Download Macromolecular structure • Macromolecules are held together by a

Macromolecular structure
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Macromolecules are held together by a variety of forces
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Covalent bonds impose geometrical restrictions on molecular shape
− the length of the bond has negligible variability
− the angle between bonds has small variability
− the dihedral angle (rotation about the bond) is least constrained
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Stabilizing interactions provided by weak interactions
o Noncovalent bonds (hydrogen bonds or van der Waals forces)
o electrostatic attraction or repulsion
o hydrophobic forces
DNA
DNA backbone configuration is determined by a list of torsional angles
The dominant interaction is the stacking of base pairs.
RNA single stranded RNA can fold into variety of structures by pairing with itself
group 1
intron
88-nucleotide RNA
construct with two
distinct folds
X-ray crystal structure of bacterial ribosome
Protein structure is to large extent determined by the polypeptide backbone
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peptide bond is planar
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the backbone is parametrized
by two dihedral angles per
amino acid, φ and ψ
Because of steric constraints
(molecular groups bumping
into each other) limited
combinations of φ and ψ
are possible
Main secondary structures are:
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α-helix
β-sheet
right-handed α-helix
antiparallel β-sheet