Cell Cycle and Cell Division Flashcards
Mitosis
- Makes two daughter cells (almost identical to parent cell)
Meiosis
- Daughter cells get half of the parent cell’s genetic information
Interphase Phases
G1: Grows in preparation for cell division. 46 chromosomes are organized in tangled chromatin fibers
S: Each Chromatid is copied. Still 46 chromosomes but each chromosome has 2 sister chromatids joined at a centromere (92 chromatids todal)
G2: More growth prior to entering mitosis. Cell duplicates organelles.
Chromatid
Single copy of the genetic material
G0
Phase where cells live but don’t divide (example: some neurons)
The 4 Phases of Mytosis
- ) Prophase
- ) Metaphase
- ) Anaphase
- ) Telophase
Prophase
- Chromatin fibers condense and untangle into individual chromosomes (each with 2 sister chromatids)
- Centrosomes (each with 2 centrioles) are at opposite sides of the cell outside the nucleus –> Send out spindle fibers (microtubule proteins) to centromere of each chromosome –> align chromosomes in the exact middle between the two centrosomes
Metaphase
- ) Prometaphase:
- Nuclear membrane & nucleolus disintegrate - ) Metaphase:
- Chromosomes align along the metaphase plate
- Spindle fibers continue to attach to a specific place (Kinetochore) on each centromere
Anaphase
- Centrosomes pull the sister chromatids apart
- Sister chromatids move to opposite poles of the cell
Telophase
- New nuclear envelope forms around each group of centrosome and the chromosomes
- Cytokinesis divides the cell into two cells
Meiosis
- ## Formation of gametes (Haploid cells: 1 set of 23 chromosomes)
Meiosis (Basics)
- Formation of gametes (Haploid cells: 1 set of 23 chromosomes)
- One parent cell with 46 chromosomes undergoes Two rounds of division to form Four daughter cells each with 23 chromosomes
Haploid Cells
A cell that contains a single set of chromosomes (Ex. Human Gamete Cells)
Meiosis Phases (Basics)
Meiosis I
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
Meiosis II
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
Prophase I (5 Phases)
- ) Leptotene: 46 chromosomes, each with 2 sister chromatids, condense + Nuclear membrane disintegrates
- ) Zygotene: Each chromosomes binds (Synapsis) to its homologue
- ) Pachytene
- ) Diplotene
- ) Diakinesis
Prophase I (5 Phases)
- ) Leptotene
- ) Zygotene
- ) Pachytene
- ) Diplotene
- ) Diakinesis
Leptotene
- First phase of Prophase I of Meiosis
- 46 chromosomes, each with 2 sister chromatids, condense
- Nuclear membrane disintegrates
Leptotene
- 1st phase of Prophase I of Meiosis I
- 46 chromosomes, each with 2 sister chromatids, condense
- Nuclear membrane disintegrates
Zygotene
- 2nd phase of Prophase I of Meiosis I
- Synapsis occures: each chromosomes binds to its homologue
- Each pair of homologous chromosomes pair with each other loosely (this structure is called a Tetrad)
Pachytene
- 3rd phase of Prophase I of Meiosis I
- Crossover event: Exchange of genetic material between Homologous chromosomes (where and how often this occurs is random) which produces additional genetic variation
Diplotene
- 4th phase of Prophase I of Meiosis I
- Homologous chromosomes uncoil and begin to pull away (remain attached at Chiasmata: where the exchange of genes in a crossover event took place)
Diakinesis
- 5th phase of Phrophase I of Meiosis I
- Homologous chromosomes remain connected in at least one of the Chiasmata
Metaphase I
- Tetrad go to the Metaphase Plate at the center of the cell
Anaphase I
- Tetrads split up and homologous chromosomes are pulled to opposite poles
Telophase I
- Cytokenesis occurs and produces two haploid daughter cells (which will undergo additional division in Meiosis II)
What happens following Meiosis I?
- There is another Interphase with G1 phase, S phase (except in this S phase the chromosomes don’t get replicated!), and G2 phase
- The cell is then ready for Meiosis II
How does Meiosis II progress?
Exactly like mitosis! :D
The only difference is that Meiosis produces 4 haploid daughter cells with 23 chromosomes each
Labile Cells
- Cells that never enter G0, rapidly progress through the cell cycle, and replicate fast
- Examples: Skins cells, Bone Marrow stem cells, gut epithelial cells
Stable Cells
- Cells in G0 that can re-enter G1 to divide when needed or when stimulated
- Examples: Liver cells, Lymphocytes in the blood, and Smooth Muscle cells
Permanent Cells
- Cells that are always in G0 phase, post-mitotic cells
- Examples: Neurons in the brain, cardiac muscle cells
G1 Checkpoint
- Checkpoint at the end of G1 where the cell checks to ensure that the right proteins have been synthesized in the correct amount and their is no cell damage
- If there is DNA damage, the cell tries to repair it in G0 or initiates Apoptosis
G2 Checkpoint
- Checks for DNA damage
- If no DNA damage then the cell can enter Mitosis
