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Lecture 13

CHEM 06101 Lecture Notes - Lecture 13: Spindle Apparatus, Sister Chromatids, Keratin

Chemical Engineering Biochemistry
Course Code
CHEM 06101
Lawrence Boni

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1. Why do microtubules disassemble at the ends instead of falling
apart in the middle? Hint: consider the protein-protein
interactions that a tubulin alpha beta dimer makes when it
assembles into the microtubule lattice.
The movement of chromomse is facilitated by the mitotic spindle, which is
consist of microtubules and associated proteins. Spindles extend from
centrioles on each end of the cell, attach to the chromosomes and pull the
sister chromatids apart.
2. Microtubules can be formed in vitro from tubulin that is bound
to GTP analogues that (unlike GTP) cannot be hydrolyzed. What
properties would you expect these microtubules to possess?
Could such microtubules still show dynamic instability?
They would be exceptionally stable because microtubules become labile when they contain
GDP-tubulin subunit at their plus end.
3. Because cytoplasmic vesicles are seen to move in both
directions within an axon, can you conclude that some
microtubules are oriented with their plus end facing the axon
terminus and others oriented with the opposite polarity? Why
or why not?
No, because all the microtubules of the axon are oriented in the same
direction; different motor proteins move vesicles in anterograde and
retrograde directions.
4. Would you agree with the statement that the centrosome plays
a key role in determining the rates of lengthening and
shortening of the microtubules of an animal cell? Why or why
No. The centrosome is located at the opposite end from that where these
events are occurring. Events at the plus end are determined by dynamic
instability and plus-end bound proteins.
5. Which type of vertebrate tissue would you expect to be an
excellent source of tubulin? of actin? of keratin? Which protein
would you expect to be the least soluble and most difficult to
extract? What types of protein would you expect as
contaminants in a preparation of tubulin? Which in a
preparation of actin?
Brain, muscle, and skin, keratin, MAPs, tropomyosin, troponin, or other
actin-binding proteins.
6. Actin is one of the most evolutionarily conserved proteins.
What does this tell you about the structure and function of this
protein in eukaryotic cells?
That virtually every residue in the protein is indispensable for either
maintaining the protein's structure or carrying out its function and that the
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