Serine, Glycine Biosynthesis

Summary

This video covers the biosynthesis of serine, glycine, and cysteine, starting from the glycolytic intermediate 3-phosphoglycerate. The pathway involves key enzymes like phosphoglycerate dehydrogenase, transaminases, and serine hydroxymethyltransferase, which convert 3-phosphoglycerate into serine. Serine then leads to the production of glycine and important molecules such as methylene tetrahydrofolate, which plays a vital role in nucleotide and SAM synthesis. The process also highlights how NADH is generated despite most biosynthetic pathways consuming energy. The video provides insights into these amino acids' biosynthesis and their implications in metabolic pathways.

Takeaways

• 😀 The biosynthesis of serine, glycine, and cysteine begins with the glycolysis intermediate 3-phosphoglycerate.
• 😀 3-phosphoglycerate is converted into 3-phosphohydroxy pyruvate by phosphoglycerate dehydrogenase.
• 😀 Transamination by serine amino transferase converts 3-phosphohydroxy pyruvate into 3-phosphoserine.
• 😀 3-phosphoserine is dephosphorylated by phosphoserine phosphatase to form serine.
• 😀 The pathway from serine to glycine is catalyzed by serine hydroxymethyltransferase, which is reversible.
• 😀 Methylene tetrahydrofolate, a product of the serine to glycine conversion, is crucial for thymine synthesis and SAM production.
• 😀 Methylene tetrahydrofolate is used in thymine synthesis and also contributes to the methylation cycle by producing SAM (S-adenosylmethionine).
• 😀 Serine, glycine, and cysteine are non-essential amino acids, meaning they can be synthesized in the body from intermediates like 3-phosphoglycerate.
• 😀 This biosynthetic pathway is unusual because it generates NADH rather than consuming it, which helps in ATP synthesis via the electron transport chain.
• 😀 While most biosynthetic pathways consume energy (e.g., ATP, NADH, or NADPH), this specific pathway can generate energy due to the high energy of 3-phosphoglycerate.

Q & A

What is the primary starting molecule for the biosynthesis of serine, glycine, and cysteine?

The primary starting molecule is 3-phosphoglycerate, which is an intermediate in glycolysis.

Which enzyme is responsible for converting 3-phosphoglycerate to 3-phospho-hydroxy-pyruvate?

The enzyme phosphoglycerate dehydrogenase is responsible for this conversion.

What is the role of transaminase in serine biosynthesis?

Transaminase replaces the carbonyl group with an amine group, converting 3-phospho-hydroxy-pyruvate into 3-phospho-serine.

What enzyme removes the phosphate group from 3-phospho-serine to form serine?

The enzyme responsible for removing the phosphate group is phosphoserine phosphatase.

How is glycine synthesized from serine?

Serine is converted to glycine by the enzyme serine hydroxymethyltransferase, which also produces methylene tetrahydrofolate.

What important molecule is produced during the conversion of serine to glycine, and what are its roles?

Methylene tetrahydrofolate is produced, which is important for thymine synthesis and for methyl group transfer in the production of S-adenosylmethionine (SAM).

What is the anabolic direction of the serine to glycine conversion, and what is the reverse catabolic direction?

In the anabolic direction, serine is converted to glycine. In the catabolic direction, glycine is converted back to serine.

What is the significance of methylene tetrahydrofolate in DNA synthesis?

Methylene tetrahydrofolate is essential for the synthesis of thymine, a nitrogenous base required for DNA synthesis.

How does methylene tetrahydrofolate contribute to SAM synthesis?

Methylene tetrahydrofolate is converted to methyl tetrahydrofolate, which donates a methyl group to form S-adenosylmethionine (SAM), a universal methyl group donor.

Why is the biosynthesis of serine, glycine, and cysteine considered unusual in terms of energy usage?

The biosynthesis of these amino acids is unusual because it generates NADH, unlike most biosynthetic pathways that consume ATP or NADPH. This is possible because 3-phosphoglycerate, the starting molecule, is already high in energy from glycolysis.