Protein - Nls

7/30/2019 Protein - Nls

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Selubung protein (kapsid) adalah selubung

yang membungkus asam nukleat (DNA atau

RNA) sehingga disebut juga nukleokapsid


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Body cells are constantly wearing out. As a

result, they are continuously in need of

replacement. Of the six nutrient groups, only

proteins can make new cells and rebuild

tissue.


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Proteins are

appropriately named.

Protein (origin from the

Greek word protos

meaning "most

important")


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What is Protein?


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Composition

Proteins contain carbon. hydrogen, and oxygen,but in different proportions. In addition, andmost important, they are the only nutrient groupthat contains nitrogen, and some contain sulfur.

Proteins are composed of chemical compoundscalled amino acids. Amino acids are sometimescalled the building block of protein because they

are combined to form the thousand of proteins inthe human body. Heredity determines thespesific types of proteins within each person.


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Classification

The quality and classification of a protein depend on thenumber and types of amino acids it contains. There are 20amino acids, but only 9 are considered essential to humans.(table)

Amino Acids

Essential Nonessential

Histidine Phenylalanine Alanine Glutamine

Isoleucine Treonine Arginine Glycine

Leucine Tryptophan Asparagine HydroxyprolineLysine Valine Aspartic acid Proline

Methionine Cysteine Serine

Glutamic acid Tyrosine


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Essential amino acids are necessary for normal

growth and development and must be

provided in the diet. Proteins containing all

the essential amino acids are of high biologic

value and are called complete proteins (high

quality). The nonessential amino acids can be

produced in the body if an adequate supply ofamino nitrogen is provided in the diet.


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Incomplete proteins (low quality) are those thatlack one or more of the essential amino acids.Consequently, incomplete proteins cannot buildtissue without the help of other proteins. Thevalue of each is increased when it is eaten in

combination with another incomplete protein,not necessarily at the same meal, but during thesame day. In this way, one incomplete proteinfood can provide the essential amino acids the

other lacks. The combination may therebyprovide all nine essential amino acids. (figure)


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Examples of Complementary Protein

Foods

Corn and Beans

Rice and Beans

Bread and Peanut butter

Bread and Split pea soupBread and Cheese

Bread and Baked beans

Macaroni and Cheese

Cereal and Milk

When this occurs, the proteins are called complementary proteins (table).

Gelatin is the only protein from an animal source that is an incomplete protein.


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Food sources


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Rich Sources of Proteins

Rich Sources of Proteins

COMPLETE PROTEIN INCOMPLETE PROTEIN

Meats Eggs Corn Grains

Fish Milk Peanuts Nuts

Poultry Cheese Peas Sunflower seeds

Navy beans Sesame seeds

Soybeans


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Function


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(The primary function of proteins is to build and repairbody tissue. This is made possible by the provision of the

correct type and number of amino acids in the diet. Also, as

cells are broken down during metabolism (catabolism),

some amino acids released into the blood are recycled to

build new and repair other tissue (anabolism). The body

uses the recycled amino acids as efficiently as those

obtained from the diet)

- Building and Repairing Body Tissue


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Proteins are important components of hormones and

enzymes that are essential for the regulation of metabolismand digestion. Proteins help maintain fluid and electrolyte

balances in the body and thus prevent edema (abnormal

retention of body fluids). Proteins also are essential for the

development of antibodies and, consequently, for a healthy

immune system.

- Regulating Body Functions

Proteins can provide energy if and when the supply ofcarbohydrates and fats in the diet is insufficient. Each gram

of protein provides 4 kcal. This is not a good use of

proteins, however. In general, they are more expensive

than carbohydrate, and most of the complete proteins also

contain saturated fats and cholesterol.

- Providing Energy


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Digestion and Absorption


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Metabolism and Elimination

All essential amino acids must be present to buildand repair the cells as needed. When amino acidsare broken down, the nitrogen-containing amine

group is stripped off. This process is calleddeamination. Deamination produces ammonia,converts it to urea, and returns it to the bloodstream for the kidneys to filter out and excrete.

The remaining parts are used for energy or areconverted to carbohydrate or fat and stored asglycogen or adipose tissue.


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Dietary Requirements


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Protein excess

it is easy for people living in the developed parts of the world to ingestmore protein than the body requires.

There are number of reason why this should be avoided. The saturatedfats and cholesterol common to complete protein foods may contribute toheart disease an provide more kcal than are desirable. Some studies seemto indicated a connection between long-term high-protein diets and colon

cancer and high calsium excretion, which depletes the bones of calciumand may contribute to osteoporosis.

People who eat excessive amounts of rotein-rich foods may ignore thealso essential fruits and vegetables, and excess protein intake may putmore demands on the liver, which converts N (nitrogen) to urea and thekidneys, to excrete excess urea than they are prepared to handle.

Therefore, the National Research Council recommends that protein intakerepresent no more than 15% to 20% og one's daily kcal intake and notexceed double the amount given in the table of Recommended DietaryAllowances.


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Protein and Amino Acid Supplements

Protein and amino acids supplements are taken for anumber of reason such as "bulking up " by athletes,growing fingernails, and to spare body protein in weightloss. It is weight lifting, not protein bars or proteinsupplements, that builds muscles. Fingernails have neverbeen affected by extra protein, and dieters need a balanceddiet using the guidelines of the Food Guide Pyramid.

High quality proteins foods are more bioavailable thanexpensive supplements. Single amino acids can be harmfulto the body and never occur naturally in food. The bodywas designed to handle food, not supplements. If a singleamino acids has been recomended, it is very important thata physician be consulted before the amino acid is used.


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Nitrogen Balance

Protein requirements may be discussed in terms ofnitrogen balance. This occurs when nitrogen intakeequals the amount of nitrogen excreted.

Positive nitrogen balance exists when nitrogen intake

exceeds the amount excreted. This indicates that newtissue is being formed, and it occurs during pregnancy,during hildren's growing years, when athletes developadditional muscles tissue, and when tissues are rebuiltafter physical trauma such as illness or injury.

Negative nitrogen balance indicates that protein isbeing lost. It may be caused by fevers, injury, surgery,burns, starvation, or immobilization.


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Protein Deficiency

When people are unable to obtain an adequate supply of proteinfor an extended period, muscle wasting will occur, and arms andlegs become very thin.

At the same time, albumin (protein in blood plasma) deficiency willcause edema, resulting in an extremely swollen appearance.

The water is excreted when sufficient protein is eaten. People maylost appetite, strength, and weight, and wounds may heal veryslowly.

Patients suffering from edema become lethargic and depressed.These signs are seen in grossly neglected children or in the elderly,poor, or incapacitated. It is essential that people following

vegetarians diets, especially vegans, carefully calculate the typesand amount of protein in their diets so as to avoid proteindeficiency.


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Protein Energy Malnutrition (PEM)

People suffering from protein energy malnutrition (PEM) lackboth protein and energy-rich foods. Such a condition is not

uncommon in developing countries where there are long-

term shortages of both protein and enerfy foods. Children

who lack sufficient protein do not grow to their potential size.

Infants born to mother eating insufficient protein during

pregnancy can have permanently impaired mental capacities.


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Maramus, a condition resultingfrom severe malnutrition, afflictsvery young children who lackboth energy and proteins foods

as well as vitamins and minerals.The infant with maramusappears emacited, but does nothave edema. Hair is dull and dry,

and the skin is thin and wrinkled.The other protein deficiencydisease that affects children aswell as adults is kwashiorkor.

Two deficiency disease that affect children are caused by a grossly inadequate supply of protein

or energy, or both.


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Kwashiorkor appears when there is a suddenor recent lack of protein-containing food (suchas during a famine). This disease causes fat to

accumulate in the liver, and the lack of proteinand hormones results in edema, painful skinlesions, and changes in the pigmentation ofskin and hair. The mortality rate forkwashiorkor patients is high.

Those who survive these deficiency diseasemay suffer from permanent mentalretardation. The ultimate cost of fooddeprivation among young children is high,indeed.

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Protein - Nls