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Questions and Answers
What is the primary location of genomic DNA in eukaryotes?
What is the primary location of genomic DNA in eukaryotes?
What is the name of the process that transfers information from DNA to mRNA?
What is the name of the process that transfers information from DNA to mRNA?
Which enzyme is responsible for the transcription process?
Which enzyme is responsible for the transcription process?
In which direction does RNA polymerase read the DNA template during transcription?
In which direction does RNA polymerase read the DNA template during transcription?
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What happens to genomic DNA in the cytoplasm of eukaryotic cells?
What happens to genomic DNA in the cytoplasm of eukaryotic cells?
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What is the direction of transcription in both prokaryotes and eukaryotes?
What is the direction of transcription in both prokaryotes and eukaryotes?
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What percentage of DNA is typically transcribed into RNA in eukaryotes?
What percentage of DNA is typically transcribed into RNA in eukaryotes?
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Which RNA type is synthesized by RNA polymerase I?
Which RNA type is synthesized by RNA polymerase I?
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What is the primary function of rRNA in protein synthesis?
What is the primary function of rRNA in protein synthesis?
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In prokaryotes, what happens to the majority of their DNA in regard to transcription?
In prokaryotes, what happens to the majority of their DNA in regard to transcription?
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What role does tRNA play in protein synthesis?
What role does tRNA play in protein synthesis?
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Which transcription system is responsible for synthesizing mRNA?
Which transcription system is responsible for synthesizing mRNA?
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Which of the following statements about eukaryotic transcription is true?
Which of the following statements about eukaryotic transcription is true?
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What is the role of RNA polymerase II during transcription?
What is the role of RNA polymerase II during transcription?
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Which is NOT a step in the maturation of mRNA?
Which is NOT a step in the maturation of mRNA?
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What is the outcome of alternative splicing?
What is the outcome of alternative splicing?
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What does RNA polymerase III primarily transcribe?
What does RNA polymerase III primarily transcribe?
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Which sequence is critical for the termination of transcription?
Which sequence is critical for the termination of transcription?
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In the translation process, which step directly follows elongation?
In the translation process, which step directly follows elongation?
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During transcription by RNA polymerase I, which molecule is produced?
During transcription by RNA polymerase I, which molecule is produced?
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What is the first event in the translation process?
What is the first event in the translation process?
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What is the correct direction of peptide synthesis during translation?
What is the correct direction of peptide synthesis during translation?
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What role does the A site of the ribosome play during translation?
What role does the A site of the ribosome play during translation?
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What happens during the transpeptidation step of translation?
What happens during the transpeptidation step of translation?
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What triggers the termination of translation?
What triggers the termination of translation?
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Which of the following is NOT a step in the peptide synthesis process?
Which of the following is NOT a step in the peptide synthesis process?
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Which of the following sites in the ribosome is where the 'empty' tRNA moves?
Which of the following sites in the ribosome is where the 'empty' tRNA moves?
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What does the tRNA's anticodon do during translation?
What does the tRNA's anticodon do during translation?
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Which of the following does NOT describe the role of decoding in translation?
Which of the following does NOT describe the role of decoding in translation?
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What is the primary role of transcription factors in the initiation of transcription?
What is the primary role of transcription factors in the initiation of transcription?
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Which RNA polymerase is responsible for the transcribing of tRNA genes?
Which RNA polymerase is responsible for the transcribing of tRNA genes?
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What occurs during the elongation phase of transcription?
What occurs during the elongation phase of transcription?
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Where are the promoter sequences located for RNA polymerases I and II?
Where are the promoter sequences located for RNA polymerases I and II?
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Which of the following statements about chromatin is true during transcription?
Which of the following statements about chromatin is true during transcription?
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What is the significance of the TATA box in transcription?
What is the significance of the TATA box in transcription?
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What distinguishes RNA polymerase III from RNA polymerases I and II?
What distinguishes RNA polymerase III from RNA polymerases I and II?
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What happens to the ribonucleotide uracil (U) during RNA transcription?
What happens to the ribonucleotide uracil (U) during RNA transcription?
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Which process is essential to begin RNA transcription after chromatin decondensation?
Which process is essential to begin RNA transcription after chromatin decondensation?
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Study Notes
Ferhat Abbas University, Setif 1-Setif
- Faculty of Natural and Life Sciences
- Department of TC/SNV
- 2nd Year LMD
- Module: Genetics
- Module Coordinators:
- Dr. BOUZID: [email protected]
- Dr. OUARET-GUIDOUM: [email protected]
- Academic Year 2023-2024
Chapter II: Protein Synthesis
- DNA carries genetic information
- In eukaryotes, genomic DNA is exclusively in the nucleus
- DNA is not found in the cytoplasm due to cytoplasmic nucleases
- Expression involves transferring genetic information from DNA to mRNA, which moves out of the nucleus
- The process of transferring DNA information to RNA is called transcription
Transcription
- Transcription is a reaction involving polymerization of ribonucleotides based on a DNA template strand (3' → 5')
- The reaction is carried out by RNA polymerase
- Transcription direction is always 5' → 3'
Transcription Systems in Prokaryotes and Eukaryotes
- In prokaryotes, approximately 100% of the DNA is transcribed into RNA. High gene density.
- In eukaryotes, only about 3% of the DNA is transcribed. Low gene density.
- At least three different transcription systems exist, based on the type of RNA synthesized.
- rRNA synthesized by RNA pol I. Gene Class I.
- mRNA synthesized by RNA pol II. Gene Class II.
- tRNA synthesized by RNA pol III. Gene Class III.
Roles of Different RNAs in Protein Synthesis
- rRNA functions as the factory for the formation of new proteins, forming polypeptide chains in association with ribosomal proteins, to create ribosomes.
- rRNA also functions as machinery, associating with ribosomal proteins to form ribosomes.
- mRNA carries genetic information from the nucleus to the cytoplasm, where it is translated at the ribosomes.
- The message is specifically transported to the ribosomes where the message is processed.
- tRNA acts as both a transporter and a synthesis enzyme for polypeptides.
- It is responsible for carrying amino acids to the ribosomes
Transcription
- The transcription process occurs in three main steps: initiation, elongation, and termination.
- Transcription machinery assembles and begins transcribing DNA into RNA during initiation.
- The RNA strand extends as nucleotides are added during elongation.
- Termination occurs when the process stops.
- Different regulatory sequences allow the initiation of transcription. E.g., a promoter sequence.
- The location of these sequences relative to the initiation site is characteristic for each RNA polymerase.
- RNA polymerases I and II are located within 100 bp upstream of the transcription unit (TU). Located in the 5' region of the gene.
- RNA polymerase III is present in the TU and is located in the coding region of the gene.
- Each enzyme requires accessory proteins called transcription factors that bind specifically to promoter regions
1- Initiation
- Similar to other enzymes, each enzyme requires accessory proteins called transcription factors that bind specifically to promoter regions.
- TFII
- TFIII
- TFI
1- Transcription by RNA polymerase I
- The first transcriptional complex is formed by transcription factors, and RNA polymerase I, UCE, core promoter, and TU.
- The complex works with a pre-rRNA molecule.
2- Transcription by RNA polymerase II
- The second transcriptional complex is formed by transcription factors, and RNA polymerase II, TATA, promoter region, and TU.
- The complex works with a pre-mRNA molecule.
3- Transcription by RNA polymerase III
- The third transcriptional complex is formed by transcription factors, and RNA polymerase III, promoter region, and TU.
- The complex works with pre-tRNA molecules..
2- Elongation
- Involves systematic addition of complementary ribonucleotides to deoxyribonucleotides.
- Replaces T with U in transcription.
- Begins with the decondesation of chromatin, and opening of the double helix to form the transcription loop.
3- Termination
- Transcription ends with a process called termination where the transcript ends.
- Termination depends on sequences within the RNA.
- Sequences that determine the end (3′) of each RNA functional are specific to each type of RNA polymerase
Translation
- Translation is a cyclical process that follows a specific order of events (initiation, elongation, and termination)
- Ribosome subunits are dissociated after termination, enabling a new cycle.
- Translation events need a large number of proteins called translation factors.
Translation - peptide synthesis stages
- Peptide synthesis
- N-terminus to C-terminus of the polypeptide chain
- Sequential amino acids add to the C-terminus of the chain.
- Decoding
- Formation of the peptide
- Translocation
Various stages of Translation
- Step 1: Decoding
- Step 2: Peptide Bond formation
- Step 3: Translocation
Termination of Translation
- Translation stops when a stop codon (UAG, UAA, or UGA) appears in the A site of the ribosome
- A release factor disassociates the ribosome subunits
Transcription by RNA polymerase I (RNA Pol I)
- The 3 transcription systems involve gene groups transcribed by different RNA polymerases
- RNA Pol I transcribes ribosomal RNA genes (rRNA).
- Transcribes long transcripts (45S) composed of rRNA sequences and spacer sequences
- Post-transcriptional cleavages generate mature rRNA. (e.g., 18S, 5.8S, 28S)
Transcription by RNA polymerase II (RNA Pol II)
- RNA Pol II transcribes mRNA genes producing long transcripts containing translated sequences (exons) and sequences needing removal (introns).
- mRNA maturation process includes:
- Addition of a 5' cap
- Splicing of introns
- Addition of a poly-A tail at 3′
- Production of mRNA (mature transcripts)
Transcription by RNA polymerase III (RNA Pol III)
- RNA Pol III transcribes tRNA genes (and other RNAs) creating long transcripts.
- Transcripts fold into a cloverleaf structure.
- One tRNA end binds to a specific amino acid, while the other end is specific to a codon on mRNA.
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Description
This quiz covers key concepts from Chapter II of the Genetics module focusing on protein synthesis. It explores the processes of transcription, the role of DNA and RNA, and differences between prokaryotic and eukaryotic transcription systems. Test your understanding of these fundamental biological processes.
