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
cell growth, DNA replication, cellular activators
Interphase
condensation of chromatids
Leptolema
lining with homologous pairs
Zygonema
crossing over
Pachynema
synaptonemal complex begin to move apart
Diplonema
nuclear envelopes disappear
microtubules enter the nucleus
Prometaphase I/II (Meiosis I/II)
homologous pairs align in the middle
Metaphase I/II (Meiosis I/II)
production of two new cells (diploid)
***Cytokinesis for cell division
Telophase I/II (Meiosis I/II)
Reductional Division
Meiosis I
Equational Division
Meiosis II
result in a reduction in the number of chromosomes in each cell from diploid to haploid (reductional division-each resulting pair of attached sister chromatids count as a single chromosome)
Meiosis I
result in the separation of the sister chromatids
Meiosis II
Meiosis I, in which the chromosome number is reduced from diploid to haploid, consists of five stages:
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
early prophase I,
Leptotene Stage
the extended chromosomes begin to condense and become visible as long, thin threads
Leptonema
early to middle prophase I
Zygotene Stage
the chromosomes continue to condense
the homologous pairs of chromosomes actively find each other and align roughly along their lengths
Zygonema
the formation along the length of the chromatids of a zipperlike structure called the SYNAPTONEMAL COMPLEX
Synapsis
aligns the two homologs precisely, base pair for base pair
Synaptonemal Complex
middle prophase I
Pachytene Stage
starts when synapsis is completed
because of the replication that occurred earlier, each synapsed set of homologous chromosomes consists of four chromatids and is called a bivalent or a tetrad
Pachynema
during pachynema, a most significant event
for genetics occurs:
Crossing-over
the reciprocal physical exchange of chromosome segments at corresponding positions along pairs of homologous chromosomes
Crossing-over
the physical exchange that occurs in crossing over is facilitated by the alignment of the homologous chromosomes brought about by the
Synaptonemal complex
a chromosome that emerges from meiosis with a combination with which it started is called
Recombinant DNA
a mechanism that can give rise to genetic recombination
Crossing-over
at the end of pachynema, the synaptonemal complex is _______, and the chromosomes have started to elongate
disassembled
middle to late prophase I
Diplotene Stage
the synaptonemal complex disassembles and the homologous chromosomes begin to move apart
Diplonema
the result of crossing-over becomes visible during diplonema as a cross-shaped structured called
chiasma (plural, chiasmata)
late Prophase I
Diakinesis
the chromosomes condense even more, making it now possible to see the four members of the tetrads
the chiasmata are clearly visible at this stage
Diakinesis
the nucleoli disappear, the nuclear envelop breaks down, and the meiotic spindle that has been forming between the separating centriole pairs enters the former nuclear area
Prometaphase I
the kinetochore microtubules align the tetrads on the metaphase plate
Metaphase I
importantly, the pairs of homologs (the tetrads) are found at
the metaphase plate
at this time, homologous chromosomes have segregated from each other, but sister chromatids remain attached at their respective centromeres. In other words, a key difference between meiosis I and mitosis is that sister chromatids remain joined after metaphase in meiosis I, whereas they separate in mitosis
Anaphase I
the dyads complete their migration to opposite poles of the cell and the spindle assemble
in some species, but not all, new nuclear envelopes form around each haploid grouping
Telophase I
after __________________, each of the two progeny cells has a nucleus with a haploid set of dyads
cytokinesis
the chromosomes condense
formation of spindle fibers
Prophase II
the nuclear envelope breakdown (if formed in telophase) breaks down, and the spindle organizes across the cell
kinetochore microtubules from the opposite poles attach to the kinetochores of each chromosome
Prometaphase II
the movement of the kinetochore microtubules aligns the chromosomes on the metaphase plate
Metaphase II
the centromeres separate, and the now-daughter chromosomes are pulled to the opposite poles of the spindle
one sister chromatid of each pair goes to one pole, and the other goes to the opposite pole
the separated chromatids are now considered chromosomes in their own right
Anaphase II
the chromosomes begin decondensing, a nuclear envelope forms around each set of chromosomes, and cytokinesis takes place
Telophase II
after __________, the chromosomes continue decondensing eventually becoming invisible under the light microscope
telophase II
The end products of the two meiotic division
are
four haploid cells (gametes in animals) from one original diploid cell
reduces the number of chromosomes sets from two (diploid) to one (haploid)
Meiosis
conserves the number of chromosome sets
Mitosis
produces cells that differ genetically from their parent cell and from each other
Meiosis
produces daughter cells that are genetically identical to their parent cell and each other
Mitosis
Three Events Unique to Meiosis Occur During Meiosis I
- Synapsis and Crossing-Over
- Alignment of homologous pairs at the
metaphase plate - Separation of homologues
during prophase I, duplicated homologs
pair up
normally do not occur during prophase of mitosis
Synapsis and Crossing-over
chromosomes are positioned at the metaphase plate as pairs of homologs, rather that individual chromosomes, as in metaphase of mitosis
Alignment of homologous pairs at the metaphase plate
at anaphase I of meiosis, the duplicated chromosomes of each homologous pair move toward opposite poles, but the sister chromatids of each duplicated chromosome remain attached
in anaphase of mitosis, by contrast, sister
chromatids separate
Separation of homologues
