Download BIO Cell Cycle SA and intro to cell cycle

Surface Area Limits Cell Size
And
Cell Reproduction
• Diffusion limits cell size.
• Diffusion is fast and efficient over short
distances, but becomes slow and inefficient as
the distances become larger.
• Imagine a mitochondrion at the center of a
cell with a diameter of 20 cm. It would have to
wait months before receiving molecules
entering the cell.
• DNA also limits cell size.
• Recall that DNA has the blueprints for proteins,
and proteins are used by almost every organelle
to perform their function.
• But there is a limit to how quickly these protein
blueprints can be copied and made into proteins.
• The cell can not survive unless there is enough
DNA to support the protein needs of the cell.
• In larger cells such as a large amoeba, there is
more than one nucleus in order to supply the
necessary amounts of proteins need by the cell.
• Surface area-to-volume ratio is another limiting
factor.
• As the cell’s size increases its volume increases
much faster than its surface area.
• If a cell doubled in size it would require eight
times more nutrients and would have eight times
more waste to excrete. The surface area by
contrast would only increase by a factor of four.
• Ultimately making it so that the plasma
membrane didn’t have enough surface area
though which oxygen, nutrients, and wastes
could diffuse.
Cell Reproduction
• There are many reasons cells reproduce:
– Old age
– Injury
– Too big
– Constantly worn out (ex: intestines)
Just to name a few
• But it all follows the same process.
• Two main parts interphase and mitosis, but these
two parts can be broken down further.
– Interphase has 3 parts to it
– Mitosis has 4-5 stages to it
Cell Cycle
• There are five main parts to the cell cycle:
– G1-Growth 1(GAP 1), this is when the cell
increases its size, new proteins and organelles
are made
– S-Synthesis, once the cell is big enough it
triggers the replication of DNA so there are
now two copies of DNA in the nucleus
– G2-Growth 2 (GAP2), In preparation for cell
division the cell grows even more so the new
cells will have enough material to survive
(Low SA to V ratio)
– Mitosis- The process of equally distributing
chromosomes into two nuclei.
– Cytokinesis-The process of actually splitting
the cell into two each with a nucleus and
enough organelles to survive.