Question

In \(N\) -linked glycoproteins, the sugar is usually attached to the protein by a bond to the \(\mathrm{N}\) atom in a side-chain amide. Which amino acids can form such a bond?

Short answer

Asparagine (Asn) forms \\(N\\)-linked glycoprotein bonds.

Step-by-step solution

Understanding Glycoproteins

Glycoproteins are proteins that have sugar molecules attached to them. These attachments occur through specific bonds on specific atoms or groups within the protein's structure. In this case, the attachment is to an \(\)-atom (nitrogen atom) via an amide bond.

Identifying Amide-Bond Forming Amino Acids

To form an \(N\)-linked glycosidic bond, the amino acid needs to have a side chain with an amide group that contains a nitrogen atom capable of forming such a bond. Asparagine (Asn) is the only amino acid that has an amide group in its side chain, allowing it to form these bonds.

Verification

VERIFY by examining the amino acid structures: Asparagine's side chain consists of -CH2-CONH2, which includes the necessary nitrogen to form a bond with sugar in \(N\)-linked glycoproteins.

Key concepts

Glycoproteins

Glycoproteins are fascinating molecules that play essential roles in various biological processes. These are proteins that have carbohydrates—or sugars—covalently attached to them. This combination imbues them with unique properties and functions.
One primary role of glycoproteins is in cell-cell recognition and signaling. They are crucial components of cell membranes and help in immune responses. They can also play a part in developmental processes and disease pathogenesis.
Importantly, glycoproteins are formed when sugar molecules are attached to proteins through specific bonds. These bonds can be to nitrogen (N-linked) or oxygen atoms (O-linked) in the protein, involving complex enzymatic reactions. This diversity makes glycoproteins adaptable to various cellular functions.

Amino acids

Amino acids are the building blocks of proteins. There are 20 standard amino acids, each with a unique structure and set of properties. They can differ based on their side chains, which can influence how they interact and bond with other molecules.
Amino acids have both an amine group and a carboxylic acid group. The side chain, called an R group, varies among different amino acids. This variability allows proteins to have intricate structures and functions.
These small molecules can form peptides and larger proteins through peptide bonds. They deliver specificity to proteins and help determine their role in biological systems.

Amide bonds

Amide bonds are a type of covalent bond that is essential in the formation of peptides and proteins. Chemically, they form when the amine group of one molecule reacts with the carboxylic acid group of another, releasing a molecule of water (a condensation reaction).
In glycoproteins, amide bonds play a crucial role in the attachment of sugar molecules to proteins, especially in N-linked glycosylation.
These bonds are characterized by their strength and stability, essential for maintaining the integrity of proteins. Amide bonds confer rigidity and help maintain specific protein shapes, necessary for proper functionality in biological processes.

Asparagine

Asparagine is an amino acid with a unique feature that sets it apart for specific biochemical roles. Its side chain, -CH2-CONH2, includes an amide group, which is key for N-linked glycosylation in glycoproteins.
This amino acid features prominently in protein sequences where glycosylation sites are required. It’s the only amino acid capable of bonding to sugars through its amide nitrogen, making it vital for the creation of glycoproteins.
Maybe subjects like asparagine in biochemistry seem intricate. However, understanding its role helps in grasping more about complex protein interactions and functions. This balance of structure and function underscores asparagine's importance in biochemistry and molecular biology.