New version page

Cytoskeleton and Cell Motility

Upgrade to remove ads

This preview shows page 1-2-3 out of 8 pages.

Save
View Full Document
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience

Upgrade to remove ads
Unformatted text preview:

B. Briefly describe how cytoplasmic streaming is most likely generated and organized at the molecular and organelle level.Comments?CommentsCommentsCommentCytoskeleton and Cell Motility CCM - 1 1. (28 pts) Amoeba proteus, a single-celled eukaryote, moves by means of psudopods attaching to and detaching from the substratum. Locomotion seems to be correlated with the forward flow of fluid cytoplasm (endoplasm) into an advancing pseudopod through a surrounding, gel-like ectoplasmic tube. The ectoplasm forms at the pseudopodial tip in a region called the Fountain Zone. As the amoeba advances the ectoplasmic tube “liquifies” at the posterior end to form endoplasm. These features are illustrated in the figure below. Both locomotion and cytoplasmic streaming are inhibited by cytochalasin B. Consider everything you’ve learned so far and answer all the following questions. A. (4 pts) When amoeba undergoes cell division, it stops streaming and rounds up into a spherical cell. Describe how this change in shape and behavior comes about and why it might be a necessary precondition for division. B. (6 pts) Briefly describe how cytoplasmic streaming is most likely organized and generated at the cellular and molecular levels. C. (5 pts) Briefly describe an additional experiment or observation that would test your hypothesis and indicate clearly what the results would show.Cytoskeleton and Cell Motility CCM - 2 D. (8 pts) Describe clearly, with the aid of a well-labeled diagram, how streaming within a pseudopod could result in movement of the amoeba across the substratum. E. (5 pts) Describe how your streaming mechanism might be regulated such that the amoeba might change its streaming pattern to form phagocytic pseudopods around a ciliate it had touched. Now evaluate some past answers to these questions, in light of your own essays. Note that better answers contain more information that you have covered at this point in the course. OnCytoskeleton and Cell Motility CCM - 3 the other hand, you may now know more about the various mechanisms than the students who answered these questions in the mid ‘90’s did! A. (4 pts) When an amoeba undergoes cell division, it first stops streaming and rounds up into a spherical cell. Describe how this change in shape and behavior comes about and why it might be a necessary precondition for division. Answer Comment Example 1. In order for the single cell to divide it must become a shape that is spherical enough for the spindle to form and an even distribution of cytoplasmic material to take place when cytokinesis happens. Also, cytokinesis cannot take place with a firm gel-like tube in the middle of the cell. In order for cell division to occur, the gel-like tube will dissolve into all endoplasm which is a liquid form. The cytoskeleton will form as a normal eukaryotic cell and cytokinesis will divide the cell. Once the cell has full divided, the endoplasm will form a new ectoplasm tube again and all will continue A good start, but more mechanistic detail is required: what sorts of cytoskeletal elements are involved? Wordy! Simply restates information provided. “normal” is vague – what does it mean in this context? Contrast the first answer with the following: Example 2. Microfilaments are needed for cytokinesis. They form a “belt” perpendicular to the spindle fibers needed for mitosis. This belt contracts, pinching off the cytoplasm from the original cell into 2 daughter cells. Microfilaments are dynamic structures, and those which previously were involved in streaming or maintaining cell shape are disassembled and used for cell division. When this occurs, the cell assumes a natural round shape and all streaming stops due to lack of microfilaments which would turn the endoplasm into ectoplasm. A well-focused mechanistic answer from the start! Connection with streaming established; dynamic properties identified. A problem: what is “natural?” How did your answer to the Question B. compare with those on the next page?Cytoskeleton and Cell Motility CCM - 4 B. Briefly describe how cytoplasmic streaming is most likely generated and organized at the molecular and organelle level. Example 1. The endoplam is a basic component of ectoplasm. This, the association of many endoplasmic forms ectoplasm in a similar way [that?] F-actin makes up G-actin to form microfilaments. The assocation forms a gel-like tube that is unstable at both ends. When endoplasm is in its component form, it is a liquid. However, when it associates with other endoplasms to make ectoplasm it forms a gel. The movement of the organism is caused by the breakdown or dissociation of the ectoplasm gel tube into its liquid endoplasm at the posterior end of the tubule causing fro?? pseudopod. This endoplasm then flows through the remain gel ectoplasm tube. The breakdown always happens at the posterior or (-) end. For each molecule of ectoplasm that dissociates, another molecules of endoplasm will associate at the (+) end toward the pseudopod. This allows the ectoplasmic tube to remain about the same length while the endoplasm at the end of the tube is allowed to flow all the way to the front. The plasma membrane is fluid so it conforms to the changing shape of the org[anism?]. Garbled fact: G-actin is a subunit of F-actin (microfilament). This is an interesting but unfocused essay. It is interesting insofar as it attempts to relate various aspects of streaming to cellular locomotion, BUT this discussion is irrelevant to the question asked. What the likely “motors” are and where are they located are not addressed. Confusing polarity of MT and MF organelles with cellular polarity. The handwriting was actually difficult to decipher, and grammatical errors increased the reader’s difficulties. By comparison, what do you think of this answer? Add your comments in the space provided. Example 2. Pseudopod extentions can be generated throug the interaction of actin (MF) and myosin. High ATP and Ca levels could be present at the pseudopod which would allow myosin to be phosphorylated. The actin would be forming microfilaments from G-actin because of the high ATP concentration at the pseudopod. Once phosphorylated, myosin could interact with the actin microfilaments to produce the force necessary to extend the pseudopod. As the pseudopod


Download Cytoskeleton and Cell Motility
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Cytoskeleton and Cell Motility and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Cytoskeleton and Cell Motility 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?