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3.38: Protein Classification

Difficulty Level: At Grade Created by: CK-12
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These pretty, colorful “ribbons” aren’t leftover ribbons from birthday gifts. The “ribbons” are a model of a molecule called hemoglobin, which is coursing through your blood vessels right now. Hemoglobin is a compound that is found in red blood cells and has the crucial job of carrying oxygen to cells throughout the body. Your life depends on hemoglobin.

Meet the Proteins

Hemoglobin is a compound in the class of compounds called proteins. Proteins are one of four classes of biochemical compounds, which are compounds in living things. (The other three classes are carbohydrates, lipids, and nucleic acids.) Proteins contain carbon, hydrogen, oxygen, nitrogen, and sulfur. Protein molecules consist of one or more chains of small molecules called amino acids.

Protein Structure

Amino acids are the “building blocks” of proteins. There are 20 different amino acids. The structural formula of the simplest amino acid, called glycine, is shown in the Figure below . Other amino acids have slightly different structures. A protein molecule is made from one or more long chains of amino acids, each linked to its neighbors by covalent bonds. If a protein has more than one chain, the chains are held together by weaker bonds, such as hydrogen bonds.

The sequence of amino acids in chains and the number of chains in a protein determine the protein’s shape. The shape of a protein, in turn, determines its function. Shapes may be very complex. You can learn more about the shapes of proteins at the URL below.

http://www.youtube.com/watch?v=lijQ3a8yUYQ

Q: What do you think the “ribbons” in the colorful hemoglobin molecule pictured above represent?

A: The “ribbons” represent chains of amino acids.

Protein Functions

Proteins are the most numerous and diverse biochemical compounds, and they have many different functions. Some of their functions include:

  • making up tissues as components of muscle.
  • speeding up biochemical reactions as enzymes.
  • regulating life processes as hormones.
  • helping to defend against infections as antibodies.
  • carrying materials around the body as transport proteins (see the example of hemoglobin in the Figure below ).

The blood protein hemoglobin binds with oxygen and carries it from the lungs to all the body’s cells. Heme is a small molecule containing iron that is part of the larger hemoglobin molecule. Oxygen binds to the iron in heme.

Summary

  • Proteins are one of four classes of biochemical compounds. Proteins contain carbon, hydrogen, oxygen, nitrogen, and sulfur.
  • A protein molecule is made from one or more long chains of amino acids, each linked to its neighbors by covalent bonds. Multiple chains of a protein are held together by weaker bonds.
  • Proteins are the most numerous and diverse biochemical compounds. They have many different functions.

Vocabulary

  • protein : Biochemical compound that contains oxygen, nitrogen, and sulfur in addition to carbon and hydrogen; consists of one or more chains of smaller molecules called amino acids.

Practice

At the following URL, watch the animation of protein folding and read the description. Then answer the questions below.

http://intro.bio.umb.edu/111-112/111F98Lect/folding.html

  1. Amino acids with hydrophobic side chains fold toward the center of the protein to avoid __________.
  2. Other amino acids pull the protein into its final shape by forming __________ and __________ bonds.
  3. Are these statements true or false?
    1. The process of protein folding proceeds by trial and error.
    2. Protein folding continues until the molecule has the largest possible shape.
    3. Amino acid side chains move through each other as folding takes place.

Review

  1. What are proteins?
  2. Describe the “building blocks” of protein molecules.
  3. What determines the shape of a protein? How is a protein’s shape related to its function?
  4. List three functions of proteins.

Vocabulary

protein

protein

Biochemical compound that contains oxygen, nitrogen, and sulfur in addition to carbon and hydrogen; consists of one or more chains of smaller molecules called amino acids.

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Description

Difficulty Level:

At Grade

Grades:

7 , 8

Date Created:

Nov 14, 2012

Last Modified:

Dec 22, 2014
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