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BASIC METABOLIC PATHWAYSMETABOLISMTerm used to describe the interconversion of chemical compounds in the body It includes;Pathways taken by the individual molecules Their interrelationships Mechanisms that regulate the flow of metabolites through the pathwaysCategories of metabolic pathways(1) ANABOLIC PATHWAYS Involved in the synthesis of larger and more complex compounds from smaller precursors Eg., synthesis of proteins from amino acids; synthesis of reserves of triacylglyc
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BASIC METABOLIC BASIC METABOLIC PATHWAYSPATHWAYS
METABOLISMMETABOLISM
Term used to describe the Term used to describe the interconversion of chemical interconversion of chemical compounds in the bodycompounds in the body
It includes;It includes;– Pathways taken by the individual Pathways taken by the individual
moleculesmolecules– Their interrelationships Their interrelationships – Mechanisms that regulate the flow of Mechanisms that regulate the flow of
metabolites through the pathways metabolites through the pathways
Categories of Categories of metabolic pathwaysmetabolic pathways(1) ANABOLIC PATHWAYS(1) ANABOLIC PATHWAYS Involved in the synthesis of larger Involved in the synthesis of larger
and more complex compounds and more complex compounds from smaller precursorsfrom smaller precursors
Eg., synthesis of proteins from Eg., synthesis of proteins from amino acids; synthesis of reserves amino acids; synthesis of reserves of triacylglycerol and glycogenof triacylglycerol and glycogen
EndothermicEndothermic
Categories of Categories of metabolic pathwaysmetabolic pathways(2) CATABOLIC PATHWAYS(2) CATABOLIC PATHWAYS Involved in the breakdown of larger Involved in the breakdown of larger
moleculesmolecules Commonly involving oxidative Commonly involving oxidative
reactionsreactions ExothermicExothermic Producing reducing equivalentsProducing reducing equivalents Mainly via the respiratory chain, Mainly via the respiratory chain,
ATPATP
Categories of Categories of metabolic pathwaysmetabolic pathways
(3) AMPHIBOLIC PATHWAYS(3) AMPHIBOLIC PATHWAYS ““cross roads” of metabolismcross roads” of metabolism Acting as links between the Acting as links between the
anabolic and catabolic pathwaysanabolic and catabolic pathways Example is the citric acid cycleExample is the citric acid cycle
aerobicanaerobic
Source of reducing equivalents (NADPH)
GLUCONEOGENESIS- is the process of
forming glucose from non-carbohydrate precursors (e.g,
lactate, amino acids, and glycerol)
1
2
3
4
Source of fatty acid
Body’s main fuel reserve
1
2
3
Acetoacetate and 3-hydroxybutyrate – important
fuels in prolonged fasting
Essential/nonessential amino acids
1
Gluconeogenesis
32
THE LIVER Glycogenesis Glycogenolysis Gluconeogenesis
Only fuel
hydrolysis
Lipogenesis
Largest plasma lipoproteins
Main fuel reserve in the body
Transported to extrahepatic tissues (acting as a fuel in prolonged fasting
Alteration of membrane permeability
GLUCONEOGENESISGLUCONEOGENESIS
Lactate and pyruvate are the Lactate and pyruvate are the substrates which are formed in the substrates which are formed in the cytosol and enter the mitochondrion to cytosol and enter the mitochondrion to yield yield oxaloacetateoxaloacetate (precursor) (precursor)
GLUCOGENIC – amino acids that yield GLUCOGENIC – amino acids that yield pyruvate and 4- and 5- C pyruvate and 4- and 5- C intermediates of the TCA cycleintermediates of the TCA cycle
KETOGENIC – amino acids that give KETOGENIC – amino acids that give rise to acetyl-CoArise to acetyl-CoA
INSULININSULIN Secreted by the Secreted by the -islet cells in response to -islet cells in response to
increased blood glucose concentration (fed state)increased blood glucose concentration (fed state) Controls glucose uptake into the muscle and Controls glucose uptake into the muscle and
adipose tissue adipose tissue GLUT-4 migrate to the cell surface in response to GLUT-4 migrate to the cell surface in response to
insulininsulin Acts to stimulate Acts to stimulate glycogen synthaseglycogen synthase and inhibit and inhibit
glycogen phosphorylaseglycogen phosphorylase (liver and skeletal (liver and skeletal muscles)muscles)
In adipose tissue, it stimulates glucose uptake, its In adipose tissue, it stimulates glucose uptake, its conversion to FA and their esterification to TGconversion to FA and their esterification to TG
Glucose uptake in the liver is insulin independentGlucose uptake in the liver is insulin independent
GLUCAGONGLUCAGON
Secreted by the Secreted by the -cells in -cells in response to the fall in blood response to the fall in blood glucose concentrationglucose concentration
Inhibits Inhibits glycogen synthaseglycogen synthase and and activates activates glycogen phosphorylaseglycogen phosphorylase
In adipose tissue, increase in In adipose tissue, increase in glucagon results to inhibition of glucagon results to inhibition of lipogenesislipogenesis
CLINICAL ASPECTSCLINICAL ASPECTS
Death occurs when essential tissue Death occurs when essential tissue protein are catabolized and not protein are catabolized and not replaced (due to prolonged starvation)replaced (due to prolonged starvation)
KETOSIS results due to high demand for KETOSIS results due to high demand for glucose by the fetus, and lactose glucose by the fetus, and lactose synthesis in lactationsynthesis in lactation
TYPE 1 DIABETES MELLITUS – due to TYPE 1 DIABETES MELLITUS – due to lack of insulin or absence of insulin to lack of insulin or absence of insulin to stimulate glucose uptake and utilization stimulate glucose uptake and utilization