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Questions and Answers
What role do checkpoint proteins play in the cell cycle?
What role do checkpoint proteins play in the cell cycle?
Which checkpoint is considered the most critical for determining if a cell can enter the division cycle?
Which checkpoint is considered the most critical for determining if a cell can enter the division cycle?
What structure is primarily responsible for organizing and sorting chromosomes during mitosis?
What structure is primarily responsible for organizing and sorting chromosomes during mitosis?
How do sister chromatids move to opposite poles during mitosis?
How do sister chromatids move to opposite poles during mitosis?
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What occurs during cytokinesis in animal cells?
What occurs during cytokinesis in animal cells?
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What is the composition of the mitotic spindle?
What is the composition of the mitotic spindle?
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What does the G0 phase signify for a cell?
What does the G0 phase signify for a cell?
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Which type of microtubule stabilizes the spindle apparatus but does not attach to chromosomes?
Which type of microtubule stabilizes the spindle apparatus but does not attach to chromosomes?
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What is the primary purpose of mitosis in eukaryotic cells?
What is the primary purpose of mitosis in eukaryotic cells?
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Which phase follows the G1 phase in the cell cycle?
Which phase follows the G1 phase in the cell cycle?
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What characteristic distinguishes human sex chromosomes from autosomes?
What characteristic distinguishes human sex chromosomes from autosomes?
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What is the role of sister chromatids during mitosis?
What is the role of sister chromatids during mitosis?
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Which of the following correctly describes the G2 phase?
Which of the following correctly describes the G2 phase?
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What occurs at the G1 checkpoint in the cell cycle?
What occurs at the G1 checkpoint in the cell cycle?
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What is the outcome of cytokinesis following mitosis?
What is the outcome of cytokinesis following mitosis?
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Which statement about homologous chromosomes is correct?
Which statement about homologous chromosomes is correct?
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How many total chromosomes are present in a human somatic cell?
How many total chromosomes are present in a human somatic cell?
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What is a karyotype used to analyze in a dividing cell?
What is a karyotype used to analyze in a dividing cell?
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Study Notes
The Eukaryotic Cell Cycle
- Cells are the fundamental units of life
- The continuity of life relies on genetic material transfer between cells
Why Do Cells Divide?
- Reproduction
- Growth and development
- Cell replacement and tissue renewal
Types of Cell Division in Humans
- Asexual (genetic clones):
- Mitosis conserves chromosome number
- Sexual (genetic variation):
- Meiosis occurs only in gamete (sex cell) production
- Reduces chromosome number
Eukaryotes and Chromosomes
- Human somatic cells have 23 pairs (46 total) of chromosomes
- Autosomes: 22 pairs
- Sex chromosomes: 1 pair (XX or XY)
- Diploid (2n)
- Human gametes have 1 member of each chromosome pair (23 total) - Haploid (n)
Homologous Chromosomes
- Members of a chromosome pair are called homologs (homologous chromosomes)
- They are nearly identical in size and genetic composition
- Example: Both carry eye color genes, but one may have brown and the other blue
Sex Chromosomes
- Not true homologs
- X and Y chromosomes differ significantly in size and genetic composition
Two Types of Nuclear Division
- Mitosis and Meiosis
- Mitosis leads to identical diploid daughter cells for growth and repair.
- Meiosis leads to haploid gametes for sexual reproduction.
- Diagrams of the cell cycle shown.
Genome and Chromosomes
- Genome usually exists as chromatin
- Chromosomes condense only to prepare for division
- DNA is organized into multiple genes along chromosomes
- Centromere: is the narrow region where replicated chromosomes join
Karyotype
- Karyotype reveals chromosome number, size, and form in dividing cells
Cell Cycle (Life Cycle of a Cell) Phases
- Interphase:
- G1 (first gap): Cell growth and development; commitment to division at G1 checkpoint
- S (synthesis): DNA replication
- G2 (second gap): Protein and structure synthesis for mitosis
- G0: cells postponing division or never dividing again
- M (mitosis and cytokinesis)
S Phase
- Each chromosome replicates
- Replicated chromosomes are called sister chromatids
- Sister chromatids remain attached at the centromere
- Human cells have 46 chromosomes in G1 phase and 92 sister chromatids in G2 phase
G2 Phase
- Synthesizes proteins and structures needed during mitosis and cytokinesis
Mitosis
- Nuclear division, separation of sister chromatids
- Followed by cytokinesis to form two daughter cells
Control of Cell Division
- External factors: environmental conditions, signaling molecules, determines if a cell divides
- Internal factors: cell cycle control molecules, checkpoints.
- Internal checkpoints: G1/S, G2/M, Metaphase
Internal Checkpoints
- G1/S checkpoint (restriction point): determines if conditions are favorable and if DNA is undamaged
- Cells that fail checkpoint exit cycle to G0
- G2/M checkpoint: Checks DNA replication; monitors protein levels needed for mitosis
- Metaphase (spindle) checkpoint: Ensures all chromosomes are attached to the spindle apparatus
Checkpoint proteins
- Cyclins and cyclin-dependent kinases (cdks) advance cells through checkpoints.
- Cyclin levels vary; Cdks are constant but require binding to a cyclin to be active
- Checkpoint proteins act as sensors determining if the cell is ready for cell division
Mitosis Stages
- Interphase
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Mitotic Spindle
- Crucial for segregation of chromosomes into daughter cells - Ensures each daughter cell receives correct # chromosomes
- Mitotic spindle apparatus/spindle is responsible for organizing and sorting the chromosomes during mitosis.
- Centrosomes are microtubule organizing centers
Spindle Microtubules
- Comprised of tubulin proteins
- Three types
- Astral microtubules
- Polar microtubules
- Kinetochore microtubules.
Chromosome movement during mitosis
- Motor proteins attached to chromosomes move during mitosis by de-polymerizing at kinetochore ends.
Cytokinesis
- Division of cytoplasm to form two new cells
- Animals: Cleavage furrow constriction
- Plants: Cell plate forms cell wall.
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Description
Explore the fascinating processes of the eukaryotic cell cycle, including the reasons for cell division and the types of cell division in humans. Understand the roles of mitosis and meiosis, as well as the structure and significance of chromosomes and homologous chromosomes.
