Cell Cycle Review PDF

**1. The Cell Cycle** **What is the Cell Cycle?** The **cell cycle** is the process that a cell goes through to grow, copy its DNA, and divide into two new cells. It ensures that cells stay healthy and that organisms grow and repair themselves. **Phases of the Cell Cycle** Use the acronym **I-PM...

**1. The Cell Cycle** **What is the Cell Cycle?** The **cell cycle** is the process that a cell goes through to grow, copy its DNA, and divide into two new cells. It ensures that cells stay healthy and that organisms grow and repair themselves. **Phases of the Cell Cycle** Use the acronym **I-PMAT-C** to remember the stages of the cell cycle. Interphase is divided into three parts: **G₁ (Growth 1), S (Synthesis), and G₂ (Growth 2)**. **Stage** **What Happens?** --------------------- --------------------------------------------------------------------------------------- **I** - Interphase The cell prepares for division: **G₁ (Growth 1)** The cell grows, performs its normal functions, and produces new organelles. **S (Synthesis)** The DNA is copied (replicated) so that each new cell will have a complete set of DNA. **G₂ (Growth 2)** The cell grows more, checks for DNA errors, and prepares for mitosis. **P** - Prophase DNA coils into chromosomes, and the nucleus starts to break down. **M** - Metaphase Chromosomes line up in the middle of the cell. **A** - Anaphase Chromosomes are pulled apart to opposite sides of the cell. **T** - Telophase Two new nuclei form around the separated chromosomes. **C** - Cytokinesis The cytoplasm splits, creating two identical daughter cells. **2. Mitosis** **What is Mitosis?** Mitosis is the process of **nuclear division** in eukaryotic cells, creating two identical cells with the same number of chromosomes as the original cell. **Steps of Mitosis** Use **PMAT** to remember the steps of mitosis. Each stage focuses on organizing and separating chromosomes (DNA). **Step** **What Happens?** ------------------- --------------------------------------------------------------------------- **P** - Prophase 1\. Chromosomes condense (visible as X-shaped structures). 2\. The nuclear membrane starts to break down, and spindle fibers form. **M** - Metaphase 1\. Chromosomes line up in the **middle** of the cell (along the metaphase plate). 2\. Spindle fibers attach to the centromeres of each chromosome. **A** - Anaphase 1\. Sister chromatids are pulled **apart** by the spindle fibers and move toward opposite ends of the cell. 2\. Each chromatid is now an individual chromosome. **T** - Telophase 1\. Chromosomes reach opposite ends of the cell and start to **uncoil** (returning to chromatin). 2\. Two new nuclear membranes form, creating two nuclei identical to the original. **3. Meiosis** **What is Meiosis?** Meiosis is the process of **cell division** that produces **gametes** (sperm and egg cells) for sexual reproduction. It ensures that the offspring have the correct number of chromosomes by reducing the chromosome number by half (from diploid to haploid). - **Diploid Cells (2n)**: Contain two sets of chromosomes (one from each parent). - **Haploid Cells (n)**: Contain only one set of chromosomes (half the total number). Meiosis creates **four unique haploid cells** from one diploid cell. It occurs in two stages: **Meiosis I** and **Meiosis II**. **Phases of Meiosis** **Meiosis I: Separation of Homologous Chromosomes** **Step** **What Happens?** --------------------- -------------------------------------------------------------------------- **P** - Prophase I 1\. Homologous chromosomes pair up to form **tetrads** (one chromosome from each parent). 2\. **Crossing over** occurs: Homologous chromosomes exchange genetic material, creating genetic diversity. 3\. The nuclear membrane breaks down, and spindle fibers form. **M** - Metaphase I 1\. Homologous chromosome pairs line up in the **middle** of the cell. 2\. Spindle fibers attach to each homologous chromosome. **A** - Anaphase I 1\. Homologous chromosomes are pulled **apart** to opposite sides of the cell. 2\. Sister chromatids remain attached. **T** - Telophase I 1\. Two nuclei form, each containing half the original number of chromosomes (haploid). 2\. Cytokinesis occurs, splitting the cell into two haploid cells. **Meiosis II: Separation of Sister Chromatids** **Step** **What Happens?** ---------------------- --------------------------------------------------------------------------- **P** - Prophase II 1\. Chromosomes condense again (each with two sister chromatids). 2\. Spindle fibers form, and the nuclear membrane breaks down. **M** - Metaphase II 1\. Chromosomes line up in the **middle** of each haploid cell. **A** - Anaphase II 1\. Sister chromatids are pulled **apart** to opposite sides of the cell. **T** - Telophase II 1\. Chromatids reach opposite ends of the cell, and nuclei form around them. 2\. Cytokinesis occurs, resulting in **four unique haploid cells** (gametes).  **4. Meiosis vs. Mitosis** **Feature** **Mitosis** **Meiosis** ------------------------------ ------------------------------------------- ------------------------------------------------- **Purpose** Growth, repair, and asexual reproduction. Produces gametes for sexual reproduction. **Number of Divisions** 1 2 **Number of Cells Produced** 2 identical daughter cells 4 unique haploid cells **Chromosome Number** Maintains same number (diploid). Reduces chromosome number by half (haploid). **Genetic Variation** None (identical cells). Yes (crossing over and independent assortment). **Occurs In** Body (somatic) cells. Sex (germ) cells. **5. DNA in the Mitotic and Meiotic Phases** **What Happens to DNA During Mitosis and Meiosis?** **Process** **What Happens to DNA?** --------------------- ---------------------------------------------------------------------------------------------------------- **DNA Replication** \- DNA is copied during the **S phase of interphase** before mitosis or meiosis begins. **Prophase** \- DNA condenses into visible **chromosomes** (each chromosome made of two sister chromatids). **Metaphase** \- Chromosomes line up in the middle of the cell to ensure proper separation. **Anaphase** \- Sister chromatids (mitosis) or homologous chromosomes (meiosis I) are pulled apart by spindle fibers. **Telophase** \- Separated DNA is enclosed in newly forming nuclei. **Crossing Over** \- Unique to **meiosis I**, homologous chromosomes exchange DNA segments, creating genetic diversity. **6. Passive and Active Transport** The **cell membrane** in **animal cells** and the **cell wall** in **plant cells** control what enters and exits the cell. These processes help cells maintain balance. **Passive Transport** Passive transport does **not require energy** to move molecules across the cell membrane. **Type** **What Happens?** --------------------------- ----------------------------------------------------------------------------- **Diffusion** Molecules move from an area of **high concentration to low concentration**. **Osmosis** The diffusion of **water** molecules across a membrane. **Facilitated Diffusion** Molecules use **protein channels** to pass through the cell membrane. **Active Transport** Active transport **requires energy (ATP)** to move molecules **against** their concentration gradient (from low to high concentration). **Example** ------------------------------------------------------------------------------------------------- Sodium-potassium pumps transport sodium (Na⁺) out of the cell and potassium (K⁺) into the cell. **7. Exocytosis** Exocytosis is an **active transport process** where a **cell's vesicles release their contents outside the cell**. This is how cells remove waste or send molecules like hormones and proteins to other parts of the body. **8. Cellular Respiration** **What is Cellular Respiration?** Cellular respiration is a series of **chemical reactions** that convert the energy in food molecules into a usable form of energy called **ATP**. It takes place in the **mitochondria**, also known as the "powerhouse" of the cell. **Equation**:\ **C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP** **Glycolysis** Glycolysis is the **first step** in cellular respiration. It occurs in the cytoplasm and is the process where **sugar (glucose) breaks down into smaller molecules**, producing a small amount of ATP. **Fermentation** Fermentation is a reaction that **eukaryotic** and **prokaryotic cells** use to obtain energy from food when oxygen levels are low. **Type** **What Happens?** ------------------------------ ---------------------------------------------------------------------------- **Lactic Acid Fermentation** Pyruvate is converted into lactic acid (e.g., in muscles during exercise). **Alcoholic Fermentation** Pyruvate is converted into alcohol and carbon dioxide (e.g., in yeast). **ATP Produced**: Only 2 ATP per glucose. **9. Photosynthesis** **What is Photosynthesis?** Photosynthesis is the process by which **plants, algae, and some bacteria** use sunlight to create their own food. It happens in the **chloroplasts** of plant cells, but the **mitochondria** are responsible for converting that energy into ATP through cellular respiration. **Equation**:\ **CO₂ + H₂O + Sunlight → C₆H₁₂O₆ + O₂** **10. Sexual and Asexual Reproduction** **Sexual Reproduction** Sexual reproduction involves **two parents**. During **fertilization**, the **egg** and **sperm** combine to form a **zygote**, which is the first cell of a new organism. **Asexual Reproduction** Asexual reproduction involves **one parent**, and the offspring are **genetically identical** to the parent. **Type** **What Happens?** -------------------------- --------------------------------------------------------------------------- **Sexual Reproduction** Egg + Sperm = **Fertilization** → Zygote (genetically unique offspring). **Asexual Reproduction** One parent produces a clone of itself (e.g., binary fission in bacteria). **11. Summary** - **Meiosis** produces four genetically unique haploid cells, while **mitosis** produces two identical diploid cells. - **Passive and active transport** occur across the **cell membrane** in animals and the **cell wall** in plants. - **Exocytosis** is how cells release materials outside the cell. - **Cellular respiration** and **photosynthesis** both rely on the **mitochondria** to create or utilize energy. - In **sexual reproduction**, fertilization combines the egg and sperm to form a zygote.