Biochemistry of Lipid Metabolism

A type of lipid composed of a glycerol backbone, two fatty acid chains attached to the glycerol backbone at C-1 & 2 positions, and a polar head group attached to C-3 of the glycerol backbone.

A type of lipid that is the main component of cell membranes, providing stability, fluidity, and permeability.

A type of lipid composed of a sphingosine backbone and different hydrophilic attachments: ceramides, sphingomyelins, and glycosphingolipids.

A type of sphingolipid that acts as a myelin sheath in the Central Nervous System (CNS), facilitating rapid and efficient transmission of electrical impulses between nerve cells.

A type of sphingolipid that are important components of cell membranes and serve as antigens in blood groups.

Complex molecules that contain both a lipidic (fatty) component and a proteinic (amino acid) component.

The process of breaking down dietary lipids (glycerolipids, glycerophospholipids, and sterides) into smaller units that can be absorbed by the body.

The process of mixing lipids with water to increase their surface area for digestion by enzymes.

The process of breaking down large fat globules into smaller droplets, coated with bile salts, to increase surface area for digestion.

Bile salts are produced by the liver and stored in the gallbladder. They are then released into the small intestine to aid in fat digestion.

Each triglyceride molecule has three ester bonds between glycerol and fatty acids. These bonds are broken down by lipases to release fatty acids and glycerol.

Phospholipid molecules contain four ester bonds. Each bond is targeted by a specific phospholipase enzyme (PL A1, PL A2, PL C, PL D).

Steride molecules, such as cholesterol esters, have an ester bond between cholesterol and a fatty acid. This bond is broken by cholesterol esterase.

β-oxidation is a process that occurs in mitochondria and peroxisomes, breaking down fatty acids into acetyl-CoA molecules. This process requires ATP, CoA, FAD, NAD, and water. It produces acetyl-CoA (or propionyl-CoA), FADH2, and NADH2.

Fatty acid activation involves attaching CoA to the fatty acid, requiring energy. The activated fatty acid then enters the β-oxidation pathway.

The oxidation of fatty acids involves a series of steps: activation, β-oxidation, the Krebs cycle, and the electron transport chain. Overall, this process generates ATP.

The breakdown of fatty acids into two-carbon units (acetyl-CoA) by a series of four enzymatic reactions.

A series of reactions that removes two carbon units from a fatty acid chain, generating acetyl-CoA, FADH2, and NADH.

The final step of β-oxidation, where a two-carbon unit is cleaved from a fatty acid chain, resulting in acetyl-CoA and a shorter fatty acid chain.

The process by which fatty acids are broken down to yield energy in the form of ATP.

The carbon unit produced by β-oxidation, which is used as fuel in the Krebs cycle to produce ATP.

The process by which molecules of acetyl-CoA are oxidized in the Krebs cycle to generate ATP.

The process by which electrons are transported through a series of proteins embedded in the mitochondrial membrane, generating ATP.

The number of ATP molecules produced from the complete oxidation of a fatty acid.

The process of breaking down fatty acids with an odd number of carbon atoms. The last round of beta-oxidation produces propionyl-CoA, which is converted to succinyl-CoA and enters the Krebs cycle.

The final product of beta-oxidation for fatty acids with an odd number of carbon atoms. It is a 3-carbon molecule that is converted to succinyl-CoA which then enters the Krebs cycle.

The conversion of propionyl-CoA to succinyl-CoA, allowing it to enter the Krebs cycle. This involves a series of enzymatic reactions.

Fatty acids with branched structures (methyl groups) are oxidized similarly to unbranched fatty acids; however, methyl groups attached to carbons create propionyl-CoA instead of acetyl-CoA during beta-oxidation.

Fatty acids with double bonds (unsaturated) are oxidized similarly to saturated fatty acids, except at the double bond position, requiring specific enzymes to handle the double bond.

The removal of two-carbon units (acetyl-CoA) from a fatty acid molecule, generating NADH, FADH2, and ATP. This process is repeated until the fatty acid is completely broken down.

Lipogenesis is the process of making fat (triglycerides) from excess carbohydrates or proteins. This process involves converting acetyl-CoA into fatty acids, which are then combined with glycerol to form triglycerides.

Malonyl-CoA is a molecule formed from acetyl-CoA and bicarbonate. It serves as a crucial building block in fatty acid synthesis, providing two-carbon units to lengthen the fatty acid chains.

Acetyl-ACP and Malonyl-ACP are activated forms of acetyl-CoA and malonyl-CoA, respectively. They are bound to acyl carrier protein (ACP), which facilitates their participation in fatty acid synthesis.

Lipogenesis involves a cycle of four reactions that repeat to lengthen the fatty acid chain. These reactions include condensation, reduction, dehydration, and reduction.

The Lipogenesis cycle continues by adding two-carbon units from malonyl-ACP to the growing fatty acid chain. This process repeats until palmitate, a 16-carbon fatty acid, is formed.

Cholesterol is a vital lipid molecule found in cell membranes and is a precursor for essential hormones like estrogen, testosterone, and vitamin D. It is sourced from food and synthesized by the liver.

Cholesterol biosynthesis is a complex process that involves several enzymatic reactions. It begins with the conversion of acetyl-CoA to mevalonate. This pathway proceeds through oxidation, cyclization, and the removal of methyl groups, ultimately producing cholesterol.

A high level of cholesterol in the bloodstream can contribute to the development of heart disease. Therefore, maintaining healthy cholesterol levels is important for cardiovascular health.

The process of converting carbohydrates to lipids involves converting glucose into pyruvate, which then becomes acetyl-CoA. Acetyl-CoA is a key precursor in the synthesis of fatty acids, cholesterol, and ketone bodies.

The conversion of proteins to carbohydrates involves deamination or transamination of amino acids to form pyruvate or oxaloacetate. Oxaloacetate is then converted to phosphoenolpyruvate (PEP), which is a precursor in gluconeogenesis, leading to glucose synthesis.

The conversion of proteins to lipids starts with the breakdown of proteins into amino acids. These amino acids can be converted to pyruvate, which then becomes acetyl-CoA. Acetyl-CoA is a precursor in the synthesis of fatty acids, cholesterol, and ketone bodies.

Lipoproteins are complex molecules containing both lipids (fats) and proteins. They are essential for transporting lipids throughout the body.

Chylomicrons are lipoproteins responsible for transporting triglycerides from the intestine to other tissues, like adipose tissue, for storage.

Low-density lipoproteins (LDLs) are lipoproteins responsible for transporting cholesterol from the liver to extrahepatic tissues (tissues outside the liver). They are often referred to as "bad cholesterol" because high LDL levels can contribute to heart disease.

Very-low-density lipoproteins (VLDLs) are lipoproteins that transport triglycerides from the liver to peripheral tissues (tissues outside the liver). They are often referred to as "bad cholesterol" because high VLDL levels can contribute to heart disease.

High-density lipoproteins (HDLs) are lipoproteins responsible for transporting excess cholesterol from extrahepatic tissues back to the liver for breakdown and excretion. They are often referred to as "good cholesterol" because high HDL levels are associated with lower risk of heart disease.