Tour of the Cell
Cell theory says:
-All living things are made up of cells…
And…
-Cells come from preexisting cells.
“Like begets like”
Eosinophils are important in combatting
parasitic diseases
The cell is the smallest unit of living matter…if you take apart the
cell, it is no longer living.
Cell size is determined by the cell’s function.
Surface to Volume ratio also keeps cells same relative size:
Cell must be large enough to perform the duties important
to the organism such as metabolism and protein making.
Cells that are too large cannot export waste quickly enough
and will eventually poison themselves.
Microscopes are important “tool” for scientists to view cells.
Microscopes provide both:
MAGNIFICATION- an increase in the apparent size of the
object.
RESOLVING POWER- the ability of the microscope to
show two objects as being separate. This is the clarity
of the objects.
Magnification and resolving power must be balanced to observe
the image. When magnification is increased, resolving
power is decreased. When resolving power is increased,
magnification is decreased.
Many kinds of microscopes available.
Most common type used in Life Sciences is the
LIGHT MICROSCOPE (LM)-visible light passes through
the image and then glass lenses enlarge the image and
project it into the human eye or a camera.
Light microscope is what you will use in lab and also what the
first “scientists” used…with a candle and mirror!!
Electron microscopes are not used as much in life science.
-use electron beams that reflect off the specimen.
-much higher resolving power than light scopes
-image must be projected onto screen or photographed
-specimens must be placed in a Vacuum for viewing…a
space void of all particles including air and water.
-not used to view living or functioning organisms
Light microscopes
very important for
viewing living
specimens and
moving parts.
Two Categories of Cells:
Prokaryotic
-Domains Bacteria and Archaea
-small cells
-first ones appeared over 3.5 billion
years ago
-lack internal organelles
-DNA is coiled in a nucleoid region
but is not separated
from rest of cell insides.
Eukaryotic
-Kingdoms Protista, Fungi, Plantae and Anamalia
-typical cell is about 10x larger than prokaryote
-first ones appeared about 1.7 billion years ago
-internal organelles compartmentalize everything
-DNA is found in cell nucleus
Comparison of a Prokaryotic Cell and a Eukaryotic Cell
Prokaryotic and Eukaryotic cells share TWO universal parts.
Plasma membrane (cell membrane)-outer layer of cell
-keeps cell contents separate from outside contents
-is fluid…allows for movement
-selectively permeable…only allows certain particles
to pass across…water has
free passage.
-made up of phospholipids
found in a bi-layer
-bi-layer composition is
important for cell shape
-insures cell membrane
will always “close off” to
protect hydrophobic tails
of phospholipids
Cytoplasm is second part.
-liquid inside of the cell
-colorless so it is not visible
-allows for movement of things inside
the cell
Cell membrane is like a bowl and cytoplasm
is like soup broth!!
Other cell parts might appear in both prokaryotic and eukaryotic
cells at different times, but they are not universal.
Cell Organelles:
Nucleus-cell “brain” controls all cell activities
-DNA is found here
-protected from cytoplasm by nuclear membrane
which controls entrance into and out of nucleus
Ribosomes-in both prokaryotic and eukaryotic cells
-assemble all proteins for the cell
-found “free floating” in cytoplasm or attached to
Endoplasmic Reticulum and the “rough ER”
Endoplasmic Reticulum-produce many types of molecules
-rough ER has ribosomes on it and produces
proteins
-smooth ER does not have ribosomes, thus it
has a “smooth” appearance
many different functions depending on the
cell type it is in.
In liver cells it detoxifies the blood
In muscle cells it stores calcium
Golgi Apparatus-works with other organelles to refine and distribute
chemicals made in the cell
Lysosomes
-digestive enzyme sacs in cytoplasm
-digest worn out and non-functioning cell organelles and
sometimes whole cells
-important for cleaning up cell “trash” and helping to digest
large molecules for the cell to use
-digest webbing between toes and fingers of developing
fetus
-digest tadpole tail
-malfunction of lysosomes
causes Tay-Sachs disease
Vacuoles-found in both prokaryotic and eukaryotic cells
-storage sacs for things such as water, food, waste,
scents, proteins, pigments and poisons
Chloroplasts and Mitochondria are important energy organelles
for some cells.
Mitochondria- “Power House”
-found in both plant and animal cells
-important in the respiration process
-have a network of cristae inside (Fig. 4.18, p. 65)
-cells ATP is manufactured in mitochondria
-cells contain different amounts of mitos depending upon
their function and energy needs
Chloroplast-found only in photosynthetic organisms (make their own
food)
-contain green pigment, chlorophyll, which captures light
-chlorophyll contained in small sacs called thylakoids,
stacked up to form grana (solar power packs)
-light eventually becomes sugar and provides energy to
plant and other organisms as well
“How do we know we are not photosynthetic?”
“Why do plants need mitochondria?”
Cell Wall-found only in photosynthetic organisms and bacteria
-provides protection and structure
-is “skeletal system” for organisms that lack a skeleton
-think about how high a tree grows without a backbone!
-don’t forget…most organisms cannot digest the cell wall
because it is made up of cellulose!!
Cytoskeleton-made up of fibers in cytoplasm
-provide shape to cells that lack a cell wall
-help anchor organelles inside the cell
Cilia and Flagella-outside of cell usually attached to cell
membrane or wall
-help cells move or move parts
-cilia are small and more numerous,
like in a paramecium
-flagella is usually a single, long tail,
like that on a euglena
Some cilia can be found
lining the nasal and throat
passages. Why??
Communication between cells:
plant cells use PLASMODESMATA
-tiny holes in cell wall between adjoining cells
-cell wall is impermeable so need plasmodesmata
to transport nutrients, relay messages, allow water
to pass in and out, export waste, etc.
-cell membrane is semi-permeable so plasmodesmata only goes through cell wall
animal cells use JUNCTIONS
-different types perform different functions
-communicating junctions similar to plasmodesmata
because they allow passage between adjoining cells
-tight and anchoring junctions hold cells together
to form sheets such as muscle or nerve
-Fig. 4.22, pg. 68