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Transcript
Biochemistry Chapter 17 Protein Protein What does protein do in the body? Protein Most people think of building muscle but protein has many functions in the body. The human body contains between 10,000 to 50,000 different proteins. Only 1,000 have been studied in detail. Macromolecules Protein molecules are very big and contain LOTS of atoms so they are called macromolecules. Elements of Proteins Protein molecules consist of carbon, hydrogen, oxygen, nitrogen, and sometimes other elements. The nitrogen atoms make proteins so variable and different from lipids and carbohydrates. Structure of a protein Protein is made of chains of substances called amino acids. Amino acids are organic compounds that contain a carboxyl group and an amine group. Amine Group The amine group consists of one nitrogen atom and two hydrogen atoms. It is written –NH2 Peptide Bonds Amino acids combine in long chains to form proteins. Amino acids attach together through peptide bonds. Peptide bonds occur between the amine group on one AA and the carboxyl group on another AA. Water is removed and the carbon bonds to the nitrogen. Polypeptide When ten or more amino acids are chained together in a single molecule, we call that a polypeptide. Most proteins contain hundreds of AA and many contain thousands. Structure of Proteins Peptide bonds cause AA to combine in long chains. Protein molecules tend to coil, fold, and tangle in complex shapes Hydrogen Bonds Hydrogen bonds between parts of the peptide chain cause the molecule to fold and coil in a particular way. Some proteins form spirals or rope-like structures. Structure and Function A protein’s shape helps determine its function. Rope-like, “fibrous” proteins serve as connective tissue in the body. Collagen and elastin are two fibrous proteins. Structure and Function More compact, “globular” proteins act as carrier molecules. Hemoglobin carries oxygen in the blood. Denaturation The tightly coiled shape of proteins prevents them from dissolving in water. Denaturation is a chemical process that changes the shape of a protein without breaking the peptide bonds. Denaturation breaks the hydrogen bonds and causes the protein to uncurl. Denaturation Methods of Denaturation Heat- think of how eggs and meat change as they cook Mixing or kneading pH Freezing Pressure Chemical compounds like metal ions Coagulation Coagulation changes a liquid into a soft, semisolid clot or solid mass. Coagulation occurs when a denaturated protein reforms some hydrogen bonds. Scrambled eggs are a good example. Protein in Food What types of food contain protein? Eggs Meat Fish Poultry Legumes (beans) Nuts and seeds Eggs Eggs are complex biological systems that contain almost every vitamin and mineral you need. The egg white or albumen contains lots of protein (ovalbumin) and not much else. The egg yolk contains all of the fat and most of the other nutrients found in eggs. It is also high in protein (livetin). Meat and Fish Animal muscle fiber is about 20% protein. Meat contains a large amount of connective tissue and can be very tough if not cooked properly. Fish has much less connective tissue and cooks very quickly. Protein from Plants Nuts and seeds are high in protein but also high in fat. Soybeans are 40% protein and contain polyunsaturated fats. Protein in Cooking Many amino acids can combine with both fats and water and are called emulsifiers. Egg yolks are the most common emulsifiers used in cooking. Gelatin Gelatin is made from the collagen in animal connective tissue. Gelatin is used to thicken everything from meat sauces to desserts. The long proteins in gelatin form a network that locks in water to form gels. Gluten Gluten is an elastic substance formed by mixing water with the proteins found wheat. Kneading dough helps to develop gluten and makes the dough springy and stretchy. Protein in the Body Proteins are denatured by hydrochloric acid in the stomach and then broken down by enzymes in the small intestine. Individual amino acids are carried through the blood stream to the cells where they are reassembled into needed proteins. Functions of body Proteins Providing structure New Growth Enzymes and hormones Transporting nutrients Functions of body Proteins Antibodies to ward off disease Stabilizing pH levels Can provide energy in an emergency Essential Amino Acids There are 20 amino acids used by the body. Our bodies are capable of making 11 of those. The other 9 must be eaten and are called essential amino acids. Complete Protein A complete protein contains all 9 essential amino acids. An incomplete protein does not. A high-quality protein like egg protein contains all the essential amino acids in the correct amounts. Dietary Allowances Protein is an essential part of the diet but we only need relatively small amounts. An adult needs to eat only about 50g of protein in one day. Most Americans eat more than that in one meal.