Transcript Chapter 9

Cell Cycle
Mitosis
Cell Reproduction
and
Cell Division
CELL REPRODUCTION
MITOSIS
• Cells continue to grow (protein synthesis)
• Cell
– Surface Area/Volume Hypothesis
• Answer to problems
– Cell Division
Cell Reproduction Problems
• I: DNA is a long and thin polymer. How does a
cell reproduce so that it is able to produce a new
cell without causing damage to the DNA?
• (Cell cycle and Mitosis)
• II: DNA must be reduced by half to produce a sex
cell. How does a cell carry out the reduction of
DNA without producing genetically deficient
gametes?
• (Cell cycle and Meiosis)
PROBLEMS THAT THE CELL MUST
OVERCOME TO REPRODUCE
•
Nuclear Nurturing
• How does a cell give DNA to the
offspring cell without losing it’s
own DNA
•
Reproductive Roulette
• What will stop the cells
reproductive cycle so that it does
not produce a large mass of
undifferentiated cells
– (Cancer)
•
Dainty DNA
• DNA is such a long thin molecule.
What can stop the cell from
fragmenting the DNA as it tries to
pass the DNA on to the new cell.
SOLUTIONS TO THE
PROBLEMS
• Nuclear Nurturing
• CELL CYCLE
• Reproductive Roulette
• CELL CYCLE
• Dainty DNA
• MITOSIS
LIFE CYCLE OF THE CELL
• Two major divisions to cell LIFE CYCLE
– GROWTH PHASE
• Cell doubles in mass
– DIVISION PHASE
• Cell divides into two smaller cells
CELL CYCLE
• G1 STAGE
• growth stage cell grows about twice it's size. Takes
about eight hours.
• S STAGE
• DNA replication process takes about six hours.
• G2 STAGE
• Growth stage. High degree of protein synthesis
• G1, S, G2
– COLLECTIVELY ARE CALLED INTERPHASE
• M STAGE
– Mitotic division stage.
Cell Cycle
Control
•
•
•
Cyclins
– a G1 cyclin (cyclin D)
– S-phase cyclins (cyclins E and A)
– mitotic cyclins (cyclins B and A)
– Their levels in the cell rise and fall with the stages of the
cell cycle.
Cyclin-dependent kinases (Cdks)
– a G1 Cdk (Cdk4)
– an S-phase Cdk ((Cdk2)
– an M-phase Cdk (Cdk1)
– Their levels in the cell remain fairly stable, but each must
bind the appropriate cyclin (whose levels fluctuate) in
order to be activated.
– They add phosphate groups to a variety of protein
substrates that control processes in the cell cycle.
Anaphase-promoting complex (APC).
– (The APC is also called the cyclosome, and the complex is
often designated as the APC/C.) The APC/C
– triggers the events leading to destruction of the cohesins
thus allowing the sister chromatids to separate;
– degrades the mitotic cyclin B.
Checkpoints
DIVISION PHASE
• TWO STAGES
– CYTOKINESIS
• DIVISION OF THE CELLS CYTOPLASM
– NUCLEAR DIVISION
• DIVISION OF THE CELLS DNA
TYPES OF NUCLEAR
DIVISION
• MITOSIS :
– DIVISION OF THE NUCLEAR MATERIAL
AN EQUATIONAL DIVISION
• MEIOSIS
– GAMETE CELL PREPARATION
– A REDUCTION _ EQUATIONAL DIVISION
MITOSIS
• DIVISION OF THE NUCLEAR MATERIAL
• Occurs in four stages that blend into each other.
Each stage is separated by distinct happenings.
– Four stages
•
•
•
•
•
P.M.A.T
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
ANALOGY
• PROPHASE
– Prepare
• METAPHASE
– Middle
• ANAPHASE
– Apart
• TELOPHASE
– Two
CHROMOSOMAL TIPS
• During interphase_-chromatin is diffuse but
firmly attached to the nuclear matrix (sometimes
called the chromatin net).
• During mitosis_-chromosomes condense.
Chromosomes tightly coiled around a protein
chromosomal scaffold. Helps prepare the
chromosome for division of nuclear material more
efficiently.
• Chromosomes come in pairs. A pair of
chromosomes are called homologue.
PROPHASE
• NUCLEAR PREPARATION
• Chromosomes condense
• Spindles (microtubule) organize at the poles may form asters.
Cytoskeleton disassembles forming a large pool of tubulin
dimers. In animal cells the paired Centriole may initiate the
production of the spindles or align them.
• Nuclear membrane disappears. The membrane breaks up into
membrane fragments indistinguishable from bits of
endoplasmic reticulum.
METAPHASE
• NUCLEAR ALIGNMENT ON EQUATOR
(MIDDLE)
– Spindles position the chromosomes midway
between each spindle pole (mitotic center) of
the cell at the equatorial plate or metaphase
plate. In animal cells the spindle pole consists
of a pair of centrioles surrounded by a radial
array of Microtubules called an ASTER.
ANAPHASE
• NUCLEAR MATERIAL IS SEPARATED
(APART)
– chromosomes are separated at the centromere.
• The two separate chromatids are now called
daughter chromosomes.
• Separation continues as the daughter
chromosomes are pulled towards their respective
poles.
• Mitotic poles of the cell move farther apart.
TELOPHASE
•
•
•
•
•
(TWO)
TWO NUCLEI AND CYTOKINESIS
Chromosomes are at the separate poles
Nuclear membrane assembles
Chromosomes Decondense
CYTOKINESIS
• Animals:
• Cell (cleavage) furrow is formed. Cell is pinched in
the middle by Microfilaments squeezing the center
(CONTRACTILE RING).
• Plants:
• Cell plate forms. Tiny vesicles form first. Cell plate
develops from vesicles pectin. The pectin fills the
plate forming the middle lamella. Primary cell wall
forms
Meiosis
Set Reduction
of
Chromosomes
SEXUAL REPRODUCTION
• CELL REPRODUCTION
– The process of cell generation. An existing cell procures the
existence of another cell.
• TYPES
– Asexual
– The genetic material of a new cell is contributed by a single
cell. Mitotic division is the mechanism of Asexual
reproduction. Varied names are applied to this type of
reproduction in organisms, such as budding, cleavage,
fission, regeneration, and others.
– Sexual
– The genetic material of a new cell is contributed by two
parent cells. The genome of the new cell is dissimilar from
both of the parent cells. Meiotic division and fertilization
are the mechanisms of sexual reproduction.
GENETIC ADVANTAGES OF
SEXUAL REPRODUCTION
• The cell ability to survive unpredictable
changes in the environment.
• This provides an ability of adaptability. (e.g.
Bacterial resistance to antibiotics)
• Genetic combination of material from one
organism to a population.
MEIOSIS AND SHUFFLING
CHROMOSOMES
• DIPLOID
– TWO COPIES OF EACH CHROMOSOME.
• HAPLOID (MONOPLOID)
– A SINGLE COPY OF EACH CHROMOSOME.
MEIOSIS
• TWO STEPS
– MEIOSIS I
• reduction division
• PMAT I
– MEIOSIS II
• equational division
• PMAT II
MEIOSIS I
•
•
•
•
Prophase I
Metaphase I
Anaphase I
Telophase I
Mitosis Review
Importance in comparison
– Leptotene
• Chromosomes coil (Condense)
– Zygotene
• Chromosomes form synaptonemal complex which
holds two homologue (Bivalent) together like a
zipper. Crossing over occurs during Zygotene.
– Pachytene
• Chromosomes continue to condense and are held
tightly by the synaptonemal complex.
– Diplotene
• Further condensation of chromosomes occur.
Individual chromosomes separate along the
synaptonemal complex and are repulsed except at
the chiasmata (chiasma).
– Diakinesis
• Nuclear membrane fragmentation, and
chromosomes are at maximum condensation.
Prophase I
METAPHASE I
Chromosome bivalents line up on the equatorial plane in a
tetrad formation. The tetrad formation is different from
the chromosome arrangement during mitotic division and
meiotic II division.
ANAPHASE I
• Chromosomes separated similar to the mitotic
process except complete homologue are
pulled towards the poles.
• This step causes a "Reduction Division".
TELOPHASE I
• Chromosomes have reached the cell's poles
and a cytokinesis may occur at this time.
Chromosomes will remain in the coiled
condition for the second stage of meiosis.
During Meiosis the paternal is separated from
the maternal.
Rr?
S
S
R
R
Rr?
Mitosis
s
s
r
r
S
S
s
s
Rr or RR
Or RS?
R
r
R
r
Rr or rr
Or rs?
Meiosis I
Homologous
Pairs
Tetrad
MEIOSIS II
• Four Stages
– Prophase II, Metaphase II, Anaphase II,
Telophase II
• Similar to mitosis
• Results: Two haploid cells produce four
haploid cells
GAMETE PRODUCTION
• Spermatogenesis
– millions produced
• Oogenesis
– 1 egg and 3 polar bodies
– Does NOT finish in humans until
fertilization
Life Cycles
• Alternation between haploid and diploid cell
structures
• Three Types
– Diplonic
– Haplonic
– Alternation between Diplonic and Haplonic
called Alternation of Generations