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What Are Proteins?
Amino Acids, Peptide Bonds & Levels of Protein Structure
CLASS NOTES from Science Prof Online
Organic molecules are large chemical compounds that contain carbon-hydrogen bonds and are found in living things. The major classes of organic molecules are carbohydrates, proteins, lipids and nucleic acids.
Amino Acid Monomers
Proteins are polymers (big organic molecules) composed of monomers called amino acids.
Each amino acid contains a…
- base amino group ( -NH2)
- acidic carboxyl group ( -COOH)
- hydrogen atom
Article Summary: Learn about the chemical bonds and different levels of structure that take amino acid monomers to a whole other level, a more complex protein polymer.
What Are Proteins?
A peptide bond (circled) between Leu and Thr in a protein structure. Green=carbon, red=oxygen, blue=nitrogen.
Protein Structure and Function
Structure of a protein is directly related to its function, so that anything that severely disrupts the shape will also disrupt the function. Denaturation is alteration of a protein shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it can’t carry out its cellular function.
Sources and Helpful Organic Chemistry Links
- Bauman, R. (2005) Microbiology.
- Park Talaro, K. (2008) Foundations in Microbiology
- Biomolecules: The Proteins interactive animated lesson from Wisc-Online.com
- Protein Denaturation animation and quiz from McGraw-Hill
- Heat Changes Protein Structure: Frying an Egg animation and quiz from Norton
- Organic Chemistry Lecture Main Page from the Virtual Cell Biology Classroom
Levels of Protein Structure
Every protein has at least three levels of structure: primary, secondary and tertiary. Quaternary structure is a grouping of more than one amino acid chain.
- Primary Structure: Amino acids linked together by peptide bonds into a peptide chains.
- Secondary Structure: Ionic bonds, hydrogen bonds, and hydrophilic / hydrophobic characteristics cause many polypeptide chains to fold into coils (α–helices), or accordion-like structures (β-pleated sheets). Proteins are typically composed of both α–helices and β-pleated sheets linked by short sequences of amino acids.
- Tertiary Structure: This is the three-dimensional structure of single protein molecule; a spatial arrangement of secondary structures.
- Quaternary Structure: This level of structure represents a complex of several protein molecules or polypeptide chains, which function as part of the protein complex.
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…all attached to same carbon atom (the α–carbon or alpha carbon). A fourth bond attaches α-carbon to a side group that varies among different amino acids. These side groups are important, as they affect the way a protein’s amino acids interact with one another, and how a protein interacts with other molecules.
Although there are hundreds of different amino acids, most organisms use only 21 to build proteins.
Peptide Bonds
Peptide bonds are the covalent bonds which link amino acids together into chains, like the beads on a necklace. A dipeptide is composed of 2 amino acids linked together, a polypeptide is more than two.
Portions of this article originally appeared on Suite101 online magazine.
Page last updated: 5/2013
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