Amino Acids and Proteins Overview
45 Questions
5 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the role of the α carbon in amino acids?

  • It serves as a chiral center. (correct)
  • It determines the pKa values.
  • It is only found in nonpolar amino acids.
  • It is the main site for peptide bond formation.

    • Which of the following amino acid classes contains the most members?

  • Nonpolar, aliphatic (correct)
  • Polar, uncharged
  • Aromatic
  • Negatively charged

    • Which amino acid is unique for having a second hydrogen atom instead of an R group?

  • Cysteine
  • Glycine (correct)
  • Alanine
  • Serine

    • How many enantiomers can amino acids have?

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

    The R group in amino acids is significant because it determines what?

    <p>The unique properties of each amino acid.</p> Signup and view all the answers

    Which of the following statements about L stereoisomers is true?

    <p>All amino acids in proteins are L stereoisomers.</p> Signup and view all the answers

    What are the four substituents attached to the α carbon in amino acids?

    <p>A carboxyl group, an amino group, a hydrogen atom, and an R group.</p> Signup and view all the answers

    Which class of amino acids is likely to be negatively charged at physiological pH?

    <p>Negatively charged</p> Signup and view all the answers

    How many amino acids belong to the aromatic class?

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

    What is the primary structure of proteins characterized by?

    <p>Covalent bonds linking amino acid residues</p> Signup and view all the answers

    Which method uses cross-linked polyacrylamide gels to visualize proteins?

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

    Which technique is NOT typically used for studying protein structure at atomic resolution?

    <p>Cohen's D</p> Signup and view all the answers

    Which of the following describes the secondary structure of proteins?

    <p>Recurring structural patterns such as alpha helices and beta sheets</p> Signup and view all the answers

    What can mass spectrometry NOT determine about proteins?

    <p>Protein localization within a cell</p> Signup and view all the answers

    What does the purification factor in chromatography represent?

    <p>The ratio of final specific activity to starting specific activity</p> Signup and view all the answers

    What is the defining feature of oligomeric proteins?

    <p>Contain at least two identical subunits</p> Signup and view all the answers

    Which amino acid contributes the highest percentage in bovine cytochrome c?

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

    What is the primary purpose of 'salting out' in protein purification?

    <p>To selectively precipitate proteins based on solubility</p> Signup and view all the answers

    Which protein class contains a non-amino acid component known as a prosthetic group?

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

    How is the number of amino acid residues in a protein estimated?

    <p>By dividing the molecular weight by 110</p> Signup and view all the answers

    Which of the following is a characteristic of metalloproteins?

    <p>They contain specific metals</p> Signup and view all the answers

    What is the first step in the process of purifying proteins?

    <p>Breaking open cells to release proteins</p> Signup and view all the answers

    In column chromatography, what factor affects the migration rates of proteins through the solid phase?

    <p>The specific properties of the proteins</p> Signup and view all the answers

    What is the average molecular weight of an amino acid used for residue estimation?

    <p>~128</p> Signup and view all the answers

    What defines a multisubunit protein?

    <p>Contains two or more polypeptides associated noncovalently</p> Signup and view all the answers

    What is the isoelectric point (pI) formula for amino acids without ionizable side chains?

    <p>pI = (pK1 + pK2) / 2</p> Signup and view all the answers

    Which R group type contributes to the hydrophobic effect in protein structures?

    <p>Nonpolar, aliphatic R groups</p> Signup and view all the answers

    Cysteine can participate in the formation of which type of bonds?

    <p>Disulfide bonds</p> Signup and view all the answers

    At a pH greater than the isoelectric point (pI), how does the amino acid’s net charge behave?

    <p>Net negative charge</p> Signup and view all the answers

    Which of the following describes the process of forming a peptide bond?

    <p>Formed through condensation of amino acids</p> Signup and view all the answers

    How many peptide bonds are found in a tripeptide?

    <p>2</p> Signup and view all the answers

    Which of the following amino acid groups does NOT form hydrogen bonds?

    <p>Nonpolar, aliphatic R groups</p> Signup and view all the answers

    At what pH does a zwitterion of an amino acid occur?

    <p>pH = 7.0</p> Signup and view all the answers

    Which of the following is true about protein molecular weight?

    <p>Polypeptides are more than 10 kDa</p> Signup and view all the answers

    Which notation indicates the sequence of amino acids in a peptide using one-letter codes?

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

    What principle does ion-exchange chromatography rely on for protein separation?

    <p>Net electric charge of the protein</p> Signup and view all the answers

    Which type of chromatography would be most effective for separating proteins based on their size?

    <p>Size-exclusion chromatography</p> Signup and view all the answers

    In ion-exchange chromatography, which factor can influence protein affinity?

    <p>The pH and concentration of free salt ions</p> Signup and view all the answers

    Which type of chromatography utilizes cation and anion exchangers?

    <p>Ion-exchange chromatography</p> Signup and view all the answers

    What will elute first from a gel filtration column?

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

    What can be used to elute proteins from affinity chromatography?

    <p>A high concentration of salt or ligand</p> Signup and view all the answers

    Considering a crude cellular extract with a total protein of 10,000 mg, which procedure would significantly reduce protein concentration?

    <p>Precipitation with ammonium sulfate</p> Signup and view all the answers

    What is the total activity after the precipitation with ammonium sulfate in the purification table?

    <p>32,000 units</p> Signup and view all the answers

    In the purification steps, what happens to specific activity as the sample size decreases?

    <p>It clearly increases</p> Signup and view all the answers

    What is the function of the bound charged groups in ion-exchange chromatography?

    <p>To attract specific proteins based on charge</p> Signup and view all the answers

    Study Notes

    Amino Acids

    • Amino acids consist of an α carbon bonded to four substituents: a carboxyl group, an amino group, a hydrogen atom, and a unique R group (side chain).
    • Glycine is unique with a second hydrogen atom in place of an R group.
    • Amino acid residues in proteins are L stereoisomers, making them optically active.
    • Amino acids are classified into five main groups based on their R groups: nonpolar aliphatic, aromatic, polar uncharged, positively charged, and negatively charged.

    pKa Values

    • Cysteine features three pKa values:
      • pK1 for the carboxyl group: 1.96
      • pK2 for the amino group: 10.28
      • pK3 for its side chain: 8.18

    Types of R Groups

    • Nonpolar, Aliphatic R Groups: Contribute to protein structure stability via the hydrophobic effect.
    • Aromatic R Groups: Absorb UV light at 270-280 nm and can enhance hydrophobic effects.
    • Polar, Uncharged R Groups: Capable of forming hydrogen bonds and disulfide bonds (e.g., cysteine).
    • Positively Charged R Groups: Display significant positive charge at physiological pH (7.0).
    • Negatively Charged R Groups: Carry a net negative charge at physiological pH (7.0).

    Protonation States and Isoelectric Point (pI)

    • Amino acids can act as weak acids or bases; zwitterions dominate at neutral pH.
    • Titration reveals cation, zwitterion, and anion forms, with pK1 and pK2 defining acidic and basic characteristics, respectively.
    • For amino acids without ionizable side chains, pI is calculated as (pK1 + pK2) / 2.

    Peptides

    • Peptides are chains of amino acids linked by covalent peptide bonds formed via condensation and cleaved by hydrolysis.
    • Types of peptides vary by the number of amino acids: dipeptide (2), tripeptide (3), oligopeptide (a few), polypeptide (many, <10 kDa), protein (thousands, >10 kDa).
    • Peptides are named from the amino-terminal (N-terminal) to the carboxyl-terminal (C-terminal) residue.

    Peptide Composition and Subunits

    • Peptides can be multisubunit, formed from multiple polypeptides noncovalently, or oligomeric with identical subunits (protomers).

    Protein Composition

    • Proteins have highly variable amino acid composition, exemplified by differences in bovine cytochrome c and chymotrypsinogen.

    Estimation of Amino Acid Residues

    • The number of amino acid residues can be estimated as molecular weight/110, factoring out the water molecule lost during peptide bond formation.

    Conjugated Proteins

    • Conjugated proteins contain non-amino acid components known as prosthetic groups, including lipids, carbohydrates, phosphate groups, heme, and specific metals.

    Protein Separation and Purification

    • Proteins can be separated based on size, charge, binding properties, and solubility. Common methods include salt precipitation, fractionation, dialysis, and chromatography.

    Column Chromatography

    • Protein migration utilizes a buffered solution through a solid phase, with the rate affected by protein properties.

    Electrophoresis

    • Utilized to visualize and analyze purified proteins based on charge-to-mass ratios. Involves polyacrylamide gels and staining methods for visualization.

    Protein Structure Levels

    • Four structural levels:
      • Primary: Linear sequence and covalent bonds of amino acids.
      • Secondary: Patterns like alpha-helices and beta-sheets.
      • Tertiary: 3D folding configuration.
      • Quaternary: Assembly of multiple polypeptide chains.

    Protein Structural Analysis Techniques

    • Traditional protein sequencing methods involve protein labeling and protease digestion.
    • Advanced techniques include X-ray crystallography, NMR spectroscopy, and Cryo-EM for atomic resolution structure.
    • Mass spectrometry offers insights into molecular mass, amino acid sequences, and proteomes.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Amino Acids, Peptides, and Proteins PDF

    Description

    This quiz covers the structural features of amino acids, including the α carbon and its four substituents. Dive into the unique characteristics of various amino acids and their role in forming peptides and proteins. Ideal for students studying biochemistry or molecular biology.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser