Summary of the Cell Cycle ~
- the amount of time spent in each stage of the cell cycle (G1, S, G2 & M
phase) is biochemically controlled
There are 4 distinct phases that make up the cell cycle.
Three are growth phases and are
; the fourth is a period of division, therefore, referred to as
, cells typically double in size.
The first part of interphase is called
This is a period marks a maintenance of basic cell activities and takes anywhere from 1 hour
to several days depending on the cell type.
This is followed by the
this period, which typically lasts 9 hours,
DNA is replicated
; this means that a copy of the DNA
The last stage of interphase is called
Here, the cell prepares to divide;
certain proteins, called spindle proteins, necessary for cell division are made at this time.
takes about 3 hours to complete. Additionally, organelles such as mitochondria, plastids, and
ribosomes double in number.
After interphase is the M phase.
Two critical events occur at this time.
The first is
which is the division of the nuclear material.
During mitosis, 2 sets of chromosomes are
distributed to opposite ends of the cell and two
The other event, which
happens near the end of mitosis, is
Here, the cytoplasm divides and the two
daughter nuclei are separated into two
The other cell constituents (organelles)
are partitioned into the daughter cells also.
of chromosomes to prepare for cell division [Mitosis]
Relatively fool proof process (1 out 100,000 replication events leads to a mistake
The error rate is controlled by evolution (some species have a higher mutation rate)
Harry’s slides shows a series of cell stages
Interphase cells – this is when Replication occurs (chromosome replicates all its
The result is two sister chromatids joined by a centromere)
Active division during the M-phase of cell cycle includes [Prophase, Metaphase,
II. SUMMARY OF MITOSIS ~
nuclear division where the chromosome number of resulting daughter cells is the
same as the original cell that underwent Mitotic divison.
At the beginning of mitosis, the DNA has already been doubled (replicated) and is packaged into
chromosomes made up of pairs of
[sister chromatids are joined together at a
central point called the
thus forming the replicated chromosomes].
The first part of mitosis is called
During early prophase, the chromosomes condense
and the nucleoli disappear. The
continues to form in the cytoplasm - this is a web
like structure made of microtubules.
Its role is to suspend and, later during mitosis, move the
They arise at microtubule-organizing centers, called
in animal cells.
The organizing centers (there are two) spin out microtubule fibers and move to opposite ends