POD
• Compare and contrast asexual and sexual
reproduction.
• What do you think triggers cells to divide?
– Give reasoning for your predictions
The structure of eukaryotic chromosomes
The Relationship between Chromosomes, DNA and
Genes
•
DNA –
deoxyribose
nucleic acid
• macromolecule,
carries genetic
information
– A gene is a
short section of
DNA
http://www.hhmi.org/biointeractive/
dna-packaging
•
•
•
•
DNA is tightly packed in the nucleus of every cell.
DNA wraps around special proteins called histones
which form loops of DNA called nucleosomes.
These nucleosomes coil and stack together to form
fibers called chromatin.
• Chromatin in turn forms larger loops and coils to
form chromosomes.
TERMS YOU NEED TO
KNOW:
Structure of a Chromosome
Chromosome Numbers
• Sex chromosomes - determine the sex of an
organism
• Autosomes - All other chromosomes in an
organism
Somatic Cells (body cells) –
- 2 Sex chromosomes X or Y
- all other chromosomes are autosomes
Gametes (Sex cells)
- half the number of chromosomes as a somatic cell
- 1 sex chromosome
- all other chromosomes are autosomes
Example: Humans
• Somatic cells have 46 chromosomes
– 2 sex chromosomes
• women have two X chromosomes
• men have an X and a Y
– 44 autosomes
• Gametes
– 1 sex chromosome
– 22 autosomes
Chromosome Numbers
• Haploid and diploid are terms referring to the number
of sets of chromosomes in a cell.
• diploid cells (2n) - Somatic cells (body cells),
contains two complete sets of chromosomes
– every organism has a characteristic diploid number
• haploid cells (n) - Gametes (sex cells) have only one
complete set of chromosomes
– the length and number of chromosomes is unique to each
species of organism.
Organism
Chromosome Number
• Carrot
• 18
• Cat
• 32
• Chimpanzee
• 48
• Dog
• Earthworm
• Goldfish
• Lettuce
• 78
• 36
• 94
• 18
http://www.ncbi.nlm.nih.gov/mapview/
Mactching sets of chromosomes in a diploid cell are
called homologous chromosomes. Both chromo in a
homologous pair contain information that code the
same trait (genes).
Example of trait: Eye color
Are sex chromosomes homologous? Why or Why not?
Cell Division and Reproduction
PBS : How Cells divide
http://www.pbs.org/wgbh/nova/baby/divide.html#
Prokaryotic chromosomes
• Lack true nuclei
• DNA found in
cytoplasm
• Most contain a single,
circular DNA
chromosome
The Prokaryotic Cell Cycle
Cell Division in Prokaryotes/Asexual Reproduction
• BINARY FISSION is the division of a
prokaryotic cell into 2 offspring cells.
(asexual reproduction)
• The cell grows in size.
• DNA replication - The chromosome
makes a copy of itself, resulting in two
identical chromosomes
• Cytokinesis - The cell splits into two
new cells. Each new cell contains
identical genetic information as the
original cell
A protozoan undergoes binary fission
Eukaryotic Cell Cycle
The stages of life of a cell
• Interphase
• Mitosis
• Cytokinesis
Eukaryotic Cell Cycle
http://highered.mheducation.com/sites/9834092339/student_view0/chapter10/control_of_the_cell_cycle.html
Cell Division in Eukaryotes
• A cell typically goes through stages during
its life, growing and developing before it
divides into new cells.
• The cell cycle is the repeating events that
make up the life of a cell
http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u4aos1p2.html#Chromosomes
Interphase
• Period of normal metabolic activity
– Carries on all usual functions
– Increases in size
– Synthesizes new proteins and organelles
• DNA Replication – DNA is duplicated (copied)
– Reminder: DNA exist as chromatin within the nucleus.
Chromatin are thin uncoiled strands of DNA wrapped around a
protein
– allows each new cell will have a complete copy of each
chromosomes
• The actual dividing of the cell consists of
two steps:
– Mitosis
– cytokinesis
Mitosis
• The division of the Nucleus
– Process by which a nucleus divides into 2 identical
nuclei
– Mitosis produces two daughter cells that are identical to
the parent cell. If the parent cell is haploid (N), then the
daughter cells will be haploid. If the parent cell is
diploid, the daughter cells will also be diploid.
–NN
– 2N  2N
– This type of cell division allows multicellular
organisms to grow and repair damaged tissue.
4 phases of Mitosis
Prophase
• the chromatin coils
(condenses) to form
visible chromosomes*
• nucleolus and the
nuclear membrane
begin to disappear
• centrosomes
(centrioles) appear
• Spindle fibers start to
form
• Centrioles begin to
move to opposite ends
• The chromatin
condensed into
chromosomes
• each chromosome
contains two identical
halves called sister
chromatids
• The constricted area
of each chromatid is
called a
centromere
Centromere
Sister
chromatids
Metaphase
• chromosomes are
moved to the center of
the cell (equator) by
the spindle fibers
attached to the
centromeres
• The two sister
chromatids of each
chromosome are
attached to spindle
fibers from opposite
ends of the cell
Anaphase
• The sister chromatids
are separated from
each other; now
considered to be
individual
chromosomes
• The centromeres of
each chromosome are
pulled by the spindle
fibers toward the
opposite ends (poles)
of the cell
Telophase
• after the chromosomes
reach opposite ends of
the cell, the spindle
fibers breakdown
• the chromosomes return
to less tightly coiled
Chromatin
• new nuclear envelope
begins to form around
the chromosomes at each
end of the cell
– End of mitosis
Nuclear
envlopes
reappear
Cytokinesis
• The cell membrane begins
to pinch the cell in two as
cytokinesis begins
• the cytoplasm of a cell and
its organelles are equally
separated into two daughter
cells
• Completes the process of cell
division
• the new cells are now in
interphase
• Cytokinesis differs between
plants and animals
• Plant cells have a rigid cell
wall, so the plasma
membrane does not pinch in.
• the material for the new cell
wall is called the cell plate
• The cell plate and membranes
gather and fuse along the
equator, between two two
nuclei forming two identical
cells
Results:
• unicellular organisms remain as single cells
• in multicellular organisms, cell growth and reproduction
result in groups of cells that work together as tissue to
perform a specific function
•
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/mitosis.html
•
•
•
http://www.johnkyrk.com/mitosis.html
http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/cells3.html
http://biology.about.com/library/blmitosisanim.htm
Normal Control of the Cell Cycle
• Proteins regulate the progress of cell division
• Occasionally, cells lose control of the cell cycle.
• uncontrolled dividing of cells can result from proteins
not functioning properly
• cancer is a malignant growth resulting from
uncontrolled cell division