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