How do NK cells discriminate between normal, healthy cells and virus-infected or tumor cells?
What will be an ideal response?
Answer: NK cells use special MHI receptors to recognize MHCI proteins on normal, healthy cells. Binding of the NK receptors to MHCI deactivates the NK cell, turning off the perforin and granzyme killing mechanisms. Many tumor and virus-infected cells reduce or eliminate MHCI protein expression patterns to evade the antigen-specific immune response. In the absence of deactivation of NK cell by MHCI proteins, the stress receptors on NK cells engage stress proteins on target cells releasing perforins and granzyme to destroy these target cells.
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Larger populations generally are killed as rapidly as smaller populations.
Answer the following statement true (T) or false (F)
Wheat is a group of grass species. Cultivation originated in the eastern Mediterranean about 10,000 years ago
In comparison to closely related wild grasses, cultivated wheat has shorter stalks and fewer, larger seeds that are firmly attached to the stalk and are unable to disperse via wind like other grasses. Which of the following provides an explanation as to why wheat is so successful despite the loss of seed dispersal? A. Wheat seeds are dropped below the parent plant and will grow the following season. This maintains the worldwide distribution of wheat. B. Wheat seeds are collected and dispersed by humans. Their worldwide distribution increases every time a new field of wheat is planted. C. Wheat seeds have evolved to be consumed by animals. Wheat seeds no longer rely on wind as its dispersal mechanism. D. Wheat seeds are not required for reproduction. Because it is a grass species, it has asexual reproduction.
The chemical process that prepares sperm for penetration of the oocyte is called ________.
A) capacitation B) differentiation C) independent assortment D) frenulation
How many replication forks are produced when DNA denatures at an origin?
A) 0 B) 1 C) 2 D) 3 E) The number varies