Enzymes And Substrates: Lock And Key Model

The Different Organs That Make up the Digestive, Respiratory, Circulatory, and Renal Systems

Enzymes are composed primarily of amino acid polymers and are capable of binding prosthetic groups like metal ions that can act as co-factors for the enzyme. The enzymes have an active site, where the substrate binds and is the place where the catalyzed reaction is carried out. Enzymes are biological molecules that are involved in catalyzing various reactions that are necessary for proper maintenance of life. These include metabolic reactions, replication, transcription, translation enzymes, among others. Substrate is the reactant that remains bound to the enzyme. Apart from prosthetic groups, enzymes also require co-enzymes for their functions. These co-enzymes are generally vitamins, which remains bound to the enzyme-substrate complex during catalysis reactions. Enzymes function at optimum pH and temperature (Naushad et al. 2012).

According to the Lock and Key model, the enzyme functions as the lock and the substrate functions as the key. Both enzymes and substrates have a fixed conformation that enable them to bind to each other. The active site of the enzyme consists of an orientation that is complementary to that of the substrate, thereby enabling proper fit. The structure and chemical composition of the active site of the enzyme determines the binding of the substrate to the enzyme.                                    

The transition state of a reaction is the highest energy state of a reaction. Enzymes carry out reaction catalysis by stabilizing the transition state, thereby increasing the rate of the reaction. Activation energy is defined as the amount of energy that is needed to break bonds in order to generate the desired products. The enzymes function by lowering the activation energy thereby enabling best fit for the transition state in the active site. 

Digestive system

Organs	Roles
Mouth	This is the organ, where the digestion of food starts with the help of the enzymes present in the saliva.
Pharynx and Esophagus	Pharynx receives the food that comes from the mouth and the esophagus transports food to the stomach by peristalsis.
Stomach and small intestine	The glands present in the walls of the stomach secretes enzymes and acids that breakdown food and convert it to chime. The pancreatic enzymes and bile obtained from liver further carry out digestion of the food in the small intestine. The duodenum breaks down the food, while the jejunum and ileum carries out nutrient absorption.
Large intestine, colon, rectum and anus	They help to solidify the waste product resulting from digestion by absorption of water. They also carry out storage of the waste product. Movement in the colon takes place by peristalsis and the water in the waste products are absorbed resulting in stool formation. Storage takes place in rectum. The sphincter muscles of the anus is responsible for regulating the release of stool.
Pancreas, Liver and Gall Bladder	Pancreas secretes insulin for maintenance of blood sugar and also secretes digestive enzymes. Liver helps in digestion, nutrient storage and toxin removal. Gall bladder secretes bile that helps in the digestion of fats.

 The digestive system consists harbors 70% of the body’s immune system. The digestive system helps to break down food and obtain the nutrients by absorption, which in turn helps to obtain energy and nourishment. It also helps in the proper elimination of waste products. Moreover, the system plays an important role in eliminating toxic wastes from the body and also helps to control the entire energy metabolism of the body. Apart from digestion and nutrient absorption the pancreas, which is a part of the digestive system plays an important role in maintaining the glucose levels of the body secreting insulin (Sherwood 2015).

Organs	Roles
Upper respiratory tract (Nose, mouth and initial part of the trachea)	Involved in breathing in and breathing out air.
Trachea	Connects the throat to the bronchi
Bronchi	The 2 bronchi leads to the two lungs i.e. right and left. They divide into smaller bronchi.
Broncheoli	The bronchi undergo subsequent branching to form broncheoles. They end in the pulmonary alveolus.
Pulmonary alveoli	These are tiny sacs, where exchange of gases takes place.
Lungs	Functions in the act of breathing, which involves inhalation and exhalation.

 The respiratory system consists of the airways, lungs, blood vessels and muscles, which helps in breathing. The function of the respiratory system is to supply oxygen to various parts of the body. It carries out by inhaling oxygen rich air and expelling air that is rich in carbon-dioxide. Thus, it also participates in removal of waste gas from the body. The respiratory system helps to maintain homeostasis by controlling pH and gas exchanges. It helps to supply oxygen to the blood stream and also helps to prevent accumulation of toxic levels of carbon-dioxide. It also helps to maintain the hydrogen ion concentration of the blood stream thereby helping to maintain pH. The respiratory system helps to maintain the water content, internal temperature and optimal blood circulation in the body. It also protects from inhaled microbes (Hall 2015).

Organs	Roles
Heart	The chambers of the heart function as pumps and supply blood to the entire body.
Blood vessels (Arteries, veins, capillaries)	Arteries take oxygen rich blood from the heart top other parts of the body. Veins take back blood to the heart and capillaries connect arteries and veins. The capillary walls enable the transfer of nutrients, oxygen and wastes.
Lungs	The lungs transfer oxygen rich blood to the heart.
Blood	Carries water, nutrients, oxygen and waste products in and out of the cells of the body.

 The circulatory system helps in the circulation of the oxygen rich blood to various parts of the body. The circulatory system is also involved in pumping nutrients to various organs of the body, so that they can carry out their functions. Apart from supplying nutrients and oxygen, the circulatory system is also involved in removing wastes. The circulatory system also enhances energy production, thereby decreasing the risk of development of chronic diseases. It also helps in the regulation of the body temperature (Noordergraaf 2012).

Organs	Roles
Kidneys	Removes wastes and excess water from the blood, helps to regulate blood pressure, stimulates red blood cell formation by producing erythropoietin and helps in the formation of Vitamin D.
Ureters	The muscles contract and relax enabling the urine to reach the urinary bladder.
Urinary bladder	The sphincter muscles of the bladder helps in controlling the release of urine.
Urethra	The urethra carries urine that is stored in the bladder to the outside.

The renal system plays an important role in maintaining homeostatic balance by eliminating wastes and excreting toxic fluids or chemicals, in order to maintain an internal balance. The renal system filters blood, removing the wastes. The blood is returned to the circulation, while the waste products exit in the form of urine. The kidneys play an important role in maintaining normal blood acidity and the nephrons present in the kidneys help to filter the toxic wastes present in blood while retaining the useful compounds (Hall 2015).

References

Biology.arizona.edu. (2018). Energy, Enzymes, and Catalysis Problem Set. Biology.arizona.edu. Retrieved 7 January 2018, from https://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/01t.html

Hall, J.E., 2015. Guyton and Hall Textbook of Medical Physiology E-Book. Elsevier Health Sciences.

Lope (2018). Lope: respiratory system diagram. [online] Lope. Available at: https://scalar.usc.edu/works/lope/respiratory-system-diagram [Accessed 11 Jan. 2018].

National Institute of Diabetes and Digestive and Kidney Diseases (2018). The Digestive System & How it Works | NIDDK. [online] National Institute of Diabetes and Digestive and Kidney Diseases. Available at: https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works [Accessed 11 Jan. 2018].

Naushad, M., ALOthman, Z.A., Khan, A.B. and Ali, M., 2012. Effect of ionic liquid on activity, stability, and structure of enzymes: a review. International journal of biological macromolecules, 51(4), pp.555-560.

Ncbi.nlm.nih.gov (2018). How does the urinary system work?. [online] PubMed Health. Available at: https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072568/ [Accessed 11 Jan. 2018].

Ncbi.nlm.nih.gov (2018). Systemic Circulation – National Library of Medicine – PubMed Health. [online] PubMed Health. Available at: https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0023062/ [Accessed 11 Jan. 2018].

Noordergraaf, A., 2012. Circulatory system dynamics (Vol. 1). Elsevier.

Prokop, Z., Gora, A., Brezovsky, J., Chaloupkova, R., Stepankova, V. and Damborsky, J., 2012. Engineering of protein tunnels: keyhole-lock-key model for catalysis by the enzymes with buried active sites. Protein engineering handbook, 3, pp.421-464.

Sherwood, L., 2015. Human physiology: from cells to systems. Cengage learning.