Transcript Cell Growth Power Point

Cell Growth
Cells have distinct phases of growth,
reproduction, and normal functions.
• Just as all species (humans) have life cycles, cells also
have a life cycle.
• The Cell Cycle is the 1regular pattern of growth, 2DNA
duplication, and 3cell division that occurs in eukaryotic
cells.
• Cell division is the process by which 2 new cells are
produced from one cell.
• The new cells are identical to
each other and to the original cell.
• Parent produces 2 daughter cells
The Cell Cycle
• The cell cycle is divided into 4 phases:
• The G1 Phase
Interphase
• The S Phase
• The G2 Phase
• The M Phase
The Cell Cycle Phases
• G1: Gap 1
• Cells grow, carry out normal functions, and
replicate their organelles
• Cell spends most of its time in this phase
• S: Synthesis
• A new set of DNA is created from the original
• G2: Gap 2
• Additional growth of cell and normal functions (job
of cell) is carried out
• M: Mitosis and Cytokinesis
• Cell division occurs.
***Mitosis occurs only if the cell is large enough and
the DNA is undamaged.
Cells divide at different rates
• Rates of cell division vary widely.
• The prokaryotic cell cycle is similar but not identical
to that of eukaryotic cells.
• This is because prokaryotic cells have no nucleus
and organelles, so they divide much faster than
eukaryotic cells.
• The rate at which your cells divide is linked to your
body’s need for those cells.
• In human cells, the S, G2, and M stages together
usually take about 12 hours.
• The rate of cell division is greater in embryos and
children than it is in adults
• The rate of cell division also varies within different
tissues of the adult body
• Some cells are unlikely to divide (G0).
• Example- Neuron cells
• This explains why most people are unable to
recover from brain injuries.
Cell size is limited
• Like most living things, cells have upper and lower size
limits.
• If cells were to small, they could not contain all the
necessary organelles & molecules.
• i.e. a cell with too few mitochondria wouldn’t have
enough energy to live
• Cell also can’t grow beyond a certain size, even if it
were surround by plenty of nutrients.
• Upper limit size is due to the RATIO OF CELL
SURFACE AREA TO VOLUME.
Cell size is limited
• Remember materials are transported via the cell membrane
•Transportation of materials must happen in adequate amounts with
adequate speed to keep cell functioning.
•But as cell size increases, its volume increases even faster.
•Therefore, a further increase in size (volume) could result in a
surface area too small for adequate exchange of materials.
Cell size is limited
• Some cells, however, must be large.
• Example:
• A neuron running down a
giraffe’s neck to it’s legs may be
several meters long
• The neuron can grow to a large
size because of it’s shape- long
and thin- instead of a cube or
sphere.
• This structure gives the neuron a
large surface area with a
relatively small increase in
volume.
Cell size is limited
• SO…
• To maintain a suitable size, growth & division must be
coordinated!
• If a cell doubles its size before division, the daughter
cells would get larger & larger with each generation.
• Quickly becoming too large to live
• On the flip side, if cell size was too small before
division, the daughter cells would get smaller &
smaller with each generation.
• Quickly becoming too small to live
• **So a cell must have a balance of both growth and
division to stay functional**