Download Basics of biological cells - Department of Mechanical Engineering

DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
Introduction to the Cell
In this discussion class we are looking at cells, the basic units of life. Even though cells are the basic units, they are still organized and
made of smaller structures.
The basic properties of a cell are,
• Cells are highly complex and organized.
The more complex a structure, the greater the number of parts that must be in their proper place, the less tolerance of errors in the
nature and interactions of the parts and more control and regulation must be exerted to maintain the system.
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•
Cells possess a genetic program and the means to use it.
Organisms are built according to the genetic information encoded in a collection of genes. This vast amount of information is
packaged into a set of chromosomes that occupy the space of a cell nucleus. The molecular structure of genes allows for changes
in genetic information that leads to variation among individuals which forms the basis of biological evolution.
•
Cells are capable of producing more of themselves
Just like the individual organisms are reproduced by organisms, even cells are reproduced to individual cells. Cells reproduce by
division, a process in which the contents of a mother cell are distributed into two daughter cells. Prior to division the genetic
material is faithfully duplicated and each daughter cell receives a complete and equal share of genetic information.
•
Cells acquire and utilize energy.
To develop and maintain the complexity of the cell, it needs an input of energy. All of the energy required on the earth surface
arrives in the form of electromagnetic radiation from the sun. Light energy is converted by photosynthesis (due to chloroplasts in
the plant cell) into chemical energy that is stored in energy rich carbohydrates, such as sucrose or starch. Once in a cell, the
glucose is disassembled in such a way that its energy content can be stored in a readily available form (usually as ATP) that is
later put to use in running all of the cell’s myriad energy-requiring activities.
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
Figure 1: The figure shows the helical structure of chloroplast in Spirogyra
•
Cells carry out a variety of chemical reactions.
Cells function like miniaturized chemical plants. Even the simplest bacterial cell is capable of hundreds of different chemical
transformations, none of which occurs at any significant rate in the inanimate world. Virtually all chemical changes that take
place in cells require enzymes-molecules that greatly increase the rate at which a chemical reaction occurs. The sum total of the
chemical reactions in a cell represents that cell’s metabolism.
•
Cells engage in numerous mechanical activities.
Cells are sites of bustling activity. Materials are transported from place to place, structures are assembled then rapidly
disassembled, and, in many cases the entire cell moves itself from one site to another. These types of activities are based on
dynamic, mechanical changes within the cells, most of which are initiated by changes in the shape of “motor” proteins. Motor
proteins are just one of the molecular machines employed by cells to carry out mechanical activities.
Cells are able to respond to stimuli.
Some cells respond to stimuli in obvious ways: a single celled protest, for example, moves away from an object in its path or
moves toward a source of nutrients. Cells within a multicellular plant or animal respond to stimuli less obviously. Most cells are
covered with receptors that interact with substances in the environment in highly specific ways. Cells possess receptors to
hormones, growth factors, extracellular materials, as well as to substances on the surfaces of other cells. A cell’s receptors
•
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
provide pathways though which external agents can evoke specific responses in target cells. Cells may respond to specific stimuli
by altering their metabolic activities, preparing for cell division, moving from one place to another, or even suicide.
•
Cells are capable of self-regulation.
The importance of a cell’s regulatory mechanisms becomes most evident when they break down. For example, failure of a cell to
correct a mistake when it duplicates its DNA may result in a debilitating mutation, or a breakdown in a cell’s growth control can
transform the cell into a cancer cell with capability of destroying the whole organism.
•
Cells evolve.
If you were to observe the bacterial cell living in the human respiratory tract and the cell lining the intestinal tract, you would be
struck by the differences between the two cells. Yet, both have evolved from a common ancestral cell that lived more than three
billon years ago. The structures, which are shared by these two distantly related cells such as the plasma membrane and the
ribosome, must have been present in the ancestral cell. Evolution is not simply an event of the past, but an ongoing process that
continues to modify the properties of cells that will be present in organisms that have yet to appear.
CELLS ARE FUNDAMENTALLY DIVIDED INTO 2 CLASSES.
Once the electron microscope became widely available, biologists ere able to examine the internal structure of a wide variety of cells. It
became apparent from these studies that there were two basic classes of cells- prokaryotic and eukaryotic- distinguished by their size and
the internal structures, or organelles, they contain. The existence of two distinct classes of cells, without any known intermediates,
represents one of the most fundamental evolutionary separations in the biological world. The structurally simpler, prokaryotic cells
include bacteria, whereas the structurally more complex eukaryotic cells include protists, fungi, plants and animals.
STRUCTURAL ORGANISATION OF THE CELL
Just as the body is made of organs, each having different shapes and functions, so the cells are made of organelles, which also have their
own shape and function. We will be studying the following organelles:
1. Centrioles
2. Cilia and Flagella
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
3. Endoplasmic reticulum
4. Endosomes
5. Golgi apparatus
6. Intermediate filaments
7. Lysosomes
8. Microfilaments
9. Microtubules
10. Mitochondria
11. Nucleus
12. Peroxisomes
13. Plasma membrane.
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
The cell can be compared to a factory. Like a factory, it makes products that need to be packaged and delivered to places inside or
outside the cell. It needs energy to make its products, and blueprints to work from. Our goal in this discussion will be to understand how
these organelles work together to help the cell do its work.
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Figure 2: The Figure shows the anatomy of animal cell (http://micro.magnet.fsu.edu/cells/animals/animalmodel.html)
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
Table 1: The table gives description of the components and their function
S.
No
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Components
Description
Function
Special
Remarks
Centrioles
Centrioles are selfreplicating organelles
made up of nine
bundles of
microtubules
Centrioles aid in cell
division or mitosis of
animal cells
Present only in
animal cells
2
Cilia and
Flagella
Mobile cellular
appendages
Cilia and flagella help
to move a cell or
group of cells or to
help transport fluid or
materials past them
Can cause
disease due to
malfunction.
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Structure
Example:
Bronchitis,
Kartagener's
syndrom
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
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The
Endoplasmic
Reticulum
The endoplasmic
reticulum is a network
of sacs
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Endosomes
Endosomes are
The endoplasmic
reticulum produces
and transports
chemical compounds
for use inside and
outside of the cell.
31/8/2006
Endoplasmic
reticulum helps
organelles to
share
information.
small sac or cyst
covered with
membranes
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
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The Golgi
Apparatus
Composes a series of
five to eight cupshaped, membranecovered sacs called
cisternae
Distributes the cell's
chemical products
Found in both
plant and animal
cells
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Intermediate
Filaments
Intermediate
filaments are a very
broad class of fibrous
proteins
Mutations in
intermediate
filament genes
can cause
uncommon
diseases.
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Lysosomes
Lysosomes are
spherical organelles
covered by a single
layer membrane
With size of 8 to 12
nm, intermediate
filaments function as
tension-bearing
elements to help
maintain cell shape
and rigidity, and serve
to anchor in place
several organelles.
Lysosomes break
down cellular waste
products, fats,
carbohydrates,
proteins, and other
macromolecules into
simple compounds,
which are transferred
back into the
cytoplasm as new
cell-building materials
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Present in large
numbers in white
blood cells
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
8
Microfilament
s
Microfilaments are
solid rods made of
globular proteins
called actin
Microfilaments are 5
to 9 nm in diameter
and can bear large
amounts of tension.
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Microtubules
Microtubules are
straight, hollow
cylinders found
throughout the
cytoplasm of all
eukaryotic cells (Not
present in
prokaryotes)
Microtubules, about
25 nanometers in
diameter, form part of
the cytoskeleton that
gives structure and
shape to a cell.
31/8/2006
Along with
myosin,
microfilaments
help to generate
the forces used
in cellular
contraction and
basic cell
movements
Eukaryotic cells
depend upon the
microtubules and
other
cytoskeletal
filaments to
maintain their
structure.
To survive many
plants produce
natural toxins to
help build the
microtubules
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
10
Mitochondria
Mitochondria are rodshaped organelles
Mitochondria are
power generators of
the cell, converting
oxygen and nutrients
into adenosine
triphosphate (ATP)
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The Cell
Nucleus
The nucleus is a
highly specialized
organelle enclosing
the nucleoplasm,
chromatin and
nucleioli
The nucleus
coordinates the cell's
activities (growth,
intermediary
metabolism, protein
synthesis, and
reproduction (cell
division).
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31/8/2006
Mitochondrial
DNA is also used
in forensic
science Causes
genetic
diseases, such
as Alzheimer's
disease and
diabetes.
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
12
Peroxisomes
Peroximes are
Microbodies(group of
organelles) which are
found in the
cytoplasm of almost
all cells. They are
roughly spherical,
and bound by a
single membrane
Peroxisomes contain
a variety of enzymes,
which function
together to get rid of
toxic substances, in
particular, hydrogen
peroxide (a common
byproduct of cellular
metabolism).
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Plasma
Membrane
A plasma membrane
encloses all living
cells, prokaryotic and
eukaryotic.
The plasma
membrane controls
transfer of molecules
in and out of the cell.
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31/8/2006
Zellweger
syndrome (lack
of enough
peroxisomes),
has no cure and
causes death
within the first
year of life.
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
14
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Ribosomes
Ribosomes are tiny
organelles(60 %
ribosomal RNA
(rRNA) and 40%
protein)
31/8/2006
Protein synthesis
Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc
DISCUSSION CLASS 1: Introduction to the Cell.
Bio Mechanics Discussion Group, ME DEPARTMENT
IISc
31/8/2006
Figure 3: The figure shows generalized overview of a plant cell and an animal cell
BIBLIOGRAPHY
1. GERALD KARP. Cell and Molecular Biology-Concepts and Experiments. 4th edition. John Wiley and Sons. 2005.
2. The description of the organelles above has been adapted from http://micro.magnet.fsu.edu/cells/animalcell.html.
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Ashwini.B.M, Project Assistant
Force Microscopy Lab
ME Department, IISc