Gene Expression and Transcription Quiz
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Questions and Answers

Which enzyme transcribes all eukaryotic tRNA genes?

  • RNA polymerase II
  • RNA polymerase I
  • RNA polymerase III (correct)
  • RNA polymerase IV

What is the first step in the initiation phase of protein biosynthesis?

  • tRNA charging
  • Formation of the 43 S pre initiation complex
  • Ribosomal dissociation (correct)
  • Binding of eukaryotic initiation factors

What is one of the significant processes required for converting pre-tRNA into mature tRNA?

  • Splicing of exons
  • Transcription initiation
  • Folding and base pairing (correct)
  • Addition of a 5' cap

Which nucleotide sequence codes for Methionine (Met) during protein synthesis?

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

What is added to the 3' end of pre-tRNA during processing?

<p>A CCA sequence (D)</p> Signup and view all the answers

What is the approximate size of eukaryotic ribosomal subunits combined?

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

What is tRNA charging?

<p>Recognition and attachment of specific amino acids to tRNA (C)</p> Signup and view all the answers

Which of the following statements about the flow of genetic information is correct?

<p>Transcription occurs prior to translation. (D)</p> Signup and view all the answers

What is the function of eukaryotic initiation factors (elFs) in the initiation phase?

<p>To facilitate ribosomal dissociation and bind to the 40 S subunit (B)</p> Signup and view all the answers

In the genetic code table, which first nucleotide results in multiple possible amino acids?

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

What modification is NOT typically associated with eukaryotic pre-rRNA processing?

<p>Addition of a Poly-A tail (A)</p> Signup and view all the answers

Which component plays an essential role in decoding mRNA during protein synthesis?

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

What is the correct order of the phases in protein biosynthesis?

<p>Initiation, elongation, termination (D)</p> Signup and view all the answers

Which of the following is TRUE regarding the structure of codons?

<p>Each codon is a triplet sequence of nucleotides. (B)</p> Signup and view all the answers

During the formation of the 43 S pre initiation complex, what binary complex forms before binding to the 40 S ribosomal subunit?

<p>elF2 and GTP (A)</p> Signup and view all the answers

What is the role of ribosomes in protein synthesis?

<p>To coordinate the interaction between tRNA, mRNA, and protein factors (A)</p> Signup and view all the answers

What is the first nucleotide added during RNA transcription?

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

What role does the cap structure serve in mRNA?

<p>It enhances ribosome binding for translation. (D)</p> Signup and view all the answers

What happens during the splicing process of mRNA?

<p>Introns are removed and exons are ligated. (A)</p> Signup and view all the answers

What is the significance of the poly(A) tail on mRNA?

<p>It aids in the transport of mRNA from the nucleus to the cytoplasm. (A)</p> Signup and view all the answers

Which of the following accurately describes the RNA polymerase function during elongation?

<p>It moves along the DNA template strand in the 5' to 3' direction. (C)</p> Signup and view all the answers

Which characteristic of the cap added to mRNA is accurate?

<p>It is composed of a tri-phosphate bridge. (D)</p> Signup and view all the answers

What does the term 'primary transcript' refer to in eukaryotic transcription?

<p>The initial RNA sequence synthesized before processing. (C)</p> Signup and view all the answers

Which of the following statements about termination in transcription is true?

<p>Termination depends on specific termination signals. (B)</p> Signup and view all the answers

Flashcards

Ribosomes

Molecular machines that coordinate the interaction between mRNA, tRNA, enzymes, and protein factors during protein synthesis.

Genetic Code

Relationship between the nucleotide sequence in DNA (or mRNA) and the amino acid sequence in a polypeptide chain.

Triplet Codon

Sequence of three nucleotides that codes for a specific amino acid.

Initiation of Protein Biosynthesis

First stage of protein synthesis, where the ribosome assembles around mRNA to begin the translation process.

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tRNA charging

Process of attaching a specific amino acid to tRNA.

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Initiator Codon

Codon (AUG) that signals the start of protein synthesis, usually coding for methionine (Met).

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Ribosomal subunits

Eukaryotic ribosomes have two subunits (large and small) that come together when protein synthesis begins.

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Protein Biosynthesis Stages

Protein synthesis happens in distinct phases: initiation, elongation, and termination.

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mRNA processing

Modification of pre-mRNA to create mature mRNA, which can then be transported to the cytoplasm for protein synthesis.

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tRNA processing

Modification of pre-tRNA to create a mature, functional tRNA molecule. This involves folding, cleavage, splicing, addition of CCA, and base modifications.

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rRNA processing

Processing of pre-rRNA to produce the mature ribosomal RNA components. This occurs within the nucleolus.

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Transcription

The process of copying a gene's DNA sequence into an mRNA molecule.

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Translation

Decoding the mRNA sequence into a specific polypeptide chain of amino acids.

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Codon

A three-nucleotide sequence in mRNA that specifies a particular amino acid.

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tRNA

Small RNA molecule that carries amino acids to the ribosome during translation. It "adapts" codons to amino acids.

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mRNA Capping

Adding a modified guanine nucleotide to the 5' end of pre-mRNA.

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mRNA Polyadenylation

Adding a string of adenine nucleotides (poly(A) tail) to the 3' end of pre-mRNA.

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Splicing

Removing introns (non-coding regions) and joining exons (coding regions) of pre-mRNA to form mature mRNA.

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Exons

Coding segments of a gene that are expressed in mRNA.

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Introns

Non-coding segments of a gene that are removed during mRNA processing.

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Transcription Unit

A segment of DNA that is transcribed into a primary transcript.

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Primary Transcript

The immediate product of transcription, a precursor to mature mRNA.

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RNA Polymerase

Enzyme that synthesizes RNA during transcription.

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Study Notes

Gene Expression

  • Gene expression is the process of protein synthesis, involving RNA transcription and translation.
  • A gene is a segment of DNA containing genetic information that codes for a polypeptide chain.
  • A genome is the total DNA content of a cell, equal to the total number of genes in a cell.

Transcription

  • Transcription is the synthesis of RNA from a DNA template by RNA polymerase enzymes.
  • Only one DNA strand (template strand) is copied. The other strand is the coding strand.
  • RNA polymerase adds ribonucleotides to the 3' end of the growing RNA strand in the 5' to 3' direction.
  • Uracil is used instead of thymine in RNA.

Steps of RNA Synthesis

  • Initiation: An initiation complex is formed using initiation protein factors and RNA polymerase, necessary to start the process.
  • Elongation: RNA polymerase moves along the template DNA, synthesizing RNA in the 5' to 3' direction. Elongation protein factors are needed for eukaryotes.
  • Termination: This step signifies the end of RNA synthesis.

Processing of Eukaryotic mRNA precursor

  • Capping: A 5' methyl guanosine cap is added to the mRNA to protect it and aid in ribosome binding.
  • Polyadenylation: A poly(A) tail is added to the 3' end of mRNA. This tail aids in mRNA stability and transport to the cytoplasm.

Genetic Code

  • mRNA contains four nucleotides (A, G, C, U).
  • Codons (three nucleotides) determine specific amino acids.
  • 61 codons code for 20 amino acids.
  • 3 codons are stop codons (UAA, UAG, UGA), signaling the end of translation.

Protein Biosynthesis

  • It's the flow of genetic information from DNA to protein.
  • Transcription produces mRNA, carrying genetic information from DNA to ribosomes.
  • Translation involves converting mRNA codons into an amino acid sequence.
  • Ribosomes act as the protein synthesis machinery, reading mRNA and assembling amino acids into a polypeptide chain.

Protein Synthesis Steps

  • Initial ribosomal dissociation into 40S and 60S subunits.

  • Formation of a pre-initiation complex including GTP, Met-tRNA, and the 40S subunit.

  • Formation of the 48S initiation complex.

  • Formation of the 80S initiation complex with the addition of the 60S subunit.

  • Elongation: involves multiple steps: -Binding of aminoacyl-tRNA to the A site. -Peptide bond formation between amino acids. -translocation moves peptidyl-tRNA to the P site.

  • Termination: release of the polypeptide chain when a stop codon is encountered. Release factors mediate hydrolysis of the peptide bond, releasing the protein.

Protein Processing

  • Proteins are modified after synthesis (proteolysis, glycosylation).
  • Proper folding is often important for protein function.
  • Molecular chaperones assist in protein folding.

Inhibitors of Protein Biosynthesis

  • Some antibiotics block prokaryotic protein synthesis, including streptomycin, tetracyclines, chloramphenicol, and erythromycin. Different antibiotics block different synthesis steps.

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Description

Test your knowledge on gene expression, including the processes of transcription and RNA synthesis. This quiz covers the key steps and components involved in transforming DNA into functional proteins. Understand the essential roles of RNA polymerase and the differences in strands during transcription.

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