Figure 1: The structure of adenosine triphosphate (ATP). In the cell, most hydroxyl groups of phosphates are ionized (-O -)
Enzyme
Enzyme
ADP P Substrate
ATP Product
12
13
STROMA Cytochrome (low H concentration) NADP Photosystem II complex Light Photosystem I reductase 4 H+ Light NADP + H Fd
Pq H2O
NADPH Pc
2 1
/ 2 O2 +2 H+
1
THYLAKOID SPACE (high H concentration)
Thylakoid membrane STROMA (low H concentration)
4 H+
To Calvin Cycle
ATP synthase
ADP + P i H+
ATP
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In the generalized reaction, substance X, the electron donor, is called the reducing agent; it reduces Y, which accepts the donated electron. Substance Y, the electron acceptor, is the oxidizing agent; it oxidizes X by removing its electron. Because an electron transfer requires both a donor and an acceptor, oxidation and reduction always go together.
Metabolic process within cells which releases energy from glucose
Cellular (internal) Glycolysis Krebs cycle Electron transport system
Respiration
External (gas exchange)
Process of obtaining O2 for respiration and removal of gaseous wastes
Respiration is a cumulative function of three metabolic stages: Glycolysis
The citric acid cycle
Oxidative phosphorylation: electron transport and chemiosmosis
Hexokinase
Phosphoglucoisomerase
1.
Glucose enters the cell and is phosphorylated by the enzyme hexokinase, which transfers a phosphate group from ATP to the sugar. The charge of the phosphate group traps the sugar in the cell because the plasma membrane is impermeable to ions. Phosphorylation also makes glucose more chemically reactive.
2. Glucose-6-phosphate is rearranged to convert it to its isomer, fructose-6-phosphate.
3.
This enzyme transfers a phosphate group from ATP to the sugar, investing another molecule of ATP in glycolysis. So far, 2 ATP have been used. With phosphate groups on its opposite ends, the sugar is now ready to be split in half. This is a key step for regulation of glycolysis, Phosphofructokinase is allosterically regulated by ATP and its products.
4.
This is the reaction from which glycolysis gets its name. The enzyme cleaves the sugar molecule into 2 different 3-carbon sugars: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. These 2 sugars are isomers of each other.
Phosphofructokinase
Aldolase
Isomerase
5. Isomerase catalyzes the reversible conversion between the 2 three-carbon sugars. This reaction never reaches equilibrium in the cell because the next enzyme in glycolysis uses only Glyceraldehyde-3phosphate as its substrate.
Triose phosphate dehydrogenase
Phosphoglycerokinase
6. This enzyme catalyzes 2 sequential reactions while it holds glyceraldehyde-3-phosphate in its active site. First, the sugar is oxidized by the transfer of electrons and H+ to NAD+, forming NADH. This reaction is very exergonic, and the enzyme uses the released energy to attach a phosphate group to the oxidized substrate, making a product of very high potential energy. The source of the phosphate is the pool of inorganic phosphate ions that are always present in the cytosol.
7.
Glycolysis produces some ATP by substrate-level phosphorylation. The phosphate group added in the previous step is transferred to ADP in an exergonic reaction. For each glucose molecule that began glycolysis, step 7 produces 2 ATP, since every product after the sugar-splitting step is doubled.
8. The enzyme relocates the remaining phosphate group.
Phosphoglyceromutase
9. This enzyme causes a double bond to form in the substrate by extracting a water molecule, yielding PEP. The electrons of the substrate are rearranged in such a way that the remaining phosphate bond becomes very unstable, preparing the substrate for the next reaction. Enolase
Pyruvate kinase
10. The last reaction of glycolysis produces more ATP by transferring the phosphate group from PEP to ADP. Overall glycolysis used 2 ATP in energy investment phase and produced 4 ATP in the energy payoff phase, for a net gain of 2 ATP.
MITOCHONDRION
CYTOSOL
CO2
Pyruvate’s Pyruvate’s carboxyl carboxyl is is removed as CO removed as CO22
Coenzyme A
Coenzyme Coenzyme A, A, sulfur sulfur containing containing compound compound attached attached to to acetate acetate by by unstable unstable bond bond that that makes makes acetyl group (the attached acetyl group (the attached acetate) acetate) very very reactive. reactive.
3
1
2
Pyruvate Transport protein
2 NAD NADH
+ 2 H
Remaining Remaining 2-carbon 2-carbon fragment fragment is is oxidized oxidized to to forming forming acetate acetate
Acetyl CoA 28
Figure.12
Kreb Cycle/Citric Acid Cycle Oxidative decarboxilation
Condensation Oxidation
Isomerization
Hydration
Oxidative decarboxilation Oxidation Substrate level phosphorylation
Oxidative decarboxilation
38
39
A rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient. A stator anchored in the membrane holds the knob stationary. A rod (or “stalk�) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Electron Transport Chain H2O Produced Occurs Across Inner Mitochondrial membrane Final electron acceptor oxygen NADH = 2.5 ATP’s
8 NADH = 20 ATP
FADH2 = 1.5 ATP’s
2 FADH2 = 3 ATP
2 NADH from glycolysis IN CYTOSOL
if NADH = 5 ATP or if FADH2 = 3 ATP IN MITOCHONDRIA
28 ATP or 26 ATP
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SOURCE Glycolysis
ATP yield (process) • 2 ATP • 2 NADH
substrate level phosphorylation
3 ATP or 5 ATP oxidative phosphorylation
Formation of Acetyl CoA
2 NADH
Krebs cycle
• 2 GTP
2X 2.5ATP
5 ATP
oxidative phosphorylation
2 ATP substrate level phosphorylation
• 6 NADH
6X2.5 ATP
15 ATP
oxidative phosphorylation
• 2 FADH2
2X1.5ATP
3 ATP
oxidative phosphorylation
TOTAL 30 or 32 ATP
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+ 26 or 28 ATP
30 or 32 ATP
Organism
Anaerobes
Obligate - cannot use free O2 for respiration. O2 may inhibit the growth or kill them
Facultative - able to alter their metabolism to grow in either the presence or absence of O2
Aerobes
Obligate - can only survive in the presence of O2