Cell biology

Biochemistry

1. CELL BIOLOGY BY Streaks

2. BIOCHEMISTRY IS A SCIENCE CONCERNED WITH THE CHEMICAL BASIS OF LIFE

3. Cell is structural and functional unit of living system Thus Biochemistry concerned with the chemical constituents of living cells, with the reactions and processes they undergo.

4. Therefore biochemistry covers large areas of CELL BIOLOGY MOLECULAR BIOLOGY MOLECULAR GENETICS

5. Aims and Objectives Aim of biochemistry is to describe and explain in molecular term, all chemical processes of living cells. The major objective is, the complete understanding at molecular level, of all the chemical processes associated with living cells.

6. Cell All organisms are built from cells, The cell is the fundamental unit of life. In general two types of cells exist in nature. prokaryotic cells bacteria and cyano bacteria (blue green algae) Eukaryotic cells (protists,( including all single cell organism, fungi, Algae, molds, protozoa) plants, and animals. Differences are shown in table

7. Human Cell

8. Plasma (cell) membrane STRUCTURE This is the boundary between the cell cytoplasm & the environment Is partially permeable Made up of 45% proteins & 45% phospholipids with the remaining 10% cholesterol, glycoprotein & glycolipids FUNCTION Controls movement of substances in & out of the cell Act as recognition sites so that the body’s immune system can recognize its own cells Acts as receptor sites for attachment of specific hormones & neurotransmitters

9. Cell Wall:- (only in plants) It is the outer most boundary in plant cells It is absent in animal cells. Its thickens varies in different cells of the plant Structure:- is composed of (1) Primary wall (2) middle lamella (3) Secondary wall (1) Primary wall:- is composed of cellulose whose molecules are arranged in criss cross arrangement. Some amount of pectin is also present. (2) Middle Lamella:- is first to be formed in between the primary walls of the neighboring cells.

10. (3) Secondary wall:- is formed on inner surface of primary wall. It is thick and chemically it is composed of inorganic salts, Silica Waxes Lignin and cutin etc Functions:- It provides definite shape to the cell. It makes cell rigid It provides protection to inner parts of cell It does not act as a barrier to the materials passing through it.

11. A) Cell organelles 1. Nucleus 2. Mitochondrion ( is the power house of cell) 3. Endoplasmic reticulum (ER) 4. Golgi complexes (Golgi apparatus) 5. Lysosomes 6. Peroxisomes 7. Cytoskeleton Microtubules b) Microfilaments c) Micro trabeculae B) Cytoplasm (cytosol)

12. Nucleus STRUCTURE Largest organelle - 10um diameter Surrounded by a nuclear membrane Double membrane – outer is continuous with the ER Nuclear pores in the membrane allow the passage of large molecules in & out (e.g. mRNA) Material inside the nucleus is called nucleoplasm – contains chromatin which makes up DNA of the cell A spherical structure called the nucleolus is found in the nucleus – this makes ribosomal RNA and assembles the ribosomes FUNCTION Acts as the control centre of the cell through the production of mRNA and protein synthesis Retains the genetic material in the cell in the form of DNA / chromosomes Manufactures ribosomal RNA ( rRNA ) & ribosomes Starts the process of cell division

13. Endoplasmic Reticulum STRUCTURE Complex system of double membranes continuous with the nuclear membrane Fluid filled sacs between the membranes called CISTERNAE which allow materials to be transported through cell Two types of ER – smooth – has no ribosomes attached (SER) rough – has ribosomes attached (RER) FUNCTION Forms an extensive transport system Site of protein synthesis (Rough ER) Site of lipid, steroid and carbohydrate synthesis (smooth ER) Stores and transports these materials Calcium ions

14. Mitochondria STRUCTURE Rod shaped organelle with double membrane The outer controls the entry & exit of materials Inner has many folds called cristae Surface of each crista is covered with stalked particles where ATP is made Mitochondria are filled with a jelly like matrix containing proteins, lipids, ribosomes and loops of DNA Mitochondria can replicate themselves when the cell divides FUNCTION Site of aerobic respiration (Krebs cycle) Responsible for production of energy rich ATP molecules (oxidative phosphorylation) No. of mitochondria reflects the metabolic activity of the cell – so large numbers are found in muscle and liver cells

15. Golgi apparatus STRUCTURE Small pieces of rough ER form vesicles which join to make a Golgi body Chemicals made in the ER collect in the Golgi body where they are modified Small vesicles can then be ‘pinched’ off the Golgi body carrying new chemicals away which are secreted when the vesicle reaches the cell membrane Some of the vesicles become lysosomes FUNCTION Assembling glycoproteins (such as mucin ) by combining carbohydrate and protein Transporting and storing lipids Formation of lysosomes Producing digestive enzymes

16. Ribosomes STRUCTURE Small dense structures found in huge numbers attached to the rough ER or free floating in the cytoplasm Are about 20 – 25 nm in diameter in eukaryotic cells Made up of two sub units FUNCTION Synthesize proteins Synthesize enzymes

17. Lysosomes STRUCTURE Small vacuoles formed when small pieces of Golgi body are pinched off Contain hydrolytic enzymes which digest materials in the cell FUNCTION Release enzymes which destroy worn out organelles Digest materials taken into the cell by phagocytosis Release enzymes to the outside of the cell which digest materials around the cell Completely break down cells after they have died – autolysis

18. Peroxisome Function They have a single membrane and are small (0.3 -1.5 µm )spherical or oval with fine network of tubules in their matrix . Over 50 enzymes catalyzing oxidative and biosynthetic reactions have been identified in peroxisomes from different tisssues . Oxidation of very long chain fatty acids and synthesis of glycerolipids ,glycerol ether lipids ( plasmalogens ) and isoprenoids . Catalase , heme enzyme present in peroxisomes catalyses the conversion of H 2 O 2 to water and oxygen and oxidation of various compounds by H 2 O 2

19. Cytoskeleton . Non muscle cell perform mechanical work like self propulsion, morphogenesis, cleavage, endocytosis, Ic transport and changing cell shape. These cellular function are carried out by extensive Ic network of filamentous structures constituting cytoskeleton. Three type of filamentus structure, 1. Microfilaments ( actin and myosin filaments) 2.Microtubule are composed of tubulin , a protein which assembles into tubular structures 3. Intermediate filaments: keratins, neurofilaments

20. Functions : Maintain cellular morphology, Intracellular cellular transport, cell motility and cell division. Cytosol : The contents of a eukaryotic cell within the cell membrane (excluding the cell nucleus ), is referred to as the cytoplasm .

21. The concentrations of ions such as sodium and potassium are different in the cytosol than in the extracellular fluid ; these differences in ion levels are important in processes such as osmoregulation and cell signaling . Function Enzymes of glycolysis , gluconeogenesis , fatty acid synthesis etc .

22. Composition,structure of cell membrane LECTURE 2

23. BIOLOGICAL MEMBRANES Major concept . To study structure, composition and functions of plasma membrane. Specific objectives: chemical composition and functions of individual constituents (lipids, protein, carbohydrate) . Fluid mosaic model of memb. Transport function: Inherited disorders:

24. The cell membranes are composed Lipids (45%) which account for almost all the mass of biological membranes, proteins (45%) carbohydrates present as part of glycoprotein's and glycolipids The relative proportions of proteins and lipids vary with the type of membrane, reflecting the diversity of biological roles

25. Each type of cell membrane has characteristic set of membrane lipids The protein composition varies Some membrane proteins are covalently linked to complex carbohydrates, or one or more lipids

26. Lipids Lipids are the basic structural components of cell membrane. Lipid molecules have a polar or ionic head hence hydrophilic and the other end is a nonpolar and hydrophobic Types of lipids present in Bio-membranes are Fatty acids:- are oleic acid, archidonic acid, linoleic and linolenic acids (50% saturated 18C and 50% unsaturated). Gylcero phospho lipids:- are phosphatidyl ethanol amine ( cephalin ), phosphatidyl choline (lecithin), and phosphatidyl serine. Sphingophospholipids :- are sphingomyclin , cerebrosides and gangliosides Phospholipids & cholesterols form a lipid bilayer in which the non-polar regions of the lipid molecules face each other at the core of the bilayer and their polar head groups face outward

27. Proteins in the cell membrane are 1. Peripheral membrane proteins:- also called extrinsic proteins Exist on the surface of membranes and they are attached by ionic and polar bonds to polar heads of lipid. They can be easily removed from the membrane . Example: The special peripheral membrane proteins participate in the stability of red cells are Spectrin Actin Ankyrin and band 4,1protein

28. 2. Integral Membrane Proteins:-   also called intrinsic membrane proteins) ,these proteins are deeply embedded in the membrane portions of these proteins are in vanderwaals contact with the hydrophobic region of the membrane EXAMPLE GLYCOPHORIN BAND -3-PROTEIN

29. The num of protein varies from dozen to 100 in different memb . Many of these function as channels, transporters, enzymes and structural components . 3. Trans Membrane Proteins:- Some of the integral proteins span the whole breadth of the membrane and are called trans membrane proteins. These proteins can serve as receptors for hormones, neurotransmitters, tissue specific antigens, growth factors etc.

30. An important disease that occurs due to genetic mutations in transmembrane proteins is : Cystic fibrosis , which is a recessive genetic disorder.

31. Clinical aspects Hereditary spherocytosis , Hereditary elliptocytosis . There is genetic defect in shape of RBCs which lead to inc haemlytic anaemia and jaundice These are due to mutation in genes coding for proteins of the membrane

32. Carbohydrates: Many memb proteins and lipids are glycosylated , (glycoprotein, glycolipids ) with one or more covalently attached oligosaccharides chains, called glycocalyx are present. They are attached to the protein either by N- glycosidic linkage b/w N- acetylglucosamine & Asparagine .

33. O- glycosidic linkage b/w N- acetylglucosamine & Ser or Thr . The variable carbohydrates components of the glycolipids and glycoproteins on the cell surface participate in molecular targeting and cell-cell recognition .

34. 1. Lipid Bilayer Model:- Was proposed by Daveson and Danielli in 1935. According to this model, the plasma membrane is composed of lipid bilayer sandwitched between two protein layers. This basic structure is found in all the membranes such as those of mitochondria, chloroplasts etc. Lipids bilayers are oriented with their hydrophobic tails inside the bilayer while hydrophilic polar heads are in contact with the aqueous solution on each side. Not all the lipids can form bilayers . A lipid bilayer can form only when the cross sectional areas of the hydrophobic tail and hydrophilic polar head are about equal. Glycerophospho lipids and sphingo lipids fulfill this criteria and hence can form bilayer . A lipidbilayer is about 6nm across and this is so thin that it may be regarded as a two dimensional fluid.

35. Depending upon the nature of lipids, three types of aggregates are formed: 1. Micelles ; Which are spherical aggregates, having hydrophobic groups clustered in the interior and hydrophilic outwards. They are important in intestinal digestion and absorption of fat. 2. Liposome; In this lipid bilayer will close in on itself to form spherical vesicles which are called liposomes.

36. Functions. Carriers of drugs, enzymes & DNA e.g. antibiotics, antimalarial , antiviral, antifungal and anti-inflammatory agents . Some drugs have longer effectiveness when encapsulated in liposomes

37. FLUIDITY The fluidity of a membrane significantly affects its functions. As membrane fluidity increases, so does its permeability to water and other small hydrophilic molecules. The lateral mobility of integral proteins increases as the fluidity of the membrane increases. The degree of fluidity depends on lipid composition & temperature. The cholesterol content of membranes is important. Its insertion prevents the highly ordered packing of fatty acyl chains and thus regulate the membrane fluidity.

38. 2. Fluid Mosaic Model:- Of membrane structure proposed by singer and Nicholson in 1972 which revealed that lipid bilayer is not sandwithched between two protein layers. Instead proteins are embedded in the lipid bilayer in a mosaic manner. The membrane proteins. Intrinsic proteins (integral) deeply embedded and peripheral proteins loosely attached, float in an environment of fluid phospholipid bilayers . It can be compared like icebergs floating in sea water. According to this, cell membrane also contains charged pores through which movements of material takes place both by a active and passive transport. The cholesterol content of the membrane maintains the fluidity.

39. Specialized structure of plasma mamb . 1.Lipid rafts . The exoplasmic leaflet of the lipid bilayers enriched in cholesterol, sphingolipids and certain proteins. It plays role in signal transduction.

40. 2. Caveolae . are flask shape indentation derived from lipids rafts and contains protein (caveoline-1). This protein detected in caveolae include various components of the signal transduction system e.g insulin receptor, G protein, folate receptor and endothelial nitric oxide synthase ( eNos ).

41. LECTURE 3 OSMOSIS ,TRANSPORT ACROSS CELL MEMBRANE

42. TRANSPORT OF MATERIALS ACROSS CELL MEMBRANE The compound must enter and leave the cells in an orderly manner for normal functioning of cells. The plasma membranes contain proteins that specifically recognize and carry solutes into the cell e.g. sugars, amino acids & inorganic ions

43. In some cases, these components are transported against The concentration gradient, Electrical charge or both Many materials are pumped out to keep their concentrations in the cytosol lower than in the surrounding medium

44. Molecules to be transported are 1. Micromolecules 2. Macromolecules. Types of transport mechanism : A) Passive Transport (Diffusion) Passive or simple diffusion Facilitated diffusion B) Active transport (a) primary active transport (b) secondary active transport

45. Membrane Transport:- Lipid – soluble molecules pass through the plasma membrane readily by dissolving in the lipid bilayer . Small molecules pass through membrane pores. The pores are positively charged and allow anions and neutral molecules to pass through more readily than cations . Large polar substances (e.g. glucose, and aminoacids ) are transported through the membrane with the help of carrier molecules.

46. MEDIATED TRANSPORT MCECHANISMS:- Mediated transport is the movement of a substance across a membrane by means of a carrier molecules, the substances transported are large, water soluble molecules. The carrier molecules have active sites that bind with either a single molecule or a group of similar molecules. Similar molecules compete for carrier molecules. Once all the carrier molecules are in use, saturation occurs.

47. Types of Mediated Transport:- Passive or simple diffusion Facilitated diffusion Active transport

48. Diffusion describes the spread of particles through random motion from regions of higher concentration to regions of lower concentration (down a concentration gradient). The concentration gradient is the difference in solute concentration between two points divided by the distance separating the points. The rate of diffusion increases with an increase in the concentration gradient. increase in temperature. Decrease in molecule size. Decrease in viscosity. Diffusion

49. The end result of diffusion is a uniform distribution of molecules. Simple diffusion requires no expenditure of energy nor any carrier proteins. It operates unidirectionally . Small uncharged molecules such as O2 , CO2, H2O and lipid soluble substances get transported across the membrane through the process of diffusion.

50. Osmosis:- Osmosis is the diffusion of a solvent across a selectively permeable membrane or Osmosis is a term used for the diffusion of water through cell membranes. When two solutions of different concentrations are separated by a semi-permeable membrane which is permeable to solvent molecules (water) but not to the solute molecules. The solvent diffuses across the membrane from the less concentrated to the more concentrated solution, till the concentration of the solutions on both sides of the membrane becomes equal. This process is called osmosis. Osmosis refers to the movement of solvent, but not of any solutes present in the solution.

51. Osmotic pressure Osmotic pressure is a measure of the tendency of water (or solvent) to move across the selectively permeable membrane OR Osmotic pressure is the amount of hydrostatic pressure required to prevent the osmotic transport of solvent across the semi permeable membrane . The Osmotic Pressure depends on the number of solute molecules in solution, irrespective of the size, shape or mass of the solute. Is- osmotic solutions have the same concentration of solute particles. Cells placed in an isosmotic solution neither swell nor shrink. Hyperosomotic solutions have a higher concentration of solute particles. Cells placed in it, they shrink. Hypoosmotic solutions have a low concentration of solute particles than a reference solution and the cells placed in it swell and may lyse .

52. Facilited Diffusion:- (b) Facilited Diffusion:- It is similar to passive or simple diffusion in that solutes move along the concentration gradient but it differs from passive diffusion in that it require a “Carrier or transport protein. Hence, the rate of diffusion is faster than simple diffusion”. The process does not require any energy. Mechanism of facilitated diffusion has been explained by Ping – pong model. (in carbohydrates) Example:- D- fructose is absorbed from intestine by facilitated diffusion

53. PING PONG MODEL Pong state Active sites are exposed to the exterior, when solute binds conformational change occur , Ping state Active sites are facing the interior of the cell this will cause the release of solute molecules and the protein molecule reverts to pong state By this mechanism inward flow is facilitated and outward flow is inhibited

54. Transport of Glucose (Ping pong Model)

55. Transport by Channels, Pores and Gap junction:- Membranes of most cells contain specific channels.. Membrane channels are differentiated from membrane pores on the basis of their degree of specificity for molecules crossing the membrane. Channels:- Channels are specific for inorganic cations and anions. Channels allow the translocation of substances from one side of the membrane to the other without undergoing conformational changes. Voltage regulation, chemical regulation and regulation by AMP are some ways in which channels function.

56. Water Channels ( Aquaporins ) Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins (MIP) that form pores in the membrane of biological cells Example; In collecting ductules of the kidney, the movement of water by simple diffusion is enhanced by movement of water through these channels. Aquaporins are of Five types Clinical Aspect : Mutation in gene encoding Aquaporin-2 have been shown to be the cause of one type of Nephrogenic diabetes insipidus (Inheritance of two mutant genes for aquaporin-2)

57. The mitotic acetylcholine channel is an example of chemically regulated channel. Pores:- Pores are not so selective and will allow sufficiently small molecules to pass freely through them The gap junction between endothelial muscle and neuronal cells is a cluster of small pores. Small molecules pass between cells through gap junction.. The pores are usually maintained in an open state. Movements of large molecules is permitted through Nuclear pores which are usually 90˚ A in diameter. The plasma membrane of gram negative bacteria contains protein pores called porins .

58. IONOPHORE An ionophore is a lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane . There are two broad classifications of ionophores . Mobile ion carriers chemical compounds that bind to a particular ion, [1] shielding its charge from the surrounding environment, and thus facilitating its crossing of the hydrophobic interior of the lipid membrane. Channel formers [2] that introduce a hydrophilic pore into the membrane, allowing ions to pass through while avoiding contact with the membrane's hydrophobic interior.

59. CARRIER IONOPHORES

60. Ionophores Ionophores disrupt transmembrane ion concentration gradients, required for the proper functioning and survival of microorganisms, and thus have antibiotic properties. They are produced naturally by a variety of microbes and act as a defense against competing microbes. Many antibiotics, particularly the macrolide antibiotics, are ionophores that exhibit high affinities for Na + or K +

61. Gap Junction It is made of protein called connexin . Certain cells have specialized region on their memb for intracellular communication which are in close proximity. They mediate and regulate the passage of ions and small molecules through a narrow hydrophilic core connecting the cytosol of adjacent cells. Mutations in genes encoding connexin is a associated with the number of conditions like cardiovascular abnormalities, a type of deafness.

62. GATED CHANNELS . These channels permit facilitated diffusion by opening or closing according to the needs of the cell, hence are called gated channels. They are; ( i ) ligand – gated (ii) mechanical gated (iii) voltage gated All the channels are selective that is the structure of the protein admits only specific types of molecules through the pores.

63. ( i ) Ligand – gated channels:- In this a specific molecule binds to a receptor and opens the channel. The binding site may be on the extracellular or intracellular side of the channel. External ligands bind to a site on the extracellular side of the channel protein. Example are acetycholine receptor is present in post synaptic membrane. It is a complex of five subunits having a binding site for Acetylcholine Acetylcholine released from the pre – synaptic region binds with the binding site of post synaptic region, which triggers the opening of the channel and influx of Na + .

64. Internal ligands bind to a site on the intracellular side of the channel protein. Examples are “Second messengers” such as cyclic AMP ( cAMP ) and cyclic GMP ( cGMP ) that regulate channels involved in the initiation of impulses in neurons that respond to odours and light respectively

65. Voltage Gated Channels:- These channels open or close in response to changes in membrane potential. As impulse passes down a neuron, the reduction in the voltage opens sodium channels in the adjacent portion of the membrane. This allows the influx of Na + in to the neuron and thus the nerve impulse is propagated. Mechanically Gated Channels:- Mechanical deformation of the cells induces the stretch receptors to open up ion channels that result in generation of nerve impulse. A good example is bending of the cilia like projections on the hair cells of the inner ear by sound waves which opens up ion channels that lead to the generation of nerve impulses. The brain interprets the nerve impulse as sound.

66. Transport of Macromolecules:- The mechanism of transport of macromolecules such as proteins, hormones immunoglobulins , LDL and even viruses takes place across the membrane by two mechanisms Exocytosis Endocytosis

67. Exocytosis :- Most cells release macromolecules to the exterior by the process called exocytosis Mechanism:- the inner membrane of the vesicle fuses with the outer plasma membrane while cytoplasmic side of vesicle fuses with the cytoplasmic side of plasma membrane thus the contents of vesicles are externalized The process induces a local and transient change in Ca ++ concentration which triggers exocytosis . They fall in 03 catagories . i ) They can attach to the cell surface and become peripheral proteins e.g. antigens. ii) They can become part of extracellular matrix e.g. collagen and glucosaminoglycans (GAGI) iii) Hormones like insulin, parathormone (PTH) and catacholamines are all packaged in granules, processed with in cells to be released upon appropriate stimuli.

68. Endocytosis :-   All eukaryotic cells are continuously ingesting part of their plasma membrane. Endocytotic vesicles are formed when segments of plasma membrane invaginates enclosing a minute volume of extracellular fluid (ECF) and its contents. The vesicle then pinches off as the fusion of plasma membranes seal the neck of the vesicle at the original site of in vagination . Factors required are energy - usually derived from ATP hydrolysis, Ca ++ Contractile element in the cell probable the microfilament system

69. Entry of material into the nucleus through endocytosis . The phagosome travels from the cell membrane to the nucleus, and then is engulfed by the nucleus, releasing its contents

70. Types:- 1) Phagocytosis 2) Pinocytosis Fluid phase pinocytosis Receptor mediated 1) Phagocytosis :- (Greek Word – Phagein – to eat) is the engulfment of large particles like viruses, bacteria, cells or debris by macrophages and granulocytes. They extend pseudopodia and surround the particles to form phagosomes which later fuse with lysosomes to form phagolysosomes in which the particles are digested. Biochemical mechanism is called respiratory burst

71. Respiratory burst Respiratory burst (sometimes called oxidative burst ) is the rapid release of reactive oxygen species ( superoxide radical and hydrogen peroxide ) from different types of cells Usually it denotes the release of these chemicals from immune cells , e.g., neutrophils and monocytes , as they come into contact with different bacteria or fungi .. NADPH oxidase , an enzyme family in the vasculature (in particular, in vascular disease ), produces superoxide , which spontaneously recombines with other molecules to produce reactive free radicals .

72. Respiratory burst plays an important role in the immune system . It is a crucial reaction that occurs in phagocytes to degrade internalized particles and bacteria . To combat infections, immune cells use NADPH oxidase to reduce O 2 to oxygen free radical and then H 2 O 2 . Neutrophils and monocytes utilize myeloperoxidase to further combine H 2 O 2 with Cl - to produce hypochlorite , which plays a role in destroying bacteria. Absence of NADPH oxidase will prevent the formation of reactive oxygen species and will result in chronic granulomatous disease

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74. 2) Pinocytosis :- It is a property of all cells and leads to the cellular uptake of fluids and fluid contents. (a) Fluid phase pinocytosis :- It is a non selective process in which uptake of a solute by formation of small vesicles is simply proportionate to its concentration in the surrounding extracellular fluid (ECF) (b) Receptors mediated absorptive pinocytosis :- The selective or absorptive pinocytosis is receptor mediated ,LDL is good example ,LDL binds to LDL receptor and complex is later internalized .,the cytoplasmic site of these vesicles are coated with filaments mainly composed of clathrin , these are called as clathrin coated pits .After the LDL receptor complex is internalized the receptor molecule are released back to cell surface but the LDL is degraded by lysosomal enzymes .

75. Clinical aspects: of receptor mediated endocytosis with viruses are responsible for many diseases like Hepatitis virus affecting liver cells Polio virus effecting motor neurons AIDS effecting ‘’T’’ cells Iron toxicity occurs due to excessive uptake by endocytosis

76. Active Transport:- Active Transport is the transport of ions or molecules across biological membrane, against concentration gradient. Such transport requires a transmembrane protein or carrier called transporter and the energy derived from the hydrolysis of ATP. Direct active Transport:- Some transporters bind ATP directly and use the energy of its hydrolysis to drive active transport they are called direct active transporters.

77. Direct active Transport:- Na + /K + AT Pase H + /K + AT Pase Ca 2+ ATpase of skeletal muscle Active transport results in solutes movement against a concentration gradient or electrochemical gradient and need energy. It is of two type 1. Primary active transport 2. Secondary active transport

78. PRIMARY ACTIVE TRANSPORT In primary active transport, the solute transportation is coupled directly to the use of energy, from ATP.` The energy released by hydrolysis of ATP drives the solute movement against an electrochemical gradient Example: Sodium-potassium pump Primary active transport of Calcium (out side to inside) Primary active transport of Hydrogen ions in gastric gland and renal tubules (distal and collecting tubules) The enzyme hydrogen potassium ATPase (H + /K + ATPase ) is unique to the parietal cells and transports the H + against a concentration gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body.

79. The H + /K + ATPase H + /K + ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents The H + /K + ATPase transports one hydrogen ion (H + ) from the cytoplasm of the parietal cell in exchange for one potassium ion (K + ) retrieved from the gastric lumen. As an ion pump the H + /K + ATPase is able to transport ions against a concentration gradient using energy derived from the hydrolysis of ATP

80. Na + K + ACTIVE COTRANSPORT The concentration of Na + is lower in the cell than outside, while K + concentration is higher within the cell This imbalance is established and maintained by a primary active transport system in the plasma membrane. The enzyme ‘Na + K + ATPase ’ couples breakdown of ATP to simultaneous movement of both Na + and K + against their electrochemical gradient

81. For each molecule of ATP converted to ADP, the transporter moves two K + ions inward and three Na + ions outward across the membrane The Na + K + ATPase is an integral protein which is inhibited by Digitalis is a drug used to treat congestive cardiac failure. It inhibits Na + efflux leading to higher concentration of Na + in cells. This activates Na + Ca + co-transporter in cardiac muscle, which increases influx of Ca + , thus strengthening cardiac contractions

82. ATP-DRIVEN Ca 2+ PUMPS The cytosolic concentration of Ca + is slightly lower than surrounding medium. Calcium ions are pumped out of the cytosol by a ATPase, The plasma membrane Ca + pump It is an integral protein. The transporter binds Ca + on the side of membrane where its conc is low and releases it on the side where its conc is high. The energy released by ATP hydrolysis drives Ca + across the membrane against a large electrochemical gradient

83. SECONDARY ACTIVE TRANSPORT Secondary active transport occurs when uphill transport of one solute is coupled to the downhill flow of a different solute that was originally pumped uphill by primary active transport A gradient of an ion e.g. Na + has been established by primary active transport. Now movement of Na + ion down its electrochemical gradient then provides energy to drive co-transport of a second solute against its concentration gradient

84. Transport system can be describe in a functional sense according to Num of mol moved and the direction of the movement. Or Whether movement is toward or away from equilibrium. So they are a two types. UNIPORT Transport system that carry only one substrate (e.g. glucose transporters) are called ‘ Uniport systems’ e.g Glucose out from the intestinal mucosal cell to blood.

85. CO-TRANSPORT When the two solutes or ions move in opposite directions, the process is ‘ Antiport ’ (Counter transport) In antiport two species of ion or other solutes are pumped in opposite directions across a membrane. One of these species is allowed to flow from high to low concentration which yields the entropic energy to drive the transport of the other solute from a low concentration region to a high one. An example is the sodium-calcium exchanger or antiporter , which allows three sodium ions into the cell to transport one calcium out When the two solutes move in the same directions, the process is ‘ Symport ’ example is the glucose symporter SGLT1 , which co-transports one glucose (or galactose ) molecule into the cell for every two sodium ions it imports into the cell. This symporter is located in the small intestines, trachea, heart, brain, testis, and prostate.

86. Examples of Inherited Diseases of Ion Channels An increasing number of human diseases have been identified as inherited mutations in genes encoding ion-channels proteins. Some examples are as follows. 1. Chloride-channel Diseases 2. Potassium-channel Diseases 3. Sodium-channel Diseases

87. 1. Chloride-channel Diseases: Cystic Fibrosis. Inherited tendency for renal stones formation is caused by a different kind of chloride channel than one involved in cystic fibrosis. 2. Potassium-channel Diseases: Some inherited life-threatening defects in the heartbeat. A rare, inherited tendency to epileptic seizures in the newborn. Several types of inherited deafness. 3. Sodium-channel Diseases: Inherited tendency to certain types of muscle spasms. Liddle’s syndrome. characterized by early, and frequently severe, hypertension , Inadequate sodium excretion through the kidneys because of a mutant sodium channel.