AP Biology: Drackett Notes
College Board:
3.A.2 – The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determines
the ultimate fate of the cell
 Interphase consists of three phases; growth, synthesis, preparation for mitosis
 The cell cycle is directed by internal control or checkpoints internal and external signals provide
stop-and-go signs at the checkpoints
– MPF
– Platelet-derived growth factor (PDGF)
– Cancer results from disruptions of the cycle controls
– Cyclins and cyclin-dependent kinases control the cell cycle
 Mitosis alternates with interphase
 After specialization, a cell enters a non-dividing state but may re-enter the cell cycle when given
appropriate cues
 Mitosis passes a genome from the parent cells to daughter cells
– Mitosis occurs after DNA replication
– Produces two identical cells
– Growth, repair, asexual reproduction
– Continuous process with observable structures (order of the processes – replication,
alignment, separation)
 Meiosis, a reduction division followed by fertilization ensures genetic diversity in sexually
reproducing organisms
– Ensures each gamete receives one complete haploid (1n) set of chromosomes
– Homologous chromosomes are paired with one homologue originating from the maternal
parent and one from the paternal parent. Orientation of the chromosome pairs is random with
respect to the cell poles
– Separation of the homologous chromosomes ensures that each gamete receives a haploid set
of chromosomes composed of both maternal and paternal chromosomes
– Homologous chromosomes may exchange genetic material via ‘crossing over’ which
increase genetic variation
– Fertilization involves the fusion of two gametes increase genetic variation in populations by
providing for new combinations of genetic information in the zygote and restores the diploid
number of chromosomes
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Terms
Anaphase
Binary fission
Cancer
Cell cycle
Cell plate
Checkpoint
Chromatin
Chromosome
Crossing over
Cleavage furrow
Cyclin
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Cyclin-dependent kinase (Cdk)
Cytokinesis
Density dependent inhibition
Diploid
G0
G1
G2
Gamete
Genome
Haploid
Homologous chromosomes
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Interphase
M phase
Meiosis
Metaphase
Mitosis
MPF
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PDGF
Prophase
S phase
Sister chromatids
Somatic cell
Telophase
BIG Idea # 3 Genetics and Information Transfer
3.A.2 – The Cell Cycle Is A complex Set of Stages That Is Highly Regulated With
Checkpoints, Which Determines the Ultimate Fate of the Cell
– Mitosis passes a genome from the parent cells to daughter cells
• Mitosis occurs after DNA replication
• Produces two identical cells for growth, repair, asexual
reproduction
• Continuous process with observable structures (order of the
processes – replication, alignment, separation)
• Alternates with interphase
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Genome - all the genes of an organism
Genes – sections of DNA with code for making proteins
Cell Division
– Prokaryote – circular DNA
– Bacteria divide by binary fission
– No coiling of DNA
– No proteins (histones) to manage
the DNA (no chromatin)
Eukaryote
– DNA ‘managed’ by proteins
– DNA is making proteins most of the
time
– DNA coils into chromosomes
Eukaryotic DNA - Chromatin - DNA + proteins (histones)
– Before mitosis, chromatin is replicated; chromatin condenses, coils and folds into a
chromosome; Chromosome = two sister chromatids connected by a centromere
– Chromatids are pulled apart by contracting spindle fibers into two new cells at the end of
mitosis/meiosis
Chromosomes are homologous pairs
– Each species has a characteristic number of chromosomes
– Human somatic cells have 46 (diploid)
– Human gametes have 23 (haploid)
– Karyotype – arrangement of chromosomes
After specialization, some cells (liver) enters a non-dividing state Go but may re-enter the cell cycle
when given appropriate signals
Interphase (longest time in cell cycle) - three phases:
– Three subphases:
– G1 (“first gap”) growth
– S (“synthesis”) DNA is copied
– G2 (“second gap”) cell completes preparations for mitosis
– G0 – after mitosis some cells do not re-enter ‘S’
College Board: The cell cycle is directed by internal control or checkpoints internal
and external signals provide stop-and-go signs at the checkpoints.
– MPF
– Platelet-derived growth factor (PDGF)
– Cancer results from disruptions of the cycle controls
– Cyclins and cyclin-dependent kinases control the cell cycle
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Checkpoints in the cycle are for control - checks to be sure all ‘steps’ are completed before moving on
Hormone signals from outside also help control the cycle
– 3 checkpoints; G1, G2, and M phases
– G1 checkpoint (restriction point) is most important
– Go signal = completes cell cycle and divides
– No Go = cell exits cycle
– Rhythmic fluctuations of proteins controls the cycle
• Kinases - activate or deactivate other proteins; constant amount
• Cyclins – levels fluctuate
• Kinases and cyclin form cyclin-dependent kinases (Cdks)
• Amount of cyclin increases during interphase, then decreases during mitosis
• MPF – “Maturation-Promoting Factor” (composed of cyclin-Cdk - ) triggers cell
past G2 checkpoint to M phase
– M phase checkpoint - ensures that the chromosomes are attached to the spindle at metaphase
plate before anaphase begins so that daughter cells do not end up with missing or extra
chromosomes; APF
Mitosis is a continuous process:
– Mitosis is ‘usually’ broken into four subphases:
– Prophase – formation of chromosomes
• Centrioles/centrosomes divide and begin to form spindle
• G2 checkpoint; MPF builds to a peak
– Metaphase – chromosomes align in the middle
– Anaphase – separation of chromatids; pulled towards ‘poles’ by spindle fibers
– Telophase - Cell elongates; nucleus reforms, chromatin uncoils
– Cytokinesis begins (splitting of the cell in two)
• Animal cells - cleavage furrow - contractile ring of actin and myosin forms
• Plants have cell walls - cell plate - vesicles from Golgi coalesce at the metaphase
plate, plate enlarges until fused with the plasma membrane
Density-dependent inhibition
• Normal cultured cells divide until they form a single layer; Cells will grow to fill a gap
Anchorage dependence – cells must be anchored
• Cancer cells - do not respond to density-dependent inhibition or anchorage dependence
• Do not stop dividing when growth factors run out
• May be ‘immortal’; HeLa cells - Henrietta Lacks
• Normal cells - 20 to 50 times in vitro
Meiosis:
Terms
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Allele
Chromosome
Crossing over
Fertilization
Gamete
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Gametogenesis
Gene
Locus
Meiosis I
Meiosis II
Sex chromosome
Sexual reproduction
Synapsis
Tetrad
Zygote
College Board:
• Meiosis, a reduction division followed by fertilization, ensures genetic diversity in
sexually reproducing organisms
• Ensures each gamete receives one complete haploid (1n) set of chromosomes
• Homologous chromosomes are paired with one homologue originating from the
maternal parent and one from the paternal parent. Orientation of the
chromosome pairs is random with respect to the cell poles
• Separation of the homologous chromosomes ensures that each gamete receives a
haploid set of chromosomes composed of both maternal and paternal
chromosomes
• Homologous chromosomes may exchange genetic material via ‘crossing over’
which increases genetic variation
• Fertilization involves the fusion of two gametes increasing genetic variation in
populations by providing for new combinations of genetic information in the
zygote and restores the diploid number of chromosomes
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Asexual Reproduction
Single parent
No genetic variation
Cloning, plant cuttings, corals; Binary
fission in bacteria
Spores – plants, fungi
Very rapid, energy efficient method
Few mutations - ‘bad’ or ‘weak’ genes also
passed along; Genes are susceptible to
environmental change
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Sexual reproduction:
Requires more energy
Slower
Gametogenesis - meiosis
Genetic variation***
Survival of the fittest
Somatic cell - any cell other than gamete
Gamete - sex cell, haploid
• Homologous Chromosomes - Homologues - same size, same genes
• Same gene loci – location of gene on the chromosome
• Autosome - non-sex chromosomes (22 pairs)
• Sex chromosome – carries gene that determines gender; dissimilar
Mitosis:
• Meiosis:
4 stages
• 8 stages
2 identical daughter cells
• 4 non-identical cells
Diploid (2n)
• Haploid (1n)
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Meiosis – Crossing Over
• Prophase I:
• Synapsis - homologous chromosomes come together as pairs
• Tetrads
Nondisjunction - chromatids fail to separate during meiosis
Gametes are ANEUPLOID (have incorrect number of chromosomes)