Download Mitosis

The cells that make up multicellular organisms come in a wide variety
of sizes and shapes.
•Two Examples
1. Red blood cell (8 micrometers in diameter)
2. Nerve cells ( can be 1 meter in large animals)
The cell with the largest diameter is an ostrich egg.
Cell Size Limitations
1. Diffusion limits cell size
1. Remember this is the job of the plasma membrane
•
•
Diffusion is an efficient process over short distances but as
distances become larger, diffusion is inefficient
Example: Mitochondria at the center of the cell
2. DNA limits cell size
1. Remember the nucleus contains the DNA blue prints
for protein production… proteins are used by almost all
organelles to perform critical functions
•
It takes time to copy and make proteins
3. Surface area-to-volume ratio
1. As the cell size grows… its volume increase much faster
than its surface area
If the cell grows too big, it reaches a point
where the surface area is not large
enough to transport resources
(food, oxygen…) or waste products to
allow the cell to survive….
The Cell Would Die!!!
In fact, cells divide before they
become too large to function properly.
• Cell Theory
Cell Reproduction
– (all cells come from preexisting cells)
• Cell division: the process
by which new cells are
produced from one cell.
• Cell division results in
two cells that are
identical to the original,
parent cell.
• 1. Size
• 2. Rate of Growth
• 3. Timing of Cell Division
Sometime the controls (enzymes) that regulate cell
division do not operate properly—the cell divides in
an uncontrolled manner—Cancer
A malignant growth resulting from uncontrolled cell
division.
Cell Characteristics
• Body Cells are autosomes or somatic cells
• Sex Cells are gametes
• Gene ..a segment of DNA that controls a
heredity trait
• All body cells have the same set of genes, but
use only the ones necessary for their functions
• Ex. Blood cells produce only what blood cells
need.
Specialized Cells
Cells that perform a
specific function in
addition to all the ordinary
activities that keep a cell
alive.
Ex. Muscle cells-also
contract
• Parent Cell: Original cell
• Daughter Cell: The two
cells that result. (They
have the same traits)
• Chromosomes: Heredity
information that
determines the traits of an
individual. (They are thick
rod-shaped bodies.)
• Chromatin: Long strands
of DNA wrapped with
protein.
Cell Division
• Traits: Characteristics that are passed on from
parent to offspring.
•
Ex. Hair color, eye color, tall, short
Diploid (2n): The full set of
chromosomes. Found in
all body cells
(autosomes/somatic cells)
In Humans (46)
Haploid (n): Half the
chromosome number.
Found in sex cells
(gametes)
In Humans (23)
Gametes (Sex Cells)
• Male sex cell (sperm) (23)
• Male sex chromosome (XY)
• Male symbol
• Female sex cell (egg) (23)
• Female sex chromosome(XX)
• Female symbol
• Sex Cells (Gametes): Have only
Gametes half(1/2) the diploid (2n) number.
Haploid consist of one member of each
chromosome.
•
(see chart p. 265)
Humans Haploid # ---23
Cats Haploid # ---19
Pg. 1001
Sperm Formation
Egg Formation
Reproductions
• Sexual Reproduction: Involving two parents
• Asexual Reproduction: (single parent)
(A) Fission
(B) Budding
Fission: Simplest form of
reproduction. A unicellular
organisms splits and forms two
organisms.
Budding: the growth of a small fragment on a
larger parent. It contains complete genetic
instructions but only a small amount of
cytoplasm.
Structure of a Chromosome (p.205)
Chromosomes duplicate
The Cell Cycle (p. 206)
• The sequence of growth and division of a cell.
• As a cell proceeds thru its cycle….it has a
period of growth and a period of division.
• Majority of a cell’s life is spent in the growth
period known as interphase.
• Mitosis: division of chromosomes into two
identical daughter cells.
• Cytokinesis: Cytoplasm divides
The Cell Cycle
Interphase: longest busiest
phase
(G-1 Phase – Growth)
(S-Phase – Replication)
(G-2 Phase – Synthesis)
Mitosis: division
(1st) Prophase
(2nd) Metaphase
(3rd) Anaphase
(4th) Telophase
Cytokinesis:
cytoplasm divides
Now get the old stand bys…….
Transparencies with totally cool
diagrams……
The Cell Cycle
**Sequence of growth and division**
MITOSIS:
The division of chromosomes into two identical cells.
Interphase
1. Not dividing (period of
growth)
2. DNA Replicates
3. Stage that cells spend
most of their time.
4 Phases of Mitosis
PROPHASE
• Chromosome become
visible
• Nuclear membrane
disappears
• Spindle Fibers appear
• The longest phase of
mitosis
Metaphase
• Chromosomes line up
along the equator
(middle of the cell)
Centromeres attach to
spindles
• Centromeres split
• Sister Chromatids
separate
• Chromitids move to
opposite poles
(ends of the cell)
Anaphase
Telophase
• Last phase of mitosis
• Chromatids reach poles
• Chromosomes are not
visible
• Spindle disintergrates
(disappears)
• Nuclear membrane
reappears
• New cell wall or cell
membrane appears
Cytokinesis (cytoplasm divides)
IN PLANT CELLS
• Division begins in the
middle with a cell
plate...laid across the
equator
IN ANIMAL CELLS
• Division begins from the
outside
• Cleavage furrow forms at
the equator of the cell and
the plasma membrane
pinches in along the
equator.
Cytokinesis in Animals
•The division begins from the
outside (pinching inward)
Mitosis in an onion root
Mitosis (stays the same)
• Each daughter cell has the same number of
chromosomes as the parent cell that produced it.
46
46
46
46
46
46
46
Meiosis
• Process by which diploid cell divides to produce
four haploid cells. These cells are called gametes
(sex cells), they combine through sexual
reproduction to form a diploid zygote. The zygote is
the first cell of a new organism. Therefore, meiosis
is essential for sexual reproduction.
• Spermatogenesis: production of sperm cells
• Oogenesis: production of eggs
Meiosis
(reduce the chromosome number)
cell
46
92
Cell replicated
End of Meiosis I
46
46
End of Meiosis II
23
23
23
23
Meiosis I and Meiosis II
• During Meiosis two nuclear divisions occur
1st Division: called Meiosis I
2nd Division: called Meiosis II
• Reduces the chromosome number to half
Meiosis I
Meiosis II
A comparison of mitosis and meiosis
HOMOLOGOUS
CHROMOSOME
• THESE ARE PAIRED CHROMOSOMES THAT ARE
INHERITED FROM EACH PARENT. THEY CARRY
THE SAME TRAIT BUT MAYBE A DIFFERENT
FORM. EXAMPLE MOTHER MAY HAVE
BROWN HAIR AND FATHER HAS BLACK HAIR.
SAME CHROMOSOME.
CROSSING OVER
• AN EXCHANGE OF GENETIC MATERIAL.. THIS
RESULTS IN GENETIC DIVERSITY, VARIATION. A
SEXUAL REPRODUCTING ORGANISM WILL
SURVIVE BETTER IN A CHANGING
ENVIRONMENT.
Example
ABCDEF
abcdef
chromosome
After crossing over the result maybe
ABCdef
abcDEF new chromosome
1. Humans have how many chromosomes?
2. Which mitotic stage does the cell spend most of its
time?
3. What is the most rapid dividing cells in the body?
Fill – in – the blank
The body cells of a cat is 38. That means its’ (4)____
number is 38. An egg cell would have (5) __
chromosomes. Sex cells are called (6)__. When an
egg was fertilized it would have
A comparison of mitosis and meiosis: summary