Amino Acids and Peptides Overview
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Questions and Answers

What is the definition of an amino acid?

A compound that contains both an amino group (-NH2) and a carboxyl group (-COOH).

There are 19 amino acids commonly found in proteins.

False (B)

Which functional group is NOT found in amino acids?

  • Alcohols (R-OH)
  • Amines (R-NH2)
  • Carboxylic acids (R-COOH)
  • Aldehydes (R-CHO) (correct)

    • Which of the following amino acids has a cyclic structure?

    <p>Proline (C)</p> Signup and view all the answers

    Which amino acid group contains a thiol group (-SH)?

    <p>Neutral Polar (A)</p> Signup and view all the answers

    The ______ group of amino acids can lose a proton, forming a carboxylate ion.

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

    Which of the following amino acids is NOT essential?

    <p>Alanine (C)</p> Signup and view all the answers

    What is the definition of an amphoteric molecule?

    <p>A molecule that can act as either an acid or a base, depending on the pH of the solution.</p> Signup and view all the answers

    What does the pKa value of an amino acid refer to?

    <p>The apparent dissociation constant, which indicates how acidic or basic a given hydrogen atom in a molecule is.</p> Signup and view all the answers

    What is the isoelectric point (pI) of an amino acid?

    <p>The pH at which the majority of molecules of a compound in solution have no net charge.</p> Signup and view all the answers

    Electrophoresis separates compounds based on their size.

    <p>False (B)</p> Signup and view all the answers

    What is a peptide bond?

    <p>The special name given to the amide bond between the carboxyl group of one amino acid and the amino group of another amino acid.</p> Signup and view all the answers

    A polypeptide is a macromolecule containing:

    <p>Many amino acids joined by peptide bonds (D)</p> Signup and view all the answers

    What is the difference between a polypeptide and a protein?

    <p>A protein is a biological macromolecule of molecular weight 5000 g/mol or greater, consisting of one or more polypeptide chains.</p> Signup and view all the answers

    What is the name given to a peptide containing two amino acids?

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

    What is the function of L-carnosine?

    <p>It comes from meat and is useful in the prevention of damage caused by too much sugar.</p> Signup and view all the answers

    Which of the following peptides is involved in regulating blood pressure?

    <p>Vasopressin (C)</p> Signup and view all the answers

    What are the two amino acids that make up oxytocin?

    <p>Cysteine and Tyrosine</p> Signup and view all the answers

    What are the two amino acids that make up vasopressin?

    <p>Cysteine and Tyrosine</p> Signup and view all the answers

    At what pH are the amino acids in a zwitterion form?

    <p>Isoelectric point (C)</p> Signup and view all the answers

    What is the charge of the amino acid at pH 1?

    <p>The amino acid will have a net positive charge.</p> Signup and view all the answers

    Amino acids that migrate towards the cathode during electrophoresis are negatively charged.

    <p>True (A)</p> Signup and view all the answers

    What process is used to separate compounds based on their electric charge?

    <p>Electrophoresis (B)</p> Signup and view all the answers

    What is an amino acid?

    <p>A compound that contains both an amino group and a carboxyl group.</p> Signup and view all the answers

    Where is the amino group located in an amino acid?

    <p>Attached to the carbon adjacent to the carboxyl group.</p> Signup and view all the answers

    What is the significance of the R group in an amino acid?

    <p>The R group gives identity to the amino acid, and it varies depending on the specific amino acid.</p> Signup and view all the answers

    There are only two steroisomers of amino acids.

    <p>True (A)</p> Signup and view all the answers

    How many amino acids are commonly found in proteins?

    <p>20</p> Signup and view all the answers

    Which of the following functional groups are NOT found in amino acids?

    <p>Ketones (B)</p> Signup and view all the answers

    What is the difference between nonpolar and polar side chains in amino acids?

    <p>Nonpolar side chains are hydrophobic, meaning they repel water. Polar side chains are hydrophilic, meaning they attract water.</p> Signup and view all the answers

    Which of the following amino acids contains an aromatic ring?

    <p>All of the above (D)</p> Signup and view all the answers

    Which of the following amino acids has a sulfur atom in its side chain?

    <p>Both A and B (B)</p> Signup and view all the answers

    Which of the following groups of amino acids contains polar hydroxyl groups in their side chains?

    <p>Ser, Thr, Tyr (D)</p> Signup and view all the answers

    Which of the following groups of amino acids contains thiol groups in their side chains?

    <p>Cys, Glu, Asn (B)</p> Signup and view all the answers

    Glutamic acid and aspartic acid are acidic amino acids because they contain carboxyl groups in their side chains.

    <p>True (A)</p> Signup and view all the answers

    Which of the following groups of amino acids contains positively charged side chains at pH 7?

    <p>His, Lys, Arg (B)</p> Signup and view all the answers

    What is a zwitterion?

    <p>A molecule that has both a positive and a negative charge.</p> Signup and view all the answers

    How is electrophoresis used to separate amino acids?

    <p>Electrophoresis separates compounds on the basis of their electric charge and is used to separate amino acids by applying an electric field to a mixture of amino acids.</p> Signup and view all the answers

    Essential amino acids can be synthesized by the body.

    <p>False (B)</p> Signup and view all the answers

    Which of the following describes a molecule containing two amino acids joined by a peptide bond?

    <p>dipeptide (D)</p> Signup and view all the answers

    What is the function of carnosine?

    <p>Carnosine is used in the prevention of damage caused by too much sugar and concentrated in the muscles, it is sometimes used in the treatment of complications of diabetes.</p> Signup and view all the answers

    What are the two hormones that contain disulfide bonds and that are important for human health?

    <p>Oxytocin and vasopressin.</p> Signup and view all the answers

    Which of the following amino acids is found in carnosine?

    <p>Both A and C (D)</p> Signup and view all the answers

    What is the structure of the peptide bond like?

    <p>Planar, with bond angles of 120° about the carbon and nitrogen atoms.</p> Signup and view all the answers

    What is the name given to a short polymer of amino acids joined by peptide bonds?

    <p>A peptide.</p> Signup and view all the answers

    Flashcards

    Amino Acid Structure

    An amino acid is a molecule containing both an amino group and a carboxyl group. The "R" group differentiates one amino acid from another.

    Alpha-Carbon

    The carbon atom adjacent to both the amino and carboxyl groups in an amino acid.

    R-group

    The unique side chain that distinguishes each amino acid.

    L- and D- Isomers

    Different spatial configurations (mirror images) of amino acids, with L-amino acids being more common in proteins.

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    20 Common Amino Acids

    The building blocks of proteins, each with a unique R-group.

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    Nonpolar Side Chains

    Amino acid side chains that do not readily interact with water.

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    Neutral Polar Side Chains

    Amino acid side chains that slightly interact with water.

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    Acidic Side Chains

    Amino acid side chains that have a negative charge at neutral pH.

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    Basic Side Chains

    Amino acid side chains that have a positive charge at neutral pH.

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    Ionization of Amino Acids

    The process of gaining or losing protons by amino acid groups (carboxyl and amino) based on pH.

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    pKa

    The pH at which half of the molecules of a particular group are protonated and half are deprotonated.

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    pI (Isoelectric Point)

    The pH at which an amino acid or protein carries no net electrical charge.

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    Electrophoresis

    A technique that separates charged molecules based on their charge and size.

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    Peptide Bond

    A covalent bond formed between the carboxyl group of one amino acid and the amino group of another.

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    Dipeptide

    A chain of two amino acids linked by a peptide bond.

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    Polypeptide

    A chain of many amino acids linked by peptide bonds.

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    Protein

    A biological macromolecule composed of one or more polypeptide chains.

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    L-carnosine

    A dipeptide with potential health benefits, especially related to sugar management.

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    What is an amino acid?

    A molecule containing both an amino group (NH2) and a carboxyl group (COOH).

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    What's the alpha carbon?

    The carbon atom directly attached to both the amino and carboxyl groups in an amino acid.

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    What is the R-group?

    The unique side chain attached to the alpha carbon, giving each amino acid its distinct properties.

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    L-isomer

    One of the two mirror-image forms of an amino acid, found in most proteins.

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    D-isomer

    One of the two mirror-image forms of an amino acid, less common in proteins.

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    How many common amino acids are there?

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    What is ionization?

    The process of gaining or losing protons (H+) from atoms or molecules based on the pH of the solution.

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    What is the isoelectric point (pI)?

    The pH at which an amino acid or protein has no net electric charge - it's neutral.

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    What is electrophoresis?

    A technique that separates charged molecules based on their size and charge by applying an electric field.

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    What is a peptide bond?

    The special covalent bond between the carboxyl group of one amino acid and the amino group of another.

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    What is L-carnosine?

    A dipeptide found in meat, potentially beneficial for sugar management.

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    Zwitterion

    A molecule that has both a positive and negative charge but overall is neutral.

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    What happens at low pH?

    Both the amino and carboxyl groups are protonated (positive charge).

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    What happens at high pH?

    Both the amino and carboxyl groups are deprotonated (negative charge).

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    What happens at neutral pH?

    The amino group is protonated (positive charge) and the carboxyl group is deprotonated (negative charge).

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    What's the charge of amino acids at their pI?

    Zero - they have no net charge.

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    How do amino acids move in electrophoresis?

    Based on their charge: positively charged move towards the cathode (negative electrode), negatively charged move towards the anode (positive electrode).

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    What determines the direction of amino acid movement in electrophoresis?

    The pH of the buffer solution - it determines the charge of the amino acids.

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    What is the difference between a peptide and a protein?

    A peptide is a short chain of amino acids, while a protein is a longer, more complex chain of amino acids, often with a specific function.

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    Study Notes

    Amino Acids and Peptides

    • Amino acids are compounds containing both an amino group and a carboxyl group.
    • Each amino acid has a central carbon atom (alpha carbon) bonded to a hydrogen atom, an amino group, a carboxyl group, and a side chain (R group).
    • The R group distinguishes different amino acids.
    • Two stereoisomers of amino acids exist: L- and D- amino acids. L-amino acids are typically found in proteins.
    • Twenty common amino acids are found in proteins.
    • These amino acids have different functional groups: alcohols (R-OH), phenols (Ph-OH), carboxylic acids (R-COOH), thiols (R-SH), amines (R-NH2), and amides (R-CONH2).

    Amino Acid Groups

    • Group A: Nonpolar side chains: These include Ala, Val, Leu, Ile, Pro, Phe, Trp, and Met.

      • Ala, Val, Leu, and Ile have aliphatic hydrocarbon side chains.
      • Proline has a cyclic structure.
      • Phenylalanine (Phe) and Tryptophan (Trp) have aromatic rings.
      • Methionine (Met) has a sulfur atom in its side chain.

    • Group B: Neutral Polar side chains: These include Ser, Thr, Tyr, Cys, Glu, and Asn.

      • Serine (Ser) and Threonine (Thr) have polar hydroxyl groups.
      • Tyrosine (Tyr) has a hydroxyl group bonded to an aromatic ring.
      • Cysteine (Cys) contains a thiol group (-SH).
      • Glutamine (Gln) and Asparagine (Asn) contain amide bonds in their side chains.

    • Group C: Acidic side chains: These include Asp and Glu.

      • Both have carboxyl groups in their side chains.
      • They can lose a proton and exist as negatively charged carboxylate ions at neutral pH.

    • Group D: Basic side chains: These include His, Lys, and Arg.

      • Arginine (Arg) has a guanidino group.
      • Histidine (His) has an imidazole group.
      • Lysine (Lys) has an amino group in its side chain that can be positively charged.

    Important Structural Features

    • All 20 amino acids are α-amino acids (with the exception of proline, which is a secondary amino acid).
    • With the exception of glycine, the α-carbon of each amino acid is a stereocenter.
    • Isoleucine and threonine have a second stereocenter.

    Essential and Non-Essential Amino Acids

    • Essential amino acids cannot be synthesized by the body and must be obtained from the diet.
    • Non-essential amino acids can be synthesized by the body.

    Peptide Bonds

    • Individual amino acids can be joined by peptide bonds to form proteins.
    • A peptide bond is a covalent amide bond formed between the carboxyl group of one amino acid and the amino group of another.
    • The peptide bond has a planar geometry.

    Peptide Nomenclature

    • Dipeptide: Two amino acids joined
    • Tripeptide: Three amino acids joined
    • Polypeptide: Many amino acids joined

    Proteins

    • Proteins are large biological macromolecules composed of one or more polypeptide chains.
    • They are crucial for various biological functions.

    Amphoteric Nature of Amino Acids

    • Amino acids are amphoteric, meaning they can act as both acids and bases.
    • The carboxyl group can lose a proton (act as an acid), and the amino group can accept a proton (act as a base).

    Isoelectric Point (pI)

    • The pI is the pH at which the amino acid exists primarily in its zwitterionic form (neutral charge).
    • The pI is calculated as the average of the pKa values.

    Electrophoresis

    • Electrophoresis is a technique used to separate molecules based on their charge, size, or mass.
    • In amino acid electrophoresis, amino acids can be separated based on the charge present at a pH of 7.1.
    • Proteins and amino acids with a negative net charge migrates toward the anode.
    • Proteins and amino acids with a positive net charge migrates toward the cathode.

    Examples of Amino Acids

    • Specific examples of their structures and pKa values (e.g. Alanine or Cysteine) are included in the text.
    • Information on the pI includes how the calculation is made from component pKa values (e g- from Alanine or Cysteine calculation.).

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    Lecture 6: Amino Acids and Peptides PDF

    Description

    This quiz covers the fundamental concepts of amino acids and peptides, including their structure and classification. Learn about different amino acid groups and their properties, which are essential for understanding protein composition. Test your knowledge on the twenty common amino acids and their functional groups.

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