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Cells Are the Units of Structure (Building Blocks) of All Animals and Plants

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Cells Are the Units of Structure (Building Blocks) of All Animals and Plants Cell Theory 4 basic concepts of cell theory are: • Cells are the units of structure (building blocks) of all animals and plants. • Cells are the smallest unit of function in all animals and plants. • Cells originate only from pre-existing cells by cell division. • All cells maintain homeostasis Cell Structure, Cell Transport and Mitosis • Cell – Cell-membrane, Cytoplasm and Nucleus • Cytoplasm – Cytosol and Cell Organelles • Nucleus – Nuclear Envelope, Nucleoplasm and Chromatin (DNA + Histones) • Fig 3-2 • Table 3-1 represents the summary of structure and function of various parts of a representative cell. IMPORTANT Cell Membrane • All cells are covered with a thin covering of a double layer of Phospholipids and associated Proteins present here and there. • Each phospholipid has a polar (hydrophilic) head and non-polar (hydrophobic) tails. In the double layer the tails face each other forming a hydrophobic barrier which keeps water dissolved contents inside. • Proteins may be Intrinsic – embedded in the lipid double layer and Extrinsic associated outside the lipid double layer. Fig 3-3 and Table 3-2 Cell Membrane and Transport • In bacteria, plants, and fungi cell membrane is surrounded by a non-living cell wall. But cell membrane is the real boundary. Most cell walls are permeable. • Semi-permeable: Cell membranes allow some materials to pass through them and prevent others from doing so. Regulators like hormones can change permeability of a cell membrane. • Transport across membrane can be Passive or Active. Passive Transport Active Transport • From high to low concentration Independent of conc. Gradient • Energy (ATP) not needed ATP needed • Mostly Carrier Protein not needed Carrier Protein needed • Diffusion, Osmosis, Facilitated Diffusion Primary & Secondary Active T. Bulk Transport Passive Transport • Passive Transport includes Diffusion, Osmosis and Facilitated Diffusion. • Diffusion: All fluids (liquids + gases) move from area of higher concentration to area of lower concentration (concentration gradient). This movement of substances is called Diffusion. It can be through cell membranes. For example, spreading of fragrance, dissolving of ink drop in water, movement of O2 and CO2 between lungs and blood • Osmosis is always the net movement of water through cell membrane from its higher concentration (dilute solution) to its lower concentration (concentrated solution) when the 2 solutions are separated by semi-permeable membrane. For example absorption of water by roots of plants. • Facilitated diffusion is faster than normal diffusion but needs a carrier protein though no ATP needed. For example, absorption of glucose and amino acids in intestine 1 Diffusion Osmosis • Movement of solute Movement of water • Membrane not needed Semi-permeable memb needed • High conclow conc Low conchigh conc of solution • Fig 3.4 Fig 3.6 • Active Transport • Only active transport can operate against concentration gradient. • It is the fastest mode of transport. Fig 3-9, Na-K pump • It always consumes ATP directly or indirectly. • It always needs one or more transport proteins. • For example absorption of minerals by plant roots, absorption of nutrients when their concentration is already higher inside the cells. Vesicular Transport • Large molecules like proteins cannot transport through membrane by passive or active transport discussed so far. These are packed into membrane bound sacs and transported across cell membrane. • Endocytosis is the bulk transport into the cell. If solid material including prey is brought in as Food Vacuole, the process is called Phagocytosis. Fig 3-11. For example, white blood cells eating bacteria. When cell brings in liquid bound in sac the process is called Pinocytosis. Fig 3-10 • Exocytosis: When the cells releases solid or liquid in sacs the process is called exocytosis. For example Amoeba throws excess water outside to maintain required concentration (osmoregulation). • IMPORTANT Table 3-3 depicts summary of mechanisms of membrane transport. Recap-1 Chapter-3 1. The liquid part of cytoplasm is --------------- 2. Structures formed of membranes and molecules, present in cytoplasm, doing a special function, are ---------- ---------------- 3. 2 halves of cell membrane are held together by -------------- bonds 4. Cell membrane is fluid due to --------------- molecules 5. Membrane bound --------- molecules regulate membrane transport 6. Movement of solute from high to low concentration is ------------- 7. Net Movement of water across cell membrane (from low concentration solution to high concentration solution) is ---------- 8. ----------- ---------------- can operate against concentration gradient and needs both a carrier protein and ATP. 9. --------- ------------- moves along the concentration gradient and needs a carrier protein but no ATP. 10. Bulk movement of solids into the cell in a vesicle is --------- and of liquids is ------------------. (also called vesicular transport) Cytoplasm • Cytoplasm is the living fluid part between cell membrane and nucleus. It has special structures called Cell Organelles in it. • Cytosol is the matrix (formless) part of cytoplasm formed of water having dissolved or suspended substances in it. • Cell Organelles are organ like each performing specific function/s but formed of molecules and membranes only (sub- cellular). • Double Membrane bound Organelles: Mitochondria, Chloroplasts, Endoplasmic Reticulum, Golgi Body, and Nucleus. • Single Membrane bound Organelles: Lysosomes, Peroxisomes, Vacuoles • Organelles lacking any membrane: Ribosomes, Centrioles, Nucleolus • IMPORTANT: Table 3.1 Nucleus and Ribosomes 1 2 Genetic Control of the Cell • Nucleus: is the most distinct structure inside cell visible with light microscope. It has inside it DNA having all the information needed to form and run the cell. The segments of DNA are called Genes. Fig 3-16 • Nuclear Envelope: is formed of 2 membranes with a gap between them. It has a large number of Nuclear Pores usually bound by a nuclear complex. The pores are large enough to allow RNA and proteins to pass through. • Nucleoplasm: is the matrix (formless) of nucleus and has a different composition than Cytosol. • Chromatin fibers: are very long molecules of DNA associated with proteins (Histones and other nuclear proteins). Each chromatin fiber, at the time of cell division, organizes into Chromosomes. Fig 3-17 • Nucleolus: is present in the nucleus when the cell is not dividing. No membrane bounds it. It assembles both units of Ribosomes. Nucleus and Ribosomes 2 Transcription Translation • DNA -------------------m-RNA -----------------------Protein • A gene (DNA) produces m-RNA by transcription. The m-RNA comes out of nuclear pores into the cytoplasm. Here Ribosomes attach one by one to m-RNA and synthesize a protein. t-RNA’s bring amino acids from cytosol to m-RNA – ribosome complex. Fig 3-18, 19 • Each ribosome has 2 sub-units larger (60S) and smaller (40S). • r-RNA and ribosomal proteins form the ribosomal subunits. • No membrane covers the ribosomal subunits. Ribosomal subunits join only around m-RNA for protein synthesis otherwise remain separate. • At the time of cell division one DNA divides and produces 2 DNA molecules by replication. DNA replication leads to produce sperms and eggs (gametes). m-RNA = messenger RNA Replication t-RNA = transfer RNA • DNA ----------------DNA + DNA r-RNA = ribosomal RNA The Endomembrane System 1 Manufacturing and Distributing Cellular Products • Endoplasmic Reticulum, Golgi Apparatus, Lysosomes and Vacuoles collectively form Endomembrane System. • Endoplasmic Reticulum: is a system of double membranes in the form of tubes and sacs throughout cytoplasm (in between cell membrane and nuclear envelope). Main manufacturing facility. • Functions include synthesis of proteins and lipids including steroids, detoxification, and cellular transportation. It transports materials inside the cell by transport vesicles. RER SER • 1 Rough ER, ribosomes fixed 1 Smooth ER, no ribosomes • 2 Flat sacs 2 Tubular • 3 Synthesis of memb proteins 3 Lipids, steroids • 4 Synthesis of secretory proteins 4 Detoxification of drugs The Endomembrane System 2 • Golgi Apparatus = Golgi Body: is a stacks of flattened sacs called cisternae. A cell may have from a few to a few hundred of Golgi stacks. Golgi Apparatus receives transport vesicles from ER on one side, modifies received chemicals, can store them and packs them in secretory vesicles and releases them on shipping side. • Lysosomes: are single memb bound organelles rich in digestive enzymes, help in breakdown of large molecules like proteins, polysaccharides, lipids and nucleic acids. Lysosomes provide a safe place for digestion of large molecules without damaging molecules of the cell. A Lysosome joins a food vacuole to digest the materials inside vacuole. Lysosomes are absent in most plant cells. • Vacuoles: are membrane bound sacs and pinch off from ER, Golgi Apparatus and cell membrane. Functions include endocytosis, exocytosis, maintain turgor pressure in a plant cell, trasnportation. 3 Mitochondria Energy Conversion • Mitochondria (sing. Mitochondrion): are the powerhouses of cells and the site for cellular respiration. Respiration is oxidation of food and chief source of energy for the cell. • These are bound with double membrane, outer smooth and inner folded. Mitochondria have enzymes for breakdown glucose derivatives, fatty acids and amino acids. • Mitochondria have Electron-Transport-System that generates ATP molecules by using the energy contained
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