Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Cell Cycle or Cell-Division Cycle – Part 2

https://www
...
com/watch?v=eqJqhA8HSJ0
https://www
...
com/watch?v=WRH7xG7q6Sg
https://www
...
com/watch?v=VLJF8Pf8spw
SRV

1

Cell Cycle Control System

Major Cell Cycle Regulatory Proteins
Role of cyclins
Role of cyclin dependent kinase (CdKs) – Several subheadings
Cell cycle checkpoints

SRV

2

Cell-cycle control system
• The cell-cycle control system is a cyclically operating biochemical device constructed from a set of
interacting proteins that induce and coordinate the essential processes involved in duplication and
division of cell's contents
• It cyclically triggers the essential processes of cell reproduction, such as DNA replication and
chromosome segregation
• It coordinates the cycle as a whole
• The sequence of cell-cycle events is governed by a cell-cycle control system

• Cell-cycle control system is similar in all eukaryotes

SRV

3

• The core of this system is an ordered series of biochemical switches that control the main events of
cycle, including DNA replication and the segregation of the replicated chromosomes
• Intracellular and extracellular signals act on the control system to regulate cell division in a
multicellular organism
• In most cells, additional layers of regulation enhance the fidelity of cell division and allow the control
system to respond to various signals from both inside and outside the cell
• Inside the cell, the control system monitors progression through the cell cycle and delays later
events until earlier events have been completed
• The control systems also monitors the conditions outside the cell
• In the multicellular animal, the system is highly responsive to signals from other cells,
stimulating cell division when more cells are needed and blocking it when they are not

• When the cell malfunctions, excessive cell divisions can result in cancer

SRV

4

• What is regulated?
• Events are properly timed
• Events are in proper order
• Events occur once per cell cycle
• Progression arrested when the
• Cell fails to complete an essential cell cycle process
• Cell encounters unfavorable environmental conditions
• DNA damage

• Regulated by extra- and intra-cellular signals
• Progression through cell cycle is regulated precisely by various inhibitory mechanisms that arrest
the cycle at various checkpoints when
• Events are not completed successfully
• DNA damage occurs (DNA is not perfect)
• Extracellular conditions are not favorable
SRV

5

Key components of the central cell-cycle control system
• It is a protein-kinase-based machine
• The proteins of this control system are well conserved in evolution

• The cell-cycle control system is based on two key families of proteins
• Cyclin-dependent protein kinases (Cdk)
• Cyclins (CdK activating proteins)
• These protein complexes exert control through their kinase activities, which are abruptly switched
on or off at particular points in the cycle
• The cyclic assembly, activation and disassembly of cyclin-Cdk complexes are the pivotal events
driving the cell cycle
• The details of cell cycle regulation, such as the number of different cyclins and kinases and the
combinations in which they act, differ from species to species, but the basic mechanism has been
conserved in the evolution of all eukaryotic cells
SRV

6

Timed and orderly events
• S and M phases are coordinated so that the genome is completely replicated, but replicated only
once, before mitosis occurs
• Some features of the cell cycle, including the time required to complete certain events, vary greatly
from one cell type to another, even in the same organism
• The timing of the cell cycle is controlled by a family of protein kinases with activities that
change in response to cellular signals
• By phosphorylating specific proteins at precisely timed intervals, these protein kinases
orchestrate the metabolic activities of the cell to produce orderly cell division
• Protein kinases and protein phosphorylations are central to the timing mechanism that
determines entry into cell division and ensures orderly passage through these events

• In the standard cell cycle, the control system is regulated by brakes that can stop the cycle at
specific checkpoints
• Feedback signals conveying information about the downstream processes can delay progress of
the control system itself
• So as to prevent it from triggering the next downstream process before the previous one has
finished
SRV
7

Cell Cycle Control Contd
...
e
...
e
...
g
...
e
...
g

---