Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

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

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 + 6H2O + light energy → C6H12O6 + 6O2
C6H12O6 is the sugar 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 excites electrons and boosts them to higher energy levels. They are trapped by electron acceptor molecules that are poised at the start of a neighboring transport system. The electrons “fall” to a lower energy state, releasing energy that is harnessed to make ATP and NADPH.

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+, NADH FAD2+, FADH2

Photosystem: light capturing units. Contain chlorophyll, the light capturing pigment. Found in the Thylacoid Disks.

Electron transport system: sequence of electron carrier molecules that move electrons, capturing the electrons energy as it’s moved to a lower energy level, to make ATP Excited electrons in chlorophyll must be replaced so that cycle may continue. Replacement 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 Overall equation for Light-dependent Reactions: 6H2O + light energy + ADP + NADP+ → ATP + NADPH +6O2

Overall Equation for Photosynthesis: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2 Overall equation for Light-dependent Reactions: 6H2O + light energy + ADP + NADP+ → ATP + NADPH + 6O2

Calvin Cycle (light independent or “dark” reactions)
ATP and NADPH generated in light reactions used to fuel the Calvin Cycle. Takes CO2 and breaks it apart, then reassembles 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

Calvin Cycle Overall Equation for Calvin Cycle:
ATP + NADPH + 6CO2 → C6H12O6 + ADP + NADP+

Light-Dependent and Calvin Reactions Together
Overall Equation for Photosynthesis: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2 Overall equation for Light-dependent Reactions: 6H2O + light energy + ADP + NADP+ → ATP + NADPH + 6O2 Overall Equation for Calvin Cycle: ATP + NADPH + 6CO2 → C6H12O6 + ADP + NADP+

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
Change chemical energy in food into energy cells can use: ATP, (Adenosine Triphosphate). These reactions proceed the same way in plants and animals. Process is called cellular respiration Overall Reaction: C6H12O6 + 6O2 → 6CO2 + 6H2O + 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 cellular respiration (aka fermentation) Aerobic cellular respiration

Glycolysis First reaction of Cellular Respiration
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 Needs 2 ATP molecules to begin Produces 4 ATP molecules Net Yield of 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 occur in 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 FAD2+ to produce NADH and FADH2 Production of only 2 more ATP but loads up the coenzymes electrons which move to the 3rd stage

Electron Transport Chain
Electron carriers loaded with electrons from the Kreb’s cycle and Glycolysis move to this chain-like series of steps (staircase). As electrons drop down stairs, energy released and captured to form ATP, (32 total ATP) Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water. Therefore, Oxygen is the final electron acceptor, and water is produced.

Energy Tally 36 ATP for aerobic vs. 2 ATP for anaerobic
Glycolysis ATP Kreb’s ATP Electron Transport 32 ATP 36 ATP Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

Photosynthesis and Cellular Respiration

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