Transcription, Translation, and Point Mutations – Step-by-Step Study Guidance

Study Guide - Smart Notes

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Q1. True/False: In transcription, primase makes an RNA primer to which RNA polymerase can attach.

Background

Topic: Transcription vs. DNA Replication

This question tests your understanding of the roles of primase and RNA polymerase during transcription and how they differ from DNA replication.

Key Terms:

Primase: An enzyme that synthesizes RNA primers during DNA replication.
RNA Polymerase: The enzyme responsible for synthesizing RNA from a DNA template during transcription.

Step-by-Step Guidance

Recall the main enzymes involved in transcription and DNA replication. Consider what each enzyme does in each process.
Think about whether primase is required for RNA polymerase to begin transcription, or if this is a feature of DNA replication.
Decide if the statement accurately describes what happens during transcription, or if it confuses the two processes.

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Q2. True/False: During transcription, the DNA double helix is unwound by RNA polymerase.

Background

Topic: Mechanism of Transcription

This question tests your knowledge of how the DNA double helix is unwound during transcription and which enzyme is responsible.

Key Terms:

RNA Polymerase: Enzyme that synthesizes RNA and unwinds DNA during transcription.
Helicase: Enzyme that unwinds DNA during replication (not transcription).

Step-by-Step Guidance

Recall the process of transcription and which enzymes are involved in unwinding the DNA.
Consider whether RNA polymerase has the ability to unwind DNA, or if another enzyme is required.
Determine if the statement is accurate based on your understanding of transcription.

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Q3. The nucleotide sequence of the start codon in an mRNA is 5’AUG3’. What was the sequence of the DNA in the template strand that gave rise to this mRNA start codon?

Background

Topic: Transcription and Base Pairing

This question tests your understanding of how mRNA is synthesized from a DNA template and the rules of complementary base pairing.

Key Terms and Concepts:

Template Strand: The DNA strand used by RNA polymerase to synthesize mRNA.
Base Pairing Rules: A pairs with U (in RNA), T with A, C with G, and G with C.

Step-by-Step Guidance

Write out the mRNA start codon: 5'AUG3'.
Recall that mRNA is synthesized in the 5' to 3' direction, using the DNA template strand as a guide.
Apply the base pairing rules to determine the DNA template sequence that would produce this mRNA codon.
Remember to write the DNA template strand in the 3' to 5' direction, as it is read by RNA polymerase in this orientation.

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Q4. What is the role of the TATA box in eukaryotic transcription? What is the role of the TBP?

Background

Topic: Transcription Initiation in Eukaryotes

This question tests your understanding of promoter elements and transcription factors in eukaryotic gene expression.

Key Terms:

TATA Box: A DNA sequence found in the promoter region of many eukaryotic genes.
TBP (TATA-binding protein): A protein that binds to the TATA box and helps initiate transcription.

Step-by-Step Guidance

Describe where the TATA box is located relative to the transcription start site.
Explain how the TATA box functions in recruiting transcription machinery.
Discuss the specific role of TBP in recognizing the TATA box and facilitating the assembly of the transcription initiation complex.

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Q5. Explain the role of the FACT protein complex during eukaryotic transcription.

Background

Topic: Chromatin Remodeling in Transcription

This question tests your understanding of how transcription occurs in the context of chromatin and the role of protein complexes in facilitating this process.

Key Terms:

FACT Complex: Facilitates Chromatin Transcription complex, involved in nucleosome disassembly and reassembly.
Nucleosome: The basic unit of DNA packaging in eukaryotes.

Step-by-Step Guidance

Recall that DNA is wrapped around histone proteins to form nucleosomes, which can impede access by RNA polymerase.
Describe how the FACT complex interacts with nucleosomes during transcription.
Explain how FACT helps RNA polymerase move through chromatin by temporarily displacing histones and then reassembling nucleosomes after transcription passes.

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Q6. Describe the sequence of events involved in each of the phases of transcription for eukaryotes: initiation, elongation, termination. Do not memorize the figures.

Background

Topic: Eukaryotic Transcription Mechanism

This question tests your ability to describe the main steps of transcription in eukaryotes, focusing on the sequence of molecular events.

Key Terms:

Initiation: Assembly of transcription machinery at the promoter and start of RNA synthesis.
Elongation: RNA polymerase moves along the DNA, synthesizing RNA.
Termination: Release of the RNA transcript and dissociation of the transcription complex.

Step-by-Step Guidance

For initiation, describe how transcription factors and RNA polymerase assemble at the promoter region.
For elongation, explain how RNA polymerase synthesizes the RNA strand, moving along the DNA template.
For termination, outline how the transcription process ends and the RNA molecule is released.

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Q7. In eukaryotes, the RNA produced by transcription is modified to form mRNA. What are the steps involved?

Background

Topic: RNA Processing in Eukaryotes

This question tests your understanding of the post-transcriptional modifications that convert pre-mRNA into mature mRNA.

Key Terms:

5' Capping: Addition of a modified guanine nucleotide to the 5' end.
Splicing: Removal of introns and joining of exons.
Polyadenylation: Addition of a poly-A tail to the 3' end.

Step-by-Step Guidance

List the three main modifications that occur to pre-mRNA in eukaryotes.
Briefly describe the purpose of each modification (e.g., stability, export, translation efficiency).
Arrange the steps in the order they typically occur.

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Q8. Describe one function of the 5’ cap and the poly-A tail for the mRNA in eukaryotes.

Background

Topic: mRNA Stability and Translation

This question tests your understanding of the roles of mRNA modifications in eukaryotic cells.

Key Terms:

5' Cap: Modified guanine nucleotide added to the 5' end of mRNA.
Poly-A Tail: String of adenine nucleotides added to the 3' end of mRNA.

Step-by-Step Guidance

Recall the main functions of the 5' cap and the poly-A tail.
Choose one function for each and explain how it benefits the mRNA molecule.

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Q9. The mutation in the FMR1 gene that leads to fragile X syndrome is in the promoter, not in the coding sequence. Why would a mutation in the promoter matter?

Background

Topic: Gene Regulation and Promoter Function

This question tests your understanding of how mutations outside the coding region can affect gene expression.

Key Terms:

Promoter: DNA sequence where transcription machinery binds to initiate transcription.
Gene Expression: The process by which information from a gene is used to synthesize a functional product.

Step-by-Step Guidance

Recall the role of the promoter in gene transcription.
Explain how a mutation in the promoter could affect the binding of transcription factors or RNA polymerase.
Discuss how changes in promoter function could impact the amount of gene product produced.

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Q10. What is alternative splicing and what does it lead to?

Background

Topic: RNA Processing and Protein Diversity

This question tests your understanding of how alternative splicing increases the diversity of proteins produced from a single gene.

Key Terms:

Alternative Splicing: The process by which different combinations of exons are joined together to produce multiple mRNA variants from one gene.
Isoforms: Different protein products resulting from alternative splicing.

Step-by-Step Guidance

Define alternative splicing and describe how it occurs during mRNA processing.
Explain the consequence of alternative splicing for protein diversity in eukaryotes.

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Q11. The mutation in the FXN gene leading to Friedreich’s Ataxia is in one of the introns. Why would increasing the length of an intron matter?

Background

Topic: Introns and Gene Expression

This question tests your understanding of the importance of intron length and sequence in gene expression and mRNA processing.

Key Terms:

Intron: Non-coding sequence within a gene that is removed during RNA splicing.
Splicing: The process of removing introns and joining exons in pre-mRNA.

Step-by-Step Guidance

Recall the role of introns in pre-mRNA and how they are removed during splicing.
Consider how increasing the length of an intron could affect splicing efficiency or accuracy.
Discuss possible consequences for gene expression if splicing is disrupted.

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Q12. A tRNA molecule carries an amino acid. Where is the amino acid attached?

Background

Topic: tRNA Structure and Function

This question tests your knowledge of the structure of tRNA and where amino acids are covalently attached.

Key Terms:

tRNA: Transfer RNA, which brings amino acids to the ribosome during translation.
Acceptor Stem: The region of tRNA where the amino acid is attached.

Step-by-Step Guidance

Recall the general structure of tRNA, including the acceptor stem and anticodon loop.
Identify the specific end of the tRNA molecule where the amino acid is covalently linked.

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Q13. What is an anticodon?

Background

Topic: Translation and tRNA Function

This question tests your understanding of how tRNA recognizes codons in mRNA during translation.

Key Terms:

Anticodon: A sequence of three nucleotides in tRNA that pairs with a complementary codon in mRNA.
Codon: A sequence of three nucleotides in mRNA that specifies an amino acid.

Step-by-Step Guidance

Define what an anticodon is and where it is found.
Explain how the anticodon interacts with the mRNA codon during translation.

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Q14. Describe the sequence of events involved in eukaryotic translation: initiation, elongation, and termination. Do not memorize the figures.

Background

Topic: Protein Synthesis in Eukaryotes

This question tests your ability to describe the main steps of translation in eukaryotic cells.

Key Terms:

Initiation: Assembly of the ribosome on the mRNA and recruitment of the first tRNA.
Elongation: Addition of amino acids to the growing polypeptide chain.
Termination: Release of the completed polypeptide when a stop codon is reached.

Step-by-Step Guidance

For initiation, describe how the small ribosomal subunit binds to the mRNA and the initiator tRNA pairs with the start codon.
For elongation, explain how amino acids are added one by one as the ribosome moves along the mRNA.
For termination, outline how the process ends when a stop codon is encountered and the polypeptide is released.

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Q15. True/False: ATP hydrolysis is required for assembly of the ribosome.

Background

Topic: Translation Initiation Energy Requirements

This question tests your understanding of the energy requirements for ribosome assembly during translation initiation.

Key Terms:

ATP Hydrolysis: The breakdown of ATP to ADP and inorganic phosphate, releasing energy.
GTP: Another nucleotide triphosphate often used as an energy source in translation.

Step-by-Step Guidance

Recall which energy molecules are used during translation initiation (ATP or GTP).
Consider the steps of ribosome assembly and which steps require energy input.
Determine if ATP hydrolysis is specifically required for ribosome assembly, or if another molecule is used.

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Q16. What is the function of the release factor?

Background

Topic: Translation Termination

This question tests your understanding of how translation ends and the role of release factors in this process.

Key Terms:

Release Factor: Protein that recognizes stop codons and promotes release of the polypeptide from the ribosome.
Stop Codon: Codon in mRNA that signals the end of translation.

Step-by-Step Guidance

Recall what happens when a stop codon enters the ribosome's A site during translation.
Describe how the release factor interacts with the ribosome and the polypeptide chain.
Explain the outcome of release factor activity for the newly synthesized protein.

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Q17. When a ribosome translates an mRNA, the polypeptide starts with Methionine. But not every protein in our cells starts with Methionine. Why?

Background

Topic: Post-Translational Modification

This question tests your understanding of how proteins can be modified after translation and why the initial Methionine may not always be present in mature proteins.

Key Terms:

Methionine: The amino acid specified by the start codon (AUG).
Post-Translational Modification: Chemical changes to a protein after it is synthesized.

Step-by-Step Guidance

Recall that translation always begins with Methionine due to the start codon.
Consider what can happen to the initial Methionine after translation is complete.
Explain how post-translational modifications can alter the final protein sequence.

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Q18. The nucleotide sequence of a DNA for a codon is 3’AGT5’. What is the nucleotide sequence of the codon in the messenger RNA molecule? What is the nucleotide sequence of the corresponding anticodon for the tRNA? What amino acid will that tRNA bring with it?

Background

Topic: Genetic Code and Base Pairing

This question tests your ability to transcribe DNA to mRNA, determine the tRNA anticodon, and use the genetic code to identify the corresponding amino acid.

Key Terms and Formulas:

Transcription: Synthesis of mRNA from a DNA template.
Codon: Three-nucleotide sequence in mRNA.
Anticodon: Three-nucleotide sequence in tRNA complementary to the mRNA codon.
Genetic Code Table: Used to determine which amino acid corresponds to a given codon.

Step-by-Step Guidance

Write the DNA template strand: 3'AGT5'.
Transcribe the DNA sequence to mRNA using base pairing rules (A-U, T-A, G-C, C-G).
Write the mRNA codon in the 5' to 3' direction.
Determine the tRNA anticodon sequence that pairs with the mRNA codon.
Use a genetic code table to identify the amino acid specified by the mRNA codon.

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Q19. Deletion of 2 base pairs in a gene’s coding sequence causes a frameshift mutation. Deletion of 6 base pairs does not. Explain why.

Background

Topic: Types of Mutations

This question tests your understanding of how the genetic code is read in triplets and how different types of deletions affect the reading frame.

Key Terms:

Frameshift Mutation: Mutation that shifts the reading frame of the genetic code.
Codon: Sequence of three nucleotides that codes for an amino acid.

Step-by-Step Guidance

Recall that codons are read in groups of three nucleotides during translation.
Explain what happens to the reading frame when 2 nucleotides are deleted versus 6 nucleotides.
Discuss why deletion of a multiple of three nucleotides does not cause a frameshift, but deletion of 2 does.

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Q20. The nucleotide sequence of a DNA for a codon is 3’AGT5’. A mutation changes the sequence to 3’AGG5’. What kind of mutation is this?

Background

Topic: Point Mutations

This question tests your ability to recognize and classify different types of point mutations based on changes in the DNA sequence.

Key Terms:

Point Mutation: A change in a single nucleotide pair in DNA.
Missense, Nonsense, Silent Mutations: Types of point mutations with different effects on the protein sequence.

Step-by-Step Guidance

Compare the original and mutated DNA sequences to identify the specific change.
Transcribe both sequences to mRNA and determine the codons.
Use the genetic code to see if the amino acid changes, and classify the mutation accordingly.

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Q21. The nucleotide sequence of a DNA for a codon is as shown below. The top strand is the template strand. 5’CAG3’ 3’GTC5’ Suggest a base pair substitution that would be a silent mutation. Suggest a base pair substitution that would be a missense mutation.

Background

Topic: Types of Point Mutations

This question tests your understanding of how different base substitutions can result in silent or missense mutations.

Key Terms:

Silent Mutation: A mutation that does not change the amino acid sequence.
Missense Mutation: A mutation that changes one amino acid in the protein sequence.
Base Pair Substitution: Replacement of one nucleotide pair with another.

Step-by-Step Guidance

Write out the original codon and determine the amino acid it codes for using the genetic code.
Suggest a single base change that would result in a codon specifying the same amino acid (silent mutation).
Suggest a different single base change that would result in a codon specifying a different amino acid (missense mutation).