Why do E. coli cells with a defective lacZ gene fail to show galactoside permease activity after the addition of lactose in the absence of glucose?
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Why do E. coli cells with a defective lacZ gene fail to show galactoside permease activity after the addition of lactose in the absence of glucose?
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- Why don't E. coli cells with a faulty lacZ gene display galactoside permease activity when lactose is added in the absence of glucose?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?Which disease occurs when homogentisic acid oxidase is defective?
- Wild-type E. coli cells can synthesize all 20 common amino acids, but some mutants, called amino acid auxotrophs, are unable to synthesize a specific amino acid and require its addition to the culture medium for optimal growth. Besides their role in protein synthesis, some amino acids are also precursors for other nitrogenous cell products. Consider the three amino acid auxotrophs that are unable to synthesize glycine, glutamine, and aspartate, respectively. Match each nitrogenous product with the mutant or mutants that would fail to synthesize it. Each mutant may fail to synthesize more than one nitrogenous product, and some nitrogenous products may fail to be synthesized by more than one mutant. glycine auxotrophs glutamine auxotrophs aspartate auxotrophs Answer Bank adenine nucleotides cytosine nucleotides guanine nucleotides uridine nucleotidesBacterial species that are capable of synthesising the amino acid histidine do not need it in their growth medium. Histidine biosynthesis requires a specific enzyme, which we shall refer to as histidine synthetase. When these bacteria are supplemented with histidine in their growth media, they cease intracellular histidine synthesis. Propose three distinct regulatory mechanisms to account for why histidine production ends when histidine is present in the growth medium. To further investigate this phenomena, you analyse the quantity of intracellular histidine synthetase protein produced when cells are cultured with and without histidine. The quantity of this protein is same in both scenarios. Which regulatory mechanism makes sense in light of this observation?How is b-galactosidase induced in cells?
- In a certain bacterial species, the amino acid arginine is synthesized by a particular enzyme so the bacterium does not require arginine in its growth medium. A key enzyme, which we will call arginine synthetase, is necessary for arginine biosynthesis. When these bacteria are given arginine in their growth media, they stop synthesizing arginine intracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why arginine biosynthesis ceases when arginine is added to the growth medium. To better understand the mechanism of regulation, you measure the amount of intracellular arginine synthetase protein when cells are grown in the presence and absence of arginine. Under both growth conditions, the amount of this protein is identical. Which mechanism of regulation would be consistent with this experimental observation?.Tazobactam is a BETA-lactam that inhibits the enzyme that bacteria secrete to resist penicillin. Draw a mechanism for the formation of the tazobactam-trapped BETA-lactamase conjugate that proceeds through the following steps.Describe which enzymes are required for lactose and tryptophan metabolism in bacteria when lactose and tryptophan, respectively, are (a) present and (b) absent.