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Protein: Categories and Functions

Published: January 20, 2017

Myosin and collagen protein in muscle
Myosin and collagen protein in muscle

Proteins consist of sequences of amino acids to which other substances may be attached. Your body can synthesise many amino acids, but some amino acids can only be obtained from dietary protein. These are known as essential amino acids.

Together exogenous (dietary) and endogenous (internally synthesized) amino acids are used by your body to synthesize 1000s of proteins necessary for the optimal function of your body.
The proteins that your body makes have specific sequences of amino acids which provide proteins with their unique characteristics that are specific to the function each protein performs. 
There are several general categories of proteins, identified by function, which are summarized below. These general categories are made up of sub-categories.
Enzymes are proteins which function as catalysts and are essential for life. In general catalysts are substances that alter the rate of chemical reactions. In your body, enzymes alter the rate of 1000s of metabolic chemical rections.
Enzymes, identified by the suffix "ase", are required by most human physiological processes and promote chemical changes in processes such as digestion, tissue synthesis and degradation, energy production, blood coagulation, and activity of nerves and muscles.
For example, lactase is the enzyme which functions in the digestion of lactose (milk sugar).
Enzymes are also identified by the way in which they react with other molecules (substrates): 

  • Hydrolases split or sever substrates
  • Isomerases move atoms from one part of molecule to another part of the same molecule
  • Ligases or synthases join substrates together
  • Oxidoreductases move electrons between molecules and within molecules 
  • Transferases move functional groups. A functional group is a collection of atoms in a molecule that participate together in a characteristic reaction


A pancreatic polypeptide hormone
A pancreatic polypeptide hormone
Hormones are chemical messengers which are transported in your blood to target tissues and organs from your glands or endocrine tissue where they are synthesized.
Not all hormones are proteins. Some hormones, known as steroid hormones, are derived from cholesterol. Protein hormones are derived from amino acids or made up of one or two polypeptide chains (amino acids linked together in specific sequences). 
Hormones, in general...link to the full article to learn more.

Related Topics

Nutrients  Protein  Your Body 


Gropper, S.S., Smith, J.L. & Groff, J.L. (2005). Advanced Nutrition and Human Metabolism (4thEd.). Belmont, CA: Thomson Wadsworth.
Whitney, E. & Rady Rolfes, S. (2005). Understanding Nutrition. Belmont, CA: Thomson Wadsworth
Steffen Dietzel
Jawahar Swaminathan and MSD staff
Gareth White: Grasp (Anthony Nicholls, Kim Sharp and Barry Honig, PROTEINS, Structure, Function and Genetics, Vol. 11, No. 4, 1991, pg. 281ff).