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2011SpringCFS364Proteins - Chapter 5 Protein Introduction...

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Chapter 5 Protein Introduction What is a protein? Made of smaller units called amino acids ; the amino acids are connected to each other by peptide bonds Different proteins occur by having different number and arrangements of amino acids Amino acids Building blocks for proteins There are 20 amino acids available to form proteins – 9 essential amino acids (must obtain from diet) – 11 nonessential amino acids (the body can make these amino acids) Each amino acid consists of: – Amine group (nitrogen containing) – Carboxyl group (acid group) – Hydrogen atom – Side chain (responsible for the 20 different amino acids) Protein structure Sequence of amino acids (order of the amino acids and the number of amino acids linked together by peptide bonds) determines protein structure and function Examples of protein shapes: – Globular-like hemoglobin – Linear
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Roles of protein and amino acids Enzymes – proteins which speed up reactions in the body (almost all enzymes are proteins) Contractile proteins (e.g. actin, myosin, troponin, and tropomyosin) – involved in skeletal muscle movement Connective tissue proteins – Collagen in tendons, bones, and cartilage – Keratin in nails and hair Protein transporters – The protein hemoglobin carries oxygen in the red blood cells – The protein albumin transports many substances in the blood, including fatty acids, some minerals, and bile acids Some hormones are proteins Water balance (proteins attract water) pH regulation Immune function (for example, antibodies are proteins which are created by the immune system in response to anything foreign) Transport proteins (proteins can act as regulators for what goes in and out of cells) Energy from amino acids - usually spared and not a significant supplier of energy – 15% of calories are from protein during intense exercise and starvation – 5% of calories are from protein if energy is adequate Digestion of protein and absorption of amino acids Step 1: Acid in stomach denatures proteins (this means that the proteins start to unravel) Step 2: Enzyme (pepsin) in stomach breaks peptide bonds Step 3: Pancreas and intestine release protein-digesting enzymes into small intestine Step 4: Enzymes on surface of small intestine split tripeptide/dipeptides into single amino acids (tripeptides are three amino acids bound together by peptide bonds and dipeptides are two amino acids bound together by a peptide bond) Step 5: Amino acids are absorbed into intestinal cells and transferred to the blood (rate of absorption varies with source; for example, free amino acids can be absorbed faster than intact (whole) proteins, and whey protein in milk is absorbed more rapidly than casein, which is another protein in milk) Protein metabolism In order for amino acids to be used in the body as glucose, pyruvate, or used in the Kreb's Cycle, the nitrogen group must be removed (by transamination or deamination reactions)
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2011SpringCFS364Proteins - Chapter 5 Protein Introduction...

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