Bioenergetics OCN 626 Lecture 4 Bioenergetics - Life Processes

• USE OF EXTERNAL ENERGY TO PRODUCE ORGANIC MOLECULES

• TRANSFORMATION OF ORGANIC MOLECULES INTO USEFUL CHEMICAL ENERGY

• USE OF CHEMICAL ENERGY TO DO BIOLOGICAL WORK Energy Flows One Way

Heat Light Entropy Phytoplankton Energy or algae Heat Photosynthesis ChemicalEnergy Respiration, Growth, Reproduction Consumers Respiration, Growth, Reproduction Matter is Recycled

Light Phytoplankton Energy 2 or algae Photosynthesis

Organics + O O Consumers +H 2 CO 2 Respiration, Growth, Reproduction Two central energy molecules of life

• ATP - the universal energy currency

• NADH (and related) - electron transfer

Catabolism vs Anabolism

Phototrophs also produce ATP and NAD(P)H using light energy Photosynthesis • Light is captured by pigments • Energy is passed to chlorophyll a • Excited electron in chl a is passed via carriers to NADP+ forming NADPH • “Lost” electron is replaced by splitting of water generating oxygen and protons • Proton gradient is used to drive ATP synthesis – “photophosphorylation” • ATP and NADPH provide the energy and electrons needed to reduce or “ﬁx” CO2 Two Linked Photosystems Non-cyclic vs. Cyclic photophosphorylation

Cyanobacteria and Chloroplasts Cyanobacteria and Chloroplasts Light vs “Dark” Reactions Respiration

• Reduced carbon compounds are oxidized by transfer of electrons to oxygen (or other electron acceptor)

• H2O and CO2 are the end products (for aerobic respiration) • Electron transport results in proton gradient • Produces ATP by “oxidative phosphorylation” Alternate electron Acceptors for Respiration

REACTION DGo´ (kcal/mole) deltaGo´

CH20 + O2 CO2 + H2O -686 - - 5 CH2O + 4 NO3 4 HCO3 + CO2 + 3 H2O + 2 N2 -570 2+ CH2O + 3 CO2 + H2O + 2 MnO2 4 HCO3- + 2 Mn -349 2+ CH2O + 7 CO2 + 4 Fe(OH)3 8 HC03- + 3 H2O + 4 Fe -114 - 2CH20 + SO4 2 HCO3 + H2S -77 CH20 CO2 + CH4 -58 deltaGo´ (kcal/mole) = free energy released per mole of glucose oxidized

CONCEPT: Some energetic transformations are more energetically favorable than others. These will usually occur first under natural conditions - i.e., the most energetically favorable terminal electron acceptor (O2) will be used until it is no longer available, then the environment will favor organisms (bacteria) capable of utilizing alternative electron acceptor to oxidize organic matter.

Photoheterotrophs

• Microbes that need to consume ﬁxed carbon for building blocks, but can produce ATP using light energy to create a proton gradient that drives ATP Synthase ATP Synthase Retinal Conformation Change Drives Pump

www.meta-synthesis.com virtuallaboratory.net Metabolic classiﬁcations

Source of: Carbon Energy e-

Photoautotrophs CO2 light H20, H2S, S Chemoautotrophs CO2 Oxid/Red rxn. H2, H2S, NH3 Heterotrophs organics Oxid/Red rxn organics Photoheterotrophs organics both organics Mixotrophs either both H2O and org

(heterotroph = organotroph) Bacterial Nutrition