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The Cell
Plant and Animal Cells
• Every living thing on Earth is
composed of cells.
• The term cell was first used by
Robert Hooke to describe the
chambers found in a piece of cork.
• Cells are the smallest living unit
of which all organisms are
composed
• Cells are classified in many ways
• One of the most important
classification methods is by
complexity.
Cell Complexity
• Simple cells are termed prokaryotic.
• Complex cells are termed eukaryotic.
• On what basis do we classify cells as
simple or complex?
Prokaryotic and Eukaryotic Cells
There are two general classes of
cells: prokaryotic and eukaryotic.
The evolution of prokaryotic cells
preceded that of eukaryotic cells by
2 billion years.
The Cell Timeline
• The major similarities between the two types
of cells (prokaryote and eukaryote) are:
• 1.They both have DNA as their genetic
material.
• 2.They are both membrane bound.
• 3.They both have ribosomes .
• 4.They have similar basic metabolism .
• 5.They are both amazingly diverse in forms.
• The major and extremely
significant differences between
prokaryotes and eukaryotes are:
• eukaryotes have a nucleus while
prokaryotes do not.
• eukaryotes have membrane-bound
organelles prokaryotes do not.
• The DNA of prokaryotes floats freely
around the cell; the DNA of
eukaryotes is held within its nucleus.
• The organelles of eukaryotes allow
them to exhibit much higher levels of
intracellular division of labor than is
possible in prokaryotic cells.
• Eukaryotic cells are, on average,
ten times the size of prokaryotic
cells.
• The DNA of eukaryotes is much
more complex and therefore much
more extensive than the DNA of
prokaryotes.
• Prokaryotes have a cell wall
composed of peptidoglycan, a single
large polymer of amino acids and
sugar.
• Many types of eukaryotic cells also
have cell walls, but none made of
peptidoglycan.
The size of cells
• prokaryotes can vary in size from
0.25 x 1.2 m to 1.5 x 4 m
• average size (E. coli 1 x 3 m)
• eukaryotes are generally larger
• – 200 m in diameter
Prokaryotic Cell
• There are many types of eukaryotic
cells but the two most common types
are plant and animal cells
• A eukaryotic cell may be divided
into major zones.
• These zones are man made divisions
used to facilitate the study of cells.
• Animal cells are the cells found in
animals. You are made up of
trillions of animal cells.
• There are two basic zones of an
animal cell:
• Nucleus
• Cytoplasm
• Cytoplasm:
• Cytoplasm is the watery-like part
of the cell where the action takes
place. It is where the nutrients are
used.
• Most chemical activity occurs here
• Nucleus:
• The nucleus is the brain of the cell.
• It controls the cell, and tells it
what to do.
• The nucleus also contains the DNA
which is like a blueprint. A
blueprint is a plan that people use
when they build.
Organelles
• In each zone (nucleus or cytoplasm) of an
animal cell (or plant cell) are specialized
units called organelles.
• Organelles perform specialized functions
• Most organelles are common to both plant
and animal cells but a few are only found
in one or the other type.
What organelles are inside the
cytoplasm:
• Organelles in 'higher' eukaryote cells:
• Endoplasmic Reticulum (ER) -This
organelle resembles a system of
parallel membranes similar to a
radiator core.
• The ER is important in protein
synthesis.
• It is also a transport network for
molecules destined for specific
locations within the cell.
• Helps give the cell its shape
There are two types:
Smooth ER - Does not have
ribosomes on its surface and
tends to be more of a tubular
network.
• Rough ER - has ribosomes on its
surface , and tends to be more in
'sheets'. Very common in the cell and
easily seen with an electron
microscope.
• Ribosomes –are small
spherical structures found in
the cell cytoplasm.
• These are the most common
organelle found in cells.
• Ribosomes are produced in the
nucleus of a cell but are
released in to the cytoplasm
where they function in protein
production.
• Half of the ribosomes are
located on the surface of the
Endoplasmic Reticulum.
• The other half are 'free' in the
cytosol or cytoplasm of the
cell.
Cell Theory:
• All organisms are made up of one or more
cells.
• The cell is the basic unit of organization
of all organisms.
• All cells come from other cells all ready
in existence.
What are cells made of?
Cells are mostly water. The rest of the
present molecules are:
•protein
•nucleic acid
•carbohydrate
•lipid
•other
What are cells made of?
By elements, a cell is composed of:
• 60% hydrogen
• 25% oxygen
• 10% carbon
• 5%
nitrogen
• Microtubules - made from tubulin,
and make up centrioles,cilia,etc.
• Cytoskeleton - Microtubules, actin
and intermediate filaments.
Mitochondria
• Second largest organelle in the cell.
• Has its own unique genetic
structure.
• Double-layered outer membrane
with inner folds called cristae.
• Energy-producing chemical
reactions take place on cristae
• The number of mitochondria in cells
is dependent on the type of cell.
• Cells with higher energy requirements
have more mitochondria than cells
with lower energy needs.
• Cells with higher numbers of
cristae also produce more energy
than cells with fewer folds or
cristae.
• Mitochondria are the site at which
cellular respiration takes place.
Golgi Apparatus
The golgi body is responsible for
packaging proteins for the cell.
Once the proteins are produced by the
rough E.R.they pass into the sack like
cisternae ( vesicles) that are the main part
of the golgi body.
These proteins are then
squeezed off into little
spheres( lysosomes) which
drift off into the cytoplasm.
What's a Golgi?
• "The golgi apparatus is a part
(organelle) of non-bacterial
(eukaryotic) cells that is the site of
several cell functions, including:
• synthesis of carbohydrates,
• secretion of proteins to the
outside of the cell,
• transport of cell wastes to the
digestive mechanism of the
cell.
• The golgi appartus has been
described in many ways but
commonly it is described as
looking a little bit like a stack
of pancakes viewed from the
side."
Plastids
• Plastids are a group of
organelles found primarily in
plant cells.
• Plastids which have color are
associated with photosynthesis
and exclusively found in plants
•The most common of these
plastids are chloroplasts
which contain the green
pigment chlorophyll.
• Other pigmment containing
plastids are called
chromoplasts.
• Some chromoplasts contain the
following pigments:
•Carotene pigments which
are responsible for the
orange and red coloration in
flowers and fruits.
•Xanthrophylls contain a
yellow pigmment.
• Plastids which store starches and
other carbohydrates are found in cells
• Amyloplast, occur in plant tissues that
do not turn green - a common form,
and are used to store starch.
• Leucoplasts are used to store glucose
in animal cells.
Lysosomes
• Lysosomes are oval structures that
contain a digestive enzyme.
• These organelles serve to defend
the cell from pathogenic
microorganisms.
• In addition lysosomes are used to
breakdown food substance that are
trapped in the vacuoles.
• If the contents of a lysosome are
accidentally opened the digestive
enzymes will destroy the cell. This
explains the nickname “suicide sac” .
Plasma Membrane
• Outer membrane of cell that controls
cellular traffic
• Contains proteins that span through the
membrane and allow passage of materials
• Proteins are surrounded by a phospholipid
bi-layer.
A phospholipid bilayer (in water) cannot have a
free edge
All bilayers form closed compartments
• Cell membranes are made up of
phospholipid molecules (fats) with
various large globular protein
molecules suspended in them.
• The lipid bi-layer is formed because
of the chemical structure of a lipid.
All biological membranes are bilayers of
phospholipid.
The proteins in each type of membrane give it its
unique properties.
• Since cells are constantly in water,
the lipids form a double layer, with
the heads towards the water and
the tails inside so that they can stay
away from the water.
• These bi-layers have proteins
scattered about in them.
• Sometimes carbohydrates (sugars)
are attached to these proteins.
• ( Carrier molecules)
• A selectively permeable (sometimes
called semi-permeable) membrane
allows some molecules across but
not others.
Plasma Membrane
Electron Microscopic View of
the Cell Membrane
Plasma Membrane Structure
OSMOSIS
• When water enters or leaves a
cell the process is called
osmosis.
Osmosis
Diffusion
of water through a semipermeable membrane from an area
where the water molecules are
more concentrated to an area
where the water molecules are less
concentrated
• This means that water would cross
a selectively permeable membrane
from a dilute solution (less
dissolved in it) to a concentrated
solution (more dissolved in it).
Solutions
 exposed
to an isotonic solution cells
will neither lose nor gain water
 exposed to a hypotonic solution cells
will swell due to the uptake of water
by the cell
 exposed to a hypertonic solution cells
will shrink due to the loss of water
from the cell
Solutions
–Hypotonic - solution with lower
solute concentration.
–Hypertonic - solution with
higher solute concentration.
–Isotonic - both solutions have
same concentration
•
DIFFUSION
Diffusion is the movement of gases
from a high concentration of
molecules to a low concentration of
molecules.
• Molecules can diffuse across
membranes through the pores in the
lipid bilayer.
Facilitated diffusion (or facilitated
transport)
• Facilitated diffusion (or facilitated
transport) is a process of diffusion, a
form of passive transport made possible
by transport proteins.
• Facilitated diffusion is the spontaneous
passage of molecules or ions across a
biological membrane passing through specific
transmembrane transport proteins.
• Small uncharged molecules can easily
diffuse across cell membranes.
• However, due to the hydrophobic nature
of the lipids that make up cell
membranes, water-soluble molecules and
ions cannot do so; instead, they are helped
across by transport proteins.
PHOSPHOLIPIDS...
• The heads of the PHOSPHOLIPIDS are
composed of glycerol and a phosphate
group and like to dissolve in water.
• Phospholipids are polar molecules
• These molecules have water tolerant area
called water-loving (or hydrophilic)
molecules.
• The tails of the PHOSPHOLIPIDS are
mostly fatty acids made up of long
carbon and hydrogen chains.
• Carbon and hydrogen chains are not
polar and do not like to dissolve in
water. Molecules that do not easily
dissolve in water are called waterhating (or hydrophobic) molecules.
Active transport
• Active transport requires energy.
• Types of actice transport include:
• Carrier molecules
• Endo and phagocytosis
Pinocytosis and Phagocytosis
• The cell membrane occasionally
invaginates or indents to capture
extracellular fluids in a process called
pinocytosis.
• The invagination becomes pinched off
to form a pinocytic vesicle.
• Taking up of solid particles is
called phagocytosis. Both
pinocytosis and phagocytosis are
types of endocytosis, the prefix
meaning in.
• Cells may expel liquids or solids
by the reverse process, exocytosis,
the prefix meaning out.
• The transport vesicle fuses
with the cell membrane and
opens to expel the contents
from the cell.
Plastids
• The most obvious difference
between plant cells and other
eukaryotic cells is that cells of
most plants contain unique
organelles called plastids, which
include chloroplasts, chromoplasts,
and amyloplasts.
• Chloroplasts contain a special
pigment known as
chlorophyll, which absorbs
sunlight energy.
• This sunlight energy is then
converted to another form of
energy utilizable by other
living organisms.
• This energy conversion process is
referred to as photosynthesis,
which combines carbon dioxide
from the air and hydrogen from
water to form sugars and other
organic compounds.
• Oxygen is returned to the
atmosphere as a by product.
• Chromoplasts synthesize and store
pigments such as yellow
xanthophylls, orange carotenes,
and various red pigments.
• Leucoplasts are organelles where
animal cells store starches,
proteins, and lipids.
Chloroplasts
• Chloroplasts are of central importance to the plant
cell.
• They contain chlorophyll which fundamentally
converts sunlight into fuel that the mitochondria
use for energy, known as photosynthesis.
• Chloroplasts and mitochondria are
closely linked to one another, as
well as very similar in structure to
one another.
The Nucleus
• The cell nucleus is a remarkable
structure because it forms the package
for our genes and their controlling
factors. It functions to:
• Store the genetic information for the
cell on the genes of chromosomes
• Controls the activity of cell organelles
by regulatory factors released through
the nuclear pores
• Produces messenger Ribonucleic acid
or mRNA
• Produce ribosomes in the nucleolus
• Organize the uncoiling of DNA for
cell division,
• Surrounding the nucleus is the nuclear
envelope. It is a double membrane
that separates the nucleus from the
rest of the cell.
• At some points along the nuclear
envelope the inner and outer
membrane are joined and they form
very small pores..
• Because of these pores, the nuclear
envelope, like the cell membrane,
is selectively permeable.
• During cell division, the
chromosomes shorten by coiling
and become thick enough to be
clearly visible when they are
stained
• It allows the contents of the nucleus, the
nucleoplasm, to have a different chemical
composition than the rest of the cell.
• Much of the nucleoplasm consists of
chromatin, various proteins bound to
DNA.
• Usually the chromatin appears as long,
thin threads called chromosomes.
The most visible structure in the nucleus is
the nucleolus, which functions in the
production of ribosomes.
Sometimes, there are two or more nucleoli;
the number depends on the species and
stage in the cell's reproductive cycle.
• The nucleus also controls the protein
synthesis in the cytoplasm. It sends
molecular messengers in the from of RNA.
Cell wall
• The CELL WALL is a very complex
structure. This structure was first
discovered some time in the seventeenthcentury, by a scientist named Robert
Hooke.
• Hooke cut a thin slice of cork and
examined it carefully through a primitive
microscope.
• Unfortunately,
these cork cells
were long dead,
and the only
remaining structure
were the cell walls.
• The main reason for the cell walls being
the only organelle left is that it is made up
of cellulose.
• Cellulose is a very strong structure that
allows for structural support. This is ideal
for the cell wall, which function is to
prevent water loss from inside the cell,
and to provide structural strength to resist
dehydration.
• Cell walls are actually composed of three
layers, the Primary cell wall, the
Secondary cell wall, and the Middle
lamella.
• These three layers give an added support
and protection to the plant cell, even long
after it has died.
• The cell wall is a non-living structure
ranging anywhere from 0.1 to several mm
thick.
The Primary Cell Wall
• The primary cell wall is the first
section of the wall to be laid down by
the plant cell.
• This primary cell wall is also able to
expand as the cell grows in size.
• This primary cell wall may be
impregnated with additional materials
(cutin and suberin).
• These materials form a waxy cuticle,
this cuticle is impermiable many types
of invading particles.
The Secondary Cell Wall
• The secondary cell wall is found
between the cell membrane and the
primary cell wall.
• The secondary cell wall has a strong
and durable matrix that gives the plant
cell support and protection.
• However some plants lack the need for a
secondary cell wall.
• Such is the case of grasses and other
flexible plants instead of the cell walls
having three layers it only contains two,
the primary cell wall and the middle
lamella.
• Wood or other non-flexible plants would
be an example of the types of plants that
would need a secondary cell wall in the
cell.
The Middle Lamella
• The primary cell walls of neighboring
cells are not in direct contact with other
cells.
• They are are separated by a layer called
the Middle Lamella, a layer of a jellylike
polysaccharide called pectin.
• The middle lamella sticks the cells
together, and acts like a bonding agent or
glue. This is so that plant cells can stay
more closely together.
Cell Wall Diagram