Fundamentals of Biology - Carbon and Molecular Diversity PDF

Interdisciplinary Research Center in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Pakistan Fundamentals of Biology Carbon and the Molecular Diversity of Life Dr. Madiha Saeed Assistant Professor Emai...

Interdisciplinary Research Center in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Pakistan Fundamentals of Biology Carbon and the Molecular Diversity of Life Dr. Madiha Saeed Assistant Professor Email: [email protected] Web: https://lahore.comsats.edu.pk/Employees/1314 1 © COPYRIGHT Carbon Compounds and Life Living organisms, such as the tiny hummingbird shown in Figure, are made up of chemicals based mostly on the element carbon. Of all chemical elements, carbon is unparalleled in its ability to form molecules that are large, complex, and varied. 2 © COPYRIGHT  Carbon Compounds and Life Hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P) are other common ingredients of these compounds, but it is the element carbon (C) that accounts for the enormous variety of biological molecules. For historical reasons, a compound containing carbon is said to be an organic compound. Furthermore, almost all organic compounds associated with life contain hydrogen atoms in addition to carbon atoms. Different species of organisms and even different individuals within a species are distinguished by variations in their large organic compounds. 3 © COPYRIGHT  Carbon Compounds and Life The critically important large molecules of all living things From bacteria to elephants fall into just four main classes: 1. Carbohydrates, 2. Lipids, 3. Proteins, 4. Nucleic acids. 4 © COPYRIGHT  Macromolecules On the molecular scale, members of three of these classes— carbohydrates, proteins, and nucleic acids—are huge and are therefore called macromolecules. For example, A protein may consist of thousands of atoms that form a molecular colossus with a mass well over 100,000 daltons. It is noteworthy that biochemists have determined the detailed structure of many of them. The structures of macromolecules can provide important information about their functions. 5 © COPYRIGHT  Macromolecules After considering how macromolecules are built, we can examine the structure and function of all four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids. Like small molecules, large biological molecules exhibit unique emergent properties arising from the orderly arrangement of their atoms. 6 © COPYRIGHT Carbon atoms can form diverse molecules by bonding to four other atoms  The key to an atom’s chemical characteristics is its electron configuration. This configuration determines the kinds and number of bonds an atom will form with other atoms,  and it is the source of carbon’s versatility. Animation: https://www.pearson.com/channels/biology/asset/2f906de4/carbon- is-an-excellent-building-block © COPYRIGHT 7  The Formation of Bonds with Carbon Carbon has 6 electrons, with 2 in the first electron shell and 4 in the second shell.  Thus, it has 4 valence electrons in a shell that can hold up to 8 electrons. A carbon atom usually completes its valence shell by sharing its 4 electrons with other atoms so that 8 electrons are present. Each pair of shared electrons constitutes a covalent bond (Figure). 8 © COPYRIGHT  The Formation of Bonds with Carbon In organic molecules, carbon usually forms single or double covalent bonds. Each carbon atom acts as an intersection point from which a molecule can branch off in as many as four directions. This enables carbon to form large, complex molecules. 9 © COPYRIGHT The Formation of Bonds with Carbon 10 © COPYRIGHT  The Formation of Bonds with Carbon When a carbon atom forms four single covalent bonds, the bonds angle toward the corners of an imaginary tetrahedron. The bond angles in methane (CH4) are 109.5° (Figure 3.2a), And they are roughly the same in any group of atoms where carbon has four single bonds. For example, ethane (C2H6) is shaped like two overlapping tetrahedrons (Figure 3.2b). When two carbon atoms are joined by a double bond, as in ethene (C2H4), the atoms joined to those carbons are in the same plane as the carbons (Figure 3.2c). Keep in mind that molecules are three-dimensional and that the shape of a molecule is central to its function. 11 © COPYRIGHT The Chemical Groups Most Important to Life 12 © COPYRIGHT The Chemical Groups Most Important to Life 13 © COPYRIGHT