BIOlecture2_9-1

BIOlecture2_9-1 - 8/31/11 Chapter 2 Chemical Components of...

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8/31/11 1 Chapter 2 Chemical Components of Cells Why is biological chemistry important? Understanding the structure and properties of major classes of biological molecules is essential to understanding cellular function at any level.
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8/31/11 2 • Understand how covalent bonds form molecules from atoms • Understand the nature and importance of noncovalent bonds • Understand the chemical basis of the unique, life- dependent proper:es of water • Understand the key role of carbon in forming biological molecules; stereochemistry is cri:cal! • Know and understand the importance of these four classes of biological molecules – Carbohydrates – Lipids – Proteins – Nucleic Acids
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8/31/11 3 An atom consists charged nucleus charged electron cloud The number of protons in an atom determines its atomic number, and its number of electrons
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8/31/11 4 Types of Chemical Bonds • Strong – Covalent bonds – Ionic bonds • Weak – Hydrogen Bonds – Hydrophobic Interactions – Van der Waals Attractions Figure 2-6 Essential Cell Biology (© Garland Science 2010) Strong Bonds
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8/31/11 5 Strength of Different Chemical Bonds Why is the strength of ionic bonds greatly affected by water but covalent bonds are not? Nonpolar covalent bonds Water has polar covalent bonds Asymmetric charge distribution
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8/31/11 6 The electrical charge effects of water can partially shield charges between ions Hydrogen bonds Electrostatic interaction between a H held in a polar covalent bond and another atom (usually O or N) also held in polar covalent bond. See Panel 2-2 and 2-7
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8/31/11 7 • Water bond angle and polar covalent bonds produces dipolar molecule • Many proper:es of water depend on ability of water molecules to form hydrogen bonds with other (polar or ionic) molecules • Unique proper:es of H 2 O – High boiling point – High speciFc heat – Liquid at RT – Lower density as solid (ice floats) – Surface tension, etc. Other types of hydrogen bonds
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8/31/11 8 Hydrogen Bond to Polar Substances Diferent covalent bond geometries
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8/31/11 9 Hydrophobic Interactions l Water fearing z attraction between nonpolar molecules caused by repulsion from water. Where in a cell might this type of interaction be needed? See Panels 2-2 and 2-7 Hydrophobic interac&ons
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8/31/11 10 van der Waals Attractions • Weak interaction caused by transient electrical charges, dependent on the distance between atoms • In large numbers can be significant in the attraction between macromolecular surfaces See Panel 2-7 Ionization of Water Acids, Bases and Buffers
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8/31/11 11 Quantities of atoms and molecules • Atoms and molecules are very small so a scale factor is generally used to describe quantities - Mole • One Mole is 6 x 10 23 individuals (Avogadro ` s number) • The mass of 1 mole of a substance is determined from its atomic or molecular weight Example:
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BIOlecture2_9-1 - 8/31/11 Chapter 2 Chemical Components of...

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