Module 2 Control of the Cell Cycle Flashcards
Typical cell cycle in Human cell (time)
G1 - 5 hrs (5-9)
G0 - varied
S - 7 hrs (7-10)
G2 - 3 hrs (3-4 1/2)
M - 1 hr (1/2 - 1)
In humans, the frequency of cell turnover ranges from ________ in early embryonic development, to an average of __________ for epithelial cells, and to an entire human lifetime spent in G0 by specialized cells, such as cortical neurons or cardiac muscle cells.
a few hours,
two to five days
When fast‐dividing mammalian cells are grown in culture (outside the body under optimal growing conditions), the length of the cycle is about
24 hours
In early embryos of fruit flies, the cell cycle is completed in about _____.
eight minutes
The timing of events in the cell cycle is controlled by mechanisms that are both ______ and ______ to the cell.
internal and external
Both the ______ and _____of cell division are triggered by _______ external to the cell when it is about to begin the replication process.
initiation and inhibition
events
An event may be as simple as (4)
- death of a nearby cell
- release of growth-promoting hormones
- crowding of cells (inhibit)
- size of cell
example of growth-promoting hormones
human growth hormone (HGH)
A lack of HGH can inhibit cell division, resulting in ______, whereas too much HGH can result in _______.
dwarfism
gigantism
as a cell grows, it becomes inefficient due to its ______________. The solution to this problem is to divide.
decreasing surface‐to‐volume ratio
three main cell cycle checkpoints and their location
- G1 checkpoint - End of G1
- G2 checkpoint - G2/M transition
- M checkpoint - Mitotic phase (end of metaphase)
The integrity of the DNA is assessed at the _________. Proper chromosome duplication is assessed at the __________. Attachment of each kinetochore to a spindle fiber is assessed at the ___________.
G1 checkpoint
G2 checkpoint
M checkpoint
_________ also called _______(in yeast) determines whether all conditions are favorable for cell division to proceed
G1 checkpoint or restriction point (in yeast)
point at which the cell irreversibly commits to the cell division process
G1 checkpoint
External influences, such as _________, play a large role in carrying the cell past the G1 checkpoint
growth factors
In addition to _______ and ______, there is a check for ___________ at the G1 checkpoint
adequate reserves
cell size
genomic DNA damage
If the G1/S checkpoint detects damage, the _______ targets the cell for regulated death (________)
p53 protein
apoptosis
In G1 checkpoint, a cell that does not meet all the requirements will not be allowed to progress into the ______. The cell can halt the cycle and attempt to remedy the problematic condition, or the cell can advance into ______ and await further signals when conditions improve
S phase
G0
Cells in _________ are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the cell cycle.
G0 phase
bars entry into the mitotic phase if certain conditions are not met.
G2 checkpoint
ensures that that all of the chromosomes have been replicated and that the replicated DNA is not damaged. If the checkpoint mechanisms detect problems with the DNA, the cell cycle is _______, and the cell attempts to either complete DNA replication or repair the damaged DNA
G2 checkpoint
halted
- occurs near the end of the metaphase stage of karyokinesis
- it determines whether all the sister chromatids are correctly attached to the spindle microtubules
M checkpoint
The M checkpoint is also known as the
spindle attachment checkpoint
During M checkpoint, the separation of the sister chromatids during anaphase is an __________, the cycle will not proceed until the kinetochores of each pair of sister chromatids are firmly anchored to at least two spindle fibers arising from opposite poles of the cell.
irreversible step
Regulator Molecules of the Cell Cycle
are direct regulators of cell cycle transitions
- Cdks, cyclins, and the APC/C (positive regulators)
- Rb, p53, and p21 (negative regulators)
- either promote progress of the cell to the next phase (positive regulation) or halt the cycle (negative regulation).
- may act individually, or they can influence the activity or production of other regulatory proteins
regulatory molecules
true or false
failure of a single regulator may have almost no effect on the cell cycle, especially if more than one mechanism controls the same event
true
True or False
the effect of a deficient or non‐functioning regulator can be wide‐ranging and possibly fatal to the cell if multiple processes are affected
true
Two groups of proteins, called ________and _______, are responsible for the progress of the cell through the various checkpoints. Cyclins regulate the cell cycle only when they are tightly bound to Cdks.
cyclins
cyclin‐dependent kinases (Cdks)
protein complex which initiates the mitotic phase of the cell cycle
Mitosis‐promoting factor
Mitosis‐promoting factor is made of two proteins:
Cyclin B and CDC2
one that oscillates in quantity during the cell cycle
Cyclin B
- constant quantity
- a kinase
- encoded by the _____ gene
CDC2 by cdc2 gene
True or False
CDC2 kinase is still functional when it is not combined with cyclin which is referred as cyclin‐dependent kinase (CDK)
False
CDC2 kinase is only functional when it is combined with cyclin which is referred as cyclin‐dependent kinase (CDK)
permits the separation of the sister chromatids at the start of anaphase
anaphase‐promoting complex (APC) or cyclosome
degrades the Cyclin B protein of MPF
anaphase‐promoting complex (APC) or cyclosome
what phase does MPF activity starts
G2
what phase does MPF activity starts and ends
G2 - M phase
check graph!
Remember that in positive regulation, __________ cause the cycle to progress
active molecules
halt the cell cycle
Negative regulators
best understood negative regulatory molecules
Rb (Retinoblastoma proteins)
p53
p21
a group of tumor-suppressor proteins common in many cells
retinoblastoma protein
The 53 and 21 designations refer to the ___________ of the proteins (p) in ________
functional molecular masses
kilodaltons
All three of these regulatory proteins were discovered to be ______ or ___________ in cells that had begun to replicate uncontrollably (became ___________). In each case, the main cause of the unchecked progress
through the cell cycle was a faulty copy of the regulatory protein.
damaged or non‐functional
cancerous
Cancer cells can become tumors
___ remain clustered and can be removed
____ are able to ___ or break away and form new tumors
____ are substances that promote cancer
Benign tumors
Malignant tumors
Metastasize
Carcinogens
Rb, p53, and p21 act primarily at the _____ checkpoint
G1 checkpoint
is a multi‐functional protein that has a major impact on the commitment of a cell to division because it acts when there is damaged DNA in cells that are undergoing the preparatory processes during G1.
If damaged DNA is detected, it halts the cell cycle and recruits enzymes to repair the DNA
p53
If the DNA cannot be repaired, ______ can trigger ______, or cell suicide, to prevent the duplication of damaged chromosomes
p53
apoptosis
As p53 levels rise, the production of ____ is triggered
p21
enforces the halt in the cycle dictated by p53 by binding to and inhibiting the activity of the Cdk/cyclin complexes
p21
As a cell is exposed to more stress, higher levels of p53 and p21 accumulate, making it less likely that the cell will move into the
S phase
- exerts its regulatory influence on other positive regulator proteins.
- monitors cell size
Rb
In the active, dephosphorylated state, Rb binds to proteins called _____________, most commonly, _____.
transcriptions factors,
E2F
“turn on” specific genes to produce certain proteins
transcriptions factors
When Rb is bound to ______, production of proteins necessary for the G1/S transition is blocked. As the cell increases in size, Rb is slowly ________until it becomes inactivated.
E2F
phosphorylated
As Rb releases E2F, it _____ the gene that produces the transition protein, and this particular block is removed.
“turned on”
For the cell to move, past each of the checkpoints, all positive regulators must be ______ and all negative regulators must be ______
turned on
turned off
Rb and other proteins that negative regulate the cell cycle are sometimes called ______
tumor suppressors
Apoptosis is also known as ____
It occurs in normal development when cells are temporarily required for a maturation process. It also occurs in genetically damaged cells and older cells that rare no longer necessary.
An example being (2)
Programmed Cell Death
Embryonic Development
Metamorphosis
A well-known example of apoptosis is in the animal ____
It is signaled by the ____ which causes the animal to digest their tail cells, reabsorbing and recycling the digestion products into new structures
Frog (frog metamorphosis)
Thyroid hormone
Cells that die from an unexpected injury undergo ____ which is an accidental death.
Necrosis
In nectrotic cells,
- the ____ does not shrink or fragment
- nuclear morphology changes
- ____ form but fuse (enlarge)
- no _______ in blebs
- the ____ bursts to release the cell contents into the extracellular environment
- organelles are ______
nucleus
Blebs
organelles
cell membrane
non-functional
In apoptosis,
- Nucleus ____
- the blebs turn into ____
- ______ spread to blebs
- _______ are not released into the extracellular environment
- organelles still _____
fragment
apoptotic bodies
organelles
cell contents
functional
Cell Division Rate
- skin cell
- RBC
- liver cell
- intestine (internal lining)
- intestine (muscle and other tissues)
- skin cell - 2 weeks
- RBC - 4 months
- liver cell - 300-500 days
- intestine (internal lining) - 4-5 days
- intestine (muscle and other tissues) - 16 years
P21 inhibits CDK __, ___, ___, & ___
CDK 2, 3 ,4, & 6
Environment determines what form of reproduction is most advantageous.
* _______ is an advantage in consistently favorable conditions.
* _______ is an advantage in changing conditions.
Asexual reproduction
Sexual reproduction
Asexual reproduction (3)
- Budding
- Fragmentation
- Vegetative reproduction
forms a new organism from a small projection growing on the surface of the parent.
budding
is the splitting of the parent into pieces that each grow into a new organism.
fragmentation
forms a new plant from the modification of a stem or underground structure on the parent plant
Vegetative reproduction
________ cells perform specific functions. Cells develop into their mature forms through the process of ____________. Cells differ because different combinations of _______ are expressed. A cell’s _____ in an embryo helps determine how it will differentiate
Specialized cells
cell differentiation
genes
location
- are unique body cells
- have the ability to:
- divide and renew themselves
- remain undifferentiated in form
- develop into a variety of specialized cell types
stem cells
Stem cells are classified into three types
totipotent
pluripotent
multipotent
growing into any other cell type
totipotent
growing into any cell type but a totipotent cell (almost any cell)
pluripotent
growing into cells of a closely related cell family
multipotent
Stem cells come from _____ and ________
adults and embryos
- can be hard to isolate and grow
- use of these may prevent transplant rejection.
Adult stem cells
- are pluripotent and can be grown indefinitely in culture
- use of this raises ethical issues
embryonic stem cells
The use of ______ offers many currently realized and potential benefits.
- are used to treat leukemia and lymphoma.
- may cure disease or replace damaged
organs. - may revolutionize the drug development
process.
stem cells
