Amino Acids and Peptide Bonds in Biochemistry
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Questions and Answers

What is the main function of the peptide bond between amino acids?

  • To catalyze enzymatic reactions
  • To provide structural importance to the protein
  • To form hydrogen bonds with other peptide units (correct)
  • To facilitate the transportation of ions and molecules

    • Which type of glycosylation involves the -NH2 group of asparagine?

  • O-linked glycosylation
  • Hydroxylation
  • N-linked glycosylation (correct)
  • Phosphorylation

    • Which of the following is NOT a type of non-covalent interaction that maintains the tertiary structure of proteins?

  • Phosphodiester bonds (correct)
  • van der Waals interactions
  • Ionic interactions
  • Hydrogen bonds

    • What is the name of the secondary structure formed by hydrogen bonds between peptide chains?

    <p>β-pleated sheet</p> Signup and view all the answers

    What determines the unique conformation of a protein?

    <p>The primary sequence of amino acids</p> Signup and view all the answers

    What is the characteristic of the side chains in a β-pleated sheet?

    <p>They alternate above and below the plane of the sheet</p> Signup and view all the answers

    Which of the following proteins is an example of a receptor protein?

    <p>Acetylcholine receptor</p> Signup and view all the answers

    What is the term for the process by which a protein assumes its unique 3D structure?

    <p>Protein folding</p> Signup and view all the answers

    Which protein has a quaternary structure consisting of two α-subunits and two β-subunits?

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

    Which of the following is a consequence of defects in amino acid metabolism and mis-folding?

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

    What is the function of hydrogen bonds in protein structure?

    <p>To stabilize the tertiary structure of proteins</p> Signup and view all the answers

    Which of the following is NOT a type of non-covalent force that stabilizes protein structure?

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

    What is the term for the covalent bond that forms between two cysteine residues?

    <p>Disulphide bridge</p> Signup and view all the answers

    What is the name of the helical structure formed by three polypeptide chains?

    <p>Collagen triple helix</p> Signup and view all the answers

    Which of the following proteins is an example of a structural protein?

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

    Which type of protein has a high percentage of β-sheet structure?

    <p>Fibrillar protein</p> Signup and view all the answers

    Which of the following atoms is NOT a hydrogen bond acceptor?

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

    What is the approximate distance of a hydrogen bond?

    <p>2.8 Å</p> Signup and view all the answers

    At physiological pH, which of the following groups is NOT ionised?

    <p>His imidazole groups</p> Signup and view all the answers

    What is the main reason for the existence of Van der Waals forces?

    <p>Unequal distribution of electrons in a covalent bond</p> Signup and view all the answers

    What is the primary reason why hydrophobic regions are unable to form hydrogen bonds?

    <p>As a result of their non-polar nature</p> Signup and view all the answers

    Which of the following is a characteristic of Van der Waals forces?

    <p>They are dependent on the distance between atoms</p> Signup and view all the answers

    What is the main driving force for hydrophobic regions of a protein to fold in a specific way?

    <p>Minimise the contact with aqueous environment</p> Signup and view all the answers

    What determines the final structure and folding pathway of a protein?

    <p>The amino acid sequence only</p> Signup and view all the answers

    Why are proteins sensitive to denaturation by pH, temperature, and ionic strength?

    <p>Since the stabilization energy in a protein is very low</p> Signup and view all the answers

    What type of bond has a typical energy of 12 kJ mol-1?

    <p>Hydrogen bond</p> Signup and view all the answers

    What is the significance of the alpha helix and beta-pleated sheet structures?

    <p>They are essential for protein function</p> Signup and view all the answers

    Which of the following side chains is NOT involved in hydrogen bonding?

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

    Why is protein misfolding a concern in human disease?

    <p>Since it results in the loss of protein function</p> Signup and view all the answers

    What is the relationship between the number of possible protein structures and their functionality?

    <p>There are thousands of possible structures, only one of which is functional</p> Signup and view all the answers

    Study Notes

    Protein Structure and Function

    • Proteins perform various biological functions, including:
      • Structural roles (e.g., collagen, keratin)
      • Movement (e.g., actin, myosin)
      • Enzymatic functions (e.g., trypsin, DNA polymerase)
      • Transport (e.g., hemoglobin, transferrin)
      • Hormone regulation (e.g., insulin)
      • Receptor functions (e.g., acetylcholine receptor)
      • Defense mechanisms (e.g., antibodies, clotting factors)
      • Gene regulation (e.g., histones)
      • Chromosome separation (e.g., tubulin)

    Primary Structure

    • A polypeptide chain consists of 20 common amino acids
    • The first amino acid has an NH3+ group (N-terminal end)
    • The last amino acid has a COO- group (C-terminal end)

    Secondary Structure

    • α-helix:
      • Formed by hydrogen bonds between peptide bonds in the same polypeptide chain
      • Regular right-handed helix with 3.6 residues per turn
      • R groups are on the outside of the helix
      • Stabilized by hydrogen bonds
    • β-pleated sheet:
      • Formed by hydrogen bonds between peptide chains
      • Linear peptide chains with side chains alternately above and below the plane of the sheet

    Tertiary Structure

    • The 3D shape of a polypeptide chain
    • Consists of a number of different supersecondary structures (domains)

    Quaternary Structure

    • The 3D shape of a functional protein formed by multiple subunits
    • Examples: hemoglobin (α2β2)

    Forces that Stabilize Protein Structure

    • Covalent:
      • Disulfide bridges (not present in all proteins)
    • Non-covalent:
      • Hydrogen bonds
      • Electrostatic interactions
      • Van der Waals forces
      • Hydrophobic effect

    Hydrogen Bonds

    • Formed between two electronegative atoms competing for the same H atom
    • H-Bond donors (D): O-H, N-H
    • H-Bond acceptors (A): C=O, =N-

    Electrostatic Interactions

    • Between charged side chains
    • At physiological pH, Asp and Glu are ionized, while Lys and Arg are also ionized

    Van der Waals Forces

    • The sum of attractive or repulsive forces between molecules
    • Excludes covalent bonds, hydrogen bonds, and electrostatic interactions
    • Dependent on the dipole effect caused by the unequal distribution of electrons

    Hydrophobic Effects

    • Hydrophobic regions of a protein fold to minimize contact with the aqueous environment
    • Hydrophobic regions are unable to form hydrogen bonds

    Protein Folding and Stability

    • The amount of stabilization energy in a protein is quite small
    • Proteins are sensitive to denaturation by pH, temperature, and ionic strength
    • Amino acid sequence encodes the final structure and the pathway that leads to that structure
    • Misfolding can cause disease

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    Description

    This quiz covers the structures and functions of amino acids, including their side chains and peptide bonds, as well as the importance of hydrogen bonds in biochemistry.

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