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1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

30. Peptides and Proteins

Quaternary Protein Structure

30. Peptides and Proteins

Quaternary Protein Structure: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

The quaternary structure of proteins represents their highest complexity, formed by interactions between multiple subunits, each a polypeptide chain with a tertiary structure. Multimeric proteins can be dimers (2 subunits), trimers (3), or tetramers (4). As proteins progress from primary to quaternary structure, they exhibit increasing complexity, involving hydrophobic and hydrophilic interactions. Additionally, prosthetic groups, like heme in hemoglobin, enhance functionality by contributing non-amino acid components essential for processes such as iron transport in metabolism.

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Quaternary Protein Structure Concept 1

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Quaternary Protein Structure Concept 1 Video Summary

The quaternary structure of a protein represents its most complex level of organization, arising from the interactions between the side chains of two or more subunits. A subunit is defined as an individual polypeptide chain that has achieved a tertiary structure, characterized by various interactions such as hydrophobic and hydrophilic interactions, as well as hydrogen bonding. These interactions are crucial as they also influence the quaternary structure.

Proteins that consist of multiple subunits are referred to as multimeric proteins. The terminology used to describe the number of subunits includes dimer (two subunits), trimer (three subunits), and tetramer (four subunits). This progression from primary to quaternary structure illustrates the increasing complexity of protein formation. The primary structure is the linear sequence of amino acids linked by peptide bonds, which then folds into secondary structures, such as alpha helices and beta-pleated sheets, through repetitive patterns within the same polypeptide chain.

As the protein continues to fold, it reaches the tertiary structure, where hydrophobic interactions cause the polypeptide chain to compact and form a three-dimensional shape. When multiple tertiary structures come together, they can form dimers, trimers, or tetramers, culminating in the quaternary structure. This structure is functional and may include additional components known as prosthetic groups, which are non-amino acid entities that contribute to the protein's functionality.

For instance, hemoglobin is a well-known example of a protein with a quaternary structure, consisting of four subunits and four heme prosthetic groups. These heme groups are essential for iron transport within cells, playing a vital role in metabolism. Overall, the transition from primary to quaternary structure highlights the intricate nature of protein assembly and function, emphasizing the importance of each structural level in achieving a fully functional protein.

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Quaternary Protein Structure Example 1

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Quaternary Protein Structure Example 1 Video Summary

In the study of protein structures, particularly in an Escherichia coli (E. coli) sample, it is essential to understand the hierarchy of protein organization. Proteins can be classified into four structural levels: primary, secondary, tertiary, and quaternary. In this case, the E. coli sample exhibits a quaternary structure, which is characterized by the assembly of multiple polypeptide chains, known as subunits.

Specifically, this sample contains three distinct peptide chains that come together to form a functional protein complex. Since there are three subunits involved, this structure is referred to as a trimer, indicating that it is trimeric in nature. The interactions between these subunits are primarily mediated by non-covalent bonds, such as hydrogen bonds, ionic interactions, and hydrophobic interactions, rather than covalent bonds.

To summarize, the protein structure of the E. coli sample is a quaternary structure that is specifically trimeric, as it consists of three tertiary structures or subunits held together by non-covalent interactions. This understanding is crucial for comprehending how proteins function and interact within biological systems.

Problem

Hemoglobin represents a commonly discussed tetramer that contains an even number of α and β subunits. Which of the following statements is true?

Hemoglobin must contain with 4 α subunits and 4 β subunits.

Hemoglobin must contain with 2 α subunits and 2 β subunits.

Hemoglobin contains R groups that only covalently bind to produce a quaternary structure.

Hemoglobin represents a multimeric protein with identical subunits.

Problem

Which of the following could be classified as a prosthetic group?

I only

I, III, IV

II only

II, IV

None of the above

Problem

Which of the following correctly orders the protein structural terms from lowest to highest complexity?

Peptide Bond < Primary structure < 2 subunits < Secondary structure < tetramer < Tertiary structure.

Primary structure < Peptide Bond < Secondary structure < 2 subunits < Tertiary Structure < tetramer.

Peptide Bond < Primary structure < Secondary structure < Tertiary structure < 2 subunits < tetramer.

Peptide Bond < Primary Structure < Secondary structure < 2 subunits < Tertiary structure < tetramer.

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What is the quaternary structure of a protein?

The quaternary structure of a protein is its highest level of complexity, formed by the interaction between multiple subunits. Each subunit is an individual polypeptide chain that possesses a tertiary structure. These subunits interact through various types of bonds and interactions, such as hydrophobic, hydrophilic, and hydrogen bonding. The quaternary structure can involve two or more subunits, leading to formations like dimers (2 subunits), trimers (3 subunits), and tetramers (4 subunits). Additionally, quaternary structures may include prosthetic groups, which are non-amino acid components that enhance the protein's functionality. An example of a protein with a quaternary structure is hemoglobin, which consists of four subunits and heme groups that help in iron transport.

What is a multimeric protein?

A multimeric protein is a fully functional protein that consists of multiple subunits. Each subunit is an individual polypeptide chain with its own tertiary structure. These subunits come together to form a complex structure, which can be a dimer (2 subunits), trimer (3 subunits), or tetramer (4 subunits). The interactions between these subunits, such as hydrophobic and hydrophilic interactions, contribute to the overall stability and functionality of the protein. An example of a multimeric protein is hemoglobin, which is a tetramer composed of four subunits and heme prosthetic groups that facilitate oxygen transport in the blood.

What are prosthetic groups in quaternary protein structures?

Prosthetic groups are non-amino acid components that are essential for the functionality of quaternary protein structures. These groups are tightly bound to the protein and play a crucial role in its biological activity. For example, in hemoglobin, the prosthetic groups are heme groups, which contain iron and are responsible for oxygen binding and transport. Prosthetic groups can be organic molecules, metal ions, or other types of non-protein components. They contribute to the protein's overall structure and function, enhancing its ability to perform specific biological tasks.

How do primary, secondary, tertiary, and quaternary protein structures differ?

Protein structures are organized into four levels of complexity:

1. Primary Structure: This is the linear sequence of amino acids in a polypeptide chain, connected by peptide bonds.

2. Secondary Structure: This involves the formation of repeating patterns, such as alpha helices and beta pleated sheets, within the polypeptide chain due to hydrogen bonding.

3. Tertiary Structure: This is the three-dimensional folding of the polypeptide chain, driven by interactions like hydrophobic interactions, hydrogen bonds, and disulfide bridges.

4. Quaternary Structure: This is the highest level of protein structure, formed by the interaction of multiple polypeptide subunits, each with its own tertiary structure. These subunits come together to form a functional protein complex, often including prosthetic groups for enhanced functionality.

What is the role of heme groups in hemoglobin's quaternary structure?

Heme groups play a crucial role in the quaternary structure of hemoglobin, a protein responsible for oxygen transport in the blood. Each hemoglobin molecule consists of four subunits, each containing a heme group. The heme group is a prosthetic group that includes an iron ion (Fe²⁺) at its center. This iron ion binds to oxygen molecules, allowing hemoglobin to carry oxygen from the lungs to tissues throughout the body. The presence of heme groups is essential for hemoglobin's functionality, as they enable the protein to efficiently bind and release oxygen, facilitating respiration and metabolism.