Biology, Eighth Edition (Raven)

Chapter 3: The Chemical Building Blocks of Life

Protein Denaturation

Why do we cook many kinds of food before we eat them? Most foods that have a significant amount of protein are cooked before consumption. Proteins are chains of amino acids. The sequence of amino acids in a chain is known as the primary structure of a protein. The chains fold up to form complex three dimensional shapes. The chains can fold on themselves locally (secondary structure) and wrap around themselves to form a specific three dimensional shape (tertiary structure). The secondary/tertiary structure of a folded protein is directly related to the function of that protein. For example, enzymes are proteins that catalyze reactions. They have binding sites that interact with other molecules. These binding sites are created through the folding of the amino acid chains that gives rise to the three dimensional shape of the enzyme. Proteins can be denatured through exposure to heat or chemicals. Denatured proteins lose their three dimensional structure and thus their function. Cooking food denatures the proteins found in the food and makes digestion more efficient.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	What type of bonds link individual amino acids together?

		A)	peptide bonds
		B)	polymerizing bonds
		C)	hydrogen bonds
		D)	organic bonds

2.	The helix that forms in a protein chain as a result of hydrogen bonds and other weak forces is an example of

		A)	primary structure of protein.
		B)	secondary structure of protein.
		C)	tertiary structure of protein.
		D)	non-linear structure of protein.

3.	In the stable form of protein, what is generally oriented to the interior of the protein molecule?

		A)	large portions
		B)	random portions
		C)	hydrophobic portions
		D)	hydrophilic portions

4.	When an egg is fried, what happens to the protein in the egg?

		A)	amino acids form new proteins
		B)	the heat converts the protein into water
		C)	because the heat removes water, the hydrophilic amino acids leave the pan
		D)	the protein is denatured

5.	When forming a semi-solid gel such as gelatin, what type of molecule does the process of protein coagulation entrap?

		A)	protein
		B)	water
		C)	carbohydrate
		D)	lipid