Biology Chapter: RNA to Protein Translation

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Questions and Answers

What is the function of glycosylation in proteins?

To stabilize protein structure

To regulate enzyme activity

To aid in biofilm formation and colonization (correct)

To attach lipid tails for membrane anchoring

Which enzyme is responsible for the removal of N-formyl Methionine?

Glycosyltransferase

Lipid transferase

Acetyltransferase

Methionine aminopeptidase (correct)

During which phase of translation do ribosomal subunits come together?

Post-translation

Elongation

Initiation (correct)

Termination

What role does adenylation play in protein activity?

It regulates enzyme activity Signup and view all the answers

Which of the following modifications serves to anchor lipoproteins to membranes?

Lipidation Signup and view all the answers

What is the main function of ribosomes during translation?

To convert RNA messages into proteins Signup and view all the answers

How many stop codons are present in the genetic code?

3 Signup and view all the answers

Which component of RNA polymerase is specifically required for the initiation phase of transcription?

Sigma Factor Signup and view all the answers

What characteristic of the genetic code allows for multiple codons to encode the same amino acid?

Degeneracy Signup and view all the answers

Which subunit of the core polymerase contains the catalytic site for RNA synthesis?

Beta-prime Signup and view all the answers

What does the term 'universal' refer to in the context of the genetic code?

It is identical in all organisms Signup and view all the answers

Which of the following is NOT a subunit of the core polymerase?

Sigma Signup and view all the answers

What role does the omega subunit of RNA polymerase play?

It assists in assembly and maintenance of the core Signup and view all the answers

What primary role do transfer RNA (tRNA) molecules serve in translation?

Shuttle amino acids to the ribosome Signup and view all the answers

What structural feature of tRNA is crucial for its interaction with mRNA?

Anticodon Signup and view all the answers

The average half-life of mRNA is approximately:

1–3 minutes Signup and view all the answers

What structure is primarily responsible for the degradation of RNA in bacteria?

RNA degradosome Signup and view all the answers

Which of the following statements about the GC-rich sequence is true?

It forms a stem-loop structure that pauses transcription Signup and view all the answers

Which of the following is NOT a type of RNA mentioned?

DNA RNA Signup and view all the answers

What is the shape of tRNA when visualized in two dimensions?

Clover leaf Signup and view all the answers

What defines the pairing between codons and anticodons?

They bond in an antiparallel manner Signup and view all the answers

What is the primary role of sigma factors in bacterial transcription?

To recruit RNA polymerase to specific DNA sequences Signup and view all the answers

In Escherichia coli, which sigma factor is primarily involved in housekeeping functions?

Sigma-70 Signup and view all the answers

What is the first step in protein synthesis?

Initiation Signup and view all the answers

What occurs during the initiation stage of transcription?

RNA polymerase forms a closed complex with DNA Signup and view all the answers

Which proteins are required for the initiation phase in E.coli?

IF1, IF2, and IF3 Signup and view all the answers

What is a key characteristic of Rho-independent termination of transcription?

It relies on a GC-rich RNA region and consecutive U residues Signup and view all the answers

During elongation, what is the role of EF-Tu?

To bind to the A site before a charged tRNA Signup and view all the answers

During elongation of transcription, how fast does RNA polymerase add ribonucleotides?

45 bases/sec Signup and view all the answers

What is the sequence of events that occurs when RNA polymerase begins transcription?

Binding, unwinding, and RNA synthesis Signup and view all the answers

What triggers termination in protein synthesis?

A stop codon entering the A site Signup and view all the answers

What is a characteristic of polysomes?

They consist of multiple ribosomes translating the same mRNA Signup and view all the answers

What binds to RNA polymerase after sigma factors dissociate during elongation?

NusA protein Signup and view all the answers

Where does coupled transcription and translation primarily occur in bacterial cells?

Near the nucleoid Signup and view all the answers

What denotes the start of the RNA transcript during transcription?

The +1 position of the DNA sequence Signup and view all the answers

What is typically required after protein synthesis to achieve proper protein functionality?

Post-translational modifications Signup and view all the answers

What process allows for the rapid production of multiple protein copies from a single mRNA molecule?

Polysome formation Signup and view all the answers

What is the role of aminoacyl-tRNA synthetases in the charging process of tRNA?

To covalently attach amino acids to the tRNA. Signup and view all the answers

Which class of aminoacyl-tRNA synthetases attaches amino acids at the 2'-OH of the terminal adenosine?

Class I Signup and view all the answers

Which of the following codons is most commonly recognized as the start codon?

AUG Signup and view all the answers

What is the significance of the Shine-Dalgarno sequence in prokaryotic translation?

It positions the start codon in the ribosome P site. Signup and view all the answers

What type of RNA is involved in peptide bond formation during translation?

rRNA Signup and view all the answers

During which stage of protein synthesis are the two ribosomal subunits brought together?

Initiation Signup and view all the answers

How do post-transcriptional modifications affect tRNA stability?

They make tRNA a poor substrate for RNase. Signup and view all the answers

What components make up the ribosome?

Proteins and rRNA Signup and view all the answers

Study Notes

Translation: Converting RNA to Protein

Translation is the decoding of RNA to synthesize proteins.
Ribosomes are the molecular machines that convert RNA's genetic code into proteins.

The Genetic Code

Codons are nucleotide triplets on mRNA representing amino acids.
61 codons specify amino acids, 3 are stop codons (UAA, UGA, UAG).
The genetic code is degenerate; multiple codons can code for the same amino acid.
Synonymous codons usually differ only in the last base.
The genetic code is nearly universal in all known species.

RNA Polymerases and Sigma Factors

RNA polymerase (DNA-dependent RNA polymerase) makes RNA copies of DNA.
Components in bacteria include core polymerase (elongation phase) and sigma factor (initiation phase).
Holoenzyme is the complex of core polymerase and sigma factor.
Core polymerase is composed of four different subunits (alpha, beta, beta prime, and omega.)
Sigma factors have different areas (σ1-σ4), interacting with core polymerase subunits.
A sigma factor helps core polymerase bind to specific sequences of DNA.

Transcription of DNA to RNA

Occurs in three stages:
- Initiation: RNA polymerase binds to a promoter, unwinds DNA, and starts RNA synthesis.
- Elongation: RNA polymerase adds ribonucleotides to the growing RNA chain.
- Termination: RNA polymerase detaches from the DNA, releasing the finished mRNA.

Transcription Initiation

RNA polymerase holoenzyme forms a loosely bound, closed complex with DNA.
The closed complex must become an open complex, unwinding DNA to allow RNA polymerase access to the template strand.
The first ribonucleotide added is typically a purine (A or G) to the newly formed RNA chain.
Sigma factor dissociates after ~9 bases, allowing RNA polymerase to elongate the RNA transcript.

Transcription Termination

Bacterial genes use two types of termination signals. -Rho-dependent termination: involves a protein called Rho and a pause site. -Rho-independent termination: requires a GC-rich region and 4-8 consecutive U residues.

Different Classes of RNA

Messenger RNA (mRNA): codes for proteins.
Ribosomal RNA (rRNA): forms ribosomes.
Transfer RNA (tRNA): carries amino acids to ribosomes.
Small RNA (sRNA): regulates mRNA stability/translation.
tmRNA: frees ribosomes stuck on damaged mRNA.
Catalytic RNA (ribozymes): carries out reactions; associated with proteins.

RNA Stability

RNA is short-lived.
Stability varies among different RNA types.
RNA degradosome is a major cellular structure for degrading most RNAs in bacteria.

tRNA Molecules

tRNAs are adapter RNAs attached to amino acids, ~80 bases long shaped like a cloverleaf.
tRNAs have an anticodon region that binds to the mRNA codon, and an acceptor end for binding amino acids.
Modified bases: unusual bases in tRNA.

Attaching Amino Acids to tRNA

Aminoacyl-tRNA synthetases: enzymes that attach the correct amino acid to its tRNA.
Two classes of aminoacyl-tRNA synthetases (Class I and Class II)

The Ribosome, a Translation Machine

Ribosomes are the sites for protein synthesis.
Composed of two subunits (large and small), containing proteins and rRNA.

Finding the Start of Translation

Start codons signal the start of translation (AUG common; others less common).
Shine-Dalgarno sequence: in prokaryotes, it is a purine-rich sequence found in mRNA upstream of the start codon, which helps position the ribosome.

Ribosome as a "Ribozyme"

Ribosomes make peptide bonds using peptidyltransferase which is part of the large ribosomal subunit (23S rRNA).

Stages of Protein Synthesis

Initiation: brings two ribosomal subunits together with the mRNA and first tRNA/amino acid.
Elongation: sequentially adds amino acids to the growing polypeptide chain.
Termination: releases the completed protein and recycles ribosome subunits.

Protein Synthesis: Requirements

Each phase requires protein factors and energy (GTP).

Protein Synthesis: Elongation

Elongation Factors (EF-Tu and EF-G) participate in the process.

Protein Synthesis: Termination

Release factors (RF1 or RF2) bind to the stop codon in mRNA, ending protein synthesis.
Polysomes are multiple ribosomes translating the same mRNA simultaneously.

Coupled Transcription and Translation

In bacteria & archaea, transcription and translation occur simultaneously.
Ribosomes bind to mRNA before transcription is fully complete.

Spatial Localization

Transcription and Translation occur near the nucleoid.
Ribosomes often localized at the cell poles.

Protein Modifications

Post-translational modifications are common, altering proteins chemically after synthesis (e.g., folding, phosphorylation, glycosylation).

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Description

This quiz covers the essential concepts of RNA translation to protein synthesis. It highlights the role of ribosomes in decoding RNA, the structure of the genetic code, and the function of RNA polymerases and sigma factors in the transcription process. Test your understanding of how genetic information is translated into functional proteins.