BIO10 ch 5-7 Energy Lecture 27 27 ENERGY Energy is the ability to do work Energy is considered to exist in two states • kinetic energy: the energy of motion • potential energy: stored energy All the work carried out by living organisms involves the transformation of potential energy to kinetic energy There are many forms of energy • all energy can be converted to heat • Heat energy is the most convenient form of energy to measure Thermodynamics: the study of energy or heat changes Organisms continually have energy changes. Laws of thermodynamics govern these energy changes • 1st Law of Thermodynamics total amount of energy in universe remains constant energy can change from one state to another but it can never be created nor destroyed during the energy conversions, some of the energy is lost as heat energy • 2nd Law of Thermodynamics the amount of disorder, or entropy, in the universe is increasing the increasing disorder means that energy is spontaneously transforming from potential to heat energy Chemical Reactions: the making or breaking of chemical bonds • Reactants/ substrates the starting molecules of a reaction • Products: molecules at the end of the reaction For example: H20 + O2 = H2O2BIO10 ch 5-7 Energy Lecture 28 28 2 kinds of chemical reactions 1. Endergonic: products w/ ↑↑ energy than reactants these reactions are not spontaneous 2. Exergonic: products with less energy than reactants these reactions are spontaneous activation energy: required to start a reaction. • stress existing chemical bonds • Reactions become more spontaneous if their activation energy is lowered • process called catalysis • catalyzed reactions proceed much faster than non-catalyzed reactions How Enzymes Work Enzymes are catalysts used by cells • bind specifically to a molecule • stress the bonds so the rxn more likely to proceed • active site: on surface of enzyme that binds to a reactant • the site on the reactant where the enzyme binds is called the binding site • Enzymes are reused. • Temperature and pH affect enzyme activity o optimum temp range o when temp ↑, the shape of the enzyme changes due to unfolding of the protein chains o optimal pH range o most enzymes work best within pH range of 6 – 8 o exceptions are stomach enzymes that function in acidic rangesBIO10 ch 5-7 Energy Lecture 29 29 ATP: The Energy Currency of the Cell Cells receive energy in forms they can not use directly (sun, food) This energy must be transferred to a usable form. adenosine triphosphate (ATP) is the energy currency of the cell The structure of ATP suits it as an energy carrier. • 3 parts to ATP molecule. a sugar • an adenine nucleotide • chain of 3 phosphate groups o phosphates are negatively charged. takes a lot of chemical energy to hold them together o the phosphates are poised to come apart When the endmost phosphate group is broken off an ATP molecule, energy is released ATP cycles in the cell with respect to its energy needs photosynthesis • some cells convert energy from the sun into ATP and then use it to make sugar where it is stored as potential energy • chloroplasts cellular respiration • cells break down the potential energy in sugars and convert it ATP • mitochondria Chemical Rxns: the passing of e- from one atom/molecule to another • Oxidation: an atom/molecule loses e- • Reduction: an atom/molecule gains e- these reactions always occur together called oxidation-reduction (re-dox) reactions the reduced form of an organic molecule has a higher level of energy than the oxidized formBIO10 ch 5-7 Energy Lecture 30 30 Photosynthesis • The process that captures light energy and transforms into the chemical energy of carbohydrates • It occurs in the Plasma membranes of some bacteria, Cells of algae or the Leaves of plants Photosynthesis take place in the chloroplast • the chloroplast contains internal membranes called thylakoids • thylakoids are stacked together in columns called grana Stroma: semiliquid substance surrounding the thylakloids • The photosystem is the starting point of photosynthesis • it is a network of pigments in the membrane of the thylakoid • the primary pigment of a photosystem is chlorophyll • pigments act as an antenna to capture solar energy • individual chlorophyll pigments pass the captured energy between them How Plants Capture Energy from Sunlight Light is comprised of packets of energy called photons sunlight has photons of varying energy levels possible range of energy levels is represented by an electromagnetic spectrum human eyes only perceive photons of intermediate energy levels this range of the spectrum is known as visible lightBIO10 ch 5-7 Energy Lecture 31 31 Pigments are molecules that absorb light energy • main pigment in plants is chlorophyll • chlorophyll absorbs light at the end of the visible spectrum, mainly blue and red light accessory pigments, absorb light levels that chlorophyll does not • these pigments give color to flowers, fruits, and vegetables • they are present in leaves too but masked by chlorophyll until the fall when the chlorophyll is broken down Photosynthesis takes place in three stages: • All 3 stages occur in the chloroplast o Capture light energy which energizes electrons o Produce high energy molecules (NADP and ATP) needed for the final stage o Use these high energy molecules to produce sugar • Pigments are molecules that absorb light energy • The pigment in human eyes is retinal Absorption: ~ 380 (violet) – 750 (red) nm • The main pigment in plants is chlorophyll o Chlorophyll a and chlorophyll b o Have slight differences in absorption spectra • Carotenoids are accessory pigments o They capture wavelengths not efficiently absorbed by chlorophyll 6H20+ 6CO2+ solar energy=C6H12O6 + 6O2BIO10 ch 5-7 Energy Lecture 32 32 Light Dependent Rxns • Many molecules in chloroplast participate • These reactions occur only when light strikes the chloroplast (thylakoid) • E- pass from one molecule to another (from splitting H2O) • The O2 released when H2O is split is the source of all atmospheric oxygen What happens to energy captured in this light dependent reaction? It is stored in • ATP • NADPH These stable molecules are used for energy