Slide 1
Cells have an internal support system known as the
cytoskeleton. This skeletal system also plays a role in moving
substances around the inside of the cell.
Slide 2
The smallest cytoskeletal fibers are microfilaments made of
contractile protein known as actin.
Microfilaments play a critical role in
cell motility such as amoeboid movement - the streaming-type movement seen in
amoeba and also seen in our white blood cells in our immune system. I
have posted a video on ANGEL of a white blood cell engulfing a bacterium -
this is possible because of the microfilaments in the cell.
Microfilaments also play an important role in muscle contractions along with
a protein known as myosin.
Slide 3
Intermediate filaments are somewhat larger than microfilaments,
yet smaller than microtubules. Intermediate filaments are made of fibrous
proteins wrapped around one another to form a thick, cable-like structure.
Intermediate filaments play an important role in supporting cell structures
and anchoring organelles in the correct position within the cell.
Slide 4
Microtubules are the largest cytoskeletal elements that we will
discuss. Microtubules are actually hollow tubes consisting of rows of
paired tubulin molecules. Microtubules play a structural role in the cell but
they also play an important role in the movement of substances around the
cell. For example, microtubules help move the chromosomes during mitosis
and meiosis. Microtubules also help move vesicles around the inside of
the cell.
You can see this elaborate movement in the "Life of the Cell" video posted on ANGEL.
Slide 5
Lysosomes are vesicles that contain digestive or hydrolytic
enzymes. These are enzymes that help to break down materials within the
cell. The lysosomes play a role in digestion of food particles,
destruction of bacteria and viruses in our immune system, and the breakdown of
cellular materials to maintain normal concentrations within our cells.
Slide 6
When there are problems with subcellular structures - disease can
result. A tragic example of this is the genetic disease Tay-sachs.
Tay sachs is a recessive genetic condition that results in a nonfunctional
lysosomal enzyme being produced. This enzymes normal role is to break
down lipids in the brain. In a person with Tay Sachs - this enzyme does
not function and the lipids build up in the brain and destroy nerve cell
function. There is no cure for this disease and the affected individual
dies in childhood.
Slide 7
Vacuoles are large membrane bound sacs that play a role in storage
of materials within the cell. Plant cells have a very large cenral
vacuole - seen here - that stores water to maintain structural support sort of
like a water balloon. These vacuoles can also house toxins, pigments,
and starches.
Animal cells often do not have vacuoles - but liver cells have vacuoles for the storage of glycogen.
Single-celled protists often have vacuoles for storing and processing food and they typically have contractile vacuoles for pushing water out of their cell. Most single-celled protists live in fresh water - so osmosis is constantly causing water to flow into their cell over the cell membrane. If they did not expel this water - they would explode like an over-filled water ballon. The contractile vacuole pushes excess water out of the cell.
Slide 8
This image shows a contractile vacuole in a paramecium. At
the top the vacuole is filling with water that is flowing into the cell - a
system of canals leadds the water to the vacuole.
When it is full - the vacuole contracts and forces the water back out.