Protein Lecture Notes PDF

Lecture three Proteins 1 objectives  Classification of amino acids and protein.  Physiological function of protein.  Protein metabolism.  Recommendations for dietary intake.  Identify Inborn error of metabolism.  Identify malnutrition.  Protein: major st...

Lecture three Proteins 1 objectives  Classification of amino acids and protein.  Physiological function of protein.  Protein metabolism.  Recommendations for dietary intake.  Identify Inborn error of metabolism.  Identify malnutrition.  Protein: major structural component of all cells within the body that allows different biological components to retain their shape  contains nitrogen, carbon, hydrogen, oxygen  may contain phosphorous, sulfur, iodine, or iron  Amino acids: building blocks of proteins  Chemical structure of amino acids: A hydrogen (H), amino group (NH2), and an acid group are all attached to a central carbon (C).  A side chain dictates the function of that amino acid: ◦ may carry electrical charges ◦ may have hydrophobic (non-polar functional groups molecules have a low affinity to water molecules and repel it) or hydrophilic (polar functional groups molecules combine with water molecules through electrostatic interaction or hydrogen bonding) properties  Peptide bonds: link amino acids together  Amino acids create proteins when they are positioned in a particular order: primary structure: the specific sequence of amino acids in each protein polypeptide: 10 or more amino acids bonded together proteins are large polypeptides Nonessential amino acides  Nonessential, or dispensable, amino acids are those that the body is:  able to synthesize.  are not required in the diet. Essential amino acids  Essential amino acids: body cannot synthesize must be provided through dietary sources  Examples of essential amino acids:  branched chain amino acids in maintaining muscles tissue: ◦ valine ◦ leucine ◦ isoleucine  limiting amino acids found in the smallest quantity in foods: ◦ lysine and threonine in cereals ◦ methionine and cysteine in legumes Conditionally essential amino acids  Conditionally essential (acquired indispensable) amino acids:  can usually be synthesized by the body  become essential under certain physiological conditions  Physiologic functions of proteins include: tissue growth and maintenance synthesis of other proteins regulation of body processes and immune function provision of energy  Primary function of protein: supplies material for growth and maintenance of body tissues anabolism: the production of new cellular material catabolism: the breaking down or destruction of body tissues anabolism and catabolism: continuous and simultaneous  Dietary proteins: provide about 1 gram of nitrogen for every 6.25 grams of protein consumed when degraded, nitrogen is excreted through urine, feces, and sweat  Nitrogen balance: difference between nitrogen intake and loss ◦ nitrogen equilibrium: nitrogen intake = nitrogen loss ◦ negative nitrogen balance: nitrogen intake < nitrogen loss (burn, hyperthyroidism, fasting, fever) ◦ positive nitrogen balance: nitrogen intake > nitrogen loss (pregnancy, growth, tissue repair)  Proteins—necessary for manufacturing enzymes  Enzymes: proteins that exist in all cells of living things: allow biochemical reactions to accelerate necessary for digestion and metabolism catalysts for many biochemical reactions specific to their substrates and reactions that they catalyze.  Proteins—necessary for manufacturing hormones  Hormones: chemicals synthesized in the body act as messengers or signals to stop or start certain physiological processes  Proteins—component of some hormones: thyroid hormones—regulate metabolic rate and cellular development insulin and glucagon—maintain stability of blood glucose concentrations  Proteins—act as buffers  Buffer: compound that allows fluids and tissues to keep a constant PH  Amino acids: contribute to buffering system by releasing or accepting hydrogen ions  Proteins—maintain proper fluid balance  Oncotic pressure: the effect of proteins on fluid balance  Proteins in blood vessels connecting arteries and veins pull fluid back into the capillaries.  Edema: inadequate protein intake → accumulation of fluid in the tissue → causing swelling  Proteins—component in cells used during an immune response  body synthesizes antibodies to attack antigens that are present  each antibody is created to attack one specific antigen  body keeps a record of the characteristics of each antibody manufactured  able to produce same antibodies more quickly in the future  Proteins—energy source during inadequate supply of energy from fats and carbohydrates:  body breaks down own muscle tissue for energy  results in depletion of lean body tissue  to prevent this, intake of all macronutrients is essential Process of protein digestion:  In the stomach:  Denaturation: hydrochloric acid (HCL) breaks apart some of the bonds that hold the proteins together.  HCL activates the enzyme pepsin to break remaining bonds.  Polypeptides and some free amino acids are emptied into the small intestine for further digestion. Process of protein digestion:  In the small intestine:  Partially digested proteins elicit release of regulatory peptides.  Regulatory peptides signal the pancreas to release pancreatic juice and digestive proenzymes.  Proenzymes activate other enzymes to further degrade polypeptides and amino acids. Process of protein digestion ◦ After intestinal degradation:  Some small peptides and free amino acids are used by intestinal cells for energy and synthesis of other compounds.  Remaining amino acids are transported into the liver.  Liver monitors the amount of amino acids absorbed and adjusts the rate of their metabolism. Components of amino acid catabolism:  deamination: process by which nitrogen is removed from a substance can result in accumulation of ammonia body converts ammonia to urea for excretion by the kidneys remaining carbon skeleton used for energy or to make other substances  transamination: the transfer of nitrogen from one chemical group to another without the formation of ammonia Protein turnover: the process by which proteins are continuously synthesized and degraded  new amino acids mix with amino acids already in the body → forms an amino acid pool  stable amino acid pool: allows amino acids to be used to make other compounds Protein quality Protein quality: the assessment of protein composition and digestibility Digestibility depends upon:  source of protein  other foods with which it is consumed Protein digestibility–corrected amino acid score (PDCAA):  also called biological value  method to quantify the quality of a protein based on its composition and digestibility Two main categories of proteins from food sources: ▪ complete (high-quality) proteins: contain all amino acids in correct amounts needed by humans sources include animal proteins and the plant protein soy ▪ incomplete (low-quality) proteins: contain insufficient amounts of one or more essential amino acids generally derived from plant sources. Complementary proteins: proteins from different sources that combine to form a complete protein. Recommended dietary allowances (RDA) of protein:  adults aged 19–70—approximately 0.8 g/kg/day  infants, children, and pregnant women— slightly higher intakes  Average protein intakes:  adults aged 19–30: 91 gm/day  older adults: 66 gm/day Inborn error of metabolism  It is inherited defect in the way a substrate in metabolized such as: Phenylketonuria (PKU) disease:  caused by a deficiency of the enzyme phenylalanine hydroxylase.  untreated, causes harmful accumulation of phenylalanine.  results in nerve damage that causes mental retardation and other health problems  dietary implications: ◦ food consumed must have very little phenylalanine ◦ high-protein foods must be limited ◦ special phenylalanine-free dietary supplements contain additional protein, micronutrients, and energy  Results of stress induced by critical injury: accelerated tissue breakdown → negative nitrogen balance and loss of body mass Conditions necessitating elevated protein intake:  trauma, sepsis, brain injury, patients undergoing certain types of dialysis  higher intake needed during recovery from severe burns Conditions necessitating reduced protein intake:  certain types of kidney or liver failure that make the body unable to effectively metabolize proteins protein malnutrition  Insufficient intake of nitrogen-containing foods → protein malnutrition  1. Kwashiorkor ◦ adequate energy intake, but insufficient protein intake ◦ usual occurrence: children in underdeveloped countries, after weaned from breast milk ◦ symptoms: edema, hair discoloration, altered skin pigmentation protein malnutrition  2. Marasmus ◦ inadequate consumption of energy, with compromised protein status ◦ usual occurrences:  underdeveloped countries where food sources are scarce  persons with severe wasting diseases ( a condition that causes significant weight loss and muscle loss.)  elderly population ◦ symptoms: abnormally dry or loose skin folds, altered pigmentation of the hair, severe loss of tissue from normal areas of fat deposits Treatment of malnutrition:  identify cause and formulate interventions  ensure adequate intake of protein and energy  https://youtube.com/shorts/Lhuh_Mz8sig? si=2_q_xA1u13Xct2Cx (roles of proteins) Thank you for listening QUESTIONES???? protein 34