23. TCA Cycle II

TL;DR

The tricarboxylic acid (TCA) cycle, also known as the citric acid or Krebs cycle, is a series of reactions that occurs in the mitochondria to oxidize two-carbon units, derived from various sources, and release lots of energy. The cycle is regulated by levels of ATP, NADH, ADP, and various intermediates.

Transcript

[SQUEAKING] [RUSTLING] [CLICKING] MATTHEW VANDER HEIDEN: Hello, everybody. Last time, I introduced the idea of the TCA cycle, tricarboxylic acid cycle. Also known as the citric acid cycle, because citric acid is a tricarboxylic acid, as you'll see later today. Also known as the Krebs cycle, named after Hans Krebs, who discovered it in the early par... Read More

Key Insights

• 🏍️ The TCA cycle is a central metabolic pathway that enables the complete oxidation of carbon and provides energy for the cell.
• 🏍️ The cycle is regulated based on the energy needs of the cell, with high levels of ATP and NADH inhibiting the cycle while low levels of ADP activating it.
• 🤩 The TCA cycle not only releases energy but also generates key intermediates for other metabolic processes.
• 🖤 Humans lack the ability to convert two-carbon units into four-carbon oxaloacetate, limiting the ability to convert acetate or acetyl-CoA into glucose.
• 😒 The glyoxylate cycle is an alternative pathway that certain microbes use to convert two-carbon units into four-carbon intermediates for anabolic processes.

Questions & Answers

Q: What are some other names for the TCA cycle?

The TCA cycle is also known as the citric acid cycle and the Krebs cycle.

Q: How does the TCA cycle regulate energy production?

The TCA cycle is regulated by the levels of ATP, NADH, and ADP. High levels of ATP and NADH inhibit enzymes in the cycle, while low levels of ADP activate enzymes, facilitating energy production.

Q: How does the TCA cycle generate intermediates for other metabolic processes?

The TCA cycle generates intermediates such as citrate, which can be used to make fatty acids. These intermediates serve as building blocks for other molecules in the cell.

Q: How does the TCA cycle handle two-carbon units from acetyl-CoA?

The TCA cycle requires the presence of oxaloacetate to combine with acetyl-CoA. However, humans lack enzymes to convert two-carbon units into oxaloacetate, limiting the ability to convert acetate or acetyl-CoA into glucose.

Summary & Key Takeaways

• The TCA cycle is a series of reactions in the mitochondria that allows the complete oxidation of two-carbon units derived from various sources, including pyruvate from glucose.

• The cycle starts with the combination of acetyl-CoA and oxaloacetate to form citrate, which is then oxidized back to oxaloacetate, allowing the entry of two carbons and release of two carbons as CO2.

• The TCA cycle not only releases energy but also generates intermediates that can be used to make other molecules, such as fatty acids and amino acids.