BIOC 503 - ELectron Transport Chain (ETC)

30-32

total yield of ATP molecules from the ETC

• depends on the type of shuttle used

functions of ETC

oxidize electron carriers from TCA cycle (NADH and FADH2) and donate electrons to molecular O2 to reduce it to H2O and use the energy for the formation of ATP

cytoplasm

location of glycolysis

mitochondrial inner membrane

location of ETC

mitochondrial matrix

location of TCA cycle

protons

the inner mitochondrial membrane is NOT permeable, even to ___ allowing the maintenance of their electrochemical gradient necessary for ATP production 

surface area

the inner mitochondrial membrane is folded to offer more ___ for the ETC aka ATP production

• MORE folded in mitochondria of organs demanding a lot of energy such as the brain, the heart, or the kidneys.

reduction potential

The process of ETC is passing of electrons from a lower ___ (E0) carrier to a higher one, then to a higher one etc.

• all of them are embedded in inner mitochondrial membrane

• higher ___ = higher tendency to accept electron

• reason why the process is thermodynamically favorable

proton pumping

the energy derived from favorable transfer of electron to a carrier with a higher E0 than the previous one is used for ___ into the intermembrane space

• maintain electrochemical gradient used for ATP synthesis

pH, electrical

there is both a __ gradient aka chemical potential gradient (low in the intermembrane space and high in the matrix), as well as the ___ gradient (intermembrane space more positive and inside matrix more negative)

acidic

the intermembrane space is __

alkaline

the matrix is ___

complex I

• NADH dehydrogenase

• contains Flavin mononucleotides (FMN)

• contains iron-sulfur centers

• transfer 2 electrons to coenzyme Q (ubiquinone becoming ubiquinol)

• pumps 4 protons into intermembrane space

prosthetic group

flavin mononucleotide works as a __ for the NADH dehydrogenase complex I in ETC

iron-sulfur centers

centers allowing electrons to jump from one iron molecule to another until it reaches final electron carrier of complex

ubiquinone

aka coenzyme Q

• found in complex 1

• electron carrier between complexes

• reduced form = ubiquinol

• receive electrons from complex I and II and ETF (electron transferring flavoproteins, come from fatty acid oxidation)

complex II

• succinate dehydrogenase complex

• also part of TCA cycle

• produces FADH2

• FADH2 binds and electrons jump using iron-sulfur center to reduce ubiquinone

complex III

• aka cytochrome b-C1 complex

• dimer of 2 identical monomers

• contains iron-sulfur centers, cytochromes, and, as other complexes, binding for coenzyme-Q

• energy from passage of electrons pumps 4 protons into the intermembrane space

cytochrome

proteins containing heme groups

• Fe2+ when receiving electrons

• Fe3+ when re-oxidized after passing electrons to next component

complex 4

• aka cytochrome oxidase complex

• dimer of 2 monomers

• copper centers

• cytochromes

• transfer the electrons to molecular oxygen forming water

• energy from passage of electrons used to pump 2 protons into the intermembrane space

shuttles

mechanisms used by the cell to bring the NADH produced by glycolysis in the cytoplasm inside the mitochondria to the ETC

• glycerol-3-phosphate ___

• malate-aspartate ___

glycerol-3-phosphate

• shuttle used in the skeletal muscles and brain

• moves reducing equivalents from cytosolic NADH to the mitochondria as FADH2

• shuttle get reduced by NADH, and then reduce FAD into FADH2 into complex II of ETC

malate-aspartate

• shuttle used in the liver, kidneys, and heart

• use NADH to reduce oxaloacetate into malate which then can cross into the matrix and get oxidized to regenerate NADH on the other side

• oxaloacetate in matrix then turned into aspartate so it can go back into intermembrane space and start the cycle again

ATP synthase

pumping protons into intermembrane space led to chemical and electrical potential (accumulated energy) which is used to make ATP via a process returning the protons into the matrix via ___ enzyme

F1

• describe the headpiece of ATP synthase enzyme

• located in the matrix

• contains the Beta subunits (each of them has a site for ATP synthesis (ADP binding site))

F0

• part of ATP synthase located in the inner mitochondrial membrane

• contain the rotor part of the enzyme made of 12 C subunits

• C subunits rotate as H+ (protons) pass through

phosphate translocase

symporter bringing phosphate groups at the same time as bringing proton into the matrix to make ATP 

embedded in inner mitochondrial membrane

adenine nucleotide translocase

antiporter

brings ADP in as ATP gets out of matrix

embedded in inner mitochondrial membrane

thermogenin

protein found in babies

• embedded in inner mitochondrial membrane

• brown fat cells

• let protons in the mitochondrial matrix bypassing ATP synthase and releasing energy as heat to warm up baby