The Cell Cycle (Mitosis and Asexual Reproduction) Review
Chapter 9: The Cell Cycle (Mitosis and Asexual Reproduction)
Evolution and Ecology: Unit 2 Genetics
Core Principle: All organisms live to reproduce.
Key Goal: Maintaining genetic variation over generations.
Cellular Processes Discussed:
Mitosis: Involves cloning and reproduction.
Meiosis: Involves shuffling alleles, life cycles, and considers haploid and diploid stages.
Replication and Reproduction: Learning Objectives
What to Know: Details of mitosis.
What to Think About: How asexual reproduction is essentially cloning.
What to Understand:
Asexual reproduction is successful under certain conditions.
Only about 1,000 truly asexually reproducing species exist.
Overview: The Key Roles of Cell Division
Distinguishing Feature of Life: The ability of organisms to produce more of their own kind is a primary characteristic separating living from nonliving matter.
Continuity of Life: This is fundamentally based on the reproduction of cells, or cell division.
Unicellular Organisms: For these organisms, the division of one cell directly reproduces the entire organism.
Concept 9.1: Most cell division results in genetically identical daughter cells
Genetic Material Transfer: Identical genetic material (DNA) is passed from parent to two daughter cells.
Accuracy of DNA Transmission: DNA is passed between generations with very little error.
Cellular Organization of the Genetic Material
Genome: All the DNA in a cell constitutes the cell's genome.
Prokaryotes: A genome can consist of a single DNA molecule.
Eukaryotes: A genome usually consists of a number of DNA molecules.
Chromosomes: DNA molecules in a cell are packaged into chromosomes.
Eukaryotic Chromosomes: Consist of chromatin, which is a complex of DNA and protein.
Species-Specific Chromosome Number: Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.
Distribution of Chromosomes During Eukaryotic Cell Division
DNA Replication and Condensation: Before division, DNA is replicated, and chromosomes condense.
Sister Chromatids: Each duplicated chromosome consists of two sister chromatids.
Centromere: These sister chromatids are joined together at a specialized region called the centromere.
S Phase: DNA replication and duplication of chromosomal proteins in eukaryotes occur specifically during the S phase of the cell cycle.
Result of Duplication: This process produces two exact copies (sister chromatids).
Separation During Cell Division: During cell division, the two sister chromatids of each duplicated chromosome separate and move into two distinct nuclei.
Post-Separation Terminology: Once separated, the individual chromatids are then considered and referred to as full chromosomes.
Visual Representation: A chromosome arm is present, and sister chromatids are identical chromosomal DNA molecules.
Eukaryotic Cell Division: Mitosis and Cytokinesis
Two Main Stages:
Mitosis: The division of the genetic material (DNA) within the nucleus.
Phases of Mitosis:
Prophase: Chromosomes condense, early mitotic spindle forms, nuclear envelope begins to break down.
Prometaphase: Nuclear envelope fragments, kinetochore forms at centromeres, microtubules attach to kinetochores.
Metaphase: Chromosomes align at the metaphase plate (equator of the cell), centrosomes are at opposite poles.
Anaphase: Sister chromatids separate (now individual daughter chromosomes) and move to opposite poles.
Telophase: Daughter nuclei form at the two poles, nuclear envelopes reform, chromosomes decondense, nucleoli reappear.
Cytokinesis: The division of the cytoplasm, which typically overlaps with the latter stages of mitosis (anaphase and telophase).
Cytokinesis: A Closer Look
Animal Cells:
Occurs via a process known as cleavage.
Involves the formation of a cleavage furrow, which is a contractile ring of microfilaments that pinches the cell in two.
Plant Cells:
A cell plate forms in the middle of the cell, eventually developing into a new cell wall that separates the two daughter cells.
Asexual Reproduction: Various Forms
Binary Fission:
Organisms: Prokaryotes (bacteria, archaea), protozoans (e.g., Euplotes).
Process in E. coli:
Chromosome replication begins at the origin of replication.
One copy of the origin moves to each end of the elongating cell.
Replication finishes, and the cell continues to elongate.
The plasma membrane pinches inward, dividing the cell into two genetically identical daughter cells.
Mitosis:
Organisms: Diatoms, yeast (e.g., fungi).
Parthenogenesis:
Organisms: Aphids, bees, Daphnia, lizards, salamanders.
The Evolution of Mitosis
Evolutionary Origin: Mitosis in eukaryotes likely evolved from binary fission, the simpler cell division process seen in prokaryotes.
Intermediate Forms: Certain protists and yeasts exhibit types of cell division that appear intermediate between prokaryotic binary fission and eukaryotic mitosis.
Dinoflagellates: Intact nuclear envelope, microtubules pass through the cytoplasm and attach to the nuclear envelope.
Diatoms and some yeasts: Intact nuclear envelope, kinetochore microtubules form a spindle within the nucleus.
Not All Asexually Reproducing Species are "Primitive"
Examples of Complex Asexual Organisms:
Strawberry Plant (via runners)
Maternity Plant (via plantlets)
Quaking Aspen (via root suckers)
These examples demonstrate that diverse and advanced organisms can utilize asexual reproduction very effectively.
Chapter 9: The Cell Cycle (Mitosis and Asexual Reproduction)
Evolution and Ecology: Unit 2 Genetics
Core Principle: All organisms live to reproduce.
Key Goal: Maintaining genetic variation over generations.
Cellular Processes Discussed:
Mitosis: Involves cloning and reproduction.
Meiosis: Involves shuffling alleles, life cycles, and considers haploid and diploid stages.
Replication and Reproduction: Learning Objectives
What to Know: Details of mitosis.
What to Think About: How asexual reproduction is essentially cloning.
What to Understand:
Asexual reproduction is successful under certain conditions.
Only about 1,000 truly asexually reproducing species exist.
Overview: The Key Roles of Cell Division
Distinguishing Feature of Life: The ability of organisms to produce more of their own kind is a primary characteristic separating living from nonliving matter.
Continuity of Life: This is fundamentally based on the reproduction of cells, or cell division.
Unicellular Organisms: For these organisms, the division of one cell directly reproduces the entire organism.
Concept 9.1: Most cell division results in genetically identical daughter cells
Genetic Material Transfer: Identical genetic material (DNA) is passed from parent to two daughter cells.
Accuracy of DNA Transmission: DNA is passed between generations with very little error.
Cellular Organization of the Genetic Material
Genome: All the DNA in a cell constitutes the cell's genome.
Prokaryotes: A genome can consist of a single DNA molecule.
Eukaryotes: A genome usually consists of a number of DNA molecules.
Chromosomes: DNA molecules in a cell are packaged into chromosomes.
Eukaryotic Chromosomes: Consist of chromatin, which is a complex of DNA and protein.
Species-Specific Chromosome Number: Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.
The Cell Cycle
Definition: The life of a cell from the time it is first formed during division of a parent cell until its own division into two daughter cells.
Two Major Phases:
Interphase: Cell growth and copying of chromosomes in preparation for cell division. This phase typically makes up about 90\% of the cell cycle.
G1 phase ("first gap"): Cell grows, carries out normal metabolic functions, and synthesizes proteins and organelles.
S phase ("synthesis"): DNA replication and duplication of chromosomal proteins in eukaryotes occur specifically during the S phase of the cell cycle. This process produces two exact copies (sister chromatids).
G2 phase ("second gap"): Cell grows further, completes preparations for cell division, and synthesizes proteins and organelles needed for mitosis.
M phase (Mitotic phase): Consists of mitosis and cytokinesis.
Distribution of Chromosomes During Eukaryotic Cell Division
DNA Replication and Condensation: Before division, DNA is replicated (during S phase), and chromosomes condense.
Sister Chromatids: Each duplicated chromosome consists of two sister chromatids.
Centromere: These sister chromatids are joined together at a specialized region called the centromere.
Result of Duplication: This process produces two exact copies (sister chromatids).
Separation During Cell Division: During cell division, the two sister chromatids of each duplicated chromosome separate and move into two distinct nuclei.
Post-Separation Terminology: Once separated, the individual chromatids are then considered and referred to as full chromosomes.
Visual Representation: A chromosome arm is present, and sister chromatids are identical chromosomal DNA molecules.
Eukaryotic Cell Division: Mitosis and Cytokinesis
Two Main Stages:
Mitosis: The division of the genetic material (DNA) within the nucleus.
Phases of Mitosis:
Prophase: Chromosomes condense, early mitotic spindle forms, nuclear envelope begins to break down.
Prometaphase: Nuclear envelope fragments, kinetochore forms at centromeres, microtubules attach to kinetochores.
Metaphase: Chromosomes align at the metaphase plate (equator of the cell), centrosomes are at opposite poles.
Anaphase: Sister chromatids separate (now individual daughter chromosomes) and move to opposite poles.
Telophase: Daughter nuclei form at the two poles, nuclear envelopes reform, chromosomes decondense, nucleoli reappear.
Cytokinesis: The division of the cytoplasm, which typically overlaps with the latter stages of mitosis (anaphase and telophase).
Cytokinesis: A Closer Look
Animal Cells:
Occurs via a process known as cleavage.
Involves the formation of a cleavage furrow, which is a contractile ring of microfilaments that pinches the cell in two.
Plant Cells:
A cell plate forms in the middle of the cell, eventually developing into a new cell wall that separates the two daughter cells.
Asexual Reproduction: Various Forms
Binary Fission:
Organisms: Prokaryotes (bacteria, archaea), protozoans (e.g., Euplotes).
Process in E. coli:
Chromosome replication begins at the origin of replication.
One copy of the origin moves to each end of the elongating cell.
Replication finishes, and the cell continues to elongate.
The plasma membrane pinches inward, dividing the cell into two genetically identical daughter cells.
Mitosis:
Organisms: Diatoms, yeast (e.g., fungi).
Parthenogenesis:
Organisms: Aphids, bees, Daphnia, lizards, salamanders.
The Evolution of Mitosis
Evolutionary Origin: Mitosis in eukaryotes likely evolved from binary fission, the simpler cell division process seen in prokaryotes.
Intermediate Forms: Certain protists and yeasts exhibit types of cell division that appear intermediate between prokaryotic binary fission and eukaryotic mitosis.
Dinoflagellates: Intact nuclear envelope, microtubules pass through the cytoplasm and attach to the nuclear envelope.
Diatoms and some yeasts: Intact nuclear envelope, kinetochore microtubules form a spindle within the nucleus.
Not All Asexually Reproducing Species are "Primitive"
Examples of Complex Asexual Organisms:
Strawberry Plant (via runners)
Maternity Plant (via plantlets)
Quaking Aspen (via root suckers)
These examples demonstrate that