Question

The \(\beta\) -pleated sheet is a structure that commonly arises in proteins. Part of a \(\beta\) -pleated sheet is shown in the following figure. This type of structure is an example of which level of protein structure: primary, secondary, tertiary, or quaternary?

Short answer

Secondary structure.

Step-by-step solution

Understanding the Levels of Protein Structure

Protein structures have four levels: primary, secondary, tertiary, and quaternary. The primary structure refers to the sequence of amino acids. The secondary structure includes local folded structures, such as alpha helices and beta pleated sheets, formed by hydrogen bonds. Tertiary structure refers to the overall 3D shape of a single polypeptide chain. Quaternary structure refers to complexes of multiple polypeptide chains.

Identifying the Structure in Question

The given structure is a \(\beta\)-pleated sheet. This is a specific folded pattern found in proteins. Beta-pleated sheets are formed by hydrogen bonds between the backbone atoms in polypeptide chains and are categorized under secondary structures.

Conclusion

Since beta-pleated sheets are a type of secondary structure formed through hydrogen bonding, the level of protein structure in question is the secondary structure.

Key concepts

Understanding Beta Pleated Sheets

Beta pleated sheets are fundamental components in the structure of proteins. They form when polypeptide chains lie next to each other in a zigzag shape. This zigzagging creates a sheet-like structure that appears "pleated." This name comes from the way the polypeptide chains align and fold together.

In beta pleated sheets, the polypeptide strands can run in the same direction, known as "parallel" sheets, or they can run in opposite directions, called "antiparallel" sheets. Both of these structural types are stabilized by hydrogen bonds, which contribute to the overall strength and stability of the structure.

• Parallel beta sheets have hydrogen bonds that are evenly spaced.
• Antiparallel beta sheets have hydrogen bonds that occur at alternating distances.

Beta pleated sheets provide the protein with strength and flexibility which are essential for their biological functions.

Exploring Secondary Structure of Proteins

The secondary structure of a protein refers to the regular local structures formed by the backbone atoms within a polypeptide chain. It is one of the four levels of protein structure. This particular level includes both alpha helices and beta pleated sheets. These structures are typically regular and repeated, creating stable 3D shapes.

The formation of secondary structures is primarily due to hydrogen bonding between the backbone amide and carbonyl groups.

• Alpha helices form when the polypeptide chain curves into a right-handed helix.
• Beta pleated sheets form when polypeptide chains lie side-by-side, creating a sheet.

These secondary structures are crucial because they provide proteins with their necessary structural and functional properties.

Amino Acids: Building Blocks of Proteins

Amino acids are the basic building blocks of proteins. Each amino acid has a central carbon atom, called the alpha-carbon, to which an amino group, a carboxyl group, a hydrogen atom, and an R group are attached. The R group, or side chain, varies in each amino acid and determines the characteristics and function of the amino acid.

When amino acids connect via peptide bonds, they form polypeptide chains, which eventually fold into functional proteins. The unique sequence of amino acids in a polypeptide chain determines the protein’s primary structure and influences its ability to form secondary, tertiary, and quaternary structures.

• There are 20 standard amino acids found in nature.
• Amino acid sequences dictate the protein's shape and function.

Understanding these building blocks is essential as they are key to forming proteins with specific roles in the body.

Role of Hydrogen Bonds in Protein Structure

Hydrogen bonds are vital for maintaining the structure and function of proteins. They occur when a hydrogen atom covalently bound to an electronegative atom, like oxygen or nitrogen, forms an interaction with another electronegative atom. These interactions are not as strong as covalent bonds but are crucial for stabilizing protein structures, particularly at the secondary level.

In the context of protein secondary structure, hydrogen bonds form between the carbonyl oxygen and the amide hydrogen in the polypeptide backbone. This bonding is what stabilizes structures like beta pleated sheets and alpha helices.

• They assist in organizing proteins into stable, functional shapes.
• They play a role at the secondary, tertiary, and even quaternary levels of protein structure.

Without hydrogen bonds, proteins would not maintain their proper shape and, consequently, would not perform their intended functions efficiently.