Transcript cell structure and function 2010

2.1 A Background to Cell
Structure
Cell Theory
• 1. All known
living things are
made up of cells.
• 2. The cell is
structural &
functional unit of
all living things.
• 3. All cells come
from pre-existing
cells by division.
Modern cell theory adds the
following:
• Cells contains hereditary information
which is passed from cell to cell during cell
division
• All cells are basically the same in
chemical composition.
• All energy flow (metabolism &
biochemistry) of life occurs within cells.
Cell Theory
• The discovery of
cells and their
structure is linked
to the
development of
the magnifying
lenses, particularly
the microscope.
Robert Hooke
• The first description of
the cell is generally
attributed to Robert
Hooke (1635−1702)
• He described the
microscopic units that
made up the structure
of a slice of cork and
coined the term
"cells" to refer to
these units.
Antoni van Leeuwenhoek
(1632−1723).
• This Dutch microscopist
made over 500
microscopes.
• He observed moving
particles in his
microscopes and
described the
microorganisms that he
saw in great detail.
• He is considered the
father of microbiology.
Rudolf Virchow
• In 1855, Rudolf
Virchow proposed an
important extension of
cell theory.
• "All living cells arise
from pre-existing
cells".
• This statement has
become what is
known as the
"Biogenic law".
How do new cells arise?
• Until the 18th century, many scientists
believed in spontaneous generation. This was
the idea that non-living objects can give rise
to living organisms.
• It was common “knowledge” that simple
organisms like worms, beetles, frogs, amd
salamanders could come from dust, mud,
etc., and food left out, quickly “swarmed” with
life.
• Jan Baptista van Helmont’s recipe for mice:
– Place a dirty shirt or some rags in an open pot or
barrel containing a few grains of wheat or some
wheat bran, and in 21 days, mice will appear.
There will be adult males and females present,
and they will be capable of mating and
reproducing more mice.
Franscesco Redi
• In 1668, he did an experiment with flies and
wide-mouth jars containing meat.
• This was a true scientific experiment
• In the control group of jars, flies were seen
entering the jars. Later, maggots, then more
flies were seen on the meat.
• In the gauze-covered jars, no flies were seen in
the jars, but were observed around and on the
gauze, and later a few maggots were seen on
the meat.
• In the sealed jars, no maggots or flies were
ever seen on the meat.
Conclusion(s): Only flies can make more flies.
• In the uncovered jars, flies entered and laid
eggs on the meat. Maggots hatched from
these eggs and grew into more adult flies.
• Adult flies laid eggs on the gauze on the
gauze-covered jars. These eggs or the
maggots from them dropped through the
gauze onto the meat.
• In the sealed jars, no flies, maggots, nor
eggs could enter, thus none were seen in
those jars. Maggots arose only where flies
were able to lay eggs.
This experiment disproved the idea of
spontaneous generation for larger
organisms
Louis Pasteur-1861
Pasteur’s conclusion
• There is no life force in air, and organisms
do not arise by spontaneous generation in
this manner.
• “Life is a germ, and a germ is Life. Never
will the doctrine of spontaneous
generation recover from the mortal blow of
this simple experiment.”
Cell Structures
Compare prokaryotic cells
and eukaryotic cells:
How are they similar?
How are they different?
Cell structure and function
ANIMAL CELL
Plant Cell
Cell membrane
Structure: Phospholipid bilayer with embedded
proteins
Function:
• Acts as a barrier
between the inside of
the cell and the
outside environment.
• Import and export of
substances from the
cell
• Cell recognition: self
vs non-self.
• Communications/
connections with
other cells
Cytoplasm
CYTOPLASM
• Consists of all the contents between the nucleus and the
cell membrane.
• Made up of the cytosol and organelles such as
mitochondria and ribosomes.
• The fluid part of the cytoplasm is the Cytosol. It is clear
in color and has a gel-like appearance. It is composed
mainly of water and also contains enzymes, salts, and
various organic molecules.
• Also located within the cytoplasm is the cytoskeleton, a
network of fibers that help the cell maintain its shape and
give it support.
• Function: The cytoplasm helps to move materials
around the cell and also dissolves cellular waste.
Nucleus
• The nucleus is the largest organelle in a cell.
It directs all activity in the cell.
• It also controls the growth and reproduction of
the cell.
• It is the location for most of the nucleic acids
(DNA and RNA) a cell makes.
• The nucleus controls the shape and features
of the cell.
• Double membrane with pores
• The nucleolus is an
area of the nucleus
where ribosomes
are constructed.
• It is not membrane
bound
• It is rich is proteins
and nucleic acids,
so it appears darker.
• There may be more
than one nucleolus
• Nuclear
pores: allow
for passage of
materials
between
cytoplasm
and
nucleoplasm
Cytoplasmic Organelles
Mitochondria
• Site of cellular respiration:
provide the energy a cell
needs to carry out its
activities
• Membrane-bound
organelles, and like the
nucleus have a double
membrane.
• They are about the size of
bacteria but may have
different shapes
depending on the cell type.
• The outer membrane is fairly smooth.
• The inner membrane is highly convoluted,
forming folds called cristae.
• The cristae greatly increase the inner
membrane's surface area.
• It is on these cristae that food (sugar) is
combined with oxygen to produce ATP the primary energy source for the cell.
Endoplasmic Reticulum
• Comes in two forms:
Rough ER and
Smooth ER
• Rough ER: - sheets of unit membrane
with ribosomes on the outside
- forms a tubular network
throughout the cell
• Function - transports chemicals between
cells and within cells
- provides a large surface area
for protein synthesis
• Smooth ER: functions in the synthesis
and transport of lipids (fats)
Ribosomes
• Ribosomes are molecular machines that make all
the proteins found in every living thing on the
planet.
• They are made in the nucleolus
• They are found in the cytoplasm and attached to
the ER
Golgi Apparatus
• AKA Golgi Body, Golgi
Complex
• The Golgi is principally
responsible for
directing molecular
traffic in the cell
• Molecules are
modified and
packaged into vesicles
for transport
Vacuoles
• Compartments which are filled with water
and various molecules in solution.
(dissolved salts, minerals, ions, proteins)
• They may contain solids which have been
engulfed.
• In plants: usually one large vacuole
• In animals: many small vacuoles (look like
vesicles)
Centrioles
• Found only in animal cells
• Paired organelles usually located together
near the nucleus
• The centrioles are positioned so that they
are at right angles to each other
• Function: form the spindle fibers in mitosis
and meiosis- cell reproduction.
Lysosomes
• Double membrane sacs
that contain chemicals to
break down large food
particles into smaller
ones
• Break down old cell parts
and release the
substances to be used
again.
• Keeps the harsh
chemicals from escaping
and breaking down the
rest of the cell
Cell wall
• Plant cell walls are
made of cellulose. It
is a polysaccharide
that forms long
straight chains and
can be woven into
fibers.
• The cell wall is
structurally strong,
but it is porous.
Chloropasts
•
•
•
•
•
Found only in plant cells
They are the site of photosynthesis
Carbon dioxide + water
glucose + oxygen
6 CO2 + 6 H2O
C6H12O6 + 6 O2
This is the most important chemical reaction
on the planet…it takes the energy from the
sun and changes it to chemical energy that
can be used by living things.
Endosymbiosis Theory