Cansel Kussan  ‘Using a relevant example explain the importance of structure in relation to function in biology’               We see the importance of structure in relation to function throughout biology, particularly human biology.

 All biological functions are dependent on events that occur at the molecular level. The shape and structure of a protein is extremely important for a protein to correctly carry out its function. The overall structure of a protein is determined by its primary structure. When a mutation occurs in the genes instructions for making a specific protein, this has consequences, such as disrupting normal development or resulting in medical conditions.  Proteins are large, complex molecules and have four different levels of structure, this includes, primary, secondary, tertiary and quaternary. ‘Primary protein structure is defined by the sequence of amino acids held together by rather rigid peptide bonds’ (Larry R Engelking, 2015).

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 The secondary structure of a protein involves the way in which the polypeptide chain determined by the primary structure is folded. These folds include alpha helixes and beta pleated sheets, that form as a result of hydrogen bonding. The tertiary structure of a protein is the overall shape of that polypeptide. The protein will bend in different ways as to achieve lowest energy state and/or maximum stability.

 The bonds involved include disulphide bridges, hydrogen bonds among polar side chains, ionic bonds between charged R groups and hydrophobic attractions. Finally, some proteins also have a quaternary structure. The quaternary structure refers to the way more than one protein subunit interact with each other and form bonds to make a larger aggregate protein complex. The human brain demonstrates various examples of how important protein structure is in relation to function in biology, and how disruptions in structure leads to a variety of medical consequences. Many proteins are important in the function of the human brain. Huntingtin is a protein assembled by the instructions on the HTT gene.

 Huntington’s protein plays critical roles in the human body and is essential for normal development. It is involved in transporting materials, chemical signaling, binding to proteins and other structures, as well as protecting the cell against apoptosis.  Mutations in the primary structure of the Huntington protein results in its altered shape which prevents it from being able to carry out its normal functions. Mutations on the HTT gene can result in huntingtins disease, this is an example of how disrupting the structure of a huntingtins protein directly impacts its function and consequently results in a medical condition. ‘Huntington’s Disease is an adult-onset dominant heritable disorder characterized by progressive psychiatric disruption, cognitive deficits, and loss of motor coordination’ (Joost Schulte, 2011). According to Joost, Huntington’s disease is caused by expansion of a polyglutamine tract within the N-terminal domain of the Huntingtin protein.

 The unstable, expanded trinucleotide repeat in the huntingtin gene, translates as a polyglutamine repeat in the Huntington protein. The repercussions of this mutation is major. Huntington’s disease results in symptoms that include involuntary jerking, difficulty with speech, swallowing and many more. Although Huntington’s disease is not fatal itself, the symptoms combined eventually result in the an individual unable to continue living as they normally would if they hadn’t inherited the mutated HTT gene. ‘Pneumonia and heart disease are the two leading causes of death for people with Huntington’s disease’ (Stephanie Liou, 2010). Here, we can Cleary see the importance of the HTT protein, and how altering the shape results in complications. There are many more proteins that are essential for the normal functioning of the human body.

Another example includes the CFTR protein. The CFTR gene codes for the cystic fibrosis transmembrane conductance regulator protein. This protein functions as a chloride channel across the membrane of certain cells. These cells produce sweat, tears, saliva, digestive enzymes and mucus.

The channel works by transporting negatively charged chloride ions in and out of cells. This is important because is controls the movement of water in tissues, which directly impacts the thickness of the mucus produced. It is vital that the mucus produced is thin and not thick, as thick mucus can cause many problems. The mucus must lubricate various organs in the human body. This prevents the organs from getting infected or becoming too dry. The CFTR protein also functions as a regulator of other ion channels. This includes sodium ions that are positively charged and move across cell membranes, for organs such as the pancreas, lung, liver and intestines these channels are essential. When mutations of the CFTR gene happen and therefore resulting is an incorrect structure of the cystic fibrosis transmembrane conductance regulator protein, many complications occur.

 The medical condition associated with a mutated CFTR gene is known as cystic fibrosis. Cystic fibrosis is another example of how disruptions in protein structure results in problems related to function. ‘Cystic fibrosis is a life-limiting autosomal recessive disorder that affects 70,000 individuals worldwide’ (Nat Rev Genet, 2015).

 People with the cystic fibrosis condition experience large amounts of thick sticky mucus build up in various organs. This causes a range of challenging problems affecting the whole body. Symptoms of cystic fibrosis include respiratory problems and digestive problems. The respiratory problems range from shortness of breath to other problems such as a constant cough that involves coughing up thick mucus. Once again, we can see how important the structure of the CFTR protein is, as incorrect structure leads to medical conditions such as cystic fibrosis. The beta-globin protein is assembled according to the instructions on the HBB gene.

 Beta-globin is a protein subunit of the quaternary structure of haemoglobin. Haemoglobin is found in red blood cells. Normal hemoglobin results in red blood cells with a disc shape. Its function is to carry oxygen from the lungs to the rest of the body, and also to carry carbon dioxide from the body tissues to the lungs where it is removed. The disc shape of the red blood cells allows the cell to be flexible. This is important as it allows them to deliver oxygen to where it is needed. The human body needs an efficient supply of oxygen to cells in order to function. Without oxygen the cells in the body cannot respire and will die.

 Mutations on the HBB protein may results in a medical condition called sickle cell anemia. This mutation causes the production of a different version of beta-globin called hemoglobin S. Sickle cell anemia is a condition that affects red blood cells. The abnormal hemoglobin caused by mutations on the HBB gene results in distorted red blood cells.

The amino acid called glutamic acid is replaced with a different amino acid called valine at position 6 in beta-globin. People with sickle cell anemia have red blood cells with a different shape, that differs from people with normal red blood cells. Red blood cells with normal hemoglobin have a disc shape whilst red blood cells in sickle hemoglobin are sickle shaped. This sickle shape becomes a major disadvantage for the person carrying the genes for sickle cell anemia. Sickle shaped red blood cells are not flexible. The different shape causes them to sick to vessel walls.

 This is a problem as it results in blockage, which slows down and can possibly even stop blood flow. The sickle shaped red blood cells have a short life span and die prematurely, which leads to a shortage and is known as anemia. The decrease in oxygen being delivered to body cells can causes severe pain. More importantly the lack of oxygen being delivered to vital organs can cause major damages to them.

Once again, with another example, we can see how important structure is in relation to function in biology. When genes are altered or inherited with faults, this causes problems in protein structure which then impacts and changes the way that specific protein should originally function. Using the human body as the relevant example, we have seen the importance of structure in relation to function in biology. Various proteins in the brain and other organs have a specific structure which enable them to carry out their functions.

Changes in these structures due to mutations, in the genetic code of the proteins, result in various complications that interrupt with normal development, or result in medical condition. Specific mutations in the HTT gene may cause huntingtins disease. Mutations in the CFTR gene results in cystic fibrosis.

Mutations in the HBB gene results in sickle cell anemia. This is just a few ways in which structure is important in relation to function in biology. Problems arise when structures are altered, as function cannot be carried out correctly.  


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