Cell
Review/Chapter
3
By Becky
• Cytology is the study of the structure and functions of
cells.
• The cell was first discovered by Robert Hooke while
viewing a dried cork.
• The cells have been researched for 175 years.
• This research has led to the cell theory.
The Cell
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The cell theory has five basic concepts.
1. Cells are the building blocks of all plants and animals.
2. Cells are produced by the division of preexisting cells.
3. Cells are the smallest units that perform all vital
physiological functions.
• 4. Each cell maintains homeostasis at the cellular level.
• 5. Homeostasis at the tissue, organ, system, and
individual levels reflects the combined and coordinated
actions of many cells.
The Cell Theory
• Outside the cell is a fluid known as Extracellular Fluid.
This fluid is a watery medium where the cell floats.
• The Cell Membrane separates the cell’s contents and
cytoplasm from the extracellular fluid.
• The cytoplasm can further be broken down into a fluid
known as Cytosol.
• The cytoplasm has a very different composition than the
extracellular fluid and must be kept separate.
Cell Fluid
• The cytoplasm includes a lot more protein than the
extracellular fluid.
• The cytosol contains a high concentrations of potassium, while
extracellular fluid contains a high concentration of sodium.
• The cytosol contains dissolved nutrients, ions, soluble and
insoluble proteins, and waste products.
• Cytosol has about 200 amino acids while as the Extracellular
fluid only has 30.
• There are major differences between the cytoplasm and
extracellular fluid which need them to be separated.
Cytoplasm VS.
Extracellular Fluid
• The cell membrane ( also known as the Plasma
Membrane) forms the outer boundary of the cell. It is the
cell’s bodyguard.
• The major components of the cell membrane are
phospholipids, proteins, glycolipids, and cholesterol.
• The cell membrane is also a Phospholipid bi-layer
because the phospholipids form two distinct layers.
• Ions and water soluble compounds cannot enter the
interior of the membrane because the lipid tails of the
phospholipid molecules are hydrophobic.
The Cell Membrane
• Peripheral proteins are attached to the inner membrane
surface of the cell membrane.
• Internal proteins are embedded in the membrane.
• Some of the internal proteins form channels that let water
molecules, small water- soluble compounds and ions into
or out of the cell.
• The cell membrane also contains a variety of receptors
that allow the cell to recognize and respond the specific
molecules in its environment.
Cell Membrane
• Cells work together to maintain homeostasis at the tissue,
organ, and system levels.
• The essential communication and coordination activities
involve the cell membrane, which forms the interface
between each cell and the cell’s surroundings.
• Regulation is essential because the intercellular and
extracellular environments are quite different. Those
differences must be maintained to preserve homeostasis.
The cell and its
environment
• Organelles are found in most cells that are able to grow
and reproduce.
• Each organelle performs a function that is essential to
normal cell structure, maintenance, and the metabolism.
• Organelles can be divided into two categories:
Nonmembranous organelles and membranous organelles.
Organelle
Cytoskeleton
Microfilament
• An internal protein
framework that gives the
cytoplasm strength and
flexibility.
• It has four major
components:
• Are slender protein strands,
commonly composed of the
protein called actin.
• In most common cells,
microfilaments are scattered
throughout the cytoplasm.
• They form a dense layer under
the cell membrane.
• Have two major functions:
• Microfilaments, intermediate
filaments, thick filaments,
and microtubules.
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Nonmembranous
organelles.
Anchor the cytoskeleton to integral
proteins of the cell membrane.
Actin microfilaments can interact
with filaments composed of
another protein called Myosin.
Intermediate Filaments
Thick filaments
• Are defined chiefly by their
size: their composition varies
from one cell type to another.
• They provide strength,
stabilize the positions of
organelles, and transport
materials within the cytoplasm.
• A specialized filament is called
neurofilaments.
• Are relatively massive
strands composed of myosin
protein subunits.
• They are also abundant in
muscle cells.
• This is where they react
with actin filaments to
produce powerful
contractions within the cell.
Microtubules
Microvilli
• Are hollow tubes built from
the globular protein called
tublin.
• They have a variety of
functions:
• Are small, finger-shaped
projections of the cell
membrane.
• Are found in cells that are
engaged in absorbing materials
from the extracellular fluid.
• Are important because they
increase the surface area
exposed to the extracellular
environment.
• Form the main components
of the cytoskeleton, giving
the cell strength and
anchoring the organelles into
the right position.
Centrioles
Cilia
• Is a cylindrical structure
composed of short microtubules.
• All animal cells are capable of
reproducing themselves contain
a pair of centrioles.
• The centrosome is the
cytoplasm surrounding this pair.
• Centrioles direct the movement
of DNA strands through the
cytoplasm.
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contains nine pairs of
microtubules surrounding a
central pair.
• Cilia are anchored to a compact
basal body located just beneath
the cell’s surface.
• Cilia lining the respiratory tract
beat in a synchronized manner to
move sticky mucus and trapped
dust particles towards the throat
and away from the delicate
respiratory surfaces.
Flagella
Ribosomes
• Resemble cilia but they are
bigger than cilia
• Moves a cell through the
fluid surrounding the cell,
rather than moving the fluid
past the cell.
• The sperm cell is the only
human cell that has a
flagellum.
• Small, dense structures that
cannot be see clearly with a
light microscope.
• They are found in all cells.
• Consists of about 60% Rna
and 40% protein.
• Two major types of
ribosomes:
• Free Ribosomes
• Fixed Ribosomes
Mitochondria
Nucleus
• Small organelles that have
an unusual double
membrane.
• The inner membrane
contains many fold called
Cristae.
• Cristae increase the surface
area exposed to the fluid
contents (Matrix).
• Respiratory enzymes are
attached to the cristae and
produce most of the ATP
generated by mitochondria.
• The control center for cellular
operation.
• Most cells contain a single
nucleus, but there are
exceptions.
• A nuclear envelope surrounds
the nucleus and separates it from
the cytosol.
• The nuclear envelope is a double
membrane containing a narrow
pronuclear space.
• Chemical communication
between the nucleus and cytosol
occurs through the nuclear
pores.
Membranous Organelles
Endoplasmic Reticulum
Golgi Apparatus
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Is a network of intracellular membranes.
Three major functions:
Synthesis: manufactures protein, carbs,
and lipids
Storage: hold synthesized molecules
Transport: materials travel through place
to place.
The ER forms hollow tubes, flattened
sheets, and round chambers called
Cisternae.
There are two types of ER:
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Rough ER
Smooth ER
Consists of flattened membrane discs,
called saccules.
• Major Functions:
1.
Synthesis and packaging of secretions
2.
Packing of special enzyme
3.
Renewal or modification of the cell
membrane.
• Materials move from saccule to saccule
by means of small transfer vesicle.
• Vesicles containing secretions that will be
discharged from the cell and are called
secretory vesicles.
• The ejection process is called exocytosis.
• The cell has many way to obtain energy.
• It can receive energy through lipids, carbohydrates, and
proteins.
• Lipids are fats and carbohydrates are your typical carbs that
provide you with energy. They also provide the cells with the
same energy so that their organelles can function correctly.
• The organelle, Mitochondria, provides 95% of the energy
needed to keep a cell alive.
• It produces ATP through the breakdown of organic molecules
in a series of reactions that also consume oxygen and generate
carbon dioxide.
Cell’s Energy
Lysosomes
Peroxisomes
• Are vesicles filled with
digestive enzymes.
• They may function in the
defense against disease.
• This is called endocytosis.
• When enzymes rapidly
destroy the proteins and
organelles of the cell it is
called autolysis.
• Are smaller than lysosomes
and carry a different group
of enzymes.
• They absorb and neutralize
toxins that are absorbed
from the extracellular fluid
or generated by chemical
reactions in the cytoplasm.
• The nucleus is the control center for the cell.
• The nucleus directs processes that take place in the cytosol and
must in turn receive information about conditions and
activities in the cytosol..
• In the nucleoplasm in the nucleus is where the DNA and RNA
are found.
• Our cell nuclei contains 23 chromosomes which is what makes
a person look the way they do.
• The nucleus controls the actions of the organelles within the
cell.
• The nucleus copies the chromosomes when it is time for the
cell to divide.
The Nucleus
• The lifespan of a cell varies from hours to decades.
• This depends on the type of cell and the environmental
stresses involved.
• A typical cell does not live near as long as a typical
person, so over time cell populations must be maintained
by cell division.
• Even when development has been complete cell division
continues to be essential to survive.
Cell Life Cycle
• There are two types of cell division.
• Central of cell reproduction is the accurate duplication of the
cell’s genetic material and its distribution to the two new
daughter cells formed by division. This is called Mitosis.
• Mitosis occurs during the division of somatic cells.
• Somatic cells include all the cells in the body other than the
reproductive cells, which give rise to sperm or eggs.
• Most cells spend only a small part of their time actively
engaged in cell division.
• Somatic cells spend the majority of their functional lives in
interphase.
Cell Division
• During interphase the cell performs all of its normal functions
and making preparations for division.
• There are numerous stages during interphase:
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G0 phase
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G1 phase
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S phase
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G2 phase
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Gm phase
• An interphase cell in the G0 Phase is not preparing for mitosis.
Interphase
• A cell that is going to divide first enters G1 Phase.
• In this phase, the cell produces enough mitochondria,
centrioles, cytoskeleton elements, endoplasmic reticulum,
ribosomes, golgi membranes, and cytosol to make two
functional cells.
• In cell dividing at top speed, G1 may last as little as 8-12
hours.
• When preparations have been completed, the cell enters the S
phase.
• Over the next 6-8 house the cell duplicates its chromosomes.
Interphase
• Throughout the life of a cell, the DNA strands in the nucleus
remain intact. DNA synthesis or DNA Replication occurs in
cells preparing to undergo mitosis or meiosis.
• The goal of replication is to copy the genetic information in
the nucleus so that one set of chromosomes can be given to
each of the two daughter cells produced.
• Once DNA replication has been completed, there is a brief 2-5
hours G2 phase devoted to last minute protein synthesis.
• The cell then enters the Gm phase and mitosis begins.
• Stage 1: prophase begins when the chromosomes of the
cell coil so tightly that they become visible.
• As a result of DNA replication during the S phase, there
are two copies of each chromosome called chromatids.
• They are connected at a single point called the
centromere.
• Spindle fibers begin to form between the centriole pairs.
• Prophase ends with the disappearance of the nuclear
envelope.
Mitosis
• Stage 2: Metaphase. The chromatids now move to a narrow
central zone called the metaphase plate.
• A microtubule of the spindle apparatus attaches to each
centromere.
• Stage 3: Anaphase. As if responding to a single command, the
chromatid pairs separate and the daughter chromosomes move
towards opposite ends of the cell
• Stage 4: Telophase. This stage is in many ways the reverse of
prophase.
• The nuclear membranes form, the nuclei enlarge, and the
chromosomes gradually uncoil.
• Once the chromosomes disappear, nucleoli reappear and the nuclei
resemble those of interphase cells.
• Telophase marks the end of mitosis, but the daughter cells have yet to
complete their physical separation.
• This separation process is called cytokinesis.
• As the daughter chromosomes near the end of the spindle apparatus,
the cytoplasm constricts along the metaphase plate.
• This process continues through Telophase and the completion of
cytokinesis marks the end of cell division.
• Meiosis is the cell division of sex cells.
• It has the same phases, but creates four daughter cells instead of two.
• They reproduce sex cells instead of somatic cells.
• Two factors, one passive and one active, interact to create and
maintain the Transmembrane potential.
• The Transmembrane potential is a characteristic of all living
cells because it results from the active and passive properties
of their cell membranes.
• The Transmembrane potential is just as important as any
structural characteristics or organelles.
• Many cell functions that involve the cell membrane involve
changes in the Transmembrane potential.
• But the Transmembrane potential has its own significant
functions.
Transmembrane
Potential
• In addition to the open sodium and potassium channels it has, the cell
membrane contains gated ion channels that are closed at the normal
resting potential.
• Because the concentration gradients are large, any stimulus that
opens one of these gates will produce a sudden rush of ions into or
out of the cell.
• If it can affect a channel protein, even a relatively weak stimulus can
have a significant impact on the cell.
• Because the Transmembrane potential can increase a stimulus in this
way, it greatly increases the cell’s sensitivity to its environment.
• The Transmembrane is maintained by the sodium-potassium
exchange pump in the membrane. It makes sure the sodium and the
potassium in the Transmembrane potential is stabilized.
• Most cells in the body are firmly attached to other cells or to
extracellular protein fibers. The attachment occurs at cell
junctions that are not involved in membrane flow. There are
four types of cell junctions: gap junctions, tight junctions,
intermediate junctions, and desmosomes.
• Gap junction: in a gap junction the two cells are held together
by an interlocking of membrane proteins.
• Gap junctions are most common in cardiac muscle ad smooth
muscle tissue. They are also occasionally found between nerve
cells
• Tight junctions: at a tight junction, there is a partial fusion of
the lipid portions of the two cell membrane.
Attachment of Cells
• Because the membrane is fused together, tight junctions are the
strongest intercellular connections.
• The tight junction also blocks the passage of water or solutes
between cells.
• Intermediate junctions: at an intermediate junction the
opposing cell membranes, while remaining distinct, are held
together by a thick layer of proteoglycans.
• The cytoplasm at an intermediate junction contains a dense
network of microfilaments that anchor the junction to the
cytoskeleton.
• This arrangement adds strength and helps to stabilize the shape
of the cell.
• Desmosomes: at desmosomes there is a very thing
proteoglycan layer between the opposing cell membranes,
reinforced by a network of intermediate filaments that lock the
two cells together.
• Desmosomes are very strong and the connection can resist
stretching and twisting.
• The desmosomes create links so strong that even dead skin
cells are usually shed in thick sheets rather than individually.
• Junctional complexes: cells lining the digestive tract,
respiratory tract, or other passageways are held together by
Junctional complexes. A single Junctional complex consists of
a tight junction, an intermediate junction, and a desmosome,
with the tight junction closest to the surface.