CELL CYCLE AND CELL DIVISION
CELL CYCLE
-The cell cycle is a series of events that takes place in a cell as it grows and
divides.
-Cell division is part of the cell cycle.
CELLS MUST DIVIDE FOR:
REPRODUCTION
GROWTH
HEALING AND TISSUE REPAIR
CONTROL OF THE CYCLE
The cell is controlled by internal and external signals. (HGH, death of
Cell and surface-volume ratio)
These signals ensure that the stages follow one another in the normal
sequence and that each stage is properly completed before the next
stage begins.
THE STAGES OF INTERPHASE
•This is the time when a cell carries on its usual functions, which are
dependent on its location in the body.
•It also gets ready to divide: it grows larger, the number of the
organelles doubles, and the amount of DNA doubles.
•It is divided into three stages: the G1 stage, the S stage and the G2
stage.
The G1 STAGE
•Cell carries on its normal metabolic activities
•A cell doubles its organelles ( such as mitochondria and ribosomes).
•G1 phase is the time during which the cell makes more proteins so
that it can grow to its proper size.
•The late end of the G1 phase is also when the mitochondria of the cell
fuse together into a network of mitochondria, which helps these
organelles become more efficient at producing energy molecules.
The S STAGE
•DNA Replication occurs.
•At the beginning of this stage, each chromosome is composed of one
DNA molecule, which is called CHROMATID.
•At the end of this stage, each chromosome consists of two sister
chromatids.
•New packaging proteins must also be made to wrap the copied DNA.
•These package proteins are called histones.
The G2 STAGE
•The cell has twice the amount of DNA during G2 than it did during G1.
•G2 is necessary for the cell to make sure that all of the DNA is in intact;
no breaks and no nicks.
•The G2 to mitosis transition is the last checkpoint before the cell
commits to entering mitosis.
•The cell synthesizes the proteins needed for cell division, such as
proteins found in microtubules.
•The G2 phase is the time during which a cell replicates its organelles in
preparation for mitosis.
•Not only does the DNA need to be divided, but so do the organelles.
G2 is the last chance for the cell to make more protein in preparation
for division.
