The Cell Cycle
Reproduction
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Organisms can reproduce:
1. Sexually
AND/OR
2. Asexually
Cell Division
• Multicellular organisms undergo asexual
cellular division (mitosis) for growth and
repair.
Asexual Reproduction
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Cloning
Binary fission
Mitosis
Regeneration
Fragmentation
• Any variations that arise are due to
mutations.
Sexual Reproduction
• Requires gametes
• Gametes form through meiosis
• Fertilization of gametes creates a
genetically unique individual.
Chromosomes
• DNA and proteins iare organized into
chromosomes.
• Somatic cells (non-sex cells) have two of
each type of chromosome. The set is
called a homologous pair.
• Somatic cells are diploid or 2n cells.
Gametes
• Sex cells- egg and sperm
• Haploid or n cells.
Fertilization
• Union of gametes to form a zygote.
• Restores the diploid number of
chromosomes.
Diplonic Life Cycle
• Animals and some plants
• The only haploid cells are the gametes.
• Gametes unite to form the diploid
organism.
Haplonic Life Cycle
• Fungi and some protists
• Only diploid cell is the zygote
• Gametes are formed through mitosis, and
spores are produced through meiosis
which germinate to form the organism.
Alternation of Generations
• Most plants and some protists
• Diplonic and haplonic life forms
• Spores formed through meiosis and grow
into the gametophyte.
• Gametes formed through mitosis which
unite to form the sporophyte.
The Cell Cycle
• Interphase (preparation for cell division)
• Mitosis (Splitting of the chromosomes)
• Cytokinesis (Splitting of the cytoplasm)
Interphase
• Chromatin
• Visible nucleus
• 3 Subphases
– G1
– S (DNA replication)
– G2
Mitosis
• Prophase
– Chromatin condenses
– Spindle and centrosomes appear
• Metaphase
– Chromosomes align at the equator
• Anaphase
– Sister chromatids are pulled apart,
• Telophase
– Nuclear envelope reforms around daughter
chromosomes.
Cytokinesis
• Splitting of the cytoplasm to form two
identical cells.
• Animal cells form a contractile ring and
pinch.
• Plant cells form a cell plate and then a cell
wall originating from golgi apparatus
vesicles.
Regulation
• Cells divide due to growth factors.
• Check points regulate timing.
• Cdks, or cyclin-dependent kinases,
phosphorylate proteins using ATP to allow
the cell cycle to proceed from one step to
the next.
Important Proteins
• G1-S cyclin binds to Cdk which then
inhibits RB (retinoblastoma protein) so that
transition to the S phase can occur.
• M phase cyclin binds to Cdk which allows
separase to hydrolyze cohesin so that
chromatids can separate.
• Cytoplasmic dynein hydrolyzes ATP for
chromosomes to move to poles.
Meiosis
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Creation of gametes
2 nuclear divisions
Reduction division
Genetic variation
Meiosis I separates homologues
Meiosis II separates sister chromatids
Genetic variation
• Mutations
• Crossing over resulting in recombinant
chromosomes
• Independent assortment
Prophase I
• Crossing over
• Males-lasts about a week
• Females- occurs prior to birth
• Crossing over between non-homologues is
called a translocation.
Nondisjunction
• Meiotic error resulting in abnormal
chromosome numbers.
• Aneuploidy
• Polyploidy
Cell Death
• Necrosis
• Apoptosis