cell,subcellular organelles,and transport

cell,subcellular organelles,and transport

1. Cell and Sub-cellular Structures Dr.GANESH

2. Cell Cell is the Basic Structural and Functional Unit of all Living Organisms Therefore, Evolution of cell is a crucial milestone in the evolution of life .

3. Cell structure A eukaryotic cell contains a) plasma membrane , b) cytosol and c) subcellular organelles . Cell is a closed compartment containing aqueous fluid called – cytosol surrounded by cell membrane called – plasma membrane

4. Cell Subcellular organelles are bathed by cytosol and include – nucleus, mitochondria, endoplasmic reticulum, ribosomes golgi apparatus ( golgi complex), lysosomes , peroxisomes , and cytoskeleton.

5. Cell Cell = Plasma membrane + cytoplasm Cytoplasm = Cytosol + Subcellular organelles

6. Cell All subcellular organelles , except ribosomes and cytoskeleton, are compartments within the cell, surrounded by cell membrane and containing their own aqueous fluid

7. Cell Diversity of cell types serves the function of the particular tissues and organs in which they are present. Depending on the function , different cell types differ in their organelle content, or their organelles may contain different amounts of particular enzymes or structural molecules.

8. Cell Membrane Contents: Structure Function Transport Across Cell Membrane

9. Cell Membrane thin hydrophobic sheet in fluid state which envelopes the cell made up of lipid bilayer (two layers) containing also proteins Lipid and Protein molecules are bound to each other by non-covalent bonds Carbohydrates, found in lesser amounts are bound to lipid and protein molecules by covalent bonds

10. Cell Membrane Membranes Define the external boundaries of cells and organelles Maintain their integrity and Serve to compartmentalize functions within the cells.

11. Salient features of Cell Membrane Membranes are flexible (because they are fluid), elastic and self-sealing flexibility permits the shape changes that accompany cell growth and movement of cells, gives stability Also enables the cell to perform exocytosis and endocytosis

12. Membranes are selectively permeable to molecules. -Being hydrophobic membranes are permeable to only lipid soluble/hydrophobic substances and impermeable to hydrophilic/polar substances. -However, membranes have transport systems (made of proteins) to permit and regulate the movement of polar compounds across its thickness.  

13. Functions of Cell Membrane Cell Membranes maintain the shape and size of the cells. Protects the cytoplasm and the cell organelles from the external environment The intracellular membranes serve to compartmentalize functions within the cells. Membranes regulate the transport of substances like nutrients, ions, gases, water, various products, wastes into and out of cells and their organelles.

14. 5.Membranes bound enzymes carry out metabolic reactions near the inner surface of the cell membrane. Egs:Succinate dehydrogenase . 6.Membranes are involved in signal transduction; i.e. proteins in membranes detect specific signals transmit such signals to the cell interior by specific chemical events. 7. Membrane mediates cell-to-cell communication between adjacent cells by gap-junctions. 8 . Membrane regulates the flow of information between cell and its environment

15. Structure of Cell Membrane Membranes are sheet-like complex structures composed of - Lipids Proteins and Carbohydrates

16. Structure of Cell Membrane Lipid bilayer conformation is the basic structure of all biological membranes. lipid bilayer is made up of amphipathic lipid molecules ( having both hydrophilic or polar part and a hydrophobic or non-polar part) crucial in the formation of membrane structure

17. Structure of Cell Membrane Fluid Mosaic Model proposed by Singer and Nicolson to explain the structure of cell membrane According to this, membrane is a fluid lipid bilayer with a mosaic of embedded proteins

18. Phospholipids Cholesterol Proteins (peripheral and integral) Carbohydrates Membrane Components

19. In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model !

20. Structure of Cell Membrane In other words, the model is compared to icebergs ( membrane proteins ) floating in a sea ( predominantly phospholipid molecules )

21. Structure of Cell Membrane Membranes are 5-8 nm thick and appear trilaminar when viewed through an electron microscope

22. Structure of Cell Membrane Different membranes within the cell and between cells have different compositions This difference reflects the diversity of biological roles of these membranes

23. Structure of Cell Membrane For e.g. myelin sheath of neurons, which acts as an electrical insulator, is rich in lipids whereas inner mitochondrial membrane in which many enzyme-catalyzed processes take place contains more proteins than lipids

24. Lipids All Lipids present in cell membrane are – Amphipathic Lipids Compound Lipids and Cholesterol (Free Cholesterol) Phospholipids Glycolipids conceived as having a – polar head and a non-polar tail.

25. Amphipathic Lipid Polar Head Non-polar Tails

26. Lipids Amphipathic lipids self-assemble in aqueous medium into bilayer sheets (lipid bilayer) with their hydrophobic parts (non-polar tails) of each layer facing and interacting with each other forming a hydrophobic membrane core and hydrophilic parts (polar heads) facing towards the two surfaces interacting with the aqueous medium

27. Lipid Monolayer Non-polar Medium Aqueous Medium

28. Lipid Bilayer Aqueous Medium Aqueous Medium Hydrophobic Core

29. Lipids of cell membrane Ampipathic lipids such as phospholipids (e.g. lecithin,cephalin,sphingomyelin ) glycolipids and cholesterol .

30. Lipids Specific type of lipid may be present in particular tissues Example: Nerve tissues have large quantity of glycolipids and sphingomyelins . Mitochondrial membrane rich in cardiolipin .

31. Proteins Make up about 50% of total membrane mass In a typical cell Distributed Asymmetrically in the lipid bilayer

32. Proteins Membrane proteins are of 2 types. 1.Peripheral membrane proteins attached to the lipid bilayer on either surface E.g. succinate dehydrogenase (TCA Cycle), endoplasmic reticulum enzymes, etc 2. Integral membrane proteins deeply embedded in the lipid bilayer. Some integral membrane proteins may completely span the lipid bilayer – transmembrane proteins e.g. receptor proteins, transport proteins, channel proteins, etc).

33. Peripheral membrane proteins Integral membrane proteins Transmembrane proteins Cell Membrane proteins Examples Integral membrane proteins Receptor proteins Transport proteins Channel proteins

34. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

35. Membrane Carbohydrates relatively minor components 5-8% of the total membrane mass. covalently linked to lipids and proteins as glycolipids and glycoproteins . Located on the extra cellular side of the membrane, which forms a loose outer carbohydrate coat called Glycocalyx

36. Functions of Glycocalyx Gives a net negative surface charge and repel from other electrically negative particles. Cell to cell attachment is possible. Part of receptor substances for binding hormones such as insulin Some of the carbohydrate moieties enter into immune reaction.

37. Glycoprotein Glycolipid Glyccalyx Cell Membrane Carbohydrates

38. Oligosaccharide Glycoprotein Peripheral Membrane Protein Integral Membrane Proteins Glycolipid

39. Glycoprotein Glycolipid Lipid Bilayer Polar head Non polar tail Cell Membrane Structure Integral membrane proteins Transmembrane proteins Peripheral membrane proteins

40. Phospholipids Cholesterol Proteins (peripheral and integral) Carbohydrates Membrane Components

41. Fluidity of Membranes Membrane consists of a mosaic of lipids and proteins that can move laterally (so fluid) in the plane of the membrane. fluidity makes the membrane flexible (which in turn permits the shape changes that accompany cell growth and cell movements), increases permeability ,gives stability and enables them to invaginate or evaginate allowing them to ingest or to expel materials .

42. Factors Affecting the Fluidity Unsaturated cis -fatty acids Short chain fatty acids and High temperature Increase the membrane fluidity . Whereas, Cholesterol decreases the membrane fluidity

43. Specialised Membrane Structures Tight Junction seen in epithelial cells, where the lateral membrane of a cell is fused with lateral membrane of adjacent cell. This prevents the movement of molecules through the gap between the cells. This ensures that, molecules move only through the luminal side to the serosal side. E.g. : Seen in gastrointestinal epithelial cells. Myelin Sheath Specialized structure for the conduction of nerve impulse, rich in lipids.

44. Specialised Membrane Structures Synaptic membranes : Cell membranes associated with synapses. Required for the release or reception of neurotransmitters . Microvilli : Hair like projections produced by the membrane evagination , which increases absorptive surface area. Eg : intestinal epithelial cells.

45. Specialized Membrane Structures Tight Junction Synaptic membrane Microvilli Tight Junction Eg: gastrointestinal epithelial cells Eg: gastrointestinal epithelial cells Eg: neurons For cell to cell communication Enhance absorption of food Transmit information between neurones Myelin Sheath Myelin sheath Eg: neurons For conduction of nerve impulse

46. Any Questions??

47. Cell membrane is the boundary between inside & outside… separates cell from its environment IN food carbohydrates sugars, proteins amino acids lipids salts, O 2 , H 2 O OUT waste ammonia salts CO 2 H 2 O products cell needs materials in & products or waste out IN OUT Can it be an impenetrable boundary? NO!

48. Transport Across Cell Membrane Membranes act as effective barrier for the passage of molecules, thereby keeping some substances inside the cell and others out. Yet they also contain transport systems which confer on membranes the important property of selective permeability by allowing specific molecules to be taken up and unwanted compounds to be removed from the cell

49. Transport Across Cell Membrane As the membrane core is hydrophobic in nature hydrophobic molecules move more readily across the membrane than hydrophilic ones. As the membrane fluidity increases, permeability to hydrophilic substances also increases

50. Transport across cell membrane What molecules can get through directly? fats & other lipids inside cell outside cell lipid salt aa H 2 O sugar NH 3 What molecules can NOT get through directly? polar molecules H 2 O ions salts, ammonia large molecules starches, proteins

51. Transport across cell membrane Membrane becomes semi-permeable with protein channels specific channels allow specific material across cell membrane inside cell outside cell sugar aa H 2 O salt NH 3

52. Classification of Transport Across Cell Membrane Small Molecules Macromolecules & Particles Passive transport (Energy independent) Endocytosis Membrane Transport Simple Diffusion Facilitated Transport (Carrier mediated) Ion-channels Active transport (Energy dependent, Carrier mediated ) Eocytosis

53. Facilitated Transport (Passive transport) Transport of Small Molecules Simple Diffusion Active transport (Energy dependent, ) Non-mediated transport (no carrier proteins) Carrier mediated Ion-channels Another Way to Classify

54. Contents Transport of Small Molecules Non-mediated transport (no carrier proteins) -- Simple Diffusion -- Ion-channels Carrier mediated -- Facilitated Transport (Passive) -- Active transport (Energy dependent ) Macromolecules & Particles

55. Non-mediated Transport (no carrier proteins) Simple Diffusion -   Very Small molecules (like water) and gases (CO 2 ,O 2 ) enter the cell by this method. -    It is a very slow process. -    Doesn’t require energy ( energy independent/passive ). -  It is a non-mediated transport ( no carrier proteins involved). -  Molecules diffuse from a region of higher concentration to a region of lower concentration (down the concentration gradient) -   diffusion occurs through a membrane opening or through intermolecular spaces.

56. Simple diffusion Eg : Respiratory exchange of gases between pulmonary alveolar membrane and tissue capillary wall b) Intestinal absorption of pentoses , some mineral ions and water-soluble vitamins and c) renal reabsorption of urea

57. Ion-channels specialized protein molecules that span the membranes & permit the rapid transport of ions such as Na + , K + , Cl - . The channels generally remain closed but in response to stimulus, open allowing rapid flux of ions down the gradient

58. Carrier Mediated Transport specific carrier molecules are required protein in nature. Have specific binding sites for the molecules to be transported Transport is dependent on availability of free binding sites on the carrier protein more rapid than simple diffusion .

59. Classification of Carrier Mediated Transport There are 2 Ways of Classification Depending upon Number of Molecules Transported and Direction of Transport Depending upon Whether Energy is Required or not

60. Classification of Carrier Mediated Transport 1. Uniport Co-transport - Symport and - Antiport 2. Facilitated Transport (Passive) Active transport (Energy dependent )

61. Carrier Mediated Transport Uniport Movement of one molecule from one side to another E.g.: movement of glucose from the cells of GIT to ECF. Co-transport Movement of one molecule depends on simultaneous or sequential transfer of another molecule Co-transport may be - Symport Two molecules move in the same direction E.g.: Na + /Glucose transport. -Anti-port Two molecules move in opposite directions E.g.: Cl - – HCO 3 - exchange in RBCs

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65. Carrier Mediated Transport Based on energy need, carrier-mediated transport are of two types : -- Facilitated Transport (energy independent/passive ) and -- Active transport (energy independent/active )  

66. Facilitated Transport It is passive transport and carrier mediated . Here transport is down the concentration gradient . Once the molecule binds to the biding site, a conformational change occurs in the carrier making the binding site exposed to the opposite direction Now the molecule is released from the carrier. Another conformational change in the carrier leads to the exposure of the binding site to the region where free molecules to be transported are present. Structurally similar solutes can inhibit the entry of one another by competitive inhibition . E.g. There are four different facilitated carrier systems for carbohydrates and five for amino acids.

67. Facilitated transport Diffusion through protein channels channels move specific molecules across cell membrane no energy needed “The Bouncer” open channel = fast transport facilitated = with help high low

68. Mechanism : Ping pong model Transport Across Cell Membrane Facilitated transport

69. Active Transport Transport is carrier mediated against the concentration gradient and hence energy-dependent . Transport occurs only in one way, against the concentration gradient. The energy comes usually from hydrolysis of ATP molecules About 40% of the total energy of the cell is used for the active transport.

70. Active Transport “The Doorman” conformational change Cells may need to move molecules against concentration gradient shape change transports solute from one side of membrane to other protein “pump” “costs” energy = ATP ATP low high

71. Active Transport E.g. Na + –K + pump or Na + -K + ATPase is the best example for active transport because virtually all cells have it. Other examples Ca + –dependent ATPase (in sarcoplasmic reticulum of skeletal muscles), H + –dependent ATPase located in the membrane of epithelial cell lining the stomach and has the function of acid (H + ) secretion

72. Na + -K + ATPase Na + -K + ATPase establishes and maintains a high intracellular K + concentration and a low Na + concentration compared to their concentrations in ECF. The Na + – K + ATPase , expels 3 Na + ions and brings 2K + ions from outside to inside with a concomitant hydrolysis of ATP. Drugs like digitalis (a cardiac glycoside) and ouabain inhibit Na + – K + ATPase .

73. ADP + Pi 2 K + 2 K + 3 Na + 3 Na + ATP Active Transport Na + -K + ATPase

74. Sodium pump or Na + -K + ATPase

75. Classification of active transport based on the source of energy 1. Primary active transport - Transport of molecules is directly linked to the hydrolysis of ATP, which provides energy. E.g. Na + –K + pump or Na + -K + ATPase 2.Secondary active transport- Transport of molecules is indirectly linked to the hydrolysis of ATP. Eg : Glucose and galactose are absorbed from the intestine by secondary active transport. Concentration gradient of Na + is maintained by Na + – K + ATPase .

76. Physiological importance of active transport - Responsible for the generation of the resting membrane potential, basis for excitability in nerve and transmission of nerve impulse - Na+ pump is driving force for several secondary active transport of nutrients into the cell. For example, glucose is co-transported with sodium into the cell - Calcium pump (Ca ++ dependent ATPase ): found in sarcoplasmic reticulum of skeletal muscles. It transports calcium from the cytosol to the sarcoplasmic reticulum. It regulates muscle contraction -Proton pump (H + dependent ATPase ): located in the parietal cells of the stomach . It is responsible for the secretion of Hcl into stomach lumen, to maintain the highly acidic pH essential for gastric digestion.  

77. Clinical application : Cardiotonic rugs like digitalis (a cardiac glycoside) and ouabain inhibit Na+ – K+ ATPase . They are used in treatment of heart failure. 

78. Transport of Macromolecules & Particles -transported by Endocytosis and Exocytosis - Macromolecules such as proteins, polysaccharides, hormones and particles like viruses, bacteria etc are transported by these mechanisms.

79. Endocytosis - internalize extra-cellular macromolecules by invagination of cell membrane -  Endocytosis may be either Phagocytosis or Pinocytosis .

80. Endocytosis: Process by which cells take up the large molecules Transport Across Cell Membrane

81. Phagocytosis (Gk: Phagein = to eat) Occurs in specialized cells such as macrophages and granulocytes . ingestion of large particles such as viruses , bacteria , cells or debris. endocytic vesicle ( phagosome ) fuses with the lysosome . hydrolytic enzymes of lysosomes break down the macromolecular contents released in to the cytosol reused or further catabolized

82. Pinocytosis(cell drinking)   Cellular uptake of fluid and fluid contents containing small particles. E.g.: -Intake of chylomicron by the hepatocytes; -internalization of LDL by LDL receptor

83. Exocytosis extrusion of particulate or macromolecular materials, which can’t pass out through the intact membrane. secretory vesicle is pinched off from the Golgi apparatus; moves towards and fuses with the plasma membrane. E.g. a) Release of Trypsinogen by pancreatic acinar cells.       b) Release of Insulin by  -cells of Langerhans . c) Release of acetylcholine by pre-synaptic cholinergic nerves.

84. Exocytosis: Process of extrusion of a macromolecule from the cell Transport Across Cell Membrane

85. Disorders of Membrane Structure and Transport Abnormality in membrane structure or transport can cause diseases.  Respiratory distress syndrome Defect in biosynthesis of dipalmitoyl lecithin (lung surfactant) Familial hypercholesterolemia Mutations in the gene encoding LDL receptor Cystic fibrosis Mutations in the gene encoding Cl - transporter

86. Sub-cellular Organelles include -- nucleus, Ribosomes endoplasmic reticulum, golgi apparatus/complex, mitochondria, lysosomes , peroxisomes and cytoskeleton.

87. Sub-cellular Organelles All eukaryotic cells contain all these organelles RBC is not a true cell and contain only the plasma membrane and cytoskeleton

88. Nucleus largest sub-cellular organelle. double membrane – nuclear membrane , surrounds it. At intervals nuclear membrane has nuclear pores , permit the passage of molecules in and out of the nucleus. nucleus of eukaryotic cell contains a dense body known as nucleolus rich in rRNA .

89. Nucleus Nucleoplasm ground material of nucleus rich in enzymes such as, DNA polymerases, RNA polymerases, etc. Nucleus of an interphase (non-dividing) cell filled with a diffuse material – chromatin . During the cell division, chromatin condenses to form chromosomes . Humans have 23 pairs of chromosomes compactly packed in the nucleus.

90. Nucleus –Functions Nuclear DNA --the repository of genetic information serves two purposes -- i ) By DNA replication provides genetic information to offspring or daughter cells during cell division ., thus it is blue print of life. ii) By transcription (RNA synthesis) provides information for the synthesis of all protein molecules of the cell. Both replication and transcription take place in the nucleus. Function of nucleolus : -Synthesis of rRNA and ribosomes

91. Mitochondria spherical, oval or rod like bodies. have two membranes – outer and inner membrane . outer membrane is smooth while the inner membrane is for folded to form cristae components of electron transport chain (ETC) and oxidative phosphorylation buried in the inner mitochondrial membrane.

92. Mitochondria-structure

93. Mitochondria The central cavity of the mitochondrion contains the matrix Matrix contains enzymes and chemical intermediates of -- TCA cycle Heme synthesis Urea cycle, etc. Also present in the matrix are, mitochondrial DNA, RNA and ribosomes.

94. Functions ETC and oxidative phosphorylation - - situated in inner mitochondrial membrane are involved in ATP synthesis, hence mitochondria are regarded as ‘powerhouse of the cell ’ Some of the major pathways operate in the mitochondria. They are, TCA cycle,  -Oxidation of fatty acid, ketone bodies formation, gluconeogenesis (partly), urea cycle (partly), heme synthesis (partly), pyrimidine synthesis (partly) . Mitochondrial DNA codes for some of the mitochondrial proteins involved in oxidative phosphorylation

95. Endoplasmic Reticulum (ER) network of membrane-enclosed spaces extends throughout the cytoplasm. classified into rough and smooth ER rough appearance (when observed under electron microscope) is due to ribosomes attached to the cytoplasmic side of the membrane. smooth ER does not have ribosomes .

96. Functions of ER Rough ER : involved in synthesis of proteins (lipoproteins, glycoproteins ) Smooth ER: Metabolism of drugs and toxic compounds ( cyt P450 monooxygenases are present in liver cell smooth ER) Synthesis of lipids (TAG, phospholipids, cholesterol) and Ca 2+ storage in skeletal and cardiac muscle.(note- sarcoplasmic reticulum of muscle is a modified ER)

97. Golgi Complex/Golgi Apparatus group of membrane bound flattened tubes or sacs placed one over another in a pile or stack.

98. Golgi Apparatus - Functions Main functions of Golgi apparatus are protein sorting, packaging and secretion . newly synthesized proteins are handed over to the Golgi apparatus, which catalyze the addition of carbohydrates, lipids or sulfate moieties to the proteins.

99. Lysosomes membrane bound vesicle containing various hydrolytic enzymes ( hydrolases . Lysosomal enzymes are capable of digesting proteins, carbohydrates, lipids and nucleic acids pH inside the lysosomes is less than that of cytosol necessary for its digestivse function

100. Lysosomes -Functions hydrolases breakdown complex molecules brought into the cell by endocytosis , phagocytosis or worn-out organelles from the cells own cytoplasm. Lysosomes - termed as ‘ suicide-bags’ as their lysis can lesad to digestion and death of the cell Sphingolipidosis – group of disorders in which excess of sphingolipids accumulates in lysosomes

101. Peroxisome small spherical or oval membranous bodies contain enzymes -- peroxidases and catalase

102. Peroxisome - Functions Free radicals formed by peroxidation of PUFA capable of damaging cell membranes, tissues, and genes Such reactions are implicated in inflammatory diseases, ageing process and malignant transformation. Catalase and peroxidase enzymes destroy such unwanted peroxides and other free radicals

103. Ribosomes : nucleoproteins present either freely in cytosol or bound to ER Function: provide necessary infrastructure for mRNA, tRNA & amino acid to interact with each other for translation process.

104. Cyto skeleton Made up of microtubules and actin filaments role in maintaining the cellular structure, mobility and cell division. Hereditary spherocytosis due to mutations in genes encoding spectrin or other structural proteins in red blood cell membrane, leading to excessive hemolysis

105. Organelle Function Nucleus Provides genetic information to offspring RNA transcription, directs protein synthesis Mitochondria Energy production from the oxidation of food substances and the release of adenosine triphosphate Endoplasmic reticulum Translation and folding of new proteins (rough endoplasmic reticulum), synthesis of lipids (smooth endoplasmic reticulum) summary

106. Golgi appartus Sorting, packaging, and modification of proteins Endoplasmic reticulum Translation and folding of new proteins (rough endoplasmic reticulum), synthesis of lipids (smooth endoplasmic reticulum) Lysosome Breakdown of large molecules Peroxisome breakdown of metabolic hydrogen peroxide and free radicals

107. Organelle Function Ribosome Translation  of RNA to form proteins Cytoskeleton Maintaining the cellular, shape, motility and cell division.

108. Sub-Cellular Fractionation isolation of an organelle in a relatively pure form in order to study its functions Cell membrane is disrupted usually by mechanical means called homogenization subcellular organelles can then be separated from the homogenate by differential centrifugation using the instrument ultracentrifuge

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