Lecture 4: Biomolecules PDF

‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4 ‫قسم الكيمياء الحيوية والطبية‬ BIOMOLECULES More than 99% of the human body is composed of 6 elements, i.e. oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus. Human body is composed of about 60% water, 15% proteins, 15% lipids,...

‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4 ‫قسم الكيمياء الحيوية والطبية‬ BIOMOLECULES More than 99% of the human body is composed of 6 elements, i.e. oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus. Human body is composed of about 60% water, 15% proteins, 15% lipids, 2% carbohydrates and 8% minerals. These are 20 amino acids, 2 purines, 3 pyrimidines, sugars (glucose and ribose), palmitate, glycerol and choline. These biomolecules are covalently linked to each other to form macromolecules of the cell, e.g. glucose to glycogen, amino acids to proteins, etc. Major complex biomolecules are Proteins, Polysaccharides, Lipids and Nucleic acids. The macromolecules associate with each other by noncovalent forces to form supramolecular systems, e.g. ribosomes, lipoproteins STABILIZING FORCES IN MOLECULES 1. Covalent Bonds Molecules are formed by sharing of electrons between atoms . 2. Ionic Bonds or Electrostatic Bonds 1 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4 ‫قسم الكيمياء الحيوية والطبية‬ Ionic bonds result from the electrostatic attraction between two ionized groups of opposite charges. They are formed by transfer of one or more electrons from the outermost orbit of an electropositive atom to the outermost orbit of an electronegative atom. This transfer results in the formation of a ‘cation’ and an ‘anion’, which get consequently bound by an ionic bond. Common examples of such compounds include NaCl, KBr and NaF 3. Hydrogen Bonds These are formed by sharing of hydrogen between two electron donors. Hydrogen bonds result from electrostatic attraction between an electronegative atom and a hydrogen atom that is bonded covalently to a second electronegative atom. Normally, a hydrogen atom forms a covalent bond with only one other atom. However, a hydrogen atom covalently bonded to a donor atom, may form an additional weak association, the hydrogen bond with an acceptor atom. In biological systems, both donors and acceptors are usually nitrogen or oxygen atoms, especially those atoms in amino (NH2) and hydroxyl (OH) groups 2 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4 ‫قسم الكيمياء الحيوية والطبية‬ Elements and Compounds All matter in the natural world is composed of one or more of the 92 fundamental substances called elements. An element is a pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means. While your body can assemble many of the chemical compounds needed for life from their constituent elements, it cannot make elements. They must come from the environment. A familiar example of an element that you must take in is calcium (Ca++). Calcium is essential to the human body; it is absorbed and used for a number of processes, including bones. When you consume dairy products your digestive system breaks down the food into components small enough to cross into the bloodstream. Among these is calcium, which, because it is an element, cannot be broken down further. The elemental calcium in cheese, therefore, is the same as the calcium that forms your bones. Some other elements you might be familiar with are oxygen, sodium, and iron , beginning with the most abundant: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). All the elements in your body are derived from the foods you eat and the air you breathe. 3 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4 ‫قسم الكيمياء الحيوية والطبية‬ Major Classes of Compounds in the Human Body Most of the elements are found within compounds. Water and minerals are inorganic compounds. Organic compounds include fat, protein, carbohydrates, and nucleic acids.     Water: Water is the most abundant chemical compound in living human cells, accounting for 65 percent to 90 percent of each cell. It's also present between cells. For example, blood and cerebrospinal fluid are mostly water. Fat: The percentage of fat varies from person to person, but even an obese person has more fat. Protein: In a male, the percentages of protein and water are comparable. It's about 16 percent by mass. Muscles, including the heart, contain a lot of muscle. Hair and fingernails are protein. Skin contains a large amount of protein, too. Minerals: Minerals account for about 6 percent of the body. They include salts and metals. Common minerals include sodium, chlorine, calcium, potassium, and iron. 4 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4  ‫قسم الكيمياء الحيوية والطبية‬ Carbohydrates: Although humans use the sugar glucose as an energy source, there isn't that much of it free in the bloodstream at any given time. Sugar and other carbohydrates only account for about 1% of body mass. Elements in the Human Body Six elements account for 99% of the mass of the human body. The acronym CHNOPS may be used to help remember the six key chemical elements that are used in biological molecules. C is carbon, H is hydrogen, N is nitrogen, O is oxygen, P is phosphorus, and S is sulfur. While the acronym is a good way to remember the identities of the elements, it doesn't reflect their abundance.       Oxygen is the most abundant element in the human body accounting for approximately 65% of a person's mass. Each water molecule consists of two hydrogen atoms bonded to one oxygen atom, but the mass of each oxygen atom is much higher than the combined mass of the hydrogen. In addition to being a component of water, oxygen is essential for cellular respiration. Carbon is contained in all organic compounds, which is why carbon is the second most abundant element in the body, accounting for about 18% of body mass. Carbon is found in proteins, carbohydrates, lipids, and nucleic acids. It's also found in carbon dioxide. Hydrogen atoms are the most numerous type of atom in a human, but because they are so light, they only make up around 10% of the mass. Hydrogen is in water, plus it's an important electron carrier. Nitrogen is about 3.3% of body mass. It's found in proteins and nucleic acids. Calcium accounts for 1.5% of body mass. It's used to build bones and teeth, plus it's important for muscle contraction. Phosphorus is about 1% of body mass. This element is found in nucleic acids. Breaking bonds connecting phosphate molecules is a major component of energy transfer. 5 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ ‫كليه الطب‬ lecture 4      ‫قسم الكيمياء الحيوية والطبية‬ Potassium is around 0.2-0.4% of the mass of a person. It's used in nerve conduction. Potassium is a key cation or positivelycharged ion in the body. Sulfur is found in some amino acids and proteins. It's about 0.2-0.3% of body mass. Sodium, like potassium, is a positively-charged ion. It's about 0.1-0.2% of body mass. Sodium helps regulate the electrolyte balance in the body and maintain homeostasis with respect to the volume of water in the blood and cells. Although aluminum and silicon are abundant in the earth's crust, they are found in trace amounts in the human body. Other trace elements include metals, which are often cofactors for enzymes (e.g., cobalt for vitamin B12). Trace elements include iron, cobalt, zinc, iodine, selenium, and flourine. Reference TEXTBOOK OF BIOCHEMISTRY Sixth Edition For Medical Students DM VASUDEVAN MBBS MD FAMS FRCPath Distinguished Professor of Biochemistry College of Medicine, Amrita Institute of Medical Sciences, Cochin, Kerala (Formerly Principal, College of Medicine, Amrita, Kerala) (Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim) E-mail: [email protected] SREEKUMARI S MBBS MD Professor, Department of Biochemistry Sree Gokulam Medical College and Research Foundation Thiruvananthapuram, Kerala E-mail: [email protected] KANNAN VAIDYANATHAN MBBS MD Clinical Associate Professor, Department of Biochemistry and Head, Metabolic Disorders Laboratory Amrita Institute of Medical Sciences, Kochi, Kerala Email: [email protected] 6