Protein w Review notes.pdf

VIDEO ANIMATIONS for your preference. https://www.youtube.com/watch?v=gG7uCskUOrA https://www.youtube.com/watch?v=2dV5s6v2v8Q https://www.youtube.com/watch?v=oefAI2x2CQM https://www.youtube.com/watch?v=hok2hyED9go https://www.youtube.com/watch?v=bKIpDtJdK8Q “to hold first place”, or ”is of prime i...

VIDEO ANIMATIONS for your preference. https://www.youtube.com/watch?v=gG7uCskUOrA https://www.youtube.com/watch?v=2dV5s6v2v8Q https://www.youtube.com/watch?v=oefAI2x2CQM https://www.youtube.com/watch?v=hok2hyED9go https://www.youtube.com/watch?v=bKIpDtJdK8Q “to hold first place”, or ”is of prime importance” amino = containing nitrogen Reminder: H forms one bond. O forms two bonds. N forms three bonds. C forms four bonds. All amino acids have the same basic structure—a central carbon (C) atom with a hydrogen atom (H), an amino group (NH2), and an acid group (COOH) attached to it. However, carbon atoms need to form four bonds, so a fourth attachment is necessary. This fourth site distinguishes each amino acid from the others. Attached to the central carbon at the fourth bond is a dis- tinct atom, or group of atoms, known as the side group or side chain The side groups on the central carbon vary from one amino acid to the next, making proteins more complex than either carbohydrates or lipids. for example let us compare amino acids to carbohydrates, A polysaccharide (starch, for example) may be several thousand units long, but each unit is a glucose molecule just like all the others. A protein, on the other hand, is made up of about 20 different amino acids, each with a different side group. All amino acids have a central carbon with an amino group (NH2), an acid group (COOH), a hydrogen (H), and a side group attached. The side group is a unique chemical structure that differentiates one amino acid from another These are examples of amino acids and their structure. The simplest amino acid, glycine, as seen from the farthest left, has a hydrogen atom as its side group. A slightly more complex amino acid, alanine, has an extra carbon with three hydro- gen atoms. although all amino acids share a common structure, they differ in size, shape, electrical charge, and other characteristics because of differences in these side groups. There are 22 amino acids. In some references, 20. Nonessential Amino Acids More than half of the amino acids are nonessential, meaning that the body can synthesize them for itself. Proteins in foods usually deliver these amino acids, but it is not essential that they do so. The body can make all nonessential amino acids, given nitrogen to form the amino group and fragments from carbohydrate or fat to form the rest of the structure. It is not a dietary essential. The body can synthesize it as long as the materials for synthesis are adequate. There are nine amino acids that the human body either cannot make at all or cannot make in sufficient quantity to meet its needs. These nine amino acids must be supplied by the diet; these are dietary essentials. From Krause’s Food, Nutrition, and Diet therapy here are the 9 essential amino acids. From Krause’s Food, Nutrition, and Diet therapy In older references there are only 11 non-essential amino acids: 1. Alanine 2. Arginine 3. Asparagine 4. Aspartic acid 5. Cysteine 6. Glutamic acid 7. Glutamine 8. Glycine 9. Proline 10.Serine 11.Tyrosine 12.Arginine, glycine, serine and tyrosine are not included from the 11 A semi essential or semi indispensable amino acid May reduce the need for an Essential Amino Acid or partially spare it BUT cannot completely replace it. Sometimes a nonessential amino acid becomes essential under special circumstances. For example, the body normally uses the essential amino acid phenylalanine to make tyrosine (a nonessential amino acid). But if the diet fails to supply enough phenylalanine, or if the body cannot make the conversion for some reason (as happens in the inherited disease phenyl- ketonuria), then tyrosine becomes a conditionally essential amino acid. From Krause’s Food, Nutrition, and Diet therapy Cells link amino acids end-to-end in a variety of sequences to form thousands of different proteins. A peptide bond unites each amino acid to the next. in carbohydrates, what is the process of creating a simple substance into a more complex one? Condensation reactions connect amino acids just as they combine two monosaccharides to form a disaccharide in carbohydrates In fats, condensation connects three fatty acids with a glycerol to form a triglyceride In proteins, two amino acids bond together to form a dipeptide, by another such reaction, a third amino acid can be added to the chain to form a tripeptide. Four to nine amino acids that bind together are called oligopeptides. As additional amino acids join the chain, a polypeptide is formed. Most proteins are a few dozen to several hundred amino acids long. Di – two Tri – three Oligo – few Poly - many Review: a protein molecule contains: Amino group NH2, an acid or hydroxyl group COOH, a hydrogen atom, and a side chain. Central carbon needs a fourth bond. This is how condensation in amino acids occur An OH group from the acid end (COOH) of one amino acid and an H atom from the amino group (NH2) of another join to form a molecule of water. Then, a peptide bond (the one highlighted in red in the picture) forms between the two amino acids, creating a dipeptide. Cells link amino acids end-to-end in a variety of sequences to form thousands of different proteins. A peptide bond unites each amino acid to the next. The primary structure of a protein is determined by the sequence of amino acids. amino acid sequences within proteins vary. the 20 amino acids can be linked together in a variety of sequences THESE SHAPES ARE MADE DURING PROTEIN FOLDING. The primary structure of a protein is determined by the sequence of amino acids. amino acid sequences within proteins vary. the 20 amino acids can be linked together in a variety of sequences THESE SHAPES ARE MADE DURING PROTEIN FOLDING. The secondary structure of proteins is determined not by chemical bonds as between the amino acids but by weak electrical attractions within the polypeptide chain. As positively charged hydrogens attract nearby negatively charged oxygens, sections of the polypeptide chain twist into a helix or fold into a pleated sheet, for example. These shapes give proteins strength and rigidity. The tertiary structure of proteins occurs as long polypeptide chains twist and fold into a variety of complex, tangled shapes. The unique side group of each amino acid gives it characteristics that attract it to, or repel it from, the surrounding fluids and other amino acids. Some amino acid side groups are attracted to water molecules; they are hydrophilic. Other side groups are repelled by water; they are hydrophobic. As amino acids are strung together to make a polypeptide, the chain folds so that its hydrophilic side groups are on the outer surface near water; the hydrophobic groups tuck themselves inside, away from water. Fibrous proteins form linear structures that are more than ten times as long as they are wide. They are found in the protective tissues of animals such as skin, hair, tendons, feathers, scales and fins. These are insoluble in water and are able to provide support for cells and tissues Examples at page 67 Keratin – chief protein in hair, Collagen – connective tissue, in tendons and bone matrices, Fibrin – of a blood clot, Myosin of muscles, and Elastin in blood vessels. Some form globular or spherical structures than can carry and store materials within them. Globular proteins are proteins wherein its structure is coiled and tightly wounded and is relatively soluble in water. Examples of which are casein in milk, cheese, albumin in egg whites and milk, and globulin in red blood cells. Some polypeptides are functioning proteins just as they are; others need to associate with other polypeptides to form larger working complexes. The quaternary structure of proteins involves the interactions between two or more polypeptides. One molecule of hemoglobin—the large, globular protein molecule that, by the billions, packs the red blood cells and carries oxygen—is made of four associated polypeptide chains, each holding the mineral iron hemoglobin (HE-moh-GLO-bin): the globular protein of the red blood cells that carries oxygen from the lungs to the cells throughout the body. When proteins are subjected to heat, acid, or other conditions that disturb their stability, they undergo denaturation—that is, they uncoil and lose their shapes and, and also, lose their ability to function. Past a certain point, denaturation is irreversible. Familiar examples of denaturation include the hardening of an egg when it is cooked, the curdling of milk when acid is added, and the stiffening of egg whites when they are whipped. In the body, proteins are denatured when they are exposed to stomach acid. Lack additional acidic or basic groups and can be further divided into aliphatic (straight-chain) and aromatic (ring structure) amino acids. Examples include glycine, serine, and threonine for aliphatic, and tryptophan and phenylalanine for aromatic amino acids. Aliphatic – threonine, glycine, serine, alanine Aromatic/cyclic – tryptophan, phenylalanine, tyrosine  On an adequate diet much of the carbon residues of glucogenic and ketogenic amino acids are oxidized directly to carbon dioxide and water. During carbohydrate deficiency, glucogenic amino acids tend to form glucose and ketogenic amino acids tend to form ketone bodies.  Examples are gliadin and hordein.  Examples are zein and gelatin.  These proteins yield only amino acids upon hydrolysis. Examples include: - Albumins: Water-soluble and coagulated by heat (e.g., egg white). - Globulins: Insoluble in water but soluble in dilute salt solutions (e.g., blood serum proteins). - Glutenins and Prolamines: Found in grains, soluble in dilute acids and alkalis. - Scleroproteins: Fibrous and insoluble proteins, resistant to digestion (e.g., keratin, collagen).  Compound proteins, conjugated proteins or proteids are combinations of simple proteins and some other non-protein substance called a prosthetic group attached to a molecule. They perform functions that a constituent could not properly perform by itself. These proteins include the following: Examples include: - Lipoproteins: Proteins bound to lipids, important in fat transport. - Glycoproteins: Contain carbohydrates (e.g., mucoproteins in connective tissue). - Nucleoproteins: Bound to nucleic acids, essential for genetic information storage and transfer (e.g., DNA and RNA) Review this before proceeding. Chemically speaking, proteins are more complex than carbohydrates or lipids; they are made of some 22 different amino acids, 9 of which the body cannot make (the essential amino acids). Each amino acid contains an amino group, an acid group, a hydrogen atom, and a distinctive side group, all attached to a central carbon atom. Cells link amino acids together in a series of condensation reactions to create proteins. The distinctive sequence of amino acids in each protein determines its unique shape and function. Digestion of Protein 1. Mouth Enzyme - none Action - only mechanical mastication 2. Stomach Enzyme. - pepsin, produced first as inactive precursor to pepsinogen, then activated by the hydrochloric acid Action - converts protein into proteoses and peptones In infants, enzyme rennin converts casein into coagulated curd. 3. Small intestine (Alkaline) a. Pancreas a.1 Trypsin (produced first as inactive precursortrypsinogen and then activated by enterokinase) converts proteins, proteoses, and peptones into polypeptides and peptides. a.2 Chymotrypsin (produced first as inactive precursor chymotrypsinogen and then activated by active trypsin) converts proteoses and peptones into polypeptides and dipeptides; also coagulates milk. a.3 Carboxypeptidase converts polypeptides into simpler peptides, dipeptides, and amino acids. b. Intestine b.1 Aminopeptidase converts polypeptides into peptides and amino acids. b.2 Dipeptidase converts dipeptides into amino acids. Tandaan: hydrolysis ang nag b-break ng bonds ng complex substances (di- to polysaccharides for carbs), sa proteins di-, tri-peptides, or more (poly) Tripeptidases cleave tripeptides; dipeptidases cleave dipeptides. Endopeptidases cleave peptide bonds within the chain to create smaller fragments, whereas exopeptidases cleave bonds at the ends to release free amino acids. Take Note: Tri = three Di – two Endo = within Exo = outside The major event in the stomach is the partial breakdown (hydrolysis) of proteins. Hydrochloric acid uncoils (denatures) each protein’s tangled strands so that digestive enzymes can attack the peptide bonds. The hydrochloric acid also converts the inactive form of the enzyme pepsinogen to its active form, pepsin. Pepsin cleaves proteins—large polypeptides—into smaller polypeptides and some amino acids. The term we use to call an inactive form of an enzyme is called a proenzyme or zymogen TAKE NOTE Pepsin is a gastric enzyme that hydrolyzes protein. Pepsin is secreted in an inactive form, pepsinogen, which is activated by hydrochloric acid in the stomach. When polypeptides enter the small intestine, several pancreatic and intestinal proteases hydrolyze them further into short peptide chains (oligopeptides) tripeptides, dipeptides, and amino acids. Then peptidase enzymes on the membrane surfaces of the intestinal cells split most of the dipeptides and tri- peptides into single amino acids. Only a few peptides escape digestion and enter the blood intact. In the next pages, you will see the protein digesting enzymes and describe each of their actions. Cleaves – break or cut bonds A number of specific carriers transport amino acids (and some dipeptides and tripeptides) into the intestinal cells. Once inside the intestinal cells, amino acids may be used for energy or to synthesize needed compounds. Amino acids that are not used by the intestinal cells are transported across the cell membrane into the surrounding fluid where they enter the capillaries on their way to the liver. enzymes in foods are digested, just as all proteins are. Even the digestive enzymes— which function optimally at their specific pH—are denatured and digested when the pH of their environment changes. The enzyme pepsin, for example, which works best in the low pH of the stomach becomes inactive and digested when it enters the higher pH of the small intestine. SUMMARY (Review first! Then proceed) Digestion is facilitated mostly by the stomach’s acid and enzymes, which first denature dietary proteins, then cleave them into smaller polypeptides and some amino acids. Pancreatic and intestinal enzymes split these polypeptides further, to oligo-, tri-, and dipeptides, and then split most of these to single amino acids. Then carriers in the membranes of intestinal cells transport the amino acids into the cells, where they are released into the bloodstream. Next topic: Proteins in the body The human body contains an estimated 30,000 different kinds of proteins. Of these, only about 3000 have been studied As you will see later on, each protein has a specific function, and that function is determined during protein synthesis. Each human being is unique because of small differences in the body’s proteins. These differences are determined by the amino acid sequences of proteins, which, in turn, are determined by genes. Dito natin makikita kung bakit “body building” and “repairing” ang functions ng protein. Protein synthesis depends on a diet that provides adequate protein and essential amino acids. The instructions for making every protein in a person’s body are transmitted by way of the genetic information received at conception. This body of knowledge, which is filed in the DNA (deoxyribonucleic acid) within the nucleus of every cell, this information never leaves the nucleus. Taglish explanation: Sa nucleus ng cell daw ay may DNA na may laman ng “genetic information” na unique sa bawat tao. Dito nanggagaling kung paano daw gagawin yung proteins. Transforming the information in DNA into the appropriate sequence of amino acids needed to make a specific protein requires two major steps. In the first step, ♦ a stretch of DNA is used as a template to make a strand of RNA (ribonucleic acid) known as messenger RNA. Messenger RNA then carries the code across the nuclear membrane into the body of the cell. There it seeks out and attaches itself to one of the ribosomes (a protein-making machine, which is itself composed of RNA and protein), Taglish Explanation: May tinatawag na mRNA or messenger RNA na pupunta sa DNA (didikitan niya yung DNA) at kokopyahin yung code or instructions kung paano gagawin yung proteins. Remember guys hindi lang isa yung mRNA pero marami yan. Pagkatapos ng mRNA kunin yung code, lalabas sya at pupunta sa mga ribosomes (from nuclear membrane papuntang body ng cell). Tignan nyo yung picture. Read Codon and Anticodon CODON CHART – for biochemists already where the second step takes place. Situated on a ribosome, messenger RNA specifies the sequence in which the amino acids line up for the synthesis of a protein. Taglish: Si mRNa kapag nakadikit na kay ribosome, sasabihin nya kung paano yung sequence or arrangement ng mga amino acid para makagawa ng protein. Remember : nagkakaiba lang ang proteins depending sa amino acid sequence nila. Si DNA ang nagsasabi kung anong sequence ang gagawin for a specific protein. Isipin nyo na lang na for example, si hair may sariling amino acid sequence ganun din kay skin, muscles, etc. nagdedepend ito kung ano kailangan ng body. Isipin nyo na yung ginagawa ni mRNA sa ribosome ay parang seating arrangement. Sinasabi nya kung aling amino acid ang mapupunta sa specific place sa sequence. At si DNA naman ang nagsabi kay mRNA kung paano ito gagawin. When the messenger’s list calls for a specific amino acid, the transfer RNA carrying that amino acid moves into position. Then the next loaded transfer RNA moves into place and then the next and the next. In this way, the amino acids line up in the sequence that is genetically determined, and enzymes bind them together. Finally, the completed protein strand is released, and the transfer RNAs are freed to return for other loads of amino acids. When a cell makes a protein, the gene for that protein gas been “EXPRESSED” Taglish: ang product ng protein synthesis ay PROTEIN or PROTEIN STRAND. Si tRNA ang tagadala ng Amino acid kay mRNA. Sinusundo ni tRNA ang mga amino acids sa CELL FLUID papunta sa ribosome kung saan nakapwesto si mRNA. Next step ay pipila ang mga tRNA (kasama ng amino aids na dala nila) at aantayin nila si mRNA na tawagin sila para mag unload (or ibigay si amino acid) at pum- westo sa line o sequence. Kapag nakapwesto na si Amino acid, pababalikin ang mga tRNA para magsundo pa ng mga panibagong Amino acids. (take note: ang tRNA ay merong 20 kinds, kumbaga tigiisang kind sila per amino acid) Yung mga nakapwestong amino acid kay mRNA ay iseseal or ididikit na with the help of ENZYMES. Kumbaga dito na nagkakaroon ng “peptide bonds” and “PROTEIN STRANDS” at narerelease na ito sa site ng katawan kung saan kailangan. Taglish: Pwedeng mahkamali si mRNA ng pagkopya ng genetic information sa DNA or pwede din magkaron ng genetic error sa loob ng cell(DNA) part at pwede itong makopya ni mRNA. Yung mga ito ay pwede mag result ng errors na pwede mag lead sa masamang results. If a genetic error alters the amino acid sequence of a protein, or if a mistake is made in copying the sequence, an altered protein will result, sometimes with dramatic consequences. The protein hemo-globin offers one example of such a genetic variation. In a person with sickle-cell anemia, two of hemoglobin’s four polypeptide chains have the normal sequence of amino acids, but the other two chains do not— they have the amino acid valine in a position that is normally occupied by glutamic acid This single alteration in the amino acid sequence changes the characteristics and shape of hemoglobin so much that it loses its ability to carry oxygen effectively. The red blood cells filled with this abnormal hemoglobin stiffen into elongated sickle, or crescent, shapes instead of maintaining their normal pliable disc shape—hence the name, sickle-cell anemia. Sickle cell anemia rises energy needs, causes many medical problems, and can be fatal. Taglish: For example: yung protein na hemoglobin sa red blood cells, pwedeng magkaroon ng genetic variation (pagkakaiba). Yung sa sakit na “SICKLE CELL ANEMIA” : yung dalawa sa apat na polypeptide chains ng hemoglobin ay merong normal sequence ng amino acids pero yung dalawang chains naman ay wala (abnormal) Yung amino acid na glutamic acid na dapat nasa sequence/position ay naging valine. Kahit itong small change or alteration lang ay nag affect ng big deal sa hemoglobin. Nawalan tuloy ito ng ability to carry oxygen effectively. When a cell makes a protein as described earlier, scientists say that the gene for that protein has been “expressed.” Cells can regulate gene expression to make the type of protein, in the amounts and at the rate, they need. Nearly all of the body’s cells possess the genes for making all human proteins, but each type of cell makes only the proteins it needs. For example, cells of the pancreas express the gene for insulin; in other cells, that gene is idle. Similarly, the cells of the pancreas do not make the protein hemoglobin, which is needed only by the red blood cells. Taglish: Merong common genetic information kayong nashare ng parents mo. It was passed on to you. This is why you look like one of your parents or you look like a mix of both of them, sometimes sharing most of their physical qualities. Meron ng instructions na nakalagay sa cell (particularly nucleus DNA) kung paano ma-build and repair yung body mo. Meron din naming common genetic information sa lahat ng tao such as kung paano ang itsura or struture ng organs such as lungs, heart, etc. Protein synthesis can happen anywhere (any site or cells in the body) kung saan kailangan ng body. Building or repairing.  There are several methods to enhance the quality of proteins consumed:  For example, adding lysine to bread increases its nutritional value.  such as adding lysine back into cereals after milling.  For instance, pairing legumes with grains ensures a complete protein profile. Review: Cells synthesize proteins according to the genetic information provided by the DNA in the nucleus of each cell. This information dictates the sequence in which amino acids are linked together to form a given protein. Sequencing errors occasionally occur, sometimes with significant consequences. Next Topic: Roles of Proteins Whenever the body is growing, repairing, or replacing tissue, proteins are involved. Sometimes their role is to facilitate or to regulate; other times it is to become part of a structure. Versatility is a key feature of proteins. Proteins have three key functions in the body:  Although proteins can be broken down to provide energy, this is not their primary function. One gram of protein provides 4 kcal of energy. In a balanced diet, carbohydrates and fats should be the primary energy sources, allowing proteins to be used for growth and repair  Proteins regulate various body processes, including maintaining osmotic pressure, balancing acid-base levels, and transporting essential nutrients. For instance, proteins in the blood help maintain fluid balance, while enzymes and hormones control metabolic reactions. From the moment of conception, proteins form the building blocks of muscles, blood, and skin—in fact, of most body structures. For example, to build a bone or a tooth, cells first lay down a matrix of the protein collagen and then fill it with crystals of calcium, phosphorus, magnesium, fluoride, and other minerals. Collagen also provides the material of ligaments and tendons and the strengthening “glue” between the cells of the artery walls that enables the arteries to with- stand the pressure of the blood surging through them with each heartbeat. Also made of collagen are scars that knit the separated parts of torn tissues together. Proteins are also needed for replacing dead or damaged cells. The life span of a skin cell is only about 30 days. As old skin cells are shed, new cells made largely of protein grow from underneath to replace them. Cells in the deeper skin layers synthesize new proteins to form hair and fingernails. Muscle cells make new proteins to grow larger and stronger in response to exercise. Cells of the GI tract are replaced every few days. Both inside and outside, then, the body continuously deposits protein into the new cells that replace those that have been lost. enzymes: proteins that facilitate chemical reactions without being changed in the process; protein catalysts. Some proteins act as enzymes. Enzymes not only break down substances, but they also build substances (such as bone) and transform substance into another (amino acids into glucose, for example). Enzymes synthesize large compounds from smaller ones. One enzyme can perform billions of synthetic reactions Enzymes can hydrolyze larger compounds into smaller ones (like digestive enzymes) Enzymes themselves are not altered by the reactions they facilitate; they are atalysts Breaking down reactions are catabolic, whereas building up reactions are anabolic. The body’s many hormones are messenger molecules, and some hormones are proteins. Various endocrine glands in the body release hormones in response to changes that challenge the body. The blood carries the hormones from these glands to their target tissues, where they elicit the appropriate responses to restore and maintain normal conditions. The hormone insulin provides a familiar example. After a meal, when blood glucose rises, the pancreas releases its insulin. Insulin stimulates the transport proteins of the muscles and adipose tissue to pump glucose into the cells faster than it can leak out. After acting on the message, the cells destroy the insulin. As blood glucose falls, the pancreas slows its release of insulin. Many other proteins act as hormones, regulating a variety of actions in the body Fluid Balance - maintenance of the proper types and amounts of fluid in each compartment of the body fluids Edema - he swelling of body tissue caused by excessive amounts of fluid in the interstitial spaces; seen in protein deficiency (among other conditions). Proteins help to maintain the body’s fluid balance. Normally, proteins are found primarily within the cells and in the plasma (essentially blood without its red blood cells). Being large, proteins do not normally cross the walls of the blood vessels. During times of critical illness or protein malnutrition, however, plasma proteins leak out of the blood vessels into the tissues (between the cells). Because proteins attract water, fluid accumulates and causes swelling. Swelling due to an excess of fluid in the tissues is known as edema. The protein-related causes of edema include: Excessive protein losses caused by inflammation and critical illnesses Inadequate protein synthesis caused by liver disease Inadequate dietary intake of protein Whatever the cause of edema, the result is the same: a diminished capacity to deliver nutrients and oxygen to the cells and to remove wastes from them. As a consequence, cells fail to function adequately. acids: compounds that release hydrogen ions in a solution. bases: compounds that accept hydrogen ions in a solution. acidosis - higher-than-normal acidity in the blood and body fluids. alkalosis - higher-than-normal alkalinity (base) in the blood and body fluids. Compounds that keep a solution’s pH constant when acids or bases are added are called buffers. Proteins also help to maintain the balance between acids and bases within the body fluids. Normal body processes continually produce acids and bases, which the blood carries to the kidneys and lungs for excretion. The challenge is to do this without upsetting the blood’s acid-base balance. In an acid solution, hydrogen ions (H+) abound; the more hydrogen ions, the more concentrated the acid. Proteins, which have negative charges on their surfaces, attract hydrogen ions, which have positive charges. By accepting and releasing hydrogen ions, proteins maintain the acid-base balance of the blood and body fluids. The blood’s acid-base balance is tightly controlled. The extremes of acidosis and alkalosis lead to coma and death, largely because they denature working proteins. Disturbing a protein’s shape renders it useless. To give just one example, denatured hemoglobin loses its capacity to carry oxygen. Some proteins move about in the body fluids, carrying nutrients and other molecules. The protein hemoglobin carries oxygen from the lungs to the cells. The lipoproteins transport lipids around the body. Special transport proteins carry vitamins and minerals. The transport of the mineral iron provides an especially good illustration of these proteins’ specificity and precision. When iron is absorbed, it is captured in an intestinal cell by a protein. Before leaving the intestinal cell, iron is attached to another protein that carries it through the blood- stream to the cells. Once iron enters a cell, it is attached to a storage protein that will hold the iron until it is needed. When it is needed, iron is incorporated into proteins in the red blood cells and muscles that assist in oxygen transport and use. Some transport proteins reside in cell membranes and act as “pumps,” picking up compounds on one side of the membrane and releasing them on the other as needed. Each transport protein is specific for a certain compound or group of related compounds.. The balance of these two minerals is critical to nerve transmissions and muscle contractions; imbalances can cause irregular heart- beats, muscular weakness, kidney failure, and even death.  antigens: substances that elicit the formation of antibodies or an inflammation reaction from the immune system. A bacterium, a virus, a toxin, and a protein in food that causes allergy are all examples of antigens. antibodies: large proteins of the blood and body fluids, produced by the immune system in response to the invasion of the body by foreign molecules (usually proteins called antigens). Antibodies combine with and inactivate the foreign invaders, thus protecting the body. immunity: the body’s ability to defend itself against diseases Proteins also defend the body against disease. A virus—whether it is one that causes flu, smallpox, measles, or the common cold—enters the cells and multiplies there. One virus may produce 100 replicas of itself within an hour or so. Each replica can then burst out and invade 100 different cells, soon yielding 10,000 viruses, which invade 10,000 cells. Left free to do their worst, they will soon overwhelm the body with disease. Fortunately, when the body detects these invading antigens, it manufactures antibodies, giant protein molecules designed specifically to combat them. The antibodies work so swiftly and efficiently that in a normal, healthy individual, most diseases never have a chance to get started. Without sufficient protein, though, the body cannot maintain its army of antibodies to resist infectious diseases. Each antibody is designed to destroy a specific antigen. Once the body has manufactured antibodies against a particular antigen (such as the measles virus), it “remembers” how to make them. Consequently, the next time the body encounters that same antigen, it produces antibodies even more quickly. In other words, the body develops a molecular memory, known as immunity Without energy, cells die; without glucose, the brain and nervous system falter. Even though proteins are needed to do the work that only they can perform, they will be sacrificed to provide energy and glucose during times of starvation or insufficient carbohydrate intake. The body will break down its tissue proteins to make amino acids available for energy or glucose production. In this way, protein can maintain blood glucose levels, but at the expense of losing lean body tissue. Protein provides 4 kcal/g. The making of glucose from noncarbohydrate sources such as amino acids is gluconeogenesis. As mentioned earlier, proteins form integral parts of most body structures such as skin, muscles, and bones. They also participate in some of the body’s most amazing activities such as blood clotting and vision. When a tissue is injured, a rapid chain of events leads to the production of fibrin, a stringy, in- soluble mass of protein fibers that forms a solid clot from liquid blood. Later, more slowly, the protein collagen forms a scar to replace the clot and permanently heal the wound. The light-sensitive pigments in the cells of the eye’s retina are molecules of the protein opsin. Opsin responds to light by changing its shape, thus initiating the nerve impulses that convey the sense of sight to the brain.  Marasmus left Kwashiorkor right Protein-Energy Malnutrition (PEM) is a critical health concern that primarily affects children in developing countries. It occurs when there is insufficient intake of protein and calories, leading to severe deficiencies that impair growth, immune function, and overall health. The two most well-known forms of PEM are Marasmus and Kwashiorkor, each with distinct characteristics and causes  Marasmus is the result of extreme calorie and protein deficiency, often referred to as "wasting syndrome." This condition is primarily caused by long-term starvation, where the body lacks both protein and energy (calories) needed to maintain basic physiological functions. It is prevalent in regions facing famine, chronic food shortages, or poverty, where access to adequate nutrition is severely limited  Clinical Features of Marasmus: Severe Weight Loss: Children suffering from marasmus exhibit extreme weight loss, with their body fat and muscle mass severely depleted. The skin appears thin and wrinkled, hanging loosely due to the loss of subcutaneous fat. This is sometimes referred to as the "old man" or "wizened" appearance. Stunted Growth: The lack of essential nutrients leads to stunted growth, where the child’s height remains far below the expected level for their age.  Muscle Wasting: Muscle tissues are broken down as the body turns to protein stores for energy, leading to significant muscle atrophy. Impaired Immune Function: The immune system is severely weakened, leaving children vulnerable to infections, diseases, and prolonged recovery times. Common infections include respiratory and gastrointestinal infections, which can be fatal if untreated. Emaciation: The overall appearance of a child with marasmus is one of extreme emaciation, with ribs, bones, and joints prominently visible through the skin. Fat stores are completely depleted, and muscle mass is significantly reduced. Absence of Edema: Unlike kwashiorkor, children with marasmus do not exhibit edema (swelling) because fluid balance is maintained, despite severe nutritional deficiencies.  Causes of Marasmus: Marasmus typically develops as a result of chronic malnutrition over an extended period. Contributing factors include: Food Scarcity: Prolonged food shortages or unavailability of nutritious food, especially in famine-prone areas. Inadequate Weaning: Poor or delayed weaning from breast milk to solid foods in infants, particularly in impoverished settings where suitable weaning foods are scarce. Infections: Frequent infections such as diarrhea and respiratory illnesses drain the body of nutrients, exacerbating the effects of poor diet.  Treatment of Marasmus: The primary goal in treating marasmus is to gradually reintroduce calories and protein into the diet to rebuild lost body mass. Treatment involves: 1. Rehydration: Since many children with marasmus suffer from dehydration due to diarrhea, oral rehydration therapy (ORT) is essential to restore fluid and electrolyte balance. 2. Nutritional Rehabilitation: A carefully planned diet that gradually increases caloric intake with nutrient-dense foods is introduced to promote  weight gain and recovery. Protein-rich foods, carbohydrates, fats, and essential vitamins and minerals must be included. 3. Monitoring and Care: Continuous monitoring of growth and development, as well as the treatment of any underlying infections or complications, is critical to recovery. Without intervention, marasmus can lead to fatal outcomes due to the body’s inability to sustain basic life functions.  Kwashiorkor is another form of severe malnutrition, primarily caused by a deficiency in dietary protein while calorie intake may remain relatively adequate. This condition often affects children who are weaned from breast milk too early and fed diets high in carbohydrates (such as maize or rice) but low in protein. The word "kwashiorkor" originates from Ghana and refers to "the sickness the baby gets when the new baby comes," highlighting its prevalence in children who are displaced from breastfeeding by a younger sibling.  Clinical Features of Kwashiorkor: Edema (Swelling): One of the hallmark signs of kwashiorkor is edema, which is the accumulation of fluid in body tissues, particularly in the feet, legs, and face. This swelling masks the underlying muscle and fat wasting, making children appear puffy or bloated despite being severely malnourished. Thin, Brittle Hair: Hair becomes thin, brittle, and may lose its natural color, taking on a reddish or blonde hue. In some cases, patches of hair may fall out.  Flaky Dermatitis: The skin becomes dry, flaky, and cracked, leading to sores and lesions. The skin changes are often described as "flaky paint" dermatosis. Enlarged Liver: Children with kwashiorkor frequently develop fatty liver, which leads to an enlarged liver. This is due to the inability of the liver to process fat efficiently in the absence of sufficient protein. Apathetic Behavior: Affected children may exhibit apathy, lethargy, and irritability. Cognitive function is often impaired, and developmental delays are common. Impaired Growth and Muscle Wasting: Like marasmus, children with kwashiorkor suffer from muscle wasting, but it is less visible due to the presence of edema. Growth is also stunted, with significant delays in both physical and cognitive development.  Causes of Kwashiorkor: Kwashiorkor results from a severe deficiency of dietary protein while overall calorie intake may remain sufficient. Factors contributing to its development include: Inadequate Protein Intake: Diets high in carbohydrates but low in protein, such as cassava, rice, or maize, are a primary cause. Children weaned onto these diets without adequate protein sources are especially vulnerable. Infections: Like marasmus, recurrent infections increase protein needs, and the immune  system's ability to function properly is compromised without adequate protein intake. Poor Weaning Practices: In some cultures, infants are weaned from breast milk prematurely, particularly when a new baby is born, and are fed starchy gruels or porridges lacking in protein.  Treatment of Kwashiorkor: Effective treatment for kwashiorkor requires addressing both the immediate symptoms and the underlying causes of protein deficiency: 1. Nutritional Intervention: The child’s diet must be carefully managed to increase protein intake. Protein-rich foods such as eggs, milk, fish, meat, and legumes are introduced gradually. Special therapeutic foods like ready- to-use therapeutic food (RUTF) are commonly used in emergency situations. 2. Treating Infections: Since infections are  common in children with kwashiorkor, antibiotics and other medications may be necessary to treat concurrent illnesses. 3. Rehydration: As with marasmus, rehydration is crucial, particularly in cases where diarrhea or vomiting is present. However, care must be taken when rehydrating children with kwashiorkor to prevent worsening edema.  Differences Between Marasmus and Kwashiorkor Though both conditions are forms of PEM, they have distinct differences: Energy and Protein Deficiency: Marasmus is caused by a deficiency in both protein and calories, while kwashiorkor is primarily a result of protein deficiency with sufficient caloric intake from carbohydrates. Physical Appearance: Marasmus leads to extreme wasting and a "skeletal" appearance, while kwashiorkor is marked by edema and a bloated appearance, masking muscle wasting.  Hair and Skin Changes: Kwashiorkor is associated with changes in hair texture and color, as well as flaky skin lesions, which are not typically seen in marasmus. Outcomes and Long-Term Effects Both marasmus and kwashiorkor, if left untreated, can result in severe developmental delays, compromised immune function, and death. Children who survive may suffer long-term physical and cognitive impairments, depending on the duration and severity of malnutrition. Early intervention is critical to preventing permanent damage.  While excess protein is not stored in the body, it is broken down into amino acids, which are then deaminated. The nitrogen is converted to urea and excreted by the kidneys. Although high protein intake is generally not harmful to healthy individuals, it may place a strain on the kidneys, particularly in those with pre-existing kidney conditions. Once ingested, proteins are broken down into amino acids, which enter the bloodstream and are used to build new proteins or converted into energy.  Positive Nitrogen Balance: Occurs when nitrogen intake exceeds output, indicating that the body is building more tissue (e.g., in growing children or pregnant women). Negative Nitrogen Balance: Occurs when nitrogen output exceeds intake, typically during illness, injury, or malnutrition.  Complete proteins, which contain all essential amino acids, are primarily found in animal products like meat, fish, eggs, and dairy. Plant- based proteins, such as those in legumes, grains, and vegetables, are often incomplete but can be combined to create complete proteins.  Complementary proteins are two or more dietary proteins whose amino acid patterns complement each other in such a way that the essential amino acids missing in one are supplied by the other. In general, plant proteins are of lower quality than animal proteins. The strategy of combining plant protein foods with different but complementary amino acid patterns yields a protein that contains all the essential aino acids in quantities sufficient to support health. Adding small amounts of meat or fish to a promarily cereal diet will supplement an otherwise inadequate amino acid pattern. Combining cereals and legumes, which are low in lysine and methionine, respectively, will result in an adequate mixture for protein synthesis. Adding milk to a cereal-based meal will increase efficiency of the cereal protein.