Lecture 14- Cell Division and cell cycle Flashcards
(45 cards)
Regulation of the Cell Cycle
uncontrolled cell division is?and can lead to?
cells do not proceed to cell division until they are?
certain criteria must be met for example?
if the criteria is not met cell halts progression through?
what controls this?
Cell division cannot occur all the time
* uncontrolled division is dangerous and can lead to cancer.
* Cells do not proceed to cell division until they are ready
* Certain criteria must be met, for example:
* DNA accurately replicated in S phase
* Cell must be large enough to be able to divide into daughter cells
* If the many criteria are not met, cell halts progression through cell cycle
Regulatory mechanisms control this
What if division occurs when cell isn’t ready?
Abnormal daughter cells
* May not be viable
* May divide inappropriately
Regulation of the Cell Cycle
Progression through cell cycle is controlled by?
protein that appear and disappear cyclically are called?
the cyclins activate the ____ and cell division is promoted
Cyclical proteins (appear and
disappear)
* Several enzymes that become active
and inactive, also in cycles
* The proteins that appear and
disappear cyclically are called
cyclins
* The enzymes are called cyclindependent kinases (CDKs)
* The cyclins activate the cyclindependent kinases and cell division is promoted
Regulation of cell cycle cyclins bind to activate ______ to control progression through the cell cycle?
Cyclin-CDK complexes phophorylate?
1) cyclins bind to and activate cyclin-dependent kinases to control progression through the cell cycle
2)cyclin- CDK complexes phosphorylate target proteins that promote cell division
The cyclin activate what?
cyclindependent kinases and cell division
is promoted.
Cyclin-CDK Complexes
when are cyclin-dependent kinases present and active
and what types of cyclins and CDK’s exist at specific steps of the cycle? G1/S cyclin-CDK complex–>
S cyclin-CDK complex initiaties?and prevents DNA
M cyclin-CDK complex prepares the cell for?
- Cyclin-dependent kinases
(CDKs) are always present in
the cell but are active only
with the appropriate cyclin
bound - Several types of cyclins and
CDKs exist; act at specific
steps of cycle - G1/S cyclin-CDK complex-> prepare the cell for DNA synthesis
- S cyclin-CDK complex–> initiates DNA synthesis and prevents DNA from replicating more than once per cycle
- M cyclin-CDK complex->prepares the cell for mitosis
Checkpoints
To progress through cell cycle certain checkpoints must be passed first
DNA replication checkpoint?
DNA damage checkpoint?
Spindle assmebly checkpoint
DNA replication checkpoint (at the end of G2)
DNA damage checkpoint (before entering S phase)
Spindle assembly checkpoint (before anaphase)
Details of DNA Damage Checkpoint
When DNA is damaged by radiation, which specific protein is activated?
When DNA is damaged by radiation, a specific protein kinase is activated that phosphorylates a protein called p53
* Normally exported from nucleus therefore occurs at very low levels in
nucleus
*P53 is a protein found in the nucleus, DNA damages activates protein kinases that phosphorylates P53, phosphorylated p53 turns on genes that inhibit cell cycle, inhibiting the cell cycle gives the cell time to repair the damaged DNA
Genes Involved in Cancer
- When cell division is not properly regulated
cancer can result - Cancer is characterized by uncontrolled cell division
what is cancer characterized as?
uncontrolled cell division
How might uncontrolled cell division happen
Mechanisms that promote cell division are tunred on when they shoudnt be
Mechanisms that promote cell division are turned on
when they shouldn’t be
* Cells lose the normal checks that prevent cell division
* So, if cell cycle control fails, it can lead to cancer
oncogenes
are cancer causing genes
proto-oncogenes
are normal cellular genes
– Important in normal cell division
what do normal proto-oncogenes encode?
they encode a variety of proteins such as?
encode a variety of proteins (cell surface receptors (receptor kinase), G proteins, protein kinases) and growth
factors
Human proto-oncogenes can be mutated into cancer causing oncogenes because of?
Environmental, chemical pollutants; cigarette smoke
Mutated Proto-Oncogenes May Promote Cancer
Example:
PDGF promotes cell division by binding to receptor
kinase–>dimerization–> many signaling pathways–>cell division promoted
One type of leukemia involves what?
a mutation in the
gene that encodes the PDGF receptor
* Result: receptor missing extracellular portion to bind
PDGF
* Mutant receptor dimerizes without PDGF binding
therefore always turned on–> activates too many target
proteins over long time–>too many blood cells produced
what are Tumor Suppressors?
Tumour suppressors: encode proteins whose normal activities inhibit cell division
Tumour suppressors different roles:
participate in?
repress?
trigger?
act in?
Participate in cell cycle checkpoints
* Repress expression of genes that promote cell division
* Trigger cell death
* Act in opposition to proto-oncogenes
Whether cell division occurs or not depends on both?
For cell to divide:
* proto-oncogenes –> on
* Tumour suppressor genes–> off
* P53 is an example of a tumour suppressor
Multiple Mutation Model for Cancer Development
Most Cancers need a accumulation of multiple?
When several different cell cycle regulators fail it is likely that ____ will develop?
Most cancers need accumulation of multiple mutations
* When several different cell-cycle regulators fail, it is likely that cancer will develop
gradual accumulation of mutations in multiple genes over a period of
years correlated with progression of benign to malignant forms of cancer
Different types of cancers and their inactivation’s
(benign to metastatic cancer)
1.Inactivation of first tumor suppressor gene
2.Activation of oncogene -Benign cancer (slow growing and non invasive)
3.Inactivation of second tumor suppressor gene-malignant cancer (grows rapidly and invades surrounding tissue)
4.Inactivation of third tumor suppressor gene-Metastatic cancer
Meiotic Cell Division
what is produced by meiotic cell division?
how many rounds of nuclear division>
what does it result in?
Sex cells, or gametes, are produced by meiotic
cell division
Includes two rounds of nuclear division
– meiosis I and meiosis II
Results in four daughter cells.
* Each daughter cell contains half the number of
chromosomes as the parent.
* Each daughter cell is genetically unique.
Meiotic Cell Division
*DNA replication takes place
before Prophase I (same as
mitosis)
Prophase I (Meiosis I)
1. Chromosomes first become visible, Replicated chromosomes
condense
- Replicated chromosomes
undergo synapsis–>two
sister chromatids visible - each pair of homologous chromosomes forms a bivalent, each chromosome consists of two sister chromatids Synapsis: the homologous
chromosomes pair with each
other side by side, gene for
gene (unique to meiosis!)
* Result: a four-stranded structure called a bivalent
Prophase I (Meiosis I) -
continued
- The chromosomes continue to shorten and thicken and the chiasmata between nonsister chromatids become apparent: Chiasmata within
bivalents are visible
crossovers between nonsister chromatids - Nuclear envelope breakdown begins
