Biology Chapter: Ribosomes and Translation

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Questions and Answers

What is the term used for the process by which the language of the nucleotide sequence on the mRNA is translated into the language of the amino acid sequence?

  • Transcription
  • Splicing
  • Replication
  • Translation (correct)

In which direction is the mRNA translated?

  • Both directions are possible
  • It depends on the specific mRNA sequence.
  • 3' to 5'
  • 5' to 3' (correct)

What is the name of the process which attaches a specific amino acid to a tRNA molecule?

  • Aminoacylation (correct)
  • Elongation
  • Transcription
  • Translation

What is the role of the anticodon in tRNA?

<p>It recognizes and binds to a specific codon on mRNA. (A)</p> Signup and view all the answers

What is the name for the sequence in prokaryotic mRNA that helps initiate translation?

<p>Shine-Dalgarno sequence (D)</p> Signup and view all the answers

Which of the following is NOT a site found on a ribosome?

<p>T site (A)</p> Signup and view all the answers

What is the function of the anticodon loop in a tRNA molecule?

<p>Binds to the mRNA codon (C)</p> Signup and view all the answers

In which site on the ribosome does the first tRNA occupy during initiation?

<p>P site (B)</p> Signup and view all the answers

Which of the following statements about eukaryotic mRNAs is TRUE?

<p>Each eukaryotic mRNA typically codes for only one polypeptide chain. (B)</p> Signup and view all the answers

What is the role of rRNA in protein synthesis?

<p>Provides the structural framework for the ribosome (C)</p> Signup and view all the answers

Which of the following best describes the function of tRNA in protein synthesis?

<p>tRNA serves as an adaptor molecule, linking a specific amino acid to its corresponding mRNA codon. (D)</p> Signup and view all the answers

What is the direction of polypeptide chain synthesis during translation?

<p>From the amino terminal to the carboxyl terminal (A)</p> Signup and view all the answers

What type of bond is formed between two amino acids during polypeptide synthesis?

<p>Peptide bond (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of tRNA?

<p>tRNA molecules bind directly to DNA. (A)</p> Signup and view all the answers

What is the role of aminoacyl-tRNA synthetase in protein synthesis?

<p>It attaches the correct amino acid to its corresponding tRNA molecule. (D)</p> Signup and view all the answers

Which of these is the most accurate description of the process of translation?

<p>Translation is the process of converting a sequence of RNA nucleotides into a sequence of amino acids. (A)</p> Signup and view all the answers

What is the primary role of initiation factors in protein biosynthesis?

<p>To facilitate binding and positioning of mRNA on the ribosomal subunits (A)</p> Signup and view all the answers

Which sequence is recognized by the ribosome in bacteria to initiate translation?

<p>Shine Dalgarno sequence (A)</p> Signup and view all the answers

What codon is specifically recognized by the initiator tRNA during translation initiation?

<p>AUG (B)</p> Signup and view all the answers

In eukaryotes, what type of methionine does the initiator tRNA carry?

<p>Methionine (C)</p> Signup and view all the answers

What happens to initiation factors when the 50 S subunit arrives during translation initiation?

<p>GTP is cleaved and they are released (A)</p> Signup and view all the answers

Which of the following components is NOT involved in the initiation phase of translation?

<p>DNA polymerase (A)</p> Signup and view all the answers

How many initiation factors are found in prokaryotes as mentioned?

<p>Three (B)</p> Signup and view all the answers

What is the result of the base pairing between the Shine Dalgarno sequence and the 16 S rRNA?

<p>Facilitation of mRNA positioning on the ribosomal subunit (A)</p> Signup and view all the answers

Flashcards

Prokaryotic ribosome

Ribosome consisting of 70s with rRNA and proteins.

Eukaryotic ribosome

Ribosome consisting of 80s with more rRNA and proteins.

Ribosomal RNA (rRNA)

RNA that forms the core of ribosome structure and function.

mRNA-binding site

Site on small ribosomal subunit that binds messenger RNA.

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E site (Exit site)

Site where uncharged tRNA exits the ribosome.

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P site (Peptidyl site)

Site where the tRNA holds growing polypeptide chain.

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A site (Aminoacyl site)

Site where new aminoacyl tRNA enters the ribosome.

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Aminoacyl-tRNA synthetases

Enzymes that match specific amino acids to their corresponding tRNA.

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Amino Acid Activation

Specific enzymes attach amino acids to their corresponding tRNA.

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tRNA Anticodon

The sequence in tRNA that pairs with mRNA codon.

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Codon Recognition

The matching of tRNA anticodon with mRNA codon.

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Translation Stages

The three main steps of protein biosynthesis: initiation, elongation, termination.

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Initiation in Translation

The small ribosomal subunit binds to mRNA to find the start codon.

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Shine Dalgarno Sequence

A ribosomal binding site in bacterial mRNA facilitating initiation.

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Elongation in Translation

The process of tRNAs adding amino acids to the growing polypeptide chain.

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Post-Translational Modifications

Changes made to polypeptides after translation, affecting protein function.

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Initiation in Protein Biosynthesis

The first step involving assembly of ribosomal subunits, mRNA, tRNA, GTP, and initiation factors.

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16 S rRNA

Part of the 30 S ribosomal subunit that pairs with the Shine Dalgarno sequence in mRNA.

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Initiator tRNA

tRNA that carries the first amino acid, methionine or fMet, to the ribosome for translation.

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fMet

N-formylmethionine, the first amino acid in bacterial protein synthesis.

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eukaryotic Initiation Factors

At least eight factors (eIF) that assist in initiating protein synthesis in eukaryotes.

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30 S Initiation Complex

Complex formed with initiation factors and mRNA, preparing for translation.

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70 S Initiation Complex

Formed when the 50 S subunit joins the 30 S initiation complex.

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Study Notes

Prokaryotic Ribosomes

  • Composed of a 50S and 30S subunit
  • 5S rRNA and 34 proteins in 50S subunit
  • 16S rRNA and 21 proteins in 30S subunit

Eukaryotic Ribosomes

  • Composed of a 60S and 40S subunit
  • 5S rRNA and 45 proteins in 60S subunit
  • 18S rRNA and 33 proteins in 40S subunit
  • 5.8S rRNA is also present

Ribosomal RNA (rRNA)

  • rRNA is part of the ribosome
  • Three sites on ribosome:
    • mRNA binding site
    • E site (exit site for uncharged tRNA)
    • P site (peptidyl-tRNA binding site)
    • A site (aminoacyl-tRNA binding site)

Transfer RNA (tRNA)

  • tRNA transports amino acids to ribosomes
  • Single-stranded molecule with a cloverleaf shape due to base pairing
  • Has 3 unpaired regions to form loops
  • Anticodon loop with the sequence of nucleotides that complements the codon on mRNA.
  • Aminoacyl-tRNA synthetase binds amino acids to specific tRNA
  • Amino acid attachment site is at the 3' end.

Protein Biosynthesis - Translation

  • Three stages: initiation, elongation, termination
  • Initiation:
    • Small subunit of ribosome binds to mRNA at the 5' end.
    • Charged tRNA binds to the start codon.
    • Large subunit joins the initiation complex.
  • Elongation
    • Amino acids are added to the polypeptide chain one at a time.
  • Termination
    • Stop codon is reached.
    • Polypeptide is released and ribosome dissociates.

Steps in Protein Biosynthesis

  • Pathway of protein biosynthesis is known as "translation."
  • mRNA is translated from its 5' end to 3' end.
  • Proteins are synthesized from the amino-terminal to the carboxyl terminal.
  • Prokaryotic mRNAs can have multiple coding regions producing separate types of polypeptides.
  • Eukaryotic mRNAs generally have a single polypeptide-coding region.

Codon Recognition by tRNA

  • Recognition of a codon on mRNA is done by the tRNA's anticodon
  • Base pairing rules are followed during binding.
  • Sequence MUST ALWAYS be written, written in the 5' to 3' order.

Initiation Complex

  • Assembly of components for protein synthesis
  • Components include ribosome subunits, mRNA, aminoacyl-tRNA, GTP, and initiation factors.

Translation Initiation Steps in Prokaryotes

  • Mechanism 1: Shine-Dalgarno sequence aligns ribosome on mRNA.
  • Mechanism 2: AUG codon in the beginning is recognized by initiator tRNA (which carries f-methionine in bacteria).

Translation Initiation Steps in Eukaryotes

  • Initiation complexes assemble around the 5′ cap of the mRNA.
  • Mechanism: Special initiator tRNA binds to the start codon AUG, assisted by initiation factors and GTP.

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Protein Biosynthesis - Translation PDF

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