Amino Acid Structure and Classification
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Amino Acid Structure and Classification

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Questions and Answers

What distinguishes α, β, and δ amino acids?

  • The position of the amino group in the carbon chain (correct)
  • Their side chain composition
  • Their occurrence in prokaryotic organisms
  • The number of carbon atoms in the chain

    • Why do amino acids have optical activity?

  • They are zwitterionic in nature
  • They contain a chiral carbon atom (correct)
  • They are all saturated compounds
  • They have symmetrical structures

    • Which statement is true regarding amino acids found in mammalian proteins?

  • Some amino acids do not exhibit amphoteric properties
  • D-amino acids are predominant
  • All standard amino acids have only L-forms (correct)
  • There are 12 standard amino acids in mammalian proteins

    • Which group is found at the alpha carbon of amino acids?

    <p>Carboxyl group and amin group</p> Signup and view all the answers

    What unique property do amino acids exhibit due to being zwitterions?

    <p>Can act as both acids and bases</p> Signup and view all the answers

    Which of the following amino acids is classified as an imino acid?

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

    What is the significance of L- and D- amino acids in biological systems?

    <p>Only L-amino acids are used to build proteins in mammals</p> Signup and view all the answers

    What results from the modification of standard amino acids?

    <p>Creation of non-standard amino acids</p> Signup and view all the answers

    Which of the following amino acids is classified as an essential amino acid?

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

    What is the characteristic of complete proteins?

    <p>They contain all essential amino acids.</p> Signup and view all the answers

    Which of the following amino acids is considered semi-essential?

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

    How are amino acids generally grouped?

    <p>According to their side chain properties</p> Signup and view all the answers

    Which non-polar amino acid has a hydrogen atom as its R group?

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

    What type of proteins are most vegetable proteins classified as?

    <p>Incomplete proteins</p> Signup and view all the answers

    Which of the following amino acids is NOT an aromatic amino acid?

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

    Which amino acids are involved in hydrophobic interactions due to their hydrocarbon R groups?

    <p>Leucine and valine</p> Signup and view all the answers

    Which of the following amino acids is classified as basic?

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

    What distinguishes essential amino acids from non-essential amino acids?

    <p>Essential amino acids must be obtained from the diet.</p> Signup and view all the answers

    Which amino acid is known for functioning as a neurotransmitter?

    <p>L-Dopamine</p> Signup and view all the answers

    What role does the -OH group in tyrosine play in proteins?

    <p>It acts as a site for phosphorylation and hydrogen bonding.</p> Signup and view all the answers

    Which of the following amino acids is negatively charged at pH 7.0?

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

    Which of the following classifications includes both glucogenic and ketogenic amino acids?

    <p>Semi-essential amino acids</p> Signup and view all the answers

    Which amino acid contains a sulfur atom in its side chain, contributing to hydrophilic interactions?

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

    Which amino acid belongs to the polar category?

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

    What is a primary source of essential amino acids?

    <p>Dairy products</p> Signup and view all the answers

    What characteristic of proline affects its flexibility in protein structures?

    <p>It contains an imino group forming a five-membered ring.</p> Signup and view all the answers

    Which statement accurately describes electrically charged amino acids?

    <p>Electrically charged amino acids can be either acidic or basic.</p> Signup and view all the answers

    Which of the following amino acids is NOT classified as an aromatic amino acid?

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

    What is the significance of the side chain properties in amino acids?

    <p>They affect the amino acid's solubility and reactivity.</p> Signup and view all the answers

    Which amino acid is a dimer of cysteine?

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

    What is the pK value of the α-carboxylic group in amino acids typically in the range of?

    <p>2.2</p> Signup and view all the answers

    At what point is an amino acid considered electrically neutral?

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

    What occurs in solutions that are more basic than the isoelectric point for amino acids?

    <p>The amino acid donates a proton</p> Signup and view all the answers

    Which of the following amino acids is polar and uncharged?

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

    Which amino acid has a second carboxyl group that affects its acidic properties?

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

    What does the term 'zwitterion' refer to in relation to amino acids?

    <p>An amino acid with both positive and negative charges</p> Signup and view all the answers

    What happens at the pH of an amino acid's isoelectric point?

    <p>The positive and negative charges are equal</p> Signup and view all the answers

    Study Notes

    Amino Acid Structure

    • Amino acids are organic molecules containing both carboxyl and amino groups.
    • Amino acids are the building blocks of proteins.
    • They contain a carboxylic acid group and an amino group on the alpha (α) carbon.
    • Amino acids differ in their properties due to differing side chains.
    • Side chains are called R groups.

    α-Carbon

    • The alpha carbon is an asymmetrical carbon atom giving the amino acids optical activity.

    Amino Acid Structure

    • Amino acids can be characterized as α, β, or δ depending on the location of the amino group in the carbon chain.
    • α amino acids are found on the carbon adjacent to the carboxyl group.
    • β amino acids are found on the 2nd carbon from the carboxyl group.
    • δ amino acids are found on the 3rd carbon from the carboxyl group.

    Amino Acids

    • 20 standard amino acids are present in mammalian proteins.
    • All amino acids have amphoteric properties, meaning they can act as both an acid and a base.
    • All amino acids except glycine have optical activity.
    • Amino acids are dipolar, having both charges.
    • The positive end is NH3+.
    • The negatve end is COO-.
    • Non-standard amino acids come from modifications of standard amino acids.
    • Amino acids have Stereoisomers.
    • All amino acids except glycine have chiral carbon (asymmetrical carbon atom).
    • L-amino acids are natural amino acids found in protein.
    • D-amino acids are found in antibiotics and plant and bacterial cell walls.

    Proline

    • Proline is an imino acid, meaning it has a secondary amino group.

    Amino Acid Abbreviations

    • Each amino acid has a three letter abbreviation and a one letter symbol.
    • The three letter abbreviation is commonly the first three letters of the amino acid name.
    • The one-letter symbol is typically the first letter of the amino acid name.
    • When these abbreviations are confusing, alternative abbreviations are used.

    Amino Acid Functions

    • Amino acids are the building blocks of proteins.
    • Some amino acids and their derivatives function as neurotransmitters and other regulators.
    • Neurotransmitters and regulators include L-dopamine, epinephrine, thyroxine, and histamine.

    Classification of Amino Acids

    • Essential or Non-Essential
    • Glucogenic, ketogenic, or Glucogenic & ketogenic
    • Neutral, acidic, and basic
    • According to the side chain properties

    Essential & Non-Essential Amino Acids

    • Essential amino acids are not synthesized by the human body and must be obtained from the diet.
    • Essential amino acids are present in dairy products.
    • Sources of protein come from both animal and vegetable sources.
    • Animal sources are complete proteins, meaning they contain all essential amino acids.
    • Vegetable sources usually lack some essential amino acids.
    • They are classified as semi-essential or conditionally essential amino acids, including arginine, cysteine, glutamine, glycine, and proline.

    Essential Amino Acids

    • Essential amino acids are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.
    • Non-Essential amino acids are: alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine.

    Complete Protein

    • Complete protein contains all 10 essential amino acids.
    • Incomplete protein lacks one or more essential amino acids.
    • Most vegetable proteins are incomplete proteins with the exception of beans.
    • Beans contain some complete protein.

    Classification According to Side Chain Properties

    • Non-polar (Hydrophobic)

    • Side chain does not bind or give off protons.

    • They promote hydrophobic interactions.

    • They are clustered in the interior of a protein when in aqueous solution.

    • They help give 3D shape to the protein structure.

    • Non-polar (Hydrophobic), Aliphatic Amino Acids

    • Glycine (Gly or G)

    • Alanine (Ala or A)

    • Valine (Val or V)

    • Leucine (Leu or L)

    • Isoleucine (Ile or I)

    • Methionine (Met or M)

    • Non-polar (Hydrophobic), Aromatic Amino Acids

    • Phenylalanine (Phe or F)

    • Tryptophan (Trp or W)

    • Proline (Pro or P)

    Polar (Hydrophilic) Uncharged Amino Acids

    • Serine (Ser or S)

    • Threonine (Thr or T)

    • Cysteine (Cys or C)

    • Tyrosine (Tyr or Y)

    • Asparagine (Asn or N)

    • Glutamine (Gln or Q)

    • The six amino acids with polar, uncharged R groups are more hydrophilic due to the presence of hydroxyl groups, sulfur atoms, or amide groups.

    • The SH group of two Cysteine residues in proteins can be oxidized to form a covalent disulfide bond.

    • Cys often participates in hydrophobic interactions.

    • Pro has a five-membered ring structure, being rigid in conformation and offering the least flexibility.

    • Pro is often found in the bends of folded protein chains and on the surface of proteins.

    Positively Charged (Basic) and Negatively Charged (Acidic) R Groups

    • The most hydrophilic R groups are those either positively or negatively charged.
    • Asp and Glu have a carboxyl group in their R groups.
    • They have a net negative charge at pH 7.0.
    • They are typically named aspartate and glutamate.
    • Arg, Lys, and His have positively charged R groups at pH 7.0.
    • Their R groups contain a guanidino, amino, or imidazole group respectively.
    • The side chain of His can be positively or uncharged depending on the local environment near pH 7.0.

    Polar (Hydrophilic) Charged Amino Acids

    • Negatively charged

    • Aspartic Acid (Asp or D)

    • Glutamic Acid (Glu or E)

    • Positively charged

    • Lysine (Lys or K)

    • Arginine (Arg or R)

    • Histidine (His or H)

    Cystine

    • Cystine is a dimer of cysteine.

    Sickle Cell Disease

    • Sickle cell disease is a pathology that results from the substitution of polar glutamate by the non-polar valine in the B subunit of hemoglobin.

    pK Value

    • pK value measures the ability of an acid to donate a proton (dissociate).
    • It is also known as pKa or the acid dissociation constant.
    • pK value represents the pH at which 50% of the acid is dissociated.
    • The pK values of α-carboxylic groups are typically in the range of 2.2.
    • The pK values of α-amino groups are typically in the range of 9.4
    • The smaller the pK value, the stronger the acid.
    • The larger the pK values, the weaker the acid.

    Zwitterion

    • Zwitterion is a double ion.
    • Zwitterion is formed when both NH3+ and COO- are ionized.
    • At the isoelectric point (pI), the positive and negative charges in the zwitterion are equal.
    • pI is the pH at which the molecule is electrically neutral.

    Amino Acids as Acids or Bases

    • Amino Acids as Acids

      • In solutions that are more basic than the pI, the —NH3+ in the amino acid donates a proton.

    • Amino Acids as Bases

      • In solutions more acidic than the pI, the COO- in the amino acid accepts a proton.

    pH and Ionization

    • Acidic amino acids, such as aspartic acid, have a second carboxyl group that can donate and accept protons.
    • The pI for aspartic acid occurs at a pH of 2.8.

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    Lecture 1 Amino Acids PDF

    Description

    This quiz explores the structure of amino acids, their classification based on the position of amino groups, and their role as building blocks of proteins. Test your knowledge about α, β, and δ amino acids, as well as their unique properties and functions in biological systems.

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