Biochemistry (Respiratory) PDF

Respi Biochemistry SYLLABUS Cellular Respiration/Oxidation: (P. 1029) Biological oxido-reduction: mechanism, examples Citric acid cycle (P. 1029): feeder pathways (P. 1029), pathways leading form, Overview of reactions, regulation (P. 1031), amphibolism (P. 1031) and clinical...

Respi Biochemistry SYLLABUS Cellular Respiration/Oxidation: (P. 1029) Biological oxido-reduction: mechanism, examples Citric acid cycle (P. 1029): feeder pathways (P. 1029), pathways leading form, Overview of reactions, regulation (P. 1031), amphibolism (P. 1031) and clinical application (P. 1031), energetics of TCA (P. 1031) Electron transport chain: (P. 1032) Cellular location, channeling of reducing equivalents (P. 1033), mechanism of ATP synthesis (P. 1033) Oxidative phosphorylation: (P. 1034) Chemiosmotic theory (P. 1035), clinical application of inhibitors / uncouplers (P. 1036) Brown adipose tissue energy metabolism (P. 1037), thermogenin (P. 1037) Oxidative Stress and Antioxidant Systems: (P. 1037) Free redical (P. 1037), sources of free radicals, antioxidant systems (P. 1038), other biological anti-oxidants, failure of antioxidant systems- clinical implications (P. 1039) Vitamin E: (P. 1039) Dietary sources, metabolism and antioxidant function (P. 1040) IV  FAST TRACK BASIC SCIENCE MBBS -1027-  Biochemistry IV -1028- FAST TRACK BASIC SCIENCE MBBS  Respi BIOCHEMISTRY CELLULAR RESPIRATION /  Glucose gives off energy as it is oxidised. BIOLOGICAL OXIDATION Note: Past Questions: i. Gain or loss of electron is often in the form of hydrogen. 1. Define intermediary metabolism. Write the ii. The H-atom is passed to coenzyme (NAD+) sequence of reactions of TCA cycle, its site and control. (1+2+2=5) [08 July] iii. 1H = 1e¯ + 1H+ iv. Various enzymes are required for biological 2. What do you mean by common metabolic pool oxidation collectively called as oxido-reductase pathway? (4) [05 June] and is classified into 4 group: 3. Enumerate the steps of citric acid cycle; explain - Oxidases, dehydrogenases, hydroperioxidase, in brief its regulation and point of substrate level oxygenases. phosphorylation. (3+2+1=6) [06 June] 4. Explain why TCA cycle is known as amphibolic Citric acid cycle pathways? Sketch the explanatory diagram of  Also called as TCA cycle, krebs cycle. TCA cycle and show the site of substrate level of  Proposed by hans krebs in 1937. ATP generation  An aerobic cyclic pathway occuring in (2+1+4=7) [11 July] mitochondrial maitrix. 5. Write the steps of TCA cycle and calculate the  Act as final common pathway for the oxidation of IV energy and show how it is regulated. (6) [05 June] carbohydrates, lipid, and protein 6. Describe systematically the TCA cycle and briefly  Amphibolic in nature. explain its control. (8)  Oxidise Acetyl-CoA to produce GTP, NADH, Biological oxidation-reduction reaction: FADH2, CO2 and oxaloacetate.  Oxidation: it is loss of electrons (e¯) or H atoms. Overview of citric acid cycle  Reduction: It is the gain of electrons (e¯) or H Pyruvate atoms. + NAD  Oxidation always occurs with reduction Pyruvate CoA-SH dehydrogenase  When both reactions occur in biological living NADH+H+ CO2 system it is called biological oxido-reduction Acetyl CoA (2C) reaction. Eg. CoA Loss of hydrogen Oxaloacetate (4c) atoms Citrate (6c) C6H12O6 + 6O2 6CO2 + 6H2O + energy/(ATP) Succinyl CoA (4c) CO2 Gain of hydrogen atom -Ketoglutarate (5c) FAST TRACK BASIC SCIENCE MBBS -1029-  Biochemistry Reaction of citric acid cycle [03,05,06,08,11] IV -1030- FAST TRACK BASIC SCIENCE MBBS  Respi Note:  The accumulation of NADH and FADH2 will lead to inhibition of enzymes as stated i. Citrate →Isocitrate (rearrangement reaction) above. ii. Isocitrate →-ketoglutarate (1st oxidative  And also limit the supply of NAD+ and FAD decarboxylation) which are essential for TCA cycle to iii. -ketoglutarate → succinyl-CoA (2nd oxidative proceed. decarboxylation) Energetics of citric acid cycle [05,08] iv. Succinyl-CoA → Succinate (substrate level - During process of oxidation of Acetyl-coA via phosphorylation) citric acid cycle for reducing equivalent (3- v. Succinate → Fumarate (oxidation reaction) NADH and 1-FADH2) vi. Fumarate → Malate (hydra on) Reaction(enzymes Energy ATP vii. Malate → Oxaloacetate (oxida on reac on) involved) producing equivalents Net reaction product - Acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O Isocitrate NADH 3 2CO2 + CoA - SH + 3NADH + 3H+ + FADH2 + GTP dehydrogenase Regulation of TCA Cycle [03,05,06,08] α-KG dehydrogenase NADH 3 - The regulation is brought about either by Succinyl-CoA synthase GTP 1 enzymes or level of ADP. Succinate FADH2 2 1. There are 3 main enzymes that regulate TCA dehydrogenase cycle, namely complex i. Citrate synthase Malate dehydrogenase NADH 3 ii. Isocitrate dehydrogenase Total 12 iii. -ketoglutarate dehydrogenase IV Amphibolism [10,11] 2. It also depends on availability of ADP - TCA cycle is both catabolic and anabolic in i. Citrate synthase nature hence regarded as amphibolic and the - Activated by ADP property is called amphibolism. - Inhibited by ATP, NADH, Acetyl CoA and - TCA cycle is actively involved in gluconeogenesis, succinyl COA. transamination, and deamination. ii. Isocitrate dehydrogenase - The most important synthetic reaction - Activated by ADP, Ca2+ connected with TCA cycle are: - Inhibited by ATP and NADH i. Oxaloacetate and -KG, respectively serve iii. -ketoglutarate dehydrogenase as precursor for the synthesis of aspartate - Activated by Ca2+ and glutamate which in turn are required - Inhibited by succinyl CoA and NADH for the synthesis of other non essential - Availability of ADP amino acids purines and pyrimidines.  It is very important for TCA cycle to ii. Succinyl COA is used for the synthesis of proceed. porphyrins and heme.  This is due to fact that unless sufficient level iii. Mitochondrial citrate is transported to the of ADP are available, oxidation (coupled cytosol, where it is cleaved to provide acetyl with phosphorylation of ADP to ATP) of COA for the biosynthesis of fatty acids, NADH and FADH2 through ETC stops. sterols etc. FAST TRACK BASIC SCIENCE MBBS -1031-  Biochemistry Anaplerotic reactions ELECTRON TRANSPORT CHAIN - The reactions concerned to replenish or to fill up Past Questions: the intermediates of citric acid cycle are called 1. Define "Redox potential". Sketch the diagram anaplerotic reactions or anaplerosis. showing the arrangement of component of - The salient features of important anaplerotic electron transport chain and mention how it is reactions are: controlled. (1+2+1=4) [08 July] i. Pyruvate carboxylase catalyses the conversion 2. Trace sequence of electron transport chain of pyruvate to oxaloacetate (ATP dependent indicating sites of ATP synthesis and name any carboxylation treatment) two inhibitors of electron transport chain. ii. Pyruvate is converted to malate by NADP+ (8) [03 June] dependent malate dehyrogenase. 3. Sketch the diagram of e- transport chain. Explain iii. Transamination helps to form -KG and showing inhibitors & its site of action. oxaloacetate by transmination mechanism. (3+2=5) [05 Dec] iv. -KG can be synthesized from glutamate by  It refers to a series of redox reactions occuring in glutamate dehydrogenase action. the inner mitochondrial membrane in which electrons derived from various substrate are v. Certain AAs and FAs also replenish TCA cycle transferred to oxygen. intermediates e.g.KG, succinyl coA and  It represents final stage in the oxidation of fumarate. carbohydrates, fats and amino acids. Clinical Application  It primes the process of ATP generation via - Citric acid cycle is final common pathway for oxidative phosphorylation. carbohydrates, fat and amino acids. It utilizes  It consist of four large protein complex (I-IV). (indirectly) about 2/3 of the total oxygen, Cellular location (05,08) IV consumed by body and generates about 2/3 of  The electron transport chain and ATP synthesizing total energy/ATP. system are located in the inner mitochordrial - Very few genetic diseases of krebs cycle are membrane. known.  Inner mitochondrial membrane is specialized Genetic diseases of krebs cycle: structure rich in proteins impermeable to H+, K+  Includes several distinct but very rare and Na+. diseases.  Enzymes of ETC are embedded in the inner  Result from defective enzymes membrane.  Fumarase deficiency: Component of ETC (03,08) Results in elevated plasma urine and Complex Name No. of Prosthetic tissue level of fumarate, pyruvate and protein group lactate. Complex I NADH 43 FMN, 9Fe-S Also result into muscular hypotonia Dehydrogenese centres and severe neurological impairment Complex II Succinate 4 FAD, Cytb560, (encephalopathy and seizure etc). CoQreductase 3Fe-S centres  Deficiency of succinate dehydrogenase Complex III CoQ- 11 CytbH, Cytbc. and -KG dehydrogenase: Cytcreductase Cytc1 Fe-S rieske Are also associated with lactic Complex IV Cytochrome 13 Cyt a, Cyta3, acidosis and major neurological Oxidase CuA, CuB problems. -1032- FAST TRACK BASIC SCIENCE MBBS  Respi Channeling of Reducing Equivalent/ Organization of ETC [03,05,08] Complex I - Oxidises CoQ in the membrane and reduces a - It is also called NADH ubiquinone mobile Cyt. C on the anterior surface. oxidoreductase. - Transports 4H+ ions from the matrix to the - Contains FMN and Fe-S protein as prosthetic cytosol. group. Complex IV - Oxidizes NADH and reduces coenzymes Q. - Also called cytochrome C oxidase. IV - Passes electron to complex III via coenzyme Q. - Consist of 13 subunits, 3 are encoded by the + mitochondrial DNA and the remainder by the - Transports 4H ion from matrix to cytosol. Complex II nuclear DNA. - Also called as succinate-Ubiquinone - Contains 2 heme group: heme a and heme a3 oxidoreductase. and 3 Cu ions (arranged as 2 cupper centres CuA and CuB) - Contains FAD, FeS protein and Q as the electron carrier. - Oxidizes reduced cytochrome C produced by complex III and transfer electrons from it to - Unlike other complexes, doesnot transport H+ molecular O2. ions. - Translocate 2H+ ions across the mitochondrial - Accepts electrons from succinate and then membrane. transfer it to coenzyme Q. - Also catalyses one of the reaction of TCA cycle. Mechanism of ATP synthesis Complex III  ATP is synthesized by two mechanism: - Also called as ubiquinol - cytochrome C i. Oxidative phosphorylation (described later in oxidoreductose or cytochrome bC1 complex. details) - Consist of 3 main subunits: CytC1, Cytb and ii. Substrate level phosphorylation [10,11} Rieske Fe-S protein (ISP). - ATP may be directly synthesized during substrate oxidation in metabolism. FAST TRACK BASIC SCIENCE MBBS -1033-  Biochemistry - The high energy compounds such as  Three possible sites of action for inhibiters of ETC phosphoenolpyruvate and 1,3 are as follow bisphosphoglycerate (intermediates of Sites Inhibitor glycolysis) and succinyl CoA (intermediate of 1. NADH and Fish poison, rotenone, TCA cycle) can transfer high energy coenzyme Q barbiturate drug amytal and phosphates to ultimately to produce ATP. antibiotic piercidin A Inhibitor of ETC [03,05] 2. Between cyt band C1 Antimycin A, British  The inhibitors bind to one of the compoment of antilewisite (BAL) ETC and block the transport of electrons. 3. Cytochrome oxidase Carbonmonoxide, cyanide,  This causes the accumulation of reduced hydrogen sulphide, and azide components before the inhibitor blockade step and oxidized component after that step. IV Regulation of ETC 3. What is chemi-osmotic theory? Draw a diagram i. Availability of ADP of the electron transport chain showing events leading to the synthesis of ATP. ii. Availability of substrate (1+5+1=7) [11 July], (1+4 =5) [10 Jan] iii. Availability of O2 4. Explain in brief chemi-osmotic theory. Write two OXIDATIVE PHOSPHORYLATION examples of substrate level phosphorylation. (4+4=8) [06 Dec] Past Questions: 5. What is oxidative phosphorylation? Mention the 1. What is oxidative phosphorylation? Sketch complexes involved. Why NADH gives 3 ATP and labelled diagram of oxidative phosphorylation FADH only 2 ATP ? Sketch the diagram of ETC and and location of action of uncouplers. inhibitors acting. (2+3+3=8) [04 Nov] (1+2+3=6)[06 June] 6. What is oxidative phosphorylation? Sketch 2. What is chemiosmotic theory? Show the labelled diagram of oxidative phosphorylation pathways of oxidative phosphorylation also show and location of action of uncouplers. the sites where inhibitors act. (1+3+2=6) [10 July] (1+2+3=6)[06 June], (3+2=5) [05 Dec] -1034- FAST TRACK BASIC SCIENCE MBBS  Respi 7. What is chemiosmotic theory? Show the  Occurs in mitochondria (complex V of inner pathways of oxidative phosphorylation also show mitochondrial membrane). the sites where inhibitors act  Sites of ATP synthesis in ETC [05,08,11] (1+3+2=6) [10 July] - Oxidation of FMNH2 by coenzymes Q. 8. What is chemi-osmotic theory? Draw a diagram - Oxidation of cytochrome b by cytochrome C1 of the electron transport chain showing events - Cytochrome oxidase reaction. leading to the synthesis of ATP. (1+4 =5) [10 Jan]  Each of above reaction represents a coupling site 9. Explain in brief chemi-osmotic theory. Write two for 1 ATP production resulting in total 3 ATP. examples of substrate level phosphorylation. Mechanism of oxidative phosphorylation 10. What is oxidative phosphorylation? - Following hypothesis are described: 11.Explain the Chemosmotic theory and show the  Chemical coupling site of ATP generation. [1+1+1 =3]  Chemiosmotic theory (Discussed in detail) 12.Short notes on: a. Substrate level phosphorylation (4) [05 June, ChemiosmoticTheory [03,06,10,11] 03 June]  It was 1st proposed by British biochemist peter b. Oxidative phosphorylation(5) [ 03 June] mitchell in 1961 and is widely accepted theory. c. Chemiosmotic theory (4) [02 Dec]  Postulates of chemiosmotic theory: d. Uncouplers (2) [11 July] - Electron transport through ETC generates H+ e. Chemiosmotic theory gradient across inner mitochondrial membrane.This is due to the translocation of protons f. Brown adipocytes (2) [11 July] through the inner mitochondrial membrane g. Functions/significance of brown adipose from matrix to the intermembranous space. tissue (3) [05 Dec, 03 Dec] - proton gradient/ H+ gradient generates a proton motive force (PMF) which link Oxidative phosphorylation (oxidative) and ATP synthesis [03,04,05,06,10,11] (phosphorylation). IV  The process of synthesizing ATP from ADP and Pi - H+ flow back to the matrix through ATP coupled with the electron transport chain is synthase to equalize the distribution, PMF known as oxidative phosphorylation. drives the ATP synthesis. FAST TRACK BASIC SCIENCE MBBS -1035-  Biochemistry Enzyme of ATP synthesis: second has loose conformation(l), third has - ATP is synthesized by enzyme system i.e. ATP tight conformation(T) synthase which is present in complex V. - Binding charge mechanism for ATP synthesis - It acts as rotating molecular motor. involves following steps: - It consist of two functional unit: F1 and F0. 1 mol of ADP and 1 mol of Pi bind to an L site a. F1 consists of α (α3), β (β3), subunits  and catalyzes ATP synthesis. Rotation of γ shaft causes each of the 3 catalytic b.- F0 unit is an aggregate of integral sites to change conformation. membrane proteins.  - Consist of 3 subunits a, b and c. L site (with bound ADPand Pi) becomes T site with - Form a transmembrane pore through the formation of ATP which H+ ions move to drive ATP  synthesis. T site containing ATP becomes an O site.  ATP is released from the O site IV Rotatory motor model for ATP generation: Note: - The conformational change in the - Three ATP are generated for each revolution mitochondrial membrane protein(ATP Release of ATP from O site is energy dependent synthase) leads to synthesis of ATP. not ATP formation. - Proposed by Boyer in 1964 - The proton flux induces the rotation of γ subunit. This rotation induces conformational Uncouplers / Inhibitor of oxidative change in the β3 subunit. phosphorylation [05,06,10,11] - The three subunits adopt different  Uncouplers are defined as the compounds which conformation, one has open (O) conformation, uncouple or delink the electron transport from oxidative phosphorylation. -1036- FAST TRACK BASIC SCIENCE MBBS  Respi  Such compounds increase the permeability of Thermogenin inner mitochondrial membrane to proton (H+)  It is a protein which acts as natural uncoupler resulting into arrest of ATP synthesis i.e. it allows (UCP1) located at the inner mitochondrial oxidation of substrates without ATP formation. membrane.  he energy linked with transport of electrons is  It uncouples e¯ transport from oxidative dissipated as heat so that no ATP is produced. phosphorylation and thus generates heat in the E.g 2, 4 dinitrophenol (DNP), pentachlorophenol, brown adipocytes. trifluorocarbonylcyanide, phenyl hydrazone  It doesnot play a major role in energy balance. aspirin (in high doses)  Thermogenesis is controlled by free FAs and in Physiological uncouplers turn is controlled by norepinephrine. - Certain physiological compound acts act as OXIDATIVE STRESS AND ANTIOXIDANT physiological uncoupler at high dose, these SYSTEM include. Past Questions:  Thermogenin 1. Importance of antioxidants. (2+2=4) [08 July]  Thyroxine 2. Define antioxidant. Write names of endogenous  Long chain fatty acids and dietary antioxidants. (1+4=5) [07 Dec]  The unconjugated bilirubin 3. What are the various pro-oxidants spontaneously Clinical Application: generated in the body? Explain the role of anti- - -2, 4 dinitrophenol, a small lipophilic molecule oxidant systems in combating these pro- is a proton carrier which can easily diffuse oxidants. (1.5 + 3.5 = 5) [10 Jan] through inner mitochondrial membrane. 4. Free radicals & dietary anti-oxidants. (3) [09 July] - In the people seeking wt. loss, it is used as drug 5. One example of free radicals and their harmful IV diet pills and its side effect is hyperthermia. effects (3) [07 July] 6. List the functions of vitamin E and mention its Brown adipose tissue energy sources [07 Dec] metabolism [03,05,11]  Brown adipose tissue is characterized by presence Oxidative stress [03,04] of numerous mitochondria which makes it brown  A condition in which the rate of generation of in colour. It has got well developed blood supply reactive oxygen species/reactive nitrogen species with low activity of ATP synthases. exceeds our ability to protect ourselves against  This is extremely significant for maintenance of them, resulting in an increase in oxidative damage to biomolecule. body temperature in hairless animal, hibernating animals, new burns and animal adopted to cold. Free radical  It uses 90% of its respiratory energy for - It is defined as a molecule or a molecular species thermogenesis in response to cold for new born that contains one or more unpaired electrons and hibernating animals. and is capable of independent existence. - It persists for very short time 10-9 to 10-12 sec.  Here oxidation and phosphorylation are not coupled so energy is dissipitated in the form of - It is characterized by: heat.  Highly active  It contains a protein called UCP1 (thermogenin) at  Can generate new radicals by chain Inner mitochondrial membrane. treatment. FAST TRACK BASIC SCIENCE MBBS -1037-  Biochemistry  Can damage biomolecules, cell and tissues. - Radiation  Can cause cancer, atherosclerosis, CAD and - Ultraviolet light auto immune diseases. - Certain drugs, pesticides, anaesthetics  May be electrically neutral or either and industrial solvents positively or negatively charged. - Ozone - It is constantly generated in vivo: Antioxidant system  By accident of chemistry  A biological antioxidant may be defined as a  For specific metabolic purposes. substance present in low concentration in body - Precursors of free radicals: which act as defense mechanism system to  Oxygen (O2) protect us against potentially harmful free  Hydrogen peroxide (H2O2) radicals.  Hypochlorous acid (HClO)  In normal healthy state, balance is maintained  Ozone (O3) between free radical and antioxidant.  Nitrous acid (HNO2)  Classification: - Types of free radicals: I. Antioxidants in relation to lipid peroxidation. I. Reactive oxygen species (ROS) a. Preventive antioxidant: It blocks the initial - Superoxide (O2¯) production of free radicals. - Hydroxyl (OH.) E.g. catalase, glutathione peroxidase - Hydroperoxyl (HO2.) b. Chain breaking antioxidant: It inhibit the - Peroxyl (RO2.) propagative phase of lipid peroxidation e.g. - Alkoxyl (RO.) superoxide dismutase, vitamin E, uric acid. IV II. Reactive nitrogen species (RNS) II. Antioxidant according to their location - Nitric oxide (NO) a. Plasma antioxidants: -carotene, ascorbic - Nitrogen dioxide (NO2) acid, bilirubin, ceruloplasmin, transferrin. - Sources: I. Internally generated sources due to normal b. Cell membrane antioxidant: -tocopherol. cellular metabolism e.g. c. Intracellular antioxidant: Superoxide - Mitochondria dismutase, catalase, glutathione peroxide. - Phagocytes III. Antioxidant according to their nature and - Xanthine oxidase action. - Reaction involving iron and other a. Enzymatic antioxidant (biological) transition metals. Anti oxidant Location Properties - Arachidonate pathways Super oxide Mitochondria Removes - Peroxisomes dismutase cytosol superoxide radical - Exercise Glutathione Mitochondria Removes H2O2 + - Inflammation, ischemia/reperfusion. peroxidase cytosol organic II. Externally produced due to environmental hydroperoxide effects. - Cigarette smoke Catalase Mitochordria Removes H2O2 - Environmental pollutants cytosol -1038- FAST TRACK BASIC SCIENCE MBBS  Respi b. Non-enzymatic antioxidant system  Reperfusion can result in either survival of i. Nutrient antioxidant: Carotenoid, - cells or proceed to death of even normal tocopherol, ascorbic acid. cell by ROS production. ii. Metabolic antioxidant: Glutathione, vii. Male infertility: ceruloplasmin, albumin, bilirubin,  Free radicals are known to be reduce sperm transferrin, uric acid. motility and viability. Clinical Application [08,10] viii. Others:  Antoxidant neutralizes the effects of free radical  Role in parkinson disease, Alzheimer's and thus protects from harmful effects of it. disease, multiple sclerosis.  When there is failure of antioxidant system  Beneficial effect of free radicals: Phagocytosed following clinical manifestation can be appeared. bacteria are killed by activated macrophages by i. Dermatological manifestation in porphyria: reactive oxygen species Myelopero  porphyrin absorbs UV radiation NADH Superoxide dismutase xidase generation of singlet oxygen induces O2 oxidase O2¯ H2O2 HClO inflammatory reaction erythematous eruption. Kills bacteria ii. Respiratory diseases:  Direct exposure of lungs to 100% pure VITAMIN E oxygen is harmful, generates ROS and is  An antioxidant vitamin. known to destroy endothelium and causes  It includes eight naturally occurring tocopherols. lung edema.  The most active one is D--tocopherol.  Reactive oxygen species for long time is  Chemically they are isopreroids with 6-hydroxy responsible for: chromone ring. IV - Bronchopulmonary dysplasia. Source iii. Cataract: - Vegetable oils are rich sources of vitamin E,  Mostly due to aging and free radical leads where as liver and eggs are moderate. to lens protein degeneration. Daily requirement: iv. Atherosclerosis - RDA for -tocopherol:  Deposition of the fibrofatty plaque in the  For men - 10 mg intima of any artery endothelial cells  For women - 8 mg release ROS homocysteinethiolactone  Requirement increases as the intake of poly oxidation of LDL Nature of unsaturated fatty acid (PUFA) increases. apolipoprotein is altered attract phagocyte phagocytosis of LDL Metabolism Conversion of macrophage to foam cell  Vitamin E is absorbed along with fat in the small heaping atherosclerosis. intestine. v. Cancer:  Bile salts are necessary for the absorption.  Due to mutation of cells.  In liver, it is incorporated into lipoprotein (VLDL vi. Reperfusion injury: and LDL) and transported.  This is due to restoration of blood flow to  It is stored in adipose tissue, liver and muscle. ischemic area.  Normal plasma level < 1 mg/dl. FAST TRACK BASIC SCIENCE MBBS -1039-  Biochemistry Antioxidant function of Vit. E [10,11]  Prevents the peroxidation of PUFA in various  It serves as a chain breaking, free radical trapping tissues and membrane. Also protect RBC from antioxidant in cell membrane and plasma hemolysis by oxidizing agents. lipoproteins i.e. act as membrane antioxidant.  Prevents oxidation of vitamin A and carotenes. IV Respiratory acidosis [11, 06, 05, 04] Blood gas analysis - Respiratory acidosis occurs when there is pH PCO2 HCO3– accumulation of CO2 due to reduced effective Acute resp. acidosis   Normal or  alveolar ventilation. - Ratio of bicarbonate to carbonic acid: less than Chronic acidosis    20 Compensatory mechanism Cause - Excess carbonic acid is buffered by hemoglobin i. Airway obstruction: COPD, bronchospasm, and protein buffer system. asthma, pneumothorax - Kidney responds by conserving HCO3- and ii. Depression of respiratory centre: Anaesthesia, excreting H+ as NH4+. sedative, cerebral trauma, tumors, narcotics Clinical features iii. Neuromuscular disease: Poliomyelitis, tetanus, - Decreased respiratory rate, hypotension and motor neuron disease coma. iv. Pulmonary disease: Pulmonary fibrosis, - Dominated by the cause of hypoventilation (eg. Pneumonia paralysis, chest wall injury, chronic obstructive v. CNS trauma, tumor lungs disease) vi. Ascites, peritonitis - CO2 accumulation leads to drowsiness, peripheral vasodilation, tachycardia and vii. Sleep apnea tremors. -1040- FAST TRACK BASIC SCIENCE MBBS  Respi Respiratory Alkalosis [11, 06, 05, 04] Blood Gas Analysis - Respiratory alkalosis develops when there is a pH PCO2 HCO3 period of sustained hyperventilation resulting in a reduction of pCO2 and increase in plasma pH. Acute resp. alkalosis    - Ratio of bicarbonate to carbonic acid: more Chronic resp. alkalosis   Normal or  than 20 Compensatory mechanism Cause i. Hypoxia - Reduction in plasma bicarbonate ii. Increased intracranial pressure - Decrease in renal re-absorption of bicarbonate iii. Stimulation of respiratory centre by drugs like and decreased urinary excretion of H+ salicylates Clinical features iv. High altitude - Hyperventilation, muscle cramps and v. Excessive artificial ventilation paraesthesia vi. Psychoneurosis - Perioral and digital tingling vii. Hysteria - Trousseau's sign: Positive viii.Septicaemia - Chvostek's sign: positive ix. Febrile conditions - Tetany or seizures x. Meningitis xi. Congestive cardiac failure. IV FAST TRACK BASIC SCIENCE MBBS -1041-  Biochemistry SPECIAL POINT FOR MCQs 1. Biological oxidation: - Oxidases use oxygen as hydrogen acceptor. - Cytochrome oxidases consist of cyt.a and cyt.a3 and each contains heme, iron and copper. - Cytochrome oxidases catalyzes the transfer of electron from cytochrome-C to molecular oxygen. - Xanthine oxidase contain Mb and play role in conversion of purine bases to uric acid. - The high energy compound possess acid anhydride bonds (mostly phosphoanhydride bonds). - ATP is energy currency of cells which consist of adenine, a ribose, a triphosphate moiety (KU). - Two phosphoanhydride bonds in the triphosphate unit is responsible for high energy in ATP (KU). - In vertebrate, creatinine phosphate (phosphocreatinine) is stored in muscle and brain as energy rich compound whereas in intervebrates, phosphoargirine is energy rich compounds. - 1 molecules of ATP produces 7.3 cal energy (KU). IV - Phosphoenolpyruvate is compound with greatest free energy. 2. Citric acid cycle - Citric acid cycle enzymes are present in mitochondrial matrix. - Oxaloacetate is considered to play a catalytic role in citric acid cycles. - Oxidative decarboxylation of pyruvate to acetyl-CoA is catalyzed by pyruvate dehydrogenase complex (DDH) - PDH catalyzed reaction is irreversible. - Acetyl CoA is connecting between glycolysis and TCA cycle. - Substrate level phosphorylation in TCA cycle is phosphorylation of GDP to GTP when succinyl CoA is converted no succinate by succinate thiokinase. - Conversion of succinate to fumarate by succinate dehydrogenase results in formation of FADH2, not NADH. - There is not direct participation of oxygen in TCA cycle. - Aerobic nature of TCA cycle is due to fact that NAD+, FAD required for operation of the cycle can be regenerated in respiratory chain only in the presence of O2. - ATPs formed in TCA cycle -1042- FAST TRACK BASIC SCIENCE MBBS  Respi  ATP formed from 1 molecule of pyruvate is 15 ATP.  ATP formed from 1 molecule of acetyl COA 12 ATP.  ATP formed from complete oxidation of 1 molecule of glucose. One molecule of glucose 2 pyruvate By glycolysis 8 ATP. 2 molecule of pyruvate (BYTCA cycle) = 30 ATP. Total = 38 ATP. - No direct ATP synthesis takes place in TCA cycle. - TCA cycle mainly functions in mitochondria and order aerobic condition. - In TCA cycle, citrate is first formed so called citric acid cycle. - TCA cycle doesnot occur in RBC's. - Specific substrate for oxidative phosphosylation is ADP. - Fumarate of TCA cycle is an unsaturated dicarboxylic acid. - NADH is generated TCA is 3 in following reaction:  Isocitrate to - ketoglutarate.  -KG to succinyl COA  Malate to oxaloacetae : Final NADH is regerated. IV - FADH2 is generated in when succinate is converted to fumarate. - 1 NADH is equivalent to 3ATP. 1 FADH2 is equivalent to 2 ATP. 1 GTP is equivalent to 1 ATP. 3. Electron transport chain - It occurs in inner mitochondrial membrane. - It does not occur in RBC, cornea and lens of eye. - It is active when ATP need is high. - Inner mitochondrial membrane is impermeable to H+, K+ and OH¯. - ATP synthase activity is associated with mitochondrial enzyme complex -V (KU). - The P: 1 ratio for oxidation of FADH2 is 2. - The site of ETC inhibited by cyanide is cytochrome oxidase. - CN binds to Fe3+ of cytochrome oxidase. FAST TRACK BASIC SCIENCE MBBS -1043-  Biochemistry - In cyanide poisoning, venous blood is as red as arterial blood since O2 consumption is blocked. - Mutation in NADH- Q reductase results in leber's optic myopathy. - Valinomycin inhibits oxidative phosphorylation by making mitochondria permeable to potassium. 4. Vitamin E - Vitamin E is least toxic fat soluble vitamin. - Vitamin E is the most powerful anti-oxidant. - Selenium has to be found to decrease the requirement of Vitamin E and vice versa. - Requirement increases as the intake of poly unsaturated fatty acid (PUFA) increases. - It is stored in the adipose tissue. - It is absorbed along with fatty acids with the help of bile salts. - Dose above 1000 IU per day cause hypervitaminosis. 5. Respiratory acidosis and alkalosis - pCO2 > 45 mmHg = Respiratory acidosis - pCO2 > 35 mmHg = Respiratory alkalosis - Mechanisms of maintenance of acid-base disturbance are: IV - First line of defense: Blood buffer system, acts within fraction of seconds - Second line of defense: Respiratory mechanism, acts within 1-12 minutes - Third line of defense: Renal mechanism, acts within 2-3 days -1044- FAST TRACK BASIC SCIENCE MBBS