Photosynthesis and Cellular Respiration

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Photosynthesis and Cellular Respiration
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Outline

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

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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

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Photosynthesis

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

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Overall Reaction

• 6CO2 6H2O ? C6H12O6 6O2
• carbon dioxide water light
  energy sugar
  oxygen
• 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

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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

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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

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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)

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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

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Harvesting Chemical Energy

• So we see how energy enters food chains
  (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 dont come to us
  the way our cells can use them

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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 cellular respiration
• Overall Reaction
• C6H12O6 6O2 ? 6CO2 6H2O
• sugar
  oxygen energy carbon dioxide
  water
• 
  out

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Where Does Cellular Respiration Takes Place?

• takes place in two parts of the cell

Glycolysis occurs in the Cytoplasm
Krebs Cycle ETC Take place in the Mitochondria
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Review of Mitochondria Structure

• Smooth outer Membrane
• Folded inner membrane
• Folds called Cristae
• Space inside cristae called the Matrix

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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 (fermentation)
• Aerobic cellular respiration

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Cellular Respiration Reactions

• Glycolysis
• Series of reactions which break 6-carbon glucose
  molecule into two 3-carbon molecules 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

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Glycolysis Summary
1. Takes place in the Cytoplasm
2. Anaerobic (Doesnt Use Oxygen)
3. Requires input of 2 ATP
4. Glucose split into two molecules of
Pyruvate or Pyruvic Acid
5. Produces 2 NADH and 4 ATP
6. Pyruvate is oxidized to Acetyl CoA and CO2 is
removed
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Anaerobic Cellular Respiration

• Some organisms thrive in environments with little
  or no oxygen
• Marshes, bogs, gut of animals, sewage treatment
  ponds
• No oxygen used anaerobic not 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)

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Fermentation (2 forms)
Occurs when O2 NOT present (anaerobic) 1. Called
Lactic Acid fermentation in muscle cells (makes
muscles tired) 2. Called Alcoholic fermentation
in yeast (produces ethanol and CO2) Nets only 2
ATP
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Aerobic Cellular Respiration

• Oxygen required aerobic
• 2 more sets of reactions which occur in a
  specialized structure within the cell called the
  mitochondria
• 1. Krebs Cycle
• 2. Electron Transport Chain

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A Little Krebs Cycle History

• Discovered by Hans Krebs in 1937
• He received the Nobel Prize in physiology or
  medicine in 1953 for his discovery
• Forced to leave Germany prior to WWII because he
  was Jewish

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Krebs 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

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Krebs Cycle Summary

• Requires Oxygen (Aerobic)
• Cyclical series of oxidation reactions that give
  off CO2 and produce one ATP per cycle
• Turns twice per glucose molecule
• Produces two ATP
• Takes place in matrix of mitochondria

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Krebs Cycle Summary

• Each turn of the Krebs Cycle also produces 3NADH,
  1FADH2, and 2CO2
• Therefore, For each Glucose molecule, the Krebs
  Cycle produces 6NADH, 2FADH2, 4CO2, and 2ATP

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Kreb Cycle
ATP
NETS 3NADH, 1ATP, 1FADH2, 2CO2
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Electron Transport Chain

• Electron carriers loaded with electrons and
  protons from the Krebs cycle move to this
  chain-like a series of steps (staircase).
• As electrons drop down stairs, energy released to
  form a total of 32 ATP
• Oxygen waits at bottom of staircase, picks up
  electrons and protons and in doing so becomes
  water

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Electron Transport Summary

• 34 ATP Produced
• H2O Produced
• Occurs Across Inner Mitochondrial membrane
• Uses coenzymes NAD and FAD to accept e- from
  glucose
• NADH 3 ATPs
• FADH2 2 ATPs

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Electron Transport Chain Animation
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Glycolysis Diagram
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Energy Tally

• 36 ATP for aerobic vs. 2 ATP for anaerobic
• Glycolysis 2 ATP
• Krebs 2 ATP
• Electron Transport 32 ATP
• 36 ATP
• Anaerobic organisms cant be too energetic but
  are important for global recycling of carbon

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