Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Kim Jackson  

Introduction[edit | edit source]

Protein image

Proteins are biopolymeric structures composed of amino acids, of which there are 20 common ones found in biological chemistry[1], participating in nearly all cellular activities.

  1. Proteins are synthesised in the cytoplasm in a process termed translation.
  2. The typical protein is constructed from a single set of amino acids. Every protein is specially equipped for its function.
  3. Any protein in the human body can be created from permutations of only 20 amino acids.
  4. There are seven types of proteins: antibodies, contractile proteins, enzymes, hormonal proteins, structural proteins, storage proteins, and transport proteins.[2]
Protein rich foods

Protein is a vital part of the human diet.

The protein content of eg. Muscles contain about 30 percent protein, the liver 20 to 30 percent, and red blood cells 30 percent. Higher percentages of protein are found in hair, bones, and other organs and tissues with a low water content[3].

Classification[edit | edit source]

While there are hundreds of amino acids in nature, humans use only 20 of them. One way to further classify them is by defining which ones healthy bodies can and cannot make.

The three classes of proteins are: Non-Essential; Conditionally Essential; Essential Amino Acids

  1. Non Essential: There are five amino acids termed non-essential because they can be obtained from foods and also generated within the body. The non-essential amino acids are: Alanine; Asparagine; Aspartic acid; Glutamic acid; Serine
  2. Conditionally-Essential Amino Acids: There are six amino acids termed conditionally-essential because healthy bodies can generate them under normal physiologic conditions. They become essential under certain conditions lIke starvation or inborn errors of metabolism. The conditionally essential amino acids are: Arginine; Cysteine ; Glutamine; Glycine; Proline; Tyrosine
  3. Essential Amino Acids: There are nine amino acids termed essential because they cannot be generated within the body. Dietary protein, therefore, provides these amino acids, which are needed to make certain hormones and other important molecules. The essential amino acids are: Histidine; Isoleucine; Leucine; Lysine; Methionine; Phenylalanine; Threonine; Tryptophan; Valine[1].

Types of Proteins[edit | edit source]

There is a total of seven different protein types under which all proteins fall. These include antibodies, contractile proteins, enzymes, hormonal proteins, structural proteins, storage proteins, and transport proteins.

Antibodies: Antibodies are specialized proteins that defend the body against antigens or foreign invaders. Their ability to travel through the bloodstream enables them to be utilized by the immune system to identify and defend against bacteria, viruses, and other foreign intruders in blood. One way antibodies counteract antigens is by immobilizing them so that they can be destroyed by white blood cells.

Contractile Proteins: Contractile proteins are responsible for muscle contraction and movement, see Molecular Motors).

  • The cytoplasm of cells is a colloidal network of contractile proteins. Actin filaments are the major components of this network[4]. See Muscle Cells (Myocyte)
  • Eukaryotes tend to possess copious amounts of actin, which controls muscle contraction as well as cellular movement and division processes. Myosin powers the tasks carried out by actin by supplying it with energy.
Enzyme activation energy

Enzymes: All enzymes identified thus far are proteins.

  • Enzymes, which are the catalysts of all metabolic reactions, enable an organism to build up the chemical substances necessary for life—proteins, nucleic acids, carbohydrates, and lipids—to convert them into other substances, and to degrade them.
  • Life without enzymes is not possible[3].

Hormonal Proteins: Hormonal proteins are messenger proteins that help coordinate certain bodily

  • Growth factors are highly specific proteins, a subdivision of cytokines. Growth factors stimulate the division and differentiation of a particular type of cell. In skeletal muscle hypertrophy, growth factors include insulin-like growth factor (IGF). IGF is secreted by skeletal muscle. It regulates insulin metabolism and stimulates protein synthesis.[5].
  • Testosterone is an androgen, or a male sex hormone. The primary physiological role of androgens are to promote the growth and development of male organs and characteristics. Testosterone affects the nervous system, skeletal muscle, bone marrow, skin, hair and the sex organs.
  • Cortisol is a steroid hormone (hormones which have a steroid nucleus that can pass through a cell membrane without a receptor) which is produced in the adrenal cortex of the kidney. It is a stress hormone.

Structural Proteins: A large group of structural proteins maintains and protects the structure of the animal body[3].

  • The most common example of a structural protein is collagen which is found in the bones, cells and skin.
  • Structural proteins are also found in cells. They are used to provide an internal structure to the cell (the cytoskeleton) and are sometimes involved in cell movement. Structural proteins are especially important in larger cells.

Storage Proteins: Storage proteins reserve amino acids for the body until ready for use. Examples of storage proteins include

  • Ferritin a storage protein that stores iron.
Membrane proteins

Transport Proteins: Transport proteins are carrier proteins that move molecules from one place to another in the body.

  • The respiratory protein hemoglobin acts as oxygen carrier in the blood, transporting oxygen from the lung to body organs and tissues[3].
  • Cytochromes, another type of transport protein, operate in the electron transport chain as electron carrier proteins.[2]See Adenosine triphosphate (ATP)

Diet[edit | edit source]

Protein is a vital part of the human diet and is present in various foods eg eggs, meats, dairy, seafood legumes, nuts, and seeds. Irrespective of the source of the protein consumed, it gets broken down in reformed into new proteins in our bodies.

Most animal proteins are referred to as complete proteins as they contain all nine essential amino acids whereas most plant proteins are considered to be incomplete as they are missing at least one of the essential amino acids[6]. Soy products, quinoa and the seed of a leafy green called amaranth are a few of the plant-based proteins that contain all nine essential amino acids.[6]

Protein powder

Human beings aren't able to store protein, for the most part. The human body can break down its muscle tissue to get certain amino acids, or the building blocks of protein, but it has no specialized cells to store protein efficiently, as it does fat and carbohydrate. For this reason, eating protein regularly is of paramount importance.[7]

  • The amount of protein we need changes throughout our lifetime and elderly people will actually need more protein than younger adults.
  • Protein-rich foods tend to make people feel fuller for longer compared to fats or carbohydrates[6]. Proteins do this by increasing thermogenesis and through the direct effect of its constituent amino acids (notably leucine) on the brain[8].
  • Millions of people take sports supplements hoping for a range of health benefits, from weight loss to muscle building. But some supplements are being sold illegally and can be very harmful.[9]

Related Medical Conditions[edit | edit source]

Girl with kwashiorkor

Proteins serve crucial roles in human biochemistry. The major role is to provide the body's building blocks. They are the precursors of several biologically relevant molecules. Therefore either the excess or deficiency of protein can lead to disease result in nervous system defects, metabolic problems, organ failure, and even death. eg the most severe form of protein deficiency is called kwashiorkor[6]; Anorexia Nervosa.

  • A dysfunctional protein can lead to a variety of medical conditions and, often, death.
  • Dysfunctional proteins can lead to childhood obesity, breakdown of the retina leading to blindness, hearing loss, and type 2 diabetes.

Eg the protein cilia and how its dysfunction manifests.

  • Inadequate cilia in flagella lead to sperm dysmotility.
  • Defective cilia in the respiratory tract lead to chronic lung infections.
  • Dysfunctional cilia in Fallopian tubes cause infertility[1]

References[edit | edit source]