Mitochondria and Chloroplasts

1
Mitochondria and Chloroplasts
2
Introduction to Mitochondria and Chloroplast
Function

• Mitochondria use energy in chemical fuels to
  synthesize ATP via aerobic respiration of
  sugars/fatty acids.
• Up to 36 molecules of ATP produced/glucose
  molecule in aerobic respiration versus 2
  molecules of ATP/glucose molecule using
  glycolysis (anaerobic catabolism).
• Chloroplasts use energy from sunlight to drive
  formation of ATP via photosynthesis.
• This ATP is used in chloroplasts to synthesize
  simple sugars (e.g. to fix C atoms into organic
  molecules).
• - Therefore, chloroplasts are ultimately
  responsible for production of almost all chemical
  fuels used by mitochondria to generate ATP
  required for all other cellular processes.

3
(No Transcript)
4
(No Transcript)
5
Chemiosmotic Couplinglinkage between ATP
synthesis ("chemi") and membrane transport
("-osmosis")

• There are four major players
• - sources of high-energy electrons
• - membrane
• - electron transport chain
• - ATP synthase

6

• There are two stages
• Stage 1 - Electron transport chain
  energetically-favorable movement of electrons
  between carriers causes proton pumping to make H
  gradient
• Stage 2 - ATP synthase uses electrochemical
  energy of proton gradient to make ATP from ADP
  Pi
• Membrane (e.g., inner mitochondrial membrane)
  maintains H gradient essential for coupling

7
Fig. 17-18 in FOB
8
Source of Most ATP synthesis

• Depending upon the organism/organelle,
  electron transport chains can move electrons
  from
• Reduced co-enzymes (NADH/FADH2) to O2 - e.g.,
  mitochondria
• H20 to NADP (requires light energy) e.g.,
  chloroplasts
• Inorganic molecules (H2, sulfur, etc.) to CO2,
  etc. - e.g., Archaebacteria

9
Mitochondrial Structure

• Double membrane structure
• Outer membrane
• Inner membrane
• Intermembrane space
• Inner membrane
• folded into "cristae"
• Matrix

Fig. 16-7 in MCB
10
(No Transcript)
11
Oxidative Phosphorylation The Electron
Transport Chain

• NADH/FADH2 are oxidized to NAD and FAD
• Generates ATP
• Consumes O2, releases H2O
• Requires intact membrane/integral membrane
  proteins

12
Oxidative Phosphorylation in Mitochondria

• Properties of the Electron Transport Chain (ETC)
• 3 complexes that move electrons and pump H
  across the inner mitochondrial membrane
• NADH dehydrogenase complex oxidizes NADH,
  reduces ubiquinone
• Cytochrome b-c1 complex oxidizes ubiquinone,
  reduces cytochrome c
• Cytochrome oxidase oxidizes cytochrome c,
  reduces O2 (to H2O).
• Each complex consists of numerous polypeptide
  subunits and redox co-factors.
• Lateral diffusion of ubiquinone (aka Coenzyme Q)
  and cytochrome C in membrane allows sequential
  reduction of each complex.
• Each electron carrier or complex in the ETC has a
  higher e- affinity increasing redox potential
  means free energy is released at each step.
• Under standard conditions, the overall change
  from NADH to O2 is 1.14 V, or -52 kcal/mole for
  two electrons (vs. 7.3 kcal/mole of ATP
  synthesized from ADP).

13
Properties of the Electron Transport Chain (ETC)

• Electron carriers/ redox centers in the ETC
• organic ubiquinone, flavin (first group reduced
  in NADH dehyd.)
• iron-sulfur centers 5 or more in NADH dehydr.
  complex these are reduced in a specific sequence
  as e- move from the flavin to ubiquinone
• iron in cytochromes (b, c1, c, etc) heme
  protein cytochrome b-c1 complex, etc
• copper cytochrome oxidase (also has cytochromes/
  heme iron) (Cyanide targets metal ions in ETC)
• Each complex pumps protons out of matrix as
  electrons are transported
• 10 H per NADH 5 H per electron ( 2 for
  each of three complexes)
• FADH electrons (from succinate dehydrogenase)
  feed in to ETC at ubiquinone, so fewer protons (6
  total) are pumped than with NADH
• Electrochemical proton gradient is established
  with
• Higher pH in matrix (8 vs. 7 in cytosol) e.g.
  matrix has lower concentration of protons than IM
  space
• Negative membrane potential proton pumping moves
  charges out of matrix

14
Functions of the Electrochemical H gradient

• ATP synthesis
• 3 protons move into the matrix per ATP
• ATP synthetase
• F1 ATPase in matrix/peripheral to membrane
• Transmembrane H carrier ("F0") - blocked by
  oligomycin
• Reversible gives either net synthesis or
  hydrolysis of ATP depending on free energy of
  electrochemical H gradient
• Transport movement of solutes across IMM is
  driven by energy of gradient
• ATP/ADP exchange (antiport)
• electrogenic, net export of - charge to cytosol
  as ATP is pumped out "costs one charge
• helps keep ADP high in matrix, ATP high in
  cytosol (ATP/ADP is 10)
• single ATP molecule can be recycled thousands of
  times per day
• Pi and Pyruvate symported with H
• other charged solutes (Ca2, etc.)
• After deducting energy of transport
• 2.5 ATP/ mitochondrial NADH (20 ATP/glucose)
• 1.5 ATP / FADH2 or cytosolic NADH (6
  ATP/glucose)

15
Fig. 17-8 in FOB
16
Electron Transport Generates a Proton Gradient
Across the Membrane
17
Fig. 16-18 in MCB
18
Fig. 16-17 in MCB
19
(No Transcript)
20
Fig. 16-19 in MCB
21
Reduction Potentials

• Reduction potential (E) electric energy change
  (in volts) that occurs when an atom or molecule
  gains an electron (e.g. it is a measure of the
  readiness with which an atom or molecule gains an
  electron).
• The more positive the reduction potential value,
  the higher the electron affinity of the oxidized
  form (e.g., the greater the tendency of the
  oxidized form of the redox pair to accept
  electrons and become reduced).
• Molecules with large positive Eo values are
  strong electron acceptors (oxidizing agents) and
  their conjugate is a weak electron donor.
  Atoms/molecules with large negative Eo values
  are strong electron donors (reducing agents), and
  their conjugate is a weak electron acceptor.
• Electrons move spontaneously from low to high
  reduction potentials (e.g., go down Table 2-6 in
  MCB).

22
(No Transcript)
23
(No Transcript)
24
Fig. 16-28 in MCB
Fig. 16-29
25
(No Transcript)
26
Binding Change Mechanism of ATP Synthesis by ATP
Synthase
Fig. 17-21 in FOB (or Fig. 16-30 in MCB)
27
Fig. 16-31 in MCB
28
Properties of the Electron Transport Chain (ETC)

• Electron carriers/ redox centers in the ETC
• organic ubiquinone, flavin (first group reduced
  in NADH dehyd.)
• iron-sulfur centers 5 or more in NADH dehydr.
  complex these are reduced in a specific sequence
  as e- move from the flavin to ubiquinone
• iron in cytochromes (b, c1, c, etc) heme
  protein cytochrome b-c1 complex, etc
• copper cytochrome oxidase (also has cytochromes/
  heme iron) (Cyanide targets metal ions in ETC)
• Each complex pumps protons out of matrix as
  electrons are transported
• 10 H per NADH 5 H per electron ( 2 for
  each of three complexes)
• FADH electrons (from succinate dehydrogenase)
  feed in to ETC at ubiquinone, so fewer protons
  are pumped than with NADH
• Electrochemical proton gradient is established
  with
• Higher pH in matrix (8 vs. 7 in cytosol)
• Negative membrane potential proton pumping moves
  charges out of matrix

29
Functions of the Electrochemical H gradient

• ATP synthesis
• 3 protons move into the matrix per ATP
• ATP synthetase
• F1 ATPase in matrix/peripheral to membrane
• Transmembrane H carrier ("F0") - blocked by
  oligomycin
• Reversible gives either net synthesis or
  hydrolysis of ATP depending on free energy of
  electrochemical H gradient
• Transport movement of solutes across IMM is
  driven by energy of gradient
• ATP/ADP exchange (antiport)
• electrogenic, net export of - charge to cytosol
  as ATP is pumped out "costs one charge
• helps keep ADP high in matrix, ATP high in
  cytosol (ATP/ADP is 10)
• single ATP molecule can be recycled thousands of
  times per day
• Pi and Pyruvate symported with H
• other charged solutes (Ca2, etc.)
• After deducting energy of transport
• 2.5 ATP/ mitochondrial NADH
• 1.5 ATP / FADH2 or cytosolic NADH

30
Chloroplasts and Photosynhesis

• MCB- pages 648-655, 658-667
• FOB pages 530-537, 540-547, 549-551

31
Strategy of Photosynthesis (PS)

• Photoreduction light energy is trapped by
  chlorophyll and used to remove electrons and
  protons from water, forming O2.
• Electrons are transferred through protein
  complexes in the thylakoid membrane (electron
  transport chain - ETC) to the ultimate electron
  acceptor, NADP.
• NADPH is formed on stromal side of the thylakoid
  membrane.
• NADPH can then diffuse into stroma to be used in
  Calvin-Benson cycle.
• Electron movement through the ETC provides energy
  to actively transport protons from stroma into
  thylakoid lumen resulting proton gradient used
  to synthesize ATP (see below).
• Photophosphorylation ATP synthesis due to
  protons moving down their concentration gradient
  from the intrathylakoid space into the stroma
  through the chloroplast ATP synthase (CF0F1
  complex)
• Carbon-fixation ATP and NADPH are used to fix
  CO2
• CO2 added to ribulose 1,5-bisphosphate (5C) and
  subsequently rearranged to produce two molecules
  of glyceraldehyde-3-phosphate (3C).
• Known as Calvin-Benson cycle (a.k.a. dark cycle,
  since only steps 1 and 2 require light) and
  occurs in stroma

32
Chloroplast Structure

• The chloroplast has a triple membrane that
  creates three compartments in the organelle
• Outer membrane
• Inner membrane
• Thylakoid membrane
• Functions
• Absorption of light by chlorophyll
• Electron transport
• Synthesis of ATP (ATP synthase)
• Synthesis of NADPH and H
• Grana
• Stroma

See Fig. 18-1 in FOB or Fig. 16-34 in MCB
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Structure and Function of Chlorophylls
Fig. 16-35 in MCB
37
(No Transcript)
38
Excited Chlorophyll Molecules Funnel Energy into
a Reaction Center
39
Fig. 16-38 in MCB
40
Fig. 16-39(a) in MCB
41
Fig. 18-11 in FOB
42
Fig. 16-44 in MCB
43
Fig. 16-42 in MCB
44
Fig. 16-46(a) in MCB
45
Fig. 16-47 in MCB
46
Fig. 16-49 (top) in MCB
47
Fig. 16-49 (bottom) in MCB
48
Mechanisms Contributing to ATP Conservation

• 1. The pH in the stroma is 7 in the dark and
  8 in the light .
• The stromal concentration of Mg 2 increases in
  during illumination.
• Thioredoxin (Tx) becomes inactivated.
• 4. The activated form of rubisco requires
  catalysis by rubisco activase.

49
Photorespiration
50
(No Transcript)
51
(No Transcript)