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The Cell Theory
Some Random Cell Facts
• The average human being is composed of
around 100 Trillion individual cells!!!
• It would take as many as 50 cells to cover
the area of a dot on the letter “i”
Discovery of Cells
• 1665- English Scientist, Robert Hooke, discovered cells
while looking at a thin slice of cork.
• He described the cells as tiny boxes or a honeycomb
• He thought that cells only existed in plants and fungi
Anton van Leuwenhoek
• 1673- Used a handmade microscope to observe pond
scum & discovered single-celled organisms
• He called them “animalcules”
• He also observed blood cells from fish, birds, frogs,
dogs, and humans
• Therefore, it was known that cells are found in animals
as well as plants
• 1838- German Botanist, Matthias Schleiden,
concluded that all plant parts are made of cells
• 1839- German physiologist, Theodor Schwann, who
was a close friend of Schleiden, stated that all
animal tissues are composed of cells.
Development of Cell Theory
• 1858- Rudolf Virchow, German physician, after
extensive study, concluded that cells must arise
from preexisting cells.
The Cell Theory Complete
• The 3 Basic Components of the Cell Theory
were now complete:
• 1. All organisms are composed of one or more cells.
• 2. The cell is the basic unit of life in all living things.
• 3. All cells are produced by the division of
preexisting cells.
2 Basic Types of Cells
1) Prokaryotic examples ???
2) Eukaroytic examples????
Plasma membrane
• Structure
– Main component is
phospholipids that are
arranged in a double
layer (bilayer)
– Has scattered proteins
within the
phospholipids
Function of the Plasma
Membrane
• Regulate what gets
into or leaves the
cell
• Structure
Nucleus
– Surrounded by a
double membrane
– This “nuclear
membrane” has pores
• Function
– Holds the
chromosomes
(DNA) and the
nucleolus
Nuclear envelope
• Double layer of
membrane
• Has pores
• Surrounds the
nucleus
• Regulates what
goes into and out
of the nucleus
Chromosomes
• Structure
– String-like
structures in the
nucleus made of
DNA and protein
• Function
– Contain your genes
Nucleolus
• Structure
– Small dark
structure in the
nucleus
• Function
– Produce ribosomes
Ribosomes
• Small structures
(NOT made of
membrane)
• Make proteins
Central Vacuole
• Structure
– LARGE sac made
of membrane
– Found in center of
plant cells
• Function
– Stores chemicals
and water
Smooth Endoplasmic Reticulum
• Structure
– Canals and tubes
made of membrane
• Function
– Makes lipids (oils,
phospholipids,
steroids)
– Detoxifies poisons
Rough Endoplasmic Reticulum
• Structure
– Canals and tubes
made of membrane
– Have ribosomes
attached to the
outside
• Function
– Transport materials
in the cell
– Make proteins
(those exported
from the cell, those
found on the
plasma membrane,
those found in
lysosomes)
Golgi Apparatus
• Structure
• Function
– Stacks of membrane
– Chemically modifies
sacs
substances
– has a receiving end (from – Packages material for
ER) and a shipping end
transport out of the
cell or to other
locations within the
cell
Vesicles
• Structure
– Small membrane
“bubbles” that bud
off the ER or Golgi
• Functions
– Transport materials
to new locations
Lysosomes
• Structure
– Sacs of membrane
that contain
hydrolytic enzymes
– -found mostly in
animal cells
• Function
– Use enzymes to
break down old
organelles
– In white blood cells
are used to destroy
bacteria
Mitochondria
• Structure
– Surrounded by a
double membrane
• Folds found on the
inside
• Function
– Cellular Respiration
• Converts energy in
sugars into the
energy of ATP
molecule
Chloroplasts
• Structure
– Surrounded by a
double layer of
membrane
• Disks found inside
• Function
– Convert solar
energy into
chemical energy
(food)
– Site of
photosynthesis
Perioxisome
• Structure
– Small membranous
sac
• Function
– Some reactions
occurring here
produce H2O2 (toxic)
• So, it also contains an
enzyme (catalase) that
converts this to water
and oxygen gas
• Structure
Cell Wall
– Found outside the
plasma membrane
– Plant  made of
cellulose
• Function
– Give support to
certain cells (plant)
– Does NOT
determine what can
get into/out of the
cell
Cytoskeleton
• Structure
• Made of protein fibers
– Microtubules
• Hollow tube
– Microfilaments
• Small rods
– Intermediate filaments
• Function
– Give the cell shape
– Help to move
organelles around the
cell
Fig. 4-17
Nucleus
Nucleus
Actin subunit
Fibrous subunits
7 nm
Microfilament
Tubulin subunit
10 nm
25 nm
Intermediate filament
Microtubule
Centrioles
• Structure
– Made of rings of
microtubules
– Found in pairs that
lie at right angles
• Look similar to a
pair of barrels
• Function
– Found in animal
cells
– Help organize the
tubulin required for
cell division
Cilia
• Structure
– Microtubules that
extend from the cell
(still covered by the
plasma membrane)
– Short and many of
them
• Function
– In single-celled
organisms, they can
move the organism
from place to place
– If anchored in place,
can set up a current,
moving fluid across
the surface of a cell
Fig. 4-1c
Fig. 4-18a
Cilia
http://www.youtube.com/watch?v=YHb2Ja
ujIPo&feature=related&safety_mode=true&
persist_safety_mode=1
Flagella
Structure
• Same as cilia, but
are longer and there
are just a few of
them
• Prokaryotes also
have them
– Not made of
microtubules
Function
• Move the cell within its
environment
How large can cells get?
-depends on how efficiently they can get nutrients in
and wastes out
10 µm
30 µm
30 µm
Surface area
of one large cube
= 5,400 µm2
10 µm
Total surface area
of 27 small cubes
= 16,200 µm2
Fig. 4-20
Glycoprotein
complex with long
polysaccharide
EXTRACELLULAR FLUID
Collagen fiber
Connecting
glycoprotein
Integrin
Plasma
membrane
Microfilaments
CYTOPLASM
Fig. 4-21
Tight junctions
Anchoring junction
Gap junctions
Plasma membranes
of adjacent cells
Extracellular matrix
Fig. 4-22
Walls
of two
adjacent
plant cells
Vacuole
Plasmodesmata
cell wall
Cytoplasm
Plasma membrane
B
C
D
A
CD (CONTAINING
DIGESTIVE
ENZYMES)
E
BE
AB
BD
AC
BC
AE
AD
BE
A
BD
BC
B
AE
C
AD
AC
D
AB
E
D
B
C
A