Function of Proteins in Cells & Enzymes

PROTEINS Copyright © 2009 Pearson Education, Inc.

Functions of Proteins in Cells There are THOUSANDS of proteins at work in most cells. A PROTEIN is a macromolecule made up of one or more chains of amino acids folded together into a complex three-dimensional structure.

Examples of Proteins As soon as it is synthesized, each protein folds into a specific three-dimensional shape that is essential for it to function properly. This folding takes place as a result of disulfide bonds and weak interactions, such as hydrogen bonds, that form spontaneously between amino acids at various points in the amino acid chain or between amino acids in other chains. The complex shape of a protein forms binding sites that are essential to the protein’s function. For example, hemoglobin has binding sites that fit oxygen molecules. If the shape of a hemoglobin protein is altered, it changes the shape of the binding site; an oxygen molecule would no longer fit, and that protein will not function properly, even if its amino acid sequence stays intact. similarly, an enzyme has a binding site for its substrate(s). If the shape of the enzyme is altered in a way that affects this binding site, it can no longer act as a catalyst.

Functions of Proteins in Cells Each protein performs a certain function, such as transporting a specific molecule in or out of the cell (what type of diffusion could this be?) or fighting disease speeding up a chemical reaction. We could also say that this molecule catalyzes the reaction! (what type of protein is this called?) VOCAB ALERT! Catalyze = speed up the rate of a reaction

Eight is GREAT!  8 classes of proteins Enzymes also catalyze the metabolism of food to release energy. The other groups of proteins are transport pro- teins (such as hemoglobin), motor proteins, signaling proteins (including hormones, such as insulin), receptor proteins, pro- teins of the immune system (antibodies), storage proteins, and structural proteins (such as those involved in the structure of bone, muscle, and hair). For the purposes of this activity, proteins involved in the interactions of microbes with host cells have been included with antibodies in a category called immune system and disease proteins.  8 classes of proteins

Proteins are made of monomers called amino acids N, C, H, O, S Proteins are made of monomers called amino acids

Structure of Proteins The R(radical) group on amino acids is a variable like X in algebra It makes each amino acid different. There are 20 different amino acids

Structure of Proteins The polymer of amino acids bonded together is a polypeptide/ protein Proteins are used in our muscles and also to carry out all of our genes!

Protein Shape and Function If for some reason a protein’s shape is altered, it can no longer function Denaturation: The loss of shape/unraveling of proteins which causes them to not function properly Proteins can be denatured by changes in salt concentration, temperature, and pH Excessive heat can also denature a protein. A good example is frying or boiling an egg. The proteins in the egg “white” become solid, white, and opaque upon denaturation. Student Misconceptions and Concerns 1. The functional significance of protein shape is an abstract molecular example of form and function relationships, which might be new to some students. The binding of an enzyme to its substrate is a type of molecular handshake, which permits specific interactions. To help students think about form and function relationships, share some concrete analogies in their lives—perhaps flathead and Phillips screwdrivers that match the proper type of screws or the fit of a hand into a glove. Teaching Tips 1. Most cooking results in changes in the texture and color of food. The brown color of a cooked steak is the product of the denaturation of proteins. Fixatives such as formalin also denature proteins and cause color changes. Students who have dissected vertebrates will realize that the brown color of the muscles makes it look as if the animal has been cooked. Copyright © 2009 Pearson Education, Inc.

Changes in primary structure can have huge effects! Example: Sickle cell anemia (one wrong amino acid)

Hey, let’s take a closer look at ENZYMES! Enzymes are a type of Protein Enzymes are workers in your cells that help chemical reactions happen!

ENZYMES! Enzymes CATALYZE reactions These reactions sometimes SYNTHESIZE large biological molecules, including: DNA, RNA, proteins, fats, & complex carbohydrates (such as starch How does an enzyme work?

Chemical Reactions When enzymes are present, they lower the activation energy needed to run the reaction! This makes the reaction more likely to happen.

Enzyme Properties Enzymes look like big blobs of folded up protein! They have an active site where the reaction that they control happens. Active Site

Enzyme Properties Substrate: the substance that the enzyme works on Product: the substance that is created at the end of the reaction

VOCAB ALERT! Substrate = molecule being changed When an enzyme catalyzes a reaction, it does so by binding to the reactant(s), which in enzymatic reactions are called substrates. The shape of the enzyme includes a binding site that fits its substrate(s). The analogy of a lock and key helps illustrate the close molecular fit of the binding site of an enzyme and its substrate, as shown on Transparency 11.1, “How Enzymes Work.” A change in the shape of the enzyme is analogous to changing the lock so that the key—the substrate of an enzyme—no longer fits; thus the reaction does not occur. VOCAB ALERT! Substrate = molecule being changed

Enzyme Properties Enzymes are awesome because they never get tired and never get used up! Enzymes will continue to work on their substrates until they run out of stuff to work on!

Anything outside of this temp. and pH range is bad for enzymes Enzyme Properties Things that prevent enzymes from working: Temperature pH change These things will denature the enzyme Enzymes have a pH and temperature where they work their best! Anything outside of this temp. and pH range is bad for enzymes

Enzyme Properties Enzymes are very specific! Enzymes typically only work on 1 substrate, and are actually named after the things they work on! Lactase works on lactose Sucrase works on sucrose