3. Series of events that take place in cell leading to its
division & duplication (replication)
Cell cycle can be divided in three periods: interphase—
during which cell grows, accumulating nutrients needed
for mitosis & duplicating its DNA & mitosis, during which
cell splits itself into two distinct cells, often called
"daughter cells" & final phase, cytokinesis, where new
cell is completely divided
Cell-division cycle is vital process by which zygote
develops into mature organism, as well as process by
which hair, skin, blood cells, & some internal organs are
renewed
Definition
4. Cell cycle consists of four distinct phases: G1 phase, S
phase (synthesis), G2 phase (collectively known as
interphase) & M phase (mitosis, cytokinesis)
M phase is itself composed of two tightly coupled
processes: mitosis, in which cell's chromosomes are
divided between two sister cells, & cytokinesis, in which
the cell's cytoplasm divides in half forming distinct cells.
Activation of each phase is dependent on proper
progression & completion of previous one. Cells that
have temporarily or reversibly stopped dividing are said
to have entered state of quiescence called G0 phase
Phases
5. • After cell division, each of the daughter cells begin
interphase of new cycle. Although various stages of
interphase are not usually morphologically
distinguishable, each phase of cell cycle has distinct
set of specialized biochemical processes that prepare
cell for initiation of cell division
8. Term "post-mitotic" is sometimes used to refer to both
quiescent & senescent cells
Nonproliferative cells generally enter quiescent G0 state
from G1
Some cells remain quiescent for long periods of time,
possibly indefinitely (as is often case for neurons). This
is very common for cells that are fully differentiated
Some cells enter G0 phase semi-permanentally e.g.,
some liver & kidney cells
Cellular senescence occurs in response to DNA damage
or degradation that would make cell's progeny nonviable;
it is often biochemical reaction; division of such cell
could, for example, become cancerous.
G0 Phase
9. Interphase
Before cell can enter cell division, it needs to take in
nutrients. All of preparations are done during interphase
Interphase is series of changes that takes place in newly
formed cell & its nucleus, before it becomes capable of
division again
It is also called preparatory phase or intermitosis
Previously it was called resting stage because there is
no apparent activity related to cell division
Interphase proceeds in three stages, G1, S, G2
Preceded by previous cycle of mitosis & cytokinesis
The most significant event is replication of genetic
material (DNA) in S phase
10. G1 phase
First phase within interphase, from end of previous M
phase until beginning of DNA synthesis, is called G1 (G
indicating gap)
It is also called growth phase
During this phase biosynthetic activities of cell, which
are considerably slowed down during M phase, resume
at high rate
This phase is marked by use of 20 amino acids to form
millions of proteins & later on enzymes that are required
in S phase, mainly those needed for DNA replication.
Duration of G1 is highly variable, even among different
cells of same species
It is under control of p53 gene
11. S phase
S phase starts when DNA replication occur
When it is complete, all of chromosomes have been
replicated, i.e., each chromosome has two (sister)
chromatids
During this phase, amount of DNA in cell has effectively
doubled, though ploidy of cell remains same.
During this phase, synthesis is completed as quickly as
possible due to exposed base pairs being sensitive to
external factors such as any drugs taken or any
mutagens
12. G2 phase
Gap between DNA synthesis and mitosis
Cell will continue to grow
G2 checkpoint control mechanism ensures that
everything is ready to enter M (mitosis) phase & divide
13. Interphase
Before cell can enter cell division, it needs to take in
nutrients. All of preparations are done during interphase
Interphase is series of changes that takes place in newly
formed cell & its nucleus, before it becomes capable of
division again
It is also called preparatory phase or intermitosis
Previously it was called resting stage because there is
no apparent activity related to cell division
Interphase proceeds in three stages, G1, S, G2
Preceded by previous cycle of mitosis & cytokinesis
The most significant event is replication of genetic
material (DNA) in S phase
14. M phase
Consists of karyokinesis & cytokinesis
Mitosis is process by which cell separates chromosomes
in its cell nucleus into two identical sets in two nuclei:
during process of mitosis pairs of chromosomes
condense & attach to fibers that pull sister chromatids to
opposite sides of cell, followed immediately by
cytokinesis, which divides nuclei, cytoplasm, organelles
& cell membrane into two cells containing roughly equal
shares of these cellular components
15. Mitosis & cytokinesis together define mitotic (M) phase
of cell cycle - division of mother cell into two daughter
cells, genetically identical to each other and to their
parent cell
This accounts for approximately 10% of cell cycle
Sequence of events is divided into phases
* Prophase
* Metaphase
* Anaphase
* Telophase
* Cytokinesis (part of M phase, not part of mitosis)
16. State Description Abbreviation
Quiescent/
Senescent
Gap 0 G0
Resting phase where cell has left cycle &
has stopped dividing
Interphase
Gap 1 G1
Cells increase in size in Gap 1. G1
checkpoint control mechanism ensures that
everything is ready for DNA synthesis
Synthesis S DNA replication occurs during this phase
Gap 2 G2
During gap between DNA synthesis &
mitosis, cell will continue to grow. G2
checkpoint control mechanism ensures that
everything is ready to enter M (mitosis)
phase & divide
Cell
division
Mitosis M
Cell growth stops at this stage & cellular
energy is focused on orderly division into
two daughter cells. checkpoint in middle of
mitosis (Metaphase Checkpoint) ensures
that cell is ready to complete cell division
27. * Definition: heterodimeric protein composed of cyclin B &
cyclin-dependent kinase (CDK1)
* Function: promotes entrance into mitosis (M phase) from
G2 phase by phosphorylating multiple proteins needed
during mitosis
Maturation Promoting Factor
28. * Function: activates cyclin-CDK complex
by phosphorylation. CAK itself is member
of the Cdk family & functions as positive
regulator of Cdk1, Cdk2, Cdk4, Cdk6
Cdk Activating Kinases
29. * Definition: protein which inhibits cdK
* Two families
- cip/kip family: p21, p27 & p57
- INK4a/ARF family: p16INK4a, p19ARF
cdk inhibitory subunits
30.
31. * Definition: E3 ubiquitin ligase that marks
target cell cycle proteins for degradation
by 26S proteasome
Anaphase Promoting Complex
33. Sister chromatid separation from prometaphase to anaphase
Securin
Separase
Cohesin
metaphase
Securin
Separase
Cohesin
prometaphase
APC
Check
point
Separase
APC
Separase
anaphase
Check
point
34. * Definition: Skp, Cullin, F-box containing complex
(or SCF complex) is a multi-protein E3 ubiquitin
ligase complex catalyzing ubiquitination of
proteins destined for proteasomal degradation. It
has important roles in ubiquitination of proteins
involved in cell cycle & also marks various other
cellular proteins for destruction
cdc34/SCF Pathway
