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UT Arlington BIOL 2457 - Chapter 2: The Chemical Level of Organization

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BIOL 2457 1st Edition Lecture 4 Outline of Last Lecture I Metabolism and Responsiveness Outline of Current Lecture I II III IV V VI VII VIII IX X XI XII XIII XIV XV XVI XVII Introduction Since chemicals compose your body and all body activities are chemical in nature it is important to become familiar with the language and fundamental concepts of chemistry How Matter is Organized Chemical Elements a All forms of matter are composed of chemical elements which are substances that cannot be split into simpler substances by ordinary chemical means b Elements are given letter abbreviations called chemical symbols c Trace elements are present in tiny amounts Structure of Atoms Units of matter of all chemical elements are called atoms An element is a quantity of matter composed of atoms of the same type a Atoms contain Nucleus protons p neutrons no Electrons e surround the nucleus as a cloud electron shells are designated regions of the cloud Two Representations of the Structure of an Atom a Atomic Number and Mass Number Atomic number is the number of protons in the nucleus Mass number is the sum of the protons and neutrons in the nucleus Atomic Mass Mass is measured as a dalton atomic mass unit Masses of subatomic particles a Neutron mass of 1 008 daltons b Proton mass of 1 007 daltons c Electron has mass of 0 0005 dalton Atomic mass atomic weight is close to the mass number of the element s most abundant isotope Atomic Number and Mass Number Atomic Mass a The atomic mass also called the atomic weight of an element is the average mass of all of its naturally occurring isotopes and reflects the relative abundance of isotopes with different mass numbers XVIII XIX XX XXI XXII XXIII XXIV XXV XXVI XXVII XXVIII XXIX XXX XXXI XXXII XXXIII XXXIV XXXV XXXVI XXXVII XXXVIII b The mass of a single atom is slightly less than the sum of the masses of its neutrons protons and electrons because some mass less than1 was lost when the atom s components came together to form an atom Ions Molecules Compounds Ions a An atom that gave up or gained an electron b Written with its chemical symbol and or Molecule a Formed when atoms share electrons b Written as a molecular formula showing the number of atoms of each element H2O Free Radicals A free radical is an electrically charged atom or group of atoms with an unpaired electron in its outermost shell They are unstable and highly reactive but can become stable a By giving up an electron b By taking an electron from another molecule Antioxidants are substances that inactivate oxygen derived free radicals Free Radicals Chemical Bonds The atoms of a molecule are held together by forces of attraction called chemical bonds The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell also called the valence shell Ionic Bonds When an atom loses or gains a valence electron ions are formed Figure 2 4a a Positively and negatively charged ions are attracted to one another b Cations are positively charged ions that have given up one or more electrons they are electron donors c Anions are negatively charged ions that have picked up one or more electrons that another atom has lost they are electron acceptors Covalent Bonds Covalent bonds are formed by the atoms of molecules sharing one two or three pairs of their valence electrons a Covalent bonds are common and are the strongest chemical bonds in the body b Single double or triple covalent bonds are formed by sharing one two or three pairs of electrons respectively Covalent bonds may be nonpolar or polar a In a nonpolar covalent bond atoms share the electrons equally one atom does not attract the shared electrons more strongly than the other atom Polar Covalent Bonds Formed by the unequal sharing of electrons between atoms Example In a water molecule oxygen attracts the hydrogen electrons more strongly a Oxygen has greater electronegativity as indicated by the negative Greek delta sign Hydrogen Bonds Approximately 5 as strong as covalent bonds XXXIX XL XLI XLII XLIII XLIV XLV XLVI XLVII XLVIII XLIX L LI LII LIII LIV LV LVI LVII LVIII LIX LX LXI LXII LXIII Useful in establishing links between molecules or between distant parts of a very large molecule Form large 3 D molecules which are often held together by a large number of hydrogen bonds Hydrogen Bonds Are weak intermolecular bonds servings a links between molecules Help determine three dimensional shape of some molecules Result from attraction of oppositely charged parts of molecules rather than from sharing of electrons In water provides considerable cohesion which creates a very high surface tension Chemical Reactions Occur when new bonds form and or old bonds are broken Metabolism the sum of all the chemical reactions in the body Law of conservation of energy a The total mass of reactants equals the total mass of the products Forms of Energy and Chemical Reactions Energy is the capacity to do work Kinetic energy is the energy associated with matter in motion Potential energy is energy stored by matter due to its position Energy Transfer in Chemical Reactions An exergonic reaction is one in which the bond being broken has more energy than the one formed so that extra energy is released usually as heat occurs during catabolism of food molecules An endergonicreaction is just the opposite and thus requires that energy be added usually from a molecule called ATP to form a bond as in bonding amino acid molecules together to form proteins Activation Energy Energy required to break chemical bonds in the reactant molecules so a reaction can start Factors that Cause a Collision Chemical Reaction Concentration Temperature Catalysts chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur a A catalyst does not alter the difference in potential energy between the reactants and products It only lowers the amount of energy needed to get the reaction started b A catalyst helps to properly orient the colliding particles of matter so that a reaction can occur at a lower collision speed c The catalyst itself is unchanged at the end of the reaction it is often re used many times Catalysts Chemical Reactions LXIV LXV LXVI LXVII LXVIII LXIX LXX LXXI LXXII LXXIII LXXIV LXXV LXXVI LXXVII LXXVIII LXXIX LXXX LXXXI LXXXII LXXXIII LXXXIV LXXXV LXXXVI LXXXVII LXXXVIII LXXXIX XC Types of Chemical Reactions Synthesis reactions Anabolism a A B AB Decomposition


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UT Arlington BIOL 2457 - Chapter 2: The Chemical Level of Organization

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