Scientific Discoveries 3. An important clue to the structure of DNA was provided by
A. a protein analysis of a muscle cell.
B. an X-ray diffraction photograph of DNA.
C. an MRI image of a brain cell.
D. a microscopic examination of a fruit fly.
Check Answer

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?

Which statements about the fluid mosaic structure of a membrane are correct? select the three correct statements.which statements about the fluid mosaic structure of a membrane are correct? select the three correct statements.the framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center.because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane.the diverse proteins found in and attached to membranes perform many important functions.the kinky tails of some proteins keep the membrane fluid by preventing the component molecules from packing solidly together.membranes include a mosaic, or mix, of carbohydrates embedded in a phospholipid bilayer.

Which of these substances does not protect against invaders in the nonspecific immune response? a. saliva b. mucus c. tears d. urine