When AZT is used to treat HIV infections, why does resistance to AZT usually develop?
What will be an ideal response?
Mutations present in the viral population, due to the lack of proofreading and high error rate of the viral reverse transcriptase, enable mutant virions to discriminate against the incorporation of AZT during transcription.
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The higher order structure of chromatin contains topologically constrained loops. What would happen if a single loop was cleaved?
A. The entire chromosome would unravel. B. The genes of that loop could not be transcribed. C. Only that loop would relax because each loop is separately constrained by proteins. D. The genes in the cleaved loop could not be replicated. E. Supercoiling in the cleaved loop would not be affected.
Which of the following is NOT a characteristic of a morphogen?
A. a morphogen will only elicit effects in areas where it is at a high enough concentration B. morphogens can be distributed asymmetrically throughout a cell C. morphogens can be secreted to act on neighboring cells D. morphogens can cause cell death E. morphogen gradients are always established in the oocyte
Which of the following is true of glycolipids?
A) Glycolipids are usually found on the exterior surface of the plasma membrane. B) Glycolipids are found in plastids and are used to store energy. C) Fructose and sucrose are often part of glycolipids. D) Glycolipids contain steroids. E) Usually more than 10 sugar units are attached to the glycolipid.
Cells regulate gene expression by
A. producing termination factors. B. turning on DNAase genes. C. adding histones to the DNA. D. limiting the length of time that mRNA is available for translation.