Vitamin B12 & Why We Need It | Biochemistry, Absorption, & Important Enzymes

Summary

This video lesson delves into the critical role of Vitamin B12 in two key enzymes: homocysteine methyl transferase (methionine synthase) and methylmalonyl-CoA mutase. It explains how Vitamin B12 supports protein synthesis, DNA synthesis, and energy production through complex biochemical pathways. The video also covers the absorption process of Vitamin B12 and the consequences of its deficiency, including macrocytic anemia and neurological damage due to methylmalonic acid buildup. This lesson emphasizes the importance of Vitamin B12 for overall health and its vital functions in the body.

Takeaways

• 😀 Vitamin B12 is essential for the functioning of two enzymes: homocysteine methyltransferase and methylmalonyl-CoA mutase.
• 😀 Homocysteine methyltransferase (methionine synthase) converts homocysteine into methionine, which is important for protein synthesis and cellular functions.
• 😀 Methionine can enter the activated methyl cycle to produce S-adenosylmethionine (SAM), which is crucial for synthesizing neurotransmitters like catecholamines and melatonin.
• 😀 Vitamin B12 deficiency can impair DNA synthesis, leading to macrocytic anemia, characterized by large, immature red blood cells.
• 😀 Methionine synthase also helps regenerate tetrahydrofolate, a vital cofactor needed for pyrimidine base synthesis and DNA replication.
• 😀 Methylmalonyl-CoA mutase is involved in converting methylmalonyl-CoA into succinyl-CoA, which is essential for energy production in the Krebs cycle.
• 😀 Methylmalonyl-CoA comes from the metabolism of amino acids, short-chain fatty acids, and cholesterol.
• 😀 A Vitamin B12 deficiency can cause a buildup of methylmalonyl-CoA, which leads to the production of toxic methylmalonic acid that damages neurons.
• 😀 Accumulation of methylmalonic acid can cause axonal neuropathy, affecting the sensory neurons in the dorsal column-medial lemniscus system, leading to issues with balance and coordination.
• 😀 Vitamin B12 is primarily obtained through dietary sources like meat, fish, dairy, and eggs and is absorbed in the terminal ileum after binding to intrinsic factor.
• 😀 Inadequate absorption or intake of Vitamin B12 can impair its essential functions, leading to both hematological and neurological issues.

Q & A

What is the primary function of Vitamin B12 in the body?

Vitamin B12 is essential for the proper functioning of two key enzymes: homocysteine methyl transferase (methionine synthase) and methylmalonyl-CoA mutase, which are involved in amino acid metabolism, DNA synthesis, and energy production.

How is Vitamin B12 absorbed in the body?

Vitamin B12 is absorbed through a complex process beginning in the stomach, where it binds to haptocorrin. It then travels to the duodenum, where pancreatic enzymes break the complex, allowing Vitamin B12 to bind to intrinsic factor. This complex is absorbed in the terminal ileum of the small intestine.

What are the two enzymes that require Vitamin B12 for proper functioning?

The two enzymes that require Vitamin B12 are homocysteine methyl transferase (methionine synthase) and methylmalonyl-CoA mutase.

What is the role of homocysteine methyl transferase in the body?

Homocysteine methyl transferase (methionine synthase) converts homocysteine to methionine, which is important for protein synthesis and the activated methyl cycle. It also helps regenerate tetrahydrofolate, which is essential for DNA synthesis.

Why is methionine synthesis important for the body?

Methionine is an essential amino acid involved in protein synthesis. It also participates in the activated methyl cycle, which produces S-adenosylmethionine (SAM), a critical cofactor for various biochemical processes, including neurotransmitter synthesis.

What is the consequence of a Vitamin B12 deficiency on homocysteine methyl transferase?

A Vitamin B12 deficiency leads to impaired functioning of homocysteine methyl transferase, resulting in a buildup of homocysteine and a reduction in methionine and tetrahydrofolate, which can impair DNA synthesis and contribute to macrocytic anemia.

How does Vitamin B12 deficiency affect DNA synthesis?

Vitamin B12 deficiency reduces the availability of tetrahydrofolate, a critical cofactor for pyrimidine base synthesis, impairing DNA replication and leading to the development of macrocytic anemia.

What is methylmalonyl-CoA mutase and why is it important?

Methylmalonyl-CoA mutase is an enzyme that converts methylmalonyl-CoA into succinyl-CoA, an important intermediate in the Krebs cycle. This process is essential for the metabolism of various energy substrates, including amino acids, fatty acids, and cholesterol.

What happens when methylmalonyl-CoA mutase is not functioning properly due to Vitamin B12 deficiency?

When methylmalonyl-CoA mutase is impaired due to Vitamin B12 deficiency, methylmalonyl-CoA accumulates and is converted into methylmalonic acid, which is toxic to neurons and can cause neurological damage, particularly axonal neuropathy.

What are the neurological effects of long-term Vitamin B12 deficiency?

Long-term Vitamin B12 deficiency can lead to the buildup of methylmalonic acid, causing axonal neuropathy. Symptoms may include balance problems, numbness, tingling, and other cognitive or sensory issues, particularly in the dorsal column-medial lemniscus system.