Chapter 18 Smartwork (Exam 4) Part 1

p27 is a

Cdk/cyclin inhibitor that blocks activity of M-Cdk

What purified protein complexes would successfully drive the oocyte into M phase?

purified M-Cdk/cyclin incubated with Wee1 and Cdc25

M-cdk alone is

NOT active

• M-cyclin must also be bound

Wee1 adds inhibitoryy phosphattes to

M-Cdk, blocking kinase activity

M-Cdk/cyclin treated with Wee1 and Cdc25 is

active and able to trigger the events of M phase

The Rb protein regulates

the cell cycle near the end of G1

The Rb protein regulates the cell cycle near the end of G1. How would cell proliferation be altered by a mutation that switched all the phosphorylated serines and threonines in Rb to alanine?

• Rb would no longer be phosphorylated

• transcription of genes required for entry into S phase would decrease

When p53 is not phosphorylated,

it is rapidly degraded and unable to block cell growth

If p52 no longer triggers apoptosis,

cancer cells can continue to proliferate

Increasing DNA binding activity and increasing p21 gene expression would

both block tumor growth

Kinetochores facilitate the conncection between

the sister chromatids and the spindle microtubules during mitosis

Kinetochores signal to thte spindle assembly checkpoint. What would cause the spindle assembly checkpoint to stay active, inhibiting the initiation of anaphase?

• dynein fails to leave the kinetochore

• the kinetochore on one sister chromatid fails to capture any microtubules

Treatment with Wee1 RNAi would lead to

active M-Cdk/cyclin since the inhibitory phosphates are not added

Active M-Cdk would trigger

the premature oocyte maturation

During necrosis,

• cells usually swell and burst

• can result from acute injury

• triggers an inflammatory response

During apoptosis,

• process is regulated

• cells round up, bleb, and shrink

• cells are engulfed by phagocytic cells

What two processes constitute the M phase of the cell cycle?

mitosis and cytokinesis

In mitosis,

the nucleus divides

In cytokinesis,

the rest of the cell splits in two

What processes occur ONLY in S phase of the cell cycle?

DNA replication

The entire period between one M phase and the subsequent M phase is called what?

interphase

Interphase consists of

S phase plus the two gap phases, G1 and G2

The cell-cycle control system ensures

• that all chromosomees are attached to the mitotic spindle before the chromosomes are segregated to the 2 daughter cells

• that the environment is favorable for the cell to initiate DNA replication

• that all DNA is replicated before M phase begins

What is true of the basic organization and machinery of the cell cycle?

it’s essentially the same in all eukaryotes

All eukaryotes appear to use similarr machinery and control systems to

drive and regulate cell-cycle events

Cyclins have NO

enzymatic activity on their own

Cyclin-Cdk complexes are

regulated by the activity of other kinases and phosphatases

Cyclins are degraded at

specific times in the cell cycle

Cyclins vary in

concentration at diffeerent stages of the cell cycle

Different cyclin-dependent protein kinases (Cdks) trigger different stages of the cell cycle in part because

their activities increase at different stages of the cycle

What must happen for a Cdk to be active?

it must bind to its cyclin partner

A Cdk must bind its cyclin before

it can become enzymatically active. A Cdk unbound to a cyclin does not retain kinase activity

The loss of its cyclin causes a Cdk to do what?

become inactive

Dissociation from cyclins inactivates

Cdks, shutting off their kinase activity

Activated M-Cdk triggers entry into M phase, where

the replicated chromosomes will be distributed into two daughter cells

Activated G1-Cdks and G1/S-Cdks help drive cells through

G1 into S phase

Activated S-Cdk initiates

DNA replication

The inactivation of M-Cdk leads to

the exit from mitosis

The degradation of M cyclin and inactivation of M-Cdk leads to the molecular events that

takes the cell out of mitosis and into interphase

The cell-cycle control system uses Cdk inhibitory proteins to do what?

arrest the cell cycle at specific transition points

The cell-cycle control system initiates chromosome segregation only after what has occured?

the duplicated chromosomes are correctly aligned on the mitotic spindle

Chromosome segregation takes place after the duplicated chromosomes are

correctly attached to kinetochore proteins that interact with the microtubules of the mitotic spindle

The cell-cycle control system uses what methods to delay progress through the cyclee?

• uses Cdk inhibitors

• inhibits the activation of APC to prevent the degradation of cyclins

What is true of the inhibition of APC activation?

it blocks exit from mitosis

Without APC activation, the sister chromatids will

remain glued together and anaphase cannot begin

Inhibiting APC activation will block the destruction of

M cyclin, preventing the exit from mitosis

What do cells do during G1 phase?

• destroy cyclins

• repair DNA damage

Rb binds to transcription regulators which

prevents them from turning on the genes required for cell proliferation

In the presence of severe DNA damage,

the transcription regulator p53 can promote cell death

Cells in G0:

• retain the ability to reassemble the cell-cycle control system

• divide if the need arises but normally do so infrequently

• can be stimulated to proliferate if the surrounding tissue is damaged

The inactivation of M-Cdk prevents

the onset of M phase

The activation of S-Cdk does NOT

prevent the onset of M phase

DNA replication occurs only in

S phase

The activation of S-Cdk initiates

DNA replication

The activation of S-Cdk helps prevent

DNA replication occuring more than once each cycle

The signal to commence DNA replication comes from

S-Cdk

If DNA is damaged or incompletely replicated in S phase, the inhibition of what molecules prevents the cell from entering M phase?

Cdc25