Molecular Biology Exam 4 - Answer Key
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Questions and Answers

How does region A differ from region B in terms of gene transcription?

  • Genes in region A will be transcribed at a lower rate
  • Region A has an open conformation (correct)
  • Region A has a closed conformation
  • Genes in region B will be transcribed at a higher rate

What is the correct nucleotide sequence of the tRNA anticodon for tryptophan?

  • 3' – UGG – 5' (correct)
  • 5' – ACC – 3'
  • 5' – UGG – 3'
  • 3' – ACC – 5'

Which strand does RNA polymerase read during transcription?

  • RNA coding strand
  • DNA template strand (correct)
  • Polypeptide strand
  • DNA coding strand

What are the current environmental conditions of the cell based on the lac operon?

<p>Low glucose, high lactose (D)</p> Signup and view all the answers

If the cell is exposed to high levels of glucose, how does it affect the operon?

<p>The expression of the operon will remain unchanged (A)</p> Signup and view all the answers

What is the role of the repressor in the lac operon under low glucose conditions?

<p>It remains inactivated allowing gene expression (D)</p> Signup and view all the answers

Which of the following best describes the function of tRNA?

<p>It carries amino acids to the ribosome (A)</p> Signup and view all the answers

What happens to the lac operon when both glucose and lactose are present?

<p>The operon remains inactive due to glucose inhibition (D)</p> Signup and view all the answers

How will the XLM1 gene differ in skin and muscle cells with respect to mRNA processing?

<p>The gene and the mRNA will be the same length in both types of cells. (D)</p> Signup and view all the answers

What is the anticodon sequence for the exposed codon in the A-site according to standard base pairing?

<p>3' – AGU – 5' (D)</p> Signup and view all the answers

What will be the final polypeptide sequence post-translation?

<p>Met – Gly – Pro – Leu (D)</p> Signup and view all the answers

A cluster of genes controlled by one promoter is known as what?

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

What does a segment of a chromosome becoming attached to a different chromosome exemplify?

<p>Chromosomal translocation (D)</p> Signup and view all the answers

During the translation process, which phase follows initiation?

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

In transcription, RNA polymerase synthesizes mRNA based on which template?

<p>Non-coding DNA strand (C)</p> Signup and view all the answers

The process through which ribosomes decode mRNA to produce polypeptides is termed?

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

Which factor plays an important part in RNA polymerase binding to DNA?

<p>Sigma factor (D)</p> Signup and view all the answers

Which of the following sequences are transcribed by RNA polymerase in prokaryotes?

<p>Promoter, coding region, and terminator (A)</p> Signup and view all the answers

What is the significance of the formation of a stem-loop in prokaryotic cells?

<p>It promotes termination of transcription. (B)</p> Signup and view all the answers

Which enzyme belongs to Gene S in the described metabolic pathway?

<p>Enzyme 1 (B)</p> Signup and view all the answers

Based on the growth results with media supplemented with A, B, C, D, or E, which enzyme is likely affected by Gene Q's mutation?

<p>Enzyme 3 (B)</p> Signup and view all the answers

If Gene P has a mutation, which media supplement could still allow the cell to grow?

<p>Only media E (C)</p> Signup and view all the answers

Which statement about the roles of the enzymes in the metabolic pathway is correct?

<p>Enzyme 4 is encoded by Gene L and is essential for converting compound D to E. (B)</p> Signup and view all the answers

In the context of enzymatic reactions, what does each arrow in the metabolic pathway denote?

<p>A catalyzed enzymatic reaction (C)</p> Signup and view all the answers

What effect does proline have on the operon?

<p>Proline binds to DNA and inhibits transcription. (C)</p> Signup and view all the answers

What is the outcome of having mutation #1 in the RNA sequence?

<p>The protein will be shorter due to a premature termination. (A)</p> Signup and view all the answers

Identify the type and effect of mutation #2.

<p>Nonsense mutation; the resulting protein will be shorter. (A)</p> Signup and view all the answers

Where do transcription, translation, and splicing occur in a prokaryotic cell?

<p>Transcription and translation both occur in the cytosol; splicing does not happen. (B)</p> Signup and view all the answers

What is the role of proline as an effector in relation to the operon?

<p>Proline causes a repressor protein to bind to the operon. (D)</p> Signup and view all the answers

What happens to the encoded protein if mutation #2 is a frame shift?

<p>The protein will be shorter due to a shift in the reading frame. (D)</p> Signup and view all the answers

In gene expression, which of the following correctly describes the input and output?

<p>DNA, protein (C)</p> Signup and view all the answers

What occurs immediately after transcription factors bind to the promoter?

<p>RNA polymerase recognizes the start codon. (D)</p> Signup and view all the answers

What does the small ribosomal subunit recognize in eukaryotic cells?

<p>5’ cap, tRNAMet will recognize the start codon. (C)</p> Signup and view all the answers

What can be inferred from a deletion mutation 250 bases upstream of the transcription start site of the VRN4 gene resulting in lower transcription levels?

<p>It deletes an enhancer sequence. (A)</p> Signup and view all the answers

The KRAS gene, which is mutated in colorectal cancer to increase activity, is classified as what?

<p>Oncogene (D)</p> Signup and view all the answers

What effect does adding methyl groups to the core promoter region of a eukaryotic gene have on gene expression?

<p>Transcription will decrease, resulting in less protein. (B)</p> Signup and view all the answers

Which mechanism primarily regulates the translation process in eukaryotic cells?

<p>Recognition of the 5’ cap by the ribosome. (D)</p> Signup and view all the answers

Which of the following statements is correct regarding transcription in eukaryotic cells?

<p>Transcription takes place in the nucleus. (C)</p> Signup and view all the answers

What is the potential consequence of a mutation that decreases the stability of mRNA?

<p>Decreased protein synthesis. (A)</p> Signup and view all the answers

Which mutation is expected to produce the largest change to the structure and function of a protein?

<p>A nonsense mutation in the 5’ end of the gene. (D)</p> Signup and view all the answers

Under what condition will the trp operon be expressed?

<p>Absence of tryptophan with an inactive repressor. (D)</p> Signup and view all the answers

Is it possible to determine a person’s hair color from the DNA of cheek cells?

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

What is the normal function of the chocolate gene when it is not mutated?

<p>To stop the cell cycle when DNA damage is detected. (B)</p> Signup and view all the answers

Which statement is NOT TRUE of the proteins synthesized by a polysome?

<p>They will contain different functional groups. (B)</p> Signup and view all the answers

Which mutation would likely NOT affect the protein function significantly?

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

What mechanism regulates the trp operon's expression?

<p>Feedback inhibition when tryptophan levels are high. (C)</p> Signup and view all the answers

How do missense mutations affect protein function?

<p>They can lead to the incorporation of a different amino acid. (C)</p> Signup and view all the answers

Flashcards

Nucleosome Structure

A nucleosome is a fundamental unit of DNA packaging in eukaryotic cells. It consists of a DNA segment wrapped around a core of eight histone proteins (an octamer).

Open Conformation of DNA

When DNA is in an open conformation, it is more accessible to enzymes like RNA polymerase, allowing for gene transcription.

Transcription Rate

The rate at which a gene is transcribed into mRNA. A higher transcription rate means more mRNA molecules are produced, leading to more protein synthesis.

Anticodon

A three-nucleotide sequence on a tRNA molecule that recognizes and binds to a complementary codon on mRNA during translation.

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RNA Polymerase

An enzyme that reads the DNA template strand and synthesizes a complementary RNA molecule during transcription.

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Lac Operon

A group of genes in bacteria that are regulated together and involved in lactose metabolism.

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High Glucose Environment

When glucose is abundant, bacteria prefer to use glucose as their energy source and repress lactose metabolism.

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Repressor Protein

A protein that binds to the operator region of an operon, blocking the transcription of genes.

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Alternative Splicing

A process where different mRNA molecules are produced from the same gene, depending on which exons are included or excluded from the final transcript.

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Exon

A coding region of a gene that is included in the final mRNA transcript.

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Intron

A non-coding region of a gene that is removed from the mRNA transcript during splicing.

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Codon

A three-nucleotide sequence in mRNA that codes for a specific amino acid.

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Polypeptide

A chain of amino acids linked together by peptide bonds.

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Operon

A cluster of genes under the control of a single promoter, which allows for coordinated regulation of gene expression.

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Chromosomal Translocation

A type of chromosomal rearrangement where a segment of one chromosome is moved to a different chromosome.

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Proline and Operon Regulation

Proline acts as a small effector molecule that binds to a repressor protein. This binding causes the repressor to bind to the operon, preventing transcription. This is a form of negative regulation.

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Mutation #1 Impact

Mutation #1 leads to a change in the primary structure of the encoded protein. This alteration may affect the protein's folding, function, or stability.

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Nonsense Mutation

A nonsense mutation introduces a premature stop codon, leading to a truncated protein. The protein will be shorter than the wild-type protein.

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Frameshift Mutation

A frameshift mutation inserts or deletes nucleotides, altering the reading frame. This leads to a protein with a drastically different amino acid sequence, often resulting in a non-functional protein.

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Eukaryotic Transcription Order

The correct order of events in eukaryotic transcription is: III (Transcription factors bind to the promoter), I (Addition of the 5'-cap), and IV (Addition of the poly-A tail). RNA polymerase recognizes the start codon, but only during translation, not transcription.

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Prokaryotic Transcription and Translation

In prokaryotic cells, both transcription and translation occur in the cytoplasm. Splicing does not occur as prokaryotes lack a nucleus and introns.

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Difference between Prokaryotic & Eukaryotic Transcription

Prokaryotic transcription and translation occur simultaneously in the cytoplasm, while in eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm. Additionally, eukaryotes undergo splicing to remove introns, which is not present in prokaryotes.

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Why a 5' cap is important for transcription

The 5' cap protects the mRNA transcript from degradation, which is important for the mRNA to reach the ribosome.

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Gene Expression Input

The initial molecule that contains the genetic information for a protein. This molecule serves as the template for the production of other molecules.

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Gene Expression Output

The final product of a gene, a functional molecule that performs a specific job within the cell. This molecule is synthesized using the information encoded in the initial molecule.

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Transcription Location

The process of converting DNA into RNA occurs within the nucleus of eukaryotic cells.

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Translation Location

The process of converting RNA into protein occurs in the cytoplasm of eukaryotic cells.

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Splicing in Eukaryotes

The process of removing non-coding regions (introns) from RNA before it is translated into protein. This only occurs in eukaryotes.

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Small Ribosomal Subunit

The smaller part of the ribosome, responsible for binding to mRNA and starting protein synthesis. It recognizes the 5' cap of mRNA.

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Start Codon Recognition

Once attached to mRNA, the small ribosomal subunit scans for the start codon (AUG) to initiate protein synthesis.

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Mutations Affecting Transcription

Changes in DNA sequence that occur upstream of the transcription start site can affect the rate of transcription and protein production.

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Missense Mutation Impact

A missense mutation changes a single amino acid in a protein. The impact on protein structure and function depends on the location and type of amino acid change.

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Nonsense Mutation Impact

A nonsense mutation introduces a premature stop codon, resulting in a truncated and often non-functional protein.

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Silent Mutation Impact

A silent mutation changes a nucleotide in a gene, but the resulting amino acid remains the same, often having little to no effect on protein function.

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Trp Operon Regulation

The trp operon is a set of genes involved in tryptophan synthesis in bacteria. It is regulated by a repressor protein that binds to the operator region when tryptophan is present, blocking transcription.

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Tumor Suppressor Genes

Tumor suppressor genes normally prevent uncontrolled cell growth by regulating the cell cycle. Mutations in these genes can lead to cancer.

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Polysome Protein Synthesis

A polysome is a group of ribosomes translating the same mRNA molecule simultaneously. All proteins synthesized by a polysome will have the same primary structure but may differ in length and amino acid sequence due to alternative splicing or other factors.

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Why Cheek Cells Can't Reveal Hair Color

Different cells in the body express different genes, leading to specialized functions. Cheek cells don't express the genes that control hair color, so DNA analysis of cheek cells won't reveal hair color.

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Loss-of-Function Mutation

A loss-of-function mutation disrupts the normal function of a gene, often resulting in a non-functional protein. These mutations can be associated with diseases or disorders.

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C-terminus

The end of a polypeptide chain where the last amino acid is located.

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Prokaryotic Gene Structure

The basic structure of a prokaryotic gene includes a promoter, a coding region, and a terminator.

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Sigma Factor

A protein in prokaryotes that helps RNA polymerase bind to the promoter region of a gene and initiate transcription.

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Stem-Loop Structure

A secondary structure formed in RNA where a single strand folds back on itself to create a loop.

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Metabolic Pathway

A series of connected enzymatic reactions in a cell that convert a starting molecule into a final product.

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Enzyme Knockout

An experiment where a gene encoding a specific enzyme is disabled.

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Complementation Test

A technique used to identify the order of enzymatic reactions in a metabolic pathway.

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Mutational Rescue

When a cell with a mutation in a particular enzyme can still grow if provided with the missing product.

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Study Notes

Exam 4 - Answer Key

  • Full Name/Discussion Section/TA Name: Record these on the scantron.
  • Codons Table: The codon table is on the last exam page. Consult it as needed.
  • Genetic Code: Turn in the genetic code with your answer sheet.

Question 1 - Nucleosomes

  • Region A vs Region B Differences: Region A is an open configuration, making genes in Region A more likely to be transcribed at a higher rate than B.

Question 2 - Anticodon for Tryptophan (trp)

  • Nucleotide Sequence: The anticodon for tryptophan (trp) is 3'-UGG-5'.

Question 3 - RNA Polymerase

  • Strand Read During Transcription: RNA polymerase reads the DNA template strand.

Question 4 - Lac Operon Environmental Conditions

  • Current Conditions: High glucose, low lactose.

Question 5 - Glucose and Lac Operon Expression

  • Glucose Effect: Yes, the repressor would become inactive in increased glucose levels.

Question 6 - XLM1 Gene Differences

  • mRNA and DNA Length Differences: The gene will be the same length in both skin and muscle cells. However, the mRNA will be longer in the muscle cells.

Question 7 - Ribosome and A-site Anticodon

  • A-site Anticodon Sequence: The sequence of the anticodon for the exposed codon in the A-site is 5'-UCA-3'.

Question 8 - Final Polypeptide Sequence

  • Sequence After Translation: Met-Gly-Pro-Leu-Ser-Arg-Val-Ser

Question 9 - Cluster of Genes

  • Definition: A cluster of genes under the control of one promoter is called an operon.

Question 10 - Chromosome Segment Attachment

  • Example: Chromosomal translocation

Question 11 - RNA Polymerase & DNA Sequence

  • mRNA Sequence: (The required sequence depends on the specific region depicted in the diagram, which isn't explicitly shown in the provided text).

Question 12 - Mutation and Lac Operon Expression

  • Effect of Operator Mutation: The operon will be expressed in the presence of lactose, with lactose able to be metabolized by the cell.

Question 13 - Mutation Location and Gene Expression

  • Least Likely Impact: Intron

Question 14 - Scenario 1 and 2 Gene Regulation

  • Cause in Scenario 1: Repressor, negative control, prokaryotic cell
  • A in Scenario 2: Regulatory transcription factor

Question 15 - Proline and Operon Expression

  • Hypothesis: Proline binds to the enzymes in the operon, inactivating them; thus, the operon is not expressed in high proline levels.

Question 16 - Mutation and Amino Acid Change

  • Mutation #1: A point mutation (C to G) in this situation would potentially lead to a change at the amino acid level.
  • Mutation #2: An insertion of a uracil (U) nucleotide will cause a frame-shift mutation.

Question 17 - Mutation 1 and Protein Change

  • Change in Protein: The encoded protein will be shorter than the wild-type protein due to premature termination of translation.

Question 18 - Mutation 2 and Protein Change

  • Change In Protein: Mutation #2 changes the amino acid sequence and will likely result in a protein of different length than the wild-type. More specifically, the frame shift is in play.

Question 19 - Eukaryotic Transcription Events

  • Correct Order: III, I, IV

Question 20 - Prokaryotic Transcription Splicing Location

  • Location: Transcription and translation in the cytosol. Splicing doesn't occur.

Question 21 - Gene Expression Input and Output

  • Input/Output: DNA/mRNA

Question 22 - Small Ribosomal Subunit Function

  • Target in Eukaryotes: The 16s rRNA, the small subunit of the ribosome will recognize the tRNA.

Question 23 - VRN4 Gene Mutation and Transcription Levels

  • Mutation Effect: Deletion of an enhancer sequence negatively affecting transcription and mRNA levels.

Question 24 - KRAS Gene and Cell Proliferation

  • KRAS Gene Description: An oncogene

Question 25 - Methylation of Gene and Transcription

  • Effect of Methylation: Transcription decreases.

Question 26 - mRNA Transcript Sequence from DNA

  • mRNA Sequence: 5'-AAUCGUGGGUGAUACUUUGUAAUUUAU-3'

Question 27 - Polypeptide Sequence

  • Amino Acid Sequence: Met-Phe-His-Ser-Gly-Cys

Question 28 - Methionine-tRNA Mutation

  • Likely Effect: Translation will not be initiated, and no protein will be made.

Question 29 - Eukaryotic Ribosome Components

  • Component Absent: DNA

Question 30 - DNA Coding Strand mRNA

  • mRNA Transcript: 5'-AUG TAC UCA TGT GGT CGT TAG-3'

Question 31 - Missense and Nonsense Mutations

  • Largest Change: Nonsense mutation (in the 3′ end).

Question 32 - TRP Operon Expression Conditions

  • Conditions for TRP Expression: Absence of tryptophan with an inactive repressor.

Question 33 - Hair Color from Cheek Cells

  • Possibility: No, cheek cells contain specific genes related to function as opposed to hair color genes.

Question 34 - Function of Chocolate Gene

  • Normal Function of Chocolate Gene: To stop the cell cycle when DNA damage is detected.

Question 35 - Polysome Protein Properties

  • False Statement: Polysome proteins will differ in length and amino acid sequence.

Question 36 - Prokaryotic Gene Sequences

  • Important Sequences: TATA box, coding region, and terminator.

Question 37 - Stem-loop Formation

  • Process: Termination of transcription (in prokaryotes).

Question 38 - Enzyme Order in Metabolic Pathway

  • Correct Enzyme Order: (This would require the provided data from the diagram). The correct enzyme order can be deciphered from the knockout data given.

Question 39 - Rescuing Mutated Cell with Supplement

  • Supplement for Rescue: D or E

Question 40 - Gene Regulation Differences in all Organisms

  • Inaccurate Statement: Mutations in DNA sequences can alter transcription levels and all other statements are true regarding gene regulation.

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BIOL1001 Exam 4 FA'24 PDF

Description

This document serves as the answer key for Exam 4 in Molecular Biology. It covers key concepts such as nucleosomes, the genetic code, RNA transcription, and the Lac operon. Use this key to guide your understanding of the exam materials and assess your answers.

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