Cell Cycle Control & Mitosis Notes PDF

**CONTROL CELL OF THE CYCLE** [Checkpoint] is a critical control point in the Cell Cycle where 'stop' and 'go-ahead' **3 Major Checkpoints** 1. The **G1 Checkpoint** (the ***Restriction Point***) ensures that the cell is large enough to divide and that enough nutrients are available to s...

**CONTROL CELL OF THE CYCLE** [Checkpoint] is a critical control point in the Cell Cycle where 'stop' and 'go-ahead' **3 Major Checkpoints** 1. The **G1 Checkpoint** (the ***Restriction Point***) ensures that the cell is large enough to divide and that enough nutrients are available to support the resulting daughter cells. If a cell receives a 'go-ahead' signal at the G1 checkpoint, it will usually continue with the Cell Cycle. **NOTE:**\ If the cell does not receive the ['go-ahead'] signal, it will exit the Cell Cycle and switch to a non-dividing state called G0. Most cells in the human body are in the G0 phase.  2. The **G2 Checkpoint** ensures that DNA replication in S phase has been successfully completed. 3. The **Metaphase Checkpoint** ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore. - is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart.  **Cell Division** - a fundamental process of growing, dividing and repairing in the human body. It involves the distribution of identical genetic material or DNA to two daughter cells. ***Why Do Cells Divide?*** - Cells divide for growth, development, repair of worn-out tissues and reproduction - To facilitate the exchange of materials - To control Deoxyribonucleic acid (DNA) overloading  **[2 Ways by which cells increase in numbers]** ***EUKARYOTIC CELL DIVISION*** ** Cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent cell** 1. **Mitosis** ** Two (2) main steps:** 1. ***Mitosis Fours steps*[; ]** **\[Prophase\>Metaphase\>Anaphase\>Telophase\]** 2. ***Cytokinesis*** **Cytoplasm [ ] divides forming two new daughter cells [ ]** - **Each daughter cell is Genetically Identical to parent cell** **2. Eukaryotes** - **Mitosis** - **Cell or organism growth** - **Replacement or repair of damaged cells** - **Meiosis** - **formation of sex cells or gametes** **HISTORY** - **Strasburger (1875) -- first discovered *Mitosis* in plant cells.** - **W. Flemming (1879) -- discovered *Mitosis* in animal cells. He then coined the term *Mitosis* in 1882**  **OCCURRENCE** - ***Mitocytes --* are cells undergoing mitosis.** - **In plants, they are mostly *meristematic cells.*** - **In animals, they are stem cells, germinal epithelium and embryonic cells.** - **It also occurs during regeneration. Root tip is the best material to study mitosis.** **REASONS FOR MITOSIS** - **Growth** - **Repair/healing** - **Asexual reproduction**  **Depending on Cell Type** - **Mitosis can take a few minutes or a few days** - **Muscles cells** - **Nerve cells** - **Skin Cells** - **Digestive tract cells** ***\ ***   Telophase is followed by [cytokinesis], which denotes the division of the cytoplasm to form two daughter cells. Thus, it marks the completion of cell division. **MEIOSIS** **& ITS STAGES** **Why Is It Important?** - Meiosis makes sure that all organisms produced via sexual reproduction contain the correct number of chromosomes -- half from each parent.  **PROPHASE 1** - the chromosomes condense and the nucleus breaks down. - as chromosomes move around, crossing over happens -- this means genetic material can be exchanged. **METAPHASE 1**  **ANAPHASE 1** **TELOPHASE 1** - Two new nuclei form around each set of chromosomes. - The cytoplasm splits and two (***haploid)*** daughter cells are formed.  **PROPHASE 2** **METAPHASE 2** - the chromosomes align single file in the centre of the cell. - this occurs to ensure sister chromatids separate in the next stage. **ANAPHASE 2** \- sister chromatids separate and move to opposite ends of the cell. \- this ensures that the daughter cells remain haploid -- that means they have half the genetic material of the original parent cell. **TELOPHASE 2** - four new nuclei form around each set of chromosomes. - the cytoplasms split and four (***haploid)*** daughter cells are formed.