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BI236 lecture 2.docx

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Renuka Karunagoda

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BI236: Cell and Molecular Biology Lecture 2 Cells and Organelles • Cell walls of bacteria, archaea, and eukaryotes • Plasma membrane and cytoplasm o Movement of solutes across plasma membrane o Endocytosis  Pinocytosis  Phagocytosis  Receptor –mediated endocytosis o Exocytosis • Cell organelles • Cell Types o Aprokaryotic cell  Cell wall  Plasmids: have extra chromosomal DNA, circular, common in bacteria, antibiotic resistance(not necessary for the survival of the cell, but there are advantages).  Certain bacteria that fix atmospheric nitrogen-symbiotic relationship- risobium ((bacteria)(legumes: beans, pea’s)), it can absorb the nitrogen in the environment then. o An eukaryotic cell  Lacks cell wall  Rough ER: ribosomes  Smooth ER: no ribosomes  Mitochondria: respiration takes place  Centrioles (2)(animal):  Golgi vesicles  Microtubules  Pinocytotic vesicles: wants to get rid of wastes, it secretes materials from the cell.  Lysosomes: digestive sites, unwanted material; • Lysosomes and vacuoles have similar function • Cell wall o Found in plants, bacteria, fungi, algae, and some archaea o Animals and protozoa do not have cell walls o It surrounds the plasma membrane o Plant cell walls—contain mostly cellulose o Fungi-contain chitin • Bacterial cell wall o Around the outside of the cell membrane is the bacterial cell wall. Bacterial cell walls are made of peptidoglycan(also called murin(is only found in bacteria)) o 2 different types of cell wall in bacteria  Gram-positive • Thick cell wall containing many layers of peptidoglycan and teichoic acid (bacterial polysaccharide)  Gram-negative • Relatively thin cell wall consisting of few layers of peptidoglycan surrounding by second lipid membrane containing lipopolysaccharides and lipoproteins  Most bacteria are gram-negative.  The cell wall is essential to the survival of many bacteria • Cell wall of archaea o Lacks peptidoglycan, with the exception of one group methanogen o In that group, the pepidoglycan is a modified form, very different from the kind found in bacteria  Example: Methanococcus janaschii, Methanosarcina barkeri, Methanothermus fervidus. • 4 types of cell wall currently known among theArchaea o 1) composed of pseudopeptidoglycan (also called pseudomurein) o 2) composed entirely of thick layer polysaccharides o 3) consists of glycoprotein o 4) composed only of surface-layer proteins, known as the s-Layer. • Cell membrane o Composed of a mixture of protein and lipids. o Within the cell, it’s a watery environment. o Exterior of the cell is also watery environment. o Hydrophillic head, hydrophobic tail o Glycoprotein and glycolipid- communication o Protein: across the membrane, for transportation • Movement across the plasma membrane o Molecules which move freely  Water, carbon dioxide, ammonia, oxygen o Carrier proteins transport some molecules  Proteins embedded in lipid bilayer  Fluid mosaic model by Singer and Nicholson(1972) • Molecule movement and cells o Passive transport-no energy required, move due to gradient, move to equalize gradient o Active transport o Endocytosis-taken inside the cell  Phagocytosis+pinocytosis o Exocytosis-excrete materials outside the cells • Types of Passive Transport o Diffusion- molecules move to equalize concentration o Osmosis-fluid flows lower solute concentration, often involves movement of water. Into cell, out of cell. o Facilitated diffusion- Differentially permeable membrane is involved. Channels (or transport proteins) help molecule or ions to aid ions, water or other solutes enter or leave the cell. • Passive Transport o Movement of molecules DOWN the concentration gradient. It goes from high to low concentration, in order to maintain equilibrium in the cells. Does not require cellular energy. o Types of Transport: Diffusion, facilitated diffusion, and osmosis. o Types of Particles transported:Anything soluble(meaning able to dissolve) in lipids, small monosaccharide, water, oxygen, carbon dioxide, etc o Importance of Passive Transport: It maintains equilibrium in the cell. Wastes (carbon dioxide, water, etc.) diffuse out and are excreted; nutrients and oxygen diffuse in to be used by the cell. o Functions: Maintains dynami
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