Introduction to Cell Cycle Flashcards
Why do cells divide?
Reproduction for single-celled organisms
Development for multicellular organisms
Healing of wounds
Replacement of cells lost to normal wear and tear
What is the lifespan of erthryocytes in the human body?
120 days
What are the four phases of the cell cycle?
G1, S, G2, M
How long does the mammalian cell cycle last?
Approximately 24 hours
In mammals, the G1 phase lasts from ___ hours to years, and the S phase lasts from ___ to ___ hours. Meanwhile, G2 phase lasts for ___ to __ hours, and M phase lasts only ___ hour(s).
8 hours
10 to 12 hours
1 to a few hours
1 hour
What phases make up interphase?
G1, S, G2
To what does G0 phase refer?
Cells that have terminally differentiated
At the end of the cell cycle, some cells begin the process of _____________ or _________ ________________, meaning they will become one type of cell and remain as such for the remainder of their lives and they are incapable of returning to the cell cycle.
Differentiation
Terminal differentiation
Lee Hartwell studied budding yeast or _______________ _______________, which are small, ovoid cells that can be easily observed in a microscope.
Saccharomyces cerevisiae
How do yeast divide?
Budding
In yeast, cell division occurs by budding. First, a _____ appears in late ____ and grows continuously through S and ____ phases until it is equal in size to the original cell. After _______, one set of chromosomes enters the bud, and the daughter cell then “pinches” or buds off.
Bud
G1
M
Mitosis
What are the advantages of a yeast model?
They are single-celled organisms, and yeast can grow and divise as either haploid or diploid, making identification of mutations and mutant genes much easier (i.e., only a single mutation is required for a mutation to occur in a haploid organism)
Hartwell gained experience as an undergraduate studying ____________ mutants in the replication cycle of ________, a bacteriophage. He created mutant strains of yeast that were defective in different aspects of the cell cycle by treating them with __________________, a DNA mutagen. He _____-____ and screened for mutants.
Hartwell found that at higher temperatures some colonies were not present that were at lower temperatures and determined that something was preventing the colonies’ growth. They were _____________ _______________.
Conditional
T4
Nitrosoguanidine
Replica-plated
Temperature sensitive
Hartwell’s experiments in yeast led him to identify 35 mutant cell lines that he called ___ mutants for _____ ______ _______.
cdc mutants
Cell division cycle mutants
Hartwell’s undergraduate student realized that in yeast ____ ______ correlates with the position in the _____ _______.
Bud size
Cell cycle
Ultimately, Hartwell mapped each mutant to specific cell cycle events by monitoring where each mutant stalled in the cycle and could not move further, using this information to determine which proteins were critical to each stage of the cell cycle
What cdc mutation did Hartwell find to be crucial for the initiation of cell division?
cdc 28
Hartwell identified the _____________ of the cell cycle.
Start
There are three major checkpoints within the cell cycle: ______________, _________________________, and __________________.
Start transition
G2/M transition
Metaphase-to-anaphase transition
At which transition of the cell cycle does the cell confirm whether the environment is favorable to division?
The start transition
At which transition of the cell cycle does the cell confirm all DNA is replicated and the environment is favorable for division?
G2/M transition
At which transition of the cell cycle does the cell check to see if the chromosomes are properly attached to their spindles?
Metaphase-to-anaphase
G0 phase leads to _____________ that may or may not be terminal.
Differentiation
Through what types of experiments did Hartwell begin to identify the individual genes responsible for mutations in yeast cell cycle division?
Complementation experiments
Explain the principle behind complementation experiements.
- Hartwell closed every yeast gene into its own plasmid
- He placed each plasmid into mutant yeast cells
- The appropriate wild-type gene would “rescue” the mutant
- This enabled Hartwell to locate exactly which gene was responsible for each mutation
What virus did Rao and Johnson use to induce mammalian cells to fuse at different stages of the cell cycle?
Sendai virus
What was the ultimate conclusion Rao and Johnson made in their studies of the Sendai virus?
Mitotic nuclei release mitosis-promoting factors that affect interphase nuclei
How did Rao and Johnson determine that the presence of mitosis-promoting factors were responsible for triggering cell division?
Rao and Johnson took nuclei from different stages of the cell cycle and merged them with nuclei from other stages. What they found was that something in the S phase nucleus and mitotic nuclei was released that drove the other nuclei into the S phase or mitosis, respectively
Yoshio Masui studied ________________ using North American leopard frog oocytes. Oocytes are arrested in the ____ phase until the hormone ________________________ stimulates their entry into meiosis, where they are again arrested in ________ _____ until fertilization occurs.
Oocytes
Arrested in G2 phase
Progesterone
Meiosis II
What does MPF stand for?
Maturation promoting factor
How did Masui discover maturation promoting factor (MPF)?
He isolated cytosolic factors from oocytes at different times following progesterone stimulation and then injected them into oocytes that had not been exposed to progesterone; these oocytes were triggered into meiosis, and Masui called these cytoplasmic factors maturation promoting factors (MPFs)
Wasserman and Smith discovered ______ activity in North American leopard frogs underwent rapid cycling following fertilization, and similar results were found in the African claw-toed frog. They determined that the more rapid fluctiations, the more rapid rates of _________.
MPF
Cleavage
Rao synchronized HeLa cells by serum-starvation, isolated cytoplasmic extracts at different time points, and found that cytoplasmic extracts from the late _____ phase cells of frog oocytes stimulated meiosis in a non-mammalian animal.
Late G2 phase
While Hartwell studied budding yeast, Paul Nurse studied _______ yeast.
Fission
Schizosaccharomyces pombe or fission yeast are ____-shaped yeast that grow until they are _____ times their original length and then enter ______ followed by cytokinesis.
Rod-shaped
Two times
Mitosis
Nurse, like Hartwell, did _________________ __________________ and determined that ______ is required for the ___________ transition.
Complementation experiments
cdc2
G2/M transition
Nurse found that cdc2 from S. pombe or fission yeast rescued cdc28 from S. cerevisiae or budding yeast, leading to the conclusion that there is some functional ____________ between cdc2 and cdc28.
Redundancy
Tim Hunt studied ______________________ and surf-clam eggs at Cambridge and found that _________________, an inhibitor of protein synthesis, prevented cell division following fertilization. He determined that protein synthesis is required for cell division following fertilization.
Sea urchins
Cycloheximide
In addition to determining the protein requirment for cell division, Hunt also discovered what?
He also discovered that proteins appear and disappear during the cell cycle, and he named them cyclins
How did Hunt identify cyclins?
He incubated cells with heavy methionine, isolated the newly made proteins, separated them on polyacrylamide gels, and exposed them to film
Why did Hunt use 35S-methionine as opposed to another radiolabel?
Because only proteins contain sulfur
Cyclin ____ levels drop raidly near the end of mitosis.
A
Cyclins are the ____________________________ factors identifed by Hartwell.
Maturation promoting factors
cdc genes are very highly ______________ from yeast to humans.
Conserved
In the 1980s, cdc mutations 28 and 2 were found to be _______________.
Kinases
In the late 1980s, multiple labs purified the maturation promoting factor (MPF) and determined that it was composed of two polypeptide units, one of which had kinase activity. cdcs are now known as ______ _______ _______.
Cyclin dependent kinases
Cyclin-dependent kinase 1 (CDK1) is composed of the previously identified cyclin ______________ and yeast mutants ________ and ________.
Cyclin B
- cdc*2
- cdc*28
There are four cyclin-dependent kinase complexes for each stage of the cell cycle: ____, _____, ______, and ______.
G1 Cdk
G1/S Cdk
S Cdk
M Cdk
The G1-Cdk complex in vertebrates is composed of cyclin ___ and cyclin-dependent kinases ____ and ____. In yeast, this same complex is composed of cyclin (Cln) _____ and cyclin-dependent kinase _____.
Cyclin D
Cdk4 &Cdk6
Cln3
Cdk1
The G1/S-Cdk complex in verebrates is composed of cyclin ____ and cyclin-dependent kinase _____ while in yeast it is composed of cylcin (Cln) _____ and cyclin-dependent kinase ____.
Cyclin E
Cdk2
Cln1, 2
Cdk1
The S-Cdk complex is composed of cyclin _____ and Cdk ____ and ____ in vertebrates and cyclin (Clb) ______ and Cdk1 in yeast.
Cyclin A
Cdk2 & Cdk1
Clb5, 6
In the M-Cdk complex, cyclin _____ and cdk _____ are present in vertebrates and cyclin ________ and cdk ____ in yeast.
Cyclin B
Cdk1
Clb 1, 2, 3, 4
Cdk1
