Download Chapter 14 - Part I

Chapter 14
Energy Generation in
Mitochondria and Chloroplasts
Generation of Energy
• Millions of years ago there was no O2 available for oxidative
phosphorylation to occur
• Organisms produced energy from fermentation, still see this
today
• As O2 became available, a more efficient method of energy
production developed
– Based on the transfer of e- along the membrane
Organism’s Energy Source
• Small amount of ATP from glycolysis in the cytosol of cells
• Majority made by a membrane based process in 2 stages
– Stage 1 – e- transport chain
• e- transferred along e- carriers in the membrane
– Stage 2 – flow of H+ down an electrochemical gradient
to produce ATP
• Use a complex called ATP synthase
Stage 1
• NADH (from the Kreb’s cycle)
brings in the e- and transfers
them to the carrier molecules
• The e- moves down the chain
and looses energy at each step
– as this happens, H+ are
pumped across the membrane
• This creates an electro-chemical
gradient across the membrane
Stage 2
• The electrochemical gradient
is a form of stored energy – it
has the potential to do work
• The H+ can now move down
the gradient and return to the
other side of the membrane
thru ATP synthase – in this
process, generates ATP from
ADP and Pi
Chemiosmotic Coupling
• Once called the chemiosmotic hypothesis
– Chemi from making ATP, osmotic because of crossing the
membrane
• Now known as chemiosmotic coupling
Mitochondria
• Produce most of a cells ATP – acetyl groups in the Kreb’s
cycle producing CO2 and NADH
• NADH donates the e- to the electron transport chain and
becomes oxidized to NAD+
• e- transfer promotes proton pump and ATP synthesis in
process called oxidative phosphorylation
• Cells that require large amounts of energy such as the
heart have large numbers of mitochondria
Mitochondria
• Contain their own copies of DNA and RNA along with
transcription and translation system (ribosomes)
• Are able to regenerate themselves without the whole cell
undergoing division
• Shape and size dependent on what the cell’s function is
Mitochondria
• Double membrane creates 2 spaces
Matrix: large internal space
Intermembrane space:
between the membranes
Outer membrane
Inner membrane
Mitochondria
Inner Membrane
• Inner membrane is the site of the e- transport chain,
across which the proton pump occurs and contains ATP
synthase
• Inner membrane is highly folded – called cristae –
increasing the surface area on which the above reactions
can take place
High Energy e• Mitochondria use pyruvate and fatty acids and convert it
to acetyl CoA in the matrix
• Citric acid cycle generates NADH and FADH2 which carry
the e- to the electron transport chain
Summary – MUST KNOW
Proton Pumping
• Many molecules can supply the e- - carbohydrates and
fatty acids
• O2 ultimate e- acceptor producing H2O as waste
Movement of Electrons
Oxidative Phosphorylation
Electron Transport Chain
• Resides in the inner mitochondrial membrane – also
called respiratory chain
• 15 proteins involved in the chain – grouped in 3 large
respiratory enzyme complexes
– NADH dehydrogenase complex
– Cytochrome b-c1 complex
– Cytochrome oxidase complex
• Pumps protons across the membrane as e- are
transferred thru them
Respiratory Enzyme Complexes
Proton Gradient
• e- transfer is an oxidation/reduction reaction
• NADH has high-energy e- has a low electron affinity so
the e- is readily passed to NADH dehydrogenase and so
on down the chain
• Each transfer couples the energy released with the
uptake of a H+ from the matrix to the intermembrane
space setting up the electrochemical gradient
Proton Gradient
• Gradient of proton (H+) concentration across the inner
mitochondrial membrane – a pH gradient with the pH in
the matrix higher than in the intermembrane space
• Proton pumping also generates a membrane potential
– matrix side is negative and intermembrane space is
positive
4 Complexes in Membrane
Location of H+
Electrochemical Gradient
Oxidative Phosphorylation
• ATP synthase is the protein complex responsible for making
ATP by creating a path for H+ thru the membrane
• ATP synthase is an enzyme
ATP Synthase
• Multisubunit
protein
responsible for
making ATP
Summary
Bidirectional Pump
Coupled Transport Can Move Other
Molecules
Oxidation of Sugar and Fats