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Photosynthesis and Cellular Respiration. Outline. I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions. Review: What is ATP?. Review: What is ATP?. Adenosine Triphospate Adenine + Ribose + 3 Phosphate groups
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Outline I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions
Review: What is ATP? • Adenosine Triphospate • Adenine + Ribose + 3 Phosphate groups • One of the principle chemical compounds that cells use to STORE and RELEASE energy.
Storing Energy • ADP (Adenine diphospate) • Only 2 phosphates (hence the “di”) • Key to how living things STORE energy! • (When energy is available, the cell stores it by adding phosphate to make ATP=stored battery ready to power cell).
Releasing Energy • “Shooting off” 1 phosphate ENERGY!! • ATP provides energy for a variety of cellular activities! • Ex: active transport across cell membranes, protein synthesis, and muscle contraction
ADP ATP • Cells regenerate ATP from ADP as needed by using energy in FOOD, aka …
ADP ATP • Cells regenerate ATP from ADP as needed by using energy in FOOD, aka … GLUCOSE!
Photosynthesis • Photo = light • Synthesis = putting together
Photosynthesis • Converting sun energy into chemical energy usable by cells (glucose) • Autotrophs: self feeders, organisms capable of making their own food • Photoautotrophs: use sun energy e.g. plants photosynthesis-makes glucose from light • Chemoautotrophs: use chemical energy, NOT sunlight • e.g. bacteria that use sulfide or methane
Photosynthesis • Photosynthesis takes place in specialized structures inside plant cells called chloroplasts • Light absorbing pigment molecules e.g. chlorophyll
Why are leaves green? • Chlorophyll absorbs all of the light waves except green. Because the green is not absorbed, it is reflected, so that is the only color wavelength our eye can pick up. • Accessory pigments – help to fill in this gap • Carotenoids – orange (like carrots) • Xanothphyl – yellow
Inside the chloroplast • Thylakoids: Sac-like photosynthetic membranes arranged in stacks. • Organize chlorophyll/other pigments into photosystems (clusters that collect light).
Overall Reaction • 6CO2 + 6H2O + light energy → C6H12O6 + 6O2 • Carbon dioxide + water + light glucose + oxygen KNOW BOTH OF THESE EQUATIONS. YOU WILL SEE THEM AGAIN!
2 types of reactions in photosynthesis • Light dependent • Light independent (CALVIN CYCLE)
Electron Carriers • Overview: • Sun excites electrons = gain energy • Need special carrier! (Think red-hot coal!) • Electron acceptor molecules (ex: NADP+) • NADP+ uses hydrogen ions (H+) to trap some of the sunlight in chemical form = converts to NADPH. • Carries e- to other chemical reactions in the cell
Light Dependent Reactions • Occur in the thylakoid! • Produce oxygen gas • Converts ADP and NADP+ into energy carriers ATP + NADPH
Light Dependent Reactions • Overview: Pigments in Photosystems absorb light = electrons gain energy • Electrons are passed on to the Electron Transport Chain • Does the chorophyll run out of electrons?
Light Dependent Reactions • In Thylakoid: • System that provides new e- to chlorophyll to replace ones lost • Electrons come from water! H2O • Enzymes on inner surface membrane of thylakoid break up each H2O into: • 2 e- (replace e- lost to the ETC) • 2H+ions (released inside thylakoid membrane) • 1 oxygen atom (released into the air!)
Light-dependent Reactions 5. H+ ions cant cross membrane directly • ATP synthase! • Allows H+ ions to pass through it! • As it turns, binds ADP and phosphate group …. • Producing ATP!
Energy Shuttling • Recall ATP: cellular energy-nucleotide based molecule with 3 phosphate groups bonded to it, when removing the third phosphate group, lots of energy liberated= superb molecule for shuttling energy around within cells. • Other energy shuttles-coenzymes (nucleotide based molecules): move electrons and protons around within the cell NADP+, NADPH NAD+, NADP FAD, FADH2
This light dependent reaction is the source of nearly ALL of the oxygen in Earth’s atmosphere! Thanks photosynthesis!
Light-dependent Reactions • Photosystem: light capturing unit, contains chlorophyll, the light capturing pigment • Electron transport system: sequence of electron carrier molecules that shuttle electrons, energy released to make ATP • Electrons in chlorophyll must be replaced so that cycle may continue-these electrons come from water molecules, Oxygen is liberated from the light reactions • Light reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)
Calvin Cycle (light independent or “dark” reactions) • ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and H+ to make glucose. • Simplified version of how carbon and energy enter the food chain
Harvesting Chemical Energy • Plants and animals both use products of photosynthesis (glucose) for metabolic fuel • Heterotrophs: must take in energy from outside sources, cannot make their own e.g. animals • When we take in glucose (or other carbs), proteins, and fats-these foods don’t come to us the way our cells can use them
Cellular Respiration Overview • Transformation of chemical energy in food into chemical energy cells can use: ATP • These reactions proceed the same way in plants and animals. Process is called cellular respiration • Overall Reaction: • C6H12O6 + 6O2→ 6CO2 + 6H2O
Cellular Respiration Overview • Breakdown of glucose begins in the cytoplasm: the liquid matrix inside the cell • At this point life diverges into two forms and two pathways • Anaerobic cellular respiration (aka fermentation) • Aerobic cellular respiration
C.R. Reactions • Glycolysis • Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate • Process is an ancient one-all organisms from simple bacteria to humans perform it the same way • Yields 2 ATP molecules for every one glucose molecule broken down • Yields 2 NADH per glucose molecule
Anaerobic Cellular Respiration • Some organisms thrive in environments with little or no oxygen • Marshes, bogs, gut of animals, sewage treatment ponds • No oxygen used= ‘an’aerobic • Results in no more ATP, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis. • End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)
Aerobic Cellular Respiration • Oxygen required=aerobic • 2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria • 1. Kreb’s Cycle • 2. Electron Transport Chain
Kreb’s Cycle • Completes the breakdown of glucose • Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2O • Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2 • Production of only 2 more ATP but loads up the coenzymes with H+ and electrons which move to the 3rd stage
Electron Transport Chain • Electron carriers loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase). • As electrons drop down stairs, energy released to form a total of 32-34 ATP • Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water
Energy Tally • 34-36 ATP for aerobic vs. 2 ATP for anaerobic • Glycolysis 2 ATP • Kreb’s 2 ATP • Electron Transport 32-34 ATP 36-38 ATP • Anaerobic organisms can’t be too energetic but are important for global recycling of carbon