Protein Types of proteins Protein is essential for daily living because of their constituent amino acids which the body uses to make a variety of proteins and nitrogen containing molecules necessary for life Protein is made up of amino acids and its functions include growth and maintenance enzymes hormones fluid balance acid base balance transportation antibodies and energy It is important to categorize proteins according to their function in order to provide a basis for understanding how important it is to have properly functioning proteins Enzymes are protein molecules that act as catalysts they change the rate of reactions occurring in the body o Found both intracellularly and extracellularly o They are designed to combine selectively with other molecules substrates in the cell o All enzymes are proteins but not all proteins are enzymes Hormones act as chemical messengers that are synthesized and secreted by the endocrine gland and transported throughout the body o Regulate metabolic processes o They are derived from 1 or more AA s o Insulin 2 polypeptide chains disulfide bridge made in one location and transported in blood stream to location of function Contractile proteins o Actin and myosin found in cardiac skeletal and smooth muscles Fibrous proteins are found in bone teeth skin tendons o Include collagen elastin and keratin Immunoproteins inactivating them o Immunoglobulins or antibodies that function by binding to antigens and Transport proteins combine with other substances to provide a means of carrying those substances into the blood or cells o Membrane channels transporters glucose tranporter and Na transporter o Receptors LDL receptors and insulin receptors Plasma proteins o Albumin is synthesized in the liver and released into the blood It transports nutrients and maintains oncotic pressure Buffer protein is a compound that ameliorates a change in pH that would otherwise occur in response to the addition of alkali or acid to a solution o In addition to acid base balance proteins also influence fluid balance The presence of protein in the blood helps attract water and contribute to osmotic pressure Other roles o Function in cell adhesion transmit signals into and out of cell serve as receptors on cell membranes and storage Protein structure Primary structure involves strong covalent bonds among AA s that occur as the polypeptide chain is synthesized on the ribosomes The structure is the linear sequence of its AA structural units o This picture shows the primary structure of a protein Secondary structure is achieved through hydrogen bonding because the H bonds are weak electrical attractions that occur bw H atoms and negatively charged O2 or N atoms Secondary structure refers to the coiling or folding of a polypeptide chain from H bonding o There is alpha helix resembles a coiled spring and is secured by hydrogen bonding in the polypeptide chain makes hair and myosin in the muscle o The second type of the beta pleated sheet which appears to be folded pleated and is held together by H bonding bw polypeptide units of folded chain that lie adjacent to one another makes silk protein o Alpha helix and beta pleated sheet are on the same strand o Tertiary structure refers to the 3 D structure of polypeptide chain of a protein It s the looping and binding of AA s located at considerable distance apart on 2nd structure Quaternary structure involves two or more polypeptide chains and each chain is o Sulfide bonds cys met referred to as a subunit o Hemoglobin is an example of this and is found in the blood it is an iron containing protein that binds to O2 molecules o Antibodies are another example Amino acid classification Amino acids can be classified by structure net charge polarity and essentiality Structure o Every amino acid has a central carbon at least one amino group at least one carboyx group and a side chain o Differences in structure determine whether certain AA s can be synthesized or injested o o Essentiality o Categorized amino acids found in proteins as nutritionally essential or nutritionally nonessential Sources of protein Exogenous proteins are sources of essential amino acids and are the primary source of the additional nitrogen needed to synthesize the nonessential AA s and nitrogen containing compounds The quality of exogenous proteins includes digestibility and amino acid composition o Animal products meat poultry fish digest 90 99 o Plant products grains legumes veggies digest 70 90 Due to plants having more fiber so it is more difficult to digest completely o Amino acids are comprised of complete essential and incomplete 1 or more essential protein is missing Complete proteins contain all essential amino acids and come from all animal sources Gelatin no tryptophan and soy plant complete are exceptions Incomplete proteins are low in one or more amino acid Beans low in methionine and rice low in lysine are examples o Complementary proteins are two or more proteins that when combined provide all essential amino acids Requirements o EAR estimated average requirement 66 g kg day and is the lowest amount of protein needed to maintain nitrogen balance of 0 in the average healthy adults It is based on a reference protein which has all essential amino acids and is highly digestible o RDA recommended dietary allowance 8 g kg day is 2 SD and covers 98 of US population The EAR can be used to set the RDA RDA EAR 2 x SD requirement Special needs o BCAA s are often used in supplements for those with decreased liver function o HN formulas have high nitrogen to promote the healing in those with low intake o Arginine promotes wound healing and plays a role in collagen synthesis o Glutamine enteral formulas and induces protective response in gut Calculating protein requirements o 1kg 2 2lbs o Protein contributes 10 30 of total kcal o 1g Protein 4 kcal o 1 g Protein 0 16 g Nitrogen If we ingest too much protein is goes from amino acids urea and is excreted by kidneys High protein diets should be avoided if an individual has kidney disease only 1 functioning kidney or decreased kidney function or in infants o Alpha keto acid from metabolized amino acid is converted to ATP and stored as fat Amino acid supplements o Transporters on intestinal cells and there are 11 transporters for 20 amino acids There is a competition for tranporters but it is not a problem when consuming whole proteins Amino acid supplements can limit absorption of whole proteins which is not good Protein
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