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I know that human proteins are synthesized using only 20 different amino acids. However, how can there be thousands of different proteins in human cells, if we only use 20 amino acids to make them?
There are only 26 letters in the English language, and more than 80% of words are under 10 letters. Yet there are over a million English words. Nonsense words don't count.
Now imagine the possibilities of a 20 letter alphabet, where the average "word" length is about 375 letters, and where words of up to 800 letters are possible. And that also does not include "nonsense words".
That should give you an idea of the possibilities, and why "thousands of different proteins in human cells" can exist.
How big is the “average” protein?
Principles of Nutrition and Balanced Diet
Food may be defined as any solid or liquid substance which when taken by the body provides it with necessary materials to enable it to grow, replace the worn-out and damaged parts and provide energy to function normally. The daily food intake has a direct influence on the health and well-being of an individual. Food is composed of different chemical elements.
Nutrients are molecules which the body uses to function appropriately and stay in a healthy condition.
It is the study of nutrients and their relationship with food and living beings.
The food that a person normally takes everyday.
Malnutrition means an incorrect or imbalanced intake of nutrients.
Means insufficient total intake of nutrients.
Basic dietary components:
There are five classes of basic components or nutrients:
(5) Minerals and trace elements.
The components under 1 to 3 are known as macronutrients, those under 4 and 5 are known as micronutrients.
Carbohydrates are not at all required in the diet. Yet, we consume large amounts of carbohydrates every day because they are the cheapest source of energy and easily available dietary sources. Carbohydrates are the main sources of energy to the body which provide about 70% of the daily calorie requirements. Carbohydrates, in addition to the supply of energy also serve as the components of cell mem­brane and receptors. Carbohydrates are very well synthesized in our body from non-carbohydrate sources.
Cellulose and stretch reflex:
Cellulose (polysaccharide) materials present in the diet form the bulk (fiber) of the food and cannot be digested by human beings because of the absence of the enzyme cellulase. The cellulose helps in the movement of the food through the G.I tract. The cellulose material of the diet absorbs the waste from large intestine and while doing so it stretches the wall of the large intestine and as a result, defecation takes place. This is called stretch reflex.
There is a metabolic disorder called diabetes mellitus wherein there is an increased level of glucose in the blood (hyperglycemia). Hyperglycemia affects the normal functioning of the kidney and brain leading to hypertension and other abnormalities. Hence, in diabetes mellitus patients, the blood glucose level should be kept under control, for which the carbohydrates should be restricted in the diet.
The energy requirements can be met with proteins and to a little extent by fats. But as human beings first and the foremost food i.e. milk tastes sweet due to the presence of a carbohydrate lactose, he has a craving for sweet and hence he should be supplied with some non-carbohydrate sweeteners.
Some of the non-carbohydrate sweeteners are saccharin, sodium cyclamate, monallin and aspartame. These sweeteners are also used in the milk powder supplied to children with lactose intolerance, wherein the milk is free from lactose but contains one of these sweeteners.
It is 400 times sweeter than table sugar. Saccharin is commercially used in large scales though it is banned scientifically at present. It is used as sweetener in diabetes and obesity. But it is harmful to human beings. When saccharin is given in large quantities in drinks and food it causes cancer. However as the risk is too low it is still used as an artificial non-calorie sweetener in the diet drinks specially of those who are diabetes.
It is 30 times sweeter than table sugar. It is a carcinogenic agent and has been banned from prepared foods.
It is 180 times sweeter than table sugar. It is a methyl ester of a dipeptide of two amino acids that normally occur in protein (i.e., aspartate and phenylalanine). As it is non-toxic, it is used as a sugar substitute in many foods. The sugar free tablets available in the market are all made up of aspartame.
It is a protein with a molecular weight of 11,000. It is 2100 times sweeter than table sugar. Its sweetness is due to the three dimensional conformation of the polypeptide. But this cannot be used in prepared foods because it looses its sweetness on heating or denaturation.
Fats are also not needed in our diet. But we consume it because of its high calorific values (1 g gives 9 Kcal) and also it can be easily stored with less amount of water and therefore occupy less space. These fats are also taken because of their essential fatty acid content. Essential fatty acids are those which cannot be synthesized in our body, hence they should be supplied through the diet.
They are ‘linoleic acid’ and ‘linolenic acids’. Arachidonic acid is also an essential fatty acid but it can be synthesized from linolenic acid. They are also a good source of fat soluble vitamins viz., A, D, E & K. Plant fats are superior to animal fats because they contain more of polyunsaturated fatty acids i.e. essential fatty acids and less of cholesterol. The cholesterol in the diet should be restricted because excess intake of cholesterol leads to its deposition in the tissues thereby causing atherosclerosis.
Proteins are needed for their content of certain amino acids that are essential to human body for the biosynthesis of proteins, body repair in adult and for body building and body repair in children. Human body proteins are made up of only 20 standard amino acids out of which nearly 10 amino acids can be synthesized in the body but the remaining 10 cannot be synthesized in the body hence they have to be supplied through the diet. Therefore they are known as essential amino acids.
The essential amino acids are:
M — Methionine (semi essential)
A — Arginine (semi essential)
The nutritional value of a protein depends on two factors:
(1) Its content of the essential amino acids
The amino acid content of all the proteins is not the same. One will be deficient in one amino acid and the other in another type of amino acid. Some proteins are not completely digested to liberate all the amino acid contents, ex. the protein rich portions of wheat grains are not completely digestible.
It is a condition in which the intake of protein nitrogen (AA) exactly balances the loss of nitrogen in the urine and faeces. If the intake is more than the output due to nitrogen retention as tissue protein then the subject is said to be in positive nitrogen balance. If the intake is less than the output (as in old age and illness) then the subject is said to be in negative nitrogen balance.
Biological value of protein:
The biological value of a protein is a factor that is inversely proportional to the amount of a given protein source that must be consumed to keep an adult human in nitrogen balance. If the protein taken in the diet has all the essential amino acids in good proportions, is completely digested and is completely absorbed then that protein is said to be a good protein or it is said to have 100% biological value.
A protein of cent percent biological value should also completely replace the nitrogen lost in the urine. Generally animal proteins have higher biological value than plant proteins, because the animal pro­teins are much alike the human proteins and hence they have more digestibility and absorbability, for example egg and milk portions have their biological values near 100% (94% & 96% respectively).
Most of the plant proteins have low biological values and are said to be poor proteins. If two vegetable proteins are taken in combination, called succotash, then this mixture of proteins will have good biolog­ical value (though not 100%). Ex. the corn proteins are low in lysine but contain adequate amounts of tryptophan whereas bean proteins contain adequate amounts of lysine but are low in tryptophan.
Neither is a good protein. But a mixture of the two is a good source of having balanced amino acids. If beans are taken in the breakfast and corn in the lunch (i.e. after 5-6 hours) then it will be of no biological value because amino acids cannot be stored. Therefore the biological value of vegetable proteins can be im­proved if taken along with animal proteins for the daily protein supply. It is recommended that 1/3 rd to 1/2 of the proteins may be derived from animal proteins like egg, meat and milk.
Protein sparing action of carbohydrates and fats:
Carbohydrates and fats spare the proteins and make then available for anabolic or constructive purpose. Carbohydrates and fats supply the required energy and so proteins will not take part in energy metabolism, especially in patients needing tissue repair, this action is seen.
A balanced diet can be defined as the nutrients required for sustaining and keeping the human body in metabolic health. It can also be defined as nourishment (food) required for maintaining normal life. Balanced diet is one which contains all the food constitutes in proper proportion to meet the energy and nutritional requirements of the individual. The components of a well-balanced diet will vary depend­ing on age, sex, physiological needs such as pregnancy and lactation and nature of physical activity.
While designing the quality and quantity of a balanced diet the total calories are distributed among 3 classes of food in the following proportion:
Proximate principles of diet:
The proximate principles of diet are:
i. Carbohydrates: the energy yielding substances.
ii. Fats: yield energy and act as insulating materials.
iii. Proteins: act as building materials and bear the wear and tear of the body.
Construction of a diet-the spectrum of food:
The food is divided into four basic food groups:
Two glasses of milk or servings of cheese, cottage cheese, ice creams, or other dairy products.
Two servings of meat, fish, poultry or eggs, peas, beans or nuts.
3. Vegetable and fruit groups:
Four servings of green or yellow vegetables, tomatoes, citrus fruits.
4. Bread and cereal group:
Four servings of whole grains or fortified cereal products. There is no single perfect food that provides all nutritional needs for everyone. The 40 different required nutrients occur in very different proportions in different foods. Therefore a variety, within each group is essential.
1. Milk, egg and meat:
They provide the essential amino acids and have high nutritional values ranging from 98-100%. Butter supplies the fat soluble vitamins A, D and E.
Cereals supply vitamin B, and roughage (fibrous or cellulose material).
3. Essential fatty acids:
Prevents atherogenic disorders. Vegetables contain phytosterol which helps in reducing serum total cholesterol.
Citrus fruits like orange prevent diseases like scurvy, constipation etc. Fruits supply potas­sium required by the body to prevent diabetic coma.
Green leafy vegetables will help in the synthesis of Hb and provide some vitamins like vitamin A, folic acid, etc. Vegetables including green leafy vegetables prevent constipation by acting as roughage (cellulose materials).
Recommended dietary allowances (RDA):
The food and nutritional board of National Academy of Sciences, National Research Council has developed a table of recommended daily dietary allowances (RDA) of various nutrients for optimum nutrition of infants, children, adults, pregnant & lactating women and various conditions of health and diseases to provide an ample safety margin of life.
Formulation of a diet:
A correct diet must provide for maintenance of the body as well as energy requirements, for growth and reproduction. The essential elements lost by the body by excretion must be replaced.
The important factors are:
The average caloric requirement of an adult male and female should be met by the food provided daily.
2. Quality and quantity of the constituents of food:
(a) Primary foods (proteins, fats and carbohydrates):
Proteins, fats and carbohydrates are con­sumed in the ratio of 1: 1: 4. 3000 calories are provided by 100 grams of protein, 100 grams of fat and 400 grams of carbohydrates. It is advisable that 10-15% of the total calories should be obtained from protein, 20-30% from fat and 50-70% from carbohydrate.
(b) Secondary foods (vitamins and minerals):
These are essential in the diet but in very minute quantities to enable utilization of primary foods.
Although water is not a food, it is ordinarily consumed in the diet and serves a prime role in the health of the body. Hence it is one of the components of food.
3. Variation in the diet:
There is a risk of missing some essential elements or vitamins in a varied diet. Eskimos live mainly on fish and meat and poor Orientals chiefly live on rice with small amounts of fish and meat.
4. Digestibility of the food:
The food is of no use if it is not digested in the alimentary canal. Digestibility is more concerned with absorbability. When fats and starch are largely used, vege­tables and animal proteins are not absorbed. Absorption is enhanced with a mixed diet than when the substance is taken alone.
Food consistency is considerably changed on cooking. Harmful organisms are destroyed. Cooking breaks down the connective tissue fibres of meat and makes meat easier to masticate and helps in digestion. Overcooking shrinks the coagulated protein and decreases the digestibility.
Cooking increases the water content and digestibility of vegetables. Cellulose frame work is loosened and starch from starch grains is liberated. Fats are not changed much upon cooking. Cooking enhances the flavour of the food. However, vitamins B and C are destroyed when vegetables are cooked.
6. Psychological factors:
Appetite is reduced by worry and anxiety. Digestion is also upset due to imperfect mastication and secretion of digestive juices. Consumption of food is increased while taken in pleasant surroundings and good company with different items.
Dietary food is much influenced by family income. When the income is good, consumption is high with all the protective foods. A poor income has poor protective foods. Lowest income group having low protective foods suffer form rickets and nutritional anemia. They are less resistant to infectious diseases.
How Cells Work
A protein is any chain of amino acids. An amino acid is a small molecule that acts as the building block of any protein. If you ignore the fat, your body is about 20-percent protein by weight. It is about 60-percent water. Most of the rest of your body is composed of minerals (for example, calcium in your bones).
Amino acids are called "amino acids" because they contain an amino group (NH2) and a carboxyl group (COOH) that is acidic. In the figure above, you can see the chemical structure of two of the amino acids. You can see that the top part of each one is the same. That is true of all amino acids -- the little chain at the bottom (the H or the CH3 in these two amino acids) is the only thing varying from one amino acid to the next. In some amino acids, the variable part can be quite large. The human body is constructed of 20 different amino acids (there are perhaps 100 different amino acids available in nature).
As far as your body is concerned there are two different types of amino acids: essential and non-essential. Non-essential amino acids are amino acids that your body can create out of other chemicals found in your body. Essential amino acids cannot be created, and therefore the only way to get them is through food. Here are the different amino acids:
- Alanine (synthesized from pyruvic acid)
- Arginine (synthesized from glutamic acid)
- Asparagine (synthesized from aspartic acid)
- Aspartic acid (synthesized from oxaloacetic acid)
- Cysteine (synthesized from homocysteine, which comes from methionine)
- Glutamic acid (synthesized from oxoglutaric acid)
- Glutamine (synthesized from glutamic acid)
- Glycine (synthesized from serine and threonine)
- Proline (synthesized from glutamic acid)
- Serine (synthesized from glucose)
- Tryosine (synthesized from phenylalanine)
Protein in our diets comes from both animal and vegetable sources. Most animal sources (meat, milk, eggs) provide what's called "complete protein", meaning that they contain all of the essential amino acids. Vegetable sources usually are low on or missing certain essential amino acids. For example, rice is low in isoleucine and lysine. However, different vegetable sources are deficient in different amino acids, and so by combining different foods you can get all of the essential amino acids throughout the course of the day. Some vegetable sources contain quite a bit of protein. Nuts, beans and soybeans are all high in protein. By combining them, you can get complete coverage of all essential amino acids.
The digestive system breaks all proteins down into their amino acids so that they can enter the bloodstream. Cells then use the amino acids as building blocks to build enzymes and structural proteins.
How much protein does a person need?
Protein is an important part of every diet. The amount of protein an individual needs depends on their age and sex.
Protein is a part of every cell in the body. It helps the body to build and repair cells and tissues. Protein is a major component of the skin, muscle, bone, organs, hair, and nails.
According to the Food and Drug Administration (FDA), most people in the United States get enough protein from their diets to meet their needs.
This article looks at protein, its function, sources, and how much protein different groups of people need each day.
Protein is one of three macronutrients, which are nutrients the body needs in larger amounts. The other macronutrients are fat and carbohydrates.
Protein is made up of long chains of amino acids. There are 20 amino acids. The specific order of amino acids determines the structure and function of each protein.
The 20 amino acids that the body uses to create protein are:
- aspartic acid
- glutamic acid
There are nine essential amino acids that the human body does not synthesize, so they must come from the diet.
Proteins may be either complete or incomplete. Complete proteins are proteins that contain all essential amino acids. Animal products, soy, and quinoa are complete proteins.
Incomplete proteins are proteins that do not contain all essential amino acids. Most plant foods are incomplete proteins, including beans, nuts, and grains.
People can combine incomplete protein sources to create a meal that provides all essential amino acids. Examples include rice and beans, or peanut butter on whole wheat bread.
What does protein do in the body?
Protein is present in every body cell, and an adequate protein intake is important for keeping the muscles, bones, and tissues healthy.
Protein plays a role in many bodily processes, including:
- blood clotting
- fluid balance
- immune system responses
Protein is important for growth and development, especially during
childhood, adolescence, and pregnancy.
According to the Dietary Guidelines for Americans 2015–2020 , a healthful eating pattern includes a variety of foods containing protein. Both animal and plant foods can be excellent sources of protein.
The guidelines classify the following foods as protein foods:
- lean meats and poultry
- legumes, which include beans and peas
- soy products
Dairy products, such as milk, cheese, and yogurt, also contain protein. Whole grains and vegetables contain some protein, but generally less than other sources.
Animal products tend to contain higher amounts of protein than plant foods, so people following a vegetarian diet or a vegan diet may need to plan their meals to ensure they meet their protein needs.
The FDA advise that people can tell if a food product is high or low in protein by checking the label.
Foods that provide 5% or less of a person’s daily value (DV) are considered low in protein.
Foods with 20% DV or more are considered high in protein.
A person does not need to consume foods containing all the essential amino acids at each meal because their body can use amino acids from recent meals to form complete proteins. Eating a variety of protein foods throughout the day is the best way for a person to meet their daily protein needs.
The FDA recommend that adults consume 50 grams (g) of protein a day, as part of a 2,000-calorie diet. A person’s daily value may be higher or lower depending on their calorie intake.
The Dietary Guidelines for Americans 2015–2020 provide the following recommended daily amounts (RDA) for protein by sex and age group:
|child aged 1–3||13 g|
|child aged 4–8||19 g|
|child aged 9–13||34 g|
|female teen aged 14–18||46 g|
|male teen aged 14–18||52 g|
|female adult aged 19+||46 g|
|male adult aged 19+||56 g|
Many factors can affect how much protein a person needs, including their activity level, weight, height, and whether they are pregnant.
Other variables include the proportion of amino acids available in specific protein foods and the digestibility of individual amino acids.
The USDA provide a calculator to help people work out how much protein and other nutrients they need.
Protein and calories
Protein is a source of calories. Generally, protein and carbohydrates contain 4 calories per gram. Fats contain 9 calories per gram.
The Dietary Guidelines for Americans recommend that between 10–35% of an adult’s daily calories should come from protein. For children, it is 10–30%.
Most people in the U.S. meet their daily protein needs. On average , men get 16.3% of their calories from protein, and women 15.8%.
Some diets recommend eating more protein in order to lose weight.
Aa 2015 review suggests that following a particular type of high-protein diet may encourage weight loss, but researchers need to do further studies to establish how to implement such a diet effectively.
When increasing protein intake, it is important to make sure that the diet still contains adequate amounts of fiber, such as fruit, vegetables, and whole grains.
Replacing processed foods and sources of unhealthful fats or sugar in the diet with protein can promote a healthful diet.
Before making significant changes to their diet, it is a good idea for a person to talk to their doctor about the best strategies and tips.
Protein deficiency due to a low intake of protein in the diet is unusual in the U.S.
However, a lack of protein in other countries is a serious concern, especially in children. Protein deficiency can lead to malnutrition, such as kwashiorkor and marasmus, which can be life threatening.
Protein deficiency can arise if a person has a health condition, including:
- an eating disorder, such as anorexia nervosa
- certain genetic conditions
- advanced stages of cancer
- difficulty absorbing nutrients due to a health issue such as irritable bowel syndrome (IBS) or gastric bypass surgery
Very low protein intake can lead to:
- weak muscle tone or swelling due to fluid retention
- thin, brittle hair
- skin lesions
- in adults, a loss of muscle mass
- in children, growth deficits
- hormone imbalances
Protein shakes and protein powders contain high amounts of protein. Protein powders may contain 10–30 g of protein per scoop. They may also contain added sugars, flavorings, vitamins, and minerals.
Protein in protein shakes or powders can come from:
Building and repairing muscle requires protein. Many athletes and bodybuilders use protein products to boost muscle growth.
A wide range of protein supplements is currently available, many claiming to encourage weight loss and increase muscle mass and strength.
A 2018 review reported that taking protein supplements significantly improved muscle size and strength in healthy adults who do resistance exercise, such as weight lifting.
However, protein shakes and powders count as dietary supplements, and so they are not regulated by the Food and Drug Administration (FDA). This means people cannot guarantee that the products contain what the manufacturer claims they do.
Some supplements may also contain banned or unhealthy substances, such as heavy metals or pesticides.
Many protein products are high in added sugar and calories, which can lead to spikes in blood sugar and weight gain, so it is important to check the labels.
Most people, including athletes, can get enough protein from a balanced diet without supplements. Getting too much protein consistently can cause serious health problems.
Some people may benefit from using protein powder to address health concerns, including those with:
- a reduced appetite, which may result from older age or cancer treatment
- a wound that is not healing well, as protein can help the body repair and replace cells
- a medical condition, such as a serious burn, that requires additional calories and protein
For most people, a varied and healthful diet will provide enough protein. For the best health benefits, people can get their protein from a variety of sources. These include fish, meat, soy, beans, tofu, nuts, and seeds.
Here are some suggestions for adding more protein to diet:
- Replace regular snacks with high protein snacks, such as nuts, roasted chickpeas, and peanut butter.
- Add beans and peas to soups, side dishes, or salads. These also make great main dishes.
- Include one high protein food with each meal.
- Replace a source of carbohydrate with a source of protein, such as swapping out a piece of toast for an egg in the morning.
- Before adding protein bars to the diet, check the labels, as they can be high in sugar.
To limit fat intake while increasing protein intake, choose lean meat, poultry, and dairy products, or trim the fat before eating. Try using cooking methods that do not add extra fat, such as grilling.
Avoid processed meats and other processed foods, as these can have negative health effects. Choose nutrient-rich foods instead of processed foods when possible.
Protein is an important part of every diet. The FDA recommend that adults consume 50 grams (g) of protein per day as part of a 2,000-calorie diet, though a person’s specific needs depend on their age, sex, activity levels, and other factors.
Proteins: Sources, Uses in the Body, and Dietary Requirements
Proteins are composed of 20 different amino acids, about half of which are essential, meaning they must be obtained from the diet.
Evaluate protein sources and uses in the body
- Protein -based foods (plant and animal) provide amino acids however, the best source of essential amino acids is animal.
- If the diet does not provide adequate protein, the body will obtain what it needs from itself, especially from its own muscles.
- While adequate protein is required for building skeletal muscle and other tissues, there is ongoing debate regarding the use and necessity of high-protein diets in anaerobic exercise, in particular weight training and bodybuilding.
- This use of protein as a fuel is particularly important under starvation conditions as it allows the body’s own proteins to be used to support life.
- amino acid: Any of the twenty naturally occurring α-amino acids (having the amino, and carboxylic acid groups on the same carbon atom), and a variety of side chains, that combine, via peptide bonds, to form proteins.
- denaturation: Denaturation is a process in which proteins or nucleic acids lose their tertiary and secondary structure which is present in their native state, by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, an organic solvent (e.g., alcohol or chloroform), or heat.
- protein: Any of numerous large, complex naturally-produced molecules composed of one or more long chains of amino acids, in which the amino acid groups are held together by peptide bonds.
Most microorganisms and plants can biosynthesize all 20 standard amino acids, while animals (including humans) must obtain some of the amino acids from the diet. The amino acids that an organism cannot synthesize on its own are referred to as essential amino acids. Key enzymes that synthesize certain amino acids are not present in animals. One example is aspartokinase, which catalyzes the first step in the synthesis of lysine, methionine, and threonine from aspartate.
Amino Acid: Ball-and-stick model of the cystine molecule, an amino acid formed from two cysteine molecules.
In animals, amino acids are obtained through the consumption of foods containing protein. Ingested proteins are then broken down into amino acids through digestion, which typically involves denaturation of the protein through exposure to acid and hydrolysis by enzymes called proteases. Some ingested amino acids are used for protein biosynthesis, while others are converted to glucose through gluconeogenesis, or fed into the citric acid cycle. This use of protein as a fuel is particularly important under starvation conditions as it allows the body’s own proteins to be used to support life, particularly those found in muscle. Amino acids are also an important dietary source of nitrogen.
Protein: Muscle meat, such as steak, is an excellent source of the essential amino acids the body needs to create all necessary proteins.
A high-protein diet is often recommended by bodybuilders and nutritionists to help efforts to build muscle and lose fat. It should not be confused with low-carb diets, such as the Atkins Diet, which are not calorie-controlled and which often contain large amounts of fat. While adequate protein is required for building skeletal muscle and other tissues, there is ongoing debate regarding the use and necessity of high-protein diets in anaerobic exercise in particular weight training and bodybuilding. Extreme protein intake (in excess of 200g per day), coupled with inadequate intake of other calorie sources (fat or carbohydrates), can cause a form of metabolic disturbance and death commonly known as rabbit starvation.
Relatively little evidence has been gathered regarding the effect of long-term high intake of protein on the development of chronic diseases. Increased load on the kidney is a result of an increase in reabsorption of NaCl. This causes a decrease in the sensitivity of tubuloglomerular feedback, which, in turn, results in an increased glomerular filtration rate. This increases pressure in glomerular capillaries. When added to any additional renal disease, this may cause permanent glomerular damage.
First up are the essential amino acids. These are the nine amino acids that your body cannot create on its own, and that you must obtain by eating various foods. Adults need to eat foods that contain the following eight amino acids: methionine, valine, tryptophan, isoleucine, leucine, lysine, threonine and phenylalanine. Histidine, the ninth amino acid, is only necessary for babies.
Instead of storing up a supply of the essential acids, the body uses them to create new proteins on a regular basis. Therefore, the body needs a continual – ideally daily – supply of these amino acids to stay healthy.
The order of the amino acids in a protein dictates the primary structure of the protein. While other levels of structure are important, they all follow from the order of the residues. The primary structure is dictated by genetic information found in a cell deoxyribonucleic acid ( DNA ) contains the code that directs which amino acids are linked together. The processes by which the genetic code is read and proteins are synthesized are called transcription and translation.
The next level of protein structure is called the secondary structure. The side chains of the residues have various functional groups that can have different types of forces: some are hydrophobic and others are hydrophilic some participate in hydrogen bonding interactions while others do not. These forces lead to conformations (geometric arrangements of the residues) that result in lower energies. Two specific arrangements that are found regularly are shown in Figure 2: a helix (which looks like a corkscrew) and a pleated sheet (which looks like a paper that has been folded and opened).
The secondary structure of the protein is the result of interactions of side chains that are located within a few residues of each other. Proteins are sufficiently long that they can eventually fold back on themselves, allowing residues that are farther apart in the primary structure to interact with each other. These interactions give rise to the tertiary structure of the protein
(Figure 2). Some proteins can form structures with multiple units (dimers, trimers, or tetramers). These collections of units provide yet another level of structure called the quaternary structure.
Solubility is one property that can be used to classify the proteins that result from the various levels of structure. For example, fibrous proteins are not soluble in water. Many familiar components of tissues are composed of fibrous proteins, including keratin (the protein present in hair), collagen (a structural protein found in tendons and cartilage), myosin (a protein found in most muscle tissue), and fibrin (the protein that allows blood to clot and form scabs). Conversely, globular proteins are soluble in water. For example, albumins are water-soluble proteins that provide a familiar example of what happens when a protein loses its secondary and tertiary structure, a process called denaturation. When an egg is cooked, the egg white changes from translucent to white this color change is indicative of the change in structure that has taken place in the albumin proteins.
In many cases, the structure of a protein defines a key location called the active site, the region that is associated with the primary activity of a protein, even though it is often made up of only a small number of residues.
All food proteins that originate from animals contain the full complement of essential amino acids. These proteins – from meat, seafood, eggs, poultry and milk – are considered nutritionally complete. Most plant-based proteins are missing at least one essential amino acid, making them incomplete. However, combining plant sources of proteins in a complementary fashion provides your diet with all essential amino acids. For instance, the amino acids lacking in whole grains are available in legumes and vice versa, so eating a barley and lentil stew provides your diet with every essential amino acid.
Unlike the other macromolecules, lipids are not soluble in water, and they don’t form long sequences made up of similar or repeating smaller units. The fats you consume are molecules called triglycerides, consisting of three fatty acids attached to a glycerol. The chemical nature of the fatty acids contained within the lipid determines its physical characteristics. For instance, a fatty acid that is saturated with as many hydrogen atoms as it can hold is solid at room temperature, while unsaturated fatty acids are liquid. These macromolecules store energy within fat tissue, and they cushion your internal organs against trauma. They also form the structure of cell membranes and contribute to the synthesis of hormones.
There are 22 Amino Acids
These above are the 20 more well-known amino acids however, just how many amino acids exist actually are counted as being over 200 in numbers, but the 22 proteinogenic amino acids are the ones that are commonly known. These more commonly known aminos can be found in food (all meat such as beef, pork, chicken, seafood, and even eggs are excellent sources of all 22 amino acids). They can also be bought as amino acid supplements individually or as a complex of many in balanced forms for their health benefits. But haven’t we missed some? What about ornithine and citrulline? Just as phenylalanine and tyrosine are interchangeable, so are ornithine, citrulline, and arginine. Although they have different chemical structures, they have similar benefits and effects on the body and can be interchanged in the diet. For example, both arginine and citrulline act to increase nitric oxide in the body. How many amino acids have you had in your diet today?