Cell Biology PDF

UNIT 1: CELL BIOLOGY 1.1 Introduction to cells Cells are the basic building blocks of all living organisms. 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of life. 3. All cells arise from pre-existing cells. Caveats to cell theory Striated muscl...

UNIT 1: CELL BIOLOGY 1.1 Introduction to cells Cells are the basic building blocks of all living organisms. 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of life. 3. All cells arise from pre-existing cells. Caveats to cell theory Striated muscle - one nucleus Giant Algae - simple and small Aseptate hyphae - single unite Functions of life (MR SHENG) Metabolism, Reproduction, Sensitivity, Homeostasis, Excretion, Nutrition, Growth Endosymbiosis theory: Some organelles in eukaryotic cells, specifically mitochondria and chloroplasts, originated from free-living prokaryotic organisms that were engulfed by larger cells and eventually became integrated as part of the host cell's structure. Eukaryotic cells believed to have evolved from aerobic prokaryotes, engulfed by endocytosis. Host Cell+Prokaryotic → Eukaryotic Cell with Organelle Cell Size Calculating Magnification (MIA): Magnification = Image Size ÷ Actual Size 1. Convert ruler to um 1 mm = 1,000 um Example Magnification = 20 000 um/10 um = 2000x (times magnified) Calculating Actual Size (AIM): Actual Size = Image Size ÷ Magnification 1. Measure the part of the image and divide it by the magnification Cell Organization Cells group to form tissues, tissues interact to form organs, organs combine to form body systems Stem cells: are undifferentiated cells that have the ability to develop into various specialized cell types and can self-renew through cell division. Key characteristics 1. Self-renewal: Ability to divide and produce more stem cells. 2. Potency: Capacity to differentiate into different cell types. Note: The use of embryonic stem cells in research is a topic of ethical debate due to the destruction of embryos in the process of harvesting these cells. Therapeutic examples: Stargardt’s disease, macular degeneration and treatment with stem cells to replace the retinal cells Ethics of its use 1.2 Types of cells Prokaryotic Cells: lack a nucleus Escherichia coli (E. coli) Features Generally smaller and simpler than eukaryotic Single, circular DNA molecule 70s Ribosomes Structure: Cell wall (protection) Membrane (Movement of substances) Pili (for attachment) Flagella (for movement) Plasmids (autonomous DNA molecules, contain antibiotic resistance) Binary Fission: Circular Dna copied, DNA loops attached to membrane, cell elongates separating the loops, cytokinesis occurs to form two cells. Eukaryotic Cells: Animal or Plant, fungi, protists Escherichia coli (E. coli) Features Generally larger and complex than prokaryotic Nucleus and membrane organelles and linear DNA molecule 80s Ribosomes Structure: Mitochondria (produces energy ATP) Membrane (Movement of substances) Golgi apparatus (packages proteins and lipids) Endoplasmic Reticulum (synthesizes proteins rough, lipids smooth) Animal cells: Lysosomes (digestive enzymes to breakdown macromolecules) Plant cells: Chloroplasts (site of photosynthesis), Vacuoles (storage of substances) Eukaryotic cells are more complex and can b e specialized to perform specific functions within multicellular organisms. Feature Prokaryotic Cells Eukaryotic Cells Cell size Smaller - Typically 0.1-5 μm Larger - Usually 10-100 μm Nucleus Absent Present DNA Circular, in nucleoid region Linear, in nucleus Present (e.g., mitochondria, ER, Membrane-bound organelles Absent Golgi) 80S (except in mitochondria and Ribosomes 70S chloroplasts)  Present in plants and fungi Cell wall Usually present (peptidoglycan) (cellulose or chitin), absent in animals Cell division Binary fission Mitosis or meiosis Examples Bacteria, Archaea Plants, animals, fungi, protists Feature Animal Cells Plant Cells Cell wall Absent Present (cellulose) Cell shape Generally round or irregular Usually rectangular or cubic Plastids Absent Present (e.g., chloroplasts) Central vacuole Absent Present (large) Lysosomes Present Typically absent Centrioles Present Absent in most plants Plasmodesmata Absent Present Energy storage Glycogen Starch 1.3 Membrane Structure Fluid Mosaic Model: Describes the structure of the plasma membrane as a mosaic of components that gives the membrane a fluid character. This model was proposed by S.J. Singer and G.L. Nicolson in 1972. Phospholipid Bilayer Phospholipids: The basic building blocks of the membrane are phospholipids, which have hydrophilic (water-attracting) heads and hydrophobic (water-repelling, fatty acid) tails. Bilayer Formation: Hydrophobic tails facing inward shielded from the polar fluids and the hydrophilic heads facing outward towards the water. Amphipathic properties, restrict passage of substances (semipermeable) MEMBRANE PROTEINS: Junctions, Enzymes, Transport, Recognition, Anchorage, Transduction Cholesterol Membrane Stability: Cholesterol fits between phospholipids, providing stability and reducing fluidity at high temperatures. Preventing Solidification: At low temperatures, cholesterol prevents the membrane from becoming too rigid by disrupting the regular packing of phospholipids. Importance: At low temperatures: It prevents phospholipids from packing too tightly, maintaining some fluidity. At high temperatures: It restrains phospholipid movement, preventing excessive fluidity Types of Membrane Proteins 1. Integral Proteins: Embedded within the lipid bilayer, often spanning the entire membrane (transmembrane proteins). 2. Peripheral Proteins: Loosely attached to the exterior or interior surfaces of the membrane. 1.4 Membrane Transport Cell membranes have 2 key properties: semi permeable (transport) and selective (regulate material passage) Passive transport is the movement of molecules across a cell membrane without the need for energy input Process: High concentration gradient → low concentration (example: simple diffusion, facilitated diffusion, osmosis) 1. Simple diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, down their concentration gradient. Characteristics: a. Occurs until equilibrium is reached. b. Only small, nonpolar molecules (e.g., , ) can diffuse directly through the lipid bilayer. Example: Oxygen diffuses from the alveoli in the lungs into the blood because the concentration of oxygen is higher in the alveoli than in the blood. 2. Facilitated diffusion involves the use of membrane proteins to help larger (ions, glucose) or polar molecules pass through the cell membrane. Characteristics: a. Utilizes channel proteins and carrier proteins.  b. Does not require energy (ATP). Example: Glucose enters cells through facilitated diffusion using a specific carrier protein known as GLUT1. 3. Osmosis is diffusion of water through a selectively permeable membrane. Characteristics: a. Moves from an area of low solute concentration (high water potential) to an area of high solute concentration (low water potential). b. Utilizes aquaporins (water channels). Osmolarity: Measure of solute concentration Hypertonic: water leaves cell (wrinkles) Isotonic: solute and water same Hypotonic: cell inflates Solute: what is dissolving Solvent: water Active transport: is the movement of molecules across a cell membrane against the concentration gradient, requiring energy input. (ATP form) Process: low concentration → High concentration gradient 1. Primary: directly uses ATP to transport molecules. Sodium-potassium pumps moves ions in neuron 2. Secondary: uses the energy from the electrochemical gradient created by primary active transport. Gradient pump to move glucose into the cell Vesicular transport: involves the movement of large molecules or particles via vesicles and requires energy. 1. Endocytosis: Materials internalized within a vesicle. cells engulf substances into a pouch which then becomes a vesicle. Example: White blood cells use phagocytosis to engulf and destroy pathogens. 2. Exocytosis is the process by which vesicles fuse with the cell membrane to release their contents outside the cell. It is used to expel waste products and secrete substances like hormones and enzymes. Example: The release of insulin from pancreatic cells into the bloodstream. 1.5 Origin of Cells Abiogenesis theory: life originated from non-living chemical substances through natural processes. - Non living synthesis of simple organic molecules - Assembly of organic molecules into complex polymer  - Polymers that can self replicate - Create membranes internal chemistry different from their surrounding Endosymbiosis Theory: Double Membrane, Antibiotic resistance, Circular DNA, Division like fission, 70S Ribosomes Biogenesis theory: states that all living things come from pre-existing living things. Conditions no longer exist on Earth therefore can only be formed from division of pre-existing cells. Louis Pasteur's Experiment (1861): Pasteur used swan-neck flasks to show that microorganisms in the air were responsible for the growth of life in nutrient broths, not spontaneous generation. 1.5 Cell Division 1. G1 Phase (First Gap): The cell grows and synthesizes proteins necessary for cell division. 2. S Phase (Synthesis): DNA replication occurs, doubling the genetic material. 3. G2 Phase (Second Gap): The cell continues to grow and prepares for mitosis. 4. M Phase (Mitosis): The cell divides its copied DNA and cytoplasm to form two new cells. Interphase: DNA replication – DNA is copied during the S phase of interphase Organelle duplication – Organelles must be duplicated for twin daughter cells Cell growth – Cytoplasmic volume must increase prior to division Transcription / translation – Key proteins and enzymes must be synthesized Obtain nutrients – Vital cellular materials must be present before division Respiration (cellular) – ATP production is needed to drive the division process Mitosis: Division of a diploid nucleus into two genetically identical diploid cells 2n → 2n x2 Important for tissue repair, organism growth, asexual reproduction, development of embryos Cytokinesis: process of dividing the cytoplasm to form two distinct daughter cells. In animal cells, this involves the formation of a cleavage furrow, while plant cells form a cell plate. Mitotic Index: Measure of the status of a cell population. Elevated during growth and repair processes Cells in mitosis (PMAT) / total number of cells (Mitosis + Interphase + Cytokinesis) Stage Diagram Events Interphase ​ DNA is uncondensed (chromatin) ​ DNA is replicated (S phase) to form genetically identical sister chromatids ​ Cell grows in size and organelles are duplicated (G1 and G2) Prophase DNA super coils and condenses (2n = (forms visible chromosomes) Diploid cell) Nuclear membrane dissolves Centrioles move to poles and begin to produce spindle fibers Metaphase Centrosome spindle fibers attach to (2n = the centromere of each chromosome Diploid cell) Spindle fibres contract and move the chromosomes towards the cell centre Chromosomes form a line along the equator (middle) of the cell Anaphase Spindle fibres continue to contract 2n → 4n Sister chromatids separate and move to opposite sides of the cell Sister chromatids are now regarded as two separate chromosomes Telophase Chromosomes decondense (DNA 4n forms chromatin) Nuclear membranes form around the two identical chromosome sets Cytokinesis occurs concurrently Cytokinesis Cytoplasmic division occurs to divide 2n x2 the cell into two daughter cells Each daughter cell contains one copy of each identical sister chromatid Daughter cells are genetically identical Cyclins: a family of regulatory proteins that control the progression of the cell cycle Cyclins activate cyclin dependent kinases (CDKs), which control cell cycle processes through phosphorylation (process catalyzed by enzymes called kinases) In the cell cycle control: Cyclin-dependent kinases (CDKs) phosphorylate various proteins. This phosphorylation activates or deactivates these proteins. The activated/deactivated proteins then carry out specific functions to progress the cell cycle. Cyclin-dependent kinases control cell cycle processes Cancer: diseases caused by uncontrolled cell division. Resulting in abnormal cell growth called tumors Tumor cells can be benign and remain in their location or malign and invade other tissues. Metastasis is the spread of malignant tumor cells. Mutagens: agents that change the general material of cells, can be physical, chemical or biological. Mutagens that cause cancer are called carcinogens.