Mitochondria

• Structure of a mitochondria:

  • outer membrane
  • inner membrane - contains circular DNA molecules and respiratory enzymes
  • intermembrane space
  • cristae
  • matrix - free ribosomes are present, and respiratory enzymes
• Endosymbiotic theory:

  Integration alphaproteobacterium into a host cell related to archaea
• Evidence for endosymbiotic theory: mitochondria contain

  • own circular genome
  • double membrane
  • similar in size to prokaryotic cell
  • divide by binary fission
• Outer membrane:

  Major protein component is porin large aqueous channels
• Inner membrane:

  contains 3 major types of membrane complexes (electron transport chain, ATP sythase, specific transporters of metabolites which vary according to cell/tissue type
• Cristae:

  Increase membrane surface area

  energy transducing membrane

  impermeable to most small ions
• Matrix:

  contains:

  • enzymes whihc catalyse kreb cycle and fatty acid oxidation
  • ribosomes
  • mitochondrial DNA
• ATP hydrolysis: 2 ATP + 2 H2O -> 2 ADP + Pi
• Chemical use of ATP

  ATP hydrolysis is an exergonic process (releases energy) so is used to drive endergonic processes.
• Mechanical or transport use of ATP

  Hydrolysis of ATP causes changes in the shape and binding affinities of proteins. Occurs directly by phosphorylation (membrane proteins activate transport) or indirectly by noncovalent binding of ATP and its hydrolytic products (motor proteins)
• oxidation of organic molecules generates energy to synthesise ATP:

  Mitochondria uses high energy electron that are derived from organic molecules, C-H electrons are higher in energy than C-O or H-O.
• Glycolysis: The breakdown of glucose to produce two pyruvate molecules.
• In eukaryotes pyruvate enters the mitochondria undergoes the link reaction to form acetyl CoA. Acetyl CoA undergoes further oxidation to CO2 in the citric acid cycle this reduces electron carriers e.g NADH and FADH2 which carry electrons to the inner mitochondrial membrane to undergo oxidative phosphorylation.
• NAD = nicotinamide adenine dinucleotide
• NAD+

  • electron carrier
  • accepts high energy electrons from organic molecules
  • donates them to the electron transport chain
  • cannot be transported into/out of the mitochondria directly so must be regenerated
• Enzamtic transfer of NAD+

  2 electrons and 1 protein
• Electron transport chain breaks the fall of the high energy electron back to gorund state, using the energy release by the electron to make ATP
• Substrate level phosphorylation:

  in glycolysis substrate with high energy phosphate bond, transferred directly to ADP to form ATP
• Stages of glycolysis to form Glyceraldehyde 3-phosphate (G3P) and Dihydroxyacetone phosphate (G3P):

  1. Hexokinase transfers a phosphate group from ATP to glucose to make it more chemically reactive, the phosphate charge tranps more sugar in the cell
  2. glucose 6-phosphate is converted to fructose 6-phosphate by phosphoglucoisomerase
  3. Phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar
  4. Aldolase cleaves the sugar molecule into 2 different 3-carbon sugars (G3P and DHAP)
• What occurs to G3P

  1. Sugar is oxidized by transfer of electrons to NAD+, forming NADH

  2. Using energy from exergonic redox reaction, phosphate group is attached to oxidized substrate, making high-energy product

  3. Phosphate group is transferred to ADP (substrate-level phosphorylation) in exergonic reaction

  4. Carbonyl group of G3P oxidized to carboxyl group (-COO-) of organic acid (3-phosphoglycerate)

  5. Phosphoglyceromutase relocates phosphate group, forming 2-phosphoglycerate

  6. Enolase causes double bond to form in substrate by extracting water molecule, forming phosphoenolpyruvate (high potential energy)

  7. Phosphate group is transferred from phosphoenolpyruvate to ADP (substrate-level phosphorylation), forming pyruvate
• Pyruvate enters the mitochondria by active transport via a transport protein.
• What happens to pyruvate when in the mitochondria?

  Several enzymes known as the pyruvate dehydrogenase complex catalyze the reduction of NAD+, decarboxylation (CO2) forms, and integration of coenzyme A
• What atom does coenzyme A contain?

  Sulfur
• Where is the electron transport chain located in prokaryotes?

  plasma membrane
• What is the krebs cycle also known as?

  citric acid cycle

  tricarboxylic acid cycle (TCA)
• Krebs cycle:

  High energy electron from acetyl group are passed onto electron carriers NAD+ and FAD

  FAD accepts electrons of slightly lower energy than NAD+, only a small amount of ATP is produced
• Stages of citric acid cycle

  A) 1

  B) 3

  C) 1

  D) 2

  E) citrate

  F) isocitrate

  G) a-ketoglutarate

  H) succinyl CoA

  I) succinate

  J) fumarate

  K) malate

  L) oxaloacetate

  M) acetyl CoA

  N) citric synthase

  O) aconitase

  P) isocitrate dehydrogenase

  Q) a-ketoglutarate dehydrogenase

  R) succinyl CoA synthetase

  S) succinate dehydrogenase

  T) fumarase

  U) malate dehydrogenase

  V) CO2

  W) NAD+

  X) NADH

  Y) co2

  Z) NAD+

  [) NADH

  \) GDP

  ]) GTP

  ^) FAD

  _) FADH2

  `) h2o

  a) NAD+

  b) NADH

  
• Electron transport chain

  Consists of a collection of multiprotein complexes embedded in the inner membrane of the mitochondria

  Most common component of the chain are proteins with a prosthetic group attached.

  Each member of the electron transport chain becomes reduced when it accept an electron and will pass on the electron to a its downhill neighbor and will return to its oxidised state
• What is the first molecule of the electron transport chain?

  Flavoprotein
• Stages of electron transport chain:

  Flavoprotein -> iron-sulphur protein -> ubiquinone -. series of electron carrier (Cytochromes)
• What occurs at the last stage of the electron transport chain?

  The last cytochrome in the chain passes its electron on to oxygen and picks up a pair of H+ to form water
• Where does FADH2 transfer its electrons to in the electron transport chain?

  As it accepts lower energy electrons it transfers electrons to ubiquinone
• What is the overall energy drop of the electron transport chain?

  53Kcal/mol
• Is ATP made directly in the electron transport chain?

  No, the electron transport chain establishes a H+ gradient across the inner mitochondrial membrane
• Chemiosmosis: Electron transport chain pumps H+ ions into intermembrane space diffusion of H+ through ATP synathse (exothermic process) this attaches inorganic phosphate to ADP producing ATP
• What are the two mobile electron carriers?

  Cytochrome c and ubiquinone
• Chemical energy from food is converted into a proton motive force by the mitochondria. Harnessed by ATP synthase
• ATP synthase:

  F0 portion is the H+ channel

  F1 head is site of ATP synthesis

  A) intermembrane space

  B) H+

  C) Rotor

  D) Stator

  E) F0

  F) F1

  G) central stalk

  H) catalytic portion

  
• What occurs when H+ move through F0?

  • causes rotation of rotor and central stalk, while the stator keeps the enzymatic F1 stationary
  • Forces sequential conformational changes in the central stalk and F1
  • Provides the energy for ATP synthesis
  • 10 H+ moving back into matrix generates ~3 ATP molecule
• Describe mitochondrial poisions

  • cyanide prevents passage of electrons from one of the cytochromes thereby blocking electron transport chain
  • 2,4-dinitriophenol (DNP) makes the inner membrane leaky to H+ so the gradient cannot be established, electron transport chain still works but energy is released as heat