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biology 2.1Unit 2.1: Mitosis and Meiosis Introduction By the end of this section, you should be able to: Define a chromosome. Define DNA as the genetic material. Define genes. Describe the structure of chromosomes. Describe the components of DNA. Define mitosis and describe its stages. Define meiosis and describe its stages. Relate the events of meiosis to the formation of sex cells. Compare mitosis and meiosis. Chromosomes, Genes, and DNA Almost all the cells of your body—except for mature red blood cells—contain a nucleus, which acts as the control center of the cell. The nucleus holds all the information needed to make a new cell and, ultimately, a new individual. Inside the nucleus are chromosomes, thread-like structures that store genetic information passed from parents to offspring. Chromosomes are made up of DNA (deoxyribonucleic acid), a molecule that carries the instructions needed to make all the proteins in your body. Many of these proteins are enzymes, which control the production of other chemicals and affect everything about how your body functions. Each species has a specific number of chromosomes: Humans have 46 chromosomes (23 pairs). Tomatoes have 24 chromosomes (12 pairs). Elephants have 56 chromosomes (28 pairs). Half of your chromosomes come from your mother, and the other half from your father. These chromosomes are arranged in homologous pairs, meaning they contain matching sets of genes. A karyotype is a special photograph that arranges chromosomes into their pairs. In humans, 22 pairs of chromosomes are called autosomes, which control most body functions. The 23rd pair is the sex chromosomes, which determine whether you are male or female: Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY). DNA Structure DNA is a long, twisted molecule shaped like a double helix (a spiraled ladder). Each strand of DNA is made up of smaller molecules called nucleotides, which consist of: A phosphate group A sugar (deoxyribose) A nitrogen base The four nitrogen bases in DNA are: Adenine (A) → Always pairs with Thymine (T) Cytosine (C) → Always pairs with Guanine (G) Genes are small segments of DNA that carry instructions for making proteins. The sequence of these bases acts like a biological code, directing the cell to create specific proteins. In 1953, James Watson and Francis Crick, using data from Rosalind Franklin’s X-ray photographs, discovered the double-helix structure of DNA. Their discovery led to a huge increase in genetic research, including the Human Genome Project, which mapped all human genes. Mitosis (Cell Division for Growth and Repair) All body cells (somatic cells) divide using mitosis, a type of cell division that creates two identical daughter cells. Mitosis is essential for: Growth (producing new cells). Tissue repair (replacing damaged or old cells). Asexual reproduction (producing offspring with identical DNA). Stages of Mitosis Interphase The cell prepares for division by copying its DNA. Chromosomes are not visible under a microscope. Prophase Chromosomes condense and become visible. The nuclear membrane breaks down. Metaphase Chromosomes line up in the center of the cell. Spindle fibers attach to each chromosome. Anaphase The spindle fibers pull the sister chromatids apart to opposite ends of the cell. Telophase A new nuclear membrane forms around each set of chromosomes. The cell is almost ready to split. Cytokinesis The cytoplasm divides, forming two identical daughter cells. Mitosis is constantly occurring in areas like your skin and bone marrow, where new cells are needed regularly. Meiosis (Cell Division for Reproduction) Unlike mitosis, meiosis occurs only in the reproductive organs (testes in males, ovaries in females) and produces gametes (sperm and egg cells). Gametes have half the number of chromosomes (haploid, n=23) so that when fertilization occurs, the new cell has the correct chromosome number (diploid, 2n=46). Stages of Meiosis Meiosis consists of two rounds of cell division, resulting in four non-identical cells. Meiosis I: Prophase I – Chromosomes pair up and exchange genetic material (crossing over). Metaphase I – Chromosome pairs line up in the center of the cell. Anaphase I – Chromosome pairs separate and move to opposite ends of the cell. Telophase I & Cytokinesis – The cell splits into two haploid daughter cells. Meiosis II (similar to mitosis): 5. Prophase II – Chromosomes condense again. 6. Metaphase II – Chromosomes line up in the center. 7. Anaphase II – Sister chromatids separate and move to opposite sides. 8. Telophase II & Cytokinesis – Four unique haploid gametes are formed. Each gamete is genetically different due to crossing over and random chromosome distribution. Mitosis vs. Meiosis: Key Differences Importance of Mitosis and Meiosis Mitosis ensures that cells grow, repair damage, and replace old cells. Meiosis allows genetic diversity, which is essential for evolution and survival. Summary Chromosomes carry genetic information in the form of DNA. Genes are sections of DNA that code for proteins. Mitosis produces two identical daughter cells for growth and repair. Meiosis creates four non-identical sex cells for reproduction. Mitosis ensures genetic stability, while meiosis introduces genetic diversity

The Separation of Sister Chromatids and Homologous Chromosomes

Meiosis II: separate sister chromatids

Cell and Structures Cell vs. Viruses • Cells: Simplest living structures capable of performing all life functions independently. • Viruses: Non-living entities requiring a host cell to replicate and survive. Microscopes • Light Microscope: Uses visible light, magnifies up to 1,000x; resolution limited by wavelength of light. • SEM (Scanning Electron Microscope): Creates detailed 3D images of surfaces; does not show internal structures. • TEM (Transmission Electron Microscope): Produces high-resolution images of internal cellular structures. Magnification and Resolution • Magnification: Enlarges an object’s appearance. • Resolution: Measures the clarity of an image by distinguishing two points as separate. Robert Hooke • Coined the term "cells" after observing cork under a microscope. • Published his findings in Micrographia (1665), advancing the study of cells. Cytology and Biochemistry • Cytology: The study of cell structure and function. • Biochemistry: The study of chemical processes and substances within organisms. Cell Fractionation • A laboratory technique to break apart cells and isolate organelles for detailed study. Size Limitations of Cells • Smaller cells have a higher surface area-to-volume ratio, which is essential for efficient exchange of materials. Prokaryotes vs. Eukaryotes • Prokaryotes: No nucleus or membrane-bound organelles; simpler and smaller (e.g., bacteria). • Eukaryotes: Have a nucleus and membrane-bound organelles; larger and more complex. Cell Structures and Functions • Nucleus: Stores genetic material (DNA). • Plasma Membrane: Protects the cell; regulates material exchange. • Cytosol: Fluid portion of the cytoplasm where cellular processes occur. • Microvilli: Increases surface area for absorption in some animal cells. • Cytoskeleton: ◦ Microfilaments (actin): Provides structural support. ◦ Microtubules: Involved in transport and motility. • Animal Cell-Specific Structures: ◦ Desmosomes: Anchor cells together. ◦ Gap Junctions: Channels that allow communication between cells. ◦ Tight Junctions: Create a watertight seal between cells. • Extracellular Matrix (ECM): Nonliving material outside cells, providing structural and biochemical support. • Plant Cell-Specific Structures: ◦ Plasmodesmata: Channels connecting cytoplasm between plant cells. Cellular Respiration Definition • Process of extracting energy from glucose to produce ATP, the cell's main energy currency. ATP • Made by the enzyme ATP synthase, powered by hydrogen ion (H⁺) movement across the inner mitochondrial membrane. Three Stages of Respiration 1 Glycolysis (Cytoplasm): ◦ Reactants: Glucose. ◦ Products: 2 Pyruvate, 2 ATP (net), and NADH. 2 Krebs Cycle (Mitochondrial Matrix): ◦ Reactant: Acetyl CoA. ◦ Products: CO₂, NADH, FADH₂, and 2 ATP. 3 Electron Transport Chain (ETC) (Inner Mitochondrial Membrane): ◦ Reactants: NADH and FADH₂ (electron carriers). ◦ Products: Water and ~32-34 ATP. Key Points • No oxygen = no Krebs cycle or ETC; only 2 ATP are produced via glycolysis. • Fermentation occurs in anaerobic conditions: ◦ Converts pyruvate into lactic acid (in animals) or ethanol (in yeast). Photosynthesis Overview • Process where plants convert light energy into chemical energy (sugars). • Formula: CO2+H2O→O2+G3PCO_2 + H_2O \rightarrow O_2 + G3PCO2​+H2​O→O2​+G3P. Key Concepts 1 Light Reactions (Thylakoid Membranes): ◦ Products: ATP and NADPH (used in the Calvin Cycle). ◦ Oxygen is produced by Photosystem II. 2 Calvin Cycle (Stroma): ◦ Uses ATP and NADPH to fix carbon dioxide into G3P (a sugar precursor). Photosystems • Photosystem II: Produces oxygen and ATP. • Photosystem I: Produces NADPH. Adaptations • C4 Pathway: Spatial separation of steps to avoid photorespiration. • CAM Pathway: Temporal separation, stomata open at night to reduce water loss. Mitosis and Meiosis Mitosis • Division of a eukaryotic somatic (non-reproductive) cell into two identical diploid cells. • Phases: 1 Prophase: Chromosomes condense; spindle forms. 2 Metaphase: Chromosomes align at the cell's equator. 3 Anaphase: Sister chromatids separate. 4 Telophase: Nuclear envelopes reform. 5 Cytokinesis: Cytoplasm splits into two cells. Meiosis • Specialized cell division in germ cells (ovaries/testes) to produce gametes. • Key Features: ◦ Two divisions produce four genetically unique haploid cells. ◦ Crossing over occurs during Prophase I for genetic diversity. Binary Fission • A simple form of cell division in prokaryotes producing two identical cells. Genetics • Haploid: Single set of chromosomes (e.g., gametes). • Diploid: Two sets of chromosomes (e.g., somatic cells). • Punnett Squares and Pedigrees: Tools to predict genetic inheritance. Cell and Structures Cell vs. Viruses • Cells: Simplest living structures capable of performing all life functions independently. • Viruses: Non-living entities requiring a host cell to replicate and survive. Microscopes • Light Microscope: Uses visible light, magnifies up to 1,000x; resolution limited by wavelength of light. • SEM (Scanning Electron Microscope): Creates detailed 3D images of surfaces; does not show internal structures. • TEM (Transmission Electron Microscope): Produces high-resolution images of internal cellular structures. Magnification and Resolution • Magnification: Enlarges an object’s appearance. • Resolution: Measures the clarity of an image by distinguishing two points as separate. Robert Hooke • Coined the term "cells" after observing cork under a microscope. • Published his findings in Micrographia (1665), advancing the study of cells. Cytology and Biochemistry • Cytology: The study of cell structure and function. • Biochemistry: The study of chemical processes and substances within organisms. Cell Fractionation • A laboratory technique to break apart cells and isolate organelles for detailed study. Size Limitations of Cells • Smaller cells have a higher surface area-to-volume ratio, which is essential for efficient exchange of materials. Prokaryotes vs. Eukaryotes • Prokaryotes: No nucleus or membrane-bound organelles; simpler and smaller (e.g., bacteria). • Eukaryotes: Have a nucleus and membrane-bound organelles; larger and more complex. Cell Structures and Functions • Nucleus: Stores genetic material (DNA). • Plasma Membrane: Protects the cell; regulates material exchange. • Cytosol: Fluid portion of the cytoplasm where cellular processes occur. • Microvilli: Increases surface area for absorption in some animal cells. • Cytoskeleton: ◦ Microfilaments (actin): Provides structural support. ◦ Microtubules: Involved in transport and motility. • Animal Cell-Specific Structures: ◦ Desmosomes: Anchor cells together. ◦ Gap Junctions: Channels that allow communication between cells. ◦ Tight Junctions: Create a watertight seal between cells. • Extracellular Matrix (ECM): Nonliving material outside cells, providing structural and biochemical support. • Plant Cell-Specific Structures: ◦ Plasmodesmata: Channels connecting cytoplasm between plant cells. Cellular Respiration Definition • Process of extracting energy from glucose to produce ATP, the cell's main energy currency. ATP • Made by the enzyme ATP synthase, powered by hydrogen ion (H⁺) movement across the inner mitochondrial membrane. Three Stages of Respiration 1 Glycolysis (Cytoplasm): ◦ Reactants: Glucose. ◦ Products: 2 Pyruvate, 2 ATP (net), and NADH. 2 Krebs Cycle (Mitochondrial Matrix): ◦ Reactant: Acetyl CoA. ◦ Products: CO₂, NADH, FADH₂, and 2 ATP. 3 Electron Transport Chain (ETC) (Inner Mitochondrial Membrane): ◦ Reactants: NADH and FADH₂ (electron carriers). ◦ Products: Water and ~32-34 ATP. Key Points • No oxygen = no Krebs cycle or ETC; only 2 ATP are produced via glycolysis. • Fermentation occurs in anaerobic conditions: ◦ Converts pyruvate into lactic acid (in animals) or ethanol (in yeast). Photosynthesis Overview • Process where plants convert light energy into chemical energy (sugars). • Formula: CO2+H2O→O2+G3PCO_2 + H_2O \rightarrow O_2 + G3PCO2​+H2​O→O2​+G3P. Key Concepts 1 Light Reactions (Thylakoid Membranes): ◦ Products: ATP and NADPH (used in the Calvin Cycle). ◦ Oxygen is produced by Photosystem II. 2 Calvin Cycle (Stroma): ◦ Uses ATP and NADPH to fix carbon dioxide into G3P (a sugar precursor). Photosystems • Photosystem II: Produces oxygen and ATP. • Photosystem I: Produces NADPH. Adaptations • C4 Pathway: Spatial separation of steps to avoid photorespiration. • CAM Pathway: Temporal separation, stomata open at night to reduce water loss. Mitosis and Meiosis Mitosis • Division of a eukaryotic somatic (non-reproductive) cell into two identical diploid cells. • Phases: 1 Prophase: Chromosomes condense; spindle forms. 2 Metaphase: Chromosomes align at the cell's equator. 3 Anaphase: Sister chromatids separate. 4 Telophase: Nuclear envelopes reform. 5 Cytokinesis: Cytoplasm splits into two cells. Meiosis • Specialized cell division in germ cells (ovaries/testes) to produce gametes. • Key Features: ◦ Two divisions produce four genetically unique haploid cells. ◦ Crossing over occurs during Prophase I for genetic diversity. Binary Fission • A simple form of cell division in prokaryotes producing two identical cells. Genetics • Haploid: Single set of chromosomes (e.g., gametes). • Diploid: Two sets of chromosomes (e.g., somatic cells). • Punnett Squares and Pedigrees: Tools to predict genetic inheritance.

Cell Division and Reproduction Asexual Reproduction Only 1 parent required for asexual reproduction. Fast and simple process. Results in identical offspring without genetic variation. Examples include binary fission in bacteria. Sexual Reproduction Involves 2 parents contributing to offspring. Offspring genetically different from parents. Slower and more expensive compared to asexual reproduction. Leads to genetic variation, aiding evolution in changing environments. Modes of Reproduction Asexual reproduction involves a single parent producing genetically identical offspring through binary fission. Example: Amoeba divides by binary fission to form daughter cells. Sexual reproduction requires two parents contributing to genetically diverse offspring. Genetic variation in sexual reproduction allows adaptation to environmental changes. Eukaryotic Cell Division Mitosis produces identical daughter cells for asexual reproduction, growth, and repair. Meiosis generates different daughter cells for sexual reproduction and gamete formation. Meiosis results in four unique daughter cells compared to two identical cells in mitosis. Cell Cycle and Mitosis Eukaryotic Cell Division Mitosis results in daughter cells identical to the parent cell. Occurs in asexual reproduction, growth, development, and repair. Meiosis produces daughter cells different from parents for sexual reproduction. Involves the formation of gametes like sperm and egg. Eukaryotic Chromosomes Chromosomes are tightly coiled DNA structures. Human cells (except gametes) typically have 46 chromosomes. Genes are specific DNA sequences on chromosomes. Chromatin, a looser DNA form, condenses into chromosomes before cell division. The Cell Cycle Ordered sequence of events from cell formation to division. Consists of interphase (cell growth and DNA replication) and mitotic phase (DNA and cytoplasmic division). Interphase includes G1 (cell growth), S (DNA duplication), and G2 (preparation for division). Stages of Mitosis Prophase: Chromosomes coil tightly, spindles form. Prometaphase: Nuclear envelope breaks, microtubules attach to chromatids. Metaphase: Chromosomes align at the cell's equator. Anaphase: Sister chromatids separate and move to opposite ends. Telophase: Chromosomes decondense, nuclear envelope reforms. Cytokinesis: Cytoplasm divides, forming two daughter cells. Mitosis and Cell Division Mitotic Spindle Microtubules that separate chromosomes during mitosis. Aids in pulling DNA to opposite ends of the cell. Essential for proper chromosome distribution. Ensures accurate division of genetic material. Mitosis Summary Results in two daughter cells identical to the parent cell. Utilized in asexual reproduction, growth, and repair. Mathematically, chromosome count doubles during S phase and halves after cytokinesis. Ensures genetic stability and continuity in cell populations. Comparing Binary Fission and Mitosis Both processes involve chromosome duplication and cell division. Mechanics and timing differ between bacterial binary fission and eukaryotic mitosis. DNA replication and separation occur simultaneously in binary fission, unlike in mitosis. Mitotic spindle formation is unique to eukaryotic cell division. Cancer and Cell Cycle Cell cycle checkpoints regulate cell division. Disruption of checkpoints, like the G1/S checkpoint, can lead to cancer. Tumors result from uncontrolled cell growth. Benign tumors stay localized, while malignant tumors can metastasize. Eukaryotic Chromosomes and Cell Cycle Chromatin and Chromosomes Chromatin organizes DNA into chromosomes before cell division. Gene: a sequence of nucleotides on a chromosome. Sister chromatids are duplicated chromosomes held by a centromere. The Cell Cycle Phases Interphase: cell growth and DNA replication stages. Mitotic Phase: includes mitosis and cytokinesis for cell division. Mitosis stages: Prophase, Prometaphase, Metaphase, Anaphase, Telophase.

MitMei Review

Chromosomes/ Sister Chromatids