Protein Structure 2

Flashcards about Protein Structures

Ribbon model

Presents the peptide backbone as a ribbon and reveals secondary structure elements, but does not show side chains.

Tertiary structure

The overall three-dimensional shape of a protein made by a single polypeptide chain.

Fibrous proteins

Chains as long strands or sheets; usually single secondary structures; structural - provide support, shape, protection.

Globular proteins

Chains folded into spherical or globular shapes; often several secondary structures present; often enzymes and regulatory proteins.

Examples of fibrous proteins

α-keratin, collagen, and silk fibroin.

Silk fibroin - structure & properties

Rich in Ala & Gly; predominantly b – conformation fully extended chains; layered antiparallel b sheets stabilised by H-bonding & hydrophobic interactions.

Collagen

Repeating AA sequence Gly-X-Pro or Gly-X-Hyp; left-handed helix – 3 AAs per turn; triple helix - 3 chains supertwisted about each other.

Globular proteins key feature

Polypeptide chain is folded back on itself extensively to form a compact structure; provides diversity of structures for many functions.

Myoglobin features

Single polypeptide chain, 153 AA; single iron porphyrin (haem) group; 8 a-helices (>70% of its AAs) + bends; muscle oxygen storage.

Haem group

Is a prosthetic group found in many proteins including myoglobin and haemoglobin; is formed by an iron ion contained in the centre of an heterocyclic organic compound named porphyrin; it is often involved in the binding, transport or storage of oxygen.

Protein quaternary structure

The arrangement of protein subunits in three- dimensional complexes.

Proteins with multiple polypeptide chains have a quaternary structure

Multisubunit or multimeric proteins; allows possibility of small molecule binding to affect protein-protein binding to produce large changes in activity.

Haemoglobin (Hb) structure

64000 Da, 4 polypeptide chains (tetramer); 4 haem groups (one per polypeptide chain); “Globin” (protein part) is 2 α chains + 2 β chains.