ap biology- mitosis
Terms in this set (73)
what does the mitotic phase consist of?
it consists of mitosis and cytokinesis
what percentage of the cell cycle does interphase account for?
what happens during interphase?
the cell grows and copies its chromosomes in preparation for cell division. the cells grows by producing proteins and cytoplasmic organelles.
what three sub phases can interphase be divided into?
G1 (gap 1), S, G2 (gap 2)
what happens during the S of interphase?
the chromosomes are duplicated.
how often will a human cell undergo division?
once every 24 hours
how long will the S of interphase take in relation to the whole cell cycle?
10-12 hours, or about half of the cycle
how long will the M phase (mitotic phase) take in relation to the whole cell cycle?
less than an hour
what are the five stages that mitosis is broken down into?
prophase, prometaphase, metaphase, anaphase, and telophase
when does cytokinesis occur?
it overlaps with the latter stages of mitosis
what is the mitotic spindle and when does it begin to form?
it begins to form during prophase. it consists of fibers made of microtubules and associated proteins. The spindle is able to elongate by adding more units of the protein tubulin.
where does the assembly of the mitotic spindle start?
at the centrosome
what is the centrosome?
a nonmembranous organelle that functions throughout the cell cycle to organize the cell's microtubules. (it contains centrioles in animal cells, but the centrioles are not necessary for their division)
what is an aster?
a radial array of short microtubules that extends from each centrosome
what is included in the spindle?
the centrosomes, the spindle microtubules, and the asters.
what is a kinetochore?
a structure of proteins associated with specific sections of chromosomal DNA at the centromere
what are the major events that occur in prophase?
1. the chromatin fibers condense into discrete chromosomes
2. the nucleoli disappear
3. the duplicated chromosomes appear as a set of sister chromatids
4. the mitotic spindle begins to form, and the centrosomes start to move away from each other
what are the major events that occur in pro metaphase?
1. the nuclear envelope fragments
2. the microtubules of the spindle can now invade the nuclear area and interact with the chromosomes
3. each chromosome now has a kinetochore
4. some microtubules attach to the kinetochores
what are the major events that occur in metaphase?
1. the centrosomes are now at opposite ends of the spindle
2. the chromosomes line up along the metaphase plate.
what are the major events that occur in anaphase?
1. it begins when two sister chromatids of each pair suddenly part.
2. the liberated chromosomes begin moving toward the opposite ends of the cell, as their kinetochore microtubules shorten.
3. the cell elongates as the nonkinetochore microtubules lengthen
4. by the end of anaphase, the two ends of the cell have equivalent collections of chromosomes
what are the major events that occur in telophase?
1. two daughter nuclei begin to form in the cell
2. nuclear envelopes arise from the fragments of the parent cell's nuclear envelope
3. the chromosomes become less condensed
what happens in cytokinesis?
the division of the cytoplasm. (this usually starts to happen by the end of telophase). There is a cleavage furrow in animal cells, which pinch the cell in two.
what happens to the asters during metaphase?
the microtubules of the asters have also grown and are now in contact with the plasma membrane. the spindle is complete at the end of metaphase
what triggers the start of anaphase?
the proteins holding together the sister chromatids of each chromosome are inactivated.
how do kinetochore microtubules function in this poleward movement of the chromosomes?
the primary mechanism of movement involves motor proteins what "walk" a chromosome along the attached microtubules toward the nearest pole. the microtubules shorten by depolymerizing at their kinetochore end.
what is the function of nonkinetochore microtubules?
they are responsible for elongating the whole cell during anaphase. (during anaphase, the region of overlap is reduced as motor proteins attached to the microtubules walk them away from one another. but as the microtubules are pushed apart from each other, the spindle poles are pushed apart, elongating the cell. simultaneously, the microtubules lengthen somewhat by the addition of tubulin subunits to their overlapping ends)
what is cleavage?
the process in which cytokinesis occurs in animal cells.
what is the first sign of cleavage?
the appearance of the cleavage furrow. on the cytoplasmic side, the furrow is a contractile ring of actin microfilaments associated with molecules of the protein myosin. the actin microfilaments interact with the myosin molecules, causing the ring to contract.
how is cytokinesis in plants different than cytokinesis in animals?
in plant cells, there is no cleavage furrow. Instead, during telophase, vesicles derived from the golgi apparatus move along microtubules to the middle of the cell, forming the cell plate.
what are the steps of binary fission?
1. the chromosome replication begins. Then, one copy of the origin moves rapidly toward the other end of the cell.
2. replication continues. one copy of the origin is now at each end of the cell
3. replication finished. the plasma membrane grows inward, and the new cell wall is deposited.
4. two daughter cells result
what is the origin of replication?
the spot where a bacterial chromosome begins to replicate
do bacteria have spindles?
what explains how bacterial chromosomes move and how their specific location is established and maintained
its not fully understood, but proteins are known to play important roles
what drives the cell cycle?
the cell cycle is driven by specific molecular signals present in the cytoplasm.
what is the cell cycle control system?
a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle. it is regulated at certain checkpoints by both internal and external controls
what is a checkpoint?
a critical point where stop and go-ahead signals can regulate the cycle. (animal cells usually have built in stop signals that halt the cell cycle at checkpoints until overridden by go-ahead signals)
where are the three major checkpoints found?
the G1, G2, and M phases
what is the most important checkpoint in mammalian cells?
the G1 checkpoint.
what happens if the cell receives a go-ahead signal at the G1 checkpoint?
it will complete the cycle and divide
what happens if the cell doesn't receive the go-ahead at the G1 checkpoint?
it will exit the cycle, switching into a nondividing state called the G0 phase
what is the G0 phase?
a nondividing state that a cell enters if it does not receive the go-ahead signal at a G1 checkpoint
what paces the sequential events of the cell cycle?
rhythmic fluctuations in the abundance and activity of cell cycle control molecules
what are the two main types of regulatory molecules?
kinases and cyclins.
what are protein kinases?
enzymes that activate or inactivate other proteins by phosphorylating them. (proteins give the go-ahead at the G1 and G2 checkpoints)
how does the concentration of protein kinases fluctuate throughout the cell cycle?
protein kinases are present in a constant concentration in the growing cell (but are mostly in inactive form)
how does a kinase get activated?
a kinase must be attached to a cyclin.
what is the name for kinases that are dependent on cyclin to be activated?
cyclin-dependent kinases, or Cdks
how is the activity of the Cdks determined?
its activity falls and rises its changes in the concentration of its cyclin partner.
what is MPF?
cyclin Cdk complex. it stands for "maturation-promoting factor", or "M phase promoting factor" (bc it triggers the cell's passage past the G2 checkpoint into the m phase.)
-acts directly as a kinase, and indirectly by activating other kinases.
-MPF switches itself off during anaphase by destroying its own cyclin.
-the noncyclin part of the MPF, the Cdk, is in active form until it associates w/ new cyclin molecules synthesized during the S and the G2 phases.
what is involved in the G1 checkpoint?
three Cdk proteins and several different cyclins
what seems to control all stages of the cell cycle?
the fluctuating activities of different cyclin Cdk complexes
what are the 5 steps of molecular control of the cell cycle at the G2 checkpoint
1. synthesis of the cyclin begins late in the S phase and continues through G2. Cyclin is protected from degradation during this stage; thus, it accumulates
2. accumulated cyclin molecules combine with recycled Cdk molecules of MPF to pass the G2 checkpoint and initiate the events of mitosis
3. MPF promotes mitosis by phosphorylating various proteins. MPFs activity peaks during metaphase.
4. during anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G1 phase.
5. during G1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled.
how do active Cdks function?
active Cdks function by phosphorylating substrate proteins that affect particular steps in the cell cycle.
what is an example of an internal signal that ensure that the daughter cells do not end up with missing or extra chromosomes?
the M phase checkpoint; anaphase does not begin until all the chromosomes are properly attached to the spindle at the metaphase plate
what is a growth factor?
a protein released b certain cells that stimulates other cells to divide. it is an internal regulator
what is another name for a growth factor?
what is density-dependent inhibition?
a phenomenon in which crowded cells stop dividing. (this is an external physical factor of cell division)
why causes density-dependent inhibition?
physical contact may have some influence, but the amount of required growth factors and nutrients available to each cell has a more important effect. (overpopulation causes a nutrient shortage, which causes cell division to decrease.
what is anchorage dependence?
for a cell to divide, it must be attached to a substratum, such as the extracellular matrix of a tissue. anchorage is signaled to the cell cycle control system via pathways involving cell membrane proteins, and elements of the cytoskeleton that are linked to them.
what are cancer cells?
cells that do not respond normally to the body's control mechanisms. the respond to neither density-dependent inhibition nor anchorage dependence.
why do cancer cells keep growing, even if there are no growth factors?
1. the don't need a growth factor
2. they may make their own growth factor
3. they could have an abnormality in the signaling pathway that conveys the grow factor's signal to the cell cycle control system even in the absence of that factor.
do cancer cells ever stop dividing?
sometimes, but they do so at random points in the cycle, rather than the checkpoints
how many times do normal cells divide?
what is transformation?
the process that converts a normal cell to a cancer cell.
what is a benign tumor?
if abnormal cells remain at the original site. they do not cause serious problems
what is a malignant tumor?
a tumor that becomes invasive enough to impair the functions of one or more organs. (cancer)
what 6 things contrast a cancer cell and a normal cell?
1. their metabolism is disabled
2. they may have an unusual number of chromosomes (this could be a cause or an effect of cancer)
3. the cells disconnect themselves from the ECM and other neighboring cells and spread into nearby tissues
4. they can secrete signal molecules thta cause blood vessels to grow toward the tumor
5. they are said to be "immortal"
6. they do not respond to density-dependent inhibition, or anchorage dependence
what is metastasis?
the spread of cancer cells to locations distant from their original site
why can radiation be used to treat localized cancer cells?
because cancer cells have lost their ability to repair such damage
how does chemotherapy treat metastatic tumors?
chemotherapy interferes with certain steps in the cell cycle. certain drugs freezes the mitotic spindle by preventing microtubule depolymerization, and stops dividing cells from proceeding past metaphase
what are some of the side-effects of chemotherapy/
nausea, hair loss, and susceptibility to infection
what causes cancer?
the alteration of genes that somehow influence the cell cycle control system
what are the specific steps in metastasis?
1. a tumor grows from a single cell
2. cancer cells invade neighboring tissue
3. cancer cells spread through lymph and blood vessels to other parts of the body
4. a small percentage of cancer cells may survive and establish a new tumor in another part of the body