__________ contain all nine essential amino acids

A. Simple carbohydrates.

B. Incomplete proteins.

C. Complete proteins.

D. Complex carbohydrates.

The correct answer is C. Complete proteins

Diagram of the 20 amino acids
Diagram of the 20 amino acids

A complete protein is a protein which does contain all nine of the essential amino acids. Our bodies are unable to synthesize certain of these acids. These are the molecules that are referred to as essential amino acids since it is important that we take them in through our diet.

Nonessential amino acids are those that can be made in the human body and therefore do not have to be taken in with food. It is important to remember that amino acids are the basic units of protein. These are the structures that bond together in various ways to form each type of protein molecule.

The essential amino acids include the following: tryptophan, isoleucine, leucine, lysine, threonine, methionine, valine, histidine, and phenylalanine. It is therefore important that people are able to consume enough protein that will supply all of these amino acids.

People can obtain all the essential amino acids from such foods as animal protein like beef, eggs, and poultry. Soy also is a complete protein for vegetarians.

It is possible to eat complementary proteins to get all the amino acids you need. Certain combinations of foods can ensure this so that an individual does not have to always eat complete protein sources.

The structure of proteins

The basic unit of all proteins is the amino acid. This molecule consists of a central carbon atom to which a carboxyl and an amino group are bonded.

There is also a functional side group that attaches to the central alpha carbon atom, which actually determines what a particular type of amino acid is.

Only 20 amino acids are used to form all of the proteins, and plants are actually able to make all of these, unlike animals which cannot make 9 of the amino acids. It is these molecules that animals can’t make that have to be consumed that are called the essential amino acids.

Amino acids link together by covalent bonds that form between them. These are known as peptide bonds and are the first level of protein structure, known as the primary structure of the protein.

Proteins, however, are not linear polypeptide chains and in fact, they bond further to form complex structures. The secondary structure of these molecules is formed by hydrogen bonding, and an alpha helix or pleated sheet is formed at this stage.

All proteins then further fold and bond to form a tertiary structure and some even form a larger folded quaternary structure.

The structure of polypeptides ties in directly with their function and this is most clearly seen with enzymes that can only work with specific substrate molecules that they can bind to.

The function of proteins

Proteins serve several functions in the human body. They form the precursors of several hormones, they form enzymes and become incorporated into cell membranes. Amino acids are therefore essential for the survival of living cells and tissues.

Furthermore, proteins are important in the functioning of the immune system and help form all the organs of the body. Proteinaceous receptors on cells and protein-based hormones play a crucial role in cell signaling in the body.

Essential amino acids are important at every stage of a person’s life in helping the growth and repair of tissues. Research has indicated that older adults also benefit greatly from adequate amounts of essential amino acids.

The amino acids are in fact important in helping muscle growth, even in the elderly. It is these essential nutrients that are actually most important in the building of muscle in people.

Some people advocate increasing protein intake and reducing carbohydrate intake to promote weight loss. However, although many animal proteins contain all the essential amino acids that the body needs, the diet may eliminate needed vitamins and minerals and increase saturated fat intake, which is not healthy.

Sources of complete protein

Complete proteins include many proteins that are from animal sources.  Eating poultry, pork or beef can supply all the amino acids that are needed. Eggs and dairy products along with seafood are also good sources of protein that contain all the essential acids that are needed.

Vegetarians may be worried about getting all their amino acids, but there are sources of complete protein in vegetarian diets, in the form of soy. An alternative for people who do not want to eat soy is to eat what is known as complementary proteins.

These are proteins that when eaten together provide all the amino acids that are needed. Eating rice and beans together or peanut butter with wholegrain bread can work to provide all the amino acids you need. Such combinations mean that a person does not need to necessarily eat one complete protein source such as meat or soy.

A person eating 2000 calories a day needs to take in 50g of proteins. A deficiency of amino acids can lead to serious health problems.

Protein deficiencies

A lack of protein in the diet can lead to muscle wasting and poor growth. Children may have stunted growth and the lack of amino acids also impacts mood. In fact, some amino acids such as tryptophan play a role in the production of serotonin which helps us to feel good.

Antibodies that are produced in the immune system are proteins. Thus, a severe lack of amino acids can lead to a seriously suppressed immune system which is the body’s defense system. This makes a person vulnerable to infections and illness.


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