PROTEINS

Recall: Nutrients in the human body have three general functions: They can supply energy for processes such as growth, movement, electrical signalling, metabolism 2. They can regulate body processes such as metabolism, growth, membrane transport, cellular communication 3. They can provide the building blocks for making the structures of our cells and our bodies ` Proteins in our diet serve all three functions

Proteins Proteins can supply energy: Although cells of the body prefer to use carbohydrates and lipids as sources of energy, many cells can also use proteins as fuel molecules if necessary. That means that extra dietary protein can be converted to carbohydrate or lipid molecules and stored for future energy needs. 3

Proteins 2. Proteins can regulate cellular processes: They help form “receptors” which allow cells to respond to hormones

Proteins 2. Proteins can regulate cellular processes: They help form “receptors” which allow cells to respond to hormones They form “channels” in the membrane which allow things to get into and out of cells

Proteins 2. Proteins can regulate cellular processes: They help form “receptors” which allow cells to respond to hormones They form “channels” in the membrane which allow things to get into and out of cells They form “junctions” on membranes which allow cells to communicate with each other.

Proteins 2. Proteins can regulate cellular processes: They form enzymes which catalyze cellular reactions

Proteins 2. Proteins can regulate cellular processes: They form enzymes which catalyze cellular reactions They slide past each other to make muscles contract

Proteins 2. Proteins can regulate cellular processes: They form enzymes which catalyze cellular reactions They slide past each other to make muscles contract They fom the cytoskeleton which holds organelles in place and moves them around in the cell

Proteins 2. Proteins can regulate cellular processes: They form antibodies all over the body, proteins in the blood, and many hormones.

Proteins 3. Proteins can make structures our bodies need: Proteins such as collagen form tendons and ligaments

Proteins 3. Proteins can make structures our bodies need: Proteins such as collagen form tendons and ligaments Collagen and another protein called elastin form the dermis is the skin. The protein keratin forms hair and the top layer of the epidermis.

Proteins All of these proteins in the body must constantly be replaced. That means your diet must contain the building blocks of proteins, called amino acids 13

Proteins Food sources Meat, Chicken, Fish Milk & cheese Eggs Beans, peas, grains, nuts, seeds, vegetables 14

Amino Acids 15

Amino Acids 16

Amino Acids Amino acids bond together by a process called dehydration synthesis. 17

Amino Acids Amino acids bond together by a process called dehydration synthesis. Bonding two amino acids together forms a dipeptide 18

Amino Acids Amino acids bond together by a process called dehydration synthesis. Bonding two amino acids together forms a dipeptide Bonding many amino acids together forms a polypeptide or protein 19

Amino Acids While proteins are long, unbranching chains of amino acids, they do not remain straight. Different side-groups cause the chain to bend and coil. In fact, the three dimensional stucture of a protein is what gives it a specific function. 20

Amino Acids Changing the three-dimensional shape of a protein is called denaturing, and changes the function of a protein, often permanently. Proteins can be denatured many ways: heat alcohol acids or alkalis digestive enzymes (“proteases”) etc. 21

Protein Digestion Protein digestion begins in the stomach. Hydochloric acid denatures the protein, unfolding it so proteases can reach the amino acids to break the peptide bonds between them. 22

Protein Digestion Along with the hydrochloric acid, one of these proteases, pepsin, begins protein digestion in the stomach. 23

Protein Digestion It is then continued in the small intestine by proteases secreted by the pancreas and cells of the intestine. 24

Protein Digestion & Amino Acids Individual amino acids are absorbed into the blood vessels in the mucosa of the small intestine. They are carried first to the liver, which can remove excess amino acids, after which they enter the general circulation and become available to cells all around the body. 25

Amino Acids All cells of the body have the ability to take those amino acids out of the blood and use them to build the proteins they need. 26

Amino Acids All cells of the body also have the ability to break down proteins to release the individual amino acids back into the blood. 27

Amino Acids Thus, there is a pool of amino acids available for building all of the proteins the body needs. 28

Amino Acids Thus, there is a pool of amino acids available for building all of the proteins the body needs. Some amino acids can be used to make other molecules such as hormones, nucleotides, or neurotransmitters. 29

Amino Acids Cells of the liver can break amino acids apart, separating the amino groups (nitrogen atom and two hydrogen atoms) from the rest of the amino acid molecules, called their “carbon skeleton”, which can be used to form lipids or carbohydrates which can be used to produce or store energy. The amino groups are hooked together to form urea 30

Amino Acids That urea can then safely travel to the kidneys, where it is removed and excreted in the urine. 31

Amino Acids Your body needs to take in new amino acids from your diet, but this must be balanced by the excretion of nitrogen in the form of urea. 32

Amino Acids Your body needs to take in new amino acids from your diet, but this must be balanced by the excretion of nitrogen in the form of urea. If your liver can’t form enough urea, the nitrogen produced by the breakdown of amino acids can be toxic to the body. This is called “nitrogen balance”: Your intake of nitrogen (in the form of proteins) must equal Your output of nitrogen (in the form of urea in the urine) 33

Nitrogen Balance Nitrogen equilibrium Nitrogen intake = nitrogen output Healthy adults Positive nitrogen balance Nitrogen intake > nitrogen output Necessary during growth; recovery from illness Negative nitrogen balance Nitrogen intake < nitrogen output Results from injury and illness 34

Proteins in the Diet Recommended protein intake: Adult RDA = 0.8 gram per kilogram body weight More in children, pregnancy, recovery from injury, etc 35

Proteins in the Diet Recommended protein intake: Adult RDA = 0.8 gram per kilogram body weight More in children, pregnancy, recovery from injury, etc Thus: A 50 kg adult (110 pounds) should eat 50 x .8 = 40 grams of protein per day 36

Proteins in the Diet Recommended protein intake: Adult RDA = 0.8 gram per kilogram body weight More in children, pregnancy, recovery from injury, etc Thus: A 50 kg adult (110 pounds) should eat 50 x .8 = 40 grams of protein per day A 70 kg adult (154 pounds) should eat 70 x .8 = 56 grams of protein per day 37

Proteins in the Diet Recommended protein intake: Adult RDA = 0.8 gram per kilogram body weight More in children, pregnancy, recovery from injury, etc Thus: A 50 kg adult (110 pounds) should eat 50 x .8 = 40 grams of protein per day A 70 kg adult (154 pounds) should eat 70 x .8 = 56 grams of protein per day A 90 kg adult (198 pounds) should eat 90 x .8 = 72 grams of protein per day 38

Proteins in the Diet Recommended protein intake: Adult RDA = 0.8 gram per kilogram body weight More in children, pregnancy, recovery from injury, etc Thus: A 50 kg adult (110 pounds) should eat 50 x .8 = 40 grams of protein per day A 70 kg adult (154 pounds) should eat 70 x .8 = 56 grams of protein per day A 90 kg adult (198 pounds) should eat 90 x .8 = 72 grams of protein per day In the United States: protein intake > protein needs 39

Proteins in the Diet Excess protein can strain kidney function There are links between high-protein diets and Osteoporosis Obesity Heart disease Some forms of cancer 40

Proteins in the Diet At the other extreme, it is possible to have too little protein in your diet. This can occur in diets which are not properly designed, but it is most often associated with extreme poverty, and occurs together with insufficient intake of fuel molecules such as carbohydrates or lipids. Kwashiorkor and Marsmas 41

Proteins in the Diet Not all dietary proteins are equally useful for the body. 42

Proteins in the Diet Tyrosine Serine Proline Valine Glycine Tryptophan Glutamine Threonine Glutamic acid Phenylalanine Cysteine Methionine Aspartic Acid Lysine Asparagine Leucine Arginine Isoleucine Alanine Histidine Nonessential AA Essential AA Not all dietary proteins are equally useful for the body. Of the 20 amino acids which are used to make proteins in the human body, only 11 of them can be synthesized. The remaining 9 must be obtained through the diet. 43

Proteins in the Diet Protein quality: Complete proteins supply all of the essential amino acids (e.g. animal proteins; soy proteins) 44

Proteins in the Diet Protein quality: Complete proteins supply all of the essential amino acids (e.g. animal proteins; soy proteins) Incomplete proteins are low in one or more essential amino acid ( e.g. most plant proteins) 45

Proteins in the Diet Protein quality: Complete proteins supply all of the essential amino acids (e.g. animal proteins; soy proteins) Incomplete proteins are low in one or more essential amino acid ( e.g. most plant proteins) This can create problems for people on vegetarian or vegan diets, or for people on special diets low in meats, milk, eggs, etc. 46

Proteins in the Diet Protein quality: You can ensure that you get all essential amino acids by combinig two or more incomplete proteins which are missing different ones. These are called complementary proteins 47

Proteins in the Diet A healthy diet should include a variety of proteins from meats, eggs, dairy, soy products, legumes and other vegetables. A vegetarian diet must include complementary proteins such as those in - rice and beans - whole grains and vegetables - corn and beans to ensure that all essential amino acids are available Total protein intake should be moderated