Download The Cell - Walton High

Introduction to the Cell
Introduction
• Every living thing-from the tiniest
bacterium to the largest whale-are made
of one or more cells.
• Before the seventeenth century, no one
knew that cells existed.
• Most cells are too small to be seen with
the unaided eye.
• Cells were not discovered until after the
invention of the microscope in the early
seventeenth century.
The Microscope
• One of the first
microscopes was made
by the Dutch drapery
store owner Anton von
Leewenhoek (16321723).
• With his hand-held
microscope,
Leewenhoek became
the first person to
observe and describe
microscopic organisms
and living cells.
• Leeuwenhoek is known to
have made over 500
"microscopes," of which
fewer than ten have
survived to the present day.
In basic design, probably all
of Leeuwenhoek's
instruments -- certainly all
the ones that are known -were simply powerful
magnifying glasses, not
compound microscopes of
the type used today.
• In 1665, the English
Scientist Robert Hooke
(1635-1703) used a
microscope to examine a
thin slice of cork and
described it as
consisting of "a great
many little boxes". It
was after his
observation that Hook
called what he saw
"Cells". They looked like
"little boxes" and
reminded him of the
small rooms in which
monks lived, so he called
the "Cells".
•
The invention of the microscope lead to
several important statements:
• In 1838, German Botanist Matthias Schleiden
studied a variety of PLANTS and concluded that
all PLANTS "ARE COMPOSED OF CELLS".
• The next year, German Zoologist Theodor
Schwann reported that ANIMALS are also made
of CELLS and proposed a cellular basis for all
life.
• In 1855- 1858, German Physician Rudolf Virchow
induced that "THE ANIMAL ARISES ONLY
FROM AN ANIMAL AND THE PLANT ONLY
FROM A PLANT" OR " THAT CELLS ONLY
COME FROM OTHER CELLS".
Fundamental Ideas of Cell Theory
1. All living matter is composed of cells.
2. All cells arise from cells.
3. The cell is the basic unit of structure and
function. (Smallest unit of life.)
The Cell Theory
A. Major Contributors.
1. Robert Hooke- 1600’s
2. Anton von Leewenhoek
3. Mattias Schleiden 1838 German botanist
4. Theodor Schwann 1839 German Zoologist
5. Rudolf Virchow 1858
How Cells are Studied - Microscopy
1. Light
Compound
Microscope
How the light microscope works:
• Most microscopes
are called light
microscopes
because they
accomplish their
task by using lenses
to bend light rays.
Observing and Drawing Objects
• Because the light rays from an object
cross before reaching your eye, the image
you see through our light microscopes will
be inverted and upside down.
Important terms with the microscope:
• Magnification: the increase of an
object's apparent size.
• Field of view: the area visible through
the microscope lenses. Field of view
decreases as magnificaiton increases.
• Resolution: the power to show details
clearly. Resolution allows the viewer to
see two objects that are very close
together as two objects rather than
as one.
How Cells are Studied con’t…
2. Scanning Electron Microscope (SEM)
3. Transmission Electron (TEM)
Micrograph – a
photograph of the view
through a microscope
Light microscope
SEM
TEM
How Does an Electron Microscope Work?
• Electrons are very tiny negatively-charged particles.
Because they are negatively-charged, they are
attracted to anything that is positively-charged.
• By applying voltage to a metal plate, we are able to
make the plate positively-charged so that it attracts
the electrons.
• Some of the electrons flow through a small hole that
is in the plate, creating a beam of electrons that we
aim at our sample with the help of magnetic lenses.
• When the electrons hit our sample, the interaction is
detected and transformed into an image.
Microscopy and Amoeba proteus
Microscopy and Cheek Cells
How Cells are Studied (even more!)
4. Cell Fractionation and Differential
Centrifugation
Cell Fractionation and Differential Centrifugation
• Cell fractionation is the breaking apart of
cellular components
• Differential centrifugation:
– Allows separation of cell parts
– Separated out by size & density
• Works like spin cycle of washer
• The faster the machine spins, the smaller
the parts that settled out
Cell Structure and Size
• Structure is related to function!
• Cells take the shape that best allows
them to perform their job.
– Ex. Nerve cells
– Ex. Skin cells
• The ratio of cell
surface to cell
volume limits cell
size.
Cell Size
• Most much smaller than one millimeter
(mm)
• Some as small as one micrometer (mm)
• Size restricted by Surface/Volume (S/V)
ratio
– Surface is membrane, across which cell
acquires nutrients and expels wastes
– Volume is living cytoplasm, which demands
nutrients and produces wastes
– As cell grows, volume increases faster than
surface
– Cells specialized in absorption modified to
greatly increase surface area per unit volume
Surface to Volume Ratio
TotalSurfaceArea
(HeightWidthNumberOfSidesNumberOfCubes)
96 cm2
192 cm2
384 cm2
TotalVolume
(HeightWidthLengthXNumberOfCubes)
64 cm3
64 cm3
64 cm3
SurfaceAreaPerCube/VolumePerCube
(SurfaceArea/Volume)
1.5/1
3/1
6/1
Structure and Function
The Prokaryotic Cell
• Two domains: Bacteria
and Archaea
• Lacks a nucleus and most
other organelles
• DNA concentrated in
nucleoid region
• Contains ribosomes, cell
wall, and in some cases a
capsule, pili, and flagella.
• 1-10 micrometers
•Appear earliest
in earth’s fossil
record
Figure 7.4x1 Bacillus polymyxa
Figure 7.4x2 E. coli
Prokaryotes
PROKARYOTES were the only life form for 2 BY!
Prokaryotic Cells: Visual Summary
Prokaryotic Cells: The Envelope
• Cell Envelopes
– Glycocalyx
• Layer of polysaccharides outside cell wall
• May be slimy and easily removed, or
• Well organized and resistant to removal
(capsule)
– Cell wall
– Plasma membrane
• Like in eukaryotes
• Form internal pouches (mesosomes)
Prokaryotic Cells: Cytoplasm & Appendages
• Cytoplasm
– Semifluid solution
• Bounded by plasma membrane
• Contains inclusion bodies – Stored granules
of various substances
• Appendages
– Flagella – Provide motility
– Fimbriae – small, bristle-like fibers that sprout
from the cell surface
– Sex pili – rigid tubular structures used to pass
DNA from cell to cell
The Eukaryotic Cell
A. True nucleus
B. Membrane-bounded
organelles
C. Size: 10-100 microns
(much bigger!)
D. Members of Kingdom Animalia,
Plantae, Fungi and Protista
Eukaryotic cell
• Nucleus surrounded
by its membrane
• Internal organelles
bounded by
membranes
• 10 – 100
micrometers
• Domain Eukarya
• Kingdoms: Protists,
Fungi, Plants,
Animals
Membranes Allow for More Efficient
Cellular Metabolism
• Membranes separate areas to
maintain specific chemical conditions.
(Think about your stomach and
intestines!)
– This way different chemical processes
can take place simultaneously.
• Membranes increase the surface area
needed for many chemical reactions.
• In other words, the cell can increase in size
and combine together to form tissues!
• There is no such thing as a multicellular
prokaryotic organism!
• More on the eukaryotic cell in the next power
point…
• Wait… how did membranes and organelles
evolve?
Hypothesized
Origin of
Eukaryotic Cells
Theory of
Endosymbiosis
Prokaryotes vs. Eukaryotes
•
–
–
–
–
Prokaryotes
NO nuclear
membrane
No membrane
bound organelles
•
contain ribosomes
1-10 microns
Found in the
kindgoms:
Eubacteria,
Archaebacteria
• Eukaryotes
– nuclear membrane
– membrane bound
organelles (Golgi
bodies, lysososome,
mitochondria,
vacuoles, etc.)
– 10-100 microns
– Found in the
kindgoms: Plantae,
Animalia, Fungi,
Protista
Sizes of Living Things
The size range of cells