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Proteins
The Structure and Function of Proteins
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"Ribosomes are the organelles in which proteins are synthesized. Cell growth and reproduction require the constant synthesis of proteins."
                   Brody
 
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• Amino Acid Properties
 
Proteins are very important molecules in cells. By weight, proteins are collectively the major component of the dry weight of cells. They can be used for a variety of functions from cellular support to cellular locomotion. While proteins have many diverse functions, all are typically constructed from one set of 20 amino acids.

Amino Acids

Most amino acids have the following structural properties:

A carbon (the alpha carbon) bonded to four different groups:
  • A hydrogen atom (H)
  • A Carboxyl group (-COOH)
  • An Amino group (-NH2)
  • A "variable" group


Of the 20 amino acids that typically make up proteins, the "variable" group determines the differences among the amino acids. All amino acids have the hydrogen atom, carboxyl group and amino group bonds.

Amino acids glycine and alanine. The variable group in glycine is H. The variable group in alanine is CH3.
Image credit: Steven Berg


Polypeptide Chains

Amino acids are joined together through dehydration synthesis to form a peptide bond. When a number of amino acids are linked together by peptide bonds, a polypeptide chain is formed.

Proteins

One or more polypeptide chains twisted into a 3D shape forms a protein. The unique shape of the protein determines its function. For instance, structural proteins such as collagen and keratin are fibrous and stringy. Globular proteins like hemoglobin, on the other hand, are folded and compact.

Hemoglobin
Image courtesy of Robert J. Huskey



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