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Chapter 14: Problem 21

Using three examples, describe how allosteric sites are important in the function of genetic regulatory proteins.

Short Answer

Expert verified
Allosteric sites are crucial for the function of genetic regulatory proteins, as demonstrated by the Lac operon, where lactose binds to an allosteric site to induce lactose metabolism; in glycolysis regulation where ATP binds to allosteric sites on phosphofructokinase to regulate energy production; and in hemoglobin, where oxygen binds to allosteric sites for efficient transport to the body tissues.

Step by step solution

01

Example 1: Lac Operon

The function of genetic regulatory proteins can be seen in the lac operon found in E.coli. Here, an allosteric protein known as the lac repressor binds to the operator site on the DNA when lactose is absent. This stops RNA polymerase from transcribing the genes needed for lactose metabolism. However, when lactose is present, it binds to the allosteric site on the repressor, causing a conformational change that prevents the repressor from binding to the operator. This allows for transcription and subsequent lactose metabolism.
02

Example 2: Glycolysis Regulation

The process of glycolysis, critical for energy production in the cell, is controlled via allosteric regulation of enzymes involved in the process. Phosphofructokinase is a key enzyme involved in glycolysis and has allosteric sites for ATP. When ATP levels rise, ATP binds to these allosteric sites, causing the enzyme to decrease the rate of the reaction, thus decreasing ATP production. This allows the cell to maintain the balance of energy production.
03

Example 3: Hemoglobin Protein

Hemoglobin is a protein responsible for oxygen transport in the bloodstream. It consists of four protein subunits, each holding an allosteric site for oxygen. Binding of oxygen at one site increases the affinity of the remaining sites for oxygen. This cooperative binding allows hemoglobin to pick up oxygen in the lungs efficiently and release it in the tissues where it's needed the most. This is another way of how allosteric sites are vital in the function of genetic regulatory proteins.

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Most popular questions from this chapter

Transcriptional regulation often involves a regulatory protein that binds to a segment of DNA and a small effector molecule that binds to the regulatory protein. Do each of the following terms apply to a regulatory protein, a segment of DNA, or a small effector molecule? A. Repressor B. Inducer C. Operator site D. Corepressor E. Activator F. Attenuator G. Inhibitor

Would a mutation that inactivated lac repressor and prevented it from binding to the lac operator site result in the constitutive expression of the lac operon under all conditions? Explain. What is the disadvantage to the bacterium of having a constitutive lac operon?

As described in Chapter 13, enzymes known as aminoacyl-tRNA synthetases are responsible for attaching amino acids to tRNAs. Let's suppose that in a mutant bacterium tryptophanyl-tRNA synthetase has a reduced ability to attach tryptophan to tRNA: its activity is only \(10 \%\) of that found in a normal bacterium. How would attenuation of the \(\operatorname{trp}\) operon be affected? Would the operon be more or less likely to be attenuated? Explain your answer.

What is meant by the term attenuation? Is it an example of gene regulation at the level of transcription or translation? Explain your answer.

A species of bacteria can synthesize the amino acid histidine, so they do not require histidine in their growth medium. A key enzyme, which we will call histidine synthetase, is necessary for histidine biosynthesis. When these bacteria are given histidine in their growth medium, they stop synthesizing histidine intracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why histidine biosynthesis ceases when histidine is in the growth medium. To explore this phenomenon further, you measure the amount of intracellular histidine synthetase protein when cells are grown in the presence and absence of histidine. In both conditions, the amount of this protein is identical. Which mechanism of regulation is consistent with this observation?
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