Download I. Cell Diversity A. Cell Shape 1. Cell shape reflects the different

I. Cell Diversity
A. Cell Shape
1. Cell shape reflects the different functions of cells
2. The shape has evolved to allow the cell to perform its function effectively
B. Cell Size (pg. 243 figure 10-2)
1. Cells differ in shape and size
2. Examples; a nerve cell from a giraffe's spinal cord to its foot is 6.5 ft. long. A
human egg cell is about the size of a period at the end of a sentence.
3. Most cells are 10 to 50 um in diameter
4. The size of a cell is limited by its surface area-to-volume ratio
5. As a cell grows, its volume increases faster than its surface area
6. If the cell got to big, the surface area would not allow materials to enter or
leave quickly enough to meet the cell's needs
7. This is why most cells are microscopic
Ch. 10-2 & 10-3 Mitosis and Cell Division
I.
Cell Division in Prokaryotes (bacteria)
A. Prokaryotes have cell walls but lack nuclei and membrane-bound
organelles
B. Prokaryotes have DNA that is a circular chromosome attached to
the inner surface of the plasma membrane
C. Cell division in bacteria occurs in 2 stages
1. DNA is copied
2. The cell splits
D. Once DNA is copied, the bacterium splits into two equal halves by a
process called binary fission
E. Prokaryotes make copies of themselves when the DNA unzips
lengthwise to make 2 strands. Each of these strands makes a new
circular DNA molecule
F. A new cell membrane then begins to develop between the two DNA
copies
G. The cell grows until it reaches twice its original size
H. The cell membrane pushes inward squeezing the cell like a balloon;
then a new cell wall develops around the new cell membrane
I. Eventually the prokaryote is split into two independent cells
J. This is a type of asexual reproduction that produces identical
offspring
II.
Cell Division in Eukaryotes
A. Some eukaryotic organisms are protists, fungi, plants, and animals
B. In eukaryotic cell division, both the cytoplasm and the nucleus
divide
C. There are two types of cell division in eukaryotes:
1. Mitosis
2. Meiosis
D. Mitosis results in new cells with genetic material that is identical to
the genetic material of the original cell (the division of the nucleus)
E. Mitosis occurs in organisms undergoing growth, development,
repair, or asexual reproduction
F. Asexual reproduction is the production of offspring from one parent
G. Meiosis occurs during the formation of gametes (reproductive cells)
H. Meiosis reduces the chromosome number by half in new cells
(haploid)
I. Each new cell can join with another haploid cell to produce a
diploid cell with a complete set of chromosomes
III.
Cell Cycle (Figure 10-4)
A. The cell cycle a repeating sequence of growth and division through
which many kinds of eukaryotic cells pass throughout their life
B. Interphase is the time between cell divisions
C. Interphase is divided into three phases and cell division is divided
into two phases
D. During cell division, the chromosomes and cytoplasm are equally
divided between two offspring cells
E. Cell division consists of mitosis and cytokinesis
F. Cytokinesis is the division of the cell’s cytoplasm
G. The five phases of the Cell Cycle
G1 → S → G2 → M → C
H. Interphase (cells spend most of their life)
1. G1 Phase
a. Growth phase of the cell
b. Cell grows rapidly and carries out its routine functions
c. It is the time gap following cell division and preceding
DNA replication
d. For most organisms, this phase occupies the major portion
of the cell’s life between divisions
2. S Phase
a. DNA is copied (synthesized)
b. At the end of the phase, an individual chromosome
consists of 2 chromatids attached at the centromere
3. G2 Phase
a. The time gap following DNA synthesis and preceding cell
division
b. Preparations for nuclear division are made
c. Mitochondria and other organelles replicate
d. Microtubules are assembled for use
4. M phase
a. Mitosis is the process by which the nucleus of a cell is
divided into two nuclei, each with the same number and
kinds of chromosomes
5. C phase
a. Cytokinesis; the division of the cytoplasm
I. Cells can exit the cell cycle and enter the G0 phase
J. During the G0 phase, cells don’t copy their DNA or prepare for cell
division
K. Nerve cells once fully developed, remain in the G0 phase
IV.
What occurs during Mitosis?
A. Cells spend most of their lives in the G1, S, and G2 phases which is
called Interphase
B. Mitosis is the division of the nucleus, which occurs during cell
division
C. Mitosis is a process that distributes a cell’s copied DNA to offspring
cells
D. Events that occur during Mitosis
1. Forming Spindle Fibers
a. In animal cells, centrioles move from the center of the
cell to the poles in opposite directions to form a spindle
b. Each spindle formed is referred to as a spindle fiber
2. Attaching Spindle Fibers to Centromeres
a. As chromosomes condense, microtubules called
kinetochores extend from the centromere
b. A kinetochore is a disk of protein that serves as a
platform for assembling microtubules
c. They continue to extend until they reach the poles of
the cell
d. The result is one chromatid attached to one pole, and
the other chromatid attached to the other pole
3. Separating Chromatids
a. Centromeres split the chromatid is dragged to one of
the poles as the fibers are dismantled, the chromosomes
move closer until they reach the pole
4. Dividing The Cell
a. A new nuclear envelope forms around each pole,
forming 2 nuclei and the chromosomes uncoil
b. Cytokinesis occurs, dividing the cytoplasm in half
V.
Stages of Mitosis (Figure 10-5)
A. Prophase (1st stage)
1. Chromsomes condense and become visible
2. The nucleolus and nuclear envelope break down and
disappear
3. Two pairs of dark spots called centrosomes appear; each
centrosome contains a pair of centrioles in animal cells
4. In plant cells centrosomes lack centrioles
5. The centrosomes in both plant and animal cells move
toward opposite poles of the cell
6. A network of spindle fibers made of microtubules, radiate
from the centrosome to form the mitotic spindle
7. The mitotic spindle is made of kinetochore fibers and polar
fibers
8. The kinetochore fibers attach to the kinetochore of the
centromere of a chromosome
9. The polar fibers extend the length of the cell from
centrosome to centrosome
B. Metaphase
1. The chromosomes move to the center of the cell and line up
along the “equator”
C. Anaphase
1. The two chromatids separate when the centromere divides
2. The chromatids are now called chromosomes that move
toward opposite poles of the cell
D. Telophase
1. The chromosomes are at opposite ends of the cell, uncoil to a
chromatin form
2. A new nuclear envelope and nucleolus form
3. The spindle fibers break down
4. Mitosis is complete
VI.
Cytokinesis (Figure 10-6)
A. The division of the cytoplasm
B. Begins with a pinching inward of the cell membrane between the
two poles
C. This area is called the cleavage furrow
D. Microfilaments pinch the cell forming two cells
E. In plant cells, a cell plate forms in the midline of the cell, where a
cell wall forms
VII.
Control of Cell Division (Figure 10-8)
A. In eukaryotic cells, proteins regulate the progress of cell division at
certain checkpoints
B. Feedback signals from the cell trigger the proteins to initiate the
next phase of the cell cycle or stop the cycle
C. 3 main checkpoints
1. Cell growth (G1) checkpoint
a. Proteins at this site control whether the cell will divide
b. If the cell is healthy, the proteins initiate DNA synthesis
c. The proteins stop at this point if the cell needs rest or is
unhealthy
d. Certain cells may enter the G0 phase at this checkpoint;
many cells that do will never divide again
2. DNA synthesis (G2) checkpoint
a. DNA repair enzymes check the results of DNA
replication
b. If the checkpoint is passed, proteins will signal the cell
to begin mitosis
3. Mitosis checkpoint
a. If the cell passes this checkpoint, proteins signal the cell
to exit mitosis
b. The cell then enters the G1 phase
D. When Control is Lost: Cancer (Figure 10-9)
1. The proteins that regulate cell growth and division are
coded for by genes
2. If a mutation occurs in one of the genes, the proteins may
not function properly
3. This could cause cell growth and division to be disrupted
4. The disruption could cause cancer; the uncontrolled growth
of cells
5. Some mutations cause cancer by overproducing growthpromoting molecules, which increases cell division
6. Other mutations interfere with the ability of control
proteins to slow or stop the cell cycle