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Chapter 5a Cell Respiration

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Title: Chapter 5a Cell Respiration


1
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.

2
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.

4
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

5
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.

7
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.

8
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.

9
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)?

10
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.

11
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.

12
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

13
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.

14
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.

15
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).

16
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).

17
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

18
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.

19
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.

20
Cell Respiration Fill all the boxes (24)
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