Biochemistry: Reactions of amino acids (Part-1)

Learn-at-ease

20 Sept 201507:17

Summary

TLDRThis video explores the chemical reactions of amino acids, focusing on those involving both the amino and carboxylic groups. It covers salt formation, peptide bond synthesis, ester and amino acyl chloride formation, decarboxylation, and amide formation. The explanation includes laboratory synthesis techniques and the reactions' underlying mechanics.

Takeaways

🧬 Amino acids are organic biomolecules with two oppositely charged functional groups, an amino group and a carboxylic group, attached to the same carbon atom.
🌐 Amino acids exist in a zwitterion form, where the amino group is protonated and the carboxylic group is deprotonated.
🔗 The chemical reactions of amino acids can involve both the amino and carboxylic groups or be due to one group alone.
🧂 Salt formation is a reaction where amino acids react with acids or bases to form salts, such as the chloride salt with hydrochloric acid.
🤝 Peptide bond formation is a key reaction involving both the amino and carboxylic groups of different amino acids, leading to the formation of proteins.
🧪 Laboratory synthesis of peptide bonds involves the use of phosgene to create an active residue that polymerizes to form peptide chains.
🍾 Ester formation is a reaction where amino acids react with alcohol in the presence of dry HCl to form esters, which can be reduced to alcohols.
🧪 Amino acyl chlorides are formed by acetylating and then treating amino acids with PCl5, followed by removal of the acetyl group with HCl.
♨️ Decarboxylation is a reaction where amino acids lose carbon dioxide upon heating with barium hydroxide or diphenylamine, resulting in amines.
🍀 Amide formation involves treating amino acid esters with ammonia to produce amides, as demonstrated with the preparation from amino acid esters.
📚 The video promises a follow-up to explain reactions occurring exclusively due to the involvement of the amino group of amino acids.

Q & A

What are amino acids and what makes them unique?
-Amino acids are organic biomolecules that contain two oppositely charged functional groups, an amino group and a carboxylic group, covalently bonded to the same carbon atom. They are unique because they can participate in various chemical reactions due to these functional groups.
What is the significance of the amino group and carboxylic group in amino acids?
-The amino group is positively charged and the carboxylic group is negatively charged. These groups are significant as they allow amino acids to engage in various chemical reactions, including salt formation, peptide bond formation, and others.
What is the zwitterion form of an amino acid?
-The zwitterion form is when the amino group gets protonated and the carboxylic group gets deprotonated, resulting in a molecule with both positive and negative charges.
How do amino acids form salts with acids and bases?
-Amino acids form salts when they react with acids like hydrochloric acid to form chloride salts, or with bases like sodium hydroxide to form sodium salts, with the loss of a water molecule.
What is a peptide bond and how is it theoretically formed?
-A peptide bond is a linkage formed between the amino group of one amino acid and the carboxylic group of another. Theoretically, it is formed when two amino acids fuse and their respective functional groups react with each other.
Can you describe the laboratory synthesis of a peptide bond?
-In the laboratory, an amino acid is heated with phosgene to yield an active residue, which polymerizes to form a peptide chain. The active residues react with each other to form the peptide bond.
What is the purpose of the ester formation reaction in amino acids?
-Ester formation is a reaction where an amino acid reacts with an alcohol in the presence of dry HCl to form an ester. This reaction is used to study and modify the properties of amino acids.
How are amino acyl chlorides formed from amino acids?
-Amino acyl chlorides are formed by first acetylating the amino acid for protection, then treating it with PCl5, and finally removing the acetyl group with HCl to yield the amino acyl chloride.
What is decarboxylation and how does it relate to amino acids?
-Decarboxylation is a reaction where an amino acid, when heated in the presence of barium hydroxide or diphenylamine, loses carbon dioxide and forms an amine. For example, histidine decarboxylates to form histamine.
How can amino acid amides be prepared?
-Amino acid amides can be prepared by treating amino acid esters with alcoholic or anhydrous ammonia, which yields the corresponding amino acid amide.
What will be discussed in the next video by the same channel?
-The next video will explain the reactions of amino acids that occur exclusively due to the involvement of the amino group.

Outlines

00:00

🧬 Introduction to Amino Acid Reactions

This paragraph introduces the topic of amino acid reactions in biochemistry. Amino acids are organic biomolecules with two oppositely charged functional groups (an amino group and a carboxylic group) covalently bonded to the same carbon atom. These groups participate in various chemical reactions, such as salt formation, peptide bond formation, ester formation, amino acyl chloride formation, decarboxylation, and amide formation. The video will focus on reactions involving both the amino group and the carboxylic group, starting with salt formation and peptide bond formation. The theoretical and laboratory synthesis of peptide bonds are also discussed, highlighting the process of linking amino acids through a covalent bond.

05:03

🧪 Reactions Involving Carboxylic Group and Both Groups

This paragraph delves deeper into the reactions of amino acids, focusing on those involving the carboxylic group and both the amino and carboxylic groups. Ester formation is explained, where amino acids react with alcohol in the presence of dry HCl to form esters. Amino acyl chlorides are formed by acetylating the amino acid and then treating it with PCL5, with the acetyl group being removable by HCl. Decarboxylation is discussed, where heating an amino acid in the presence of barium hydroxide or diphenylamine results in the loss of carbon dioxide and the formation of an amine. Finally, amide formation is described, where amino acid esters are treated with alcoholic or anhydrous ammonia to yield amino acid amides. The video promises to cover reactions involving the amino group in a subsequent video, and references are provided for further information.

Mindmap

Keywords

💡Amino Acids

Amino acids are the building blocks of proteins and are organic biomolecules that contain an amino group and a carboxylic acid group attached to the same carbon atom. In the context of this video, they are highlighted as having the ability to participate in various chemical reactions due to their functional groups. The script discusses the chemical properties of amino acids and the reactions they undergo, which is central to understanding biochemistry.

💡Amino Group

The amino group is a functional group in amino acids that is positively charged and contains a nitrogen atom bonded to two hydrogen atoms. It plays a crucial role in the formation of peptide bonds and other reactions discussed in the video. The script mentions that the amino group gets protonated in the zwitterion form of amino acids.

💡Carboxylic Group

The carboxylic group is a functional group in amino acids that is negatively charged and contains a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group. It is involved in various reactions such as the formation of esters and amide bonds, as detailed in the script.

💡Zwitterion

A zwitterion is a molecule that has both positive and negative charges, which is the state of amino acids at physiological pH. In the script, it is mentioned that amino acids exist as zwitterions where the amino group is protonated and the carboxylic group is deprotonated.

💡Salt Formation

Salt formation is a reaction where amino acids react with acids or bases to form salts. In the script, it is explained that amino acids form salts with hydrochloric acid or sodium hydroxide, which involves the interaction of both the amino and carboxylic groups.

💡Peptide Bond

A peptide bond is a chemical bond that links two amino acids together in a protein. The script describes the theoretical and laboratory synthesis of peptide bonds, which is a fundamental concept in understanding protein structure and function.

💡Ester Formation

Ester formation is a reaction where an amino acid reacts with an alcohol in the presence of dry HCl to form an ester. The script explains this reaction as one that is purely due to the involvement of the carboxylic group of the amino acid.

💡Amino Acyl Chlorides

Amino acyl chlorides are reactive compounds formed from amino acids by acylation with thionyl chloride (PCl5). The script describes the process of forming amino acyl chlorides, which involves the protection of the amino group and subsequent reaction with PCl5.

💡Decarboxylation

Decarboxylation is a reaction where a carboxylic acid loses carbon dioxide, resulting in the formation of an amine. The script provides an example of decarboxylation with histidine, which is converted to histamine upon heating with barium hydroxide or diphenylamine.

💡Amide Formation

Amide formation is a reaction where an amino acid ester is treated with ammonia to form an amide. The script explains this reaction as a process that involves the carboxylic group of the amino acid ester, resulting in the formation of an amide bond.

💡Sanger's Reagent

Sanger's reagent is a chemical used in the identification of amino acids. Although not detailed in the script, it is mentioned as a reaction involving the amino group of amino acids, which is part of the broader discussion on reactions due to the involvement of the amino group.

Highlights

Amino acids are organic biomolecules with two oppositely charged functional groups, an amino group and a carboxylic group, covalently bonded to the same carbon atom.

Amino acids exist as zwitterions, where the amino group is protonated and the carboxylic group is deprotonated.

Amino acids participate in various chemical reactions, including salt formation, peptide bond formation, ester formation, and more.

Salt formation occurs when amino acids react with acids or bases, leading to the formation of salts such as the chloride salt with hydrochloric acid.

Peptide bond formation is a key reaction involving both the amino and carboxylic groups of different amino acids, creating a covalent linkage.

Laboratory synthesis of peptide bonds involves heating amino acids with phosgene to form an intermediate that polymerizes into a peptide chain.

Ester formation is a reaction where amino acids react with alcohol in the presence of dry HCl to form esters.

Amino acyl chlorides are formed by acetylating and then treating amino acids with PCl5, followed by removal of the acetyl group with HCl.

Decarboxylation is a reaction where amino acids lose carbon dioxide when heated in the presence of certain compounds, forming amines.

Amide formation involves treating amino acid esters with alcoholic or anhydrous ammonia to yield amides.

The video discusses reactions due to the involvement of both the amino and carboxylic groups, as well as those due to the carboxylic group alone.

The theoretical representation and laboratory synthesis of peptide bonds are explained, highlighting the complexity of the process.

Ester formation is detailed, including the role of dry HCl in breaking the zwitterion structure to form amino acid hydrochloride.

Amino acyl chlorides are shown to be intermediates in the protection and activation of amino acids for further reactions.

Decarboxylation is exemplified by the conversion of histidine to histamine, demonstrating a specific application of the reaction.

Amide formation is described as a two-step process starting from amino acid esters and involving the use of ammonia.

The video promises a follow-up to explain reactions occurring exclusively due to the involvement of the amino group.

Previous videos and references are mentioned for further information on amino acid structure and properties.

The video is prepared by Dr. Dre Pauline Goswami, providing credibility and专业性 to the content.