What Is Serine? Structure, Occurrence & Key Roles in Biology
Serine is described as a non-essential amino acid that can be used in the biosynthesis of proteins. These are derived from the amino acid glycine. And, they are obtained by the process of hydrolysis. These acids do not need any literary resources and are synthesized from glucose.
About Serine
L-isomer is one and the only form of Serine that is involved in the process of protein synthesis in humans. It is considered one of the twenty amino acids that are needed for normal body functioning. Since it is a type of non-essential amino acid, it can be synthesized by the human body from many compounds via various chemical reactions. Serine acid forms an integral part of the phospholipids class that is found in the biological membrane, where Ethanolamine is an example.
Structure of Serine
(Image to be added soon)
The word amino acid in biochemistry categorically refers to the alpha-amino acids primarily consisting of the carboxyl group and amino. The structure of alpha-amino acid is illustrated as follows.
R
|
H2N-C-COOH
|
H
Where R is given as the Side Chain that is specific to every amino acid.
These two optical isomers of amino acids are termed L and D. They also represent the huge majority of amino acids that sunder in many amino acids. Also, they actively participate in protein synthesis. However, mammalian protein synthesis involves only L-Stereoisomers.
(Image to be added soon)
Occurrence of Serine
This compound is one of the most naturally occurring amino acids of proteinogenic. Only L-stereoisomer naturally appears in proteins. It is not required in the human diet because it is synthesized in the body from the other metabolites, including glycine. Serine was first obtained in 1865 from the silk protein, which is a specific rich source, by Emil Cramer. The name was derived from the Latin for silk, known as sericum. At the same time, the structure of Serine was established in 1902. Food sources containing high L-Serine content among their proteins include edamame, eggs, lamb, pork, liver, salmon, seaweed, sardines, tofu, and many more.
Function of Serine
Let us look at the important functions of Serine
Serine plays an essential role in the synthesis of several biological vital compounds, namely cysteine, glycine, purines, phosphides, pyrimidines, proteins, and many more. It also plays a vital role in metabolism. Serine protease, which is found in the digestive system, breaks down the proteins that help an enzyme catalyze in its chemical reaction.
A serine protease is defined as an enzyme that sunders the peptide bonds in proteins. They are found in eukaryotes and prokaryotes. The side chain of Serine as a residue of proteins can undergo O-linked glycosylation. The residues of the phosphorylated Serine are referred to as phosphoserine. Also, D-Serine consists of a musty aroma, and it is an off–white crystalline powder. In contrast, L- Serine tastes sour at much higher concentrations.
Phosphatidylserine
Phosphatidylserine (otherwise called PS or Ptd-L-Ser) is a phospholipid and is more specifically described as a glycerophospholipid. It contains two fatty acids that are attached in ester linkage to both the first and second carbon of glycerol, and the series will be attached through a phosphodiester linkage to the glycerol’s third carbon.
Phosphatidylserine also helps in blood coagulation (called clotting). It is a cell membrane component and plays a vital role in the cell cycle signalling, specifically in relation to apoptosis. It is defined as a key pathway for viruses to enter cells through apoptotic mimicry.
Phosphatidylserine can be found in several food products that we take. It is also noted that the ones coming from animals and the ones coming from the plants differ in fatty acid composition. It is present in chickens, pigs, turkeys, and milk for animal sources and also in rice, potato, carrot, and barley for plant sources.
Sirtuins
Sirtuins are the family of NAD-dependent protein deacetylases that are present in various cellular components. They promote the expression of genes whose products increase the life span.
Before going into the details regarding how Sirtuins help increase longevity, we should first reflect upon the reasons that cause ageing.
Most of the Common Causes of Ageing Are Given as Follows
Increased free radicals and decreased levels of the antioxidants present in the body.
Telomere shortening (Telomeres are the short DNA stretches at the end of the chromosome that get shortened after every cell division).
Increased collagen cross-linking (most be the abundant protein of the human body).
Now Coming Back to the Action of Sirtuins Mechanism, They Prolong a Life Span in the Following Ways:
Inhibition of the apoptotic and metabolic activity of the cell.
Reducing the damage occurred by free radicals.
Increasing the metabolism of glucose that increases insulin sensitivity of the body.
An interesting thing about the Sirtuins is that they get induced by the Calorie restriction (hence, we should listen carefully to our dietician or nutritionist) and a component present in the red wine.
FAQs on Serine: Structure, Properties, and Functions
1. What is the basic structure of the amino acid serine?
Serine is an α-amino acid with the chemical formula C₃H₇NO₃. Its structure consists of a central carbon atom (the α-carbon) bonded to four different groups: an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (-H), and a distinctive side chain. The side chain for serine is a hydroxymethyl group (-CH₂OH), which defines its unique properties.
2. Why is serine classified as a polar, hydrophilic amino acid?
Serine is classified as a polar amino acid because its side chain contains a hydroxyl (-OH) group. The oxygen atom in this group is highly electronegative, creating a dipole that can form hydrogen bonds with water molecules. This ability to interact with water makes serine hydrophilic (water-loving) and is crucial for its role in protein folding, where it is often found on the surface of proteins.
3. What are the key metabolic functions of serine in the human body?
Serine plays several vital roles in metabolism. Its primary functions include:
- Precursor for other molecules: It is a precursor for the biosynthesis of other amino acids like glycine and cysteine.
- Biosynthesis: It participates in the synthesis of purines and pyrimidines, which are essential building blocks of DNA and RNA.
- One-Carbon Metabolism: Serine is a major donor of one-carbon fragments, which are crucial for the synthesis of various other metabolites, including folate.
- Component of lipids: It is a precursor to other important molecules like sphingolipids and phospholipids.
4. What is the main structural difference between serine and threonine?
Both serine and threonine are polar amino acids with hydroxyl (-OH) groups in their side chains. The key difference lies in the structure of that side chain. Serine has a primary alcohol (-CH₂OH) in its side chain. In contrast, threonine has a secondary alcohol (-CH(OH)CH₃), meaning the hydroxyl group is attached to a carbon that is also bonded to a methyl group. This makes threonine's side chain bulkier and introduces a second chiral center.
5. What does it mean for serine to be a 'non-essential' amino acid?
The term 'non-essential' means that the human body can synthesize serine on its own and does not need to obtain it directly from the diet. The synthesis typically occurs from the glycolytic intermediate 3-phosphoglycerate. While it can be produced endogenously, it is still a critical component for protein synthesis and other metabolic functions.
6. How does the hydroxyl (-OH) group of serine contribute to enzyme function?
The hydroxyl group in serine's side chain is highly significant for enzyme function, especially in a class of enzymes called serine proteases (e.g., trypsin, chymotrypsin). In the active site of these enzymes, the serine's -OH group acts as a powerful nucleophile that attacks the peptide bond of a substrate protein, initiating the process of hydrolysis (breaking the bond). This nucleophilic role is fundamental to their catalytic activity.
7. Can serine exist as a zwitterion? Explain why.
Yes, like all amino acids, serine can exist as a zwitterion at physiological pH (around 7.4). In this form, the acidic carboxyl group (-COOH) deprotonates to become a negatively charged carboxylate ion (-COO⁻), and the basic amino group (-NH₂) protonates to become a positively charged ammonium ion (-NH₃⁺). The molecule has both a positive and a negative charge but is electrically neutral overall. This zwitterionic nature explains its high melting point and solubility in water.
8. How is serine's structure important in the process of phosphorylation?
The hydroxyl (-OH) group in serine's side chain makes it a primary target for phosphorylation, a key post-translational modification. Enzymes called kinases can attach a phosphate group to this -OH group, converting serine into phosphoserine. This addition of a bulky, negatively charged phosphate group can drastically alter a protein's shape and function, acting as a molecular 'on/off' switch to regulate cellular processes like cell signalling and enzyme activity.
