Introduction to the study of cell biology

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Chapter 6
Mitochondria Energy Conversion
Mitochondria in all eukaryotic cells Mit
Oxidative phosphorylation ? ATP
ZHOU Yong Department of Biology XinJiang Medical
University
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Teaching Requirements

• 1. Mastering ultrastructure of mitochondria
  function of mitochondria oxidative
  phosphorylation.
• 2. Comprehending relationship between structure
  and function of mitochondria.
• 3. Understanding genomes of mitochondria
  proliferation of Mitochondria

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• I. Distribution of Mitochondria

• The size and number of mitochondria reflect the
  energy requirements of the cell.

Figure. Relationship between mitochondria and
microtubules.
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Figure. Localization of mitochondria near sites
of high ATP utilization in cardiac muscle and a
sperm tail. 
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Figure. Mitochondrial plasticity.     Rapid
changes of shape are observed when a
mitochondrion is visualized in a living cell.
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Figure. Fractionation of purified mitochondria
into separate components.    
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• II. Mitochondrial ultrastructure

1. Inner membrane
2. Out membrane
3. Intermembrane space
4. Matrix

• Inner and outer mitochondrial membranes enclose
  two spaces the matrix and intermembrane space.

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Electron micrograph of a mitochondrion
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1.Ribosome 2.Cristae 3.DNA 4.ATP synthase
particles
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The inner membrane is folded into Cristae
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Some morphology of mitochondrial cristae
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ATP synthase particles Elementary particles F0-F1
ATPase complex F0-F1 coupling factor

1. Head sector
2. Stalk sector
3. Membrane sector

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The structure of the ATP synthase particle

• Molecular basis of phosphorylation

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Outer membrane Contains channel-forming
protein, called Porin. Permeable to all
molecules of 5000 daltons or less.
Inner membrane (Impermeability) Contains
proteins with three types of functions (1)
Electron-transport chain Carry out oxidation
reactions (2) ATP synthase Makes ATP in
the matrix (3)
Transport proteins Allow the passage of
metabolites
Intermembrane space Contains several enzymes
use ATP to phosphorylate other nucleotides.
Matrix Enzymes Mit DNA, Ribosomes, etc.
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III. Oxidative phosphorylation
Fig. Three stages of cellular catabolism that via
controlled burning conserve energy for use in
heterotrophic cells. Food is hydrolysed into
small molecules in the cytoplasm. Glycolysis is
also cytoplasmic. Pyruvate and other substrates
are taken up by mitochondria under aerobic
conditions and through TCA - Krebs cycle and
electron transport converted into waste molecules
and products ATP and NADH.
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• Localization of metabolic functions within the
  mitochondrion

Inner membrane
Outer membrane
Phospholipid synthesis
Electron transport
Fatty acid desaturation
Oxidative phosphorylation
Fatty acid elongation
Metabolite transport
Intermembrane space
Matrix
Nucleotide phosphorylation
Pyruvate oxidation
TCA cycle
ß oxidation of fats
DNA replication, RNA transcription, Protein
translation
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Complete lysis of glucose can be divided into
four steps

1. Glycolysis
2. Formation of the acetyl CoA
3. Tricarboxylic acid cycle (TCA)
4. Oxidative phosphorylation

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ATP molecule energy currency or energy carrier
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A. Glycolysis
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• Fig. Summary of glycolysis.
• glycolysis can provide sufficient energy for
  growth of anaerobic organisms and tissues, or
  autotrophic cells in the dark.
• the reactions only partially oxidize glucose to
  ethanol or pyruvate
• occur in cytoplasm.

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B. Formation of the acetyl CoA

1. Pyruvate enter into mitochondrial matrix from
   cytoplasm.
2. Catalyzed by pyruvate dehydrogenase

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C. Tricarboxylic acid cycle (TCA)
Krebs cycle Citric acid cycle
1. Occur in mitochondrial matrix. 2. Require
oxygen.
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• Fig. TCA (tricarboxylic acid) cycle.
• MAIN FUNCTIONS
• oxidation of substrates
• reduction of cofactors
• substrate level phosphorylation
• regeneration of acceptor
• release of 3CO2 per turn

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The main points to remember 1.The cycle uses
acetyl CoA as the immediate substrate - this can
come from beta oxidation of fatty acids OR from
pyruvate via glycolysis. 2.The products are
reducing molecules NADH and FADH2 GTP CO2 and a
molecule of oxaloacetate is regenerated. 3.One
way of describing the stoichiometry of the TCA
cycle is as follows Glucose 6H2O 10NAD
2FAD 4ADP 4Pi gt 6CO2 10NADH 10H
2FADH2 4ATP 4H2O
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Net result of the glycolytic pathway and the
citric acid cycle
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D. Oxidative phosphorylation

1. Electron carriers (cofactors)

(1) nicotinamide adenine dinucleotide (NAD)
RH
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(2) Flavoproteins a. flavin mononucleotide
(FMN)
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b. flavin adenine dinucleotide (FAD)
Oxidized form
Reduced form
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(3) Ubiquinone
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(4) Cytochromes
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(5) Iron-sulfur proteins
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2. Electron-transport chain (respiratory chain)
Electron-carrying prosthetic groups in the
respiratory chain
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Mitochondrial electron transport chain shown in
the context of redox potential (I.e. free energy
content per electron) of the components. Most of
the energy is CONSERVED in the proton gradient
and membrane potential - this energy is harvested
in the next step, by the ATPase complex.
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Primary and secondary electron-transport chains
NADH?O2 3ATP/2e FADH2 ?O2 2ATP/2e
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3. ATP synthesis
Energy contained in the reduced molecules formed
in TCA cycle is converted into high energy of ATP
by 1) ELECTRON TRANSPORT CHAIN (forming a proton
gradient and membrane potential) and B) proton
gradient dissipating ATPase which SYNTHESIZES
ATP. 2) SUBSTRATE LEVEL PHOSPHORYLATION
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• F1 particles have ATP synthase activity

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• Mithchells Chemiosmotic theory (1961)

• The electrochemical gradient resulting from
  transport of protons links to oxidative
  phosphorylation.
• When electrons are transported along the chain,
  the H is translocated across the inner membrane.
• The mitochondrial inner membrane is impermeable
  to H .
• When protons flow in the reverse direction
  through the F1-F0 coupling factor complex, the
  potential energy is released. It drive ATP
  synthesis.

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Inhibitors affect the respiratory chain and ATP
synthesis in mitochondia
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• Summary of the major activities during aerobic
  respiration in a mitochondrion

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IV. Mitochondrial semi-independence
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IV. Mitochondrial proliferation
Direct division of Mitochondria in mouse liver
cell
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REVIEW QUESTIONS

• 1. Describe the main opinions briefly about
  Mithchells Chemiosmotic theory.
• 2. Describe the ultrastructure of Mitochondrion.
• 3. Compare the permeability of outer membrane and
  inner membrane of Mitochondrion.