Transcript The Cell Cycle

Ratio of Surface Area to Volume
 As the cell grows, its volume increases
much more rapidly than the surface area.
 The cell might have difficulty supplying
nutrients and expelling enough waste
products.
Transport of Substances
 Substances move by diffusion or by
motor proteins.
 Diffusion over large distances is slow and
inefficient.
 Small cells maintain more efficient
transport systems.
The Cell Cycle
 Cell division prevents the cell from becoming
too large.
 It also is the way the cell reproduces so that
you grow and heal certain injuries.
 Cells reproduce by a cycle of growing and
dividing called the cell cycle.
The Cell Cycle
 Interphase - the cell grows, carries out
cellular functions, and replicates.
 Mitosis - the cell’s nucleus and nuclear
material divide.
 Cytokinesis - a cell’s cytoplasm divides.
The Cell Cycle
• Interphase
–G1 (Gap1)
–S (DNA Synthesis)
–G2 (Gap2)
• Mitotic (M) Phase
• Cytokinesis
The Cell Cycle
The Stages of Interphase
 1st stage - G1
 The cell is growing, carrying out normal cell
functions, and preparing to replicate DNA.
The Stages of Interphase
 2nd Stage – S
 The cell copies its DNA in preparation for
cell division.
S phase
Genetic material (chromosomes) duplicate)
The Stages of Interphase
 3rd Stage - G2
 Cell prepares for division of nucleus (mitosis).
Stages of Mitosis
Prison
(Prophase)
Men
(Metaphase)
Are
(Anaphase)
Thin
(Telophase)
Prophase
 The cell’s chromatin tightens.
 Sister chromatids are attached at the
centromere.
 Spindle fibers form in the cytoplasm.
 The nuclear
envelope seems
to disappear.
 Spindle fibers
attach to the sister
chromatids.
Metaphase
 Sister chromatids line
up in the middle of
the cell.
Anaphase
 Microtubules of the
spindle apparatus
begin to shorten.
 Sister chromatids
separate.
 Chromosomes
move toward the
poles of the cell.
Telophase
 The chromosomes arrive at the poles and
begin to relax.
 Two new nuclear membranes begin to
form and the nucleoli reappear.
 The spindle apparatus disassembles.
Cytokinesis
Process by which the cytoplasm of a
cell is divided in two; usually follows
mitosis and meiosis.
Cytokinesis in Animal Cells
Microfilaments constrict,
or pinch, the cytoplasm to
create a cleavage furrow
Cytokinesis in Plant Cells
Cell wall too rigid for
microfilaments to constrict
cell.
Cell plate created.
How Cytokinesis Differs in Plants
Quality Control Checkpoints
 The cell cycle has built-in checkpoints that
monitor the cycle and can stop it if something
goes wrong.
 Spindle checkpoints also have been
identified in mitosis.
Cancer
A disease caused by severe
disruption of the mechanisms
that normally control the cell
cycle.
Causes of Cancer
 The changes that occur in the regulation of
cell growth and division of cancer cells are
due to mutations.
 Various environmental factors can affect the
occurrence of cancer cells.
Causes of cancer
•
•
•
•
•
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Food
Genetic mutations
Hormones
Radiation
Tobacco
Weight & physical activity
Workplace environment
Types of Tumors
Benign: An abnormal mass of essentially
normal cells.
Malignant: A mass of abnormal cells
resulting from uncontrolled cell
division.
Malignant Tumor
A mass of abnormal cells
resulting from uncontrolled cell
division
Metastasis
The spread of cancer cells
beyond their original site
Cancerous cells reproduce at an abnormally fast rate!
Cancer Treatment
•
•
•
•
Surgery
Radiation therapy
Chemotherapy
A mix of the three
Abnormal Cell Cycle: Cancer
 Cancer is the
uncontrolled growth
and division of cells.
 Cancer cells can kill
an organism by
crowding out normal
cells, resulting in the
loss of tissue function.
Stem Cells
 Unspecialized cells that can develop into
specialized cells when under the right conditions
Embryonic Stem Cells
 After fertilization, the resulting mass of cells
divides repeatedly until there are about
100–150 cells. These cells have not become
specialized.
Adult Stem Cells
 Found in various tissues in the body and might
be used to maintain and repair the same kind of
tissue
 Less controversial because the adult stem cells
can be obtained with the consent of their donor
 Producing offspring that are clones of
the parent
 No Diversity with asexual reproduction
Next
Slide
Asexual reproduction
Process in which a single cell or
set of cells produces offspring
that inherit all their genetic
material from one parent.
Offspring are not diverse.
Types of Asexual Reproduction
1. Binary Fission
2. Budding
3. Parthenogenesis
4. Regeneration
Binary Fission
A type of asexual reproduction in which a
prokaryote replicates DNA, and divides in
half, producing two identical daughter cells.
Budding
Offspring grows out of body of
parent.
Yeast
Hydra
(Unicellular fungi)
(Multicellular cnidarian)
Regeneration
In this form, if a piece of a parent is
detached, it can grow and develop
into a completely new individual.
Echinoderms exhibit this type of
reproduction.
 Genetic material from two parents
combines to produce offspring that
are genetically different from the
parents
Next
Slide
 The egg from a female & the sperm
from the male combine through
fertilization to form a zygote
 Egg and sperm are called Gametes
(sex cells)
Next
Slide
Two Methods of Reproduction
Asexual
– Offspring identical to the original cell or
organism
– Involves inheritance of all genes from one
parent
Sexual
– Offspring similar to parents, but show
variations in traits
– Involves inheritance of unique sets of genes
from two parents
Sexual reproduction
Process in which genetic material from two
parents combines and produces offspring
that differ genetically from either parent.
Leads to diversity in offspring.
Sperm, Eggs, & Fertilization
Testes - male organ that produces
sperm
Ovaries - female organ that produces
eggs.
Meiosis
A type of cell division that produces four cells,
each with half the # of chromosomes (haploid
#) as the parent cell.
23
Parent Cell
46
chromosomes
23
23
23
In meoisis, the final cells have half the number
of chromosomes as the parent cell.
Humans have 46 Chromosomes
(23 homologous pairs)
• 1 chromosome of each pair is from your mother
and 1 from your dad.
• 22 are alike, whether male or female (autosomes)
• The 23rd chromosome is called the Sex
Chromosome. It occurs as either X or Y.
XY = male
XX = female
Karyotype
A display of the chromosomes of
an individual.
Male Karyotype
Female Karyotype
Homologous Chromosomes
Two chromosomes in a matching pair.
Homologous Chromosomes
1. Each has the same sequence of genes. If
one has gene for eye color, the other will
too - at the same location.
2. However, the genes
might
be
slightly
different versions.
Mitosis & Meiosis Difference
Meiosis – 4 daughter cells with ½ the
number (haploid number) of original
chromosomes.
 Mitosis – 2 daughter cells with the same
number of original chromosomes.

Comparison of Meiosis & Mitosis
Meiosis
Mitosis
DNA Replication
1 time
1 time
Nuclear divisions
2
1
Number of daughter cells
4
2
Daughter cell chromosome number Haploid (n) Diploid (2n)
Daughter cells identical to parent
No
Yes
Meiosis increases genetic
variation
Crossing-over
Fertilization

In humans, (223)2 different
zygotes – over 70.3 trillion!
possible

If crossover occurs only once, then (423)2
4 octillion possible combinations. (27 0’s)