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Chapter 34: The Cell Cycle
The cell cycle is a sequence of growth and division for living and dividing cells.
Growth and development are dependent on the timing and rate of cell division.
Red and white blood cells can be produced from bone marrow cells.
The cells can be regenerated when the tissue is damaged.
Human intestine cells divide about twice a day.
Nerve cells do not divide at all.
The entire process is tightly regulated by a complex mechanism.
If something goes wrong, the result can be cancer.
The ratio of the volume of a cell to its surface area and the capacity of the nucleus to control the entire cell are two important factors that limit cell size and promote cell division.
As a cell grows, the surface area of the cell grows with the square of the radius, and the volume of the cell grows with the cube of the radius.
As a cell grows larger, the volume inside the cell increases at a faster rate than the volume inside the cell.
The ratio of cell volume to the size of the cell is important in determining when the cell splits.
The nucleus needs to be able to give enough information to meet the needs of the cell.
The cells are usually small.
Cells that have evolved a strategy to exist as large, active cells exist in several kingdoms.
The paramecium has two nuclei that control different functions.
Human muscle cells are multinucleate cells.
There is a giant cell in the mold that has thousands of nuclei.
The five major phases of the cell cycle are G 1, S, and G 2.
The events that occur in the cell cycle can be described.
Interphase consists ofGap 1 and 2.
The G 1 phase is a period of growth and activity.
S is for the synthesis of DNA.
The phase when the cell continues to grow is called G 2.
Interphase is where most of the life of a cell is spent.
The cell is very active when it is in interphase.
The chromatin is threadlike.
There are at least one or more nucleoli in the nucleus.
A single centrosome, consisting of two centrioles, may be seen in an animal cell.
During the S phase, the centrosome is duplicated.
The two centrosomes move to opposite poles at the G 2 -M transition.
Microtubule organizing centers are the same as centrosomes in plant cells.
An animal cell is shown during interphase.
There is a dividing of the nucleus.
The process is remarkable because the DNA is passed from one generation to the next with great fidelity.
It's a continuous process.
Scientists have divided it into four different phases: prophase, metaphase, anaphase and telophase.
The characteristics of each phase are listed here.
Although the College Board doesn't require you to know the names of specific phases, you may find this information useful in understanding the process.
The nuclear structure begins to break down.
The strands of chromosomes begin to form observable structures.
The centrosome is the starting point for the mitotic spindle to form.
The chromosomes are located in a single file on the equator.
The centrosomes are positioned at opposite poles.
The fibers come from the centrosomes to the kinetochores in the centromeres.
The sister chromosomes that move toward the poles are separated by spindle fibers.
The supercoiled chromosomes begin to fall apart and return to their pre-cell division condition as long, threadlike strands.
Once two individual nucleoli form, it is complete.
The dividing of the cytoplasm is called cytokinesis.
It begins during anaphase.
During telophase in plant cells, Golgi cells form in the middle of the cell.
Plants do not separate from each other.
Normal cells divide until they become too crowded, then they stop dividing and enter G 0 Density- dependent inhibition is a reaction to overcrowding.
anchorage dependence is a characteristic of normal animal cells.
A cell must be attached or anchored to a surface in order to divide.
Cancer cells do not show contact inhibition or anchorage dependence.
They do not have to be anchored.
Cancer cells can migrate to other parts of the body.
Natural selection and evolution rely on the genetic diversity generated by meiosis.
In meiosis I, there are different pairs.
ova and sperm are produced by meiosis, a form of cell division.
Half the genetic material of the parent cell can be found in these gametes.
Each gamete has its genetic material separated and recombined to make it different from the other gametes.
Sexual reproduction involves the fusion of two haploid gametes.
There are two cell divisions in meiosis.
The reduction division is the process by which chromosomes separate.
A structure known as a tetrad or bivalent is formed by a process called synapsis, in which the chromosomes first pair up with each other.
This process is important.
Accurate crossing-over is likely to occur if the homologues are aligned and binding together.
The process of crossing-over is the exchange of genetic material.
While crossing-over is happening, what is visible under a microscope are the Xs on the chromosomes.
Increased variation among gametes is ensured by crossing-over.
The connection between meiosis and increased genetic diversity is necessary for evolution.
Meiosis is a disease.
In this process, sister chromatids are separated.
There are two stages of meiosis.
The four stages of the meiotic cell division are prophase, metaphase, anaphase, and telophase.
There are visible manifestations of the events.
Segregation of DNA is set up in Prophase I.
There are two pages on spermatogenesis and oogenesis.
The double file is along the metaphase plate.
The fibers from the poles of the cell are attached to the centromeres.
There is a separation of chromosomes when they migrate to opposite poles.
Homologous pairs are separated until they reach the poles of the cell.
Each pole has a number of chromosomes.
telophase I andkinesis occur at the same time.
There is an interphase between meiosis I and II in some species.
This doesn't happen in other species.
The difference between meiosis I and II is that chromosomes already exist as double or replicated chromosomes.
The same phases of prophase, metaphase, anaphase, and telophase are found in Meiosis II.
The number is haploid.
The parent cell has four chromosomes.
The cell undergoes meiosis.
They are independent assortment of chromosomes, crossing-over and random fertilization of an ovum by a sperm.
Heritable information is passed to the next generation by the cell cycle.
Depending on the random way in which the chromosomes line up on the metaphase plate, there are different pairs of chromosomes.
There is a 50 percent chance that a particular gamete will receive a maternal or paternal chromosomes.
The number of possible combinations of maternal and paternal chromosomes in each gamete is about 8 million.
The genes from both parents are combined in Crossover.
Humans have an average of two or three events in each pair.
This increases the possibilities of gametes even more.
Fertilization increases the amount of genes in a population.
The diploid number is restored.
There are approximately 8 million possible combinations of the human ovum.
The same can be said for the human sperm.
8 million x 8 million recombinations are possible when one spermfertilizes one ovum.
The rate at which cells divide is regulated by a cell cycle control system.
If go-ahead signals are not used, several checkpoint act as stop signals that stop the cell.
The signals are registered from inside and outside the cell.
There are three checkpoints in G 1, G 2 and M. The restriction point is known as the G 1 checkpoint and is the most important checkpoint in mammals.
The cell will most likely be complete if it gets the go-ahead.
If the cell doesn't get the signal, it will exit the cycle and become a nondividing cell in the G 0 phase.
The rate at which a cell needs to divide varies due to the activity of the cell.
The timing of the cell cycle is initiated by growth factors and controlled by two kinds of molecule.
This is an example of cell signaling.
The name cyclins comes from the fact that their levels rise and fall in dividing cells.
They are broken down after every M phase.
Kinases are a class of proteins thatphosphorylates other proteins.
Only when they bind to a cyclin can the kinases be activated.
They are called cyclin-dependent kinases or Cdks.
A cyclin-Cdk complex is formed when a Cdk binding to a cyclin.
The cell's passage from G 2 to M is triggered by the MPF complex.
You may think of it as M phase promoting factor if you think of it as a maturation promoting factor.
During prophase, there are required events for chromosome condensation and spindle formation.
During anaphase,MPF starts a process that leads to the breakdown of cyclin.
The inactive form of the noncyclin part of MPF is called the Cdk.
To help you understand how internal and external signals regulate the cell cycle, the details of MPF andPDGF are presented as illustrative examples.
Changes in the concentration of the cyclin partner can affect the activity of a Cdk.
During the S and G 2 phases, the cyclin levels rise and then fall abruptly.
The cell goes past the G 2 checkpoint into the M phase.
The cell cycle is driven by an external signal.
fibroblasts are specialized cells that have a receptors on their surface.
The signal pathway that allows cells to pass the G 1 checkpoint is triggered when PDGF binding to a receptor.
When an injury occurs in the body, platelets release PDGF near the injury, and a massive proliferation of fibroblasts heals the wound.
Big ideas were supported by this chapter.
There is a chapter about the cell cycle.
The transmission of information from one generation to the next is called Big Idea IST.
Heritable information is packaged into chromosomes that are passed from parent to daughter cells.
The cell cycle is a highly regulated and complex process.
Some mature cells, like neurons, are no longer dividing.
The cell cycle is directed by internal and external controls.
Cancer is a disease in which normal controls of the cell cycle go awry.
Cancer cells never stop dividing.
G 1 is the most important restriction point in mammals.
The cell cycle is initiated by growth factors and is controlled by two kinds of molecule.
The cell's passage from G 2 to M is triggered by the maturation promoting factor.
There are identical daughter cells.
It allows organisms to reproduce asexually.
Understand what happens in each stage.
Each gametes has a haploid chromosome number.
During meiosis I, chromatids exchange genetic material before they separate.
Genetic diversity is necessary for evolution.
Fertilization is the random fusion of gametes that increases genetic diversity and restores the original diploid chromosomes in the egg.
Interphase (G1, G2, and S) is a part of the cell cycle.
The graph shows the different levels of DNA during the various stages of the cell cycle.
There are differences and similarities in the cell cycles of different organisms in the animal kingdom.
Interphase is a part of the cell cycle.
Each figure represents a cell that will divide and produce two daughter cells.
One pair has experienced one event.
The drug suppresses actin formation in a cell while preserving the structure of the rest of the cytoskeleton.
Taxol comes from the Pacific yew tree and is used to stop the spread of breast cancer.
The disruption of the microtubule assembly is the main mechanism by which it works.
Predict the cellular process that Taxol would most directly interfere with, as a result of its function.
Two questions refer to an experiment.
Two researchers conducted an experiment to see if the progression of the cell cycle is controlled by the outside world.
They chose cells from different phases of the cell cycle to investigate the hypothesis.
There are two cells at the beginning of the experiment.
Pick the image that predicts the result of the experiment after fusion if the researchers' hypothesis is correct.
Refer to the two cells sketched in the question.
The kinetochore is a part of the chromosomes.
Microtubules that connect the kinetochore to the poles shorten during anaphase.
There are two possible theories about the role of the kinetochore.
The kinetochore is pulling on the fibers and dragging the chromosomes to the poles.
The opposing theory suggests that kinetochores walk on the microtubules.
Three researchers carried out an experiment to find out which theory is correct.
They labeled the microtubules of the pig kidneys cell with yellow fluorescent dye.
They used a laser to photobleach and eliminate the YFD from the region of the microtubule between the pole and the chromosomes.
The microtubules were intact.
The researchers monitored the changes in the microtubule length by measuring the length of the spindle on both sides of the mark.
Choices A and C are related to meiosis and the production of gametes.
The question asks for the statement that is only a characteristic of the disease, but Choice D is something that occurs in both.
The amount of DNA is decreasing, not doubling, as it does in the S phase.
There is no increase in the number of genes in G 1 and G 2.
Although stage III shows no change in the amount of DNA, interphase includes the S phase of cell division, where the amount of DNA doubles.
Maturation promoting factor (MPF) is a complex of genes that cause a cell to die.
Choice A isn't the most relevant scientific question because it doesn't relate to the cell cycle.
Microtubules, not microfilaments, make up spindle fibers, so choice B is not the most relevant scientific question.
This would have been a relevant scientific question if the question had used the term microtubules.
ribosomes don't have anything to do with the cell cycle, so choice C isn't the most relevant scientific question.
Condensed chromosomes pair up and homologous chromosomes exchange.
During meiosis, there is an event that shuffles genes.
Under a light microscope, chromosomes are invisible.
There is a phase of interphase called the S phase.
The haploid number is not contained in the cell.
Interphase should be the largest slice of the pie chart.
It doesn't matter that G 1, S, and G 2 aren't labeled as part of interphase in choice C. Interphase is shown as a small slice of the pie by Choices A and D.
The M phase occurs after G 2.
There is a significant feature of meiotic cell division.
Each daughter cell will contain half the number after meiosis I.
Plant cells don't have centrioles.
Normal cells grow in culture.
Cancer cells don't show this characteristic.
Cancer cells do not stop dividing.
synapsis is the process when chromosomes pair up.
They prepare for crossing-over, not the other way around.
Cells in the gut are not arrested.
Cells that have been damaged during digestion are replaced every day.
The cell's passage from G 2 into the M phase is triggered by MPF.
Normal cells don't divide because they spend most of their time and energy in interphase.
Interphase consists of G 1, S and G 2 so Choice B is incorrect.
Cancer cells can travel throughout the body, which is why Choice D is incorrect.
I or II could be the other choices.
The cells have half the number of chromosomes.
Before the crossing-over event, each homologue had two identical sister chromatids.
The A, d, and G genes must have been in the sister chromatid.
There are a, D, and g genes in both sister chromatids.
The left side's inner chromatid becomes A, d, and g.
A cell will divide if it passes G 1.
The cell will stop dividing if it does not pass this point.
Cancer cells have one nucleus, which is less than the number of chromosomes.
Cancer cells are not taken into custody.
They duplicate their genes and divide them.
Human cells don't undergo meiosis, so there are choices A, B, and C. Gametes are only produced by the emiotic cell division.
This is what happens in human muscle cells.
The cells are multinucleated and large.
Microtubules are what connect chromosomes from the metaphase plate to centrioles.
Microfilaments are not involved in DNA synthesis.
Microfilaments are not required for the condensing of chromosomes.
There are no microtubules in the center of the configuration.
The progression of those phases of the cell cycle is controlled by the presence of molecules in the cytoplasm.
The researchers' hypothesis that the cell in the S phase goes backward into G 1 is not confirmed by Choice B.
It doesn't make sense that Choice C shows both cells changing into the other's phase.
Choice D doesn't confirm the researchers' hypothesis because it doesn't show any change from the original sketch.
A cell in G 1 would move into S and G 2.
The end of the chromosomes is shorter than the beginning.
The attachment site for the spindle fiber is on the kinetochore.
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