How cells make ATP ? Energy releasing pathways Chapter 7, pages: Csaba Bödör,

Before we start … REVIEW !! : Metabolism, anabolism, catabolism exergonic, endergonic coenzymes: NAD, FAD, ATP oxidation, reduction

Energy and Metabolism Metabolism: sum of all chemical activities taking place in an organism 2 types: Catabolism and Anabolism CATABOLISM: larger molecules are broken down to smaller ones (energy is released) ANABOLISM: complex molecules are synthesized from simpler ones (energy is required)

CATABOLISM: larger molecules are broken down to smaller ones (energy is released) ANABOLISM: complex molecules are synthesized from simpler ones (carbohydrates, lipids, proteins, nucleic acids) (energy is required) Energy and Metabolism ATP ADP + P

ATP links endergonic and exergonic reactions Energy and Metabolism: ATP ATP: a nucleotide (base, ribose, 3 phosphate groups) is the energy currency of cells (like cash) energy stored in ATP for short period energy is donated by the transfer of terminal phosphate group a common intermediate must be present and is a common link between catabolism and anabolism continuously used and replaced Exergonic reaction

Energy transfer in cells 1, Through transfer of a phosphate group (ATP ADP + P) 2, Through transfer of electrons (NAD, FAD, cytochromes) Oxidation, reduction > together redox reactions !

REDOX reactions Redox reactions: reduction and oxidation Redox reactions involve electron transfer Important in energy conversion in cells Oxidation: chemical process in which atom, ion or molecule loses electrons Reduction: chemical process in which atom, ion or molecule gains electrons Reduction and Oxidation occur simultaneously !!!

REDOX reactions Redox reactions: reduction and oxidation Redox reactions involve electron transfer Important in energy conversion in cells Oxidation: chemical process in which atom, ion or molecule loses electrons Reduction: chemical process in which atom, ion or molecule gains electrons The transfer of an electron also involves the transfer of the energy of that electron Electrons are not easily removed from complex covalent compounds, unless an entire atom is removed (that is why a whole hydrogen atom is removed/added) So in cells: Oxidation often involves the removal of a Hydrogen atom (e - + p + ) Reduction often involves the addition of a Hydrogen atom (e - + p + ) Substance, which becomes oxidized gives up energy !! Substance, which becomes reduced receives energy !!

Special nucleotides NAD + : nicotinamide adenine dinucleotide Coenzymes, which are reduced during the catabolism: NAD +, FAD Oxidized form: NAD + Reduced form: NADH See: chapter 6 (energy and metabolism), part: energy transfer in redox reactions NADH temporarily stores large amounts of free energy NAD + receives 2e - and 1 p + > > NADH is formed Electrons (and their energy) are then transferred to further acceptor molecules NAD + is a hydrogen (electron) acceptor molecule

Special nucleotides NAD + : nicotinamide adenine dinucleotide

Special nucleotides FAD: flavin adenine dinucleotide Coenzymes, which are reduced during the catabolism: NAD, FAD Oxidized form: FAD Reduced form: FADH 2 FAD is also a hydrogen (electron) acceptor molecule important role in redox reactions, in biological oxidation + cytochromes: also important electron acceptors, they contain iron (later) oxidized and reduced form (less and more free energy)

Energy releasing pathways Energy can not be created it is captured ! (food) During catabolism the energy in food (potential energy stored in chemical bonds of macromolecules) is converted into ATP This is the process of cellular respiration ! AEROBIC RESPIRATION ANAEROBIC RESPIRATION requires oxygen does not require oxygen anaerobic resp., fermentation the most common pathway almost all are exergonic (energy is released) many steps (reactions), regulated by many enzymes

Aerobic respiration in most eukaryotes and prokaryotes nutrients are broken down (catabolized) into CO 2 and H 2 O sequence of redox reactions most cells use glucose to obtain energy by aerobic respiration C 6 H 12 O O 2 6 CO H 2 O + energy (ATP) OXIDATION REDUCTION a redox reaction: glucose becomes oxidized, oxygen becomes reduced the free energy of electrons is coupled to ATP synthesis electrons from glucose are transferred to oxygen, but NOT directly: through many reaction steps (NAD +, FAD, cytochromes)

Aerobic respiration aerobic respiration can be divided into 4 stages 1, GLYCOLYSIS: takes place in the cytosol 2, FORMATION OF ACETYL COENZYME A: takes place in the mitochondrion 3, CITRIC ACID CYCLE: takes place in the mitochondrion 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion

Aerobic respiration Types of reaction involved in aerobic respiration 1, DEHYDROGENATION reactions: two hydrogen atoms are removed from a substance and are transferred to NAD + or FAD 2, DECARBOXYLATION reactions: part of the carboxyl group (-COOH) is removed from the substance as a CO 2 molecule 3, PREPATORY reactions: the rest of the reactions, molecules undergo rearrangements and modifications Net yield !

Aerobic respiration aerobic respiration can be divided into 4 stages 1, GLYCOLYSIS: takes place in the cytosol „sugar splitting” does not require oxygen takes place in cytosol > enzymes involved in glycolysis are synth. on free ribosomes series of reactions, catalyzed by specific enzymes glucose molecule (6 carbon) is converted to 2 pyruvate molecules (3 carbon) net yield (result): 2 NADH, 2 ATP molecules per one glucose molecule HOW ??

Aerobic respiration 1, GLYCOLYSIS: takes place in the cytosol is divided into 2 major phases: 1: energy investment phase (preparatory), 2: energy capture phase 1: ENERGY INVESTMENT PHASE includes endergonic reactions, which require ATP (2 phosphorilation) 2 ATP molecules are used 2 glyceraldehyde-3-phosphate (G3P) molecules are formed SUMMARY: glucose + 2 ATP 2 G3P + 2 ADP

Aerobic respiration 1, GLYCOLYSIS: takes place in the cytosol is divided into 2 major phases: 1: energy investment phase (preparatory), 2: energy capture phase 2: ENERGY CAPTURE PHASE each G3P molecule is converted to a pyruvate molecule by removal of electrons and a phosphate group as a result: NADH and 2 ATP molecules are produced per one pyruvate Total: 2 NADH and 4 ATP molecules are produced per one glucose molecule SUMMARY: 2 G3P + 2 NAD ADP 2 pyruvates + 2 NADH + 4 ATP The phosphate group is transferred to ADP from a phosphorilated intermediate Substrate level phosphorilation

Aerobic respiration 1, GLYCOLYSIS: takes place in the cytosol 1: ENERGY INVESTMENT PHASE 2 glyceraldehyde-3-phosphate (G3P) molecules are formed SUMMARY: glucose + 2 ATP 2 G3P + 2 ADP 2: ENERGY CAPTURE PHASE SUMMARY: 2 G3P + 2 NAD ADP 2 pyruvates + 2 NADH + 4 ATP each G3P molecule is converted to a pyruvate molecule TOGETHER: glucose 2 pyruvates + 2 NADH + 2 ATP

Aerobic respiration aerobic respiration can be divided into 4 stages 2, FORMATION OF ACETYL COENZYME A: takes place in the mitochondrion pyruvate molecules enter mitochondria series of reactions, catalyzed by enzyme complex: pyruvate dehydrogenase (72 pp) first carboxyl group is split off as CO 2, which diffuses out of the cell then the remaining part is oxidized: electrons to NAD + > > NADH is formed (which is used later) finally, coenzyme A is attached to the acetyl group

Aerobic respiration aerobic respiration can be divided into 4 stages 2, FORMATION OF ACETYL COENZYME A: takes place in the mitochondrion acetyl CoA is an important intermediate substance in cellular respiration coenzyme A transfers different group: here an acetyl group is attached to CoA SUMMARY: 2 pyruvates + 2 NAD CoA 2 acetyl CoA + 2 NADH + 2 CO 2 coenzyme A is manufactured from one of the B-vitamins (pantothenic acid) A refers to adenine

Aerobic respiration aerobic respiration can be divided into 4 stages 3, CITRIC ACID CYCLE: takes place in the mitochondrion also known as tricarboxylic acid cycle (TCA) or Krebs-Szentgyörgyi cycle sequence of reactions, each is catalyzed by a specific enzyme takes place in mitochondrial matrix 2 acetyl groups enter the CA cycle for each glucose each acetyl group combines with a 4 Carbon molecule, called oxaloacetate, forming a 6 carbon molecule: citrate citrate then loses two carboxyl (COOH) groups in form of 2 CO 2 molecules energy is captured in form of 1 ATP, 3 NADH and 1 FADH 2 molecule oxaloacetate is regenerated and the cycle continues

Aerobic respiration aerobic respiration can be divided into 4 stages 3, CITRIC ACID CYCLE: takes place in the mitochondrion SUMMARY of the citric acid cycle per 1 glucose molecule: 4 CO 2 molecules (waste) 2 FADH 2 molecule (energy) 6 NADH molecules (energy) 2 ATP molecules (energy) (by substrate level phosphorilation) 2 turns of the cycle are needed for a glucose molecule

Details of citric acid cycle

Aerobic respiration What do we have so far? 1, GLYCOLYSIS: takes place in the cytosol glucose 2 pyruvates + 2 NADH + 2 ATP 2, FORMATION OF ACETYL COENZYME A: takes place in the mitochondrion 2 pyruvates + 2 NAD CoA 2 acetyl CoA + 2 NADH + 2 CO 2 3, CITRIC ACID CYCLE: takes place in the mitochondrion 2 acetyl CoA 2 ATP + 2 FADH NADH + 4 CO 2 NADH, FADH 2 : reduced coenzymes (they temporarily store energy) energy released during their oxidation is used for ATP synthesis electrons (H atoms) are removed: NAD +, FAD is formed (the oxidized forms) oxidation of 1 NADH molecule yields 3 ATP molecules !!!!!! oxidation of 1 FADH 2 molecule yields 2 ATP molecules !!!!!! BUT HOW ???

Aerobic respiration aerobic respiration can be divided into 4 stages 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion all electrons removed from glucose are parts of NADH and FADH 2 these electrons enter the electron transport chain electrons are transferred from NADH and FADH 2 to further electron acceptors from these acceptors electrons are transferred to oxygen (final electron acceptor) and water is formed (oxygen is reduced) TO BE CONTINUED … the energy of electrons is coupled to ATP synthesis

Aerobic respiration aerobic respiration can be divided into 4 stages 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion series of electron carriers embedded in the inner mitochondrial membrane they can exist in reduced and in oxidized form electrons pass down the transport chain in series of redox reactions finally they are passed to the final electron acceptor : O 2 their energy is used to drive the ATP synthesis the whole process is called: oxidative phosphorilation 4 big protein complexes in the membrane 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion

COMPLEX 1: accepts electrons from NADH COMPLEX 2: accepts electrons from FADH 2 COMPLEX 1 and 2 pass electrons to ubiquinones (Q) COMPLEX 3: accepts electrons from reduced ubiquinones (Q) and passes the to cytochrome-c COMPLEX 4: accepts electrons from reduced cytochrome-c and passes them to 0 2 (water is formed) Q Q Lack of O 2, cyanide Cyt-c *

Aerobic respiration 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion electron transport chain and ATP synthesis are coupled (!) electron transport chain establishes a H + (proton) gradient some energy of electrons is used to pump H + to the intermembr. space the potential energy of this gradient is used to synthesize ATP HOW ??? they diffuse back to the matrix through complex V. (ATP synthase) This is an exergonic process, and the released energy is used to synthesize ATP

Aerobic respiration 4, ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS: takes place in the mitochondrion ATP synthase acts as a molecular motor H + diffuses back through it, it rotates > ATP is synthesized the central part rotates, and the catalytic part allows the ATP synthesis

Aerobic respiration Complete aerobic respiration of 1 glucose molecule yields: ATP molecules !!!!!!!!!! Efficiency: ~40% 2 CO 2 4 CO 2 cytosol mitochondrion Substrate level phosphorilation: 4 ATP Oxidative phosphorilation: ATP

Aerobic respiration oxidation of 1 NADH yields 3 ATPs but NADH molecules created in the cytosol are special: sometimes their oxidation yields 2 ATPs, sometimes 3 ATPs WHY ?? electron transport (oxidation of NADH) occurs in mitochondria, but these NADH molecules are in the cytosol ! NADH is not able to pass through the inner mitochondrial membrane (problem!) but we are able to transport its electrons by different shuttle systems In liver, kidney, heart cells: 1 cytosolic NADH yields 3 ATP molecules (electrons of NADH are accepted by a NAD+ molecule in the matrix) In skeletal muscle, brain, etc cells it results in production of 2 ATP molecules (because of the different shuttle system: electrons of the NADH are accepted by FADH and ubiquinone > it generates 2 ATP molecules)

DO NOT STUDY THIS !!!!!

Aerobic respiration OTHER nutrients than glucose Lipids, proteins products of their catabolism enter the same metabolic pathways as glucose * by oxidation of fatty acids we obtain more energy than from glucose (over consumption of saturated fatty acids might cause cardiovascular diseases) * Oxidation of fatty acids:  -oxidation: 2C units are removed from the fatty acid chain, and converted to AcCoA, which enters the citric acid cycle proteins are digested by proteases then amino acids are deaminated (NH 2 group is removed, and converted to urea) (the remaining carbon part is oxidized (enters catabolic pathways)

DO NOT STUDY THIS !!!!!

Anaerobic respiration 1, Anaerobic respiration: - Electrons are transported from the fuel molecules to NADH then to electron transport chain - Final electron acceptor is an inorganic substance (nitrate, sulphate) - Typical for some prokaryotes, which live in anaerobic environment 2, Fermentation: - an anaerobic pathway, no electron transport chain - Only 2 ATPs are formed per glucose (by substrate level phosphorilation) - Produced NADH molecules must be oxidized to NAD + (it is needed for glycolysis) - Their electrons go to organic compounds: either ethanol or lactate is the end product

Anaerobic respiration 2, Fermentation: - Alcohol fermentation, Lactate fermentation - Highly inefficient processes (only 2 ATP) - Alcohol fermentation: wine, beer, etc READ: fermentation (p:152) - Lactate fermentation: also humans (for few minutes: exercise, muscles) - The last step (formation of either ethyl alcohol or lactate) is in order to oxidize NAHD to NAD + (because it is needed to continue the glycolysis)

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