Krebs Cycle,Respiratory Chain, ATP

Vladimíra Kvasnicová

Respiratory chain (RCH)

� is found in all cells containing mitochondria

� is composed of 4 enzyme complexes

� the enzymes occur in the inner mitochondrial membrane

� RCH oxidizes NADH+H+ to NAD+ and FADH2 to FAD → electrons are transported to O2

� protons (H+) are transported to the intermembrane space ⇒ proton gradient

Recommended animations

• electron transport chainhttp://vcell.ndsu.nodak.edu/animations/etc/index.htm

• ATP synthesishttp://vcell.ndsu.nodak.edu/animations/atpgradient/index.htm

The figure is found at http://plaza.ufl.edu/tmullins/BCH3023/cell%20respiration.html (December 2006)

The figure is found at http://www.grossmont.net/cmilgrim/Bio220/Outline/ECB2Figures&Tables_Ed2-Ed1/Chapter14_13/REDOX_POTENTIALS_ElectronTransportChain_Fig14-21.htm (December 2006)

Gibbs energy„G“

Redox potential

„E“

↑ reducing properties

↑ oxidizing properties

The figure is found at http://academic.brooklyn.cuny.edu/biology/bio4fv/page/mito_ox.htm (December 2006)

The figure is found at http://www.cellml.org/examples/images/metabolic_models/the_electron_transport_chain.gif (December 2006)

Citrate cycle

succinate DH

The figure is found at http://web.indstate.edu/thcme/mwking/oxidative-phosphorylation.html (December 2006)

FADH2

Complex II can not transport H+

The figure is found at http://plaza.ufl.edu/tmullins/BCH3023/cell%20respiration.html (December 2006)

ATP synthase

inner mitochondrial membrane

The figure is found at http://departments.oxy.edu/biology/Franck/Bio222/Lectures/March23_lecture_shuttles.htm (December 2006)

Uncoupling proteins(UCP)

= separate RCH from ATP

synthesis(the synthesis is

interrupted)

energy from H+

gradient is released as a heat

Synthesis of ATP in cells is called

1. oxidative phosphorylation

alternative names

aerobic phosphorylation

2. substrate level phosphorylation(= formation of ATP without direct presence of oxygen;energy source for this ATP synthesis is an energy rich compound: 1,3-bisphosphoglycerate = 1,3-BPG, phosphoenolpyruvate = PEP, succinyl-CoA, GTP, creatine phosphate,...)

ATP (GTP) can be formed in these reactions

• 1,3-BPG + ADP → 3-phosphoglycerate + ATP (in glycolysis)

• PEP + ADP → pyruvate + ATP (in glycolysis)

• succinyl~CoA + GDP+Pi → succinate + GTP (in Krebs cycle)

• GTP + ADP → GDP + ATP

• creatine phosphate + ADP → creatine + ATP (in muscles)creatine kinase (CK)

• ADP + ADP → ATP + AMP(adenylate kinase = myokinase)

Adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2

Formation of reducing equivalents (NADH, FADH2)

• glycolysis (cytosol): 2 NADH

• pyruvate dehydrogenase (PDH): 1 NADH

• β-oxidation: (n/2)-1 FADH2 / (n/2)-1 NADH(n= number of carbons of FA)

• citrate cycle: 3 NADH, 1 FADH2

• glutamate dehydrogenase (GMD): 1 NADH

• interconversion of ketone bodies: 1 NADH

• oxidation of ethanol to acetic acid: 2 NADH(alcohol dehydrogenase/cytosol, aldehyde dehydrogenase/mitoch.)

MALATE-ASPARTATE SHUTTLE

Transport of reducing equivalents to mitochondria

The figure was accepted

from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc.,

New York, 1997. ISBN 0-471-15451-2

GLYCEROL PHOSPHATE SHUTTLE

The figure was accepted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2

Color Atlas of Biochemistry / J. Koolman, K.H.Röhm. Thieme 1996. ISBN 0-86577-584-2

Oxidative metabolism in mitochondria

• pyruvate dehydrogenase (PDH) glucose, amino acids

• glutamate dehydrogenase (GMD) amino acids

• β-oxidation of fatty acids fatty acids

• ketone bodies degradation ketone bodies

• Krebs cycle all nutrients

• respiratory chain – O2 NADH, FADH2

oxidative phosphorylation= ATP synthesis in cooperation with the respiratory chain

The figure is found at: http://faculty.uca.edu/~johnc/pdhrxns.gif (December 2006)

2-oxoacid dehydrogenase is a multienzyme complex

mitochondria

„pyruvatedehydrogenase reaction“ = PDH

= oxidative decarboxylation of pyruvate

The figure is adopted from the book: Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2

The figure is found at http://www.sp.uconn.edu/~bi107vc/images/mol/krebs_cycle.gif (December 2006)

simplification:

The figure is found at http://www.holon.se/folke/kurs/Distans/Ekofys/Recirk/Eng/regcyc5.jpg (December 2006)

The figure is found athttp://www.tcd.ie/Biochemistry/IUBMB-Nicholson/gif/13.html

Amphibolic nature of the

citrate cycle

The figure is found at http://www.elmhurst.edu/~chm/vchembook/images/590metabolism.gif (December 2006)

The figure is found at http://www.hupe.hu/szerv/tanszekek/kio/im/oktat/SEJTBIO/citratkor/citr_summa_e.html(December 2006)

Products of the citrate cycle

The figure is found at http://lecturer.ukdw.ac.id/dhira/Metabolism/Respiration.html (December 2006)

„F“ → Fumarate andFADH2

The figure is found at http://lecturer.ukdw.ac.id/dhira/Metabolism/Respiration.html (December 2006)

The figure is found at http://web.indstate.edu/thcme/mwking/tca-cycle.html (prosinec 2006)

Anaplerotic reactions

The figure is found at http://www.bmb.leeds.ac.uk/illingworth/metabol/2120lec3.htm#krebs (December 2006)

pyruvate carboxylase

The most important anaplerotic reaction:

The figure is found at http://www.metabolic-database.com/html/body_glutaminolysis__zeichnung3.html (December 2006)

strongly exergonic reactions

Regulation of CC

Regulation of the citrate cycle

• ↑ NADH / NAD+

• ↑ ATP / ADP• GTP• succinyl-CoA

• Ca2+2-oxoglutarate dehydrogenase

• ↑ NADH / NAD+

• ↑ ATP / ADP• ↓ ATP / ADPisocitrate

dehydrogenase(key enzyme)

• ↑ NADH / NAD+

• succinyl-CoAcitrate synthase

inhibitionactivationregulatory enzyme

= by availability of substrates and consumption of produts

The figure is found at http://www.metabolic-database.com/html/body_glutaminolysis__zeichnung3.html (December 2006)

↑ATP

transported to the cytosol

Citrate

• is formed from oxaloacetate and activated acetic acid (acetyl-CoA)

• is transported to the cytoplasm if its concentration in a mitochondrion rises

• participates in inhibition of glycolysis

• activates fatty acid synthesis

excess of energy is stored in glycogen and fat

Recommended animations- SUMMARY -

1. Essential Biochemistry / Wiley & Sons(Exercises: 10, 11, 16, 17, 19, 20)http://www.wiley.com/college/pratt/0471393878/student/exercises/index.html

2. Interactive Concepts in Biochemistry / Boyerhttp://www.wiley.com/legacy/college/boyer/0470003790/animations/animations.htm

3. Fundamentals of Biochemistry / Voethttp://www.wiley.com/college/fob/anim/

4. Schematic Pathways / Hardyhttp://ull.chemistry.uakron.edu/Pathways/index.html

5. Virtual Cell Animation Collectionhttp://vcell.ndsu.nodak.edu/animations/home.htm