Cell Communication & Cycle unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Signal amplification
Centrosome and spindle
Negative and positive feedback
Second messenger
Independent assortment
G1 checkpoint
Ligand
Meiosis vs mitosis
p53
G protein-coupled receptor
Signal termination
Paracrine, endocrine and synaptic signaling
Short answer 1. Define or explain: Quorum sensing
3 ptsShort answer 2. Define or explain: Meiosis I vs meiosis II
3 ptsShort answer 3. Define or explain: Chromatin vs chromosome
3 ptsShort answer 4. Define or explain: G2 and M checkpoints
3 ptsFree response
9 ptsInsulin lowers blood glucose by binding a receptor tyrosine kinase on the surface of target cells. Binding causes the receptor to dimerize and autophosphorylate, which activates a cascade ending in the movement of GLUT4 glucose transporters to the plasma membrane. Researchers studied cultured muscle cells from four mouse strains: wild type; strain A, with a receptor that cannot autophosphorylate; strain B, which produces no GLUT4; and strain C, with a constitutively active (always on) kinase in the middle of the cascade. Cells were incubated with or without insulin and glucose uptake was measured. TABLE 1. GLUCOSE UPTAKE (nmol per mg protein per minute, ± 2SE) Strain Without insulin With insulin Wild type 1.2 ± 0.2 8.6 ± 0.5 Strain A 1.1 ± 0.3 1.4 ± 0.3 Strain B 0.9 ± 0.2 1.0 ± 0.2 Strain C 8.1 ± 0.6 8.4 ± 0.6
(a)(i) Describe the role of the ligand in a signal transduction pathway such as this one.
(a)(ii) Explain why insulin must bind a receptor on the cell surface rather than entering the cell directly.
(b)(i) Based on Table 1, identify the strain in which the signal is transduced but the cellular response cannot occur.
(b)(ii) Justify your identification in (b)(i) using the data.
(c)(i) Explain why glucose uptake in strain C is high even without insulin.
(c)(ii) Calculate the fold increase in glucose uptake caused by insulin in wild-type cells.
(d)(i) The researchers included the "without insulin" condition for every strain. Justify the inclusion of that condition.
(d)(ii) Predict the glucose uptake, with and without insulin, of cells from a mouse carrying both the strain A and the strain C mutations.
(d)(iii) Provide reasoning to justify your prediction in (d)(ii).