Ramachandran plots can help increase the accuracy of models derived from x-ray crystallography data. The plot below was created by measuring phi, and psi for each amino acid residue in a 2.2 A resolution crystal structure. In the plot, which excludes Gly and Pro residues, selected residues (dots) are numbered 1 through 5.

Which of the following statements can be correctly stated for this plot in reference to selected residues?

A. Residues 1 and 3 are in either B sheets

B. residue 2 is in a right-handed a helix, and residue 4 is in a left-handed a helix.

C. If residue 5 were Gly, it might be in an acceptable position in the plot

TLS Online TPP Program

#Question id: 16955

#Unit 4. Cell Communication and Cell Signaling

Stage thymocytes express neither CD4 nor CD8, markers associated with mature T cells. They are therefore called double negative (DN) cells. DN cells first travel to the region under the thymic capsule, a region referred to as the ________, where they proliferate and begin to generate their T-cell receptors. Thymocytes that successfully express TCRs begin to express both CD4 and CD8, becoming double positive (DP) cells, and populate the cortex, the site where most (85% or more) immature T cells are found.

TLS Online TPP Program

#Question id: 16954

#Unit 4. Cell Communication and Cell Signaling

match the following

A. endosteal niche	1. versatile cells that both generate bone and control the differentiation of HSCs
B. osteoblasts	2. line the blood vessels and also regulate HSC differentiation
C. reticular cells	3. send processes connecting cells to bone and blood vessels, and, unexpectedly
D. sympathetic neurons	4. can control the release of hematopoietic cells from the bone marrow.

TLS Online TPP Program

#Question id: 16953

#Unit 4. Cell Communication and Cell Signaling

The ability of any stem cell to self-renew and differentiate depends on the structural organization and cellular function of specialized anatomic microenvironments known as stem cell niches. These sequestered regions are typically populated by a supportive network of stromal cells. Stem cell niche stromal cells express soluble and membrane-bound proteins that regulate cell survival, proliferation, differentiation, and trafficking. Which statements is true about HSCs?

TLS Online TPP Program

#Question id: 16148

#Unit 4. Cell Communication and Cell Signaling

 Which statement is not true for NKT Cells?

TLS Online TPP Program

#Question id: 16147

#Unit 4. Cell Communication and Cell Signaling

 Which statement is not true for Natural killer (NK) cells?

TLS Online TPP Program

#Question id: 16146

#Unit 4. Cell Communication and Cell Signaling

If a given lymphocyte divides to form two daughter cells, both daughters bear antigen receptors with antigen specificities identical to each other and to the parental cell from which they arose, and so will any descendants they produce. The resulting population of lymphocytes, all arising from the same founding lymphocyte, is a clone. Which interleukin is responsible for clone production?