#Question id: 2537
#Unit 2. Cellular Organization
Which of the following is the smallest structure that would most likely be visible with a standard (not super-resolution) research-grade light microscope?
#Question id: 1387
#Unit 4. Cell Communication and Cell Signaling
The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes. Microinjection into the cytoplasm of a wild. type cell of a solution of a synthetic peptide possessing the same sequence as the integrin beta subunit cytoplasmic domain would be expected to yield an average fibroblast-cell migration rat
Fibroblast
Phenotype |
Level of
Integrin Heterodimer at the Cell Surface (percent of wild type) |
Rate of
Cell Migration (pm/min) |
1. Wild type |
100 |
2 |
2.
Overexpression of the wild-type integrin alpha subunit |
104 |
2 |
3. Overexpression
of an integrin beta subunit lacking the cytoplasmic domain |
96 |
0.6 |
4.
Overexpression of the soluble cytoplasmic domain of an integrin beta subunit |
98 |
0.6 |
5. Absence of
the integrin alpha subunit |
Less than 1 |
0.05 |
#Question id: 27416
#Unit 1. Molecules and their Interaction Relevant to Biology
#Question id: 24476
#Unit 3. Fundamental Processes
#Question id: 7265
#Unit 5. Developmental Biology
Following statement regarding to the cascade of regulated RNA splicing controls drosophila sexual differentiation.
A. The Sex-lethal (Sxl)
protein, encoded by the sex-lethal gene, is the first protein to act in the
cascade and present only in female embryos.
B. Early in development, the Sxl gene is transcribed from a
promoter that functions only in male embryos.
C. Later in development, this male-specific promoter is shut
off, and another promoter for sex-lethal becomes active in both male and female
embryos.
D. In male embryos, however, in the absence of early Sxl
protein, exon 3 of the sex-lethal pre-mRNA is spliced to exon 2 to produce an
mRNA that contains a stop codon early in the sequence.
Which of the following is correct?