Amino Acid Color Reactions
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Questions and Answers

What is the reason why cells are able to synthesize L-isomers of amino acids specifically?

  • The active sites of enzymes are asymmetric (correct)
  • The active sites of enzymes are neutral
  • The active sites of enzymes are flexible
  • The active sites of enzymes are symmetric

    • What is the pH at which the overall charge on an amino acid molecule is zero?

  • pH 5
  • Isoelectric point (correct)
  • pH 7
  • pH 3

    • What is the term for a molecule that can act as either an acid or a base?

  • Ampholyte (correct)
  • Ionizable
  • Electrolyte
  • Zwitterion

    • What is the term for a molecule that has both positive and negative charges, but is neutral overall?

    <p>Zwitterion</p> Signup and view all the answers

    What is the term for a simple monoamino monocarboxylic α-amino acid, such as alanine, when fully protonated?

    <p>Diprotic acid</p> Signup and view all the answers

    What happens to an amino acid at a pH more acidic than its isoelectric point?

    <p>It forms a positive ion</p> Signup and view all the answers

    What is a characteristic of amino acids that enables them to resist changes in pH?

    <p>Buffering properties</p> Signup and view all the answers

    What determines the charge of an amino acid at a given pH?

    <p>Its isoelectric point</p> Signup and view all the answers

    What determines the role of an amino acid?

    <p>The structure of the R group</p> Signup and view all the answers

    What is the main difference between amino acids in dietary proteins and structural proteins?

    <p>Their position (D/L) and attachment to alpha carbon</p> Signup and view all the answers

    What is the main characteristic of nonpolar amino acids?

    <p>They are hydrophobic</p> Signup and view all the answers

    What is the function of the peptide bond in proteins?

    <p>To connect amino acids</p> Signup and view all the answers

    At physiological pH, what happens to the carboxyl group of amino acids?

    <p>It dissociates to form a negatively charged ion</p> Signup and view all the answers

    How are amino acids classified based on their R groups?

    <p>By their polarity</p> Signup and view all the answers

    What is the effect of the hydrophobic effect on protein structure?

    <p>It stabilizes protein structure</p> Signup and view all the answers

    What is the simplest amino acid in terms of structure?

    <p>Glycine</p> Signup and view all the answers

    What is the significance of color reactions in amino acids?

    <p>To recognize amino acids and thus proteins</p> Signup and view all the answers

    What is the result of condensation between two amino acid molecules?

    <p>A dipeptide</p> Signup and view all the answers

    What is the term for a chain of many amino acids?

    <p>Polypeptide</p> Signup and view all the answers

    What is the linkage between amino acids in a peptide bond?

    <p>Substituted amide linkage</p> Signup and view all the answers

    What is the direction of the amino acid chain in the figure?

    <p>From N-terminal to C-terminal</p> Signup and view all the answers

    What is the role of ninhydrin in amino acid analysis?

    <p>To give a color reaction specific to all amino acids</p> Signup and view all the answers

    What is the term for a chain of a few amino acids?

    <p>Oligopeptide</p> Signup and view all the answers

    What is the orientation of the R groups in the peptide bond figure?

    <p>Outwards</p> Signup and view all the answers

    What is the significance of the peptide bond in protein structure?

    <p>It joins amino acids together</p> Signup and view all the answers

    What is the term for the end of an amino acid chain with a free amino group?

    <p>N-terminal</p> Signup and view all the answers

    What is the role of disulfide bonds in protein structures?

    <p>Forming covalent links between parts of a polypeptide molecule</p> Signup and view all the answers

    Which amino acid has a positively charged guanidinium group?

    <p>Arginine</p> Signup and view all the answers

    What is the role of histidine residues in enzyme-catalyzed reactions?

    <p>Serving as proton donors/acceptors</p> Signup and view all the answers

    Which of the following amino acids has a net negative charge at pH 7.0?

    <p>Aspartate</p> Signup and view all the answers

    What is the function of γ-carboxyglutamate in proteins?

    <p>Binding to Ca2+</p> Signup and view all the answers

    Which amino acid is a derivative of four lysine residues?

    <p>Desmosine</p> Signup and view all the answers

    What is unique about selenocysteine and pyrrolysine?

    <p>They are added during normal protein synthesis through a highly specialized expansion of the standard genetic code</p> Signup and view all the answers

    What is the role of basic amino acids in proteins?

    <p>They are proton acceptors</p> Signup and view all the answers

    Which amino acid is essential in children but not in adults?

    <p>Histidine</p> Signup and view all the answers

    What is the common feature of glycogenic amino acids?

    <p>They can be converted to α-ketoglutarate, pyruvate, oxaloacetate, fumarate or succinyl CoA</p> Signup and view all the answers

    Which amino acid is converted to tyrosine?

    <p>Phenylalanine</p> Signup and view all the answers

    What is the number of glycogenic amino acids?

    <p>11</p> Signup and view all the answers

    Which amino acid is not essential in humans?

    <p>Glutamate</p> Signup and view all the answers

    What is the common feature of ketogenic amino acids?

    <p>They can be converted to acetyl CoA or acetoacetate</p> Signup and view all the answers

    Which amino acid is converted to cysteine?

    <p>Methionine</p> Signup and view all the answers

    How many amino acids are essential in the human diet?

    <p>8</p> Signup and view all the answers

    Study Notes

    Amino Acids

    • Amino acids have various color reactions with the properties of their specific groups, which is important in recognizing amino acids and thus proteins.
    • Ninhydrin is a color reaction specific to all amino acids.

    Peptides and Polypeptides

    • Two amino acid molecules can be covalently joined through a substituted amide linkage, termed a peptide bond, to yield a dipeptide.
    • When a few amino acids are joined in this fashion, the structure is called an oligopeptide, and when many amino acids are joined, the product is called a polypeptide.

    Polypeptide Chain

    • A polypeptide chain consists of amino acids joined by peptide bonds.
    • The amino terminal of amino acid has a free amino group (NH3+) and the carboxy terminal has a free carboxyl group (COO-).

    Amino Acids as Acids and Bases

    • Each amino acid has a particular pH called the isoelectric point at which the overall charge on an amino acid molecule is zero.
    • At the isoelectric point, an amino acid exists as a zwitterion, with the carboxyl group donating a proton to the amino group.

    Acid-Base Properties

    • Amino acids can act as acids or bases, depending on their R groups.
    • At a pH more acidic than the isoelectric point, the amino acid forms a positive ion, and at a pH more alkaline than the isoelectric point, the amino acid forms a negative ion.

    Classification of Amino Acids

    • Amino acids can be classified into five main classes based on the properties of their R groups:
      1. Nonpolar, aliphatic R groups (e.g., alanine, valine, leucine, isoleucine)
      2. Aromatic R groups (e.g., phenylalanine, tyrosine)
      3. Negatively charged (acidic) R groups (e.g., aspartate, glutamate)
      4. Positively charged (basic) R groups (e.g., lysine, arginine, histidine)
      5. Uncommon R groups (e.g., hydroxyproline, γ-carboxyglutamate)

    Uncommon Amino Acids

    • Uncommon amino acids include 4-hydroxyproline, γ-carboxyglutamate, desmosine, and others.

    Essential Amino Acids

    • Essential amino acids must be taken in through the diet, as humans do not have the enzymes to synthesize them.
    • Essential amino acids for humans include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

    Glycogenic and Ketogenic Amino Acids

    • Glycogenic amino acids are converted to pyruvate, α-ketoglutarate, oxaloacetate, fumarate, or succinyl CoA.
    • Ketogenic amino acids are converted to acetyl CoA or acetoacetate.

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    Description

    Learn about the clinical importance of color reactions in amino acids, their properties, and how to recognize them using Ninhydrin. This is crucial in understanding proteins.

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