View
10
Download
0
Category
Preview:
Citation preview
Energy Transformation: Cellular Respiration Outline
1. Sources of cellular ATP2. Turning chemical energy of covalent bonds between C-C into
energy for cellular work (ATP)3. Importance of electrons and H atoms in oxidation-reduction
reactions in biological systems4. Cellular mechanisms of ATP generation5. The four major central metabolic pathways
Glycolysis- FermentationTransition step Krebs CycleElectron Transport chain and oxidative phosphorylation
4. Poisons of cellular respiration and their mechanisms of action.5. Use of biomolecules other than glucose as carbon skeletons &
energy sources
http://health.howstuffworks.com/sports-physiology3.htm
A cell has enough ATP to last for about three seconds
Necessary ATP is supplied to muscle cells by
1. Phosphagen system (8 to 10 seconds.)2. Glycogen-lactic acid system (90 seconds)- glucose3. Aerobic Respiration (unlimited)- glucose
Phosphagen system (muscle fibers)
(*) Arezki Azzi et al. Protein Sci 2004; 13: 575-585
• Creatine phosphate contains (a high-energy phosphate compound).
• Creatine kinase transfers the phosphate to ADP to form ATP.
Creatine-Phosphate (tri)
*
Creatine-Phosphate + ADP (Tri)
Creatine-Phosphate + ATP(Di)
Creatine Kinase
During cellular respiration the potential energy in the chemical bonds holding C atoms in organic molecules in turned into ATP.
In presence of oxygencomplete breakdown
C-C-C-C-C-C + O2……………… CO2 + H2O + ATPlarge amount
In absence of oxygenincomplete breakdown
C-C-C-C-C-C ……………… 2 C-C-C + ATPsmall amount
Cellular respiration: ATP is produced aerobically, in the presence of oxygen
Fermentation: ATP is produced anaerobically, in the absence of oxygen
Chemical bonds of organic molecules
Chemical bonds involve electrons of atoms
Electrons have energy
Chemical bonds are forms of potential energy
If a molecule loses an electron does it lose energy?
When a chemical bond is broken sometimes electrons can be released
• Oxidation: removal of electrons.• Reduction: gain of electrons.• Redox reaction: oxidation reaction paired with a
reduction reaction.
Oxidation-Reduction
The electrons associated with hydrogen atoms. Biological oxidations are often dehydrogenations
Soluble electron carriersNAD+, and FAD (ATP generation) NADP+ (biosynthetic reactions)
Electron Carriers in Biological Systems
Nicotinamide Adenine Dinucleotide (NAD+) a co-enzyme that acts as an electron shuttle (Niacin)
NAD+
Nicotinamide (oxidized form)
Dehydrogenase
2 e– + 2 H+2 e– + H+
NADH H+
H+
Nicotinamide (reduced form)
+ 2[H](from food)
+
Flavin Adenine Dinucleotide (FAD+) is another co-enzyme that acts as an electron shuttle (Vitamin B2)
In Metabolic pathwaysOxidation Reduction
• Energy loss or gain• Exergonic or endergonic• Catabolic or anabolic
In cells, energy is harvested from an energy source (organic molecule) by a series of coupled oxidation/reduction reactions (redox) known as the central metabolic pathways
becomes oxidized
becomes reduced
Dehydrogenase
Metabolic PathwaysLinear Pathways
Branched Pathways
Cyclic Pathways
An overview of the central metabolic pathways
• Glycolysis• Transition step• Tricarboxylic acid cycle (TCA or Krebs cycle)• The Electron Transport Chain and oxidative
phosphorylation
1. Oxidative phosphorylation/ Chemiosmosis
Mechanisms of ATP Generation during cellular respiration
• ADP and inorganic PO-4
• ATP synthase• Cellular respiration in mitochondria• Electron Transport Chain
2. Substrate-level phosphorylation
Generation of ATP
-Transfer of a high-energy PO4 from an organic molecule to ADP- Different enzymes- During glycolysis and theTCA or Krebs cycle
-
Glycolysis
• Multi – step breakdown of glucose into intermediates
• Turns one glucose (6-carbon) into two pyruvate (3-carbon) molecules
• Generates a small amount of ATP (substrate-level phosphorylation)
• Generates reducing power - NADH + H+
Figure 9.18 Pyruvate as a key juncture in catabolism
Fermentation
• An extension of glycolysis• Takes place in the absence of oxygen (anaerobic)• Regenerates NAD+ from NADH + H +
• ATP generated by substrate - level phosphorylation during glycolysis
• Does not use the Krebs cycle or ETC (no oxidative -phosphorylation)
• A diversity of end products produced (i.e. lactic acid, alcohols, etc.)
Figure 9.17a Fermentation
Figure 9.17b Fermentation
Figure 9.9 A closer look at glycolysis: energy investment phase
Figure 9.9 A closer look at glycolysis: energy payoff phase
Energy investment phase
Glucose
2 ATP used2 ADP + 2 P
4 ADP + 4 P 4 ATP formed
2 NAD+ + 4 e– + 4 H+
Energy payoff phase
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
Glycolysis Citricacidcycle
Oxidative phosphorylation
ATPATPATP
The energy input and output of glycolysis
Transition step
• Under aerobic conditions, the pyruvate produced during glycolysis is directed to the mitochondrion.
• A multi-enzyme complex, spanning the 2 mitochondrial membranes, turns pyruvate (3-carbon) into Acetyl-CoA (2-carbon) and releases one CO2molecule
• Uses coenzyme A (Vit B derivative)• Generates reducing power NADH + H+
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle
Krebs or TCA Cycle
• A cyclical pathway• Accepts – acetyl – CoA• Generates 2 – CO2 molecules (for every acetyl-CoA• Generates reducing power NADH + H+ and FADH2
• Generates a small amount of ATP (substrate-level phosphorylation)
A closer look at the Krebs cycle
Figure 9.12 A summary of the transition step and Krebs cycle
Figure 9.5 An introduction to electron transport chains
Electron Transport Chain and ATP generation
Electron transport chain:• membrane-embedded or
bound electron carriers• Mostly proteins with non-
protein groups.• NADH vs. FADH2
• No direct formation of ATP• Pumps H+ into the inter-
membrane space
Oxidative Phosphorylation and ATP generation
ATP Generation :• Membrane-embedded protein
complex , ATP synthase• Proton-motive force• Direct formation of ATP by
Chemiosmosis
Chemiosmosis: the coupling of the transport of H+ across membrane by facilitated diffusion with chemical reaction producing ATP
ATP Synthase Gradient: The Moviehttp://vcell.ndsu.edu/animations/at
pgradient/movie.htm
Chemiosmosis couples the electron transport chain to ATP synthesis
Certain poisons interrupt critical events in cellular respiration• Block the movement of electrons• Block the flow of H+ through ATP synthase• Allow H+ to leak through the membrane
H+
H+
H+
H+
H+
H+ H+ H+ H+
+2 H+
H+
H+H+
1 O22
H O2ADP + P ATP
NADHFADH2
NAD+
FAD
Rotenone Cyanide, carbon monoxide
Oligomycin
DNP
ATPSynthase
Electron Transport Chain Chemiosmosis
Energy yield: How many ATP molecules are generated during cellular respiration of a single glucose molecule?
Sources of cellular glucose
• glucose from food in the intestine• glycogen supplies in the muscles• breakdown of the Liver's glycogen into
glucose
The Catabolism of various food molecules
Beta oxidation
http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/carnitine/carnitine1.html
• Triglycerides consist of glycerol and fatty acids• Fatty acids broken down into through beta
oxidation
Simple lipids
Proteins
Protein Amino acidsExtracellular proteases
Krebs cycle and glycolysis Transition step
Deamination, decarboxylation,dehydrogenation Organic acid
Feedback control of cellular respiration
PhosphofructokinaseAllosteric enzymeActivity modulated by inhibitors and activatorsAdjustment of cellular respiration in response to demand
OXIDATIVE PHOSPHORYLATION(Electron Transport and Chemiosmosis)
Food, such as peanuts
Carbohydrates Fats Proteins
Sugars Glycerol Fatty acids Amino acids
Amino groups
Glucose G3P Pyruvate Acetyl CoA
CITRIC ACID CYCLE
ATP
GLYCOLYSIS
Food molecules provide raw materials for biosynthesis consuming ATP
ATP needed to drive biosynthesis
ATP
CITRIC ACID CYCLE
GLUCOSE SYNTHESIS G3P
Acetyl CoA Pyruvate Glucose
Amino groups
Amino acids Fatty acids
Glycerol Sugars
CarbohydratesFatsProteins
Cells, tissues, organisms
Recommended