CELLULAR MECHANISMS revised (3) (1).pptx

CELLULAR MECHANISMS

1. CELLULAR MECHANISMS DR MURIITHI M WARUINGI

2. THE CELL AND IT’S FUNCTION 100 TRILLION CELLS IN THE HUMAN BODY CELLLS ARE BUILDING BLOCKS OF THE BODY PROVIDING STRUCTURE for the body’s tissues and organs, ingesting nutrients and converting them to energy, and performing specialized functions. CELL- BASIC UNIT OF LIFE.

3. CELL ORGANIZATION TYPICAL CELL CAN BE SEEN THROUGH LIGHT MICROSCOPE TWO MAJOR PARTS: NUCLEUS AND CYTOPLASM DIFFERENT SUBSTANCES THAT MAKE UP THE CELL ARE COLLECTIVELY KNOWN AS PROTOPLASM PROTOPLASM INCLUDES: WATER( 70-85%), IONS, PROTEINS( STRUCTURAL AND FUNCTIONAL), LIPIDS AND CARBOHYDRATES. INTRACELLULAR AND EXTRACELLULAR COMPARTMENTS. INTRACELLULAR ORGANELLES- HIGHLY ORGANISED PHYSICAL STRUCTURES INSIDE THE CELL.

4. Continued…. THE CELL RECEIVES MESSAGES OR INSTRUCTIONS ON PROTEIN SYNTHESIS THROUGH FIRST MESSENGERS/LIGAND THE LIGAND (HORMONE OR NEUROTRANSMITTER) BINDS TO A RECEPTOR ON THE CELL MEMBRANE THE MESSAGE IS THEN CARRIED INTO THE CELL THROUGH A SIGNAL TRANSDUCTION MECHANISM INVOLVING SECOND MESSENGERS ONCE THE MESSAGE REACHES THE NUCLEUS, THE CELL WILL RESPOND BY SYNTHESIZING A PROTEIN THE PROCESS OF PROTEIN SYNTHESIS IS CARRIED OUT SYSTEMATICALLY FROM TRANSCRIPTION TO RELEASE OF A FUNCTIONAL PROTEIN BY THE CELL

5. CONTD.. A FAILURE IN THE RECEPTIN AND TRANSDUCTION OF THESE INSTRUCTIONS AT ANY LEVEL MAY INTERFERE WITH THE PROCESS OF PROTEIN SYNTHESIS THE PROTEIN MAY NOT BE FORMED AT ALL; IT MAY BE FORMED BUT IS OF AN ABNORMAL STRUCTURE; MAY BE FORMED BUT IN INADEQUATE QUANTITIES THIS WILL RESULT IN DIFFERNER OF ABNORMAL OR ABSENTT PROTEINS SUCH AS ENZYME/HORMONE DEFICINCIES; ABNORMAL RECEPTORS ETC. AN IMPAIRMENT INVOLVING ANY OF THE ORGANELLES INVOLVED IN THE PROCESS OF PROTEIN SYNTHESIS MAY RESULT IN SIMILAR PATHOLOGICAL CONDITIONS

6. CELL MEMBRANE( PLASMA MEMBRANE) ENVELOPES THE CELL. APPROXIMATE COMPOSITION: PROTEINS 55%, PHOSPHOLIPIDS 25%, CHOLESTEROL 13%, OTHER LIPIDS 4%, CARBORHYDRATES 3% BASIC STRUCTURE IS A LIPID BILAYER( THIN, DOUBLE LAYERED FILM EACH LAYER ONE MOLECULE THICK THAT IS CONTINOUS OVER THE ENTIRE CELL SURFACE AND INTERSPERSED IN IT ARE LARGE GLOBULAR PROTEINS. LIPID BILAYER: 3 MAIN LIPIDS( PHOSPHOLIPIDS- MOST ABUNDANT, SPHINGOLIPIDS AND CHOLESTEROL)

7. CELL MEMBRANE PHOSPHOLIPID MOLECULE- PHOSPHATE END-HYDROPHILIC, FATTY END-HYDROPHOBIC. HYDROPHOBIC ENDS REPELLED BY WATER BUT ARE MUTUALLY ATTRACTED TO ONE ANOTHER THUS ATTRACTING EACH OTHER IN THE MIDDLE OF THE MEMBRANE. LIPID BILAYER IS IMPERMIABLE TO USUAL WATER SOLUBLE SUBSTANCES E.g. ions, glucose and urea. Conversely fat soluble substances e.g. oxygen, carbon dioxide and alcohol can penetrate with ease.

8. Cell membrane Cell membrane proteins: integral that protrude all the way through the membrane, peripheral - attached only to one surface of the membrane and do not penetrate. Integral- provide structural channels(pores ) through which water and water soluble molecules can diffuse between extracellular and intracellular fluids. Act also as carrier proteins for transporting substances that cannot penetrate lipid bilayer. Serve as receptors f or water soluble hormones such as peptide hormones. Peripheral- attached to integral proteins. function almost entirely as enzymes or as controllers of transport of substances.

9. Cell membrane Membrane carbohydrates- occur almost invariably in combination with proteins or lipids in form of glycolipids or glycoproteins. Proteoglycans- carbohydrate compounds bound to small protein cores and are loosely attached to outer surface of the well thus the entire outside surface of the cell often has a loose carbohydrate coat called glycocalyx.

10. Cell membrane The carbohydrate moieties attached to the outer surface of the cell have several important functions: 1. Many of them have a negative electrical charge, which gives most cells an overall negative surface charge that repels other negatively charged objects. 2. The glycocalyx of some cells attaches to the glycocalyx of other cells, thus attaching cells to one another.

11. Cell membarne 3. Many of the carbohydrates act as receptor substances for binding hormones, such as insulin; when bound, this combination activates attached internal proteins that, in turn, activate a cascade of intracellular enzymes. 4. Some carbohydrate moieties enter into immune reactions,

12. Endoplasmic reticulum Interconnected Tubular and flat vesicular structures. Processes molecules made by the cell and transports them to their specific destinations inside or outside the cell. Two types: granular and agranular Granular e.r - ribosomes attached to the e.r . the ribosomes are composed of a mixture of r.n.a and proteins and function to synthesize new protein molecules in the cell Agranular e.r .- functions for the synthesis of lipid substances mainly.

13. Golgi apparatus Closely related to e.r. has membranes similar to those of Agranular e.r. Composed of a stuck of 4 or more layers of thin, flat enclosed vesicles lying near one side of the nucleus. Prominent in secretory cell. Functions in association with e.r “transport vesicles” (also called endoplasmic reticulum vesicles, or ER vesicles ) continually pinch of from the endoplasmic reticulum and shortly thereafter fuse with the Golgi apparatus. In this way, substances entrapped in the ER vesicles are transported from the endoplasmic reticulum to the Golgi apparatus. The transported substances are then processed in the Golgi apparatus to form lysosomes, secretory vesicles, and other cytoplasmic components

14. lysosomes Vesicular organelles that form by breaking off from golgi apparatus and then dispersing throughout cytoplasm. Has a typical lipid bilayer membrane, and filled with granules containing digestive(hydrolase) enzymes as many as 40. Intracellular digestive system. digest (1) damaged cellular structures, (2) food particles that have been ingested by the cell, and (3) unwanted matter such as bacteria.

15. peroxisomes Physically similar to lysosomes but different in two ways Believed to be formed by self replication or perhaps by budding off fro the smooth e.r. rather than from golgi They contain oxidases rather than hydrolases. E.g hydrogen peroxide, catalase(For instance, about half the alcohol a person drinks is detoxified into acetaldehyde by the peroxisomes of the liver cells in this manner)

16. Secretory vesicles Formed from e.r- golgi apparatus system then released into the cytoplasm.

17. mitochondria Powerhouse of the cell. Without them all cellular functions of the cell would cease. Their numbers depend on the cell function. Composed of inner and outer membrane. Inner membrane folded to form cristae( increase surface area) onto which oxidative enzymes are attached. Inner cavity filled with a matrix that contains large quantities of dissolved enzymes necessary for extracting energy from nutrients. Main function- production of atp . They are self replicative. Has its own dna .

18. Cell cytoskeleton- filament and tubular structures Cell cytoskeleton- network of fibrillary proteins organized into filaments or tubules. The cytoskeleton is made up primarily of microtubules , intermediate filaments , and microfilaments proteins and organelles move along microtubules and microfilaments from one part of the cell to another, propelled by molecular motors.

19. Cell cytoskeleton Microtubules -made up of two globular protein subunits: α- and β-tubulin. A third subunit, y-tubulin, is associated with the production of microtubules by the centrosomes. They provide the tracks along which several different molecular motors move transport vesicles, organelles such as secretory granules, and mitochondria from one part of the cell to another. They also form the spindle, which moves the chromosomes in mitosis. Cargo can be transported in either direction on microtubules. There are several drugs that disrupt their function e.g. colchicine, paclitaxel, vinblastine.

20. Cell cytoskeleton. Intermediate filaments- made up of various sub-units. form a flexible scaffolding for the cell and help it resist external pressure. In their absence, cells rupture more easily, and when they are abnormal in humans, blistering of the skin is common. proteins that make up intermediate filaments are cell-type specific, and are thus frequently used as cellular markers. E.g. vimentin is a major intermediate filament in fibroblasts, whereas cytokeratin is expressed in epithelial cells

21. Cell cytoskeleton Microfilaments- made up of actin(It is the most abundant protein in mammalian cells) Filamentous (F) actin refers to intact microfilaments and globular (G) actin refers to the unpolymerized protein actin subunits. The actin filaments interact with integrin receptors and form focal adhesion complexes, which serve as points of traction with the surface over which the cell pulls itself. In addition, some molecular motors use microfilaments as tracks.

22. Molecular motors There are three super families of molecular motors : kinesin , dynein , and myosin. Kinesin- double headed molecule that tends to move its cargo toward the “+” ends of microtubules , and sometimes to the negative end of microtubules. Some are involved in meiosis and mitosis Dyneins- have two heads, with their neck pieces embedded in a complex of proteins. have a function like that of conventional kinesin, except they tend to move particles and membranes to the “–” end of the microtubules. Myosin- divided into 18 classes. The heads of myosin molecules bind to actin and produce motion by bending their neck regions (myosin II) or walking along microfilaments, one head after the other

23. centrosomes Located near the nucleus. made up of two centrioles and surrounding amorphous peri-centriolar material. The centrioles are short cylinders arranged so that they are at right angles to each other. The centrosomes are microtubule-organizing centers (MTOCs) that contain γ-tubulin. The microtubules grow out of this γ-tubulin in the pericentriolar material. When a cell divides, the centrosomes duplicate themselves, and the pairs move apart to the poles of the mitotic spindle, where they monitor the steps in cell division. In multinucleate cells, a centrosome is near each nucleus.

24. cilia specialized cellular projections that are used by unicellular organisms to propel themselves through liquid and by multicellular organisms to propel mucus and other substances over the surface of various epithelia

25. nucleus The nucleus is made up in large part of the chromosomes(occur in pairs), the structures in the nucleus that carry a complete blueprint for all the heritable species and individual characteristics of the animal. Each chromosome made up of d.n.a ( about 2 meters long) but it can fit in the nucleus because at intervals it is wrapped around a core of histone proteins to form a nucleosome ( about 25 million in each nucleus). The whole complex of DNA and proteins is called chromatin. The ultimate units of heredity are the genes on the chromosomes.

26. nucleus The nucleus of most cells contains a nucleolus ( a patchwork of granules rich in RNA). Can be one or more. They are the site of synthesis of ribosomes( protein synthesis). The interior of the nucleus has a skeleton of fine filaments that are attached to the nuclear membrane, or envelope, which surrounds the nucleus. This membrane is a double membrane, and spaces between the two folds are called perinuclear cisterns.

27. Transport across cell membrane Primary pathways include exocytosis , endocytosis, movement through ion channels , and primary and secondary active transport Exocytosis- Vesicles containing material for export are targeted to the cell membrane where they bound via the v-SNARE/t-SNARE arrangement. The area of fusion then breaks down, leaving the contents of the vesicle outside and the cell membrane intact. This is the Ca2+-dependent process of exocytosis secretion from the cell occurs via two pathways: non-constitutive (regulated pathway- processing of prohormones to mature hormones before exocytosis) and constitutive pathway( no processing or storage)

28. endocytosis The reverse of exocytosis Is of various types depending on size of particles being transported, as well as the regulatory requirements for the particular process: phagocytosis, pinocytosis, clathrin -mediated endocytosis, caveolae -dependent uptake, and nonclathrin / noncaveolae endocytosis.

29. Membrane permeability and membrane transport protiens . Voltage gated, ligand gated- external or internal( ca2+, Cyclic amp, g-protein) When carrier proteins move substances in the direction of their chemical or electrical gradients, no energy input is required and the process is called facilitated diffusion . Active transport. na +-K+ atpase , H+-K= ATPASE . UNIPORTS, SYMPORTS, ANTIPORTS

30. INTERCELLULAR COMMUNICATION. NEURONAL COMMUNICATION ENDOCRINE PARACRINE AUTOCRINE. juxtacrine communication( CONTACT DEPENDENT SIGNALING)

31. Signal transduction Receptors and ligands Intracellular calcium as a second messenger Ca2+-binding proteins have been described, including troponin, calmodulin, and calbindin . Ca2+-binding proteins include: troponin, calmodulin, and calbindin . G protein, IP3.

32. Intercellular connections. Intercellular junctions that form between the cells in tissues can be broadly split into two groups: junctions that fasten the cells to one another and to surrounding tissues, and junctions that permit transfer of ions and other molecules from one cell to another Tight junction(zonula occludens ), desmosomes and zonula adherens , hemidesmosomes and focal adhesions. Gap junctions-two corresponding gap juctions line up with one another to allow passage of substances between the cells without passing through e.c.f . mutations in genes that code gap junctions can lead to disease. e.g. predisposition to sudden cardiac death, female sterility, abnormal bone development, abnormal growth in the liver, cataracts, hearing loss, and a host of other abnormalities

33. Cell replication Mitosis and meiosis Meiosis in germ cells Mitosis- somatic cell division.

34. PATHOPHYSIOLOGY OF CELLULAR MECHANISMS Presenter: DR. E. O. MALENJE SUPERVISOR: DR. MURIITHI

35. DEFINITION Pathophysiology : Study of the underlying changes in body physiology (molecular, cellular & organ system) occurring due to disease/injury Cellular mechanisms pathophysiology encompasses: Cellular response to stress and noxious stimuli Cellular adaption to stress Cell injury and cellular death Causes of cell injury Effects of cell injury on cellular mechanisms

36. Cellular response to stress and noxious stimuli Cells normally maintain a steady state called homeostasis ; intracellular milleu is kept within a fairly narrow range of physiologic parameters Physiologic stresses or stimuli, may lead to functional and structural changes so as to achieve a new steady state ( adaptation) Within certain limits, injury is reversible and cells return to a stable baseline If the adaptive capability is exceeded or if external stress is inherently harmful, irreversible cell injury and cell death ensue

37. Causes of cell injury Hyp o xia (d e f i ci e ncy of o x y g e n ) : Ischemia or anemia P h y si c al a g e n t : b ur n s, d e ep c old, r adi a tion, el e ctric shock and mec h ani c al t r auma Bi o l o gic a l a g e n t s : vi r uses, bac t e r ial t o xi n s, fungi and parasites Chem i c a l a g e n ts a n d drugs En d o g en o us t o xins :u r em i a, jaund i ce and d i ab e tic Immu n o l ogic r eactio n s ( h yp e r sens i tivit y ) Nutriti o n a l im b a l a n ce :PEM, st a r v a tion, ob e sit y , DM etc Gen e tic a bn o rma l ities :Down s yn d r ome & s ickle anaemia Ageing

38. Mechanisms of cell injury Depletion of ATP Mitochondrial damage Influx of calcium and loss of calcium homeostatis Accumulation of oxygen-derived free radicles (oxidative stress) Defects in membrane permeability Damage to DNA and proteins

39. Cell injury: ATP Depletion May occur due to hypoxic or chemical (toxic) injury ATP production is in two ways: Oxidative phosphorylation of ADP in mitochondria (main) Glycolytic pathway (anaerobic; uses glucose or glycogen)

40. ATP Depletition Cont... Consequences Activity of plasma membrane energy dependent Na+, K+-ATPase) is reduced; causes intracellar accumulation of Na+ and K+ diffusion out of the cell Cellular energy metabolism is altered – Cell switches to anaerobic glycolysis (to maintain cell’s energy sources from ATP) Failure of Calcium pumps – Influx of Ca2+ leading to damage of organelles Structural disruption of protein synthetic apparatus; detachment of ribosomes from rough ER and dissociation of polysomes

41. ATP DePletition cont.. 4. Misfolding of proteins and accumulation in the ER causing unfolded protein response- may lead to cell injury and cell death 5. Irreversible damage to mitochondrial and lysosomal membranes leading to necrosis

42. Mitochondrial Damage Mitochondria can be damaged by: Increases in cytosolic Ca2+ Reactive oxygen species Oxygen deprivation

43. Mitochondrial Damage Consequences Loss of mitochondrial membrane potential through formation of mitochondrial permeability transion pore (leads to failure of oxidative phosphorylation, depletion of ATP and cell necrosis) Abnormal oxidative phosphorylation leading to formation of reactive oxygen species , ROS Sequestration of mitochondrial membranes and release of proteins responsible for apoptosis

44. Calcium influx and loss of ca homeostatis Mechanisms of cell damage ATP depletion due to formation of permeability transition pore following Ca2+ influx Calcium mediated activation of phospholipases, proteases, endonucleases and ATPases Direct induction of apoptosis by activating caspases and increasing mitochondrial permeability

45. Calcium influx and loss of Ca haemostasis

46. Accumulation of Oxygen derived free radicles Common mechanism in chemical injuries, radiation, ischaemia-reperfusion, cellular aging, bacterial phagocytois by leucocytes Commonest is reactive oxygen species, ROS Superoxide anion (O . 2 ) Hydrogen peroxide (H 2 O 2 ) Hydroxyl ions (OH - ) ROS are a product of normal respiration and are removed by cellular defence systems Increased production and reduced scavenging results in an marked increase and potentiates cell injury

47. Free radicles Mechanism of cell injury 1. Lipid peroxidation in membranes – ROS attack unsatuated fatty acid membranes to yield unstable,reactive products 2. Oxidative modification of proteins –disrupts the conformation of structural proteins 3. Lesions in DNA : breakages, crosslinking etc

48. Reactive oxygen species

49. Defects in membrane permeability Lead to loss of selectivity in permeability Mechanisms Reactive oxygen species (through lipid peroxidation) Decreased phospholipid synthesis –due to defective mitochondria/hypoxia Increased phospholipid breakdown- due to activation of phospholipases Cytoskeleton abnormalities

50. DNA DAMAGE DNA carries genetic instructions related to the growth, the development, functioning and reproduction of a cell and a whole organism by extension Mutations (alterations in the genetic sequence) may occur; are inherited or acquired Most mutations are identified and corected by the cell machinery through a process known as proofreading Some mistakes may escape this step leading to a permanent alteration in fhe DNA This may result in formation of abnormal or suboptimally fuctioning proteins since the DNA is the template upon which all proteins are made This may lead to varous genetic disorders disorders due to the absence or presence of certain proteins

51. CAUSES OF MUTATIONS Chemicals-nitrous acid, alkylating agents Exposure to radiation-x-rays cause DNA fragmentation,uv light causes thymidine dimerization. Certain viruses Drugs Reactive oxygen species, ROS Metals- arsenic, nickel, cadnium

52. Disorders of ribosomes May be due to abnormal biogenesis or abnormal function (improper protein folding) Gene mutations affecting various ribosomal proteins result in abnormal biogenesis of ribosomes Examples of conditions that may be caused by abnormal ribosomal proteins Treacher-Collin Syndrome (TCS) _mutation in the gene coding for TCOF1 protein resultimg in a shorter/truncated protein; results in craniofacial abnormalitie Alopecia, neurological defects and endocinopathy syndrome (ANE Syndrome); Mutation in RBM28 gene( required for the formatoon of 60S subunit of ribosomes) Prader Willi Syndrome(PWS) Diamond Blackfan Aneamia (DBA) Primary open angle Glaucoma (POAG)

53. ER-GOLGI COMPLEX DISORDERS Correctly folded proteins leave transport vesicles that bud from the ER to the ER-Golgi intermediate compartment Later delivered to the Golgi apparatus by vesicles or tubules Those that are improperly folded accumulate in the ER Functional defects may occur at the various steps of transport and sorting within the ER and between the ER and the Golgi apparatus Example: Mutations affecting signal sequence affecting membrane translocation or processing of signals may lead to primary hypothyroidism, deficiency of coagulation factor X, Criggler Najjer Syndrome II etc

54. Endoplasmic reticulum storage diseases (ERSDs)

55. Lysosomal storage diseases Lysosomes have more than 40 enzymes working on varied subtrate s.a RNA, DNA, complex carbohydrates, phosphate esters etc If enzyme is congenitally absent (eg due to a genetic mutation), they become engorged with subtrate to be broken down Disease Deficient enzyme Substrate that accumulates Fabry’s Disease Alpha galactosidase Glycolipids;glycoproteins Tay sacchs Disease Hexosaminidase Gangliosides Gaucher’s Disease Beta galactocerebrosidase Glucocerebroside

56. Membrane damage Consequences Mitochondrial membranene – ATP depletion and apoptosis Plasma membrane – loss of osmotic balance and influx of fluids Lysosomal membranes – leakage of enzymes into the cytoplasm; cell death by necrosis

57. CYTOSKELETON DISORDERS Cytoskeleton maintains cell shape & gives support to cell. 3types:Microfilaments,Microtubules,Intermediate filaments(6 subtypes). Microfilaments disorders : Wiskott-aldrich syndrome. Congenital myopathies. (nemaline; myotubular; central core) Microtubule disorders (tauopathies) : Hyperphosphorylation of tau protein due to mutation is the main pathology in all disorder s; neuroglial cells dysfunction; dementia Alzheimer’s disease. Pick’s disease. Progressive supranuclear palsy. Corticobasal degeneration.

58. Cytoskeleton cont... Cilia dysfunction syndrome Immotile cilia syndrome Kartageners syndrome Infertility syndrome Intermediate filaments disorders : Type 1&2 disorders Epidermolysis bullosa Keratoderma disorders Hair & nail disorders Other systems involvement Type 3 disorders Desminopathies(desmin) Amyotropic lateral sclerosis(peripherin) Alexander disease(GFAP) Autosomal dominant juvenile cataract(vimentin)

59. Cytoskeleton cont… Type 4 disorders:(neurofilament) Charcot-marie-tooth disease Parkinson’s disease Type 5 disorders:(nuclear lamins) Lipodystrophy disorders Muscular laminopathies Neurological disorders Premature ageing syndrome Type 6 disorders:(nestin) Autosomal dominant cataract Autosomal recessive cataract

60. WISKOTT-ALDRICH SYNDROME WASP(wiskott aldrich syndrome protein) Expressed in WBC & megakaryocytes& involved in reorganization of actin cytoskeleton. WASP is essential for function of T cells & platelets. Pt’s with WAS has defective gene in short arm of X chromosome(Xp11.23) Causes mutations in WASP leading to inability of actin to reorganize CD3 cannot be presented,T cells not activated,so B cells not activated,only IgM Ab’s are produced. These defective cells also have problems with cell motility,difficulty attaching to other cells. Pt presents as eczema, recurrent infections, microthrombocytopaenia, nose bleeds, bloody diarrhea, auto immune disorders etc. It is a X linked recessive genetic trait.

61. NEMALINE MYOPATHY Also called rod myopathy or nemaline rod myopathy. Congenital hereditary neuromuscular disorder. Mutatons affecting 6 genes imp ortant in provid ing instructions for producing proteins in muscle sarcomeres that are necessary for muscle contraction. ACTA1-alpha actin 1 gene , TPM3-alpha tropomyosin ; NEB-nebulin gene. TPM2-tropomyosin2 ; NNT1-troponin T1 ;C FL2-coffilin2 gene. So the proteins are disorganized,can’t interact normally & disrupts the muscle contraction. Pt presents as muscle weakness arms,legs,trunk,throat,face muscles,delayed motor development also seen.

62. Continued ………. IMMOTILE CILIA SYNDROME : Autosomal recessive disorder. Cilia & flagellainner & outer dynein arms. Dynein arms Dynein ATPasesliding & cilia bending. Mutations in DNAI1,DNAH5code for proteins in dynein. Absence or shortening of dynein arms Recurrent infections,sinusitis,bronchitis,pneumonia,otitis media are seen. KARTAGENER’S SYNDROME : Chronic sinusitis,bronchiectasis,situs inversus(reversal of internal organs) INFERTILITY : Defective cilia function in F.T. female infertility. Defective flagella function sperm motility affectedmale infertility.

63. Cell messaging /SIGNAL TRANSDUCTION DISORDERS Diabetes mellitus type 2 : Insulin reistance is one of tbe underlying mechanisms Studies suggest defects at post receptor level of insulin signalling involving insulin receptor/substrate (IRS)-1 phosphatidylinositol (PI)3-Kinase pathway Results in dimished glucose uptake and utilization in insulin target tissues In pseudohypoparathyroidism (PHP) ; H ypocalcemia and hyperphosphatemia due to parathyroid hormone insensitivity rather than deficiency; Studies show that PTH fails to activate cAMP (second messenger) in renal cortical tubular tissue

64. REFERENCES Robbins & cotron textbook of pathology-8 th edition. Anderson textbook of patholog Review of physiology by Ganong Endoplasmic reticulum storage diseases, Jonas Rutishauser, Martin Spiess Swiss med wkly 2002; 132:211-222 www.smw.ch

65. Thank You

66. PROTEIN SYNTHESIS DR ALEX MUGWE

67. NUCLEUS The nucleus is the largest cellular organelle. It is basically the control centre of the cell and harbours large quantities of DNA. The nucleolus is the nuclear subdomain that assembles ribosomal subunits, harbouring large amounts of RNA and proteins types found in ribosomes

68. 1. DNA Helical, double-stranded structure Carries genetic material which control cell function by determining which substances are synthesized within the cell- structures, enzyme, chemicals. A gene is a sequence of DNA or RNA that codes for a molecule that has a specific function.

69. The basic chemical compounds involved in the formation of DNA include: Phosphoric acid, A sugar called deoxyribose , four nitrogenous bases: Two purines - adenine and guanine Two pyrimidines -cytosine and thymine

70. Components of a typical gene

71. Nucleotides; 1 st stage in DNA synthesis is the combination of one molecule of phosphoric acid, one molecule of deoxyribose , and one of the four bases to form an acidic nucleotide; deoxyadenylic , deoxythymidylic , deoxyguanylic , and deoxycytidylic acids Multiple numbers of nucleotides are then bound together to form two strands of DNA

72. the strands are usually bound together via weak hydrogen bonds between the purine and pyrimidine bases such that; Each purine base adenine of one strand always bonds with a pyrimidine base thymine of the other strand Each purine base guanine always bonds with a pyrimidine base cytosine.

73. Genetic code; When the two strands of a DNA molecule are split apart, this exposes the purine and pyrimidine bases projecting to the side of each DNA strand, these projecting bases form the genetic code. Usually consists of successive “triplets” of bases i.e each three successive bases is a code word. The successive triplets eventually control the sequence of amino acids in a protein molecule that is to be synthesized in the cell e.g proline , serine

74. 2. RNA Single stranded Because the DNA is located in the nucleus of the cell, yet most of the functions of the cell are carried out in the cytoplasm, there must be some means for the DNA genes of the nucleus to control the chemical reactions of the cytoplasm, this is achieved by the RNA The code in the DNA is transferred to the RNA through the process of transcription

75. The RNA, in turn, diffuses from the nucleus through nuclear pores into the cytoplasmic compartment, where it controls protein synthesis. Building blocks of RNA; Ribose sugar Phosphoric acid Nitrogenous bases- adenine,guanine,cytosine,uracil (in place of thymine in DNA)

76. Types of RNA Messenger RNA -which carries the genetic code to the cytoplasm for controlling the type of protein formed. Transfer RNA - which transports activated amino acids to the ribosomes to be used in assembling the protein molecule. Ribosomal RNA , which, along with about 75 different proteins, forms ribosomes , the physical and chemical structures on which protein molecules are actually assembled.

77. PROTEIN SYNTHESIS

78. TRANSCRIPTION Process of creating an equivalent RNA copy of a sequence of DNA. During this process a DNA sequence is read by DNA polymerase, which produces a complementary , antiparallel strand. Thymine (T) in the DNA segment is usually replaced by Uracil (U) in the complementary RNA strand

79. The stretch of DNA transcribed into an RNA molecule is called a transcription unit and encodes atleast one gene If the gene transcribed encodes for a protein, the result of transcription is mRNA, which will be used to create that protein via translation A DNA transcription unit encoding for a protein contains not only the sequence that will eventually be directly translated into the proteins, regulatory sequences that direct and regulate synthesis of that protein

80. Transcrption is divided into 3 stages; Initiation Elongation Termination

81. Initiation RNA polymerase identifies and attaches to promoter region( a sequence of nucleotides immediately ahead of the initial gene) The RNA polymerase has an appropriate complementary structure that recognizes this promoter and becomes attached to it. Essential for initial formation of RNA molecule

82. Elongation After the RNA polymerase attaches to the promoter, the polymerase causes unwinding of about two turns of the DNA helix and separation of the unwound portions of the two strands.

83. Then the polymerase moves along the DNA strand, temporarily unwinding and separating the two DNA strands at each stage of its movement. As it moves along, it adds at each stage a new activated RNA nucleotide to the end of the newly forming RNA chain

84. termination When the RNA polymerase reaches the end of the DNA gene, it encounters a new sequence of DNA nucleotides called the chain-terminating sequence ; this causes the polymerase and the newly formed RNA chain to break away from the DNA strand. Then the polymerase can be used again and again to form still more new RNA chains.

85. Post transcription modification After transcription, editing is done to make the RNA functional(basically converting the pre mRNA to a mature mRNA Introns - non functional segments of DNA that are removed Exons - segments of DNA coding for proteins are then rejoined by the enzyme ligase A guanine triphosphatase cap is added to the 5’ end of the newly copied mRNA A poly A tail is added to the 3’ end of the RNA

86. TRANSLATION This is the first process of protein biosynthesis, and involves production of proteins by decoding m RNA produced through transcription Each codon decoded guides the formation of a specific polypeptide/protein When a molecule of messenger RNA comes in contact with a ribosome, it travels through the ribosome, beginning at a predetermined end of the RNA molecule specified by an appropriate sequence of RNA bases called the “chain-initiating” codon .

87. While the messenger RNA travels through the ribosome, a protein molecule is formed- translation when a “stop” (or “chain-terminating”) codon slips past the ribosome, the end of a protein molecule is signaled and the protein molecule is freed into the cytoplasm. Ribosomes consist of two parts, a large subunit and a small subunit. They contain a binding site for  mRNA  and two binding sites for  transfer RNA ( tRNA ) located in the large ribosomal subunit

88. Proceeds in four phases; Activation Initiation Elongation termination

89. Activation Each amino acid is activated by a chemical process in which ATP combines with the amino acid to form an adenosine monophosphate complex with the amino acid (AMP-AA complex) giving up two high-energy phosphate bonds in the process. The activated amino acid, having an excess of energy, then combines with its specific transfer RNA to form an amino acid– tRNA complex( AA- tRNA ),and at the same time, releases the adenosine monophosphate (AMP)

90. The activated amino acid, having an excess of energy, then combines with its specific transfer RNA to form an amino acid– tRNA complex and, at the same time, releases the adenosine monophosphate .

91. Initiation The transfer RNA carrying the amino acid then comes in contact with the messenger RNA molecule in the ribosome- typically starts at the start codon AUG The anticodon of the transfer RNA attaches temporarily to its specific codon of the messenger RNA, lining up the amino acid in appropriate sequence to form a protein molecule

92. Elongation Peptide bonds are formed between the successive amino acids, thus adding progressively to the protein chain. This is under the influence of the enzyme peptidyl transferase . These chemical events require energy from two additional high-energy phosphate bonds, making a total of four high-energy bonds used for each amino acid added to the protein chain.

93. Termination Translation continues until the stop codon ( AUG ) is reached , and the polypeptide chain is released. The tRNA molecules are used again The mRNA molecules are also reused approximately 10 times beifore being replaced.

94. Post Translational Modification After the polypeptide chain is formed, it is modified to the final protein by : O ne or more of a combination of reactions that include hydroxylation, carboxylation, glycosylation, or phosphorylation of amino acid residues cleavage of peptide bonds that converts a larger polypeptide to a smaller form . folding and packaging of the protein into its ultimate, often complex configuration .

95. PATHOPHYSIOLOGY OF PROTEIN SYNTHESIS FACILITATOR:DR M W MURIITHI PRESENTER:CHRISTINE OKINDO

96. PRESENTATION OUTLINE SUMMARY OF PROTEIN SYNTHESIS ABNORMALITIES CLASSIFICATION DISCUSS IN SUMMARY ONE DISORDER IN EACH CLASS DIAGNOSIS

97. MUTATIONS Mutations are changes in the nucleotide sequence of DNA. Can either be genetic/hereditary or acquired/somatic A hereditary mutation is a mistake that is present in the DNA of virtually all body cells. Many mutations are repaired by enzymes

98. CAUSES OF MUTATIONS Spontaneous mutations Caused during DNA replication/incorporation of incorrect nucleotide into growing DNA chain Induced mutation Changes in DNA brought about by some environmental factors eg mutagens such as Chemicals-nitrous oxide, alkylating agents Smoking, Exposure to radiation Drugs-cause cross linkage of DNA thus blocking replication

99. TYPES OF MUTATIONS Classified into: genome mutation: (whole chromosome) Gene mutations-change in the nucleotide sequence of a gene May only involve a single nucleotide Chromosomal mutation-issue with chromosome structure Loss or gain of a part of a chromosome.

100. TYPES OF GENE MUTATIONS Point mutation-single nucleotide base may be substituted by a different base. Insertion-one/two base pairs may be inserted into the dna Deletion-one/two base pairs may be deleted from the dna Both insertion and deletion mutations lead to alterations in the reading frame of the DNA strand hence known as frame shift mutations.

101. TYPES OF CHROMOSOMAL MUTATIONS

102. DELETION Due to breakage. A piece of chromosome is lost

103. INVERSION Chromosome segment breaks off Segment flips around backwards Segment Reattaches

104. Duplication Occurs when a gene sequence is repeated

105. TRANSLOCATION Involves two chromosomes that aren’t homologous Part of one chromosome transferred to another chromosomes

106. Nondisjunction Failure of a chromosome to separate during meiosis Causes gamete to have too many or too few chromosomes Disorders: Klinefelter’s Syndrome- XXY chromosomes Down Syndrome- three 21 st chromosomes Turner Syndrome- single X chromosome

107. END RESULTS Interferes with protein synthesis-causes loss of function Suppress transcription with gene deletions and point mutations involving promoter sequence Produce abnormal mRNA from mutations affecting introns Defects are carried to translation. Translation is affected if a stop codon is created within an exon Abnormal proteins without impairing any step in protein synthesis

108. GENETIC DISORDERS Polygenic/multifactorial inheritance-mutation caused by both genetic and environmental factors e.g. HTN,DM Monogenic/ mendelian disorders-resulting from single gene mutations. They follow mendelian factor of inheritance . Chromosomal disorders- are associated with numerical /structural changes in chromosomes Mitochondrial –caused by a mutation in the non chromosomal DNA of the mitochondria

109. MONOGENIC DISORDER Result from mutations in the DNA sequence of single genes. As a result the protein the gene codes for is either altered or missing Gene expression is usually described as dominant or recessive Autosomal dominant Autosomal recessive Sex linked (recessive) involving x chromosome

110. AUTOSOMAL DOMINANT Manifested in the heterozygous state One parent of an index case is usually affected Both males and females are affected Both can transmit the condition Clinical features can be modified by reduces penetrance and variable expressivity Reduced penetrance-some individuals inherit the mutant gene but are phenotypically normal Variable expressivity-mutant gene is expressed differently among individuals

111. AUTOSOMAL DORMINANT DISORDERS Nervous-Huntington disease,neurofibromatosis,myotonic dystrophy, Tuberous sclerosis Gastrointestinal-familial polyposis coli Hematopoietic-hereditary spherocytosis,von willebrand disease Skeletal- marfans syndrome,ehlers danlos syndrome,osteogenesis imperfect,achondroplasia Metabolic-familial hypercholesterolemia,acute intermittent porphyria

112. AUTOSOMAL RECESSIVE Result when both alleles at a given locus are mutants Feature include The trait does not usually affect the arents but the siblings may show dx Siblings have 1 chance in 4 of being affected Expression of the defect tends to be more uniform than in AD disorders Complete penetrance is common Onset is frequently early in life

113. AUTOSOMAL RECESSIVE DISORDERS Metabolic-cystic fibrosis,phenylketonuria,galactosemia,homocysteinuria,lysosomal storage diseases,wilsons disease,hemochromatosis , Hematopoietic-sickle cell anemia,thalassemias Endochrine -congenital adrenal hyperplasia, skeletal- alkaptonuria Nervous-neurogenic muscular atrophies,friedreich ataxia,spinal muscular atrophy

114. SEX LINKED X Sex linked traits are x linked Can be dominant or recessive No y linked inheritance since all genes encoded in the male specific region of y are related to spermatogenesis.males with mutations affecting y linked genes are usually infertile. An affected male does not transmit the disorder to his sons but all daughters are carriers

115. X LINKED DISORDERS Muskuloskeletal-duchenne muscular dystrophy Blood-hemophilia A and B Immune- agammaglobulinemia,wiskott -Aldrich syndrome Metabolic-diabetes insipidus,lesch-nyhan syndrome Nervous-fragile x syndrome

116. POLYGENIC INHERITANCE Combined action of environmental influences and 2 or more mutant genes Expression defers by number of genes Continous traits eg height vs discontinuous traits eg albinism Examples include Cleft lip/palate congenital heart disease Coronary heart disease hypertension Gout diabetes mellitus Pyloric stenosis

117. CHROMOSOMAL GENETIC DISORDR In these disorders, entire chromosomes, or large segments of them, are missing, duplicated, or otherwise altered. organized into two groups: 1) Numerical Abnormalities: When an individual is missing either a chromosome from a pair ( monosomy ) or has more than two chromosomes of a pair (trisomy) 2) Structural Abnormalities: When the chromosome's structure is altered

118. Could also be divided into: Autosomes - are the first 22 homologous pairs of human chromosomes that do not influence the sex of an individual e.g. down syndrome, trisomy 13,trisomy 18 Sex chromosomes - e.g. the 23 rd pair of chromosomes that determine the sex of an individual. Examples - klinefelter xxy ,-extra sex chromosome turner xo-missing sex chromosome

119. MITOCHONDRIAL INHERITANCE Maternal inheritance This is because the ova contain numerous mitochondria within their abundant cytoplasm Spermatozoa contain few Diseases-mitochondrial myopathies e.g. chronic progressive external opthamoplegia ,myoclonic epilepsy with ragged fibers

120. DIAGNOSIS OF GENETIC DISORDERS Hx,physical exam,labworks and imaging There are several ways to determine whether a child will have a genetic disorder Two main ways to diagnose: 1.Analysis of fetal cells Amniocentesis Chorionic villus biopsy 2.Imaging techniques Ultrasonography (computerized image) Fetoscopy (direct observation)

121. SUMMARY OF PROTEIN SYNTHESIS DISORDERS CHROMOSOMAL DISORDERS MULTIGENE DISODERS SINGLE GENE DISORDERS

122. REFERENCE ROBBINS AND COTRAN,PATHOLOC BASIS OF DISEASE 7 TH EDITION GANONGS REVIEW OF MEDICAL PHYSIOLOGY 25 TH EDITION TEXTBOOK OF MEDICAL PHYSIOLOGY GUYTON AND HALL.