Photosynthesis and Cellular Respiration

Outline I. Photosynthesis II. Cellular Respiration A. Introduction Reactions II. Cellular Respiration B. Reactions

Photosynthesis Method of converting sun energy into chemical energy usable by cells Autotrophs: self feeders, organisms capable of making their own food Photoautotrophs: use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from light Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

Photosynthesis Photosynthesis takes place in specialized structures inside plant cells called chloroplasts Light absorbing pigment molecules e.g. chlorophyll

Overall Reaction 6CO2 + 6 H2O + light energy → C6H12O6 + 6O2 Carbohydrate made is glucose Water is split as a source of electrons from hydrogen atoms releasing O2 as a byproduct Electrons increase potential energy when moved from water to sugar therefore energy is required

Light-dependent Reactions Overview: light energy is absorbed by chlorophyll molecules-this light energy splits water and excites electrons and boosts them to higher energy levels. H+ are transported through the membrane through proteins to generate gradients. H+ are trapped by electron acceptor molecules (NADH, ATP) that transported to the neighboring transport system (Calvin Cycle) to fuel the dark reaction.

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

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)

Light Reaction: Photosystems

Calvin Cycle (light independent or “dark” reactions) ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose. Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose) Simplified version of how carbon and energy enter the food chain

Photosynthesis Summary

Harvesting Chemical Energy So we see how energy enters food chains (via autotrophs) we can look at how organisms use that energy to fuel their bodies. 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 (glucose) 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 +ATP (energy)

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 (NO OXYGEN) cellular respiration (aka fermentation) Aerobic (OXYGEN) cellular respiration

C.R. Reactions Glycolysis Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate Yields 2 ATP molecules for every one glucose molecule broken down Yields 2 NADH per glucose molecule Process is an ancient one-all organisms from simple bacteria to humans perform it the same way

Anaerobic Cellular Respiration No oxygen used= ‘an’aerobic Some organisms thrive in environments with little or no oxygen = Extremophiles Marshes, bogs, gut of animals, sewage treatment ponds 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)

Respiration without O2 Fermentation reduces organic molecules in order to regenerate NAD+ Ethanol Fermentation occurs in yeast CO2, ethanol, and NAD+ are produced Lactic Acid Fermentation Occurs in animal cells (especially muscles) Electrons are transferred from NADH to pyruvate to produce lactic acid

More Fermentation Total ATP gain: 2 from Glycolysis 2 from Fermentation 4 Total

Aerobic Cellular Respiration Oxygen required=aerobic Two 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 (ETC)

Kreb’s (A.k.a. Citric Acid Cycle) Cycles TWICE IN: Pyruvic acid , Acetyl CoA, NAD+, ADP+P, FAD, H+ OUT:CO2, CoA, NADH, FADH2, ATP The NADH and FADH2 carry H+ to the electron transport chain in which will be used to generate a proton gradient.

Electron Transport Chain The electron transport chain (ETC) is a series of membrane-bound electron carriers. Electron carriers loaded with electrons and protons from the Kreb’s cycle (FADH and NADH) move to this chain-like a series of steps. As the electrons are transferred, some electron energy is lost with each transfer. This energy is used to pump protons (H+) across the membrane from the matrix to the inner membrane space. A proton gradient is established. As electrons give up energy, energy released to form a total of 32 ATP Oxygen (final electron acceptor) waits at the end of the ETC and picks up electrons and protons and in doing so becomes water

Electron Transport Chain

Energy Tally 36 ATP for aerobic vs. 2 ATP for anaerobic Glycolysis 2 ATP (net) Kreb’s 2 ATP Electron Transport 32 ATP 36 ATP Anaerobic organisms can’t be too energetic but are important for global recycling of carbon theoretical energy yields 38 ATP per glucose for bacteria 36 ATP per glucose for eukaryotes

Aerobic Respiration Summary

Energy . Breakdown .

FOOD Break DOWN Where did your lunch go?

ENERGY CYCLE BIG PICTURE: What is produced in photosynthesis fuels cellular respiration and the products of cellular respiration fuels photosynthesis