|Do cells go through the same changes as human
beings, or do they go through different changes?
In other words, do they start little, go through
some kind of puberty, then get old??
Cells do in fact "age" and many cell types in our
bodies (and in those of other animals) actually
die and are replaced on a regular basis. There are
a few ways to determine the "age" of a cell. One
way is to look at the chromosomes--they actually
get shorter over time, reducing in size (at the
ends) every time there is a round of DNA
replication. Other ways involve looking at the
basic machinery of the cell-- it's ability to
create energy. This tends to decrease with
age/time. Some cells in our body are very
long-lived (that is, they don't turn over very
rapidly) while other cells are constantly dying
and being replaced. Can you determine what type of
cells might have "short lives" and are being
replaced regularly? Hints: If you cut yourself
and lose 1 pint of blood, do you live the rest of
your life with one pint less than you started
with? How often do you get a haircut? Trim your
Another aspect of this is something
called "the cell cycle."
Basically, when a
cell divides, it produces two daughter cells.
These cells "grow" a bit (in a phase called G1),
then they replicate their DNA (S phase), then they
rest a bit, growing perhaps a bit more (G2 or gap
2 phase) as they prepare to divide, which is
called Mitosis (M phase). Again, some cells go
through a very fast, regular cell cycle, replacing
dead cells. Other types may "arrest" (stop) at a
certain point or just progress through the cycle
Can you think of at least one
human disease that might be cause by something
going wrong with the cell
all of the questions: students interested in
"cells and how they are studied" as well as "what
is a cell biologist?" can contact the American
Society for Cell Biology (ASCB) for free brochures
and on-line information
We're made of cells, so whatever we're doing is
because of what our cells are doing.But our cells
don't live as long as we do - our old cells die,
and new ones grow in their place. Scientists are
very interested in your question, though - their
name for cell death is 'apoptosis.' You could
search for that on (http://www.google.com). A big
question in science is whether we could live to be
very old if we learned how to control the things
that kill our cells.
Good question! Cells are always generally very
tiny their entire lives. They don't really
increase in size very much throughout their life
and that is because of the way they are created.
New cells are created by one of two processes; one
is called mitosis and one is called meiosis.
Meiosis involves mitosis, so I am just going to
tell you about mitosis (also it is the more common
of the two). Mitosis is basically when one cells
clones itself and makes a new cell exactly like
itself. Sort of like identical twin humans. During
mitosis, one cell makes a copy of all of its
internal workings, its DNA, its nucleus, and all
of the other important cellular components. After
this one cell has copied its entire insides, it
then begins to increase its overall size slightly.
As this takes place the cell also begins to
separate the copied material from the original
material at opposite ends of the enlarging cell.
Over a few hours the middle of the cell begins to
pinch in so that the cell starts to look like a
bar bell. This process continues until finally the
one cell is almost totally divided in half by this
pinching in in the middle. Finally the process is
complete and the cell that was once one, breaks
apart into two new cells. Each of these two new
cells are perfectly in tact, nearly exact copies
of each other, and nearly the size of the
original cell when the whole process started.
So the two new cells will increase in size a
little bit, but very little. This whole process
takes a few days.
Cells do get "old" too.
Different types of cells can live for longer than
others. Some cells live less than one day! Others
can live for quite some time. As a cell gets old,
generally its membrane gets leaky (the insides of
the cell start leaking out) and other cellular
processes start to fail (like when humans are
dying and their organs begin failing). Eventually
the cell's nucleus sends a message to the entire
cell telling it to stop all processes and initiate
the death sequence and shortly thereafter the cell
dies and eventually disintegrates.
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