Cell division Flashcards
Sometimes called post mitotic cells, they are cells that no longer divide :
Static cells
E.g. central nervous system cells, cardiac muscle cells, skeletal muscle cells.
What are stable cell populations ?
Stable cell populations divide regularly and slowly to maintain organ structure and function.
E.g. Cells in bone & cartilage, smooth muscle cells, endothelial cells in blood vessels, fibroblasts in connective tissue.
Renewing cell populations may be slow or fast, may produce daughter cells, or cells that remain as stem cells. Give examples of rapidly renewing and slow renewing cells.
Rapidly renewing : blood cells or epithelial cells of the skin
Slow renewing : Epithelial cells in the lens of the eye, smooth muscle in the GIT
True or false. DNA replication occurs during interphase and cannot be seen under microscope.
True
Name the 3 phases of interphase and what occurs in them.
G1 (presynthesis)
S (DNA synthesis)
G2 (post DNA replication)
G0 is a holding point within G1 *
Cells not actively dividing are temporally or permanently suspended in _____. What king of cells hang’s out in this phase ?
G0
Stem cells
In the G1 phase, cell gather nutrients and synthesize RNA and proteins required for DNA synthesis and chromosome replication. The organelles & cytoplasm double. How many check points does that phase hold ? Briefly describe them.
- Restriction check point (aka ‘’the point of no return’’) : it is like a point of introspection of the cell where it asks itself if it is good enough to replicate.
- G1 DNA damage checkpoint (newly replicated DNA from mitosis is monitored)
During ________ the cell grows and makes a copy of its DNA. During the _______ the cell separates its DNA into two sets and divides its cytoplasm, forming two new cells.
Interphase
M phase
Cell progression is blocked by interactions of retinoblastoma susceptibility protein (pRb) and essential transcription factors (E2F) which will induce cell suicide. If this checkpoint malfunctions, cells lose contact inhibition and overgrow which can lead to mesothelomia, osteosarcoma, and ependymoma. This process refers to which checkpoint of G1 phase ?
Restriction checkpoint
Regarding Gi DNA damage checkpoint, if there is irrevocable DNA damage, high levels of __________ prevent progression.
p53 tumor suppressor protein
In the S phase of interphase, DNA synthesis occurs. New chromatids are formed in a process that lasts 7.5-10h. Chromosome replication is initiated at many sites called ______ along the chromosomal DNA. This is 1 checkpoint here : _________. It makes sure the replicated DNA is of good quality.
Replicons
S DNA damage checkpoint
The G2 phase is long or short ?
The G2 phase is very short.
In the G2 phase, cell examine the replicated DNA in preparation for cell division. Cell growth and cytoplasmic organelle reorganization can also occur. It is a very short phase in rapidly dividing cells, but other cells like primary oocytes can arrest in G2 phase for an extended amount of time. How many checkpoints are there and what is their roles ?
G2 phase has 2 checkpoints :
- Unreplicated DNA checkpoint (‘‘oops, stop here)
- DNA damage checkpoint (prevents cells from entering M phase when DNA is damaged in order to afford these cells an opportunity to repair the damaged DNA before propagating genetic defects to the daughter cells. If the damage is irreparable, checkpoint signaling might activate pathways that lead to apoptosis).
The genome is the entire set of DNA instructions found in a cell. In the ________, DNA replication involves doubling of the entire genome.
S phase
Mitosis takes about ___ hour. It concludes with separation of the 2 daughter cells. The first step is ________ (division of the nucleus) and the second step is ______, or division of the cell itself.
1
karyokinesis
cytokinesis
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What are the 2 checkpoints of M phase?
Spindle assembly checkpoint (prevents premature entry into anaphase)
Chromosome segregation checkpoint (prevents cytokinesis until all of the chromosomes have correctly separated).
What is the consequence of checkpoint malfunction in the M phase ?
Mitotic catastrophe
Malfunction in the DNA damage checkpoints or the spindle assembly checkpoint leads to failure to arrest the cell cycle.
Normally, this would lead to apoptosis (programmed cell death)
In regards to malfunction of the checkpoints in the M phase, if apoptosis does not occur, the cell are likely to divide asymmetrically and produce ______ cells which can lead to oncogenesis.
Aneuploid cells (cells that contain abnormal chromosome number)
In regards to regulation of the cell cycle
The ______ complex acts at different phases of the cell cycle and targets different proteins. The downstream targets of this complexes work to stop the progression of the cell cycle.
Cyclin-Cdk
They are actually protein that detect a problem and act as an alarm!
So basically, checkpoints interact with these complexes which targets proteins (p53 as pRb if interphase ; H1 and transcription factors if M phase) which in turn work to stop the progression of the cycle.
What are some events that occur in prophase ?
Coiling of chromatin (visible under microscope as chromatin in the nucleus)
Cellular microtubule system degrades
Centrosomes move to the cell poles
Nuclear membrane and nucleolus disappear
Chromatin condenses to form chromosomes of 2 chromatid bound at the centromere.
Mitotic spindle made of microtubules appears between 2 centrosomes.
Centrosomes are organelles containing 2 _______ and produce _______. Spindle fibers are made from a/b tubulin dimers.
centrioles
microtubules
What is the difference between centromere and kinetochore?
The centromere appears as a constricted region of a chromosome and plays a key role in helping the cell divide up its DNA during division (mitosis and meiosis). Specifically, it is the region where the cell’s spindle fibers attach.
A kinetochore is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division.
Duplication of centrosomes and centrioles occurs during interphase or M phase ?
Interphase
Sister chromatids separate and migrate to opposite poles, pulled by microtubules. This relates to what phase ?
Anaphase
Chromosomes migrate to equator of the cell where each divides longitudinally to form 2 chromosomes called sister chromatids. Chromatids are attached to the microtubules of the mitotic spindle at the kinetochore. This relates to what phase ?
Metaphase
Describe the event of telophase
Reappearance of nuclei in daughter cells
Chromosomes uncoil
Nuclear membrane and nucleolus reforms
Cleavage furrow develops between 2 daughter cells
In late prophase, kinase phosphorylate the nuclear lamins in the nuclear envelope. These proteins become soluble and the nuclear envelope disassembles. In late ______, the nuclear lamins repolymerize and the membrane is reformed.
Telophase
Be able to differentiate the stages of mitosis on microscope
Here are other examples of mitotic stages on the microscope.
Homologous means :
One member of a chromosome pair
Meiosis 1 separates _______ chromosomes and meiosis 2 separates _______.
Homologous
Sister chromatids.
The correct separation of homologous chromosomes in Anaphase 1 or sister chromatids of Anaphase 2 is called :
Disjunction
