Biology Translation and tRNA
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Questions and Answers

What process synthesizes a single-stranded RNA molecule from a DNA template?

Transcription

What is the term for the process of synthesizing a polypeptide using the mRNA template?

Translation

The _____ of the mRNA coding region dictates the amino acid sequence of the polypeptide.

sequence

What defines the boundaries of translation?

<p>Stop codon</p> Signup and view all the answers

What describes the correspondence between mRNA nucleotide sequences and the amino acid sequences of polypeptides?

<p>Genetic Code</p> Signup and view all the answers

TRNAs are adaptor molecules that interpret and act on information in DNA.

<p>False</p> Signup and view all the answers

What are charged tRNAs used during translation called?

<p>Charged tRNAs</p> Signup and view all the answers

Which enzymes catalyze the addition of the correct amino acid to tRNAs?

<p>tRNA synthetases</p> Signup and view all the answers

What is the size of the fully assembled ribosome in E. coli?

<p>70S</p> Signup and view all the answers

What component binds mRNA and identifies the start codon where translation begins?

<p>Ribosome</p> Signup and view all the answers

What are the three important sites in the ribosome during translation?

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

Which site in the ribosome is responsible for binding the tRNA that carries the next amino acid during translation?

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

What is the size of the small ribosomal subunit in the fully assembled E. coli ribosome?

<p>30S</p> Signup and view all the answers

How many proteins does the large eukaryotic ribosomal subunit contain?

<p>45 – 50 proteins</p> Signup and view all the answers

During the initiation phase of translation, what molecule provides the energy for the binding of the large ribosomal subunit?

<p>GTP</p> Signup and view all the answers

What is the composition of the fully assembled eukaryotic ribosome in terms of Svedberg units?

<p>80S</p> Signup and view all the answers

What important role does the peptidyl (P) site of a ribosome serve during translation?

<p>It holds the tRNA linked to the growing polypeptide chain.</p> Signup and view all the answers

What is the primary function of tRNA during the translation process?

<p>To transport amino acids to the ribosome.</p> Signup and view all the answers

Which of the following accurately describes the phases of translation?

<p>Translation is divided into initiation, elongation, and termination.</p> Signup and view all the answers

What is the role of the anticodon in tRNA molecules?

<p>It forms hydrogen bonds with mRNA codons.</p> Signup and view all the answers

Which of the following statements about ribosomal structure is correct?

<p>Ribosomes consist of multiple ribosomal RNAs and proteins.</p> Signup and view all the answers

What distinguishes the ribosome composition in E. coli from that in eukaryotes?

<p>E. coli ribosomes are composed of different proportions of rRNA and proteins.</p> Signup and view all the answers

During which phase of translation do ribosomes read each mRNA codon?

<p>Elongation</p> Signup and view all the answers

What is the primary function of tRNA synthetases in translation?

<p>They attach the correct amino acid to tRNA.</p> Signup and view all the answers

What is a characteristic feature of the cloverleaf structure of tRNA?

<p>It includes an anticodon loop and an acceptor stem.</p> Signup and view all the answers

Which of the following correctly describes the possible error rate in tRNA synthetase activity?

<p>Very low error rate due to proofreading systems.</p> Signup and view all the answers

What is the direction of mRNA translation by ribosomes?

<p>5′ to 3′</p> Signup and view all the answers

What is the primary role of the Shine-Dalgarno sequence in bacterial translation initiation?

<p>To pair with the 16S rRNA and position the start codon</p> Signup and view all the answers

Which of the following components binds to the start codon during the initiation of translation in E. coli?

<p>The initiator tRNA carrying fMet</p> Signup and view all the answers

What stabilizes the small ribosomal subunit during the formation of the preinitiation complex in bacteria?

<p>IF3</p> Signup and view all the answers

In eukaryotic translation initiation, which sequence helps locate the start codon within the mRNA?

<p>Kozak Sequence</p> Signup and view all the answers

Which structure is formed when the 30S and 50S ribosomal subunits join after initiation in E. coli?

<p>70S initiation complex</p> Signup and view all the answers

What modified amino acid is incorporated into the initiator tRNA during bacterial translation initiation?

<p>N-formylmethionine (fMet)</p> Signup and view all the answers

What drives the union of the small and large ribosomal subunits during translation initiation in bacteria?

<p>Hydrolysis of GTP</p> Signup and view all the answers

Which component is not part of the six molecular components required for the initiation of translation?

<p>Aminoacyl-tRNA synthetase</p> Signup and view all the answers

What occurs to IF proteins during the final step of initiation in translation?

<p>They dissociate from the complex</p> Signup and view all the answers

What is a key distinguishing feature of the eukaryotic ribosome compared to the prokaryotic ribosome?

<p>Eukaryotic ribosomes use eIF proteins</p> Signup and view all the answers

Study Notes

Translation

  • Messenger RNA (mRNA) carries the genetic code from DNA to ribosomes for protein synthesis.
  • Translation is the process of synthesizing a polypeptide (protein) using mRNA as a template.
  • Mature mRNA contains a coding region, a 5' untranslated region (5'UTR) and 3'UTR.
  • Translation begins at a start codon and ends at a stop codon, defining the N-terminus and C-terminus of the protein respectively.
  • The genetic code establishes the correspondence between mRNA nucleotide sequences and the amino acid sequences of polypeptides.

Transfer RNA (tRNA)

  • tRNA acts as an adaptor molecule, interpreting mRNA codons.
  • tRNA has an anticodon that base pairs with the corresponding mRNA codon.
  • tRNAs are charged with amino acids by tRNA synthetases, which ensure the accuracy of the genetic code.
  • tRNA synthetases have proofreading systems to minimize errors.

Ribosomes

  • Ribosomes are the sites of protein synthesis.
  • Ribosomes consist of ribosomal RNAs (rRNAs) and proteins.
  • Ribosomes translate mRNA in the 5' to 3' direction.
  • Bacterial and eukaryotic ribosomes have different sizes and compositions.
  • Bacterial ribosomes are 70S, consisting of 30S and 50S subunits.
  • Eukaryotic ribosomes are 80S, consisting of 40S and 60S subunits.

Ribosomal Subunits

  • Ribosomes have three important sites: aminoacyl (A) site, peptidyl (P) site, and exit (E) site.
  • The A site binds a new tRNA carrying the next amino acid to be added.
  • The P site holds the tRNA carrying the growing polypeptide chain.
  • The E site provides an exit pathway for empty tRNAs.
  • Ribosomes also have a polypeptide channel where the polypeptide chain emerges.

Ribosome Structure and Function

  • Ribosomes are complex molecular machines that synthesize proteins.
  • They consist of two subunits: a large subunit and a small subunit.
  • Subunit size is measured in Svedberg units (S), which reflects size, shape, and hydration.

Ribosomes in Prokaryotes (E. coli)

  • The most extensively studied bacterial ribosomes are those of E. coli.
  • The small subunit (30S) contains 21 proteins and a 16S rRNA molecule.
  • The large subunit (50S) contains 31 proteins, a 5S rRNA, and a 23S rRNA.
  • The complete ribosome is 70S.

Ribosomes in Eukaryotes (Mammals)

  • Mammalian ribosomes are the best understood eukaryotic ribosomes.
  • The small subunit (40S) contains roughly 35 proteins and an 18S rRNA.
  • The large subunit (60S) contains 45-50 proteins and three rRNA molecules: 5S, 5.8S, and 28S.
  • The fully assembled ribosome is 80S.

Important Ribosomal Regions

  • The aminoacyl site (A site) binds new tRNAs carrying amino acids to be added to the polypeptide chain.
  • The peptidyl site (P site) holds the tRNA carrying the growing polypeptide chain.
  • The exit site (E site) allows discharged tRNAs to leave the ribosome after contributing their amino acid.
  • Ribosomes also have a polypeptide channel through which the polypeptide chain emerges.

Translation Phases

  • Translation comprises three main phases: initiation, elongation, and termination.
  • These phases are similar in bacteria and eukaryotes, but with some differences.

Translation Initiation: Similarities

  • Initiation begins with the small ribosomal subunit binding near the 5' end of the mRNA and recognizing the start codon (AUG).
  • The initiator tRNA, carrying the first amino acid of the polypeptide, binds to the start codon.
  • The large ribosomal subunit associates with the small subunit forming the intact ribosome.
  • Initiation factors (proteins) regulate ribosome formation and initiator tRNA binding.
  • GTP provides the energy for initiation.

Bacterial Translation Initiation

  • Six components participate in bacterial initiation: mRNA, the small ribosomal subunit, the large ribosomal subunit, the initiator tRNA, three initiation factors, and GTP.
  • Primarily, the small (30S) subunit binds with initiation factor (IF3) preventing premature joining with the large (50S) subunit.
  • The 30S-IF3 complex binds near the 5' end of the mRNA and searches for a consensus sequence.

The Shine-Dalgarno Sequence

  • The Shine-Dalgarno sequence is a purine-rich (AG) sequence of about six nucleotides located 3-9 nucleotides upstream of the start codon.
  • A complementary pyrimidine-rich (UC) sequence is found near the 3' end of the 16S rRNA.
  • This pairing positions the start codon (AUG) in the P site of the fully assembled ribosome.

Second Step of Bacterial Initiation

  • The initiator tRNA binds to the start codon, which will become the P site.
  • The amino acid on the initiator tRNA is a modified form called N-formylmethionine (fMet).
  • IF2 and GTP bind to the tRNAfMet, and IF1 joins the complex forming the 30S initiation complex.

Final Step of Bacterial Initiation

  • The 50S subunit joins the 30S subunit to form the complete ribosome.
  • GTP hydrolysis to GDP drives subunit association.
  • IF1, IF2, and IF3 dissociate as the 30S and 50S subunits merge to create the 70S initiation complex.

Eukaryotic Translation Initiation

  • The eukaryotic small (40S) ribosomal subunit forms a complex with eukaryotic initiation factors (eIFs).
  • eIF1A, eIF3, and a charged tRNAmet bind the small subunit forming the preinitiation complex.
  • This complex binds to the 5' cap of the mRNA.

Later Steps of Eukaryotic Initiation

  • The preinitiation complex joins a group of at least four eIF4 proteins already assembled at the 5’ cap.
  • This combined complex is called the initiation complex.
  • It uses ATP to move the small subunit along the 5' UTR in search of the start codon.

Final Steps of Eukaryotic Initiation

  • The start codon (AUG) is located because it's within a consensus sequence called the Kozak sequence: 5'-ACCAUGG-3'.
  • The large (60S) subunit joins the complex (using GTP energy) and the eIF proteins dissociate.

tRNA Structure and Function

  • tRNA molecules have a distinctive cloverleaf structure with a 3' acceptor stem for amino acid attachment and an anticodon loop for pairing with mRNA codons.
  • tRNA molecules are charged when they carry an amino acid, and uncharged when they don’t.
  • tRNA synthetases, enzymes, catalyze the addition of the correct amino acid to each tRNA.

tRNA Synthetases

  • tRNA synthetases recognize specific tRNAs based on their structure, particularly the acceptor stem.
  • The active site accommodates the correct tRNA and amino acid.
  • ATP fuels the attachment process.
  • tRNA synthetases have a proofreading mechanism to minimize errors.

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Related Documents

BIOL 23373 - General Genetics Lecture 10 - Translation I PDF
BIOL 23373 General Genetics Fall 2024 Lecture 11 Translation I Lecture Notes PDF

Description

This quiz covers the process of translation in protein synthesis, focusing on the roles of messenger RNA (mRNA) and transfer RNA (tRNA). You'll explore how mRNA carries genetic information, the function of tRNA in building proteins, and the importance of ribosomes in this essential biological process.

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