11.2: How Is Eukaryotic Cell Division Controlled?
Cell Cycle: the period from one cell division to the next;
Interphase: cell nucleus visible and typical cell functions occur, this includes DNAreplication.
Cells spend most of their time in interphase.
G1 phase: each chromosome is a single, unreplicated DNAmolecule w/associated
Some cells remain in G1 for weeks/years. Cells entering a resting phase, G0.
Special internal signals are then needed to prompt a cell to exit G0 and enter
G1-to-S transition: commitment made to DNAreplication and subsequent cell division.
S phase: DNAreplication. Each chromosome is duplicated now two sister
chromatids. Sister chromatids remain together until mitosis.
G2 phase: preparations for mitosis by synthesizing and assembling the structures that
move the chromatids to opposite ends of the dividing cell.
*The initiation, termination, and operations of these phases are regulated by specific
Specific internal signals trigger events in the cell cycle
Signals that control progress through the cell cycle act through protein kinases. Progress though
the cell cycle depends on activities of cyclin-dependent kinases (Cdk’s).
Aprotein kinase is an enzyme that catalyzes the transfer of a phosphate group fromATP to a
target protein; this phosphate transfer is called phosphorylation.
• Some Cdk’s control the G1-to-S transition. This control point in the cell is called the:
restriction (R) point.
• Cdk’s are not active on their own. They need to be activated by a protein called cyclin.
This bonding is a type of allosteric regulation—activates the Cdk by altering the shape
of its active site. • Cyclin-Cdk catalyzes the phosphorylation of a protein called RB. In many