Download Name: Date: Block:___ Background: Proteins are the molecules that

Name: ____________________________________ Date: _________________ Block:___
Background: Proteins are the molecules that carry out most of the cell’s day-to-day
functions. While the DNA in the nucleus is "the boss" and controls the activities of the cell,
it is the proteins that "do the work." In this activity you will examine the structure of proteins
and how their structure is related to their function.
Proteins are made from a chain of amino acids and are folded into a variety of shapes. A
chain of amino acids is called a polypeptide chain. A protein may consist of one or more
polypeptide chains. The shape of the protein will determine its function.
Proteins can be subdivided into 4 main categories, shown below.
An Overview of Protein Types and Functions
Type
Function
Examples
Structural Proteins
Support
Spider silk, flagella of
bacteria for swimming,
muscle fibers, connective
tissue in tendons, keratin
that makes up hair and nails
Enzymes
Speed up chemical
reactions in the cell
Digestive enzymes that
break down food
Regulatory Proteins
Coordinates organisms
activities
Hormones, such as insulin,
which helps regulate the
amount of sugar in the
blood
Transport Proteins
Transport of other
substances
Hemoglobin – in red blood
cells, transports oxygen
from the lungs to other
parts of the body
Membrane proteins –
transport molecules across
cell membranes
Procedure: To help you understand how a protein is constructed and how its structure is
related to it function, you and your lab partner(s) will build a model of a protein. A protein’s
shape, and ultimately its function, is determined by four levels of structure.
Get your paper stamped as you complete each level of construction.
1. Take a pipe cleaner and some beads and string the beads onto the pipe cleaner. (Leave
a little of the pipe cleaner at each end free so that you can fold it back to prevent the
beads from falling off.) The beads represent the amino acid sequence in a polypeptide
that was specified by the DNA. Remember that all proteins are made from just 20
different amino acids in varying combinations. This string of amino acids is called
the primary structure of the protein. (Get your paper stamped before going to the
next step.)
2. The secondary structure of a protein results when parts of the polypeptide coil or
fold. Take your string of beads and either fold the strand back and forth accordion
style, or coil it around your pencil to form a spiral, or do a little of both. You have
now made the secondary structure. (Get paper stamped.)
3. The third level of organization is called the tertiary structure and this is created
when the folded, twisted chain of amino acids folds back on itself to form the overall
shape of the polypeptide. Take your polypeptide chain and fold it so that the free ends
meet. (Get paper stamped.)
4. Many proteins are made of more than one polypeptide chain. Take your polypeptide
chain and join it with the polypeptide chain of your lab partner and one or two other
students. You now have a protein model that is demonstrating quaternary (4th level)
structure. The shape of your molecule will determine its function. (Get paper
stamped.)
Look at these examples. Hemoglobin is a protein in red blood cells that is made of 4
polypeptide chains (2 of one type and 2 of a different type). Attached to each twisted chain
there is a chemical group called a heme group that contains an iron atom that will bind to
oxygen, so each hemoglobin molecule can carry 4 oxygen molecules at once.
Collagen is a structural protein made up of 3 polypeptide chains that coil around each other
to produce a rope-like structure that is very strong and reinforces tendons, ligaments, bones
and other body structures. Look at your group’s model. Look at the models of other groups
in the class. You all started with the same materials. Do all the proteins look the same?
Interpretation:
1. Why are proteins such important molecules in living cells?
2. Describe the structure of a protein molecule. Be complete. Be specific.
3. When proteins are subjected to extreme changes in temperature, pH, or salt
concentration, they may lose their shape. The coiled portions may become uncoiled
and the chains unravel. This is a process called denaturation and we say the protein is
denatured. Why can a denatured protein no longer function normally?