mini exam kt2 Flashcards
Which is the substrate and which are the products of
the TCA cycle? How much energy is produced (in ATP
equivalents)?
- Acetyl-CoA is the main substrate. Main products are CO2,
and -most important- the reduced cofactors (NADH, FADH2)
and one GTP - 12 ATP equivalents per cycle (3 NADH, 1 FADH2, 1 GTP)
1 NADH → 3 ATPs; 1 FADH2 → 2 ATPs; GTP → 1 ATP
Which enzymes of the TCA cycle provide
energy?
- Isocitrate dehydrogenase (1 NADH)
- a-Ketoglutarate dehydrogenase (1NADH)
- Malate dehydrogenase (1 NADH)
- Succinate dehydrogenase (1 FADH2)
- Succinyl-CoA synthetase (1 GTP)
The cycle consists of
_________(1) reactions, _______(2) of
them are energy-
providing key
reactions, the others
support these key
reactions
- eight
- five
What are the components of the Electron
Transport Chain (ETC)? What happens at each
of the four electron carrier complexes?
- Complex I to IV; ubiquinone, cytochrome c
- Complex I: Entrance point for electrons from NADH
- Complex II: Entrance point for electrons from FADH2
- Complex III: uptake and pass on of electrons from/to
movable components of ETC: uptake from ubiquinone;
pass on to cytochrome C - Complex IV: electrons are taken from cytochrome c and
are passed on to molecular oxygen
Why is ubiquinone called ubiquinone? Why is it
also named Co-enzyme Q10? How is it called after
take up of electrons and protons?
-ubiquinone is ubiquitious (= you find it in every
organism!)
Even obligatory anaerobic bacteria have it in their ETC. Complex
IV of the ETCs of anaerobes places the electrons on sulfur or
carbon instead of on oxygen!
- Q10 refers on the isoprene side chain consisting of 10
isoprene units
- Dihydroquinone (Co-enzyme QH2)
Why do Fe-complexes in the ETC have different
environments?
To modify (or fine-tune) their redox potential
- In Complex I are various FeS (iron sulfur) complexes for modification (= fine
tuning) of the Fe2+/Fe3+ redox potential. There is H+-transport (from matrix to
intermembrane space) - In Complex II are various FeS (iron sulfur) complexes for modification (= fine
tuning) of the Fe2+/Fe3+ redox potential. This is also part of the TCA cycle.
There is no H+-transport associated with this carrier complex. - In Complex III are both, FeS complexes and heme-iron complexes (=
cytochromes). There is H+-transport (from matrix to intermembrane space) - In Complex IV are both, copper complexes (modifying Cu1+/Cu2+ redox
potential) and cytochromes (modifying Fe2+/Fe3+ potential). The cooperation
of a heme-iron and a copper complex enables the splitting and reduction of
O2 into 2 H2O). There is H+-transport (from matrix to intermembrane space).
There are _____ (1)
alternative
entrance points. what are they (complexes)
- two
-either complex I or
complex II.
What are the two components of protonmotive
force that drives the ATP-Synthases? Which
way do the protons flow for ATP synthesis?
The proton gradient (H+ or pH) between intermembrane space and
matrix, built up during the ETC process, where at three points protons are
channeled out from the matrix into the intermembrane space.
This also leads to an electrochemical potential (V). Both together is called
the chemiosmotic theory!
For ATP synthesis, the protons are channeled through the ATPase from
the intermembrane space to the matrix.
The energy for ATP synthesis arises from an _______
across the inner mitochondrial membrane
H+ -gradient
The _____ ________ us impermeable to protons
inner membrane
Due to the out-transport of protons by
the ______ ___________ ________, a H+-
gradient (pH) builds up
the electron transport chain
the _____ _______ (1) causes a ________ _______ _____(2)
- proton gradient
- transmembrane electrochemical potential
Both pH and V are the driving force
(protonmotive force) to bring the protons
back into the matrix. This process
delivers the energy to _______ ______(1)
- synthesize atp
What are the components of the ATP-Synthase?
What happens where?
- In the F0 half of the ATPase, located in the inner mitochondrial membrane, are
the proton channel a, which turns the “wheel” c. - The F1 half of the ATPase is reaching into the matrix: It is composed of the
gamma-axle (which connects the “wheel” c with the ATP synthesis site,
consisting of the three alpha- and three beta subunits. The gamma-axle is
driven by the “wheel” c, and steers the ATP-synthesizing beta-units through the
O (open), L (loose) and T (tight) stages of ATP synthesis.
atp synthase comprises a ______ ____ (1) and ______ ____(2)
- proton channel (F0)
- ATPase site (F1)
Why is dinitrophenol (or other lipophilic phenolic
compounds with a pKA ~ 7) dangerous?
- Dinitrophenol (DNP) is a lipophilic phenol with a pKa ~ 7. Such
penolic compounds are toxins. The process is unwanted, since it
prevents ATP synthesis. - In contrast, uncoupling by thermogenin, a heat generator in brown
adipose tissue, is a wanted process, since heat is needed (e.g., in
young babies, who have not yet learned to shiver).
Uncoupling of Electron Transport Chain and ATP-
Synthase
unwanted, through chemical ‘uncouplers’ such as DNP (dinitrophenol)
- lipophilic compounds with a pKa ~ 7
- no ATP is synthesized, rapid oxidation of NADH/H+ and FADH2, heat release
What is thermogenin, and where do you find it?
Thermogenin is a transmembrane protein located in the inner
mitochondrial membrane of brown adipose cells. It is a heat
generator.
- It uncouples the electron transport chain from the ATP-Synthase by
pumping protons from the intermembrane space into the matrix - The energy normally used for the ATP synthesis is released as heat
This is a wanted process when heat is needed (e.g., in young
babies, who have not yet learned to shiver). - The potential conversion of white (no thermogenin) into brown
(thermogenin!) adipose is studied in context with the drug sildenafil
(better known as Viagra), which may have a future as anti-obesity drug,
since brown adipose is a calorie burner!
a thermogenin (heat generator) is a transmembrane protein is located in the ______ _____ (1)
membrane of _______ ________ _____ (2)
- inner mitochondrial
- brown adipose cells
Thermogenin (heat generator) does what?
uncouples the electron transport chain from the ATP-Synthase by
pumping protons from the intermembrane space into the matrix
the energy normally used for the ATP synthesis is released as _____-
heat
Which of the following coenzymes is unique to -keto
acid dehydrogenase complexes?
A. NAD
B. FAD
C. GDP
D. H2O
E. Lipoic acid
E. Lipoic acid
A patient diagnosed with thiamine deficiency exhibited
fatigue and muscle cramps. The muscle cramps have been
related to an accumulation of metabolic acids. Which of
the following metabolic acids is most likely to accumulate
in a thiamine deficiency?
A. Isocitric acid
B. Pyruvic acid
C. Succinic acid
D. Malic acid
E. Oxaloacetic acid
B. Pyruvic acid
Succinate dehydrogenase differs from all other enzymes in
the TCA cycle in that it is the only enzyme that displays
which of the following characteristics?
A. It is embedded in the inner mitochondrial membrane.
B. It is inhibited by NADH.
C. It contains bound FAD.
D. It contains Fe–S centers.
E. It is regulated by a kinase
A. It is embedded in the inner mitochondrial membrane.
