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Lesson -9 Anaerobic respiration (Fermentation) (Concept and mechanism Dr. P. K. Agrawal M.Sc., Ph.D., CSIR NET (URF), SRF, GATE, FIAZ Youtube Channel with over 1 million views 20 Years of Pre-medical teaching experience Ex Faculty, Allen Career Institute, Kota Visit following link to follow my profile https://unacademy.com/user/biologybypkagrawal-6909
Anaerobic respiration (Fermentation) It is a kind of oxidation, which occurs in the absence of oxygen (anaerobic conditions). Due to the absence of oxygen the pyruvic acid is not completely oxidised to CO2 and water In higher organisms, this kind of respiration is normally absent or if present it is not the major source of energy. . In human being, it is found mainly in skeletal muscles (also in cardiac muscles, retina and heart muscles). In lower organisms, especially in anaerobic micro-organisms and endoparasites, it is the chief form of respiration. In micro-organisms, term Fermentation is more commonly used for anaerobic respiration.
Fermentation meaning and types In micro-organisms such as Yeast, the Pyruvic acid (formed by glycolysis) undergoes anaerobic respiration to form ethyl alcohol, with the help of enzymes such as zymase. Such an anaerobic respiration is called fermentation. . Fermentation can be carried out outside the cell with the help of some enzymes such as zymase. This was first demonstrated by Buchner (1897). Fermentation is also called zymosis. . In some bacteria, fungi and in RBCs and muscles, the pyruvic acid is changed to lactic acid (instead of ethanol). This is called lactic acid fermentation. So, fermentation can be of two types (1) Alcoholic fermentation - Yeast and microorganisms (2) Lactic acid fermentation Mammalian skeletal muscles, RBCs, some microorganisms etc
Basic Concept! Remember that fermentation itself does not produce any energy. Moreover, this process consumes the NADH+H for nothing, which could generate 3 ATPS during ETS. . A cell/organism does not have an unlimited supply of NAD+. Under aerobic conditions, NADH+H are oxidised by ETS and fresh supply of NAD+ is maintained for glycolysis and Kreb's cycle. But under aerobic conditions, there is no ETS. Similarly, in RBCs, there is no mitochondria for ETS to occur. In such a situation, fermentation comes into picture. So, This process is meant to maintain a continuous fresh supply of NAD+ to the cells for glycolysis to continue during anaerobic process so, that the organism can enjoy 2ATPs from glycolysis continuously. . So, fermentation is basicallya reductive process in which main substrate i.e. pyruvic acid is reduced (to alcohol or lactic acid) and NADH+H are oxidised to NAD*.
CONCEPT Recycling of NAD Yeast Aloohol (20) NAD NADH+H'. NADH + H NAD uvio acid (3o) Angerobic condition Glucose Anaerobic condition Glycoyss (oxidation) (Fermentation) Reductior e Dr. P. K.Agrawal Laotic acid (30) RBCs, Skeletal muscles
Alcoholic fermentation It commonly occurs in many fungi, e.g., Yeast, Rhizopus etc. In this type of fermentation, the pyruvic acid (which is formed in Glycolysis) is changed to acetaldehyde with the release of a CO2 molecule. . The reaction occurs in the presence of TPP (thiamine pyrophosphate) and pyruvate decarboxylase c":-co-cooH-Pyruvate decarboxylase, TPP Pyruvic acid Acetaldehyde In the next step, acetaldehyde is reduced to ethyl alcohol (ethanol) with the help of reduced coenzyme [NADH H]. Alcohol dehydrogenase CH,CHO Acetaldehyde CH3CH2OH Ethyl alcohol NADH+H NAD+
Lactic acid fermentation It occurs in RBCs, muscles, certain bacteria and some fungi. In this process, the pyruvic acid is converted into lactic acid No CO2 is produced in the reaction. The reaction occurs in the presence of enzyme lactic dehydrogenase, FMN proteins and Zn2 ions. NADH +H NAD H O H-C-C -C LDH Pyruvic acid Lactic acid Lactic dehydrogenase + -co-cooH Pyruvic acid CHCO-COOH CH -CHOH COOH - Lactic acid NADH+H NAD*
Fermentation in humans . Red blood cells, which lack mitochondria, can use only the lactic acid pathway. . They cannot directly use oxygen for energy production. This spares the oxygen they carry for delivery to other body cells. Except for red blood cells, anaerobic metabolism occurs for only a shot period of time in tissues, which have poor oxygen supply or if they have energy requirements in excess of their aerobic ability. . For RBCs, lactic acid fermentation is a permanent feature. Anaerobic metabolism occurs in the skeletal muscles and heart when the ratio of oxygen supply to oxygen need falls below a critical level. Anaerobic metabolism in body tissues (except RBCs) is an emergency procedure that provides some ATP until the emergency (oxygen deficiency) is passed . Excessive lactic acid production by muscles, however, is associated with pain and muscle fatigue
Ischemia (Inadequate blood flow to an organ) Ischemia refers to inadequate blood flow to an organ. The rate of oxygen delivery is insufficient to maintain aerobic respiration Inadequate blood flow to the heart is called myocardial ischemia. It occurs if the coronary blood flow is occluded by atherosclerosis. People with myocardial ischemia often experience angina pectoris severe pain in the chest and left arm area This pain is associated with increased levels of lactic acid which is produced by the ischemic heart muscle. .If the ischemia is prolonged, the cells may die and produce an area called an infarct
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