Transcript Cell Growth and Reproduction

Cell Growth and
Reproduction
Limitations on Cell Size
Diffusion

Larger the cell, the longer it takes to get
nutrients from outside the cell through
diffusion.
DNA

Larger cells need more DNA to support the
functions of the cell (i.e. protein synthesis).
Limitations on Cell Size
Surface Area to Volume Ratio



Volume increases at a higher rate than
surface area.
As cell increases in volume, more nutrients
are needed and more wastes are created.
Surface area of the cell is not sufficient for the
diffusion of nutrients and wastes.
Cell Division
Occurs before the cell becomes too large
to be efficient.
Results in two cells which are identical to
the original parent cell.
Chromosomes, Chromatin, and
Sister Chromatids
Chromatin

Long strands of DNA wrapped around
proteins called histones.
Each groups of histones is called a nucleosome.

Exist between times of division.
Chromosomes, Chromatin, and
Sister Chromatids
Chromosomes


Before a cell can divide, chromatin must be
reorganized into tight coils called
chromosomes.
Appear before cell division and disappear
soon after cell division is complete.
Chromosomes, Chromatin, and
Sister Chromatids
Sister Chromatids



Accurate transmission of chromosomes
during cell division is critical, so before
division chromosomes copy themselves.
When copied, chromosomes form two sister
chromatids that are exact copies of each
other.
The two sister chromatids are held together
by a centromere.
Chromosomes, Chromatin, and
Sister Chromatids
Cell Cycle
Sequence of growth and division in a cell.
Divided into two parts:


Interphase
Mitosis
Interphase
Growth period in which a cell spends
most of its life.
Interphase
3 distinct divisions:
1.
2.
3.
Cell grows and protein production is high.
Cell copies its chromosomes and DNA
synthesis occurs.
Short period of growth during which
mitochondria and other organelles are
manufactured and cell parts needed for cell
division are assembled.
Mitosis
Period of nuclear division.
During mitosis, two daughter cells are
formed.

Each daughter cell contains a complete set of
chromosomes.
Following mitosis, the cytoplasm divides,
separating the two daughter cells.
4 Phases of Mitosis
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Prophase
Longest phase of mitosis.
Long, stringy chromatin coils up into
visible chromosomes.
Nucleus disappears as the nuclear
envelope and nucleolus disintegrate.
Prophase
In animal cells, the centrioles migrate to
opposite sides of the cell and the spindle
forms between them.
In plant cells the spindle forms without
centrioles.
Prophase
Centrioles
Small dark, cylindrical structures made of
microtubules.
Located just outside the nucleus.
Play a role in chromotid separation.
Spindle
Football shaped, cage like structure
consisting of thin fibers made of
microtubules.
Plays a vital role in separation of sister
chromatids.
Metaphase
Short
Doubled chromosomes become attached
to the spindle fibers by their centromeres.
Chromosomes are pulled by the spindle
fibers and begin to line up on the mid-line
of the spindle.
Metaphase
Each sister chromatid is attached to its
own spindle fiber. Each of these spindle
fibers extend to opposite poles to ensure
that each new cell receives and identical
and complete set of chromosomes.
Metaphase
Anaphase
Beginning is marked by the separation of
sister chromatids.
The centromeres split apart and chromatid
pairs from each chromosome separate
from each other.
Chromatids are pulled apart by the
shortening of microtubules in the spindle
fibers
Anaphase
Telophase
Begins as chromatids reach the opposite
poles of the cell.
Many of the changes that occurred during
prophase are reversed as the new cells
prepare to exist independently.
Telophase
Tightly wound chromosomes begin to
unwind.
Spindle begins to break down.
Nucleolus reappears.
New nuclear envelope forms around each
set of chromosomes.
New double membrane begins to form
between the two nuclei.
Telophase
Cytokinesis
Division of the cytoplasm following
telophase.
Animals:

Towards the end of telophase, the plasma
membrane pinches in along the equator and
the two cells begin to separate.
Cytokinesis
Plants:


A structure called a cell plate is laid down
across the equator of the cell.
A cell membrane forms around each cell and
new cell walls form on each new side of the
cell plate until separation is complete.
Cytokinesis
Results of Mitosis
Unicellular organisms produce two new
single-celled organisms.
Multicellular organisms produce groups of
cells that work together as tissues to
perform specific functions.


Tissues further organize to form organs.
Multiple organs form an organ system.