Download Coming Full Circle: From Cells to Ecosystems Review: Two Types of

4/11/11
Review: Two Types of Cells. . .
Coming Full Circle: From Cells to Ecosystems
by Dr. Evil
• PROKARYOTES:
– cell membrane
– cytoplasm
– usually a cell wall
– DNA, RNA, proteins
– circular DNA
– ribosomes
– NO nucleus
– NO complex organelles
• EUKARYOTES:
– cell membrane
– cytoplasm
– sometimes a cell wall
– DNA, RNA, proteins
– linear DNA (chromosomes)
– ribosomes
– nucleus
– complex organelles
Bacterial DNA is organized into one large loop, plus a number of
smaller loops called plasmids. Bacteria can exchange plasmids or
pick them up from the environment (remember Griffith’s
“transforming principle”?)
There’s a central region (the nucleoid) where the DNA is located, but
this isn’t bounded by a membrane sac, and so it’s not a nucleus.
Ribosomes just float free in the cytoplasm.
1
4/11/11
Some prokaryotes do
contain some gasfilled sacs and other
simple structures,
however—but
nothing very
complex.
Sometimes the nucleus
can have a rather odd
shape, as in this singlecelled organism . . . Eukaryotes (duuh!) have a defined mucleus bound by
a double-layered nuclear membrane.
Cross-section through a plant cell nucleus, showing the
nucleolus inside. The nucleolus is where ribosomes
themselves are made. . . The nucleus here, stained dark
purple, is the thing that looks like
a short string of beads.
2
4/11/11
The nuclear pores allow passage of RNA, ribosomes,
etc. out of the nucleus. Not just simple holes, they're kept
open by complex proteins, the porins.
Endomembrane System
• Endoplasmic reticulum (ER)
– Transport network within the cell
– Proteins and other products that are exported
are transferred via the ER
• Golgi body
– "Packaging and shipping center"
• Vesicles (small) and vacuoles (large)
– Membrane sacs for storage and/or transport
Endoplasmic reticulum (ER)
Smooth endoplasmic reticulum (ER)
3
4/11/11
Close-up of rough endoplasmic reticulum
showing bound and free ribosomes
Golgi body
Structure: Basically a stack of flat sacs. (Imagine ten
deflated beach balls stacked one on top of the other.)
This picture shows a cross-section through the “stack.”
Anything secreted from the cell passes from the Golgi into
small vesicles, which move to the outer membrane and fuse
with it, releasing the contents (a process called exocytosis).
Vacuoles and
vesicles
These plant cells
contain large central
vacuoles—
fluid-filled sacs that
show up as
empty spaces in this
cross-section.
4
4/11/11
Lysosomes: specialized vesicles that break down and
Vacuoles and
vesicles
digest food particles and/or worn out bits of the cell
This single-celled
organism has a
number of smaller
vacuoles, seen as
round empty spaces.
A mitochondrion in cross-section. We don't have
time to discuss what they do, but you can think of
them as the cell's "powerplant", converting food into
usable chemical energy for everything the cell does.
Chloroplasts (as you saw in Lab 2) are the organelles
where photosynthesis takes place—the harnessing of
solar energy to build the larger molecules the cell needs.
5
4/11/11
Cytoskeleton
Chloroplasts in cross-section
The interior of a chloroplast is filled with stacks of
flat membrane sacs. (I wish we had time to go into why!)
Nucleus: stained yellow. Microtubules: stained red.
This cross-section
through a sperm
flagellum reveals
that it’s basically
a bundle of
microscopic tubes
(seen as circles in
this end-on crosssectional view. . .)
6