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2016 Unit 4 - Cell Division

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Deanna Swope

on 11 October 2016

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Transcript of 2016 Unit 4 - Cell Division

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CELL DIVISION
Prokaryotes
vs.
Eukaryotes

All organisms grow and reproduce.
Fawn - growth, development
Bacteria - divide to reproduce
Cell division is a simple process in prokaryotes
Cell division is more complex
in Eukaryotes
Cell Division in Prokaryotes
Prokaryotic cell division
occurs as
binary fission,
in which the cell divides into two halves.
All eukaryotic cells store genetic information in the nucleus in a structure known as a
chromosome.

- Human cells have
46
chromosomes
-
23
nearly-identical pairs
It takes about 40 min. to make one complete copy of the E. coli genome. E. coli can divide (under ideal conditions) in as little as 20 minutes. How is this possible?

It turns out that E. coli can begin a new round of DNA replication before the previous round is complete. When the cell splits in two, each daughter cell receives a strand of DNA that is already in the process of being copied. That is, the daughter cell receives DNA that is halfway prepared for the eventual granddaughter cells.

http://www.cellsalive.com/cam2.htm
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Importance of Chromosomes







Chromosomes are composed of a relaxed form of DNA and protein called
chromatin.
This is found in the nucleus
DNA coils, so it can fit!
Structure of Chromosomes
Think about this
What are homologous chromosomes
?
Living organisms need cell division for 3 reasons:
1. growth
2. repair
3. reproduction
Above: Kevin Ware's horrific broken leg.
Below: Ware's leg during recovery. Without cell division repairing his injury, he would not be able to play b-ball again.
Photos: Muhammad Ali, Michael J. Fox, and Christopher Reeves
What type of cells are being affected in their conditions/injuries?
Why can't their bodies repair like Kevin Ware's body?
Why are these men &/or their families such strong advocates for stem cell research?

The Cell Cycle
Centrioles
will move to opposite ends of the cell and form
spindle fibers

that

help pull chromosomes apart during mitosis.
Spindle apparatus=fibers and centrioles
Mitosis =
nucleus divides and nuclear material divide
Prophase
- spindle apparatus forms with the help of
centrioles
, nuclear membrane breaks apart. Chromatid condenses into chromosomes.
Metaphase
- chromosomes align at cell's
equator
Anaphase
- sister chromatids pull apart (centromeres divide) toward
opposite poles
of the cell
Telophase
- spindle disappears, chromosomes are at opposite poles,
nuclear membrane reforms
around each set of sister chromatids. Chromosome decondense
Cytokinesis
=
cytoplasm divides
(happens after telophase)
4 Cell cycle checkpoints
= proteins that check to see if the cell is ready to move to the next stage. G1, S, G2, M
What happens in the cell cycle of a cancerous cell?
Checkpoint Proteins
can't regulate because of mutations
Cell growth continues
uncontrolled
until a
tumor
forms, crowding out normal cells
Average Cell Division Times


Cell Type Process Time



fly embryo mitosis 8 minutes



bacteria mitosis 20 minutes



yeast mitosis 2 hours



human skin mitosis 20 - 24 hours



human sperm meiosis about 64 days



human liver mitosis 1 year or more



human egg meiosis up to 40 years or more



human nerve mitosis never, once mature

Comparison of average cell division times
What causes cancer?
There are many reasons that cells can divide and grow out of control, including
genetic causes, nutritional deficiencies, some infections, or exposure to environmental causes, such as

carcinogens
(ex: pollution & tobacco)
ultraviolet (UV) radiation from the sun
x-Rays
Asbestos
Remember the Centrioles??

Stem Cells
A stem cell is an unspecialized cell that can have the potential to develop into specialized cells under certain conditions.
Stem Cell Types
Adult Stem Cells-->Come from various tisssues in the body; present from infancy through adulthood.
Embryonic-->100-150 Cells formed after fertilization; will become specialized as the embryo grow.
Centromere
center of chromosome where sister chromatids attach
Sister Chromatid
structure in a chromosome containing identical copies of DNA
Interphase
The stage of the cell cycle during which the
cell grows
carries out normal functions (metabolism)
copies its DNA (chromosomes)
prepares for division
(LONGEST phase of cell's life)
Regulating Cell Cycle
Apoptosis
-process of programmed cell death
Cyclin
--> Protein that binds to cyclin-dependent kinases to regulate the activities of the cell cycle
Cyclin-dependent kinase
--> enzymes that are activated by cyclins and serve to regulate the activities of the cell cycle

Summarize
Cells use
cyclins
and
CDK
to control the cell cycle. Different combination of
CDK
start the cell cycle at different checkpoints and monitor throughout. In the
G1 stage
the cell is growing and replicating. DNA replication happens during
S
.
G2
takes inventory before moving into
Mphase
. The cycle ends with
Cytokinesis.

Cell Size
Cells must be small to diffuse nutrients quickly
if a
cell gets too large
transport of
nutrients and wastes
by
diffusion
slows down.
therefore cells
divide
before
they become too large
As a cell grows larger, its
volume
increases more rapidly than its
surface area
, then the surface area to volume ratio
decreases
.
Chromosomes
contain DNA
are carriers of genetic mateiral
exist as chromatin in the nucleus
appear during prophase
must replicate accurately to insure cell survival
Full transcript