Chapter 9 Flashcards
What is the cell cycle?
A set of stages taht take plce between teh time a eukaryotic cell divides and the time that the resulting daughter cells are going to divide
What are some steps a cell has to take if it plans to divide?
It has to grow larger, double the number and organelles, double DNA (DNA replication occurs)
What are the phases in the cell cycle?
Interphase, G1, S, G2, M Stage
What happens in Interphase?
Cell performs it’s usual functions (depending on where it is, in the body)
For adult mammalian cells, how long could interphase last?
20 hours
What three stages are part of interphase?
G1, S, G2
What happens during the G1 stage?
During this stage, the cell recovers from the previous division. The cell increases in size, doubles its organelles,and accumulates materials that are used for DNA synthesis.
Other than preparing for DNA replication, what do cells do during the G1 cycles?
They carry out their normal duties (such as communicating with other cells, secreting substances,and respiration)
What phase are nerve and muscle cells ALWAYS in? (Hint: They don’t replicate)
G0
After the G1 stage, what stage do cells enter?
They enter the S stage
What occurs during the S Stage?
DNA syntehsis & replication occurs
What happens during DNA Replication ( during the S stage)
At the beginning, each chromosome is composed of ONE DNA double helix. After DNA replication, each chromosome is composed of two identical DNA double helix molecules
What is each double helix called?
A chromatid
Will the two chromatids be attached after S phase?
They will remain attached until mitosis
After the S stage, what is the next stage?
G2 stage
What occurs during the G2 stage?
The cell syntehsizes proteins that will assist cell division
Some of the proteins that are made during the G2 stage, assist during the formation of ______.
microtubulues
After interphase, what does the cell enter?
Mitosis and cytokinesis
What does mitosis mean?
nuclear division
What does cytokinesis mean?
It means division of cytoplasm
During mitosis, what happens?
Daughter chromosomes are distributed by the mitotic spindle to two daughter nuclei
Does the cell cycle have to be controlled?
Yes
What is a signal?
It is an agent that influences the activities of a cell
What are growth signals?
They are signaling proteins recieved at the plasma membrane
Will the cells that stay in G0 stage finish the cell cycles, if stimulated by the growth factors?
Yes
How does the cell make sure that the process of mitosis doesn’t get out of control?
There are three checkpoints. At these checkpoints, the cell cycle either stops or continues on, depending on the internal signal it recieves
What are the family of the internal signal proteins called?
Cyclins
Does the amount of cyclins stay the same throughout the cell cycle?
No, they increase/decreases as the cell cycle continues. Specific cyclins must be present for the cell to proceed from G1 to S, and G2 to M.
What is the primary checkpoint of the cell cycle?
The G1 checkpoint
What protien stops the cycle at the G1 checkpoint when DNA damange has occured?
p53
What does p53 do when the DNA is damaged?
It attempts to fix it
If there are elevated levels of p53 in the cell, what is about to occur
apoptosis
What is the protein RB do?
It is responsible for interpreting growth signals and nutrient availability signals
When the RB gene undergoes mutation, what hapens?
Retinoblastoma occurs. It is a cancer that occurs in the retina
If the DNA has not finished replicating, then where will the cell cycle stop, and why?
At G2 checkpoint. This prevents the entry into the mitosis part. If the DNA is damaged
Finally, where does the last cell cycle check point occr?
It occurs during the mitotic stage, The cycle stops if the chromosomes are not properly attached to the mitotic spindle
What does the mitotic spindle do?
It ensures that the chromosomes are distributed accurately to the daughter cells
What is apoptosis?
It is programmed cell death
How does apoptosis occur?
It occurs when the cell rounds up, causing it to lose contant with its neighbors. The nucleus fragments and the plasma membrane develops blisters. The cell fragments are engulfed by white blood cells
What are the enzymes that bring about apoptosis?
Caspases
What protein is usually associated with DNA?
histones
When a eukaryotic cell is not undergoing division where is the DNA (and associated proteins) located?
Within chromatin
What does chromatin usually look like?
It has the appearance of a tangled mass of thin threads
Where is the DIPLOID number of chromosomes found?
It is found in all cells of the individual
What does the diploid number represent?
It represents two chromosomes of each kind
What is half of the diploid number called?
Haploid
Where are haploid chromosomes found?
In sex cells (egg/sperm)
During interphase, what does the cell do to prepare for mitosis?
Replicating the chromosomes, duplicating most celllar organelles
What is the function of the centrosome?
Organizes spindle apparatus, which is necessary for the movement of chromosomes
During mitosis, what divides, and what is produced?
a 2n (diploid) cell divides, and a 2n (diploid) cell is produced
What is the dividing cell called, and what is the resulting cell called?
The dividing cell is called the parent cell, and the resulting cell is called the daughter cell(s)
What is each double helix called? The identical double helixes?
A chromatid, Sister chromatid
The region where sister chromatids are attached is called?
Centromere
What protein complex develops on either side of the centromere during cell division?
Kinetechores
What is the centrosome?
It is the main microtubule organizing center of the cell
In an animal cell, what does each centrosome contain?
It contains a pair of barrel shaped organelles called centrioles an asters
The centrosomes organize the mitotic spindle, which contains many fibers, each composd of:
Microtubules
What are microtubules
They are hollow cylinders made up of the protein tubulin
When do the microtubules assemble?
When tubulin subunits join (when they disassemble, the tubulin subunits are free)
When do microtubules begin to disassemble?
When spindle fibers begin forming
What happens during prophase?
Chromatin condensed and chromasomes are visible. The nucleolus disappears and the nuclear envelope fragments. The spindle begins to assemble as the two centrosomes migrate away from one another.
During prophase, has DNA replicated? Elaborate>
The parental chromosomes are already duplicated and composed of two sister chromaids held together at a centromere
What are asters? Are they found in plants or animals?
An array of microtubules that radiate toward the plasma membrane from the centrosome, found in plant cells
What happens in prometaphase?
Preparations for sister chromatid separation are evident, kinetochores appear on each side of the centromere, these attach sister chromatids to the kinetochore spindle fiber
Where do the kinetochore spindle fibers extend from? Where will they soon be located?
They extend from the poles to the chromosomes. They will soon be located at the center of the spindle
Where do the kinetochore fibers attach the sister chromatids? How are they pulled?
To opposite poles of the spindle, and the chromosomes are pulled back and forth until they are aligned (which happens in metaphse)
During metaphase, what happens?
The centromeres of chromosomes are aligned on a single plane at the center of the cell
What does the metaphase plate indicate?
It indicates the axis of cell division
What are polar spindle fibers, and waht do they do?
They are non attached spindle fibers, that reach beyond the metaphase plate and overlap
There’s a cell cycle checkpoint after Metaphase..what does it do?
Delays the start of anaphase until the kinetochores of each chromosome are properly attached to the spindle fibers and chromosomes are properly aligned along the metaphase plate
What happens during anaphase?
The two sister chromatids seperate at the centromere, leading to two daughter chromosomes, daughter chromosomes move toward opposite poles
In anaphase, what are the daughter chromosomes beign pulled apart by?
They are being pulled apart to the opposite poles as kinetochore spindle fibers disasemble at the regions of the kinetochores
During anaphase, as the daughter chromosomes are moving toward the spindle poles,w hat is happenign to the poles?
They are moving arther apart because the polar spindle fibers are sliding past one another
What proteins are involved during anaphase?
Kinesin and Dynein
What happens during telophase?
the spindle disppears and a new nuclear envelop forms around the daughter chromosomes.
When mitosis occurs, but cytokineses doesn’t, what is the result? Give an example.
Nultinucleated cell, such as the embryo sac in a flowering plant
When does division of the cytoplasm begin?
In anaphase, continues in telophase, but doesn’t reach completionunitl cytokinesis
What is cancer?
It is is a condition that results from uncontrolled cell growth
What two types of tumors are there?
Benign/Malignant
What are five characterisitcs of cancer?
- Cancer cells lack differentiation
- Cancer cells have abnormal nuclei
- Cancer cells do not undergo apoptosis
- Cancer cells form tumors
- Cancer cells undergo metastisis and angiogenesis
Describe this characterisitc: Lack of differentiation
They are not specialized and do not contribute to the functioning of the tissue. They are distinctingly abnormal. Cancer cells repeatedly enter the cell cycle
Describe this characteristic: Cancer cells have abnormal nuclei
The nuclei of cancer cells are enlarged and may contain an abnormal number of chromosomes.
Describe this characteristic: Cancer cells do not undergo apoptosis
These cells don’t undergo apoptosis even though the DNA is damaged.
Describe this characteristic: Cancer cells form tumors
Normal cells anchor themselves to a substratum/exhibit contact inhibition. They stop dividing when they come in contact with a neighbor. Cancer cells DO NOT exhibit contact inhibition, so the abnormal cancer cells pile on top of eachother (to form a tumor)
Describe this symptom: Cancer cells undergo metastasis and angiogenesis
Start tumors elsewhere in the body-metastisis
Angeiogenesis: Additional mutations that occur in the cell allow them to direct the growth of new blood vessels into the tumor
Mutations in what two genes could lead to cancer?
- Proto-oncogenes
- Tumor Suppressor genes
What are proto-oncogenes?
They code for proteins that promote the cell cycle and prevent apoptosis. They cause the cell cycle to speed up or go!
What are tumor suppressor genes?
They code for proteins that inhibit the cell cycle and promote apoptosis. They can cause the cell cycle to go more slowly or stop
Where are proto-oncogenes normally found?
At the end of a stimulatory pathway, extending from the plasma membrane to the nucleus
When mutations occur in proto-oncogenes, what are they called?
Oncogenes
What do oncognees do, with the cell cycle?
They keep rpomoting it
What are two good examples of tumor suppressor genes?
RB and p53
What is one other thing that can cause cancer?
Mutation of the enzyme that regulates the length of the telomeres (ends of chromosomes). Because shorter telomeres automatically stop dividing and these stay at the same length, it keeps dividign
What is cell divison in prokaryotes like?
It is asexual reprouction
What is asexual reproductions?
It is the reproduction in which the offspring are genetically identical to the parent
What is the bacterial chromosome liek?
It is an electron dense, irregularly shaped region called the nucleoid, which is not enclosed by the membrane. When streched, it appears as a circular chromosome lop
How do prokaryotes reproduce?
They reproduce via a process called binary fission
What does binary fission produce?
Two cells that are identical
Before replication occurs, what happens in prokaryotes?
The cell enlarges, DNA replication occurs, two chromosomes
