Microbial Biochemistry [STH 301] THIRD LECTURE
GLUCONEOGENESIS PATHWAY
In Gluconeogenesis seven out of the ten reactions of glycolysis are reversible while three irreversible reactions are bi-passed by alternative reactions (for example are) as shown in 1, 2, 3.
1. Synthesis of Phosphoenoyl Pyruvate: the synthesis of phosphenoyl pyruvate from pyruvate requires two enzymes namely;
i. pyruvate carboxylace.
ii. phosphoenoyl pyruvate caboxykinase.
oxaloacetate is decarboxylated and phosphorelated to form phosphoenol pyruvate in the presence of PEP carboxykinase.
2. Conversion of fructose-1,6-biphosphate to fructose-6-phosphate: Glucose-6-phosphate is converted to glucose in the presence of its enzyme glucose-6-phosphate, inorganic phosphate is also released. then glucose is subsequently released into the blood. Gluconeogenesis is an energy consuming process unlike in Glycolysis where energy are generated or formed.
LIPID METABOLISM
Lipid consist of Fat and oil. Fat is solid at room temperature while oil is liquid at room temperature, fat contains greater amount of saturated fatty acid and less amount of unsaturated fatty acid while oil contains greater amount unsaturated fatty acid and less amount of saturated fatty acids.
Fatty acids: Fatty acid consist of a long hydrocarbon chain and a terminal caboxyl group i.e.
The hydrocarbon chain can vary from n=2 to n=30
Nomenclature of fatty acid
n = 2 CH3COOH -------- ETHANOIC
n = 3 CH3CH2COOH -------- PROPANOIC
n = 4 CH3CH2CH2COOH -------- BUTNOIC
n = 5 CH3CH2CH2CH2COOH------ PENTANOIC
n = 6 CH3CH2CH2CH2CH2COOH -------- HEXANOIC
n = 8 CH3(CH2)6COOH -------- OCTANOIC
n = 10 CH3(CH2)8COOH -------- DECANOIC
n = 12 CH3(CH2)10COOH -------- DODECANOIC
n = 14 CH3(CH2)12COOH -------- TETRAANOIC
n = 18 CH3(CH2)16COOH -------- OCTAANOIC
OXIDATION OF FATTY ACID
There are three forms of oxidation of fatty acids namely:
1. alpha oxidation
2. beta oxidation
3. Omega oxidation of fatty acid.
However beta oxidation of fatty acid is the most common of oxidation in human because large amount of energy can be derived from it.
Beta oxidation of fatty acid
Fig 3.7 Beta oxidation of fatty acid.
Steps involved in beta oxidation of fatty acids
1. Activation of fatty acids: fatty acids are activated to produce fatty acylOA in the presence of ATP and coenzyme A. This process is catalysed by AcylOA synthase (thiokinase). This process occurs in the cytoplasm a protein carrier called carnitine carries the fatty acylOA across the mitochrondia for beta-oxidation to continue.
2. Fatty acylOA is converted to Trans D2-EnoylCOA in the presence of AcylCOA Dehydrogenase and FAD (Flavine adenine Dinucleotide) which remove hydrogen from carbon 2 and carbon 3.
3. Trans D2-EncylCOA is con-verted to L-Hydroxyl/COA in the presence of the enxyme EncylCOA hydratase and a water molecule is added to the compounds.
4. Convertion of L-Hydroxyl/COA to ketoacylCOA in the presence of NAD and hydroxylacylCOA dehydrogenase.
5. Conversion of ketoacylCOA to produce acetylCOA and other fatty acid chains in the presence of its enxyme ketoacylCOA thiolase: This sequence of reaction is repeated until the fatty acyl chain is completely degraded to acetyl COA.
Note: One cycle of Beta oxidation produces one mole of FAH2 and one mole of NADH2 and one mole of AcetylCOA.
1 mole of octadecanoic (18)
No of Cycles = Total number of Carbon/2 - 1
Exercise
1. Calculate the energy used i.e. total number of ATP produced when one mole of Exosanoic acid is metabolised in the body and write the general equation for the reaction where; Exosanoic acid = C19H39COOH
2. How many molecules of acetylCOA are produced and how many circles of beta-oxidation are needed to degrade the following.
i. Hexadecanoic acid CH3(CH2)14COOH
ii. Octadecanoic acid CH3(CH2)16COOH
and write the equation for the reaction.
n = 6 CH3CH2CH2CH2CH2COOH -------- HEXANOIC
n = 8 CH3(CH2)6COOH -------- OCTANOIC
n = 10 CH3(CH2)8COOH -------- DECANOIC
n = 12 CH3(CH2)10COOH -------- DODECANOIC
n = 14 CH3(CH2)12COOH -------- TETRAANOIC
n = 18 CH3(CH2)16COOH -------- OCTAANOIC
OXIDATION OF FATTY ACID
There are three forms of oxidation of fatty acids namely:
1. alpha oxidation
2. beta oxidation
3. Omega oxidation of fatty acid.
However beta oxidation of fatty acid is the most common of oxidation in human because large amount of energy can be derived from it.
Beta oxidation of fatty acid
Steps involved in beta oxidation of fatty acids
1. Activation of fatty acids: fatty acids are activated to produce fatty acylOA in the presence of ATP and coenzyme A. This process is catalysed by AcylOA synthase (thiokinase). This process occurs in the cytoplasm a protein carrier called carnitine carries the fatty acylOA across the mitochrondia for beta-oxidation to continue.
2. Fatty acylOA is converted to Trans D2-EnoylCOA in the presence of AcylCOA Dehydrogenase and FAD (Flavine adenine Dinucleotide) which remove hydrogen from carbon 2 and carbon 3.
3. Trans D2-EncylCOA is con-verted to L-Hydroxyl/COA in the presence of the enxyme EncylCOA hydratase and a water molecule is added to the compounds.
4. Convertion of L-Hydroxyl/COA to ketoacylCOA in the presence of NAD and hydroxylacylCOA dehydrogenase.
5. Conversion of ketoacylCOA to produce acetylCOA and other fatty acid chains in the presence of its enxyme ketoacylCOA thiolase: This sequence of reaction is repeated until the fatty acyl chain is completely degraded to acetyl COA.
Note: One cycle of Beta oxidation produces one mole of FAH2 and one mole of NADH2 and one mole of AcetylCOA.
1 mole of octadecanoic (18)
No of Cycles = Total number of Carbon/2 - 1
Exercise
1. Calculate the energy used i.e. total number of ATP produced when one mole of Exosanoic acid is metabolised in the body and write the general equation for the reaction where; Exosanoic acid = C19H39COOH
2. How many molecules of acetylCOA are produced and how many circles of beta-oxidation are needed to degrade the following.
i. Hexadecanoic acid CH3(CH2)14COOH
ii. Octadecanoic acid CH3(CH2)16COOH
and write the equation for the reaction.