Dipolar Nature of Amino Acids
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Questions and Answers

What primarily determines the predominant ionic form of an amino acid in solution?

The pH of the medium primarily determines the predominant ionic form of an amino acid.

Describe the zwitterion form of an amino acid.

The zwitterion form of an amino acid has both a positive and a negative charge, resulting in a net charge of zero.

What is the isoelectric pH (IpH) of an amino acid?

The isoelectric pH (IpH) is the pH at which an amino acid is electrically neutral, with balanced positive and negative charges.

How do the isoelectric pH values differ among various types of amino acids?

<p>Nonpolar amino acids have isoelectric pH values close to 7, while basic amino acids have higher values and acidic amino acids have lower values.</p> Signup and view all the answers

What role does the COOH group play in the formation of the zwitterion?

<p>The COOH group can lose an H+ ion in solution, contributing to the formation of the negative COO- charge in the zwitterion.</p> Signup and view all the answers

What differentiates the two types of enkephalins?

<p>The two enkephalins differ in the amino acid at the carboxyl end of the peptide chain.</p> Signup and view all the answers

What is the role of bradykinin in the body?

<p>Bradykinin is partly responsible for triggering pain and lowering blood pressure.</p> Signup and view all the answers

Describe the first step in protein sequencing.

<p>The first step in protein sequencing is hydrolysis, which can be performed using acid, alkali, or enzymes.</p> Signup and view all the answers

What is the typical condition used for acid hydrolysis of proteins?

<p>Acid hydrolysis typically involves heating in the presence of 6N HCl at 110 °C for 10 to 100 hours.</p> Signup and view all the answers

In the construction of a peptide sequence, what technique is used after hydrolysis?

<p>After hydrolysis, the next step is the identification of the products of hydrolysis.</p> Signup and view all the answers

What is the significance of the C-terminal end in peptide synthesis?

<p>The C-terminal end contains a free carboxyl group and is where amino acids are added by forming peptide bonds.</p> Signup and view all the answers

How are peptides named based on their amino acid composition?

<p>Peptides are named starting with the N-terminal amino acid, using the suffix -yl for each amino acid except the C-terminal amino acid, which retains its full name.</p> Signup and view all the answers

Describe the planar nature of peptide bonds and its physiological importance.

<p>Peptide bonds have partial double bond character, making them rigid and planar, which helps maintain the structure of proteins critical for their function.</p> Signup and view all the answers

What must be true about the amino acids in aspartame for it to taste sweet?

<p>Both amino acids in aspartame must be in the L-form for it to be sweet; other forms lead to a bitter taste.</p> Signup and view all the answers

Identify the components of glutathione and its primary role in the body.

<p>Glutathione is composed of Glu-Cys-Gly and functions as an antioxidant, regulating oxidation-reduction reactions.</p> Signup and view all the answers

What distinguishes the bonding in glutathione compared to typical peptides?

<p>In glutathione, Glu is bonded to Cys through the side-chain carboxyl group rather than the α-carbon carboxyl group.</p> Signup and view all the answers

Why are peptide bonds resistant to changes in salt concentration or pH?

<p>Peptide bonds are covalent and stable, not directly influenced by salt concentration or changes in pH.</p> Signup and view all the answers

Explain the concept of peptide bond trans configuration.

<p>Almost all peptide bonds have a trans configuration, where the two adjacent α-carbons lie opposite to each other, contributing to the planar structure.</p> Signup and view all the answers

What are the main disadvantages of alkaline hydrolysis in protein analysis?

<p>Alkaline hydrolysis destroys arginine, cysteine, threonine, and serine, and partially deaminates some amino acids.</p> Signup and view all the answers

How do exopeptidases function in determining the amino acid sequence of peptides?

<p>Exopeptidases cleave external peptide bonds at either the N-terminal or C-terminal ends, allowing for the identification of liberated amino acids sequentially.</p> Signup and view all the answers

What governs the formation of the beta-pleated sheet structure in proteins?

<p>Intermolecular hydrogen bonds between protein chains govern the formation of the beta-pleated sheet structure.</p> Signup and view all the answers

Compare the N-terminal identification methods: Sanger's method and Edman's method.

<p>Sanger's method uses dinitrofluorobenzene to label the N-terminal, while Edman's method utilizes phenylisothiocyanate to produce a phenylthiohydantoin compound.</p> Signup and view all the answers

What role does tryptophan play in alkaline hydrolysis compared to acid hydrolysis?

<p>Tryptophan remains intact during alkaline hydrolysis, while it is completely destroyed in acid hydrolysis.</p> Signup and view all the answers

Differentiate between parallel and antiparallel beta-pleated sheet structures.

<p>In parallel structures, chains run in the same direction, while in antiparallel structures, chains run in opposite directions.</p> Signup and view all the answers

What is the significance of the time-course analysis with aminopeptidase and carboxypeptidase?

<p>It allows researchers to determine the relative concentrations and sequences of amino acids released during hydrolysis.</p> Signup and view all the answers

What are supersecondary structures in proteins?

<p>Supersecondary structures refer to combinations of alpha-helices and beta-pleated sheets.</p> Signup and view all the answers

Explain the importance of tertiary structure in proteins.

<p>The tertiary structure determines the overall three-dimensional shape of the protein, defining its biological function.</p> Signup and view all the answers

List the amino acids that are simultaneously released during the hydrolysis with carboxypeptidase in the pentapeptide analysis.

<p>Cysteine and arginine are released simultaneously in equal amounts.</p> Signup and view all the answers

Describe the main function of aminopeptidases in protein hydrolysis.

<p>Aminopeptidases sequentially cleave peptide bonds starting from the N-terminal end of the polypeptide.</p> Signup and view all the answers

List the interactions that contribute to maintaining tertiary structure in proteins.

<p>Salt linkages, hydrogen bonds, disulfide bonds, hydrophobic bonds, van der Waals forces, and polar interactions with water.</p> Signup and view all the answers

What outcomes can result from heating proteins in alkaline hydrolysis?

<p>Proteins undergo hydrolysis, but certain amino acids like arginine, cysteine, and threonine are destroyed.</p> Signup and view all the answers

What is the role of salt linkages in protein structure?

<p>Salt linkages form between positively and negatively charged side chains, contributing to protein stability.</p> Signup and view all the answers

How does the presence of both fibrous and globular proteins affect protein function?

<p>Fibrous proteins provide structural strength, while globular proteins are involved in transport, regulatory functions, and enzymatic activity.</p> Signup and view all the answers

Why are proteins with a beta-pleated sheet structure often crystalline and insoluble in aqueous solvents?

<p>The extensive hydrogen bonding and regular arrangement of chains in beta-pleated sheets lead to crystallinity and low solubility.</p> Signup and view all the answers

Study Notes

Dipolar Nature of Amino Acids

  • Amino acids exist in various ionic forms in aqueous solution, predominance depending on the pH of the medium.
  • The carboxyl group (COOH) can lose H+ to form negative COO-.
  • The amino group (NH2) can accept H+ to become positively charged (+NH3).
  • The internal salt or zwitterion formation occurs, resulting in a neutral molecule with both positive and negative charges.
  • The isoelectric pH (IpH) is the pH at which the zwitterion form exists and the molecule is electrically neutral, not migrating toward electrodes.
  • Isoelectric points vary: nonpolar amino acids near pH 7, basic amino acids at higher pH, and acidic amino acids at lower pH.

Peptide Bond Formation

  • Peptides form by creating peptide bonds with the C-terminal amino acid.
  • Peptide names derive from their amino acid sequences, starting with the N-terminal and using the suffix "-yl" for all but the C-terminal amino acid.
  • The C-N bond in peptide linkages has partial double bond character, providing rigidity and a planar structure.
  • Peptide bonds stabilize protein structures and are resistant to salt concentration changes, pH shifts, and solvents, although they can be hydrolyzed chemically or enzymatically.

Biochemically Important Peptides

  • Aspartame (Asp-Phe): An artificial sweetener, 180 times sweeter than sucrose, requiring L-forms for sweetness.
  • Glutathione (GSH - Glu-Cys-Gly): An antioxidant tripeptide protecting cells from reactive oxygen species.
  • Enkephalins: Pentapeptides (Tyr-Gly-Gly-Phe-Leu & Tyr-Gly-Gly-Phe-Met) that bind to receptors in the brain to reduce pain.
  • Structural comparisons of peptides show variations in sequence lead to different biological activities, e.g., Bradykinin and Boguskinin.

Protein Sequencing and Hydrolysis

  • Protein sequencing involves hydrolysis (acid, alkaline, or enzyme) followed by product identification and assembly of sequences.
  • Acid Hydrolysis: Uses 6N HCl; destroys tryptophan but fully hydrolyzes proteins.
  • Alkaline Hydrolysis: Employs 4N NaOH; preserves tryptophan while damaging certain amino acids.
  • Enzymatic Hydrolysis: Utilizes proteases like exopeptidases for N-terminal and C-terminal sequence determination.

Protein Structures

  • Pleated-sheet structure (β-conformation): Characterized by hydrogen bonds creating zigzag sheets; stability differs between parallel and antiparallel structures.
  • Supersecondary structures: Comprise combinations of α-helices and β-pleated sheets, with portions of proteins typically having random structures.

Tertiary Structure of Proteins

  • The three-dimensional shape resulting from interactions among amino acid side chains, defining protein function.
  • Tertiary structures can be fibrous (insoluble, structural support) or globular (soluble, functional roles).
  • Stabilizing interactions include:
    • Salt linkages (ionic interactions),
    • Hydrogen bonds,
    • Disulfide bonds,
    • Hydrophobic interactions,
    • Van der Waals forces,
    • Polar interactions with water.

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Description

This quiz explores the dipolar nature of amino acids in aqueous solutions, focusing on their ionic forms depending on the pH. It discusses the behavior of carboxyl and amino groups in retaining or losing protons. Test your understanding of these concepts and how they influence amino acid properties.

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