Introduction to Cell Cycle

Question 1

Why do cells divide?

Answer 1

Reproduction for single-celled organisms

Development for multicellular organisms

Healing of wounds

Replacement of cells lost to normal wear and tear

Question 2

What is the lifespan of erthryocytes in the human body?

Answer 2

120 days

Question 3

What are the four phases of the cell cycle?

Answer 3

G1, S, G2, M

Question 4

How long does the mammalian cell cycle last?

Answer 4

Approximately 24 hours

Question 5

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).

Answer 5

8 hours

10 to 12 hours

1 to a few hours

1 hour

Question 6

What phases make up interphase?

Answer 6

G1, S, G2

Question 7

To what does G0 phase refer?

Answer 7

Cells that have terminally differentiated

Question 8

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.

Answer 8

Differentiation

Terminal differentiation

Question 9

Lee Hartwell studied budding yeast or _______________ _______________, which are small, ovoid cells that can be easily observed in a microscope.

Answer 9

Saccharomyces cerevisiae

Question 10

How do yeast divide?

Answer 10

Budding

Question 11

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.

Answer 11

Bud

G1

M

Mitosis

Question 12

What are the advantages of a yeast model?

Answer 12

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)

Question 13

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 _____________ _______________.

Answer 13

Conditional

T4

Nitrosoguanidine

Replica-plated

Temperature sensitive

Question 14

Hartwell’s experiments in yeast led him to identify 35 mutant cell lines that he called ___ mutants for _____ ______ _______.

Answer 14

cdc mutants

Cell division cycle mutants

Question 15

Hartwell’s undergraduate student realized that in yeast ____ ______ correlates with the position in the _____ _______.

Answer 15

Bud size

Cell cycle

Question 16

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

Answer 16

Question 17

What cdc mutation did Hartwell find to be crucial for the initiation of cell division?

Answer 17

cdc 28

Question 18

Hartwell identified the _____________ of the cell cycle.

Answer 18

Start

Question 19

There are three major checkpoints within the cell cycle: ______________, _________________________, and __________________.

Answer 19

Start transition

G2/M transition

Metaphase-to-anaphase transition

Question 20

At which transition of the cell cycle does the cell confirm whether the environment is favorable to division?

Answer 20

The start transition

Question 21

At which transition of the cell cycle does the cell confirm all DNA is replicated and the environment is favorable for division?

Answer 21

G2/M transition

Question 22

At which transition of the cell cycle does the cell check to see if the chromosomes are properly attached to their spindles?

Answer 22

Metaphase-to-anaphase

Question 23

G0 phase leads to _____________ that may or may not be terminal.

Answer 23

Differentiation

Question 24

Through what types of experiments did Hartwell begin to identify the individual genes responsible for mutations in yeast cell cycle division?

Answer 24

Complementation experiments

Question 25

Explain the principle behind complementation experiements.

Answer 25

1. Hartwell closed every yeast gene into its own plasmid
2. He placed each plasmid into mutant yeast cells
   
   1. The appropriate wild-type gene would “rescue” the mutant
3. This enabled Hartwell to locate exactly which gene was responsible for each mutation

Question 26

What virus did Rao and Johnson use to induce mammalian cells to fuse at different stages of the cell cycle?

Answer 26

Sendai virus

Question 27

What was the ultimate conclusion Rao and Johnson made in their studies of the Sendai virus?

Answer 27

Mitotic nuclei release mitosis-promoting factors that affect interphase nuclei

Question 28

How did Rao and Johnson determine that the presence of mitosis-promoting factors were responsible for triggering cell division?

Answer 28

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

Question 29

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.

Answer 29

Oocytes

Arrested in G2 phase

Progesterone

Meiosis II

Question 30

What does MPF stand for?

Answer 30

Maturation promoting factor

Question 31

How did Masui discover maturation promoting factor (MPF)?

Answer 31

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)

Question 32

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 _________.

Answer 32

MPF

Cleavage

Question 33

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.

Answer 33

Late G2 phase

Question 34

While Hartwell studied budding yeast, Paul Nurse studied _______ yeast.

Answer 34

Fission

Question 35

Schizosaccharomyces pombe or fission yeast are ____-shaped yeast that grow until they are _____ times their original length and then enter ______ followed by cytokinesis.

Answer 35

Rod-shaped

Two times

Mitosis

Question 36

Nurse, like Hartwell, did _________________ __________________ and determined that ______ is required for the ___________ transition.

Answer 36

Complementation experiments

cdc2

G2/M transition

Question 37

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.

Answer 37

Redundancy

Question 38

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.

Answer 38

Sea urchins

Cycloheximide

Question 39

In addition to determining the protein requirment for cell division, Hunt also discovered what?

Answer 39

He also discovered that proteins appear and disappear during the cell cycle, and he named them cyclins

Question 40

How did Hunt identify cyclins?

Answer 40

He incubated cells with heavy methionine, isolated the newly made proteins, separated them on polyacrylamide gels, and exposed them to film

Question 41

Why did Hunt use ³⁵S-methionine as opposed to another radiolabel?

Answer 41

Because only proteins contain sulfur

Question 42

Cyclin ____ levels drop raidly near the end of mitosis.

Answer 42

A

Question 43

Cyclins are the ____________________________ factors identifed by Hartwell.

Answer 43

Maturation promoting factors

Question 44

cdc genes are very highly ______________ from yeast to humans.

Answer 44

Conserved

Question 45

In the 1980s, cdc mutations 28 and 2 were found to be _______________.

Answer 45

Kinases

Question 46

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 ______ _______ _______.

Answer 46

Cyclin dependent kinases

Question 47

Cyclin-dependent kinase 1 (CDK1) is composed of the previously identified cyclin ______________ and yeast mutants ________ and ________.

Answer 47

Cyclin B

• cdc*2
• cdc*28

Question 48

There are four cyclin-dependent kinase complexes for each stage of the cell cycle: ____, _____, ______, and ______.

Answer 48

G1 Cdk

G1/S Cdk

S Cdk

M Cdk

Question 49

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 _____.

Answer 49

Cyclin D

Cdk4 &Cdk6

Cln3

Cdk1

Question 50

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 ____.

Answer 50

Cyclin E

Cdk2

Cln1, 2

Cdk1

Question 51

The S-Cdk complex is composed of cyclin _____ and Cdk ____ and ____ in vertebrates and cyclin (Clb) ______ and Cdk1 in yeast.

Answer 51

Cyclin A

Cdk2 & Cdk1

Clb5, 6

Question 52

In the M-Cdk complex, cyclin _____ and cdk _____ are present in vertebrates and cyclin ________ and cdk ____ in yeast.

Answer 52

Cyclin B

Cdk1

Clb 1, 2, 3, 4

Cdk1