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CELL REPRODUCTION
Cells grow but size is limited.
A. Too large, not enough DNA
to control cell functions
B. Too large, not enough
surface area for volume
Cells divide in order to survive.
Cell cycle of growth and division
has two stages:
A. mitosis
B. cytokinesis.
The Cell Cycle
Interphase:
The period of growth between
cell divisions.
G-1
cell grows larger,
proteins and organelles
are made.
S
DNA is made and
chromosomes replicate.
G-2
organelles, molecules
needed for division
are produced.
Mitosis:
The division of the cell nucleus.
Prophase:
Chromatin coils, thickens.
Chromosomes become visible.
Centrioles move to poles.
Chromatids attach to spindle.
Nuclear membrane and
nucleolus breakdown.
Metaphase:
Sister chromatids line up
along equator.
Anaphase:
Centromeres split and sister
chromatids move to poles.
Telophase:
Chromosomes uncoil
spindle breaks down,
nuclear envelope and
nucleolus reform.
Cytokinesis:
Division of the cytoplasm.
Animals: membrane pinches in.
Plants: cell plate forms.
Prokaryotes have no organized
nucleus so they do not go through
mitosis.
Eukaryotes control their cell cycle
with enzymes (special proteins)
known as regulatory proteins or
cyclins.
Internal regulators
control mitosis stages
External regulators
control cell cycle timing
Human Embryology
Multicellular organisms grow bigger
through mitosis and cytokinesis.
Cells will become specialized to
perform certain functions.
Development begins with fertilization
of egg cell by sperm cell.
The fertilized egg is called a zygote.
The zygote divides to form 2 cells.
Division occurs again to give 4 cells.
Repeated divisions result in a ball of
64 cells called a morula.
The cells in a morula are totipotent
stem cells.
They are undifferentiated cells that
have the potential to become any
kind of cell in the body.
Continued cell division eventually
results in a hollow ball of cells
called a blastula.
As cells continue to divide and move,
the blastula folds in on itself and
becomes a gastrula.
The cells are now becoming less able
to develop into any other kind of cell
and are called pluripotent.
As development continues, three
distinct kinds of cells emerge and
are located in regions called germ
layers.
Endoderm :
The innermost layer,
becomes the lining of the
digestive tract and much of
the respiratory system.
Mesoderm :
The middle layer,
becomes muscle tissue and
much of the circulatory,
reproductive and excretory
systems.
Ectoderm :
The outermost layer,
becomes the sense organs,
nerves, and the outer layer
of the skin.
Apoptosis : programmed cell death
required for proper development;
also rids the body of defective or
diseased cells.
Pluripotent stem cells will
differentiate into 4 major branches:
1. hematopoietic stem cells
erythrocytes basophils
lymphocytes thrombocytes
neutrophils
monocytes
2. mesenchymal stem cells
bone
tendon
cartilage muscle
adipose
marrow
3. endodermal stem cells
esophagus
pancreas
liver
intestines
stomach
lungs
4. neural stem cells
neurons
oligodendrocytes
glial cells
astrocytes
These four major branches will
differentiate into 210 types of
specialized somatic (body) cells
About 8 weeks after fertilization,
The embryo becomes a fetus
containing pluripotent fetal stem cells
Stem cells from the placenta and
adults have limited potential and are
called multipotent stem cells.