Basics of Metabolism

Summary

Metabolism is the balance between the body's processes of building (anabolism) and breaking down (catabolism) substances. Carbohydrates, proteins, and fats are processed into energy or stored within the body. Glucose is broken down into pyruvate and further into acetyl-CoA, which fuels the TCA cycle, producing ATP. Proteins are broken into amino acids, while fats are stored as adipose tissue. Hormones like insulin and glucagon regulate these processes, with some reactions being reversible. The cycle is driven by energy demand, explaining how excess intake can lead to fat storage.

Takeaways

• 😀 Metabolism is the sum of all chemical reactions in the body, involving both catabolic (breaking down) and anabolic (building up) processes.
• 😀 Carbohydrates are broken down into glucose, which is further converted into pyruvate and then into acetyl-CoA to produce ATP in the TCA cycle.
• 😀 The TCA cycle (also known as the Krebs cycle) generates high-energy carriers like NADH and FADH2, which are used in the electron transport chain to produce ATP.
• 😀 Oxygen is essential for the TCA cycle and ATP production, while carbon dioxide and water are byproducts of energy production.
• 😀 Proteins in the diet are broken down into amino acids, which can be used for energy or converted into other compounds like muscle tissue.
• 😀 The amino group of amino acids is removed during deamination and excreted in the urine as waste.
• 😀 Fats are composed of glycerol and fatty acids, and fatty acids are broken down into two-carbon units that enter the acetyl-CoA pathway for energy production.
• 😀 Excess nutrients (carbs, proteins, fats) are stored in the body: carbohydrates as glycogen, fats as adipose tissue, and proteins for tissue repair and growth.
• 😀 Insulin is the primary hormone that favors anabolic processes (building up and storing energy), while stress hormones like epinephrine and glucocorticoids promote catabolic processes (breaking down energy stores).
• 😀 Some metabolic reactions are reversible, such as glucose being converted into glycogen, but fatty acids cannot be converted back into glucose for energy.
• 😀 The balance between catabolism and anabolism is regulated by hormones, ensuring energy is either stored or used based on the body's needs.

Q & A

What is metabolism and how can it be defined in simple terms?

Metabolism is the balance between the reactions in the body that build things up (anabolism) and those that break things down (catabolism). In simple terms, it refers to how the body processes food for energy and how it repairs, stores, and uses substances.

What happens to carbohydrates in the body after they are consumed?

Carbohydrates are broken down into glucose, which is the primary energy source. Glucose is then further broken down into pyruvate, and eventually into acetyl-CoA. Acetyl-CoA plays a central role in generating energy through the TCA cycle, which ultimately produces ATP, the body's energy currency.

What is acetyl-CoA and what role does it play in metabolism?

Acetyl-CoA is a key molecule in energy production. It acts like a 'portable trampoline' in the body, where different chemicals 'bounce on and off' to generate energy through the TCA cycle (also known as the Krebs cycle). It is crucial for the production of ATP.

What is the TCA cycle, and why is it important?

The TCA cycle (Tricarboxylic Acid Cycle, also known as the Krebs cycle) is a series of chemical reactions that take place in the mitochondria. It is essential for generating ATP, the energy needed by the body. As acetyl-CoA moves through this cycle, it generates high-energy carriers that are used in the electron transport chain to produce ATP.

How does the body use proteins for energy and growth?

Proteins are broken down into amino acids, which can be used for energy or to build and repair tissues. Some amino acids enter the metabolic pathways at different points, and the amino groups are removed, becoming waste in the urine. These amino acids are also important for muscle growth and repair.

How are fats broken down in the body, and where do they enter the metabolic pathway?

Fats are broken down into glycerol and fatty acids. The glycerol backbone enters the metabolic pathway at the level of glucose, while the fatty acids are broken down into two-carbon units, which enter the pathway at the level of acetyl-CoA, providing energy.

What role do hormones play in metabolism?

Hormones regulate the balance between catabolic (breaking down) and anabolic (building up) reactions in the body. For example, insulin promotes storage and building up, while hormones like glucagon, epinephrine, and cortisol promote the breakdown of stored energy.

What is the role of insulin in metabolism?

Insulin is a key hormone that promotes anabolism, meaning it helps store energy and build tissues. It encourages the storage of glucose as glycogen and the storage of fat in adipose tissue, helping the body to regulate its energy stores.

What happens when the body does not use energy, such as during sedentary activity?

When the body does not need to produce ATP (such as during inactivity), acetyl-CoA can build up and favor the conversion of excess energy into adipose tissue (fat), which can lead to weight gain if too much carbohydrate, fat, or protein is consumed.

Why is oxygen important in the metabolism process?

Oxygen is necessary for the electron transport chain, which occurs after the TCA cycle. This process generates ATP, the energy currency of the body. Oxygen helps facilitate the production of ATP, and carbon dioxide and water are by-products of this reaction, which we expel when we breathe.