Advanced Cell Chapter 17

Cell Cycle

sequence of events in which the cell duplicates its contents and then divides into two; it is the essential mechanism by which all living things reproduce

Chromosome Segregation

to produce two genetically identical daughter cells, the DNA is replicated to produce two complete copies; the replicated chromosomes are then distributed (segregated) to the two daughter cells so that each receives a copy of the entire genome

Cell-Cycle Control System

a complex network of regulatory proteins that triggers the different events of the cycle

Chromosome Condensation

large scale reorganization of the intertwined sister-chromatids into compact, rodlike structures

Checkpoints

mechanism that is activated by the drug treatment and blocks progression through the metaphase-to-anaphase transition; ensures that cells do not enter anaphase until all chromosomes are correctly bi-oriented on the mitotic spindle

G1

cell growth that occurs between M phase and S phase

S Phase

where chromosome duplication occurs; requires 10-12 hours and occupies about half of the cell-cycle time in a typical mammalian cell

G2

cell growth that occurs between S phase and mitosis

Prophase

two DNA molecules are disentangled and condensed into pairs of rigid, compact rods (sister chromatids)

Prometaphase/Metaphase

alignment of the sister chromatids at the spindle equator

Anaphase

destruction of sister-chromatid cohesion; separated and pulled into the opposite poles of the spindle

Telophase

spindle is disassembled, and the segregated chromosomes are packaged into separate nuclei at telophase

Sister Chromatids

rigid compact rods, that remain linked by sister-chromatic cohesion

Homologous Chromosomes

Start Transitions

enter cell cycle and proceed to S phase; checks if the environment is favorable before proceeding

G2/M Transition

enter mitosis; checks if the environment is favorable and if all DNA is replicated

Metaphase-to-Anaphase

trigger anaphase and proceed to cytokinesis; checks if all chromosomes are attached to the spindle

Cyclin

protein that is also a Cdk regulator that controls cylindrical changes in Cdk activity

Cyclin-Dependent Protein Kinase (Cdks)

protein kinase that rise and falls as the cell progresses through the cycle, leading to cylindrical changes in the phosphorylation of intracellular proteins that initiate or regulate the major events of the cell cycle

Sister Chromatid Cohesion

force that holds the sister chromatids together; forms in prophase; lasts until the chromatids split in metaphase

Mitotic Spindle

giant bipolar array of microtubules; attaches the sister-chromatid pairs after nuclear assembly to the opposite poles of a spindle

Gap Phases

allow for cell growth to occur

Binary Importance

launch events in a complete, irreversible fashion avoiding chromosome condensation or nuclear-envelope breakdown to not be fully completed

Robust and Reliable Importance

allows the system to operate effectively under a variety of conditions and event if some components fail

Adaptable Importance

can be modified to suit specific cell types or to respond to specific intracellular or extracellular signals

G1/S-cyclins

acitvate Cdks in late G1 and thereby help trigger progression through start, resulting in a commitment to cell-cycle entry; levels fall in S phase

S-cyclins

bind Cdks soon after progression through start to help stimulate chromosome duplication; levels remain elevated until mitosis, and these cyclins also contribute to the control of some early mitotic event

M-cyclins

activate Cdks that stimulate entry into mitosis at the G2/M transition; levels fall during mid-mitosis

Cdk-Activating Kinase (CAK)

phosphorylates an amino acid near the entrance of the Cdk active site which causes a conformational change that greatly increases the activity of the Cdk subunit; activity is constant through the cell cycle, and this modification therefore occurs constitutively throughout the cell cycle

Wee1 Functions

phosphorylates a pair of amino acids near the kinase active site that inhibits Cdk activity; phosphorylates inhibitory sites in Cdks; primarily involved in suppressing Cdk1 activity before mitosis animals also contain a related kinase, Myt1, with similar functions

Cdc25 Function

phosphatase that dephosphorylates the kinase active sites; removes inhibitory phosphates from Cdks; three family membranes in mammals; primarily involved in controlling Cdk1 activation at the onset of mitosis

Cdk Inhibitor Proteins (CKI)

function by wrapping around the cyclin-Cdk complex, promoting a rearrangement in the Cdk active site that renders it inactive

Anaphase-Promoting Complex or Cyclosome (APC/C)

key regulator to the metaphase-to-anaphase transition; catalyzes ubiquitylation of regulatory proteins involved primarily in exit from mitosis, including securin and S-cyclins and M-cyclins; regulated by associated with activating subunits Cdc20 or Cdh1

Ubiquitin Ligase

used in numerous cell processes to stimulate the proteolytic destruction of specific regulatory proteins; polyubiquitylate specific target proteins, resulting in their destruction of proteasomes

Cdc20

acts first in metaphase to trigger the destruction of securin and cyclins, resulting in chromosome segregation in anaphase; APC/C activating subunit in all cells; triggers initial activation of APC/C at metaphase-to-anaphase transition; stimulated by M-Cdk activity

Cdh1

APC/C-activating subunit that maintains APC/C activity after anaphase and through late mitosis and G1, ensuring that cyclins and other proteins are kept at low levels until the next cycle; inhibited by Cdk activity

Elongation

replication machinery moves outward from the origin at two replication forks

Licensing

first step of initiation of DNA replication; initiation of DNA synthesis is permitted only at origins that are preloaded with Mcm helicases

Origin Recognition Complex (ORC)

binds to replication origins during the entire cell but functions only in late mitosis and early G1

Condensin

five-subunit protein complex called condensin; uses ATP to promote compaction and resolution

Astral Role

positioning of spindle in cell

Kinetochore Role

contact with centromeres

Non-Kinetochore Role

provides structural stability to the spindle

Kinetochore

large multilayered protein structure that is built on the heterochromatin that forms at the centromeric region of the chromosome

Bi-Orientation

microtubules growing from the opposite spindle pole attach to the kinetochore on the opposite side of the chromosome, forming a bipolar attachment

Mitogens

control the rate of cell division by acting in the G1 phase of the cell cycle; interact with cell-surface receptors that lead to intracellular signaling pathways and trigger the release suppression of Cdk activity where the S phase beings

E2F Proteins

bind to specific DNA sequences in the promoters of a wide variety of genes which increases expression of genes required for S phase entry