Skip to main content
Indietro

Biochemistry: Protein Structure and Folding

I pulsanti di controllo sono stati cambiati in modalità "navigazione".
1/31

Termini in questo insieme (31)

  • What type of bond links amino acids in a polypeptide chain?
    Peptide bonds are the covalent linkages between amino acids in a polypeptide chain.
  • How many peptide bonds are in a polypeptide with n amino acids?
    There are n-1 peptide bonds in a polypeptide chain with n amino acids.
  • What type of reaction forms a peptide bond?
    Peptide bonds form via endergonic dehydration synthesis, releasing a molecule of water.
  • Why are peptide bonds stable despite hydrolysis being thermodynamically favorable?
    Peptide bonds have a high activation energy barrier, making hydrolysis slow and peptide bonds stable under physiological conditions.
  • What is the primary structure of a protein?
    The primary structure is the amino acid composition and sequence from the N-terminal to the C-terminal.
  • How can primary protein structure be altered?
    By changing amino acid composition or sequence, even a single amino acid substitution can affect protein shape and function.
  • What is the backbone atom arrangement in two peptide bonds?
    The backbone arrangement is Cα - C - N - Cα - C - N repeating along the chain.
  • What is the peptide group in a protein?
    The peptide group consists of the six atoms around the peptide bond: C=O, N-H, and the two adjacent α-carbons.
  • Why are peptide bonds planar?
    Peptide bonds have partial double-bond character due to resonance, restricting rotation and making the peptide group planar.
  • What are the phi (φ), psi (ψ), and omega (ω) angles in peptide bonds?
    φ is rotation around Cα-N, ψ around Cα-C, and ω is the peptide bond angle, usually fixed near 180° (trans).
  • What does a Ramachandran plot show?
    It shows the allowed and disallowed φ and ψ angles for amino acid residues in proteins, predicting conformations.
  • How does glycine's Ramachandran plot differ from other amino acids?
    Glycine has a small R-group (H) allowing more φ and ψ angles due to less steric hindrance.
  • How does proline affect peptide backbone conformation?
    Proline has a cyclic R-group that restricts φ and ψ angles and often disrupts α-helices.
  • What stabilizes an α-helix structure?
    Intrachain hydrogen bonds between the C=O of residue i and N-H of residue i+4 stabilize α-helices.
  • What is the pitch and rise of an α-helix?
    Pitch is 5.4 Å per turn with about 3.6 residues per turn; rise is 1.5 Å per residue along the helix axis.
  • What is the net dipole of an α-helix?
    The α-helix has a net dipole with a partial positive charge at the N-terminus and a partial negative charge at the C-terminus.
  • Which amino acids disrupt α-helices and why?
    Glycine disrupts due to flexibility; proline disrupts due to lack of N-H for H-bonding and rigid cyclic structure.
  • What is a β-strand and how does it differ from an α-helix?
    A β-strand is an extended zig-zag backbone conformation with ~3.5 Å rise per residue, stabilized by hydrogen bonds perpendicular to strand direction.
  • What are β-sheets and how are they formed?
    β-sheets are formed by 2 or more β-strands linked by backbone hydrogen bonds, arranged in parallel or antiparallel orientations.
  • How do antiparallel and parallel β-sheets differ in stability?
    Antiparallel β-sheets have stronger, more linear hydrogen bonds and are more stable than parallel β-sheets.
  • What are β-turns and loops in proteins?
    Non-repetitive secondary structures causing abrupt changes in backbone direction, often stabilized by internal hydrogen bonds.
  • What stabilizes tertiary protein structure?
    Tertiary structure is stabilized mainly by R-group interactions: salt bridges, hydrophobic effect, hydrogen bonds, and disulfide bridges.
  • What are protein motifs and domains?
    Motifs are specific patterns of secondary structures; domains are independently folding units with discrete functions within a protein.
  • What is protein denaturation?
    Denaturation disrupts secondary and tertiary structures, causing loss of function, but leaves primary structure intact.
  • What did the Anfinsen experiment demonstrate?
    Primary structure alone determines tertiary structure; proteins spontaneously fold into their native, lowest energy conformation.
  • What is Levinthal's paradox?
    Protein folding is not random but guided by cooperative interactions, allowing rapid folding despite astronomical possible conformations.
  • What role do chaperone proteins play in folding?
    Chaperones assist slow-folding proteins by preventing aggregation and using ATP to facilitate correct folding.
  • What are prions?
    Prions are misfolded infectious proteins that induce misfolding of normal proteins, causing neurodegenerative diseases.
  • What defines quaternary protein structure?
    Quaternary structure is the assembly of multiple polypeptide subunits into a functional protein complex.
  • What distinguishes simple from conjugated proteins?
    Simple proteins contain only amino acids; conjugated proteins have permanently attached prosthetic groups.
  • What are fibrous and globular proteins?
    Fibrous proteins are insoluble, structural, and linear; globular proteins are soluble, compact, and functional.