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Protein Structure and Function
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Protein Structure and Function

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@StableEpilogue

Questions and Answers

Which of the following atoms is a hydrogen bond acceptor in a peptide bond?

  • N
  • C
  • O (correct)
  • H

    • At physiological pH, which of the following amino acid side chains is ionized?

  • Tyr
  • Trp
  • Ser
  • Asp (correct)

    • What is the primary cause of van der Waals forces between molecules?

  • Dipole-dipole interactions
  • Unequal distribution of electrons (correct)
  • Hydrogen bonding
  • Electrostatic interactions

    • What is the approximate distance of a hydrogen bond?

    <p>0.28 nm</p> Signup and view all the answers

    Which of the following is a characteristic of hydrophobic regions in a protein?

    <p>They fold to minimize contact with aqueous environment</p> Signup and view all the answers

    What is the energy of a hydrogen bond, approximately?

    <p>12 kJ mol-1</p> Signup and view all the answers

    Which of the following is an example of a hydrogen bond donor?

    <p>N-H</p> Signup and view all the answers

    What is the term for the sum of the attractive or repulsive forces between molecules, excluding covalent bonds, hydrogen bonds, and electrostatic interactions?

    <p>Van der Waals forces</p> Signup and view all the answers

    What type of glycosylation occurs at the -OH of thr and ser?

    <p>O-linked</p> Signup and view all the answers

    What is the name of the structure that forms when three chains come together and are held by H-bonds between chains?

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

    What is the primary function of the alpha helix in proteins?

    <p>To act as 'architectural' support</p> Signup and view all the answers

    What type of beta sheet structure is widespread in globular proteins?

    <p>Beta hairpin bend</p> Signup and view all the answers

    What is the sequence of amino acids in collagen?

    <p>Gly - X - Y - Gly - X - Y</p> Signup and view all the answers

    What is the percentage of alpha helix structure in haemoglobin?

    <p>60%</p> Signup and view all the answers

    What is the name of the type of protein that has a high percentage of beta sheet structure and is found in silk fibres?

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

    What type of force is responsible for the hydrophobic effect in proteins?

    <p>Van der Waals forces</p> Signup and view all the answers

    Which of the following types of bonds is responsible for maintaining the tertiary structure of proteins?

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

    What is the functional importance of amino acid side chains?

    <p>They participate in enzyme active sites</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

    What is the role of the peptide bond between amino acids?

    <p>To link amino acids together in a polypeptide chain</p> Signup and view all the answers

    What is the result of defects in amino acid metabolism and mis-folding?

    <p>The development of disease</p> Signup and view all the answers

    What is the direction of a polypeptide chain?

    <p>From the N-terminal end to the C-terminal end</p> Signup and view all the answers

    What is the role of disulphide bonds in protein structure?

    <p>To join subunits together</p> Signup and view all the answers

    What is the characteristic of most folded proteins?

    <p>They are marginally stable and readily denatured</p> Signup and view all the answers

    What is the primary reason why proteins are sensitive to denaturation?

    <p>Changes in pH, temperature, and ionic strength</p> Signup and view all the answers

    What is the role of amino acid sequence in protein structure?

    <p>It determines the pathway to the final structure</p> Signup and view all the answers

    Why are proteins stable?

    <p>Due to the stabilizing energy in their structure</p> Signup and view all the answers

    What is the consequence of misfolding in proteins?

    <p>It causes disease</p> Signup and view all the answers

    What is the significance of the case-based discussion on human disease?

    <p>It shows the relevance of protein structure in human disease</p> Signup and view all the answers

    What is essential for protein function?

    <p>Protein folding</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 various biological functions performed by proteins, including structural roles, movement, enzymatic functions, and more.

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