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BIOCHEMISTRY A2 STUDY NOTES
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LECTURE 21
SECONDARY STRUCTURE
Protein structure determines protein function. Proteins can function in:
• Catalysis (enzymes)
• Transport
• Signalling
• Regulation
• Movement
• Structural support
PROTEIN STRUCTURE LEVELS
Protein structure is organized into levels:
Level Description
Primary (1°) Amino acid sequence
Secondary (2°) Local folding patterns
Tertiary (3°) Overall 3D folding
Quaternary (4°) Arrangement of multiple subunits
Higher order Large protein assemblies
Primary Structure (1°)
Linear sequence of amino acids in a polypeptide chain.
• Determines all higher levels of structure.
• Even one amino acid change can alter function.
Example: Sickle cell anemia results from one amino acid substitution.
Secondary Structure (2°)
Regular local folding of the peptide backbone.
• α-helices
• β-sheets
• β-turns
Stabilized mainly by hydrogen bonds between backbone groups.
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Tertiary Structure (3°)
Overall 3D folding of one polypeptide chain - includes interactions between side chains.
Stabilized by:
• Hydrophobic interactions
• Hydrogen bonds
• Ionic bonds
• van der Waals interactions
• Disulfide bonds
Quaternary Structure (4°)
Association of multiple protein subunits.
Example: Hemoglobin
NON-COVALENT INTERACTIONS IN PROTEINS
Non-covalent interactions stabilize 2°, 3°, and 4° structures.
Interaction Description
Hydrogen bonds Between polar groups
Ionic bonds Between charged side chains
Hydrophobic interactions Nonpolar groups cluster together
van der Waals forces Weak temporary attractions
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More interactions = more stable protein.
PEPTIDE BOND CHARACTERISTICS
Partial Double Bond Character
Peptide bonds show resonance.
Meaning, electrons are shared across the bond causing the bond to behave partly like a
double bond.
Consequences:
• Bond is rigid.
• Little rotation around peptide bond.
Planar Structure
The peptide bond atoms lie in the same plane: this is called the amide plane
BIOCHEMISTRY A2 STUDY NOTES
, 2
LECTURE 21
SECONDARY STRUCTURE
Protein structure determines protein function. Proteins can function in:
• Catalysis (enzymes)
• Transport
• Signalling
• Regulation
• Movement
• Structural support
PROTEIN STRUCTURE LEVELS
Protein structure is organized into levels:
Level Description
Primary (1°) Amino acid sequence
Secondary (2°) Local folding patterns
Tertiary (3°) Overall 3D folding
Quaternary (4°) Arrangement of multiple subunits
Higher order Large protein assemblies
Primary Structure (1°)
Linear sequence of amino acids in a polypeptide chain.
• Determines all higher levels of structure.
• Even one amino acid change can alter function.
Example: Sickle cell anemia results from one amino acid substitution.
Secondary Structure (2°)
Regular local folding of the peptide backbone.
• α-helices
• β-sheets
• β-turns
Stabilized mainly by hydrogen bonds between backbone groups.
, 3
Tertiary Structure (3°)
Overall 3D folding of one polypeptide chain - includes interactions between side chains.
Stabilized by:
• Hydrophobic interactions
• Hydrogen bonds
• Ionic bonds
• van der Waals interactions
• Disulfide bonds
Quaternary Structure (4°)
Association of multiple protein subunits.
Example: Hemoglobin
NON-COVALENT INTERACTIONS IN PROTEINS
Non-covalent interactions stabilize 2°, 3°, and 4° structures.
Interaction Description
Hydrogen bonds Between polar groups
Ionic bonds Between charged side chains
Hydrophobic interactions Nonpolar groups cluster together
van der Waals forces Weak temporary attractions
, 4
More interactions = more stable protein.
PEPTIDE BOND CHARACTERISTICS
Partial Double Bond Character
Peptide bonds show resonance.
Meaning, electrons are shared across the bond causing the bond to behave partly like a
double bond.
Consequences:
• Bond is rigid.
• Little rotation around peptide bond.
Planar Structure
The peptide bond atoms lie in the same plane: this is called the amide plane
