Essay: Proteins

All proteins consist of amino acids, organic molecules made from Carbon, Hydrogen, Oxygen and Nitrogen. Collagen is the most ample protein in mammals, in fact collagen constitutes around 25 % of a mammals entire protein content, Collagen is more precisely a family of proteins rather than one particular protein. Fibroblasts are the cells that usually produce collagen. Collagen is a complex molecules so doesn’t have a simple chemical structure for it, diagrams usually show collagen as a fiber.(Helmenstine 2015). There are 19 types of collagen in the collagen family, the 5 most abundant are type I collagen, found in connective tissue of skin, bones, teeth, tendons, ligaments, fascia and organ capsules, type II found in joint cartilage, type III, found in connective tissue of our organs such as liver, spleen and kidneys and type IV & V are the separating layer between epithelial and endothelial cells as well as between skeletal or smooth muscle cells , lens capsule, Schwann & glial cells of the nervous system.(Cellbone® technology 2007) Collagen is fibrous, fibrous proteins tend to have the hydrophilic R groups on the amino acids tend to be brought inside of the molecule and the hydrophobic R groups tend to be pushed to the outside of the molecule making it insoluble due to the hydrophobic and hydrophilic interactions . Collagen is also a strong structural protein thus Collagen suits its function in animal connective tissues such as bone skin and muscle. (Fullick et al 2015) each fiber of Collagen consists of thousands of collagen molecules that are bound together by cross- linked and staggered covalent bonds, covalent bonds are the strongest bonds that can exist between protein molecules. the collagen molecule consists of 3 polypeptide chains wound around each other in an alpha helix joined by hydrogen bonds. the alpha helix forms because of the regular primary structure of the strands joined . The sequence of amino acids in collagen protein is glycine-proline-R where R can be any amino acid so every third amino acid is glycine . (Hughes 2015). Collagen is very useful in our skin tissues and provides tensile strength, resilience and flexibility, also collagen can allow a tissue to withstand immense pulling without being stretched. However, as we age collagen degradation occurs leading to wrinkles. In a research on women with age-related skin problems, a dietary collagen formula remarkably improved periorbital wrinkling (crow’s feet), periorbital aging, and overall facial aging. This confirms the structure and properties in collagen.(Kantor et al 2002).
keratin, like collagen is also fibrous protein so is an insoluble , strong and fairly unreactive protein . Keratin is found in many of the external structures of animals, such as skin , hair, nails feathers and horns . Keratin can be either flexible as it is in skin or hard and tough as in nails .(Fullick et al 2015) Keratin can be divided into alpha keratin and beta keratin based on their secondary structure , the geometry of their polypeptide chains which is determined by hydrogen bonding . alpha keratin which is found in the hair and skin of mammals are fibrous and have a helical structure. On the contrary , beta keratin which is fond in birds and reptiles , comprise of parallel beta pleated sheets of polypeptide chains. keratin contains the amino acid cysteine which become covalently bonded by disulphide bonds. This is why cysteine are at the helm of the great stability of keratin (Encyclopaedia Britanica 2015) . Keratin’s polypeptide backbone does not fold onto itself giving it long and straight characteristics .Keratin consists of 2 polypeptide chains coiled around each other.Keratin has a amino acid sequence of 1-2-3-4-5-6-7 where #1 and #4 are non polar, this line up along one side of the helix causes hydrophobic van der waals interaction to hold them together the two polypeptides are a dimer, 2 dimers form a tetramer ,two tetramers form an octamer and so forth until we get the largest most complex intermediate filament this may contain 16-32 separate polypeptide chains. (Pratt et al 2013) Keratin is a lightweight protein weighing in at 1.3 g/cm3, and also a robust structural biological material that serves a variety of functions, from simply waterproofing to impact resistant structures such as hooves and horns. It has excellent properties in both tension and load. Keratinaceous materials have four major morphologies these are dense waterproof layer in skin, dense shells filled with a porous material, resulting in the formation of lightweight, stiff, buckle-resistant structures for example quills, feathers, and bird beaks, Solid blocks with embedded tubules that are impact resistant such as hooves and horns and Filamentary forms in gecko feet and hagfish slime .(MCKITTRICK et al 2012)
On the other hand haemoglobin is a globular protein that carries oxygen in the blood cells and has a structure related to its functions . Globular proteins are round and compact, in a globular protein, the hydrophilic R groups on the amino acid tend to be pushed to the outside of the molecule .This is caused by the hydrophobic and hydrophilic interactions in the proteins tertiary structure this is what makes globular proteins soluble for easy transport in fluids. Haemoglobin is known as a conjugated protein this means it’s a protein with a non protein group attached . The non protein part is called a prosthetic group . each of the four polypeptide chains in haemoglobin has a prosthetic group attached called a haem . a haem group contains an iron atom that is held in the centre of a heterocyclic porphyrin ring ,which oxygen binds to. The haem group gives haemoglobin its red colour. Haemoglobin has a high affinity for oxygen, a prosthetic group can carry one oxygen molecule so a haemoglobin molecule can carry 4 oxygen molecules . In the lungs during diffusion oxygen joins to the iron in haemoglobin to produce oxyhaemoglobin, this is a reversible reaction as when oxygen dissociates from oxyhaemoglobin near the body cells ,it turns back to haemoglobin this is the equation Hb+4O2 is in equilibrium withHbO8 (Fullick et al 2015) The four subunits are two alpha chains with 145 amino acid residues and two beta chains with 146 amino acid residues. These will usually form alpha helices. Haemoglobin has the ability to alternate between the relaxed state and tensed state by rotating 15 degrees between the two similar sub units. this rotation leads to the bonds between the two similar sub units to change features vaguely and cause a strain .This causes the central haem group of the two alike sub units to change position which changes haemoglobins affinity for oxygen allowing it to bind to and release oxygen when needed.(Alberts et al 2008) Haemoglobin binds to oxygen and transports it from the lungs to working tissues. However haemoglobin also transports Carbon dioxide from tissues to lungs, and also haemoglobin acts as a buffer, by transporting protons as Hb.2H+(unaab 2015) .
similarly insulin is a globular protein so this means that most of the hydrophilic R groups are pushed to the outside of the molecule and the hydrophobic R groups are drawn to the center of the molecule making it soluble so it can be easily transported in fluids. insulin is a hormone secreted by the pancreas. it helps to regulate blood glucose levels. its solubility is important because this means it can be transported in the blood to the tissues where it acts. an insulin molecule consists of two polypeptide chains ,which are held together by disulfide bonds.(Fullick et al 2015)Insulin is made up of 2 different types of polypeptide one polypeptide has 21 amino acids and the second polypeptide has 30 amino acids. Both polypeptides contain alpha helices but no beta pleated sheets. there are 3 secured disulfide bridges which keep the the two polypeptides together (Taylor. A et al 2015) Insulin assists your body to turn glucose in the blood into energy. Insulin also helps the storing of glucose as glycogen in the fat, muscle and liver cells to use when needed. When we eat, the increase in glucose in the blood increases this activates our pancreas to releases insulin in the bloodstream. Insulin travels through the blood stream to your body cells It signals the cells to open up and allow the glucose inside, then glucose will either convert to energy or convert to glycogen and then stores until we need it .Without insulin the glucose will stay in the blood causing many problems .(Mccullock.D 2014)
In conclusion, proteins are assembled from a sequence of amino acids which bond to become polypeptide chains, these chains then fold into distinctive three dimensional structures, the last folded configuration of proteins are proficiently customized to their function. Fibrous proteins such as keratin and collagen are manufactured to be insoluble and tough this suits their structural roles. Globular proteins are built to be soluble, this suits their roles in fluids so they are easily transported to do there specific roles.
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