paksa ng konseptong papel
The Cell Cycle
A eukaryotic cell cannot divide into two, the two into four, etc. unless two processes alternate: doubling of its genome (DNA) in S phase (synthesis phase) of the cell cycle; halving of that genome during mitosis (M phase).
The period between M and S is called G1; that between S and M is G2.
So, the cell cycle consists of:
G1 = growth and preparation of the chromosomes for replication;
S = synthesis of DNA [see DNA Replication] and duplication of the centrosome;
G2 = preparation for
M = mitosis.
When a cell is in any phase of the cell cycle other than mitosis, it is often said to be in interphase.
Control of the Cell Cycle
The passage of a cell through the cell cycle is controlled by proteins in the cytoplasm. Among the main players in animal cells are:
Cyclins
G1 cyclins (D cyclins)
S-phase cyclins (cyclins E and A) mitotic cyclins (B cyclins)
Their levels in the cell rise and fall with the stages of the cell cycle.
Cyclin-dependent kinases (Cdks) a G1 Cdk (Cdk4) an S-phase Cdk (Cdk2) an M-phase Cdk (Cdk1)
Their levels in the cell remain fairly stable, but each must bind the appropriate cyclin (whose levels fluctuate) in order to be activated.
They add phosphate groups to a variety of protein substrates that control processes in the cell cycle.
The anaphase-promoting complex (APC). (The APC is also called the cyclosome, and the complex is often designated as the APC/C.) The APC/C triggers the events leading to destruction of cohesin (as described below) thus allowing the sister chromatids to separate; degrades the mitotic (B) cyclins.
Steps in the cycle
A rising level of G1-cyclins bind to their Cdks and signal the cell to prepare the chromosomes for replication.
A rising level of S-phase promoting factor (SPF) — which includes A cyclins bound to Cdk2 — enters the nucleus and prepares the cell to duplicate its DNA (and its centrosomes).
As DNA replication continues, cyclin E is destroyed,
A eukaryotic cell cannot divide into two, the two into four, etc. unless two processes alternate: doubling of its genome (DNA) in S phase (synthesis phase) of the cell cycle; halving of that genome during mitosis (M phase).
The period between M and S is called G1; that between S and M is G2.
So, the cell cycle consists of:
G1 = growth and preparation of the chromosomes for replication;
S = synthesis of DNA [see DNA Replication] and duplication of the centrosome;
G2 = preparation for
M = mitosis.
When a cell is in any phase of the cell cycle other than mitosis, it is often said to be in interphase.
Control of the Cell Cycle
The passage of a cell through the cell cycle is controlled by proteins in the cytoplasm. Among the main players in animal cells are:
Cyclins
G1 cyclins (D cyclins)
S-phase cyclins (cyclins E and A) mitotic cyclins (B cyclins)
Their levels in the cell rise and fall with the stages of the cell cycle.
Cyclin-dependent kinases (Cdks) a G1 Cdk (Cdk4) an S-phase Cdk (Cdk2) an M-phase Cdk (Cdk1)
Their levels in the cell remain fairly stable, but each must bind the appropriate cyclin (whose levels fluctuate) in order to be activated.
They add phosphate groups to a variety of protein substrates that control processes in the cell cycle.
The anaphase-promoting complex (APC). (The APC is also called the cyclosome, and the complex is often designated as the APC/C.) The APC/C triggers the events leading to destruction of cohesin (as described below) thus allowing the sister chromatids to separate; degrades the mitotic (B) cyclins.
Steps in the cycle
A rising level of G1-cyclins bind to their Cdks and signal the cell to prepare the chromosomes for replication.
A rising level of S-phase promoting factor (SPF) — which includes A cyclins bound to Cdk2 — enters the nucleus and prepares the cell to duplicate its DNA (and its centrosomes).
As DNA replication continues, cyclin E is destroyed,