1. An enzyme is discovered that selectively shortens telomeres. Its gene is isolated, cloned and transfected into a malignant cell line where it is transcribed and translated. What might happen to the cell line? What happens when a cell expresses telomerase?
2. You are experimenting with two strains of bacteria. The normal strain usually produces extremely low levels of ?-galactosidase. In the mutant strain, the operator site is altered, resulting in the constitutive synthesis of high levels of ?-galactosidase in the presence and absence of lactose. Why does this happen?
3. What happens to a bacterium that has an entirely normal lac operon in the presence of lactose and glucose? Explain fully.
4. What happens when the poly(A) tail drops to about 30 nucleotides? In one mRNA degradative pathway, what piece of evidence suggests that the two ends of the mRNA are held in close proximity?Where do deadenylation, decapping and 5′ -> 3′ degradation occur and what else can happen in this location?
5. You genetically engineer nucleoplasmin so that a stretch of amino acids near its C-terminal end (called the NLS) is removed. What happens to the resultant nucleoplasmin protein if this altered gene is transfected into an amphibian oocyte and transcribed into mRNA, which is then translated? If you were to alter the NLS of a particular nuclear protein by replacing the codon for a basic amino acid in its NLS with a codon coding for a nonpolar amino acid, what would happen if this altered gene were transfected into an amphibian oocyte and transcribed into mRNA, which is then translated? If you were to fuse an NLS to a well-known non-nuclear protein (serum albumin) and inject it into the cytoplasm of the cell, what would happen?
6. What is thought to displace nucleosomes during replication? The core histone octamer of a nucleosome consists of an (H3H4)2 tetramer together with a pair of H2A/H2B dimers. What are two contrasting models that describe how parental nucleosomes are distributed during replication?
7. What would be the likely result if single-stranded binding proteins were not working properly during replication?
8. After exonucleases have excised the damaged portion of DNA, how can DNA polymerase fill in the gap? Is there a primer?
9. What is the major reason for the multiple initiation sites for eukaryotic replication?
10. You are studying replication in a particular bacterial strain. At 37°C, the bacteria appear perfectly normal. If the temperature is raised to 43°C, however, they stop growing and are unable to replicate their DNA. If some of them are placed back at 37°C, they begin to replicate their DNA and are again perfectly normal. What is wrong?
11. Glucagon and epinephrine act to increase the activity of phosphorylase. Why is it important that they also inhibit the activity of glycogen synthase?12. A cell culture is known to respond to hormone A by the production of molecule D. The response can also be obtained in a cell homogenate. If the homogenate is centrifuged, it can be separated into soluble and particulate fractions. The particulate fraction is necessary for the response. If the particulate fraction is treated with hormone and then washed with buffer, what will happen if the wash is added to the soluble fraction? What will happen if the hormone is added to the soluble fraction?13. What disease is an inherited disease characterized by progressive degeneration of the retin and eventual blindness? What mutation can cause RP? How do some of the mutations in rhodopsin lead to the disease?
14. You provide cells in culture with 32P and treat them with insulin for 30 minutes. Following the treatment, you homogenize the cells and isolate the insulin receptors. The control cells received 32P, but no insulin. Insulin receptors from the insulin-treated cells were radiolabeled with 32P; insulin receptors from the controls were not. Why?
15. You are studying the ability of a normal SH2 protein to bind to a specific IRS and a number of mutant forms of this same protein. One of the mutant IRS proteins is unable to bind to the SH2 protein normally. Further studies reveal that this particular IRS is unable to be phosphorylated in at least one key location by the insulin RTK. This explains its inability to bind the SH2 protein properly. Why is this protein not fully phosphorylated?