Chapter 9 CELL GROWTH AND DIVISION
DNA is a long thin molecule that stores Genetic Information. The DNA in a human cell is
estimated to consist of six billion pairs of nucleotides.
Cell Growth, Division, and Reproduction
LIMITS TO CELL SIZE (3)
1.
DNA controls the cell via protein synthesis.
A. As a cell grows, info used to build molecules must grow as well.
B. As cell increases, it’s DNA does not
C. Cells must remain small as the DNA that is available can serve the cell.
2. Exchanging Materials
A. Food, oxygen, and water enter through the cell membrane
B. Waste products exit through the cell membrane
C. If the cell gets to large, it become difficult for the cell to obtain enough oxygen
and nutrients (materials going in) and for waste products to get out.
1. Cells want a large surface area to volume ratio.
3.
Division of Cell
A. The process by which a cell divides into two new daughter cells
1. Cell must replicate or copy itself
a. each daughter cell gets a complete copy of DNA
2. Two types of cell division (Asexual and Sexual reproduction)
a. Asexual reproduction
1. Offspring arise from a single parent
2. Inherit genes from only one parent
3. Example: budding (from a plant),
binary fission (bacteria)
4. Survival strategy
a. when conditions are good reproduce faster.
b. Identical offspring is good as long as conditions remain
favorable
b. Sexual reproduction
1. Offspring arise from two parents
a. two main processes occur during sexual reproduction
1. Meiosis
2. Fertilization
2. Requires more time—can be advantageous for species that live
where environment undergoes changes (seasons)
3. Promotes genetic diversity
The process of cell division.
CHROMOSOMES—Genetic information bundled into packages of DNA.
1. PROKARYOTE –
A. no nucleus or membrane bound organelles.
B. 1 circular chromosome attached to the cell membrane.
C. 1/1000 the size of a eukaryotic cell.
2. EUKARYOTE–
A. nucleus and membrane bound organelles.
B. Species specific chromosome number.
C. Located in the nucleus.
D. The DNA in Eukaryotic cells wraps tightly around Proteins called
HISTONES.
E. Each half of the Chromosome is called a
CHROMATID or SISTER CHROMATIDS.
1. Sister chromatids are only visible when the cell is undergoing cell
division.
F. The constricted area of each chromatid is called a CENTROMERE .
Cell Cycle/Cell Division
All cells are derived from preexisting cells. Cell division is the process by which cells produce
offspring cells.
1. CELL DIVISION IN PROKARYOTES
A. BINARY FISSION is the Division of a Prokaryotic cell INTO
TWO Offspring Cells.
1. The chromosome makes a COPY of Itself
2. The cell continues to grow until it reaches approximately
TWICE its normal Size.
3. Then a CELL WALL begins forms between the two
Chromosomes.
4. The cell SPLITS into TWO NEW CELLS. Each new
cell contains IDENTICAL CHROMOSOMES.
2. CELL DIVISION IN EUKARYOTES
A. A Cell typically goes through PHASES of GROWTH and DEVELOPMENT
before it DIVIDES into new cells.
1. The phases of life of a cell are called THE CELLCYCLE. The cell cycle consists of two phases
A. INTERPHASE
B. CELL DIVISION
INTERPHASE-The portion of the cell cycle
between divisions.
1. Longest phase
2. Cell grows and develops
3. Divided into 3 phases.
a. G1 PHASE – cell increases in size
b. S PHASE – The genetic material
(DNA) is duplicated (copied/replicated).
Two identical copies of chromosomes
now exist.
c. . G2 PHASE – The number of organelles
and amount of cytoplasm in the cell
increases.
CELL DIVISION—The process by which one cell produces two new identical daughter cells.
Cell division consists of two stages”
1. Mitosis
2. Cytokinesis
MITOSIS is a Series of PHASES in cell division during which the NUCLEUS of a cell divides
into TWO nuclei with identical genetic material. Mitosis occurs ONLY in EUKARYOTES!!
A. MITOSIS
1.PROPHASE
a. Chromatin condenses into chromosomes.
b. The nucleolus and nuclear membrane disappear.
c. Centrosomes appear.
1. In animal cells, each centrosome contains CENTRIOLES.
2. Plant cells lack centrioles.
d. Spindle fibers made of microtubules radiate from the
centrosomes in preparation for mitosis.
2. METAPHASE
a. The chromosomes are moved to the MIDDLE of the cell.
b. The two sister chromatids of each chromosome are attached to fibers
radiating from OPPOSITE ends of the cell.
3. ANAPHASE
a. The centromeres of each chromosome are pulled by the
spindle fibers toward the ends of the cell.
b. The sister chromatids are separated from each other.
c. They are now considered to be individual chromosomes.
4. TELOPHASE
a. After the chromosomes reach opposite ends of the cell, the spindle fibers
disassemble.
b. The chromosomes return to less tightly coiled chromatin state.
c. New nuclear envelope begins to form around the
chromosomes at each end of the cell.
THE PROCESS OF MITOSIS IS NOW COMPLETE. THE CELL
MEMBRANE BEGINS TO PINCH THE CELL IN TWO AS CYTOKINESIS
BEGINS.
B. CYTOKINESIS—The cytoplasm of the cell divides into two new cells
called daughter cells, which are identical to the parent cells.
CYTOKINESIS = division of the cytoplasms
1. CYTOKINESIS OF ANIMAL CELLS:
A. CLEAVAGE FURROW
1. forms through the middle of the parent cell
(inward pinching).
2. The cleavage furrow deepens until the parent cell
pinches into TWO new identical cells.
2. CYTOKINESIS OF PLANT CELLS:
A. Cell membrane is not flexible enough to pinch inward.
B. Structure called the cell plate forms halfway
between divided nuclei.
C. Cell plate gradually develops into cell membrane that
separates the two daughter nuclei.
D. Cell wall forms between the two new membranes.
REGULATING THE CELL CYCLE
Cells in a Petri dish will usually stop growing when they come
in contact with other cells. Cancer cells continue to grow even after
they come in contact with other cells.
A. Cyclins regulate the timing of the cell cycle in eukaryotic cells.
1. Tells the cell when to divide.
2. Tells the cell when to duplicate chromosomes
3. Tells the cell when to enter phases of the cell cycle.
B. INTERNAL REGULATORS – proteins that respond to events inside the cell.
1. Allows the cell to proceed only when certain things happen in the cell.
C. EXTERNAL REGULATORS – proteins that respond to events outside the cell.
1. Growth factors stimulate growth and division of cells.
2. Molecules on the surface of the cell cause this process to stop or speed up.
D. APOPTOSIS–
1. is the process of programmed cell death (PCD) that may occur in
multicellular organisms.
2. Biochemical events lead to characteristic cell changes (morphology) and
death factors stimulate growth and division of cells.
E.Cancer cells do not respond to the signals that regulate the growth of most cells.
1. UNCONTROLLED CELL GROWTH.
2. Tumor—forms when a single cell divides uncontrollably a tumor is created
(a group of cells)
a. Can be benign (not harmful)
b. Can be malignant (harmful)
3. p53 gene is a protein that controls cell growth. If damaged it causes the cell
to lose the information needed to respond to signals to control the growth.
4. What causes the p53 gene to not function properly?
b. This change in gene is called a mutation.
5. Causes in mutation
a. Genetic
b. Environmental
1. radiation
2. cigarette smoke
.
Cell Differentiation
Differentiation: The process by which cells become specialized. Ex: a skin cell becomes a
skin cell, a liver cell becomes a liver cell.
I. From One Cell to Many
A. Life starts at just one cell
B. Living things must pass through developmental stage called an embryo
a. The developmental process begins at this stage.
C. Differentiation
1. This cell becomes different than the embryonic cell it arose from
2. Specialized to perform certain task
D. Mapping Differentiation
1. Cell’s role can be determined at a specific point in development.
E. Differentiation in mammals
1. Flexible.
2. Controlled by a number of interacting factors.
II. Stem Cells and Development
A. Totipotent cells
1. Cell that can do everything and develop into any type of cell.
2. Only fertilized egg and cells produced by first few cell divisions are
totipotent
B. Blastocyst
1. Created after 4 days of human development
2. Hollow ball of cells with a cluster of cells inside (inner cell mass)
3. Not yet specialized
4. Outer cells attach to mother
5. Inner cells become the embryo
6. Inner cells are pluripotent
a. Can develop into most, but not all body cells.
b. Can’t form tissues around embryo
Picture of a blastocyst
C. Stem cells
**The unspecialized cells from which differentiated cells develop.
**Can give rise to other types of cells
1. Embryonic stem cells
a. Pluripotent
b. Found in early embryos
c. Can be grown in culture
d. Can produce just about any type of cell in the body
2. Adult stem cells
a. Multipotent
1. Can development into many types of cells
b. Stem cells of a certain organ or tissue produce only the types of
cells unique to that tissue.
1. Ex: Stem cells from bone marrow can develop into
different types of blood cells but NOT into nerve cells.
III. Frontiers in Stem Cell Research
A. Benefits
1. Stem cell therapy COULD potentially reverse damage cause by strokes, heart
attack, and disease
B. Ethical issues
1. Adult stem cells are harvested from willing donor—no issue
2. Embryonic stem cell harvesting causes destruction of embryo.
Human Chromosome count
Body Cells
Sex Cells
aka
aka
SOMATIC CELLS GAMETES
46 chromosomes
23 chromosomes
(2n) DIPLOID
=TWO SETS.
ALL CELLS BUT
SEX CELLS
(n) HAPLOID = ½
set
SPERM & EGG
Female (23 chromosomes from egg) + Male (23 chromosome sperm )  Fertilization of
zygote
The Chromosomes in the Zygote exist in PAIRS. For every Chromosome that was in the egg,
there is a matching Chromosome from the sperm.
Chromosomes are categorized
1. SEX CHROMOSOMES – determine sex – XX female; XY male 2 chromosomes or 1 pair
2. AUTOSOMES – all other chromosomes that aren’t sex chromosomes – 44 chromosomes
or 22 pairs
MATCH SET OF AUTOSOMES IN A DIPLOID CELL =
HOMOLOGOUS PAIRS. CONTAIN INFORMATION THAT CODE
THE SAME TRAIT (GENES). Example Eye Color.