Fundamentals of Human Nutrition/Defining Proteins

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5.1 Defining Proteins[edit]

All living cells are made up of proteins (n.d.) including substances such as hormones, enzymes and antibodies that are necessary for that organism to function correctly. Proteins are essential for life. They are a group of complex organic chemical compounds that are made up of carbon, hydrogen, oxygen and sometimes sulfur that is composed of one or more chains of amino acids. They are the true workhorses of the body. Proteins perform a vast array of functions within living organisms, including replicating DNA, catalyzing metabolic reaction and responding to different stimuli. They are an essential part of an organism and take part in nearly all processes that go on with the cells. They are extremely essential in animal diets as some amino acids cannot be synthesized and must be obtained from our food. Amino acids are used in metabolism after they are broken down through digestion.

Some foods that are rich in proteins include eggs, milk, meat, fish, tofu and legumes.

There are three different types of proteins based of their composition.

  1. Simple proteins
  2. Conjugated proteins
  3. Derived proteins

Simple proteins are proteins that are made up of amino acids joined by peptides bonds. Some examples are globulin, albumins, histones, albuminoids, protamines, glutelins and globulins.

Conjugated proteins are simple proteins joined with a prosthetic group or cofactor. Some examples are phospho- proteins, chromo proteins, nucleoproteins and glycoproteins.

Derived proteins are obtained from simple proteins using the actions of chemical agents and enzymes and they are not naturally occurring proteins. Some examples include peptides, peptones and metaproteins.

Simple proteins are proteins that are made up of amino acids joined by peptides bonds. Some examples are globulin, albumins and gliadins.

Conjugated proteins are simple proteins joined with a prosthetic group or cofactor. Some examples are phospho- proteins and chromo proteins.

Derived proteins are obtained from simple proteins using the actions of chemical agents and enzymes and they are not naturally occurring proteins. Some examples include peptides and peptones.


Amino acids and proteins are the building blocks of life. When proteins are digested or broken down, amino acids are left. The human body needs a number of amino acids to[1]:

  1. Break down food
  2. Grow
  3. Repair body tissue
  4. Other body functions


Amino acids are classified into three groups:

There are three types of amino acids: essential amino acids, nonessential amino acids and conditional amino acids.

  1. The essential amino acids, we don't produce this, so we have to eat the food for obtain. The amino acids isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine can not be synthesised by the body and therefore must be essential components of the diet. [2]
  2. Nonessential amino acids the body produce, so people don't need to eat for obtain this amino acids. They are: alanine, asparagine, aspartic acid, and glutamic acid.[3]
  3. Conditional amino acids: If your system is stressed, out of balance, or diseased, these amino acids become essential and you must get them from food or supplements. They are: arginine, glycine, cystine, tyrosine, proline, glutamine and taurine.

5.1.1 Structure[edit]

There are four levels of organization for proteins to take on. Each level lends a new layer of physical intricacy, and in turn, more diverse functionalities. The phrase “form fits function” is an appropriate mantra for proteins. The four levels are as follows:

Primary Structure

Proteins at their most basic level are patterned strings of individual amino acids linked together by peptide bonds. Think of a single protein as a beaded necklace, strung with different beads that all have unique properties (Whitney, E., & Rolfes, S., 2013). Each protein has its own pattern of amino acids that makes its form different, and thus its function different. The different effects the arrangement of amino acids has comes into play in the next level of organization.

Secondary Structure

Now is when the string of proteins starts to take a distinct shape. The forming is driven by the weak electrical attractions the individual amino acids have to other amino acids (Whitney, E., & Rolfes, S., 2013). According to Geoffrey Cooper, This is the major form of guidance for the protein, and why the sequence of amino acids in the primary structure determines the functionality of the future protein. Also, molecular chaperones aid in protein folding, and their sole purpose is to help the protein fold in ways it already is predisposed to fold (Cooper, G., 2000).

Some forms that protein strings can take are pleated sheets and helixes (Whitney, E., & Rolfes, S., 2013). Elmhurst University describes the helix shape as spring-like, with the form stabilized by the hydrogen bonding between the nitrogen and hydrogen of an individual amino acid with that of the carbon and oxygen on the amino acids that is 4 amino acids down the string from it. Elmhurst University also states that beta pleated sheets are sheets of protein strings that are bonded side to side by hydrogen bonds, and is planar in contrast to helixes.

Tertiary Structure

The tertiary structure of proteins is when form really starts to represent function. The alpha and beta riddled strings of amino acids begin to fold in on themselves, with the hydrophilic amino side groups facing outward in an aqueous environment, and the hydrophobic side groups facing inwards (Whitney, E., & Rolfes, S., 2013). It is now easy to see how the order of amino acids in the primary structure is vital to the correct form and function of a protein.

Quaternary Structure

In some cases, proteins need to be organized beyond tertiary structure. Multiple proteins that have attained tertiary structure, otherwise known as polypeptides, can group together to create a larger form (Whitney, E., & Rolfes, S., 2013).

References[edit]