Unit 4 - Cell Cycle Episode 2 Flashcards
rhythmic fluctuations in the abundance and
activity of cell cycle control molecules pace the
sequential events of the cell cycle
The Cell Cycle Clock
these regulatory molecules are mainly proteins of two types:
protein kinases and cyclins
re enzymes that activate or inactivate other proteins by phosphorylating them
many of the kinases that drive the cell cycle are actually present at a constant concentration in the growing cell, but much of the time they are in an active form
Protein Kinases
to be active, such kinase must be attached to a ________
cyclin
a protein that gets its name from cyclically
fluctuating concentration in the cell
cyclin
Because of this requirement, these kinases are
called __________________, or Cdks
the activity of a Cdk rises and falls with changes in the concentration of its cyclin partner
Cyclin-dependent kinases
the cyclin-Cdk complex, activity correspond to the peaks of cyclin concentration
the cyclin level rises during the S phase and G2 phases and then falls abruptly during M phase
Maturation-promoting factor
he initial MPF stands for “maturationpromoting factor”, but we can think of MPF as _________________ because it triggers the cell’s passage into the M phase, past the G2 checkpoint
M-phase promoting factor
when ________ that accumulate during G2 associate with __________, the resulting MPF complex phosphorylates a variety of proteins, initiating mitosis
cyclins; Cdk molecules
_________ acts both directly as a kinase and indirectly by activating other kinases
MPF
during ______, MPF helps switch itself off by initiating a process that leads to the destruction of its own cyclin
Anaphase
the noncyclin part of MPF,________, persists in the cell, inactive until it becomes part of MPF again by associating with new cyclin molecules synthesized during the S and G2 phases of the next round of the cycle
the CDK
proteins known as _____ (named because their concentration increases and decreases in a regular pattern through the cell) and enzymes known as __________________ are the key components in the regulatory events that occur at checkpoints
cyclins; cyclin-dependent kinases (Cdks)
at the ___________________, two different G1 cyclin-Cdk complexes form, resulting in activation of the kinase
G1-to-S checkpoint
the kinases catalyze a series of _______________ (additions of phosphate groups) of cell cycle control proteins, affecting the functions of those proteins and leading, therefore, to transition into the S phase
a similar process occurs at the G2-to -M
checkpoint
phosphorylations
a cyclin binds to a Cdk to form a _________
complex
until the cell is ready to enter ________, phosphorylation of the Cdk by another kinase keeps the Cdk inactive
mitosis
at that time, a phosphatase removes the key
phosphate from the Cdk, activating the enzyme
_________________________________ move
the cell into mitosis
Phosphorylations of proteins by Cdk
Three important checkpoints are those
G1, G2, and M phase
for many cells, the G1 checkpoint-dubbed
the __________________ in mammalian cells -seem
to be the most important
“restriction point”
most cells of the human body are actually in
the ____ phase
G0
T/F: Mature nerve cells and muscle cells never divide
True
other cells, such as ___________, can be “called back” from the G0 phase to the cell cycle by external cues, such as growth factors released during injury
liver cells
do not head the normal signals that regulate the cell cycle
in culture, they do not stop dividing when growth factors are depleted
do not need growth factors in their culture medium to grow and divide
Cancer Cells
they make a required growth factors themselves, or they may have an abnormality in the signaling pathway that conveys growth factor’s signal to the cell cycle control system even in the absence of that factor
Cancer Cells
can go on dividing indefinitely in the culture if they are given a continual supply of nutrients; in essence, they are “immortal”
Cancer Cells
a striking example is a cell line that has been reproducing in culture since 1951
HeLa Cells
Original source of HeLa Cells
a tumor removed from a woman named Henrietta Lacks
by contrast, nearly all normal, nontransformed mammalian cells growing in culture divide only about ________ before they stop dividing, age, and die
20 to 50 times
the abnormal cells may remain at the original site if they have too few genetic and cellular changes to survive at another site. In that case, the tumor is called
Benign tumor
most of this tumors do not cause serious
problems and can be removed by surgery
benign tumor
includes cells whose genetic and cellular changes enable them to spread to new tissues and impair the functions of one or more organs; these cells are also considered transformed cells
Malignant tumor
The process by which cancer cells spread to other parts of the body
Metastasis
also known as reduction division
Meiosis
