Basics of Protein Structure

<StructureSection load='1a3n_au' size='350' side='right' caption='Structure of Hemoglobin (PDB entry 1a3n)' scene= pspeed='8'{{Template:ColorKey_Element_C}} {{Template:ColorKey_Element_H}} {{Template:ColorKey_Element_O}} {{Template:ColorKey_Element_N}}> Proteins perform many important functions in living organisms, including movement, immune responses, sensing the environment, energy acquisition, and catalyzing reactions. Proteins are long chains of Amino Acids, and are synthesized by the ribosome, using messenger RNA as a template. There are 20 amino acids commonly found in proteins. Amino acids contain an amino group, a central carbon atom called the alpha carbon, and a carboxylic acid. The 20 amino acids differ by what is attached to the central atom; is variable portion is referred to as the side chain. The amino acid shown is alanine; its side chain is a methyl (-CH3) group. Proteins are sometimes compared to beads on a string, where each amino acid residue is a bead. These long chins form complicated structures that allow them to perform their function. Even small alterations in any level of the structure can change how the protein does its job, and can lead to diseases.

Levels of Protein Structure

There are four different levels of protein structure. The primary structure is the amino acid sequence. The amino acids are connected by an amide bond, made from the amino group (NH2) of one amino acid, and the carboxylic acid (C=O) from another amino acid. The amino acids are linked in a repeating pattern. The backbone of the protein is the repeating N-C-C=O pattern, with the side chains projecting out from the backbone. The end with the free -NH2 group is called the N terminus, while the end with a free carboxylic acid is called the C terminus. The sequence of amino acids is written from the N terminus to the C terminus.

The second level of structure is called secondary structure, and is the shape formed by short sequences of amino acids. This level of structure is stabilized by hydrogen bonds along the backbone.

For a more in depth discussion of protein structure, see Introduction to protein structure

• The Building Blocks
  • Amino Acids
  • Peptide
    • Peptide tutorial 1 part 1
    • Peptide tutorial 1 part 2
  • Phi and Psi Angles
  • Ramachandran Plots

• Secondary structure
  • Helices in Proteins
    • Secondary Structure tutorial - Helices
  • Sheets in Proteins
    • Secondary Structure tutorial - Sheets
• Structural_templates
  • Globular_Proteins
    • Turns in Proteins
  • Fibrous Proteins
    • Coiled_coil
    • Collagen - Illustrates the structure of a collagen segment as well as the structure of a mutated tropocollagen.
    • Fibroins

• Unusual Motifs in Proteins
  • Cation-pi_interactions
  • Thermal_motion_of_peptide

• Intrinsically Disordered Protein

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Ann Taylor, Eric Martz, Joel L. Sussman