Aneuploidy, Polyploidy, Mosaicism Flashcards
What are five examples of “checkpoint” control mechanisms that ensure the fidelity of the cell cycle?
- DNA damage checkpoint
- DNA duplication checkpoint
- G1 checkpoint
- G2 checkpoint
(etc. ) - Mitotic checkpoint (also called the spindle assembly checkpoint)
During what phase of the cell cycle do chromosomes typically initiate condensation?
Prophase
What are three important components of prophase during mitosis?
- Interphase microtubules start to array around the nucleus and later the chromosomes.
- Nuclear envelope disassembles.
- Fully compacted chromosomes spill into the cytoplasm so that they can align at the equator during metaphase.
Gametes that have missing or extra chromosomes can give rise to what two common problems?
- Cancer
2. Birth defects
The actual centromere consists of what two things?
- DNA
2. (Different) centromere proteins (CENP’s)
Describe the DNA organization of an alpha-satellite DNA strand with 171 base pairs.
- Higher order repeats of alpha satellite monomers.
- Tandem higher order repeats of the repeats mentioned above.
- Protects integrity of centromere functions.
What are the two main protein domains in human centromeres?
- CENP’s
2. Histones
Describe the organization of the centromere/kinetochore complex in humans.
- Extended chromatin fibers from human interphase cells demonstrate discontinuous CENP-A domains interspersed with histone H3 domains.
- Other CENP’s and core histones form important structure of centromere and support its function.
- Essential to folding centromeric chromatin in mitotic chromosomes.
What did hypotonic stretching of human chromosomes followed by immunofluorescence with human anti-centromere antibodies reveal and what do these findings suggest?
- Discontinuous distribution of centromere proteins.
- Dot-like distribution of centromere antigens
- The above suggests a multiple subunit organization of the centromere/kinetochore complex.
What is kinetochore?
A protein complex flanking the two sides of the centromere which contains microtubule attachment sites.
What are the three main elements of the centromese/kinetochore complex and what are their roles?
- Outer kinetochore (site of microtubule binding)
- Inner kinetochore (region of distinctive chromatin composition attached to the primary construction).
- Inner centromere (a heterochromatin domain that is a focus for choosiness and other regulatory proteins).
Describe the composition of the outer kinetochore.
Comprised of diverse microtubule motor proteins, regulatory kinases, microtubule binding proteins, and mitotic checkpoint proteins (usually 10-50 microtubules per kinetochore).
What are the four most commonly studied centromere proteins (CENP’s)?
- CENP-E
- CENP-A
- CENP-B
- CENP-C
What three things are important to know about CENP-E’s?
- Essential component of mitotic checkpoint.
- Links spindle microtubule capture to mitotic checkpoint signaling.
- Functions as a centromere motor powering chromosome alignment and segregation.
What is one important thing to remember about CENP-A’s?
Important for cohesion of sister chromatids.
What are four important things to remember about CENP-B’s?
- May be involved in maintenance of centromeric satellite DNA arrays
- May be involved in organization of centromeric satellite DNA arrays.
- May not be involved in centromere structure.
- Plays critical role in assembly of higher order structures.
What kind of protein are CENP-C’s?
Kinetochore proteins.
In addition to being simple attachment sites for microtubules, what four important roles do human centromeres play in cell division?
- Active components in microtubule CAPTURE.
- Active components in microtubule stabilization.
- Powering chromosome movements essential to proper segregation.
- Signaling elements for controlling cell cycle advance through mitosis.
What is the main role of the mitotic checkpoint in cell division?
Ensuring accurate segregation of chromosomes.
What is another name for the mitotic checkpoint?
Spindle assembly checkpoint.
How does the mitotic checkpoint ensure accurate segregation of chromosomes?
Acts to block cells to entry into anaphase until both kinetochores of every duplicated chromatd pair have attached correctly to spindle microtubules (uses control machinery to halt cell-cycle until all conditions are safe and appropriate for the cell to proceed to next stage).
What does the Attachment and Encounter theory describe?
A possible mechanism by which microtubules are captured by the kinetochore - that it is only a matter of chance which makes spindles from opposite poles connect to centromeres on opposite sides of the same chromosome and this is only favored by the back-to-back arrangement of chromosomes.
How are microtubules captured by the kinetochore?
Using tension and ATP (and GTP!), many random microtubule are extended and when all chromosomes have opposing tension, anaphase is signaled to begin (but will be delayed in the absence of tension).
What are errors that can happen during the spindle attachment to kinetochores and how are these errors corrected?
“Monopolar” attachments (opposite centromeres on one chromosome attached to spindles from the same pole) or centromeres missing microtubule attachments are detected from the lack of tension although this is also by chance.
