Serine is a non-essential amino acid that can be synthesized from glycolysis intermediates. It participates in one-carbon metabolism by donating methylene groups, and it is involved in the synthesis of several other amino acids, phospholipids, and sphingolipids. Serine can be converted to pyruvate through transamination and deamination reactions. Threonine is an essential amino acid that can be cleaved to form glycine, acetaldehyde, and derivatives that enter the citric acid cycle or form pyruvate and lactate. Both amino acids play important roles in biosynthesis as carriers of phosphate groups.

2. • Serine is a non-essential & glycogenic amino
acid.
• Glycine & serine are interconvertible.
• Serine is also synthesized from the
intermediates of glycolysis.

3. • Serine participates in transamination
reactions.
• It undergoes deamination to form pyruvate.
Serine
PLP, NH3
+
Pyruvate
Serine dehydratase

4. • Serine is involved in one-carbon metabolism
• It donates methylene (-CH2) moiety to
tetrahydrofolate (THF).
Serine
THF
Glycine
Serine hydroxymethyl transferase
(PLP)
CH2-THF

5. • On decarboxylation (PLP dependent) serine
forms ethanolamine
• Ethanolamine is precursor for choline synthesis.
Serine
CO2
Ethanolamine

6. • Serine is utilized for the synthesis of cysteine.
• Entire cysteine molecule is derived from
serine except the sulfur that comes from
homocysteine.
• Serine is involved in the formation of
selenocysteine, the 21st amino acid found in
certain proteins.

7. • Serine is directly participates in the synthesis
of phospholipid-phosphatidyl serine.
• Serine is involved in the synthesis of
sphingomyelins & cephalins.
• Serine OH group serves as a carrier of
phosphate which involved in the regulation
of many enzyme activities.

8. Serine
Proteins
Glucose
Glycine
Alanine
Cysteine
Cystine
One carbon metabolism
Sphingomyelins
Phosphatidyl serine
Selenocysteine
Ethanolamine
Choline

9. • Threonine is essential amino acid.
• It is glycogenic & does not participate in
transamination reactions.
• Threonine is also a carrier of phosphate group
in the protein structure.
• Threonine undergoes deamination by
threonine dehydratase to α-ketobutyrate
which is converted to propionyl CoA.

10. • Threonine can be cleaved to glycine &
acetaldehyde by serine hydroxymethyl
transferase.
• Dehydrogenation followed by
decarboxylation of threonine results in
aminoacetone which may be converted to
pyruvate or lactate.

11. Threonine
Proteins
α- ketobutyrate
Propionyl CoA
Glycine + acetaldehyde
Aminoacetone
Pyruvate
Lactate
Methylglyoxyl

12. • Textbook of Biochemistry-U Satyanarayana
• Textbook of Biochemistry-DM Vasudevan
• Textbook of Biochemistry-MN Chatterjea