What are the three levels of protein structure?

Question

What are the three levels of protein structure?

Answer 1

Primary [most basic] --> e.g.: amino acid

Secondary --> e.g.: RNA stem loop

Tertiary --> 3-d structures

Quaternary [most complex] --> e.g.: enzymes, hemoglobin

[Answer: see above]

Answer 2

Primary, secondary and tertiary. There is another one which is quaternary.

Answer 3

Different Levels of Protein Structure:

The wide variety of 3-dimensional protein structures corresponds to the diversity of functions proteins fulfill.

Proteins fold in three dimensions. Protein structure is organized hierarchically from so-called primary structure to quaternary structure. Higher-level structures are motifs and domains.

Above all the wide variety of conformations is due to the huge amount of different sequences of amino acid residues. The primary structure is the sequence of residues in the polypedptide chain.

Secondary structure is a local regulary occuring structure in proteins and is mainly formed through hydrogen bonds between backbone atoms. So-called random coils, loops or turns don't have a stable secondary structure. There are two types of stable secondary structures: Alpha helices and beta-sheets. Alpha-helices and beta-sheets are preferably located at the core of the protein, whereat loops prefer to reside in outer regions.



Tertiary structure describes the packing of alpha-helices, beta-sheets and random coils with respect to each other on the level of one whole polypeptide chain. Figure 5 shows the tertiary structure of Chain B of Protein Kinase C Interacting Protein.

Quaternary structure only exists, if there is more than one polypeptide chain present in a complex protein. Then quaternary structure describes the spatial organization of the chains.

Motifs and domains are combinations of secondary structures. Motifs only consist out of few secondary structures. They may but need not have a function. A domain is more complex. It is usually defined as a modular functional unit folding independently