زيست شناسي سلولی و مولکولی

Questions 1-3:

A gene encoding growth hormone in rats was introduced into mice. The construct used consisted in an open reading frame encoding rat growth hormone fused to a mouse promoter A. The growth hormone sequence was obtained from a rat cDNA library, the only available source of sequence information. Fertilized mouse egg cells were transformed with the rat growth hormone construct and expression of the rat growth hormone was detected. Transformation of fertilized egg cells with rat growth hormone cDNA alone did not result in expression.

1. Why was it necessary to fuse the rat growth hormone sequence to a promoter to obtain expression?
A. The rat sequence was obtained from a cDNA library and therefore did not include a promoter sequence.
B. No factors that recognized the rat promoter sequence were present in the mouse.
C. The rat promoter was contained within the rat sequence but was inactivated in the mouse.
D.  Rat growth hormone is inactive in mice.

2. When the eggs were placed under conditions conducive to activation of the mouse promoter, one of the resulting offspring grew larger than the expected size.  The appearance of the large mouse is consistent with one of the following statements:
A. That mouse grew bigger because it produced more mouse growth hormone.
B. That mouse grew bigger because it was more aggressive and ate more mouse chow.
C. That mouse grew bigger because the mouse promoter A was activated, resulting in increased production of rat growth hormone.
D. That mouse grew bigger because his nose was longer.

3. The mouse promoter used is controlled by zinc.  It controls the expression of metallothionein, a zinc-binding protein that regulates the level of that metal in mouse cells.  It is important to control intracellular zinc levels because
A. Zinc is toxic at all levels.
B. Intracellular levels of zinc must be kept within certain narrow limits to avoid toxic responses.
C. Although zinc is not required for the regulation of transcription, it is required for translational control.
D. None of the above.

Questions 4-7:

The researchers now want to get information about the corresponding gene in mice. They have identified a strain of true-breeding mice that do not grow to full size (dwarfism). Their thought is that if they could understand this sluggish growth in mice, that perhaps they could begin to understand dwarfism in humans. The research team sets out to isolate and clone the growth hormone gene in mice, starting from the rat gene. They have a mouse cDNA library available to them.

4. The first step in their new project involves:
A. Screening a mouse genomic library.
B. Probing the mouse cDNA library with cDNA encoding the rat growth hormone.
C. Probing a rat genomic library with mouse cDNA encoding mouse growth hormone.
D. Amplifying mouse cDNAs encoding growth hormone.

5. The team has now succeeded in identifying a candidate for the open reading frame encoding the mouse growth hormone.  The final step in the procedure, which resulted in a tentative identification of the sequence as a growth hormone gene involved:
A. Purifying the candidate sequence on an agarose gel.
B. Sequencing the DNA.
C. Using the sequence, once known, to scan GenBank to identify homologous cDNA sequences.
D. Using the primary sequence, once known, to infer the definitive 3-D molecular structure of the protein.

6. Armed with the mouse growth hormone cDNA, the researchers now want to get more information about regulation of the mouse growth hormone gene.   Their first step will be to:
A. Identify and clone the mouse growth hormone genomic sequence.
B. Search for transcription factors that bind to the known promoter sequence of the mouse growth hormone gene.
C. Search for transcription factors that bind to the known promoter sequence of the rat growth hormone gene.
D. Search for the promoter sequence of the rat growth hormone gene.