Chapter 14 Flashcards
Define cell division
A process where new cells arise from other living cells
What is the difference between mitosis and meiosis?
- Mitosis produces cells that are genetically identical to their parents (e.g. epithelial cells)
- Meiosis produces cells that contain half of the genetic material from the parent. (e.g. sperm and egg production)
True or false. Cell division does NOT occur in ALL organisms.
False. It occurs in ALL organisms, but very differently in prokaryotes and eukaryotes.
True or false. Cell division does NOT occur in ALL organisms.
False. It occurs in ALL organisms but is very different in prokaryotes and eukaryotes.
True or false. Cell division does NOT occur in ALL organisms.
False. It occurs in ALL organisms but is very different in prokaryotes and eukaryotes.
What are the two stages of the cell cycle?
- M phase
- Interphase
What two processes occur during the M phase?
- Mitosis
- Cytokinesis
How long does the process of mitosis last?
about an hour or so
What three processes occur during Interphase?
- G1
- S
- G2
Which cell cycle stage takes the longest time to complete?
Interphase
Recite the entire cell cycle overview (start with G1)
Who proposed dividing interphase into three separate phases?
Alma Howard and Stephen Pelc, 1953
-Based upon experiments on plant meristem cells
Cells contain _________ that stimulate entry into mitosis
factors
The cell cycle is focused on the initiation of _____________ and initiation of ___________.
DNA replication, mitosis
Which factor promotes the cell’s entry into M phase?
Activation of protein kinase maturation promoting factor (MPF)
MPF has what two subunits?
- Kinase
- Cyclin
How does cyclin control kinase?
An increased level of cyclin controls kinase
Cyclin is a _________ subunit
regulatory
Describe the fluctuations of cyclin during the cell cycle
See picture
Yeast cells contain what type of MPF-like protein?
Cyclin-dependent kinases (Cdks)
In fission and budding yeast, what are the cdc2 (cdk1) (fission) and CDC28 (budding) genes responsible for?
(CDC) = cell division control
Passage through both control points. Control points being the start and G2-M transition point.
What two points control the cell cycle?
Start and the G2-M transition
Passage through the START and the G2-M junctures requires the activation of the same cdc2 kinase via different classes of cyclins. Which cyclins?
G1/S cyclin or mitotic cyclins
Progression through the fission of yeast cells requires what?
Phosphorylation and dephosphorylation of critical cdc2 residues
A CDC-activating kinase (CAK) phosphorylates what? And Wee1 phosphorylates what?
- threonine-161
- tyrosine-15
Both on the Cdk subunit
When the Cdc-cyclin is double phosphorylated, the cyclin becomes active or inactive?
inactive
Since the double phosphorylated Cdc-cyclin is inactive, how does it become active? And what does being active entail?
Phosphatase (cdc25) removed one phosphate (Tyr 15), making Cdc-cyclin active, which drives the cell to start mitosis.
Memorize Cdk Phosphorylation/dephosphorylation
See picture
A mutation in the wee1 gene will cause what to occur to the cell?
Cdk cannot become active, and the cell will divide at an early stage in the cell cycle, causing the cell to be smaller when compared to the wild type
A mutation in the cdc25 gene will cause what to occur in the cell?
The mutant cdc25 gene cannot remove the inhibitory phosphate from the Cdk; therefore, the cell cannot enter mitosis and continues to grow
Which enzyme removes the inhibitory phosphate on the Try 15 residue?
Cdc25 phosphatase
Which kinase transfers Thr 161 to the residue?
CAK kinase
In yeast, what does the protein Sic1 do? And what happens when it is degraded?
- Acts as an inhibitor during G1
- When degraded, cyclin-Cdk, that is in the cell, initiates DNA replication
Proteolysis is controlled via which pathway?
Ubiquitin-proteasome pathway
What are the two classes of multisubunit complexes that function as ubiquitin ligases?
SCF and APC
Destruction of what allows a cell to exit mitosis and enter a new cell cycle?
mitotic cyclins
SCF ubiquitin ligases allows entry into what phase, and how does it allow the phase change?
- SCF ubiquitin ligase allows entry to the S phase
- It allows this by that degradation of the S-phase cyclin-dependent kinase inhibitor, Sic1
What is the name of the process of moving cell cycle regulators into different compartments at different stages?
Subcellular localization
Nuclear accumulation is facilitated by?
Phosphorylation of serines in its nuclear export signal, which blocks export back to the cytoplasm (the movement of B1 in the cytoplasm during G2 and how it moves into the cell nucleus during prophase of mitosis)
What are four distinct mechanisms by which a Cdk can be inactivated?
What are the two subunits of MPF (maturation-promoting factor)?
- A subunit with kinase activity
- A regulatory subunit called cyclin
What does the kinase subunit of MPF do?
Transfers phosphate from ATP to specific serine and threonine residues of specific protein substrates
Cyclin concentration controls what?
Activation or inactivation of kinase that leads to M phase
Define mitosis
A process of nuclear division in which two nuclei with identical genetic content are produced to maintain original chromosome number
What are the phases of mitosis?
Prophase, prometaphase, metaphase, anaphase, and telophase
What happens during prophase?
- Chromosomes are duplicated and prepared for segregation
- Mitotic machinery is assembled
- Chromosome compaction in early prophase (uses condensin protein for compaction)
What protein, during prophase in mitosis, is responsible for chromosome compaction?
Condensin
How many chromatids are present in a mitotic chromosome?
two
Which enzyme is responsible for chromosome compaction?
topoisomerase II
Before the replication of DNA, which protein forms a ring to encircle the two sister DNA molecules?
Cohesin
Cohesin and condensin both contain which proteins?
SMC proteins (structural maintenance of chromosomes)
SMC proteins fold back on themselves to form a highly__________, anti-parallel, coiled-coil with a globular domain at both the ____________.
elongated, N- and C-terminal
Where do centromeres occur, and how do they serve?
- They occur at primary construction
- The serve as the binding site for proteins
Where are kinetochores located?
the outer surface of the centromeres
How do kinetochores serve?
They serve as sites where chromosomes attach to the microtubules of the mitotic spindle
What is the function of the fibrous corona?
Bind motor proteins involved in chromosome movement
Motor protein cytoplasmic dynein moves toward the ______ end, and CENP-E moves toward the ________ end.
minus, plus
Which two proteins play a key role in tethering the microtubule to the kinetochore?
- cytoplasmic dynein
- CENP-E
Which protein complex is attached to the kinetochore and mediates attachment to the microtubule and kinetochore?
Ndc80
Entering mitosis. Microtubules disassemble and reassemble into what?
mitotic spindle
How many pairs of centrioles are present in the centrosome during G1?
one pair situated at right angles to one another
The _______________________ progresses in concert with the cell cycle.
centrosome cycle
Which enzymes becomes active during late mitosis and cleaves a protein link that holds the centrioles together?
Separase
During S phase, what is next to each preexisting centriole to initiate its replication?
A procentriole, which is then converted into a full-blown centriole
What do the centrosomes do during prophase?
Move apart and organize bundles of microtubules that form the mitotic spindle.
What happens during prometaphase?
A definitive mitotic spindle forms, and the chromosomes are moved by microtubules into the center of the cell
How are spindle poles formed?
A single kinetochore is attached to the microtubules (tubulin) from both spindle poles
What are the four steps in chromosome-microtubule interaction during prometaphase?
- A kinetochore has made contact with the sidewall of a microtubule and can use the kinetochore-bound motors to slide in either direction along the microtubule
- a chromosome has become attached to the plus end of a microtubule from one spindle pole (mono-oriented)
- The chromosome has become attached in an end-on orientation to microtubules from both poles (bi-orientated)
- the bi chromosome has been moved to the center and will become part of the metaphase plate (and are under tension)
What does the lack of kinesin-like protein (Kid) cause during prometaphase?
results in an alignment failure at the center of the spindle (Kid normally provides force)
What does the lack of kinesin-like protein (Kid) cause during prometaphase?
Results in an alignment failure at the center of the spindle (Kid normally provides force)
Define microtubule flux
See picture
What is the movement of chromosomes called that is toward the center of the mitotic spindle, the midway between the poles?
congression
Shortening and elongation occur primarily by_______ or ________ of subunits at the _______ end of the microtubule.
loss, gain, plus
What happens during metaphase?
chromosomes are aligned at the spindle equator on the metaphase plate
What are the three types of spindle microtubules?
- Astral
- Chromosomal
- Polar spindle
Astral microtubule function:
Radiate from the centrosome to the region outside the body of the spindle
Function of chromosomal microtubules:
Move chromosomes to the poles
Function of polar microtubules:
To maintain the integrity of the spindle
Each spindle pole contains a pair of centrioles surrounded by _______________________ at which the microtubules are nucleated
amorphous pericentriolar material
All spindle microtubules have their ____________ pointed toward the centrosome.
minus ends
How many centrioles does a cell have at metaphase of mitosis?
4
SCF acts during __________. APC (anaphase-promoting complex) acts during ____________.
- Interphase
- Mitosis and G1
APC^Cdc20 is activated prior to when and then ubiquitinates what?
- Activated prior to metaphase
- ubiquitinates the anaphase inhibitor securin, which secures the attachment between sister chromatids
What are the two different versions of APC?
- APC Cdc20
- APC Cdh1
What is the difference between Cdc20 and Cdh1 APC?
APC^Cdc20 is active early in mitosis, at a time when Cdh1 is inhibited by Cdk1-mediated phosphorylation. As Cdk1 activity drops sharply in late mitosis, Cdh1 is activated, leading to the activation of APCCdh1
What prevents APC Cdh1 from triggering anaphase until all the chromosomes are aligned at the metaphase plate?
Spindle assembly checkpoint (SAP)
How does APC^Cdc20 state anaphase?
Destroys securin protein, a protein that inhibits anaphase
What does APC^Cdh1 do?
Responsible for ubiquitinating proteins that inhibit exit from mitosis (Mitosis –> G1 entry) and helps maintain low cyclin-Cdk activity
If cyclin B isn’t broken down by proteasome, what happens?
The cell remains in an frozen late state of mitosis
What is flavopiridol?
Cdk1 inhibitor
The movement of chromosomes toward the poles is called?
anaphase A
When two spindle poles move in opposite directions due to elongation of microtubules, this is called?
Anaphase B
What do the plus and minus ends of chromosomal fibers have?
depolymerizing kinesins
What does the protein complex Ncd80 do?
forms weak linkages with an attached microtubule just behind its plus end
What provides the force required for chromosome movement?
It is provided by the release of strain energy as the microtubule depolymerizes
What force moves the chromosome toward the poles?
Poleward flux
On the microtubules, which protein is responsible for the depolymerization of the plus and minus ends?
Depolymerizing kinesins of the kinesin-13 family
What is telophase?
the final stage of mitosis
What happens during telophase?
- Daughter cell returns to interphase
- mitotic spindle disassembles
- the nuclear envelopes of the two nuclei are reformed
- Chromosomes become dispersed
- Cytoplasm is prepared for cytokinesis
How does cytokinesis start?
with the indentation of the cell surface
Explain the contractile ring theory
suggests a thin band of actin and myosin filaments generates the force to cleave the cell
How is the site of filament assembly determined?
by a signal coming from the spindle poles
Bipolar myosin filaments, composed of ___________, are essential for the ring contraction
myosin II
How is the cleavage furrow position determined?
by the anaphase mitotic spindle, which leads to the activation of RhoA in a narrow ring in the cortex
The signal for plane determination travels from the spindle poles to the cell cortex via?
astral microtubules
What is the chromosomal difference between mitosis and meiosis?
Mitosis forms the same number of chromosomes and puts them in the nuclei of two daughter cells, and meiosis produces half the number of chromosomes and puts them in four haploid cells
How many divisions are in meiosis, and how many are in mitosis?
- two
- one
What are the two divisions of meiosis?
- homologous chromosomes pair and then segregate
- two chromatids are separated
Diploid (meiosis I) –> Haploid (meiosis II)
Division of homologous chromosomes –> division of sister chromatids
In gametes, when is DNA replicated?
prior to meiosis
What are the five stages of Prophase I?
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
At which stage of prophase I do the homologous chromosomes pair?
During zygotene
Called synapsis
What is the protein complex called of the zygotene stage?
synaptonemal complex
What does the synaptonemal complex allow?
crossing over during pachytene
What is bivalent
A pair of chromosomes
What is a tetrad?
Four chromatids
What stage of prophase I is where the synaptonemal complex disappears?
diplotene
What is the point of attachment called for two separate chromosome pairs? And where does it occur?
chiasmata, and occurs at site of crossing over
What happens during diakinesis?
chromosomes are prepped for attachment to the spindle fibers
What happens at the end of diakinesis?
the nucleolus and the nuclear envelope disappears
What triggers diakinesis?
increase of MPF activity
Behavior of chromosomes during anaphase I follow what law?
Mendel’s law of independent assortment
If you were to add [3H]thymidine to a cell as it underwent replication (S phase) prior to beginning meiosis, what percentage of the chromosomes of the gametes produced would be labeled? If one of these gametes (a sperm) were to fertilize an unlabeled egg, what percentage of the chromosomes of the two-cell stage would be labeled?
- 50%
- 12.5%
What is the stage between the two divisions called?
interkinesis
In telophase I, cells during this stage have a _________ number of chromosomes and __________ amount of DNA.
haploid, diploid
Meiosis II produces cells ________ in both amounts of DNA and chromosome number.
haploid
When do sister chromatids separate?
During anaphase II
What are the differences between Metaphase and anaphase I and II?
See picture
