15 Regulation of Gene Expression

What does the operon model attempt to explain? the coordinated control of gene expression in bacteria bacterial resistance to antibiotics how genes move between homologous regions of DNA the mechanism of viral attachment to a host cell horizontal transmission of plant viruses Answer: A. © 2016 Pearson Education, Inc.

What does the operon model attempt to explain? the coordinated control of gene expression in bacteria bacterial resistance to antibiotics how genes move between homologous regions of DNA the mechanism of viral attachment to a host cell horizontal transmission of plant viruses © 2016 Pearson Education, Inc. 3

When tryptophan (an amino acid) is present in the external medium, the E. coli bacterium brings in the tryptophan and does not need to make this amino acid. Which is true when there is no tryptophan in the medium? The repressor is active and binds to the operator. The repressor is inactive, and RNA polymerase moves through the operator. The operator is bound, and mRNA is made. Genes are inactive. The corepressor binds to the repressor. Answer: B. © 2016 Pearson Education, Inc. 4

When tryptophan (an amino acid) is present in the external medium, the E. coli bacterium brings in the tryptophan and does not need to make this amino acid. Which is true when there is no tryptophan in the medium? The repressor is active and binds to the operator. The repressor is inactive, and RNA polymerase moves through the operator. The operator is bound, and mRNA is made. Genes are inactive. The corepressor binds to the repressor. © 2016 Pearson Education, Inc. 5

Each of a group of E. coli bacterial cells has a mutation in its lac operon. Which of these will make it impossible for the cell to metabolize lactose? mutation in lac (-galactosidase gene) mutation in lac (cannot bind to operator) mutation in operator (cannot bind to repressor) mutation in lac (cannot bind to inducer) Answer: A. See Figure 15.4. © 2016 Pearson Education, Inc. 6

Each of a group of E. coli bacterial cells has a mutation in its lac operon. Which of these will make it impossible for the cell to metabolize lactose? mutation in lac (-galactosidase gene) mutation in lac (cannot bind to operator) mutation in operator (cannot bind to repressor) mutation in lac (cannot bind to inducer) © 2016 Pearson Education, Inc. 7

A specific gene is known to code for three different but related proteins. This could be due to which of the following? premature mRNA degradation alternative RNA splicing use of different enhancers protein degradation differential transport Answer: B. © 2016 Pearson Education, Inc. 8

A specific gene is known to code for three different but related proteins. This could be due to which of the following? premature mRNA degradation alternative RNA splicing use of different enhancers protein degradation differential transport © 2016 Pearson Education, Inc. 9

Which methods would determine which genes are turned on in a certain cell in an organism? (Choose more than one answer.) Use RT-PCR to identify what mRNAs are present. Use RT-PCR to measure what proteins are present. Use a radioactive probe that binds only to certain mRNAs. Use a fluorescent probe that records DNA replication. Use a fluorescent probe that binds to only certain mRNAs. Answer: A, C, E. © 2016 Pearson Education, Inc. 10

Which methods would determine which genes are turned on in a certain cell in an organism? (Choose more than one answer.) Use RT-PCR to identify what mRNAs are present. Use RT-PCR to measure what proteins are present. Use a radioactive probe that binds only to certain mRNAs. Use a fluorescent probe that records DNA replication. Use a fluorescent probe that binds to only certain mRNAs. © 2016 Pearson Education, Inc. 11

Pair the following terms by their physical binding with each other: promoter, operator, RNA polymerase, repressor protein. RNA polymerase with repressor protein, promoter with operator RNA polymerase with promoter; repressor protein with operator RNA polymerase with operator; repressor protein with promoter Answer: B. © 2016 Pearson Education, Inc.

Pair the following terms by their physical binding with each other: promoter, operator, RNA polymerase, repressor protein. RNA polymerase with repressor protein, promoter with operator RNA polymerase with promoter; repressor protein with operator RNA polymerase with operator; repressor protein with promoter © 2016 Pearson Education, Inc.

Imagine an E. coli cell with a mutation that renders its trp repressor protein completely inactive. Which of the following would be true of that cell? It synthesizes tryptophan only when tryptophan is absent. It never synthesizes tryptophan. It always synthesizes tryptophan. It synthesizes tryptophan only when tryptophan is present. Answer: C. Without an active repressor, the operon would always be active. © 2016 Pearson Education, Inc.

Imagine an E. coli cell with a mutation that renders its trp repressor protein completely inactive. Which of the following would be true of that cell? It synthesizes tryptophan only when tryptophan is absent. It never synthesizes tryptophan. It always synthesizes tryptophan. It synthesizes tryptophan only when tryptophan is present. © 2016 Pearson Education, Inc.

In normal E. coli cells, under which of the following conditions is the lac operon “ON”? glucose present, lactose present glucose absent, lactose absent glucose present, lactose absent glucose absent, lactose present Answer: D. This questions highlights the dual control of the lac operon. © 2016 Pearson Education, Inc.

In normal E. coli cells, under which of the following conditions is the lac operon “ON”? glucose present, lactose present glucose absent, lactose absent glucose present, lactose absent glucose absent, lactose present © 2016 Pearson Education, Inc.

In normal E. coli cells, in which the lac operon is “ON,” which combination of CAP and lac repressor proteins is bound to the lac operon? both cap and lac repressor neither cap nor lac repressor only cap only lac repressor Answer: C. This questions highlights the dual control of the lac operon. © 2016 Pearson Education, Inc.

In normal E. coli cells, in which the lac operon is “ON,” which combination of CAP and lac repressor proteins is bound to the lac operon? both cap and lac repressor neither cap nor lac repressor only cap only lac repressor © 2016 Pearson Education, Inc.

Imagine an E. coli cell in which the lac operator has a mutation that renders it unable to bind the lac repressor. When would its lac operon be “ON”? always never when glucose levels are low only when glucose levels are low and lactose levels are high Answer: C. This questions highlights the dual control of the lac operon. The operon will not respond to lactose levels, but will still respond to glucose levels via CAP. © 2016 Pearson Education, Inc.

Imagine an E. coli cell in which the lac operator has a mutation that renders it unable to bind the lac repressor. When would its lac operon be “ON”? always never when glucose levels are low only when glucose levels are low and lactose levels are high © 2016 Pearson Education, Inc.

Histone de-acetylases (HDACs) are enzymes that remove acetyl groups from histone proteins. With regard to their effects on transcription, HDACs should do which of the following? activate transcription by opening chromatin activate transcription by condensing chromatin repress transcription by opening chromatin repress transcription by condensing chromatin Answer: D. © 2016 Pearson Education, Inc.

Histone de-acetylases (HDACs) are enzymes that remove acetyl groups from histone proteins. With regard to their effects on transcription, HDACs should do which of the following? activate transcription by opening chromatin activate transcription by condensing chromatin repress transcription by opening chromatin repress transcription by condensing chromatin © 2016 Pearson Education, Inc.

Why is a myosin gene transcriptionally expressed in muscle cells, but not in neurons? Neurons lack an enhancer in the myosin gene. Neurons lack the myosin gene. Muscle cells have an extra enhancer in the myosin gene. Muscle cells express an activator protein that binds the myosin enhancer. Answer: D. The DNA should be the same in all cells. The presence of specific proteins can be different between cell types. © 2016 Pearson Education, Inc.

Why is a myosin gene transcriptionally expressed in muscle cells, but not in neurons? Neurons lack an enhancer in the myosin gene. Neurons lack the myosin gene. Muscle cells have an extra enhancer in the myosin gene. Muscle cells express an activator protein that binds the myosin enhancer. © 2016 Pearson Education, Inc.

A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5) A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5). Which of the following arrangements of exons is not possible in a mature mRNA due to alternative splicing? 1, 2, 5 1, 3, 4, 5 1, 3, 2, 4, 5 1, 3, 3, 5 Answer: C, D. Splicing preserves the relative order of exons. Exons can be skipped, but not rearranged or duplicated. The system does not allow for repeating exons or changing the 5’ → 3’ order. © 2016 Pearson Education, Inc.

A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5) A eukaryotic gene has a pre-mRNA with five exons (1, 2, 3, 4, 5). Which of the following arrangements of exons is not possible in a mature mRNA due to alternative splicing? 1, 2, 5 1, 3, 4, 5 1, 3, 2, 4, 5 1, 3, 3, 5 © 2016 Pearson Education, Inc.

A mi-RNA binds with perfect complementarity to a target mRNA of gene X A mi-RNA binds with perfect complementarity to a target mRNA of gene X. What is/are the outcome(s) for gene X in terms of gene regulation? less gene X less pre-mRNA of gene X less mRNA of gene X less protein of gene X Answer: C, D. D follows from C. © 2016 Pearson Education, Inc.

A mi-RNA binds with perfect complementarity to a target mRNA of gene X A mi-RNA binds with perfect complementarity to a target mRNA of gene X. What is/are the outcome(s) for gene X in terms of gene regulation? less gene X less pre-mRNA of gene X less mRNA of gene X less protein of gene X © 2016 Pearson Education, Inc.

A particular oncogene with the partial mRNA sequence of 5ʹ AUG GAU GGG is expressed in certain cancer cells. What partial DNA sequence would be part of an effective probe to determine if this oncogene were being expressed in cells? 5ʹ ATG GAT GGG 5ʹ GGG TAG GTA 5ʹ CCC ATC CAT 5ʹ TAC CTA CCC Answer: C. A probe must be the reverse complement of the target sequence. © 2016 Pearson Education, Inc.

A particular oncogene with the partial mRNA sequence of 5ʹ AUG GAU GGG is expressed in certain cancer cells. What partial DNA sequence would be part of an effective probe to determine if this oncogene were being expressed in cells? 5ʹ ATG GAT GGG 5ʹ GGG TAG GTA 5ʹ CCC ATC CAT 5ʹ TAC CTA CCC © 2016 Pearson Education, Inc.