BIOL 1010 Lecture Notes - Acetaldehyde, Citric Acid Cycle, Glycolysis

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16 Oct 2012
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Cell Metabolism, Part II
Lec 19
Cellular respiration and fermentation are catabolic
- Oxidation-reduction reactions- chemical reaction which involve a partial or complete transfer of
electrons from one reaction to another; called redox reactions for short
- Oxidation partial or complete loss of electrons
- Reduction partial or complete gain of electrons
Election transport Phosphorylation
- The electron transport chain is made of electron carrier molecules embedded in the inner
mitochondrial membrane
- Each successive carrier in the chain has a higher electro negativity than the carrier before it, so
the electrons are pulled downhill toward oxygen, the final
electron acceptor and the molecule with the highest electro
negativity
- Except for ubiquinone (Q), most of the carrier molecules are
proteins and are tightly bound to prosthetic groups (non-
protein cofactors)
- Prosthetic groups alternate between reduced and oxidized
states as they accept and donate electrons
Electron transport chains
- In cellular respiration, an electron transport chain breaks
the “fall” of electron in this reaction into a series of smaller steps
- If stores some of the released energy in a form that can be used to make ATP(the rest of the
energy is released as heat)
Electron Transport Phosphorylation
Protein Election Carriers
Prosthetic Group
Flavoproteins (FVM_
Favlin mononucleotide
Iron Sulfur proteins
Iron and sulfur
Cytochromes
Heme group
- Heme group- prosthetic group composed of four carbon rings surrounding a single iron atom
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- Cytochrome- type of protein molecule that contains a heme prosthetic group and function as an
electron carrier in the electron transport chains of mitochondria and chloroplasts
o There are several cytochromes, each a slightly different protein heme group
o It is the iron of cytochromes that transfers electrons
Electron Transport Chain
- Each member of the chain oscillates between a reduced state and an
oxidized state
- A component of the chain becomes reduced when it accepts electrons
from its “uphill” neighbour (Which has a lower affinity for the electrons)
- Each members of the chain returns to its oxidized form as it passed
electrons to its “downhill “neighbour (which has a greater affinity for the
electrons)
- A the bottom of the chain is oxygen, which is very electronegative
- The overall energy from for electrons travelling from NADH to oxygen is 53
Kcal/mol, but this fall is broken up into a series of smaller steps by the
electron transport chain
- As molecular oxygen is reduced, it also picks up two protons from the
medium to form water. For every two NADHs, one is O2 is reduced to two H2O molecules
- FADH2 also donates electrons to the electron transport chain, but those electrons are added at
a lower energy level then NADH
- The electron transport chain does not make ATP directly
- It generates a proton gradient across the inner mitochondrial membrane, which stores potential
energy that can be used to phosphorylate ADP
Chemiosmosis; the energy-coupling mechanism
- Cytochromes are the molecules that pass the “hot potatoes” (electrons) along
the ETC
- Energy released by the “downhill” passage of electrons
- The ADP is reduced by the gain of elections
- ATP formed in this way is made by the process of oxidative phosphorylation.
- The mechanism for the oxidative phosphorylation process is the gradient H+ ions
discovered across the inner mitochondrial membrane
- This mechanism is known as Chemiosmotic coupling.
- This involves both chemical and transport processes.
- This protein complex which uses the energy of H+ gradient to drive ATP synthesis resides in
mitochondrial and chloroplast membranes in the plasma membranes of prokaryotes
- ATP synthase has three main parts:
o cylindrical component, within the membrane
o protruding knob in Which in mitochondria is in the matrix
o a rod or stalk connecting the other two parts
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