14.1

5. Consider the data presented from the Jacob and Monod experiments with partial diploids. In the two mutant strains, what was the percentage of beta-galactosidase when lactose was added or not added? Just put the number and don't include the % sign.

100

1. A lac operon has a mutation in the lac I gene that results in the production of a nonfunctional protein. Under conditions of no lactose, what would you predict to be true about the relative expression of beta-galactosidase and permease in this situation? A. Expression of both beta-galactosidase and permease will be greater. B. Expression of beta-galactosidase will be greater but expression of permease will be less. C. Expression of permease will be greater but expression of beta-galactosidase will be less. D. Expression of both beta-galactosidase and permease will be less. E. It isn't possible to determine based on the provided information.

A

1. Describe the function of activators and repressors.

A repressor is a regulatory protein that binds to the DNA and inhibits transcription, whereas an activator is a regulatory protein that increases the rate of transcription.

2. Distinguish between negative and positive control.

A repressor is a regulatory protein that binds to the DNA and inhibits transcription, whereas an activator is a regulatory protein that increases the rate of transcription. Transcriptional regulation by a repressor protein is termed negative control, and regulation by an activator protein is considered to be positive control.

inducer

A small effector molecule that causes transcription to increase by either 1) binding to a repressor protein and prevent it from binding to the DNA or 2) bind to an activator protein and cause it to bind to the DNA.

activator

A type of regulatory protein that binds to the DNA and increases transcription.

repressor

A type of regulatory protein that binds to the DNA and inhibits transcription.

2. Explain how small effector molecules affect the function of activators and repressors.

An inducer is a small effector molecule that causes transcription to increase. An inducer may accomplish this in two ways: It could bind to a repressor protein and prevent it from binding to the DNA, or it could bind to an activator protein and cause it to bind to the DNA. In either case, the transcription rate is increased. Genes that are regulated in this manner are called inducible genes.

5. An inducer is a _________ that _________ transcription. A. regulatory protein; enhances B. small effector molecule; enhances C. regulatory protein; inhibits D. small effect molecule; inhibits

B

3. A repressor is a _________ that _________ transcription. A. regulatory protein; enhances B. small effector molecule; enhances C. regulatory protein; inhibits D. small effect molecule; inhibits

C

3. Which of the following encodes a trans-acting factor? A. lacP B. lacO C. lacI (i) D. CAP site

C

6. Which of the following combinations would cause transcription to be activated. A. An activator and an inhibitor. B. A repressor and a corepressor C. A repressor and inducer D. An activator and an inducer.

C

2. What would expression of beta-galactosidase and permease be in a high glucose, high lactose environment be compared to an environment with no glucose and high lactose? In other words, you are describing expression how expression would differ in high glucose and high lactose conditions. Assume there are no mutations to genes associated with the lac operon. A. Expression of both beta-galactosidase and permease will be greater. B. Expression of beta-galactosidase will be greater but expression of permease will be less. C. Expression of permease will be greater but expression of beta-galactosidase will be less. D. Expression of both beta-galactosidase and permease will be less. E. It isn't possible to determine based on the provided information.

D

inducible genes

Genes that are regulated by an inducer

repressible genes

Genes that are regulated by repressors and corepressors.

effector molecules

Molecules that don't directly bind to the DNA but exerts its effects by binding to an activator or repressor to cause a conformational change and influence whether or not it can bind to the DNA.

regulatory proteins

Proteins that can bind to the DNA and affect the rate of transcription of one or more nearby genes.

gene regulation

The phenomenon in which the level of gene expression (i.e. transcription and translation) can vary under different conditions.

negative control

Transcriptional regulation by a repressor protein

positive control

Transcriptional regulation by an activator protein.

1. What are constitutive genes? What is the advantage of genes being regulated?

Unregulated genes are also called constitutive genes. Frequently, constitutive genes encode proteins that are continuously needed for the survival of the bacterium. In contrast, the majority of genes are regulated so that the proteins they encode can be produced at the proper times and in the proper amounts.

constitutive genes

Unregulated genes that are continually expressed regardless of conditions.

2. Which of the following conditions would cause transcription to be activated? a. A repressor plus an inducer b. A repressor plus a corepressor c. An activator plus an inhibitor d. None of the above

a

1. A repressor is a __________ that _________ transcription. a. small effector molecule, inhibits b. small effector molecule, enhances c. regulatory protein, inhibits d. regulatory protein, enhances

c

1. Unregulated genes are also called _____ (one word) genes.

constitutive

7. What substance directly acts to decrease the concentration of active CAP protein? One word.

glucose

4. The phrase "partial diploid" is synonmous with the term _______ (one word).

merozygote

4. Transcriptional regulation by a ___________ (2 words) is termed negative control.

repressor protein

C1. What is the difference between a constitutive gene and a regulated gene?

Answer: A constitutive gene is unregulated, which means that its e xpression level is relatively constant. In contrast, the expression of a regulated gene varies under different conditions. In bacteria, the regulation of genes often occurs at the level of transcription by combinations of regulatory proteins and small effe ctor molecules. In addition, gene expression can be regulated at the level of translation or the function of a protein can be regulated after translation is completed.

C3. If a gene is repressible and under positive control, describe what kind of effector molecule and regulatory protein are involved. Explain how the binding of the effector molecule affects the regulatory protein.

Answer: In this case, an inhibitor molecule and an activator protein are involved. The binding of the inhibitor molecule to the activator protein would prevent it from binding to the DNA and thereby inhibit its ability to activate transcription.

6. Assume a test was conducted with two mutants (lacI- and lacO-) with no F' factor present. What would be true of expression of the lac operon between these two mutants with and without lactose? A. The lacI- mutant would have higher expression than the lacO- mutant under both conditions. B. The lacI- mutant would have lower expression than the lacO- mutant under conditions with lactose. C. The lacI- mutant would have lower expression than the lacO- mutant under conditions with no lactose D. Both mutants would have similar expression under both conditions.

D

2. Which of the following is/are common points of gene regulation? A. Transcription B. Translation C. Posttranslation D. A and B E. A, B, and C

E

3. Distinguish between inducible and repressible genes.

An inducer is a small effector molecule that causes transcription to increase. An inducer may accomplish this in two ways: It could bind to a repressor protein and prevent it from binding to the DNA, or it could bind to an activator protein and cause it to bind to the DNA. In either case, the transcription rate is increased. Genes that are regulated in this manner are called inducible genes. Alternatively, the presence of a small effector molecule may inhibit transcription. This can also occur in two ways. A corepressor is a small molecule that binds to a repressor protein, thereby causing the protein to bind to the DNA. An inhibitor binds to an activator protein and prevents it from binding to the DNA. Both corepressors and inhibitors act to reduce the rate of transcription. Therefore, the genes they regulate are termed repressible genes. Unfortunately, this terminology can be confusing because a repressible gene could be controlled by an activator protein, or an inducible gene could be controlled by a repressor protein.

C2. In general, why is it important to regulate genes? Discuss examples of situations in which it would be advantageous for a bacterial cell to regulate genes.

Answer: In bacteria, gene regulation greatly enhances the efficiency of cell growth. It takes a lot of energy to transcribe and translate genes. Therefore, a cell is much more efficient and better at competing in its environment if it expresses genes only when the gene product is needed. For example, a bacterium will express only the gene s that are necessary for lactose metabolism when a bacterium is exposed to lactose. When the environment is missing lactose, these genes are turned off. Similarly, when tryptophan levels are high within the cytoplasm, the genes that are required for trypto phan biosynthesis are repressed