4.1 Protein structures display a hierarchical organization

Primary structure

________ _____ is the amino acid sequence—that is, the pattern of amino acids along a linear polypeptide chain (Figure 4.1).

secondary structure

The local conformation of the polypeptide chain is referred to as the ________ _______, which occurs mainly as α helices and β strands, with loops connecting them

amino acid

The _______ ______ sequence of a protein is referred to as its primary structure

helix, strand, loop

The local conformation of the protein backbone (α _____, β _____, or _____) is the secondary structure.

tertiary structure

The three-dimensional fold of a protein is the _________ _______

quaternary structure

Finally, the arrangement of subunits in a multi-subunit protein complex is the ________ ________.

hydrophobic

- As a general rule, the residues that form the interfaces between secondary structural elements are _______

hydrophobic core

the packing of secondary structural elements results in the formation of a protein structural domain with a ________ ______. Protein molecules contain one or more such domains

Structural domains

_________ ________ are the fundamental units of three-dimensional protein structure.

50-200

A protein domain is typically __-__ residues long and contains a well-defined hydrophobic core.

evolution

Domains are mixed and matched in ______ to produce more complex proteins

3D

Tertiary structure refers to the _____ organization of the secondary structure elements in these structural domains.

protein fold

The particular three-dimensional arrangement of the α helices and β strands in the tertiary structure is known as the _______ _____.

same

Protein fold: The visually recognizable arrangement of α helices and β strands in the three-dimensional structure of a protein is referred to as the protein fold. Different proteins can have the ___ fold, as is the case for myoglobin and the subunits of hemoglobin (see Figure 4.2)

quaternary structure

Many proteins consist of several different polypeptide chains (subunits) that associate into a multimeric complex in a specific way called the _______ _____

independently, together

These quaternary subunits can function either _____ of each other or _____ so that the function of one subunit depends on the functional states of the other subunits.