Review questions for Feb. 13th lecture:


posted February 27, 2:00 pm

a) Is there just one mechanism of amoeboid locomotion; or at least how many?

b) Be able to describe special features and differences between at least four kinds of amoeboid locomotion.

c) List and describe at least four important examples of cell locomotion being used to create anatomical structures.

d) If a photograph or drawing of a crawling tissue cell were on the exam (including wrinkles caused by the forces that the cell uses to produce its own location) then you should be able to draw the following:

Draw labeled arrows looking like this ---TRACTION--->
showing the directions and the locations in which the cell's traction forces are exerted

e) Also arrows looking like this ---ACTIN FLOW--->

f) Also label: Location of constant reassembly of actin fibers from separate actin molecules.
---actin re-assembles along this line---

g) Also: External gels and particles would be moved where and in what direction? ---ATTACHED OBJECTS--->

h) Sketch an Amoeba proteus, label the direction and location of forward cytoplasmic flow.

i) If conversion of Amoeba proteus cytoplasm from a more liquid to a more gel-like state results from re-assembly of actin from molecules into multi-molecular fibers, then what are similarities and/or differences between locomotion of human cells and Amoeba proteus cells?

j) Describe similarities and differences between locomotion of white blood cells and mesenchymal cells.

k) Describe and sketch some processes that you observed in the time lapse videos of sponge cells.

l) Describe cell movements in Labyrinthula. Where do Labyrinthula amoebae live, and what do they eat?

m) What are "shelled amoebae? Sketch one. Describe their locomotion.

n) Describe as many natural functions as you can that are accomplished by the exertion of the traction forces by which tissue culture crawl. If a chemical poison prevented all body cells from exerting this traction, then make a list of normal embryological events that would fail to occur.

o) Suppose that re-assembly of actin fibers were stimulated by some diffusible chemical; Would a diffusion gradient of such a chemical be expected to change the direction or speed of locomotion of cells inside our bodies?

p) Describe what you saw in the video of tissue culture mesenchymal cells crawling on an adhesion gradient.

q) If there are two diffusing chemicals, that can stimulate their own synthesis and breakdown, list a combination of three rules that will cause these chemicals to form regular spatial patterns (break displacement symmetry) of alternating high and low concentrations.

r) What changes in these rules will cause the wavelength to become wider or narrower? (i.e. the wavelength longer or shorter?)

s) What causes peaks on one morphogen substance to be wider at their bottom end? t) This hypothetical method for generating spatial patterns was invented by what British mathematician, who is the protagonist of a recently-released fictionalized biography?

u) ) Draw a graph of the quantitative variations of darkness of skin pigmentation in copperhead snakes.
(Note: contrast this pattern with the simple waves produced by other reaction-diffusion systems.)

v) Can you invent a combination of chemical reactions and directional pumping of chemicals that would be able to create the color pattern of copperhead snakes?
HINT: Do gradients of concentration tend to become steeper or less steep? Invent molecular or cellular processes that produce, amplify and maintain quantitative gradients that look like the ones in copperhead snake color patterns.

w) Wolpert's concept of "positional information would predict that the color pattern of copperhead snakes should be produced by cells responding to a gradient of chemical concentrations that looks like...what?
Sketch a graph of the expected chemical gradient.
(Hint: This is sort of a trick question; but it really might be asked on one of the exams, because the concept is very important to understand.)

x) Can you invent an alternative set of rules for chemical reactions that would produce alternating peaks of concentrations of two chemicals? It is easier than it might seem.
(Hint: The chemicals need to have opposite effects on each other. For a start, ask yourself what effect increased concentration of A should have on either the synthesis or breakdown of B, and vice versa, in order to continue to have alternating peaks of substances A and B? Higher concentrations of A need to cause what effect on concentrations of B, etc.)

y) Compare and contrast the geometric pattern of Liesegang Rings with those produced by other reaction diffusion systems.

z) In the photograph of Liesegang rings on the course web page, can you figure out why rows of dots form in some places, in contrast to continuous lines formed in other places? How could you test whether your hypothesis is correct?

HINT) The dark crystals precipitate wherever the concentration of silver ions multiplied by the concentration of bichromate ions gets higher than some threshold amount. {NOTE: should Turing, Meinhart and other hypthesizers of reaction-diffusion systems be paying more attention to concentrations of A multiplied by concentrations of B, rather than just their concentrations? Why or why not?}

@) Do the variables A and B need to be scalar variables, in order to produce spontaneous geometric patterns?
Could the two variables be curvature and tension? Could they be different directional components of tension?

#) Does action at a distance need to occur by diffusion? What other possibilities can you invent?

%) What are the major difference between prepatterns versus positional information?

*) What experimental or logical evidence tends to support positional information over prepatterns, and vice versa?

&) Suppose that you suspected that the sonic hedgehog protein sometimes functions as one of the morphogen proteins in a reaction diffusion system, what evidence could confirm or disprove this possibility?

+) What difference between early embryos of arthropods in contrast with vertebrates favors the formation of chemical diffusion gradients in arthropod embryos?

>) What can we learn from substituting a Czech flag for the French flag in relation to the "positional information" hypothetical mechanism for creating anatomical patterns and skin color patterns?




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