Biology Week 2 PDF

1. Three Tenets of Cell Theory 1. All living organisms are composed of one or more cells: This means that every living thing, from the smallest bacterium to the largest whale, is made up of cells. 2. The cell is the basic unit of structure and organization in organisms: Cells are the...

1. Three Tenets of Cell Theory 1. All living organisms are composed of one or more cells: This means that every living thing, from the smallest bacterium to the largest whale, is made up of cells. 2. The cell is the basic unit of structure and organization in organisms: Cells are the fundamental building blocks of all organisms, providing structure and carrying out essential functions. 3. Cells arise from pre-existing cells: New cells are produced by the division of existing cells, ensuring continuity of life. 2. Microscopy: Magnification, Resolution, and Contrast Magnification: The process of enlarging the appearance of an object using lenses or digital enhancement. For example, a 10x magnification makes an object appear ten times larger than its actual size. Resolution: The ability to distinguish two points as separate entities. Higher resolution provides more detail. For instance, a microscope with a resolution of 0.2 micrometers can distinguish two points that are 0.2 micrometers apart. Contrast: The difference in light intensity between the image and the background, which helps in distinguishing different structures within a specimen. Light Microscopes: Use visible light and glass lenses to magnify images. Types include compound microscopes (multiple lenses) and stereo microscopes (3D view). Suitable for viewing live cells and tissues, but limited to about 2000x magnification and 200 nm resolution. Electron Microscopes (SEM & TEM): Use electron beams and electromagnetic lenses. SEM (Scanning Electron Microscope): Provides detailed 3D images of surfaces by scanning with a focused electron beam. TEM (Transmission Electron Microscope): Provides detailed images of internal structures by transmitting electrons through a thin specimen. Achieve much higher magnification (up to 2 million times) and resolution (up to 0.1 nm) compared to light microscopes. 3. Structural Features of Prokaryotic and Eukaryotic Cells Prokaryotic Cells: o Nucleoid: Region where the cell’s DNA is located, not enclosed by a membrane.  o Plasmids: Small, circular DNA molecules separate from the chromosomal DNA. o Ribosomes: Smaller (70S) than those in eukaryotes, involved in protein synthesis. o Cell Wall: Made of peptidoglycan (in bacteria) or other materials (in archaea), providing shape and protection. o Flagella: Long, whip-like structures used for movement. o Pili: Hair-like structures used for attachment and conjugation (DNA transfer). Eukaryotic Cells: o Nucleus: Enclosed by a nuclear envelope, contains the cell’s DNA organized into chromosomes. o Membrane-bound Organelles: Includes mitochondria, chloroplasts (in plants), endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes. o Cytoskeleton: Network of protein filaments (actin filaments, intermediate filaments, microtubules) providing structural support and facilitating movement. o Larger Size: Typically 10-100 µm in diameter, allowing compartmentalization of functions. 4. Proteome and Cell Structure/Function The proteome is the entire set of proteins expressed by a cell, tissue, or organism at a given time. Proteins play crucial roles in: o Enzymatic Reactions: Catalyzing biochemical reactions. o Structural Support: Forming the cytoskeleton and extracellular matrix. o Transport: Moving molecules across membranes. o Signaling: Communicating between cells and within cells. o Defense: Immune responses and protection against pathogens. 5. General Features of a Bacterial Cell Capsule: A gelatinous outer layer that protects the cell and helps it adhere to surfaces. Cell Wall: Provides structural support and shape; composed of peptidoglycan in bacteria. Plasma Membrane: A lipid bilayer that controls the movement of substances in and out of the cell. Cytoplasm: The jelly-like substance inside the cell where metabolic reactions occur. Nucleoid: The region containing the cell’s DNA.  Ribosomes: Sites of protein synthesis, smaller than those in eukaryotic cells. Flagella: Tail-like structures that enable movement. Pili: Hair-like structures that help in attachment and DNA transfer during conjugation. 6. Four Main Regions of Eukaryotic Cells 1. Cytosol: The fluid component of the cytoplasm where metabolic reactions occur. 2. Nucleus: Contains the cell’s genetic material (DNA) and is the control center for cellular activities. 3. Endomembrane System: Includes the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles. 4. Semi-autonomous Organelles: Mitochondria and chloroplasts, which have their own DNA and can replicate independently. Organelle Locations and Functions: Nucleus: Located in the nucleus; stores genetic information and coordinates cell activities. Endoplasmic Reticulum (ER): Rough ER (with ribosomes) is involved in protein synthesis; Smooth ER (without ribosomes) is involved in lipid synthesis and detoxification. Golgi Apparatus: Located in the endomembrane system; modifies, sorts, and packages proteins and lipids for transport. Lysosomes: Located in the endomembrane system; contain digestive enzymes to break down macromolecules. Mitochondria: Located in the cytosol; produce ATP through cellular respiration. Chloroplasts: Located in the cytosol of plant cells; conduct photosynthesis to convert light energy into chemical energy. 7. Key Differences Between Animal and Plant Cells Animal Cells: o Lack a cell wall, allowing for a variety of shapes. o Do not have chloroplasts, as they do not perform photosynthesis. o Have small, temporary vacuoles. o Contain centrioles, which are involved in cell division. Plant Cells: o Have a rigid cell wall made of cellulose, providing structural support. o Contain chloroplasts for photosynthesis.  o Have a large central vacuole that maintains cell turgor and stores nutrients. o Lack centrioles. 8. Cytoskeleton and Motor Proteins Cytoskeleton: o Actin Filaments (Microfilaments): Thin filaments involved in cell movement and shape changes. o Intermediate Filaments: Provide mechanical support and maintain cell integrity. o Microtubules: Thick, hollow tubes that guide organelle movement and are involved in cell division. Motor Proteins: o Myosin: Interacts with actin filaments for muscle contraction and other cellular movements. o Kinesin: Moves along microtubules, transporting vesicles and organelles towards the cell periphery. o Dynein: Moves along microtubules, transporting vesicles and organelles towards the cell center. Cilia and Flagella: Hair-like structures that extend from the cell surface and are involved in movement. Cilia are short and numerous, while flagella are longer and fewer. 9. Endosymbiosis Theory Proposes that mitochondria and chloroplasts originated from free-living bacteria that were engulfed by ancestral eukaryotic cells. Evidence includes: o Both organelles have their own DNA, which is similar to bacterial DNA. o Both have double membranes, consistent with the engulfing mechanism. o Both reproduce independently within the cell through a process similar to binary fission. 10. Fluid Mosaic Model and Membrane Dynamics Fluid Mosaic Model: Describes the cell membrane as a fluid combination of phospholipids, cholesterol, and proteins that move laterally within the layer. Phospholipid Movement: Phospholipids can move laterally within the same leaflet of the bilayer; flip-flop movement between leaflets is rare and usually requires enzymes called flippases. 11. Types of Membrane Proteins  1. Integral Proteins: Embedded within the lipid bilayer, often spanning the entire membrane. 2. Peripheral Proteins: Attached to the surface of the membrane, either on the cytoplasmic or extracellular side. 3. Lipid-anchored Proteins: Covalently attached to lipids within the membrane. 12. Membrane Fluidity Influenced by the types of fatty acids in phospholipids (saturated vs. unsaturated) and the presence of cholesterol. Unsaturated fatty acids increase fluidity by preventing tight packing of phospholipids. Cholesterol stabilizes 13. Experiment on the Lateral Movement of Membrane Proteins Experiment: Fusion of mouse and human cells. Procedure: Mouse and human cells were fused, and their membrane proteins were labeled with different fluorescent markers. Observation: Over time, the labeled proteins mixed, demonstrating that membrane proteins can move laterally within the lipid bilayer. 14. Definitions of Key Terms Gradient: A difference in concentration, pressure, or electrical charge between two regions. Passive Transport: Movement of molecules across a membrane without energy input, down their concentration gradient. Passive Diffusion: Movement of molecules directly through the lipid bilayer without the aid of proteins. Facilitated Diffusion: Movement of molecules across a membrane via transport proteins, down their concentration gradient. Active Transport: Movement of molecules against their concentration gradient, requiring energy (usually ATP). 15. Osmosis Osmosis: The diffusion of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. Importance: Maintains cell turgor in plants and regulates fluid balance in animal cells. 16. Aquaporin Experiment Experiment: Demonstrated the role of aquaporins in facilitating water transport. Procedure: Cells with and without aquaporins were compared for water permeability.  Results: Cells with aquaporins showed significantly higher water permeability, confirming the role of aquaporins in water transport. 17. Channels vs. Transporters Channels: Provide a passageway for molecules to diffuse through the membrane. Examples include ion channels and aquaporins. Transporters: Bind and transport molecules across the membrane. Examples include glucose transporters and sodium-potassium pumps. 18. Types of Transporters Uniporter: Transports one type of molecule in one direction. Symporter: Transports two types of molecules in the same direction. Antiporter: Transports two types of molecules in opposite directions. 19. Endocytosis and Exocytosis Endocytosis: The process by which cells internalize substances by engulfing them in a vesicle. o Phagocytosis: “Cell eating”; engulfing large particles. o Pinocytosis: “Cell drinking”; engulfing fluids and dissolved substances. o Receptor-mediated Endocytosis: Specific molecules are taken in after binding to receptors on the cell surface. Exocytosis: The process by which cells expel materials by fusing a vesicle with the plasma membrane. o Steps: Vesicle formation, transport to the membrane, fusion with the membrane, and release of contents outside the cell.