Transcript Cell Growth and Reproduction

Cell
Growth and Reproduction
Cell Size Limitations
Cell Reproduction
Cell Cycle
Mitosis
Cell Size Limitations
Just like us, cells come in a variety of
sizes!
What determines a cell’s size?
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DNA
Diffusion
Surface Area – to – Volume Ratio
Cell Size Limitations
DNA
DNA provides the blueprints or instructions
for protein synthesis.
Cells cannot survive unless there is
enough DNA to support the protein needs
of the cell.
Cell Size Limitations
Diffusion
Nutrients and wastes are moved around a cell
using diffusion.
Usually diffusion is fast and efficient over short
distances, but when a cell gets too big it becomes
slow and inefficient!
Cells can’t be too big because they would die
before nutrients reached the organelles that need
them!
Cell Size Limitations
Surface Area –to-Volume Ratio
As a cell’s size increases, its volume increases faster
than its surface area.
If a cell size is doubled, the cell would require 8 times
more nutrients and would have 8 times more waste!
The surface area would only have increased by 4 and
therefore the plasma membrane would not have enough
surface area to let in the nutrients and let out the wastes.
The cell would either starve to death or become
poisoned by its own waste!
Usually, cells divide before they get too big to control this
factor.
Cell Reproduction
The cell theory states that “all cells come
from pre-existing cells.”
Cell division is the process by which this
happens!
Cell division results in two cells that are
identical to the original parent cell.
All organisms grow and change; worn out
tissues are repaired or replaced by newly
produced cells!
The Cell Cycle
The cell cycle is the sequence of growth and
division of a cell.
It starts with 2 general periods:
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Period of Growth
The majority of a cell’s life is spent in growth!
This phase is known as INTERPHASE!
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During INTERPHASE, a cell grows in size and carries on
metabolism.
Chromosomes are duplicated in preparation for division
Interphase is like the training before a big race!
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Period of Division
This phase is known as MITOSIS!
In MITOSIS, two daughter cells are formed each containing a
complete set of chromosomes.
INTERPHASE
3 stages
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G1 – Cell grows rapidly and protein
production is high
S – Cell copies its chromosomes and DNA
synthesis occurs
G2 – Short growth period in which
mitochondria and other organelles are made
and parts needed for cell division (centrioles)
are manufactured
INTERPHASE
MITOSIS: Many phases of Division
1) PROPHASE – longest phase of mitosis
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Chromatin (DNA strands) coil up into visible
chromosomes
They look kind of hairy!
Each chromosome is made of two identical
halves called SISTER CHROMATIDS
These halves are held together by a
CENTROMERE
PROPHASE
PROPHASE CONTINUED…
As prophase continues, the nucleus
begins to disappear as the nuclear
envelope and the nucleolus disintegrate.
At this time, the CENTRIOLES begin to
migrate to opposite poles of the cell
The SPINDLE begins to form between the
centrioles.
PROPHASE CONTINUED…
CENTRIOLES
SPINDLE
FIBERS
METAPHASE
2) METAPHASE-short second phase of
mitosis
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The doubled chromosomes become
attracted to the spindle fibers by their
centromeres
The chromosomes begin to line up on the
midline or equator of the spindle
METAPHASE
ANAPHASE
3) ANAPHASE – Third
phase of mitosis
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Sister chromatids
begin to separate
Centromeres split
apart and the
chromatids are pulled
apart
TELOPHASE
4) TELOPHASE – Fourth phase of mitosis
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Chromatids are pulled to opposite poles of the
cell
Nucleolus reappears and new nuclear
envelope forms around each new set of
chromosomes
New double membrane begins to form
between two new nuclei
TELOPHASE
CYTOKINESIS
The cell’s cytoplasm
finally divides and the
cell starts to pinch
along the equator of
the cell forming two
new cells!
MITOSIS
MITOSIS