lipolysis

What is lipolysis?

Lipolysis is the process of hydrolyzing stored triglycerides (TAGs) in the adipocytes of adipose tissue into free fatty acids and glycerol, with both products leaving the adipocytes.

What are some causes of lipolysis?

Lipolysis can be triggered by several factors, including starvation, a low or carbohydrate-free diet, periods of growth, and certain infectious diseases like tuberculosis (T.B) that induce a high catabolic state.

What is the key enzyme in the regulation of lipolysis?

The key enzyme in the regulation of lipolysis is hormone-sensitive triglyceride lipase (TAG lipase).

Where is TAG lipase sourced from?

TAG lipase is primarily sourced from adipocytes.

What is the action of TAG lipase in lipolysis?

TAG lipase hydrolyzes the ester linkage of triglycerides (TAGs), releasing free fatty acids (FFA).

What are the products of TAG hydrolysis in lipolysis?

The products of TAG hydrolysis include diacylglycerol (DAG), which is acted upon by DAG lipase to produce more FFA and monoacylglycerol (MAG). MAG is then acted upon by MAG lipase, resulting in the production of additional FFA and glycerol.

What happens to free fatty acids produced from lipolysis?

Free fatty acids are taken up by most tissues for oxidation to produce energy, with the exception of the brain due to the presence of the blood-brain barrier (BBB).

What is the fate of glycerol after lipolysis?

Glycerol passes into the bloodstream and then to the liver, where it is converted into glycerol-3-P by glycerol kinase. Glycerol-3-P can enter either glycolysis to produce energy or gluconeogenesis for the formation of glucose.

How is hormone-sensitive TAG lipase regulated?

Hormone-sensitive TAG lipase is regulated through a covalent modification mechanism involving phosphorylation and dephosphorylation.

What is the active form of hormone-sensitive TAG lipase?

The active form is the phosphorylated form, which is achieved through the action of protein kinase.

What is the inactive form of hormone-sensitive TAG lipase?

The inactive form is the dephosphorylated form, which is obtained by the action of protein phosphatase.

What are lipolytic factors that stimulate lipolysis?

Lipolytic factors that stimulate lipolysis include lipolytic hormones like catecholamines, growth hormone, glucagon, α and β melanocyte stimulating hormone (MSH), vasopressin, TSH, and ACTH. These hormones stimulate adenylate cyclase.

What are the effects of glucocorticoids and thyroxine on lipolysis?

Glucocorticoids and thyroxine stimulate adenylate cyclase by increasing its expression at the gene level and inhibit phosphodiesterase.

What are fat mobilizing substances produced by?

Fat mobilizing substances are produced by the pituitary gland, and they stimulate lipolysis.

How does methylxanthine (e.g., caffeine) affect lipolysis?

Methylxanthine, such as caffeine, inhibits phosphodiesterase, which can stimulate lipolysis.

How does the sympathetic nervous system stimulate lipolysis?

The sympathetic nervous system stimulates lipolysis by releasing noradrenaline in the adipose tissue.

What are anti-lipolytic factors?

Anti-lipolytic factors are substances that inhibit the process of lipolysis.

What effect do PGE1 and nicotinic acid have on lipolysis?

PGE1 and nicotinic acid inhibit adenylate cyclase, which in turn inhibits lipolysis.

What is the role of insulin and prolactin in inhibiting lipolysis?

Insulin and prolactin stimulate phosphodiesterase and hormone-sensitive TAG lipase phosphatase, both of which inhibit lipolysis.

What is the definition of ß-Oxidation of fatty acids?

It is the principal pathway for catabolism of fatty acids, involving the oxidation of the ß-carbon to produce ß-keto acids, catalyzed by a group of enzymes known collectively as fatty acid oxidase.

Where does ß-Oxidation of fatty acids primarily occur intracellularly?

It primarily occurs in the mitochondrial matrix.

In which organs is ß-Oxidation of fatty acids most prominent, and what percentage of their fuel comes from it?

It is most prominent in the liver and heart, which derive 80% of their fuel from ß-oxidation. It also occurs in skeletal muscles, adipose tissue, lung, and testis.

Why doesn't ß-oxidation occur in brain cells, and what do brain cells rely on for energy instead?

ß-Oxidation doesn't occur in brain cells because fatty acids can't cross the blood-brain barrier (BBB). Brain cells depend on ketone bodies as their source of energy.

What are the main steps involved in ß-Oxidation of fatty acids?

The main steps include: Uptake of fatty acids into the cell. Activation of fatty acids into acyl CoA in the cytosol. Transport of acyl CoA into the mitochondrial matrix. Utilization of mitochondrial enzymes for ß-oxidation.

How is long-chain acyl CoA transported into the mitochondrial matrix, and what is this process called?

Long-chain acyl CoA is transported by a specialized carrier called carnitine, present in the inner mitochondrial membrane. This process is called the carnitine shuttle.

What is carnitine, and where is it synthesized?

Carnitine is synthesized from lysine and methionine in the liver and kidneys. It is widely distributed in the body, particularly in muscles.

Functions of carnitine

Carnitine has the following functions: — Transport of long chain acyl CoA across the inner mitochondrial membrane to the mitochondrial matrix for ß-oxidation where enzymes of ß-oxidation are present.

What is the first enzyme involved in the carnitine shuttle, and what is it called for palmitic acid?

The first enzyme is Carnitine Acyl Transferase-I (CPT-I). For palmitic acid, it is called Carnitine Palmitoyl Transferase-I.

Where is Carnitine Acyl Transferase-I located?

Carnitine Acyl Transferase-I presents on the outer surface of the inner mitochondrial membrane.

What is the function of Carnitine Acyl Transferase-I?

It transfers the acyl group to carnitine to form acyl carnitine.

What is the second enzyme involved in the carnitine shuttle?

The second enzyme is Carnitine Acyl Carnitine Translocase.

Where is Carnitine Acyl Carnitine Translocase located?

It presents in the inner mitochondrial membrane.

What is the function of Carnitine Acyl Carnitine Translocase?

It transports acyl carnitine into the mitochondrial matrix across the inner mitochondrial membrane in exchange with carnitine.

What is the third enzyme involved in the carnitine shuttle, and what is it called for palmitic acid?

The third enzyme is Carnitine Acyl Carnitine Transferase-II (CPT-II). For palmitic acid, it is called Carnitine Palmitoyl Transferase-II.

Where is Carnitine Acyl Carnitine Transferase-II located?

Carnitine Acyl Carnitine Transferase-II presents on the inner surface of the inner mitochondrial membrane.

What is the function of Carnitine Acyl Carnitine Transferase-II?

It transfers the acyl group from acyl carnitine to form acyl CoA again.

What is the first step in ß-oxidation of fatty acids with even-numbered carbon atoms, and what is it called?

The first step is Activation

How is the acyl CoA (active fatty acid) transported to the mitochondrial matrix in ß-oxidation?

Acyl CoA is transported via the carnitine shuttle to the mitochondrial matrix.

What is the second step in ß-oxidation, and what is its coenzyme?

The second step is Desaturation or Dehydrogenation, catalyzed by acyl CoA dehydrogenase with FAD as its coenzyme. FADH2 produced is oxidatively phosphorylated in the mitochondrial respiratory chain, producing 2 ATP. This step is the only irreversible reaction in ß-oxidation.

What is the third step in ß-oxidation, and what does it involve?

The third step is Hydration, catalyzed by enoyl CoA hydratase, which adds water to saturate the double bond.

What is the fourth step in ß-oxidation, and what enzyme catalyzes it?

The fourth step is Oxidation of ß-carbon, catalyzed by ß-hydroxy acyl CoA dehydrogenase. Its coenzyme is NAD, and NADH+H+ produced in this step is oxidatively phosphorylated in the mitochondrial respiratory chain, producing 3 ATP.

What is the fifth step in ß-oxidation, and what enzyme catalyzes it?

The fifth step is Splitting, catalyzed by ß-ketoacyl CoA thiolase or acyl CoA acyl transferase. It causes cleavage between C2 & C3, producing acetyl CoA. This acetyl CoA enters the TCA cycle to be oxidized, producing 12 ATP. Additionally, it results in a new acyl CoA that is shorter than the previous one by two carbon atoms, which undergoes repetitive cycles of ß-oxidation from step II. The number of these cycles equals N/2 -1, where "N" is the total number of carbon atoms in the fatty acid.

How is the net energy gained calculated in bioenergetics?

Net energy gained is calculated as Energy produced minus energy loss. In the context of fatty acid metabolism, it can be expressed as {N/2 - 1 X 5 ATP + N/2 X 12 ATP} - 2 ATP.

What are the sources of ATP in the net energy gained during ß-oxidation?

5 ATP are obtained from {3 ATP from the oxidation of NADH+H+ and 2 ATP from the oxidation of FADH2}. Additionally, 12 ATP are generated from the oxidation of acetyl CoA in the TCA cycle.

How much ATP is used for fatty acid activation, and how often does this occur?

2 ATP are used for fatty acid activation, and this activation step occurs once.

Can you provide an example calculation for the net energy gained during the ß-oxidation of palmitic acid (16C)?

For example, ß-oxidation of palmitic acid (16C) can be calculated as {16/2 - 1 X 5 ATP + 16/2 X 12 ATP} - 2 ATP \= {8 - 1 X 5 ATP + 8 X 12 ATP} - 2 ATP \= 129 ATP.

What are the common dietary lipids, and what are their main components?

Dietary lipids contain mainly TAGs (triacylglycerols), which mainly consist of palmitic acid, stearic acid, and oleic acid.

What is the rate-limiting enzyme in the regulation of ß-oxidation?

The rate-limiting enzyme is carnitine acyl transferase-I.

How does excess ATP affect ß-oxidation, and what factor does it depend on?

Excess ATP inhibits ß-oxidation. This inhibition occurs according to the energy needs of the cell.

What is one of the important roles of ß-oxidation?

ß-oxidation is crucial for energy production during starvation.

What is produced as a result of the last four carbon atoms in ß-oxidation, and what can it be converted into?

The last four carbon atom product of ß-oxidation is acetoacetyl CoA, which can be converted into acetoacetate, one of the ketone bodies.

What is one of the important outcomes of ß-oxidation in terms of molecule production, and what are the various fates of acetyl CoA?

ß-oxidation produces acetyl CoA, which can have several fates, including ketogenesis (formation of ketone bodies), steroid formation (cholesterol, bile acids, steroid hormones, and vitamin D3), lipogenesis (fatty acid and TAGs synthesis), oxidation in the TCA cycle for energy production, and acetylation reactions used in detoxication reactions, histone acetylation, and the formation of polysaccharides, melatonin, and acetylcholine.

What are the sources of acetyl CoA?

The sources of acetyl CoA include the oxidation of fats, carbohydrates such as glucose and pyruvate (through glycolysis and oxidative decarboxylation), proteins, particularly gluconeogenic amino acids and ketogenic amino acids, and ethanol oxidation.

How is acetyl CoA produced from fats?

Acetyl CoA is produced from the oxidation of fats.

How is acetyl CoA generated from carbohydrates like glucose and pyruvate?

Acetyl CoA is generated from carbohydrates, such as glucose and pyruvate, through processes like glycolysis and oxidative decarboxylation.

What is another source of acetyl CoA besides fats and carbohydrates?

Proteins are another source of acetyl CoA.

How are gluconeogenic amino acids related to the production of acetyl CoA?

Gluconeogenic amino acids are related to the production of acetyl CoA through processes like glycolysis and oxidative decarboxylation.

What role do ketogenic amino acids play in acetyl CoA production?

Ketogenic amino acids can either directly produce acetyl CoA or generate acetoacetate, which is then converted to acetyl CoA.

How is acetyl CoA formed during ethanol oxidation?

Acetyl CoA is formed during ethanol oxidatio

What does ß-oxidation of odd-number fatty acids produce?

ß-oxidation of odd-number fatty acids produces acetyl CoA until the last three carbon atom products, which is propionyl CoA.

What happens to propionyl CoA produced in ß-oxidation of odd-number fatty acids?

Propionyl CoA is converted into succinyl CoA.

What are the fates of succinyl CoA?

Succinyl CoA has several fates, including oxidation in the TCA cycle, involvement in gluconeogenesis, activation of ketone bodies, participation in heme synthesis, and involvement in detoxication reactions.

In which metabolic pathway is succinyl CoA oxidized?

Succinyl CoA is oxidized in the TCA (Tricarboxylic Acid) cycle.

How does succinyl CoA contribute to gluconeogenesis?

Succinyl CoA plays a role in gluconeogenesis, which is the process of synthesizing glucose from non-carbohydrate precursors.

What is the significance of succinyl CoA in ketone body metabolism?

Succinyl CoA is involved in the activation of ketone bodies, a process important for energy production during fasting or low-carbohydrate conditions.

In what process is succinyl CoA utilized in heme synthesis?

Succinyl CoA is utilized in heme synthesis, a crucial step in the production of hemoglobin and other heme-containing molecules.

How is succinyl CoA involved in detoxication reactions?

Succinyl CoA participates in detoxication reactions, which are essential for the body's ability to neutralize and eliminate toxins and harmful substances.

What is ß-oxidation?

ß-oxidation is a metabolic pathway involved in the breakdown of fatty acids.

What is the significance of the ß-carbon of a fatty acid?

The ß-carbon of a fatty acid is crucial in the ß-oxidation process.

Where does ß-oxidation primarily occur within cells?

ß-oxidation primarily occurs in the mitochondrial matrix.

In which organ or tissue does ß-oxidation not occur?

ß-oxidation does not occur in the brain.

What is ß-oxidation known as in the context of fatty acid metabolism?

ß-oxidation is considered a major pathway in fatty acid metabolism.

How are carbon atoms removed during ß-oxidation?

During ß-oxidation, carbon atoms are removed two at a time in the form of Acetyl CoA.

What is required for the ß-oxidation process?

ß-oxidation requires COASH (Coenzyme A).

What is the primary outcome of ß-oxidation in terms of energy?

ß-oxidation generates energy.

What are the main products of ß-oxidation?

ß-oxidation leads to energy production, the production of acetyl CoA, and the production of ketone bodies.

What are some conditions associated with ß-oxidation disorders, such as AFLP and Jamaican vomiting sickness?

AFLP (Acute fatty liver of pregnancy) and Jamaican vomiting sickness are associated with ß-oxidation disorders.

What is α-oxidation?

α-oxidation is a metabolic pathway involved in the oxidation of certain fatty acids.

What is the significance of the α-carbon of a fatty acid in α-oxidation?

The α-carbon of a fatty acid is crucial in the α-oxidation process.

Where does α-oxidation primarily occur within cells?

α-oxidation primarily occurs in microsomes.

In which organ or tissue does α-oxidation occur, specifically in the brain and nervous tissues?

α-oxidation takes place in the brain and nervous tissues.

How does α-oxidation compare to ß-oxidation in terms of its significance?

α-oxidation is considered a minor pathway compared to ß-oxidation.

How are carbon atoms removed during α-oxidation?

During α-oxidation, carbon atoms are removed one at a time in the form of CO2 (carbon dioxide).

Is COASH (Coenzyme A) required for α-oxidation?

Unlike ß-oxidation, α-oxidation does not require COASH (Coenzyme A).

Does α-oxidation generate energy like ß-oxidation?

No, α-oxidation does not generate energy.

What is the primary purpose of α-oxidation in terms of fatty acid metabolism?

α-oxidation is a mechanism for the oxidation of branched-chain fatty acids that are methylated at the ß-position.

What is one specific outcome of α-oxidation, such as the production of certain fatty acids for brain lipids?

α-oxidation can result in the production of α-hydroxy fatty acids, which are important for brain lipid metabolism.

What is a medical condition associated with α-oxidation disorders, like Refsum's disease?

Refsum's disease is a medical condition associated with α-oxidation disorders.

What is ω-oxidation?

ω-oxidation is a metabolic pathway involved in the oxidation of certain fatty acids.

What is the significance of the ω-carbon of a fatty acid in ω-oxidation?

The ω-carbon of a fatty acid is crucial in the ω-oxidation process.

Where does ω-oxidation primarily occur within cells?

ω-oxidation primarily occurs in the endoplasmic reticulum (ER).

Does ω-oxidation occur in the brain?

No, ω-oxidation does not occur in the brain.

How does ω-oxidation compare to other pathways like ß-oxidation and α-oxidation in terms of its significance?

ω-oxidation is considered a minor pathway compared to other oxidation pathways.

Is there a removal of any carbon atoms during ω-oxidation?

No, ω-oxidation does not involve the removal of any carbon atoms.

Is COASH (Coenzyme A) required for ω-oxidation?

Unlike some other oxidation pathways, ω-oxidation does not require COASH (Coenzyme A).

Does ω-oxidation generate energy like some other oxidation pathways?

No, ω-oxidation does not generate energy.

What is the primary outcome of ω-oxidation, such as the production of specific compounds?

ω-oxidation results in the production of dicarboxylic acids.

What medical condition is associated with ω-oxidation disorders, like organic dicarboxylic aciduria?

Organic dicarboxylic aciduria is a medical condition associated with ω-oxidation disorders.

What are ketone bodies?

Ketone bodies are partially oxidized fatty acids produced by the liver.

How many types of ketone bodies are there, and what are they?

There are three types of ketone bodies, which include Acetoacetate (acetoacetic acid), ß-Hydroxybutyric acid, and Acetone.