INTRODUCTION
The Cell Theory is one of the foundations of modern
biology :
•All living things are composed of one or more cells;
•The chemical reactions of living cells take place within
cells;
•All cells originate from pre-existing cells; and
•Cells contain hereditary information, which is passed
from one generation to another.
The Cell Cycle
Stages of the cell cycle
The cell cycle is an ordered set of events, culminating in cell growth and division into
two daughter cells. Non-dividing cells not considered to be in the cell cycle. The
stages, pictured to the above, are G1-S-G2-M. The G1 stage stands for "GAP 1". The
S stage stands for "Synthesis". This is the stage when DNA replication occurs. The
G2 stage stands for "GAP 2". The M stage stands for "mitosis", and is when nuclear
(chromosomes separate) and cytoplasmic (cytokinesis) division occur.
• G1 stage : Growth & development of the
cell, Protein synthesis
• S-phase : Chromosome replication via
DNA synthesis
• G2 stage : Growth & development
Organelle Replication
DNA Replication
Chromosome Replication & Division
Every time a cell divides, each chromosome must be carefully replicated
(copied) and then distributed to assure that each daughter cell gets a
complete and accurate set of information. Thus, nuclear division includes
successive processes of chromosome replication, separation, and
distribution
The Mitotic cell cycle is essential to
cell division and growth of an
organism
Gene Expression and Cell Division conflict:
☺ Gene
expression
requires
that
chromosomal DNA be uncoiled to allow
access to enzymes such as RNA
polymerase
☺ Cell division requires that chromosomes be
tightly coiled to allow orderly migration of
chromosomes to daughter cells
Gene Expression and Cell Division
are separated into different stages
Mitosis
Mitosis is nuclear division plus cytokinesis, and
produces two identical daughter cells during
prophase, prometaphase, metaphase, anaphase,
and telophase.
Mitosis deals only with the segregation of the
chromosomes and organelles into daughter cells.
The condensed replicated chromosomes have several
points of interest. The kinetochore is the point where
microtubules of the spindle apparatus attach. Replicated
chromosomes consist of two molecules of DNA (along
with their associated histone proteins) known as
chromatids. The area where both chromatids are in contact
with each other is known as the centromere. The
kinetochores are on the outer sides of the centromere.
Remember that chromosomes are condensed chromatin
(DNA plus histone proteins).
WILL BE CONTINUED…..