Chapter 5a Cell Respiration

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Chapter 5a - Cell Respiration

• Cell respiration is a decomposition pathway that
  provides the Energy cells need to function.
• Decomposition release E by breaking down food
  molecules to simpler forms
• Synthesis Combine simple molecules to form
  complex molecules (needs E)
• Cell Respiration is a series of reactions that
  release energy as the organisms break down sugar
  and other substances to CO2 and H2O.
• Each individual reaction releases some free
  Energy, and some of it is converted to ATP, which
  is needed for life processes.
• Free E is released by oxidizing sugars or other
  organic substrates.

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Aerobic and Anaerobic respiration

• Aerobic Respiration (with Oxygen present)
• - O2 is the oxidizing agent
• - O2 receives e- from the decomposed substrates
  (complex molecules)
• Anaerobic respiration (no Oxygen present)
• - A nitrogen or sulfur compound substitutes for
  O2
• - The substrate may only be partially
  decomposed, releasing less E
• __________________________________________________
  ______

3
Cell respiration versus Breathing

• Not the same thing, but they do have a
  relationship
• Breathing ( exchange of gases CO2 and O2
  between the external environment and the
  organism). Various organisms have various
  structures for this (body surface, gills, lungs,
  stomata, etc.)
• Cell respiration (Breaking down complex molecules
  as source of E, removal of waste CO2 excess
  water from each individual cell, and renewal of
  O2).
• ____________________________________________
• - All organisms respire (use the chemical
  reactions of cell respiration).
• - Not all organisms use breathing in the same
  sense as mammals use their lungs for gas
  exchange. It depends on the specific structures
  available for different organisms.
• - Some organisms dont require oxygen, but they
  do cell respiration to obtain Energy from complex
  molecules, and to remove cellular waste.

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Aerobic Respiration- Raw materials

• 1) Carbohydrates (sugars) The main sources of
  Energy for cell respiration.
• Glucose C6H12O6, and
• Glucose-Phosphate C6H11O6 H3PO3
• - Animals Produce them by digesting
  carbohydrates (from food), or breaking down
  Glycogen (animal starch, a complex
  polysacharide) stored in liver or muscles.
• - Plants Produce them by breaking down sucrose
  and starch (complex storage polysacharide)
• 2) Fats (lipids) Used for special needs (see
  later)
• 3) Proteins Used for special needs (see later)
• __________________________________________________
  ____
• enzymes
• C6H12O6 6O2 -------------? 6CO2
  6H2O Energy
• Glucose oxygen
  carbon dioxide water

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Products of cell respiration

• By breaking down raw materials during cell
  respiration, 2 main products are made
• 1) Carbon skeletons needed in biosynthesis of
  other molecules, and
• 2) ATP needed to fuel cellular processes.

6
Crash course on oxidation / reduction

• Oxidation
• - Removal of an e- from a molecule
• - Losing a hydrogen ion (H proton). (This is
  the most frequent case in biological systems)
• Reduction
• - Gaining an e-
• - Gaining a hydrogen ion (H).
• ___________________________________
• When a molecule is oxidized, the resulting e- and
  H will be accepted by another molecule. Thus,
  whenever a molecule is oxidized, another must be
  reduced.

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Aerobic respiration The lineup of players

• 1- Glucose (6-C, C6H12O6) broken down
• 2- 3-Carbon molecules formed
• 3- CO2 released
• 4- O2 must be present for some stages
• 5- 2-Carbon molecules formed
• 6- NAD (nicotinamide adenine dinucleotide)
  reduced to NADH, then regenerated
• 7- FAD (flavin adenine dinucleotide) reduced to
  FADH2
• 8- H2O formed
• ___________________________________
• ATP is formed at each decomposition reaction
• NADH and FADH2 (reduced compounds) they carry
  hydrogen ions (protons H) and e- to the
  electron transport system.

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Aerobic respiration 3 stages

• Glycolysis (Breakdown of
• sugars). Partial ? oxidation of
  glucose (6-C) by enzymes, splitting it into 2 3-C
  molecules. ATP is produced.
• 2) Krebs Cycle. 1 CO2 ? molecule is
  released in the complete oxidation of each of the
  2 3-C molecules. An enzyme is involved, and more
  ATP is formed.

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Aerobic respiration 3 stages

• 3) Electron transport system. Synthetizes most of
  the ATP generated during respiration. Receives
  the Energy of protons (H) and e- from each
  oxydation. H and e- are transferred to O2,
  forming H2O.
• 3)?

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Some similarities of Photosynthesis and cellular
respiration

• Hydrogen-carrying molecules in cells
• - NADPH (from photosynthesis)
• - NADH, FADH2 (from respiration)
• All move H in cells
• All are oxidized and reduced in cycles, changing
  from the oxidized form (with superscript ), to
  the reduced form (with H at the end).
• At the end of the electron transport systems, the
  H carried by them will reduce oxygen to form
  water molecules.

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Where does cell respiration take place?

• Complex cells
• Bacteria
  Multicellulars
• __________________________________________________
  _________
• e-transport Cell membrane Cristae of
• System (most Mitochondria
• ATP synthesis)
• __________________________________________________
  
• Krebs Cycle Cytoplasm Matrix of Mitochondria
• __________________________________________________
  
• Glycolysis, Cytoplasm Cytoplasm
• Fermentation
• __________________________________________________
  
• Mitochondria The powerhouses of the cell
• - Membrane- double layer as in all cells
• Inner layer many folds (cristae)
• - Matrix Fluid filled
• In Complex cells, the number of mitochondria is
  related to the energy expenditure of each type of
  cells, ranging from a few to several thousand.

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Glycolysis (from glucose to pyruvate)

• 1 Glucose is converted to Glucose-6-phosphate (1
  ATP used, enzyme involved)
• Glucose-6-phosphate changed to diphosphate (gains
  1 more P)(1 ATP used, another enzyme)
• G-6-diphosphate splits into two 3-C
  sugar-phosphates
• Partial oxidation of two 3-C molecules to form
  two 3-C pyruvic acid molecules NAD reduced to
  NADH (2 ATP formed per each 3-C molecule)
• In plants, Glucose or Glucose-P can enter in step
  a), or 3-C sugar-P can enter in step c).
• In animals, Glucose enters as in diagram.
• _____________________________
• Results (per molecule of Glucose)
• 4 ATP (but 2 were spent),
• 2 NADH,
• 2 pyruvate,
• Carbon skeletons

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Glycolysis- Net results and fate of Pyruvate

• Net results of Glycolysis (from each Glucose)
• - 2 ATP
• - 2 NADH
• - 2 Pyruvate
• - Carbon skeletons
• ___________________________________
• Glycolysis begins both aerobic and anaerobic cell
  respiration
• Fate of Pyruvate
• With sufficient O2, the next step is the Krebs
  Cycle (Aerobic, the most efficient method)
• Without sufficient O2, the next step is
  fermentation (Anaerobic, less efficient).
• In animals, if insufficient O2, the process is
  lactic acid fermentation
• - NADH changes to NAD and goes back to
  glycolysis, but ending in less ATP production
• - Pyruvate changes to Lactate.

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The Krebs Cycle (from pyruvate to CO2)

• (prior to Krebs Cycle) 2 Pyruvate enter
  mitochondria. Enzymes take 1 CO2 from each,
  changing them to acetate (2-C organic acid). 1
  NAD reduced to NADH. CoA (Coenzyme A, an acetate
  carrier molecule) binds to acetate, becoming
  Acetyl-CoA and carries it to Krebs cycle.
• Acetyl-CoA brings acetate. CoA and acetate are
  separated. CoA is released and reused. Enzyme
  combines acetate with oxaloacetate (4-C acid) to
  form citrate (6-C acid).
• c-d) Citrate is oxidized in several steps,
  releasing CO2, and H atoms which reduce 2 NAD to
  2 NADH, and a 4-C organic acid.
• e-f) 4-C organic acid is oxidized, resulting in
  a new oxaloacetate that enters a new round of the
  Krebs Cycle. 1 NAD is reduced to NADH and 1 FAD
  is reduced to FADH2, and 1 ATP formed.

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The e- transport systemSynthesis of ATP

• ATP is synthesized in mitochondria and released
  to be used by the cell.
• NADH and FADH2 carry H atoms into e- transport
  system.
• Enzymes and Cytochromes (proteins) in cristae
  separate H into H and e-. Electrons are
  transported step by step thru the system, each
  step releasing free energy that drives the
  synthesis of ATP by ATP synthetase enzyme complex
  .
• Each NADH can produce 3 ATP each FADH2 can
  produce 2 ATP.
• At the end, H2O is formed by a terminal
  cytochrome, which reduces O2 with e- and H from
  NADH and FADH2 (only step requiring oxygen).

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Summary of aerobic respiration

• As glucose is oxidized in glycolysis and Krebs
  cycle, NAD and FAD are reduced to NADH and FADH2,
  and pass e- to the electron transport system.
• H20 is formed by reduction of O2 with e- and H
  from NADH and FADH2.
• NAD and FAD are recycled and re-enter respiration
  in the oxidation of more glucose.
• For each glucose molecule entering aerobic
  respiration, up to 38 ATP are produced (8 from
  glycolysis, 6 from pyruvate to Acetyl CoA, 24
  from Krebs cycle).

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Review of molecules involved

• Molecule What is it ? How it
  participates When
• Kinese enzyme cascade series of enzymes make
  glucose from glycogen
• or starch before g.lys
• Glucose 6-C sugar broken down
  (oxidized) glycolysis
• Glucose-6-phosphate 6-C sugar
  phosphate formed glycolysis
• Pyruvic acid 3-C acid formed (with
  O2) glycolysis
• Pyruvate 3-C sugar formed (with
  O2) end of g.lysis
• NAD, NADH H carrier carries H atoms
  (e-, H) g.lysis, Krebs
• FAD, FADH2 H carrier carries H atoms
  (e-, H) Krebs
• ATP storage of free E formed,
  spent g.lysis, Krebs
• Lactic acid 3-C acid formed (if no
  O2) glycolysis
• Lactate 3-C sugar formed (if no
  O2) end of g.lysis
• Ethanol (ethyl alcohol) alcohol formed (if
  no O2) bacteria
• Acetic acid (vinegar) acid formed (if no
  O2) bacteria
• Acetate 2-C organic acid formed pre-Kre
  bs
• CoA (Coenzyme A) carrier enzyme binds to
  acetate pre-Krebs
• Acetyl CoA complex of CoAacetate delivers
  acetate pre-Krebs
• Oxaloacetate 4-C acid
• (complex of AcetylCoAacetate)
  formed enters Krebs

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Bacteria do it different !

• They only have 1 cell and dont have
  mitochondria.
• Glycolysis and Krebs Cycle take place in the
  cells cytoplasm. The electron transport system
  is located in the cell membrane.
• Some bacteria (not all !!!) are anaerobic the
  oxidizing agent is not oxygen but another
  compound. They dont reduce O2 to form water, but
  produce other reduced sulfur or nitrogen
  compounds (H2S, NH3).
• Types of bacteria depending on O2 utilization
• - Facultative Aerobes Depending on O2
  availability, they can switch back and forth
  between fermentation (anaerobic) and aerobic
  respiration.
• - Obligate Anaerobes Cannot live in the
  presence of O2. They generate ATP from
  fermentation or anaerobic respiration.
• __________________________________________________
  ______
• Most higher organisms are Obligate Aerobes they
  require O2 for most processes and cannot survive
  long without it.

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Linking Cell Respiration Photosynthesis

• Oxygen is needed to oxidize glucose (not for the
  initial lysis).
• - Without O2, pyruvate from glucose must be
  fermented (anaerobically), a less efficient
  process that produces less ATP.
• - With O2, pyruvate enters Krebs Cycle,
  producing more ATP. Thus, animals gain
  proportionally more E from food than anaerobes.
• Hydrogen carriers (NADP from Photosynthesis) and
  NAD, FAD (from respiration) help cells catch free
  energy into ATP molecules.
• O2 for the e- transport system of aerobic
  respiration comes from gas exchange organs
  (lungs, stomata, gills), and distributed with
  circulation systems.
• Raw materials
• - Cell respiration O2 and carbohydrates
  (from photosynthesis)
• - Photosynthesis CO2 and water (from
  respiration)
• Both Respiration and photosynthesis produce
  carbon skeletons for biosynthesis.

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Cell Respiration Fill all the boxes (24)