Anatomy 32
Chapter 2
Cells: The Living Units
I. Introduction to the cell- The cell is the smallest
living unit. All living organisms are composed
of cells
a. Robert Hooke first observed a cell when
microscopes were invented in the 1600’s.
Matthias Schleidena nd Theodor Schawn declared
that all living things are made up of cells. Rudolf
Virchow concluded that cells arise from other living
cells.
b. All of these observations contributed to the Cell
Theory=
all living things are made up of cells,
the smallest unit of life is the cell,
cells arise from other living cells by cell
division.
c.
Organelles
are discrete
specialized
structures
that assist in
cell function
and structure.
In this
chapter you
will learn
about the
function of
cell
organelles
and how they
assist the cell
to perform its
overall
function.
II.
The plasma membrane- A thin flexible structure that separates
the cell’s internal environment from its surroundings. It controls
what enters and leaves the cell. Other cell organelles are
enclosed by a membrane structure very similar to the plasma
membrane.
a. Structure- A phospholipid bilayer with proteins and
cholesterol molecules used to stabilized the
membrane.
1. The phospholipids layer creates hydrophilic
and hydrophobic regions that controls what crosses
the membrane (semi-permeable membrane.)
2. Carbohydrates
(sugars) may be
attached to
proteins and form
glycoproteins, or
attach to lipids and
form glycolipids.
Carbohydrates are
found on the outer
surface of the
membrane and
serve as receptors
or markers.
3.
Integral
proteins
cross
through
the
membran
e and
may be
used as
transport
channels.
Periphera
l proteins
adhere to
the
underside
of the
membran
e and
stabilize
it.
b. Function- The membrane protects the cells
internal structures and controls transport
1. The side of the membrane that faces
externally presents receptors and markers
unique to each kind of cell.
2. The membrane controls what molecules cros
it based on size, polarity, solubility, and receptor
signals.
3. The membrane expels objects out of the cell
by exocytosis or surrounds them and brings
them in by endocytosis through either
phagocytosis or pinocytosis.
Exocytosis
Endocytosis
Receptor Mediated Endocytosis
III. The cytoplasm- the area within the cell that contains
organelles between the plasma membrane and the
boundary of the nucleus.
a. Cytosol- a jelly-like substance that fills the cell and suspends
the organelles
b. Membrane bound
organelles- these
are organelles
enclosed by
membranes
1. MitochondriaA double
membrane
bound
organelle
responsible
for producing
energy for the
cell in the
form of ATP
(The Power
House)
2. Endoplasmic Reticulum- A single membrane folded
over into different compartment, usually exists close
to the nucleus (The Assembly Site)
1. Smooth ER- no ribosomes on surface, processes fats,
toxins, hormones
2. Rough ER- has surface ribosomes, site of protein synthesis
3. Golgi Apparatus- Stacked membranes that take in proteins and
enclose them in vesicles (membrane sacks)
(The Packaging Site)
Collaboration between organelles. Some proteins remain in the cell and
some are excytosed.
4. Lysosomes- vesicles
containing lytic or
digestive enzymes that
break down cell debri
and foreign
substances in the cell,
like bacteria
( Demo-lition crew/
security)
5. Peroxisomesvesicles like
lysosomes but
filled with
enzymes that
fight free radicals
and break down
poisons (
Neutralizers)
C.
Non-membrane
bound organellestypically protein
structures not
surrounded by a
membrane that
perform a specific
function.
1.
Ribosomeprotein units that
specialize in
protein
production, may
be free floating
or attach to
Rough ER.
(Assembly
workers)
2. Cytoskeleton- thick and thin protein filaments that form a
supportive mesh
3.
Centriolesprotein
fibers
involved in
cell division
(Reproductive
machinery)
• FACTORY DRAWING-
IV The nucleus- Located at the center of the cell,
it hold the instructions for life (genetic material)
it is know as the “brain” of the cell.
a. Nuclear Envelope -a double membrane layer with
pores that allow transport into and out of the
nucleus.
b. Chromatin- DNA strands loosely wrapped around
histone protein. Under the microscope it make the
nucleus look cloudy. DNA is readable and
accessible in this form and thus most of the time the
cell contains chromatin
c. Chromosomes- DNA strands super coiled to form
dense discrete structures. These are seen during
cell division and resemble an X. Humans have 46
chromosomes. Chromatin condenses to form
chromosomes.
d. Nucleoli – Region within the nucleus where
ribosome production takes place
V
The Cell Life Cycle- Stages involving cell
division, preparation for cell division, and
normal cell function.
a. Interphase- The majority of the time the cell is
interphase. At this time it grows, performs its
normal cell function, and prepares for cell division.
A cell in interphase seen under the microscope
shows a distinct cloudy nucleus filled with
chromatin.
1. G1 (growth 1)- after a cell is created it enters this stage
and performs its specialized function
2. S (synthesis)- DNA is copied so there are two sets of
chromosomes
3. G2 (growth 2)- cell continues to grow and prepare for
cell division
B. Cell Division- This process occurs when cells need
to replace dead cells, heal damaged tissue, during
growth and development. Some cells never divide
once formed such as muscle cells and nerve cells
1. Mitosis- the division of the cell’s nucleus describe in four
stages that may take about 2 hours to complete.
1. Prophase- the nuclear envelope breaks down, DNA
condenses from chromatin to chromosomes, mitotic spindle
forms
2. Metaphase- mitotic spindle lines the chromosomes at the
equatorial plate
3. Anaphase- chromosome strands (sister chromatids) are
pulled apart to opposite poles of the cell
4. Telophase- the cell forms a cleavage furrow, nuclear
envelopes begins to form and chromosomes return to
chromatin
2. Cytokinesis- the division of the entire cell into two cells.
VI. Cellular Diversity- Although all the cells
in your body hold exactly the same genetic
information they do not have the same
function or structure. Activation of specific
genes causes the cell to become
specialized or differentiated.
a.
b.
c.
d.
e.
Cells that connect body parts or line organs
Cells that move organs and body parts
Cells that store nutrients
Cells that fight disease
Cells that gather information and control body
functions
f. Cells for reproduction
VII Developmental Aspects of cells
All humans originated from a single cell. This cell is
formed when the egg and sperm unite, it’s called the
zygote. All other cells are produced from this cell, thus
every cell in our body contains the exact same DNA. As
the embryo develops the cells become specialized, a
process known as cell differentiation. Their structural
differences reflect their functional difference. A group of
specialized cells forms a type of tissue and each tissue
type will have a different function.
a. Youth – before birth the fetus develops all the organs and
systems necessary for a functional body. After birth the infant
continues to mature and cells divide for growth. By adulthood
cell division reduces to only occur during repair of tissues
b. Aging- there are several theories that try to explain the cause of
aging. The end result is the same: cell greatly decrease division
rate and dead cells are replaced at a slower rate, tissue mass is
lost, and weakening occurs.
• Free radical- molecules ( primarily oxygen) that have an
unpaired electron and are highly reactive. They build up
and damage the cells. Antioxidants such as vitamin E
and C are used to reduce radicals
• Mitochondrial Theory- the mitochondria produces free
radicals as a result of cellular respiration/ high
metabolism. Those that eat less or have a slow
metabolism live longer because less radicals are
produced
• Genetic Theory- our genes have a pre-determined life
span for cells indicating that it is a normal part of human
development
• Telomeres- sections of DNA that do not contain genes
but influence the amount of times a cell divides. As the
cells divide the number of telomeres decreases. An
enzyme called telomerase, which adds telomeres, is
found in excess in cancer cells and may increase cell
division.
Cancer
• VIII. Cancer
•
Cancer results from a genetic change in the cell that causes
it to divide rapidly. The genetic change is caused by a
mutation instigated by biological factors, UV rays, exposure to
carcinogens, or viruses. The rapid division does not allow for
proper cell differentiation and function and results in mass
formation. This is called a tumor.
• Tumors may be malignant or benign. A malignant tumor has
the ability to metastasize- meaning that the cancerous cells
spread through the body. The cells enter either the circulatory
or lymphatic system, travel through the body, and re-establish
a new tumor at a different location.
• Cancer is treated with either the surgical removal of the tumor,
radiation, chemotherapy. These treatments kill healthy cells as
well as cancerous cells and cause multiple side effects. New
therapies are more specific at targeting the cancer and
causing less severe side effects.
• READ PG 46-47