Transcript Cell Division

Cell Division
Part One: Mitosis
In this lesson…
• Explain the difference between double and single
stranded chromosome, chromatin and chromatid
• List the steps of mitosis and describe what happens in
each
• Identify what stage of mitosis a cell is in by looking at
the chromosomes
• List three reasons cells divide by mitosis
• Describe cytokinesis
In the nucleus
• In non-dividing cells, the genetic material is
stored as thin DNA super coils called
CHROMATIN
• When a cell divides, the chromatin will shorten
and thicken into CHROMOSOMES
• One strand of a double stranded chromosome is
called a CHROMATID
Mitosis
• MITOSIS: a process by which the nucleus of a
cell divides while maintaining the chromosome
number
 One cell  two cells
 New cells have identical genetic material
(DNA) of the parent cell
• Four stages of division (Prophase, Metaphase,
Anaphase and Telophase - PMAT) plus a period
of growth and metabolism called Interphase
The Cell Cycle
Interphase
•
•
•
•
•
Period between divisions
Longest part of the cell cycle
Cell is growing and metabolizing
Nuclear membrane present
Genetic information in the form of chromatin and
cannot be seen with a microscope
• Before division each strand of DNA will replicate
(copy) itself to become double stranded
• Near the end of interphase the DNA begins to
condense (shorten)
Interphase
Draw a double stranded chromosome. Label
chromosome, chromatid and centromere
Chromosome
Chromatid
Chromatid
Centromere
Phase One: Prophase
• Chromatin contracts and becomes visible (spaghetti). It
is now called CHROMOSOMES
• Each is a double chromosome with a pair of SISTER
chromatids which are joined to each other by a
centromere
• Chromosomes begin to move towards the equator
(center) of the cell
• Nuclear membrane disintegrates (breaks down)
• CENTRIOLES will form SPINDLE FIBERS that will
attach to each centromere and move around the
chromosomes
Prophase
Phase Two: Metaphase
• The centromeres of each chromosome line up along
equator ( looks like praying hands)
• Centromeres divide so the doubled chromosomes
become two identical single stranded sister
chromatids
• Centrioles are now at the poles of the cell and are
attached to each centromere by spindle fibers
Metaphase
Phase Three: Anaphase
• The spindle fibers begin to shorten and the
chromosomes begin moving to opposite
ends or poles of the cell (fingers)
• Each side gets one chromatid from each
double stranded chromosome
Anaphase
chromosomes
Phase Four: Telophase
• Begins when single stranded chromosomes reach
the poles
• Chromosomes uncoil and turn into chromatin
• Nuclear membrane reappears
• Reverse of prophase
• Division of the cytoplasm or CYTOKINESIS is
completed by pinching off in animals or by building
a cell wall in plants
Telophase
What’s the point of Mitosis?
• Mitosis creates identical copies of cells for:
 1. growth
 2. Repair/regeneration of damaged tissue
 3. Asexual reproduction (animals) or
vegetative reproduction (plants)
Asexual Reproduction
• Reproduction that involves only one parent; parent and
offspring have identical genetics
• No special reproductive cells or organs used to create
offspring
• Occurs through mitosis and cytokinesis
• Both single and multi-celled organisms, plants and simple
animals can reproduce asexually
• In multi-cellular organisms, the offspring develop from
undifferentiated, unspecialized cells from the parent
• Usually a rapid form of reproduction
Binary Fission
• Simplest form of asexual reproduction
• Parent divides into two approximately equal
sized daughter cells
• Bacteria: circular chromosome attaches to
plasma membrane then replicates, cell wall
separates each copy
• Protozoa: eg. Amoeba become circular and use
mitosis
Budding
• New individuals develop from small
outgrowths of the parent (buds)
• May develop colonies (sponges) or break
off to be individuals (hydra, yeast)
• Some organisms can both bud and
reproduce sexually
Spores
• Specialized single cells that are released
from the parent organism, germinate and
grow by mitosis
• New cells differentiate to form a new
organism
• Can reproduce quickly and in large quantities
• Often have thick protective coats
• Eg. Fungi, algae, protozoa
Regeneration
• The ability to regrow lost body parts
• Some animals can regrow entire new
organisms from parts
• Ability to regenerate decreases as organisms
increase complexity
• Even simple organisms that can regenerate
entire organisms generally prefer to utilize a
different method to reproduce
Vegetative reproduction
• MERISTEM: area on plant with unspecialized cells (cells
that can become any kind of cell) that frequently divide
using mitosis
• Meristematic cells can be found in the vegetative
structures of a plant (roots, stems, leaves)
• Given proper treatment, meristem cells can reproduce
mitoticlly then differentiate into new independent plants
• Structures include bulbs, corms, tubers, runners,
rhizomes
• Can also be artificially propagated using cuttings,
layerings or grafting
Bulb
• short underground
stem with
thickened storage
leaves
• small new bulbs
sprout from the
old ones
• Eg. onions, tulips
Corm
• short underground stems with no fleshy leaves
• Eg. gladiolas, crocuses
Tuber
• enlarged part of an
underground stem
that contains stored
food
• potatoes (eyes are
tiny buds)
Runner
• AKA stolon
• is a stem that runs sideways and contains
buds
• Eg. strawberry
Rhizome
• a stem that
grows sideways
under the
ground
• ferns, irises
Cutting
• a stem, root or
leaf cutting
used to make a
new plant
Layering
• part of a stem is bent and covered in soil
• once it roots the original can be cut off
• Eg. raspberries, roses
Grafting
• stem or bud removed
from one plant and
permanently joined
to another plant
• Eg. grapes and many
seedless fruits