Honors Biology Cell Reproduction Notes PDF

# Honors Biology Unit 2C: Cell Reproduction Notes ## Cell Size - Most cells are microscopic. - Prokaryotic cells generally range from 1-10 micrometers (µm) in size. - Most animal and plant cells range between 10-100 µm. - 1 µm = 0.001 mm (there are 1000 µm in 1 mm) ## Why do cells have to be so...

# Honors Biology Unit 2C: Cell Reproduction Notes ## Cell Size - Most cells are microscopic. - Prokaryotic cells generally range from 1-10 micrometers (µm) in size. - Most animal and plant cells range between 10-100 µm. - 1 µm = 0.001 mm (there are 1000 µm in 1 mm) ## Why do cells have to be so small? - To efficiently move materials into or out of a cell - DNA must be able to make enough proteins for the cell but DNA does not increase in size if a cell gets too big. ## Calculations | Cube | Surface Area | Volume | SA/V Ratio | |---|---|---|---| | One 4-Centimeter Cube | 96cm² | 64cm³ | 1.5 | | Eight 2-Centimeter Cubes | 192cm² | 64cm³ | 3 | | Sixty-Four 1 Centimeter Cubes | 384cm² | 64cm³ | 6 | Notice: - Same volume in each example but many smaller cells making up that volume increases SA and thus ↑ SAIV ratio - Higher SA/V ratio = Smaller cells ## Model 1: - **Cell A** is smaller. - **Cell B** is larger. ### Comparing Cells **1. Which cell has a larger surface area (more cell membrane surface)?** Cell B **2. Which cell has more channels in its cell membrane that can transport molecules (nutrients, oxygen, and waste products) in and out of the cell?** Cell B **3. Which cell has more mitochondria?** Cell B **4. Propose an explanation for why the cell you chose for your previous answer would need more mitochondria for proper functioning of the cell.** A larger cell would need more ATP to function. **5. Which cell has a larger volume?** Cell B **6. Imagine a glucose molecule entering the cell membrane. Would that molecule be able to reach the mitochondria faster if the cell had a smaller volume or a larger volume? Explain.** Smaller - less distance to travel **7. So why must a cell remain small?** for efficient movement of materials in and out. **8. An efficient cell has more surface area compared to volume, or a higher SA/V ratio. Cells maintain this by remaining small. Think! How could two cells with the same volume have different SA/V ratios?** Different shapes can add surface area without increasing volume much or at all. (Ex: neuron- dendrites are covered in membrane but have very little cytoplasm/volume inside) ## Cell Division - The cell theory states that all cells come from preexisting cells. - Before a parent cell divides to produce 2 daughter cells, the DNA must first replicate. - This is important so each daughter cell gets a full copy of the DNA. ## Purposes of Cell Reproduction 1. **Unicellular** - reproduction of a full organism 2. **Multicellular** - production of new cells - Growth/development (zygote → embryo → adult) - Repair/maintenance ## Types of Reproduction - Cells can reproduce **sexually** or **asexually.** ### Sexual Reproduction - 2 parent cells - Egg + Sperm (germ cells) - Variation in offspring - Found in all kingdoms but prokaryotes ### Asexual Reproduction - 1 parent cell - No sex cells (gametes) - Identical cells (clones) - Found in all kingdoms ## Reproduction in Prokaryotes vs. Eukaryotes ### Prokaryotes (binary fission) - **NOT** mitosis! - Circular Chromosome attaches to the cell membrane and replicates. - Cell elongates, and a "cross-wall" forms. - Daughters separate. ### Eukaryotes - **Unicellular:** Genes are found in multiple chromosomes. DNA is replicated then the cell divides into 2 identical daughters - asexual involves mitosis. - **Multicellular:** Genes are found in multiple chromosomes. DNA is replicated, then either: - mitosis for making new body cells (repair + growth) - asexual - meiosis for making sex cells containing half the chromosomes - for sexual reproduction ## Packaging of DNA - In a eukaryotic cell, DNA is packaged by being wound around histone protein molecules. - Packaged DNA can exist in 2 forms: 1. **Chromatin:** Loosely packed form used in protein synthesis and in order to replicate DNA 2. **Chromosomes:** Tightly condensed form used during cell division - the replicated form ## Structure of a Chromosome - After replication and condensing, a chromosome is double armed. - **Chromatid:** One arm of a double arm chromosome (DAC). Also called a sister chromatid. Sister chromatids are identical replicates. - **Centromere:** Center region of proteins that hold the sister chromatids together. - **Spindle Fiber:** Assembly of specialized microtubule fibers that attach to the centromere and pull sister chromatids apart during the division of the nucleus (mitosis). ## Review of the Chromosomal Events in Cell Division - **Parent cell:** 2 strands of chromatin (pretend they look "looser") - **Replicated strands attach to each other at centromeres forming DACS:** 2 DACS - **DACS line up in the middle:** 2 DACS - **DACs separate into SACs:** 2 SACS - **New cells fully split apart:** 2 chromosomes → 2 strands of chromatin - **Two daughter cells (identical):** 2 chromosomes → 2 strands of chromatin - **Copies go in opposite directions:** Cell division ## Chromosome Number - Each organism has a characteristic number and kind of chromosomes in each cell. - It is possible for 2 different kinds of organisms to have the same number of chromosomes, but the type of chromosomes will differ in some ways. - They will contain different numbers and kinds of genes. | Organism | Chromosome Number (Diploid Number) | |---|---| | Alligator | 32 | | Corn | 20 | | Goldfish | 92 | | Chimpanzee | 48 | | Human | 46 | | Fruit Fly | 8 | - This number is double the amount in a sperm or egg cell (n). ## The Cell Cycle - The life of a cell can be considered to be from the time it is produced through cell division to the time it divides to produce 2 new cells or until the time it dies. - This lifespan of a cell can be represented as a cycle which includes 3 different stages: Interphase, Mitosis, and Cytokinesis. ### Interphase - The longest phase of the cell cycle. - No division during this phase. - G1 "Gap" 1 - S "synthesis" - G2 "Gap" 2 ### Mitosis - Division of the nucleus. - Replicated DNA is equally divided. - Prophase - Metaphase - Anaphase - Telophase ### Cytokinesis - Division of the cytoplasm after mitosis. ## Mitotic Phase (Mitosis and Cytokinesis) "Cell Division" Remember... Interphase (G1, S, and G2) has already occurred at this point... **Mitosis:** The division of the nucleus ### Prophase - **Important events:** - Longest phase of mitosis - Replicated chromatin condenses into DACS (replicates connected by a centromere). - nuclear envelope breaks down - cytoskeleton breaks down to form the spindle (spindle fibers) - In animal cells, centrioles move to the poles. - **Memory trick:** Prepare - **Why is it necessary for the nuclear envelope to disappear?** The spindle needs to reach the chromosomes and connect to centromeres. ### Metaphase - **Important events:** - DACS line up in the middle (equator) of the cell. - spindle fibers attach to centromeres. - **Memory trick:** Middle ### Anaphase - **Important events:** - Spindle fibers contract causing centromeres to split. - Identical chromatids separate into SACs. - SACs move to opposite poles. - Once chromatids separate they are each referred to as separate chromosomes. - **Memory trick:** Apart ### Telophase - **Important events:** - SAC / Spindle movement is complete. - Nuclear envelope reforms around each now set of chromosomes. - Spindle fibers disassembles so cytoskeleton can reform. - Chromosomes decondense back to chromatin. - Cytokinesis begins - furrow in animal cells - cell plate in plant cells. - **Memory trick:** Two nuclei ## Cytokinesis - The division of the cytoplasm. ### Animal vs. Plant Cytokinesis - **Animal cell:** Is less rigid so it pinches inward (furrow) to separate the cytoplasm - **Plant cells:** Are rigid and cannot pinch so a new wall (cell plate) forms to separate the two cells. ## Images of Real Cells in Various Phases of the Cell Cycle | | Interphase | Prophase | Metaphase | Anaphase | Telophase | |---|---|---|---|---|---| | **nucleus** | Solid color because loose chromatin (dark mass) fills entire nucleus | chromosomes visible but not organized | chromosomes lining up along equator | pulling apart | two nuclei | | **nucleolus** | | | | | early telophase (chromatin not yet condensed) plate forming | late telophase (chromatin fills the nucleus) | | | | | | | envelopes reforming | ## Cancer - Occurs when the regulation of cell division is altered and cells divide endlessly. Cells that are formed usually lose normal function. - In advanced tumors, some cells can break off and "migrate" to other areas of the body via lymph & blood (process is called "metastasis"). Defective gene(s) controlling the cell cycle lead to uncontrolled cell division. Cells grow/function/reproduce abnormally. - Cells "steal" resources from other cells, invade normal tissues. - **Tumor:** Mass of cancer cells. Cancer cells "steal" nutrients & take up space. ### Characteristics of Cancer Cells 1. **Impaired contact inhibition:** Normally cells can sense when other cells are nearby, cancer cells cannot. 2. **Abnormalities visible in cell morphology (shape and structure):** Defective apoptosis (apoptosis is programmed cell death). - Normally cells die, cancer cells are normally defective. 3. **Benign:** Do not spread to new locations and grow slowly. 4. **Malignant:** Tumors can spread and invade & destroy surrounding healthy tissue (= metastasis). ### Acquiring Cancer - Acquired during lifetime - Present in sperm or egg thus present in offspring. ## Causes of Cancer - Somatic (body cell) mutations OR inherited mutations ## Genes Affecting Cancer Growth - **Proto-oncogene:** Normal gene that helps cells grow and divide as usual. Mutations in these genes can keep them "on" all the time. - **Oncogene:** The mutated proto-oncogene that is stuck “on” is now called an oncogene. Mutation = like a stuck gas pedal. - **Tumor Suppressor Genes**: - Ex: p53, BRCA1/BRCA2 - Normally able to recognize abnormal growth & reproduction of damaged cells and interrupt their reproduction until the defect is corrected. - Mutation = like having broken brakes ## Risks - **Family history** - **Lifestyle:** Including: Diet high in saturated fat and chemical additives, smoking, sun (UV) exposure; being overweight, lack of exercise, chemical/environmental exposure, radiation - **Some viruses** (Oncoviruses such as HPV-human papilloma virus, and Hepatitis C) ## Treatment - **Surgery, Radiation, and/or Chemotherapy** (drugs that kill rapidly dividing cells). - **Newer therapies** may include: "Targeted cancer therapy" and "Immunotherapy". - **Targeted cancer therapies** are drugs designed to interfere with specific molecules necessary for tumor growth and progression. - **Immunotherapy,** also called biologic therapy, is a type of cancer treatment designed to boost the body's natural defenses to fight the cancer using materials either made by the body or in a laboratory to improve, target, or restore immune system function. ## How do problems in the cell cycle result in cancer? - **Cells die and are replaced all the time:** 1. **Accidental death by damage or injury** 2. **Programmed cell death called apoptosis:** - helps shape structures during development - kills infected cells - kills cells with DNA damage or cancer. - **There are many genes and their resulting proteins that help to regulate the cell cycle. One example is the gene "p53".** - **The p53 gene codes for the p53 protein.** - **Normally p53 halts the cell cycle until all of the DNA is replicated.** - **If a mistake occurs the p53 either helps fix the problem or signals for apoptosis to occur.** - **What will happen if the p53 gene has a mutation?** - The cell cycle will continue even with mistakes in DNA. Apoptosis will not occur despite mistakes. - **Many genes, if mutated, can lead to lack of control in the cell cycle.** - **Cancer:** a disorder in which body cells lose the ability to control division. - **Cancer cells do not respond to proteins that regulate the cell cycle and thus do not fix mistakes or go through apoptosis. This leads to uncontrolled cell division.** - **What are some possible causes for mutations in cell cycle genes?** - **Inheritance** - **Poor diet; lack of exercise** - **Carcinogens (chemicals, smoking, pollutants)** - **Radiation (including UV from sun)** - **Viruses** ## Cell Cycle Checkpoints - What do the policemen in the diagram represent? - **Proteins that act like checkpoints in the cell cycle.** - Label the policeman that represents p53. - Is p53 expressed from a proto-oncogene or a tumor suppressor gene? - **Tumor suppressor gene** - Explain: It normally stops (supresses) division if there are mistakes. - What would happen if one or more "policemen" didn't come to work? - The cell would undergo apoptosis if still possible or else it will continue to divide with mistakes. - At the cellular level, WHY might one of the "policemen" not come to work? - If the gene for a checkpoint protein is mutated the protein won't be able to do its job. - Why can we define cancer as a disease of the cell cycle? - Because cancer occurs when there are errors in cell cycle regulation.