Section
4: Types and Parts of Cells
I.
Cells are the Simplest Unit of
Life
II.
The Plasma Membrane
III.
The Cytoskeleton
IV.
Prokaryotic Cells
V.
Specialized Compartments of
Eukaryotic Cells
I. Cells are the basic units of life
v Every
living organism consists of one to many billions of membrane-enclosed units
called cells.
o
Cells compose every organ of our
bodies and determine how we look, move, and function as organisms.
o
In multicellular organisms, most
cell types are specialists at something.
o
Much of what we know about cells
came with the advent of the light microscope.
II.
The plasma membrane is an outer boundary that separates the cell from its
outside environment.
v Membranes
are composed of phospholipids arranged in a bilayer with proteins embedded
inside that allow the selective passage of materials in and out of the
cell.
o
Membranes are selectively
permeable.
v According
to the fluid-mosaic model, the proteins are free to move about sideways in the
phospholipid bilayer.
o
The type of proteins found in the
cell’s membrane determines how the cell will function.
III.
The cytoskeleton provides shape and movement for the cell.
v The
cytoskeleton acts as the internal support system for the cell, giving it
structure.
v The
cytoskeleton also includes “cables” that act as tracks along which cell
particles can move.
v The
cytoskeleton is always changing, allowing some cells to change shape and move
around on their own.
v Three
main protein filaments compose the cytoskeleton: microtubules, intermediate
filaments, microfilaments.
o
Microtubules: thickest of
filaments
§ Made
up of many monomers of tubulin
§ Can
grow and shrink in length by adding/losing tubulin monomers at either end
§ Give
cells their shape and support inner components
§ Act
as “railroad tracks” for movement of materials through cell
o
Intermediate filaments: thinner
than microtubules, thicker than microfilaments
§ Serve
as structural reinforcements and hold organelles in place
§ Ex:
skin cells; cell nucleus
o
Microfilaments: smallest in
diameter
§ Most
important of cell filaments for cell movement
§ Made
up of monomers of actin (can change length rapidly)
§ Ex:
fibroblasts
v Cilia
and flagella are part of the cytoskeleton
o
Both function due to the movement
of the protein dynein “walking” up microtubule pairs, using energy derived from
ATP
o
Cilia: hair-like projections
§ Can
be used to move around in environment or to move objects nearby
§ Move
like oars of a rowboat
o
Flagella: whip-like projections
§ Beat
in a wave-like pattern in eukaryotic cells
IV.
Prokaryotic cells
v Prokaryotic
cells lack internal compartments enclosed by membranes, and thus have little
internal organization.
v Most
are spherical/rod-shaped, though circular, round, and corkscrew shapes
exist.
v Most
have a tough cell wall that forms outside the plasma membrane.
v Most
are much smaller than eukaryotic cells.
v Inside
the prokaryotic cell:
o
Cytosol
o
Nucleoid Region
o
Ribosomes
v Prokaryotic
flagella: most widespread method that bacteria use to propel themselves through
their environment
o
Rotary “motor” rotates the
flagellum like a propeller
o
The flagellum rotates in response
to hydrogen ions that diffuse into the bacterium from the environment.
V.
Eukaryotic cells have specialized
membrane-bound compartments called organelles.
v Inside
the cell:
o
Cytoplasm: cytosol + organelles
§ Internal
space inside organelles is the lumen.
v Nucleus:
double membrane
o
Directs activities of cell in
response to signals received from other parts of the cell
o
Contains DNA
o
Surrounded by a nuclear envelope
equipped with nuclear pores
v Endoplasmic
Reticulum: single membrane connected to outer membrane of nuclear envelope
o
Where cell’s chemical building
blocks are manufactured
o
Extensive, complex network of
interconnected tubes and flattened sacs stacked and connected to one another
§ Sacs
contain lipids and proteins that are destined for other cellular compartments.
o
ER can appear smooth or rough
§ Most
ER is “Rough ER” that has ribosomes attached.
These ribosomes produce proteins that can go into the ER’s lumen, insert
into a membrane, or be exported out of the cell.
§ Smooth
ER marks sites where portions of the ER membrane actively bud off to produce
vesicles.
·
This is an effective means of
transporting proteins that are embedded in ER or lipids and proteins that float
free in ER lumen.
v Golgi
Apparatus: single membrane
o
Directs where proteins and lipids
produced by ER should go
o
Chemical groups are also added to
outbound molecules to direct them to other destinations in the cell.
§ Ex:
carbohydrate molecules and phosphate groups
o
Appears like a series of flattened
membranes stacked together and surrounded by small vesicles when viewed in the
electron microscope
§ Vesicles
transport proteins from ER to Golgi apparatus and between various sacs of the
Golgi.
v Lysosomes:
single membrane
o
Contain enzymes used to break down
macromolecules delivered to them in vesicles
§ Acidic
pH in lumen (5)
o
Broken down products are
transported into cytosol for use by the cell.
v Vacuoles:
single membrane
o
Related to lysosomes, but found in
plants and fungi
o
Central vacuole: occupies 1/3 of
plant cell’s total volume
§ Breaks
down substances, and some can also store nutrients
§ Filled
vacuoles often contribute to rigidity of plant
v Mitochondria:
double membrane
o
Breakdown sugar to synthesize
energy-rich ATP to power the cell
o
Inner mitochondrial membrane has
distinct folds called cristae.
§ Space
between 2 membranes is intermembrane space.
§ Lumen
inside the cristae is the mitochondrial matrix.
v Chloroplasts:
double membrane
o
Capture energy from sunlight and
convert it to chemical energy
o
Contain additional organelles
inside called chloroplasts (where photosynthesis takes place)
o
Beneath the double membrane lies a
third, separate internal system of membranes arranged like stacked pancakes
(stack=granum; each pancake=thylakoid).
PROKARYOTIC CELL: http://faculty.ircc.edu/faculty/tfischer/images/prokaryote%20overview.jpg
PLANT CELL: http://waynesword.palomar.edu/images/plant3.gif
ANIMAL CELL:
http://waynesword.palomar.edu/lmexer1a.htm#animal
