the role of the anticodon in the translation process?

To match with corresponding codons on mRNA Signup and view all the answers

Which amino acid is carried by the tRNA that recognizes the start codon AUG?

Methionine Signup and view all the answers

What process is used to form a peptide bond between amino acids during translation?

Dehydration synthesis Signup and view all the answers

What happens to the first tRNA after it has delivered its amino acid?

It detaches and finds more methionine Signup and view all the answers

How does the ribosome identify the start of translation?

By recognizing a specific nucleotide sequence in mRNA Signup and view all the answers

What does the ribosome do when it encounters a stop codon?

It releases the completed polypeptide chain Signup and view all the answers

Study Notes

mRNA Modification

A 5' cap is added to the start of mRNA to protect it from degradation.
A polyA tail is added to the 3' end of mRNA to enhance stability and export from the nucleus.
Introns are removed through splicing, creating a mature mRNA molecule.

Translation Initiation

Begins with a tRNA carrying methionine (start codon AUG) binding to the small ribosomal subunit.
The tRNA's anticodon (UAC) pairs with the mRNA's start codon (AUG).
The large ribosomal subunit attaches to form a functional ribosome, allowing translation to commence.

Translation Process

The second codon (GUU) on mRNA pairs with a tRNA carrying valine, binding to the ribosome's second active site.
A peptide bond forms between methionine and valine via dehydration synthesis.
The first tRNA releases and searches for another methionine, while the mRNA shifts to expose the next codon.

Continued Translation

A new tRNA with the anticodon (GUA) carrying histidine attaches to the ribosome.
Another peptide bond forms between valine and histidine, and tRNA carrying valine is released.
The process repeats until a stop codon is reached.

Gene Expression in Prokaryotes

Operon: A set of genes that are transcribed together, coding for proteins with related functions.
Key components:
- Promoter: DNA region where RNA polymerase binds to initiate transcription.
- Operator: Regulatory region controlling transcription; acts as an on/off switch.
- Repressor protein: Binds to the operator to prevent transcription.
- Corepressor: Stabilizes the repressor on the operator (e.g., trp operon).
- Inducer: Removes the repressor from the operator (e.g., lactose in the lac operon).
- Regulatory gene: Encodes the repressor protein.

Gene Expression in Eukaryotes

Regulated at multiple levels:
- Transcription
- RNA processing
- mRNA transport
- mRNA translation
- mRNA degradation
- Protein degradation

Transcription and Translation Overview

Genes in DNA encode instructions for protein synthesis; mRNA copies of these genes are created as needed.
RNA polymerase is responsible for synthesizing mRNA by unzipping DNA at the targeted gene.
mRNA base pairing occurs, matching DNA's sense strand with RNA bases, concluding with a signal to stop transcription.
The finished mRNA exits the nucleus to be translated at ribosomes in the rough endoplasmic reticulum.

DNA Replication in Eukaryotes

Eukaryotic cells, when not in G0 phase, must replicate DNA for mitosis or meiosis.
DNA replication occurs in a 5' to 3' direction, using leading and lagging strands.
Eukaryotic chromosomes may contain about 150 million nucleotides, necessitating multiple replication forks.
Key enzymes involved include:
- Topoisomerases: Untangle DNA.
- Helicase: Unzip DNA strands.
- RNA primase: Synthesizes RNA primers.
- DNA polymerase: Adds nucleotides, repairs mismatches, and removes RNA primers.
- DNA ligase: Connects Okazaki fragments, forming phosphodiester bonds.

Operon Concept in Bacteria

Operons represent clusters of genes that share a single promoter and regulatory elements, allowing for coordinated transcription.
Polycistronic mRNA can represent multiple genes, enabling simultaneous expression of related proteins.

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Description

Explore the key processes involved in mRNA processing and translation in this quiz. Learn about the addition of the 5' cap, the 3' polyA tail, and the splicing of introns. Test your knowledge on how translation begins with tRNA and the significance of the start codon.