Proteins and Amino Acids Quiz
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Questions and Answers

What is the primary element that distinguishes proteins from carbohydrates and lipids?

  • Carbon
  • Oxygen
  • Hydrogen
  • Nitrogen (correct)

    • Proteins are made up of more than 20 standard amino acids.

    False

    What are the small units that proteins can be broken down into called?

    Amino acids

    The Greek word that the term 'protein' is derived from means '______'.

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

    Match the following elements with their presence in proteins:

    <p>C = Present in proteins N = Present in proteins S = Occasionally present in proteins I = Rarely present in proteins</p> Signup and view all the answers

    How many standard amino acids can proteins be composed of?

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

    Who suggested the term 'proteins' to GJ Mulder?

    <p>JJ Berzelius</p> Signup and view all the answers

    Which of the following amino acids is classified as having a non-polar R group?

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

    All amino acids with polar but uncharged R groups are hydrophobic.

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

    What is the one-letter symbol for Cysteine?

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

    The amino acid ______________ has a positively charged R group.

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

    Match the amino acids with their classifications:

    <p>Alanine = Non-polar R group Serine = Polar but uncharged R groups Aspartic acid = Negatively charged polar R group Histidine = Positively charged polar R group</p> Signup and view all the answers

    Which amino acid is commonly considered to have an ambiguous classification due to its side chain?

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

    Glycine has the largest R group among amino acids.

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

    Name one amino acid that is classified as negatively charged.

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

    Out of the following amino acids, ______________ is classified as a polar but uncharged R group.

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

    Which amino acid has both a polar side chain and an ionizable group?

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

    Which amino acid has a thiol ether side chain?

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

    Proline is categorized as an a-amino acid.

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

    What is the formula for Tryptophan?

    <p>COO- H3N+-C-H CH2 NH</p> Signup and view all the answers

    Tyrosine is a derivative of ___________ with a phenolic group.

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

    Match the following amino acids with their characteristics:

    <p>Serine = Contains a hydroxylic group Threonine = Has a larger hydroxylic group than Serine Tyrosine = Contains a phenolic group Proline = Has a pyrrolidine ring structure</p> Signup and view all the answers

    Which amino acid is known for its aromatic side chain?

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

    Valine is classified as a polar amino acid.

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

    Which amino acid has an amide-bearing side chain?

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

    The amino acid ___________ features a side chain that can form hydrogen bonds due to its hydroxyl group.

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

    What distinguishes Proline from other amino acids?

    <p>It features a pyrrolidine ring</p> Signup and view all the answers

    Which of the following amino acids is classified as a dicarboxylic amino acid?

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

    All non-essential amino acids can be synthesized by the body.

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

    Name two essential amino acids.

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

    __________ amino acids can be converted into glucose via gluconeogenesis.

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

    Match the type of amino acid to their classification:

    <p>Lysine = Essential amino acid Aspartate = Non-essential amino acid Leucine = Essential amino acid Glutamate = Non-essential amino acid</p> Signup and view all the answers

    Which amino acid carries a positive charge at physiological pH due to its protonated side chain?

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

    Glutamic acid does not carry a negative charge at physiological pH.

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

    What is the pK of Arginine, making it the most basic amino acid?

    <p>13</p> Signup and view all the answers

    Cysteine can form _______ bonds with another cysteine through oxidation.

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

    Match the following amino acids with their corresponding formulas:

    <p>Asparagine = NH2-C-CH2-C-COOH Lysine = NH2-CH2-CH2-CH2-CH2-C-COOH Cysteine = HS-CH2-CH(COOH)-NH2 Histidine = NH2-CH2-C-COOH</p> Signup and view all the answers

    Which of the following amino acids contains an imidazoline ring in its side chain?

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

    Histidine is fully charged at physiological pH.

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

    What are the names given to aspartic acid and glutamic acid when they are ionized?

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

    The primary amino acid with a pK of ______ is Histidine.

    <p>6.0</p> Signup and view all the answers

    Which amino acid is known for its ability to form cystine by bonding with another cysteine?

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

    Study Notes

    Introduction to Amino Acids

    • Amino acids are the building blocks of proteins.
    • Proteins are large molecules with a high molecular weight, ranging from 5,000 to 25,000,000.
    • Proteins can be broken down into smaller units called amino acids by hydrolysis.
    • There are 20 standard amino acids.
    • Proteins are unbranched polymers of L-α-amino acids.
    • Amino acids are classified based on the polarity and charge of their R groups.

    Protein Composition

    • Proteins contain C, H, O, and N, with nitrogen comprising approximately 16% of their molecular weight.
    • Other elements, such as I, Cu, Mn, Zn, and Fe, may also be present in small amounts.
    • In 1839, Dutch chemist G.J. Mulder identified nitrogenous compounds in milk and eggs.
    • Swedish scientist JJ Berzelius suggested the term "proteins" derived from the Greek word "proteios" meaning "primary" or "pre-eminent."

    Amino Acids: Classification

    • The 20 amino acids encoded by DNA are classified based on different criteria.

    • One method is based on polarity and charge of their R groups.

    • These groupings are:

      • Non-polar
      • Polar but uncharged
      • Charged polar

    • Another classification method is based on structures of side chains. This includes:

      • Aliphatic amino acids
      • Aromatic amino acids
      • Heterocyclic amino acids
      • Dicarboxylic amino acids
      • Dibasic amino acids
      • Imino acid

    • A third way is based on catabolic fate, these are:

      • Glucogenic
      • Ketogenic
      • Both glucogenic and ketogenic

    Amino Acids: Classification-Cont

    • Commonly, amino acids are classified based on their essential/non-essential nature.
      • Essential Amino Acids: Cannot be synthesized by the body and must be obtained from the diet. These include valine, leucine, isoleucine, phenylalanine, threonine, tryptophan, methionine, and lysine.
      • Nonessential Amino Acids: Can be synthesized by the body, and thus are not required in the diet. These include alanine, aspartic acid, asparagine, glycine, glutamic acid, glutamine, cysteine, proline, serine, and tyrosine.
      • Semi-essential Amino Acid: These can be made by the body by they may not synthesize enough for optimal growth. Examples of semi-essential Amino Acids are arginine and histidine.

    Non-standard Amino Acids

    • These amino acids are formed from modifications of primary amino acids after protein synthesis.

    • These modifications are vital for protein function.

    • Examples include:

      • Hydroxylysine and hydroxyproline (in collagen)
      • Methylhistidine (muscle proteins)
      • Phosphoserine (casein, enzymes)
      • γ-carboxyglutamic acid (prothrombin, calcium-binding proteins)
      • Pyroglutamic acid (N-terminal in thyrotropin, several proteins)

    • Non-protein amino acids are found free in cells. Examples are ornithine and citrulline (urea cycle intermediates).

    • Taurine is an abundant human amino acid found in bile (fat digestion and absorption)

    • Other biologically important non-standard amino acids are used for functions beyond protein synthesis. Examples include chemical messengers (e.g., glycine, dopamine, GABA), local mediators of allergic reactions (e.g., histamine), and hormones (e.g., thyroxine).

    • D-amino acids are components of bacterial cell walls and antibiotics.

    New Amino Acids

    • Selenocysteine is the 21st amino acid which is often part of several enzymes.
    • Pyrrolysine is the 22nd amino acid and coded for by the UAG codon in some bacteria.

    Functions of Amino Acids

    • Amino acids serve various functions beyond serving as protein building blocks.
    • Some amino acids are converted into carbohydrates (e.g., glucogenic amino acids).
    • Other amino acids create specialized products; e.g.:
      • Proteins which are hormones (e.g. thyroid hormones, epinephrine, norepinephrine and melanin)
      • A vitamin, called niacin (B-vitamin) and serotonin from tryptophan
      • Creatine from glycine, arginine, and methionine.
      • Bile salts from glycine and cysteine.
    • Others have a role in the synthesis of glutathione from glycine, cysteine, and glutamate.
    • Histidine creates histamine on decarboxylation.
    • Several amino acids, including aspartate and glutamine, are precursors for pyrimidine and purine biosynthesis.
    • Methionine acts as an "active" methionine (SAM) transferring methyl groups to various molecules (transmethylation).
    • Methionine and cysteine are sulfur sources.

    Properties of Amino Acids

    • Isomerism: Except glycine, all amino acids are optically active and exist in D and L forms. Naturally occurring proteins primarily contain L-forms.
    • Amphoteric Nature and Isoelectric pH: Amino acids have an amino group (-NH2) and a carboxyl group (-COOH), making them capable of acting as both acids and bases. The isoelectric point (pI) is the pH at which an amino acid has no net charge.

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    BTC 312 Lecture 1: Amino Acids Structure and Properties - PDF

    Description

    Test your knowledge of proteins and amino acids with this engaging quiz. Explore various questions about the structure, classification, and properties of amino acids, and understand what makes proteins unique compared to carbohydrates and lipids. Perfect for students learning about biochemistry or molecular biology.

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