8.3-8.10: The Eukaryotic Cell Cycle and Mitosis Flashcards
How many genes do human cells have? Bacterium?
21,000; 3,000
What is the order of DNA organization?
genes–>chromosomes–> DNA
How many chromosomes does a human have? Dog? Hedgehog?
46; 78; 90.
Chromosomes are also known as
One large strand of DNA
Besides nucleotides, what macromolecule is attached to DNA? What is its significance?
Proteins are attached. They are responsible for maintaining structure and controlling the activity of genes.
What is chromatin?
The DNA-protein complex. The amount of DNA and protein are equal.
What does chromatin look like? What does it look like when a cell might begin to divide?
For most of the time, it looks like long, thin fibers in the nucleus. When a cell is preparing to divide, it coils up and forms chromosomes.
What are sister chromatids?
The duplicated chromatin when a cell is about to divide. (Chromosomes wrapped in protein connected to each other)
What is a centromere?
The “waist” of a sister chromatid, or a part where the cylinder of a chromatid radius is slightly smaller.
When is a chromatid considered a chromosome?
When it separates from its sister.
Considering what is known about the relationships between chromosomes and chromatids, how many chromatids are created when a human cell divides?
92, usually.
End of 8.3 Question: When does a chromosome consist of two identical chromatids?
When the cell is preparing to divide and has duplicated its chromosomes but before the duplicates actually separate.
How many cells in the human body?
10 trillion.
Mature muscle cells, found in cardiac muscle and the brain, do not undergo cell division. Why is this important?
It shows us why cardiac muscles cannot be revived after a heart attack; and why some brain functionality is lost forever because of a stroke.
Define the cell cycle.
An ordered sequences of events that prepares the cell for division by doubling everything, and the actual splitting process itself.
What is interphase? How long does it last within the cell cycle?
Interphase is when the cell replicates its membrane bound organelles and DNA, growing it size. it also increases metabolic activity because of the increased number of organelles. It is important to note that cells do not shut down during the cell cycle, they keep doing their assigned work. Interphase lasts for 90% of the cell cycle.
What are the processes within interphase?
G1 (first gap), S (DNA synthesis), G2 (second gap)
What happens during all the subphases of interphase?
The cell grows?
What does the S phase do? The G2 Phase?
The chromosomes double during the S phase (in the form of sister chromatids). G2 prepares for cell division.
What is the mitotic (M) phase?
The actual splitting of the cell. In its divided into two parts, which (I think) happen simultaneously. Mitosis makes two sister nuclei (DNA replication), and cytokinesis divides the cytoplasm (which, remember, includes organelles) into the new cells.
Can mitosis happen in prokaryotes?
No
How many errors are there in cell replication (at least within yeast)
one in 100,000, so very accurate.
Why is the extreme accuracy of mitosis so important? (for sexual reproduction)
because it starts as a single cell and then grows to trillions– it is essential that they receive copies of the same 46 chromosomes.
End of 8.4 Question: A researched treats cells with a chemical that prevents DNA synthesis from starting. This treatment would trap the cells in which part of the cell cycle?
G1.
What are the five stages of mitosis?
prophase, prometaphase, metaphase, anaphase, telophase (note that some people skip prometaphase). In that order.
What is the mitotic spindle?
A group of microtubules attached to two centrosomes on opposites sides of the cells; supports chromosomes.
At the end of the G2 phase in interphase, what does it look like?
The cell is very inflated and all the organelles, most importantly, centrosomes, have doubled. The nucleus has doubled its chromosomes as well, but they still look like standard chromatin and have not developed yet.
Give an overview of prophase.
The chromatin fibers tighten up and look like sister chromatids joined at the centromere. The centrosomes begin to form microtubules that grow out and create distance between them.
Give an overview of prometaphase.
The nuclear envelope breaks and the chromatids are suspended in the cytoplasm. The centrosomes’ spindles make contact with the kinetochore of sister chromatids and the kinetochore send them into agitated motion, or they connect with other microtubules from the other end of the pole. The chromosomes are moved to the center of the cell by “motors” from spindle microtubules.
What is a kinetochore?
A small region of specific DNA where the microtubules from centrosomes attach.
Give an overview of metaphase.
The mitotic spindle is fully formed, meaning that centrosomes are at opposite ends of poles and chromosomes are equidistant from both the poles, held on through two kinetochores of sister chromatids. it also seems that microtubules grow in the opposite direction in order to secure centrosomes.
Give an overview of anaphase.
The motor proteins from kinetochore separate the sister chromatids by moving them along the spindle to their respective poles. While those microtubules shorten, the ones attached to each other lengthen, moving the poles even further apart and elongating the cell.
Give an overview of telophase.
Telophase is the reverse of prophase. The chromatin uncoils and the spindle removes itself. The cell elongation continues. This considered the end of mitosis.
What is mitosis defined by?
The separation of a parent nuclei into daughter nuclei. Even if a cell hasn’t divided, mitosis can be over.
Give an overview of cytokinesis.
The actual separation of the cells after mitosis ends. Animals do this by creating a “cleavage furrow,
End of 8.5 Question: You view an animal cell through a microscope and observe dense, duplicated chromosomes scattered throughout the cell. Which state of mitosis are you witnessing?
Prophase (because the chromosomes are condensed but not yet aligned)
Why can it be inferred that cytokinesis (the actual full division of cells), would be different in plant cells as in animals cells?
Because the plant cell has a cell wall, where the animal cell only has a membrane.
How does a cleavage furrow work in an animal cell?
The cleavage furrow is a dip in the surface, that is created by a ring made of microfilaments, which are made of actin. When myosin interacts with actin (they are responsible for muscle contraction) the furrow contracts until it separates the membrane.
How do animal cells do cytokinesis.
Vesicles full of cell wall fuse at the middle of the cell, creating a cell plate which separates the two cells. The cell walls then bind with the membrane.
End of 8.6 Question: Contrast cytokinesis in animals with cytokinesis in plants.
In animals, cytokinesis involves a cleavage furrow in which contracting microfilaments pinch the cell in two, In plants, it involves formation of a cell plate, a fusion of vesicles that form new plasma membranes and new cell walls between the cells.
Is the cell cycle controlled?
Yes, by the aptly named cell cycle control system.
Where are the “checkpoints” in the cell cycle control system? What does a “checkpoint” even mean? What is the most important “checkpoint”?
They are found at the beginning of the G1 phase, the end of the G2 phase (b4 mitosis) and between metaphase and anaphase. A checkpoint is where the cell’s “breaks” must be overridden in order to continue on with the division cycle. The most important checkpoint is the first, as cell division is rarely stopped later.
How does the cell determine if it will divide or not?
By responding to the needs of the external environment, and by the intercellular signals that tell the cell whether it is ready to divide or move onto the next phase.
What is a signal transduction pathway? How does in factor into the cell control cycle?
The plasma membrane has a divot to receive certain external molecules that then set in motion the signal transduction pathway, which is a series of proteins leading to the nucleus, where cell division is prompted by overriding the breaks that the cells have.
End of 8.8 Question: At which of the three checkpoints described in this module do the chromosomes exist as duplicated sister chromatids?
G2 and M checkpoints.
Define anchorage dependence.
Cells must be in contact with a solid surface in order to begin to divide.
Define density-dependent inhibition.
if cells are in contact with each other, and they are forming some sort of layer, they will stop dividing. When there is an open space, they will begin to divide again. Most researchers believe that cells division is inhibited in some way by the contact of the cells.
Why are cancer cells so dangerous?
They don’t need anchorage dependence, meaning they can divide anywhere, and they don’t have density dependent inhibition, meaning that they can pile on top of each other.
Define growth factor.
an essential protein for the division of cells. secreted by other cells. there are about 50 known factors.
Give an example of cell division by growth factors.
When you get cut, blood platelets release a combination of growth factors that causes the epidermis cells to divide.
Go back
to add cards of VEGF, section 8.7
End of 8.7 Question: Compared to the control culture, the cells in an experimental culture are fewer but much larger in size when they cover the dish surface and stop growing. What is a reasonable hypothesis for the difference?
The experimental culture is deficient in one or more growth factors.
