Мetabolism - phases I and II

Summary

This video provides a comprehensive overview of human metabolism, detailing the breakdown and synthesis of essential nutrients. It covers the catabolic processes, including the breakdown of carbohydrates, proteins, and lipids to produce energy or building blocks like acetyl-CoA, and the anabolic processes where macromolecules such as glycogen, proteins, and lipids are synthesized. Key enzymatic reactions and hormone regulation, particularly the role of insulin, are emphasized. The video also explains glycolysis, fatty acid biosynthesis, gluconeogenesis, and the fate of pyruvate in aerobic vs. anaerobic conditions, offering a holistic view of metabolic pathways and energy production in cells.

Takeaways

• 😀 Essential nutrients for metabolism are carbohydrates, proteins, and lipids, and each type of nutrient undergoes specific breakdown processes in the body.
• 🍞 Carbohydrates are primarily broken down into monosaccharides like glucose, fructose, and galactose. This breakdown begins in the mouth and continues in the small intestine.
• 🍖 Proteins are broken down into amino acids through processes starting in the stomach and continuing in the small intestine with the help of enzymes like pepsin and trypsin.
• 🥩 Lipids (fats) are broken down into fatty acids and glycerol, primarily through the action of hormone-sensitive lipase, with the breakdown process regulated by glucagon and adrenaline.
• 💪 Our body stores carbohydrates as glycogen, lipids as triacylglycerols, but there is no dedicated storage for proteins; each protein serves a specific function and undergoes degradation when needed.
• 🔬 The first phase of metabolism involves the catabolic processes of breaking down nutrients (carbohydrates, proteins, lipids) into smaller monomers, with minimal energy release during this phase.
• 🧪 The second phase converts these monomers into acetyl-CoA, which is a crucial molecule for further energy production, either directly (fatty acids) or indirectly (glucose via pyruvate).
• ⚡ The breakdown of glucose into pyruvate (via glycolysis) and the subsequent conversion of pyruvate into acetyl-CoA (via oxidative decarboxylation) releases small amounts of energy (NADH, ATP).
• 🌱 Under anaerobic conditions, pyruvate is converted into lactate through lactate dehydrogenase instead of proceeding to acetyl-CoA, which is typical in muscle cells or cells without mitochondria.
• 💡 In the third phase of metabolism, acetyl-CoA enters the Krebs cycle for further energy production, which is where the majority of energy is harvested in the form of ATP.
• 🔄 Anabolic processes, which are the reverse of catabolic processes, involve the synthesis of complex molecules from simpler ones, such as glycogen from glucose, and fatty acids from acetyl-CoA, primarily regulated by insulin.

Q & A

What are the three essential nutrients we take in with food?

The three essential nutrients are carbohydrates, proteins, and lipids.

How are carbohydrates broken down in the body?

Carbohydrates are initially broken down in the oral cavity with salivary alpha-amylase, then further broken down in the small intestine with pancreatic amylase. The final breakdown occurs with disaccharidases converting them into monosaccharides like glucose, fructose, and galactose.

What is the primary role of glycogen in the body?

Glycogen serves as the storage form of carbohydrates in the body, primarily stored in the liver and muscles. It is broken down into glucose-1-phosphate and glucose when energy is needed.

Why do we not have a storehouse for proteins like we do for carbohydrates and lipids?

Proteins do not have a storage form because each protein has a specific function. Instead, proteins are broken down as needed, with degradation occurring in lysosomes or by ubiquitination of aged proteins.

How are lipids, such as triacylglycerols, broken down in the body?

Lipids are broken down into fatty acids and glycerol by the enzyme hormone-sensitive lipase. This process is activated by hormones like glucagon and adrenaline.

What happens in the second phase of metabolism?

The second phase involves the conversion of all breakdown products (monomers like glucose, fatty acids, and amino acids) into a single molecule called acetyl-CoA. This occurs through various metabolic pathways such as glycolysis, oxidative decarboxylation, and beta-oxidation.

How does glycolysis differ in aerobic and anaerobic conditions?

In aerobic conditions, glycolysis produces pyruvate, which is converted to acetyl-CoA, entering the Krebs cycle. In anaerobic conditions, pyruvate is converted to lactate through lactate dehydrogenase, which occurs in cells without mitochondria or during oxygen deprivation, like in muscle cells or tumors.

What is the role of acetyl-CoA in metabolism?

Acetyl-CoA is a central molecule in metabolism. It is produced from the breakdown of carbohydrates, lipids, and some amino acids, and is then used to generate energy in the Krebs cycle or to synthesize other molecules in anabolic processes.

How is energy released in the first and second phases of metabolism?

In the first phase, no energy is released because there are no oxidation reactions. In the second phase, energy is released as ATP during glycolysis and oxidative decarboxylation, although the reduced cofactors NADH+H and FADH2 produced will contribute to energy release in the third phase.

Can the body synthesize all the amino acids it needs?

No, the body can only synthesize non-essential amino acids. The essential amino acids must be obtained through food since they cannot be synthesized by the body.