Cell.pptx
- 1. Cell
- 2. • CELL • All the living things are composed of cells. • A single cell is the smallest unit that has all the characteristics of life. • Cell is defined as the structural and functional unit of the living body.
- 3. • General Characteristics of Cell • Each cell in the body: • 1. Needs nutrition and oxygen. • 2. Produces its own energy necessary for its growth, repair and other activities. • 3. Eliminates carbon dioxide and other metabolic wastes. • 4. Maintains the medium, i.e. the environment for its survival • 5. Shows immediate response to the entry of invaders like bacteria or toxic substances into the body • 6. Reproduces by division. There are some exceptions like neuron, which do not reproduce.
- 4. • TISSUE • Tissue is defined as the group of cells having similar function. There are many types of tissues in the body. All the tissues are classified into four major types which are called the primary tissues. • The primary tissues include: • 1. Muscle tissue (skeletal muscle, smooth muscle and • cardiac muscle) • 2. Nervous tissue (neurons and supporting cells) • 3. Epithelial tissue (squamous, columnar and cuboidal epithelial cells) • 4. Connective tissue (connective tissue proper, cartilage, • bone and blood.
- 5. • ORGAN • An organ is defined as the structure that is formed by two or more primary types of tissues, which execute the functions of the organ. • Some organs are composed of all the four types of primary tissues. The organs are of two types, namely tubular or hollow organs and compact or parenchymal organs. • Some of the organs in the body are brain, heart, lungs, stomach, intestine, liver, gallbladder, pancreas, kidneys, endocrine glands, etc.
- 6. SYSTEM • The organ system is defined as group of organs that work together to carry out specific functions of the body. • Each system performs a specific function. Digestive system is concerned with digestion of food particles. • Excretory system eliminates unwanted substances. • Cardiovascular system is responsible for transport of • substances between the organs. • Respiratory system is concerned with the supply of oxygen and removal of carbon dioxide. • Reproductive system is involved in the reproduction of species
- 7. • STRUCTURE OF CELL • Each cell is formed by a cell body and a membrane covering the cell body called the cell membrane. • Cell body has two parts, namely nucleus and cytoplasm surrounding the nucleus. • Thus, the structure of the cell is studied under three headings: • 1. Cell membrane • 2. Cytoplasm • 3. Nucleus.
- 9. • CELL MEMBRANE • Cell membrane is a protective sheath, enveloping the cell body. • It is also known as plasma membrane or plasmalemma. • This membrane separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF). • The cell membrane is a semipermeable membrane. • So, there is free exchange of certain substances between ECF and ICF.
- 10. • COMPOSITION OF CELL MEMBRANE • Cell membrane is composed of three types of substances: • 1. Proteins (55%) • 2. Lipids (40%) • 3. Carbohydrates (5%).
- 11. • STRUCTURE OF CELL MEMBRANE • On the basis of structure, cell membrane is called a unit membrane or a three-layered membrane. • The electron microscopic study reveals three layers of cell membrane, namely, one central electron-lucent layer and two electron- dense layers. • The two electron-dense layers are placed one on either side of the central layer. • The central layer is a lipid layer formed by lipid substances. • The other two layers are protein layers formed by proteins. • Cell membrane contains some carbohydrate molecules
- 12. • Structural Model of the Cell Membrane • 1. Danielli-Davson model • ‘DanielliDavson model’ was the first proposed basic model of membrane structure. It was proposed by James F Danielli and Hugh Davson in 1935. • And it was accepted by scientists for many years. This model was basically a ‘sandwich of lipids’ covered by proteins on both sides.
- 13. • 2. Unit membrane model • In 1957, JD Robertson replaced ‘Danielli-Davson model’ by ‘Unit membrane model’ on the basis of electron microscopic studies. • 3. Fluid mosaic model • Later in 1972, SJ Singer and GL Nicholson proposed ‘The fluid mosaic model’. According to them, the membrane is a fluid with mosaic of proteins (mosaic means pattern formed by arrangement of different colored pieces of stone, tile, glass or other such materials). • This model is accepted by the scientists till now. • In this model, the proteins are found to float in the lipid layer instead of forming the layers of the sandwich-type model.
- 14. • Lipid Layers of the Cell Membrane • The central lipid layer is a bilayered structure. • This is formed by a thin film of lipids. • The characteristic feature of lipid layer is that, it is fluid in nature and not a solid structure. So, the portions of the membrane move from one point to another point along the surface of the cell. • The materials dissolved in lipid layer also move to all areas of the cell membrane. • Major lipids are: • 1. Phospholipids • 2. Cholesterol
- 15. • 1. Phospholipids • Phospholipids are the lipid substances containing phosphorus and fatty acids. Aminophospholipids, sphingo - myelins, phosphatidylcholine, phosphatidyletholamine, • phosphatidylglycerol, phosphatidylserine and phospha tidylinositol are the phospholipids present in lipid layer of cell membrane. • Phospholipid molecules are arranged in two layers • Each phospholipid molecule resembles the headed pin in shape. • The outer part of the phospholipid molecule is called the head portion and the inner portion is called the tail portion.
- 17. • Head portion is the polar end and it is soluble in water and has strong affinity for water (hydrophilic). • Tail portion is the non-polar end. It is insoluble in water and repelled by water (hydrophobic). • Two layers of phospholipids are arranged in such away that the hydrophobic tail portions meet in the center of the membrane. • Hydrophilic head portions of outer layer face the ECF and those of the inner layer face ICF (cytoplasm).
- 18. • 2. Cholesterol • Cholesterol molecules are arranged in between the phospholipid molecules. • Phospholipids are soft and oily structures and cholesterol helps to ‘pack’ the phospholipids in the membrane. • So, cholesterol is responsible for the structural integrity of lipid layer of the • cell membrane.
- 19. • Functions of Lipid Layer in Cell Membrane • Lipid layer of the cell membrane is a semipermeable membrane and allows only the fat-soluble substances to pass through it. • Thus, the fat-soluble substances like oxygen, carbon dioxide and alcohol can pass through this lipid layer. • The water-soluble substances such as glucose, urea and electrolytes cannot pass through this Layer.
- 20. • Protein Layers of the Cell Membrane • Protein layers of the cell membrane are electron-dense layers. • These layers cover the two surfaces of the central lipid layer • Protein layers give protection to the central lipid layer. • The protein substances present in these layers are mostly glycoproteins. • Protein molecules are classified into two categories: • 1. Integral proteins or transmembrane proteins. • 2. Peripheral proteins or peripheral membrane proteins
- 21. • 1. Integral proteins • Integral or transmembrane proteins are the proteins that pass through entire thickness of cell membrane from one side to the other side. • These proteins are tightly bound with the cell membrane. • Examples of integral protein: • i. Cell adhesion proteins • ii. Cell junction proteins • iii. Some carrier (transport) proteins • iv. Channel proteins • v. Some hormone receptors • vi. Antigens • vii. Some enzymes
- 22. • 2. Peripheral proteins • Peripheral proteins or peripheral membrane proteins are the proteins which are partially embedded in the outer and inner surfaces of the cell membrane and do not penetrate the cell membrane. • Peripheral proteins are loosely bound with integral proteins or lipid layer of cell membrane. So, these protein molecules dissociate readily from the cell membrane. • Examples of peripheral proteins: • i. Proteins of cytoskeleton • ii. Some carrier (transport) proteins • iii. Some enzymes.
- 23. • Functions of Proteins in Cell Membrane • 1. Integral proteins provide the structural integrity of the cell membrane • 2. Channel proteins help in the diffusion of watersoluble substances like glucose and electrolytes • 3. Carrier or transport proteins help in the transport of substances across the cell membrane by means of • active or passive transport • 4. Pump: Some carrier proteins act as pumps, by which ions are transported actively across the cell • membrane • 5. Receptor proteins serve as the receptor sites for hormones and neurotransmitters • 6. Enzymes: Some of the protein molecules form the enzymes and control chemical (metabolic) reactions within the cell membrane • 7. Antigens: Some proteins act as antigens and induce the process of antibody formation • 8. Cell adhesion molecules or the integral proteins are responsible for attachment of cells to their neighbors or to basal lamina.
- 24. • CYTOPLASM • Cytoplasm of the cell is the jellylike material formed by 80% of water. It contains a clear liquid portion called cytosol and various particles of different shape and size. • These particles are proteins, carbohydrates, lipids or electrolytes in nature. Cytoplasm also contains many organelles with distinct structure and function. • Cytoplasm is made up of two zones: • 1. Ectoplasm: Peripheral part of cytoplasm, situated just beneath the cell membrane • 2. Endoplasm: Inner part of cytoplasm, interposed bet ween the ectoplasm and the nucleus
- 25. • ORGANELLES IN CYTOPLASM • Cytoplasmic organelles are the cellular structures embedded in the cytoplasm. • Organelles are considered as small organs of the cell. • Some organelles are bound by limiting membrane and others do not have limiting membrane. • Each organelle is having a definite structure and specific functions.
- 26. • Organelles with limiting membrane • 1. Endoplasmic reticulum • 2. Golgi apparatus • 3. Lysosome • 4. Peroxisome • 5. Centrosome and centrioles • 6. Secretory vesicles • 7. Mitochondria • 8. Nucleus • Organelles without limiting membrane 1. Ribosomes • 2. Cytoskeleton of endoplasmic reticulum contains a fluid medium
- 27. • ENDOPLASMIC RETICULUM • Endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are interconnected with one another. • It is covered by a limiting membrane which is formed by proteins and bilayered lipids. • The lumen of endoplasmic reticulum contains a fluid medium called endoplasmic matrix. • The endoplasmic reticulum forms the link between nucleus and cell membrane by connecting the cell membrane with the nuclear membrane.
- 28. • Types of Endoplasmic Reticulum • Endoplasmic reticulum is of two types, namely rough endoplasmic reticulum and smooth endoplasmic reticulum. • Both the types are interconnected and continuous with one another. • Depending upon the activities of the cells, the rough endoplasmic reticulum changes to smooth endoplasmic reticulum and vice versa.
- 31. • Rough Endoplasmic Reticulum • It is the endoplasmic reticulum with rough, bumpy or bead-like appearance. Rough appearance is due to the attachment of granular ribosomes to its outer surface. • Hence, it is also called the granular endoplasmic reticulum . • Rough endoplasmic reticulum is vesicular or tubular in structure. • Functions of Rough Endoplasmic Reticulum • 1. Synthesis of proteins • 2. Degradation of worn-out organelles
- 32. • 1. Synthesis of proteins • Rough endoplasmic reticulum is concerned with the synthesis of proteins in the cell. It is involved with the synthesis of mainly those proteins which are secreted from the cells such as insulin from β cells of islets of Langerhans in pancreas and antibodies from B lymphocytes. • Ribosomes arrange the amino acids into small units of proteins and transport them into the rough endoplasmic reticulum. • Here, the carbohydrates are added to the protein units forming the glycosylated proteins or glycoproteins, which are arranged in the form of reticular vesicles. • These vesicles are transported mainly to Golgi apparatus for further modification and processing. Few vesicles are transported to other cytoplasmic.
- 33. • 2. Degradation of worn-out organelles • Rough endoplasmic reticulum also plays an important role in the degradation of worn-out cytoplasmic organelles like mitochondria. It wraps itself around the wornout organelles and forms a vacuole which is often called the autophagosome. • Autophagosome is digested by lysosomal enzyme.
- 34. • Smooth Endoplasmic Reticulum • It is the endoplasmic reticulum with smooth appearance. • It is also called agranular reticulum. It is formed by many interconnected tubules. • So, it is also called tubular endoplasmic reticulum. • Functions of Smooth Endoplasmic Reticulum • 1. Synthesis of non-protein substance • 2. Role in cellular metabolism
- 35. • Synthesis of non-protein substance • 1. Synthesis of non-protein substance • Smooth endoplasmic reticulum is responsible for synthe sis of non-protein substances such as cholesterol and steroid. • This type of endoplasmic reticulum is abundant in cells that are involved in the synthesis of lipids, phospholipids, lipoprotein substances, steroid hormones, sebum, etc. • In most of the other cells, smooth endoplasmic reticulum is less extensive than the rough endoplasmic reticulum. • 2. Role in cellular metabolism • Outer surface of smooth endoplasmic reticulum contains many enzymes which are involved in various metabolic processes of the cell. • 3. Storage and metabolism of calcium • Smooth endoplasmic reticulum is the major site of storage and metabolism of calcium. In skeletal muscle fibers, it releases calcium which is necessary to trigger the muscle contraction.
- 36. • 4. Catabolism and detoxification • Smooth endoplasmic reticulum is also concerned with catabolism and detoxification of toxic substances like some drugs and carcinogens (cancer- producing substances) in the liver.
- 37. GOLGI APPARATUS • Golgi apparatus or Golgi body or Golgi complex is a membrane-bound organelle, involved in the processing of proteins. • It is present in all the cells except red blood cells. It is named after the discoverer Camillo Golgi. • Usually, each cell has one Golgi apparatus. Some of the cells may have more than one Golgi apparatus. • Each Golgi apparatus consists of 5 to 8 flattened membranous sacs called the cisternae. • Golgi apparatus is situated near the nucleus. It has two ends or faces, namely cis face and trans face. The cis face is positioned near the endoplasmic reticulum. • Reticular vesicles from endoplasmic reticulum enter the Golgi apparatus through cis face. The trans face is situated near the cell membrane. • The processed substances make their exit from Golgi apparatus through trans face.
- 39. • Functions of Golgi Apparatus • Major functions of Golgi apparatus are processing, packing, labeling and delivery of proteins and other molecules like lipids to different parts of the cell. • 1. Processing of materials • Vesicles containing glycoproteins and lipids are transported into Golgi apparatus. Here, the glycoproteins and lipids are modified and processed. • 2. Packaging of materials • All the processed materials are packed in the form of secretory granules, secretory vesicles and lysosomes, which are transported either out of the cell or to another part of the cell. Because of this, Golgi apparatus is called the ‘post office of the cell.
- 40. • 3. Labeling and delivery of materials • Finally, the Golgi apparatus sorts out the processed and packed materials and labels them (such as phosphate group), depending upon the chemical content for delivery (distribution) to their proper destinations. Hence, the Golgi apparatus is called ‘shipping department of the cell’.
- 41. • LYSOSOMES • Lysosomes are the membrane-bound vesicular organelles found throughout the cytoplasm. The lysosomes are formed by Golgi apparatus. • The enzymes synthesized in rough endoplasmic reticulum are processed and packed in the form of small vesicles in the Golgi apparatus. • Then, these vesicles are pinched off from Golgi apparatus and become the lysosomes. • Among the organelles of the cytoplasm, the lysosomes have the thickest covering membrane. The • membrane is formed by a bilayered lipid material. • It has many small granules which contain hydrolytic enzymes.
- 42. • Types of Lysosomes • Lysosomes are of two types: • 1. Primary lysosome, which is pinched off from Golgi apparatus. It is inactive in spite of having hydrolytic enzymes • 2. Secondary lysosome, which is the active lysosome. • It is formed by the fusion of a primary lysosome with phagosome or endosome. • Functions of Lysosomes • Lysosomes are often called ‘garbage system’ of the cell because of their degradation activity. About 50 different hydrolytic enzymes, known as acid hydroxylases are present in the lysosomes, through which lysosomes execute their functions.
- 43. • Important lysosomal enzymes • 1. Proteases, which hydrolyze the proteins into amino acids • 2. Lipases, which hydrolyze the lipids into fatty acids and glycerides • 3. Amylases, which hydrolyze the polysaccharides into glucose • 4. Nucleases, which hydrolyze the nucleic acids into mononucleotides
- 44. • Mechanism of lysosomal function • Lysosomal functions involve two mechanisms: • 1. Heterophagy: Digestion of extracellular materials engulfed by the cell via endocytosis • 2. Autophagy: Digestion of intracellular materials such as worn- out cytoplasmic organelles.
- 45. • Specific functions of lysosomes • 1. Degradation of macromolecules • Macromolecules are engulfed by the cell by means of endocytosis (phagocytosis, pinocytosis or receptor mediated endocytosis. • The macromolecules such as bacteria, engulfed by the cell via phagocytosis are called phagosomes or vacuoles. • The other macromolecules taken inside via pinocytosis or receptor-mediated endocytosis are called endosomes. • The primary lysosome fuses with the phagosome or endosome to form the secondary lysosome.
- 46. • The pH in the secondary lysosome becomes acidic and the lysosomal enzymes are activated. The bacteria and the other macromolecules are digested and degraded by these enzymes. • The secondary lysosome containing these degraded waste products moves through cytopl asm and fuses with cell membrane. Now the waste products are eliminated by exocytosis.
- 47. • 2. Degradation of worn-out organelles • The rough endoplasmic reticulum wraps itself around • the worn-out organelles like mitochondria and form • the vacuoles called autophagosomes. • One primary lysosome fuses with one autophagosome to form the secondary lysosome. • The enzymes in the secondary lysosome are activated. • Now, these enzymes digest the contents of autophagosome.
- 48. • 3. Removal of excess secretory products in the cells • Lysosomes in the cells of the secretory glands remove the excess secretory products by degrading the secretory granules. • 4. Secretory function – secretory lysosomes • Recently, lysosomes having secretory function called secretory lysosomes are found in some of the • cells, particularly in the cells of immune system. • The conventional lysosomes are modified into secretory lysosomes by combining with secretory granules (which contain the particular secretory product of the cell).