Protein Classification
Jean Brainard, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2014 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: December 12, 2014
AUTHOR
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Protein Classification
1
Protein Classification
• Identify the class of biochemical compounds named proteins.
• Describe the structure of proteins.
• List functions of proteins.
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 1.1. Other amino acids have slightly different structures.
1
www.ck12.org
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.
FIGURE 1.1
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
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5092
Q: What do you think the “ribbons” in the colorful hemoglobin molecule pictured in the opening image represent?
A: The “ribbons” represent chains of amino acids.
2
www.ck12.org
Chapter 1. Protein Classification
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 1.2).
FIGURE 1.2
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.
Explore More
At the following URL, watch the animation of protein folding and read the description. Then answer the questions
below.
http://intro.bio.umb.edu/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?
a. The process of protein folding proceeds by trial and error.
b. Protein folding continues until the molecule has the largest possible shape.
c. Amino acid side chains move through each other as folding takes place.
Review
1. What are proteins?
3
www.ck12.org
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.
References
1. Christopher Auyeung. Structure of glycine. CC BY-NC 3.0
2. Christopher Auyeung. Hemoglobin transports oxygen around the body. CC BY-NC 3.0
4