Presentation on theme: "The Chemical Basis of Life"— Presentation transcript:
1 The Chemical Basis of Life Chapter 2The Chemical Basis of Life
2 Key ConceptsMolecules form when atoms bond to each other. Chemical bonds are based on electron sharing. The degree of electron sharing varies from nonpolar covalent bonds, to polar covalent bonds, to ionic bonds.Water is essential for life. Water is highly polar and readily forms hydrogen bonds. Hydrogen bonding makes water an extremely efficient solvent.Energy is the capacity to do work or supply heat, and can be (1) a stored potential or (2) an active motion. Chemical energy is a form of potential energy, stored in chemical bonds.
3 Key Concepts, cont’dChemical reactions tend to be spontaneous if they lower potential energy and increase entropy (disorder). An input of energy is required for nonspontaneous reactions to occur.Most of the important compounds in organisms contain carbon. Key carbon-containing molecules formed early in Earth’s history.
4 The AtomThe middle of an atom is the nucleus. Two particles are found in the nucleus:Protons are positively chargedNeutrons are neutralThe outside of an atom contains electronsElectrons travel in orbitalsElectrons on the outside orbital are responsible for bondingHelium and hydrogen are stable with two outside electronsOther elements are stable with eight outside electronsTwo or more different elements share electrons (chemical bond) to achieve stability
6 Importance of Water in Biology Electronegativity: the degree of attraction an element has to electronsWater has one oxygen atomOxygen has more electronegativityOxygen has more attraction to electrons than hydrogenOxygen is partially negativeWater has two hydrogen atomsHydrogen has less electronegativityHydrogen is partially positive
7 Hydrogen Bonding in Water Hydrogen Bond (water): The positive attraction of hydrogen of one water molecule with the negative attraction of oxygen of another water moleculeSpecial properties of water due to its polarity:Adhesion- ability to H bond with other substancesUniversal Solvent- ability to dissolve substances easilyCohesion- ability to H bond with itselfHigh Specific Heat- ability to be resistant to temperature changeHigh Heat of Vaporization- ability to be resistant to vaporizing
8 Energy Energy is the capacity to do work or supply heat Two types of energy:Stored potential (potential energy) - chemical energy stored in bondsActive motion (kinetic energy)Production of heat with movement of moleculesHigh kinetic, Low potential - High potential, Low kinetic
9 Spontaneous Reactions Entropy - the amount of disorderLow entropy = organization in bondsHigh entropy = random movement of moleculesSpontaneous Reactions - low potential energy and high entropyNo energy input requiredNonspontaneous Reactions - high potential energy and low entropyRequires an input of energy
10 Important Carbon Molecules Carbon has 6 protons, 6 neutrons, and 6 electronsCarbon’s 4 valence electrons give is versatile bonding propertiesBonding of carbonCan form up to 4 stable covalent bondsCan form up to 2 stable covalent double bondsCan form up to 1 stable covalent triple bonds
11 Molecule Formation Early in Earth’s History 1. Simples molecules were present in the atmosphere of ancient EarthCarbon Monoxide (CO), Carbon Dioxide (CO2), Hydrogen, Ammonia (NH3), Water, and Nitrogen2. The energy in sunlight drove reactions among the simple molecules.Formaldehyde (H2CO) and Hydrogen Cyanide (HCN)3. Complex molecules are formed.Molecules with carbon-carbon bondsAcetaldehyde, Glycine, and Ribose