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Cellular Respiration C 6 H 12 O O 2 6 CO H 2 O + E Oxidation Reduction C 6 H 12 O 6 is oxidized to form CO 2 O 2 is reduced to form H 2 O e- are used to form ATP
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Complex Organic Molecules
Simpler waste products w/ less energy
catabolicpathway
ATP + H2O
ADP + P
LEO says GEROxidation = loss of e-
Reduction = gain of e-
Xe- + Y X + Ye- X is being oxidized
(reducing agent)
Y is being reduced
(oxidizing agent)
Cellular Respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O + E Oxidatio
n
Reduction
• C6H12O6 is oxidized to form CO2 • O2 is reduced to form H2O• e- are used to form ATP
• Enzymes lower EACT so glucose is oxidized slowly.• Hydrogens stripped from glucose are not transferred directly to oxygen, but are passed to a special e- acceptor
NAD+
NAD+ (nicotinamide adenine dinucleotide)
Acts as a coenzyme in the redox reaction• functions as an oxidizing agent by trapping e-
Reactions are catalyzed by enzymes called dehydrogenases
R–C–R’ + NAD+ R-C-R’ + NADH + H+
H
OH Ooxidation
reduction
NAD+ = oxidized coenzymeNADH = reduced coenzyme
dehydrogenase
Steps of Cellular Respiration:1. GLYCOLYSIS
• occurs in cytosol• partially oxidizes glucose (6C) into two pyruvate (3C) molecules
Energy investment phase = requires to ATP to start
GLUCOSE (6C)
FRUCTOSE DIPHOSPHATE (6C)
2 PGAL
2 ATP2 ADP
2 DPGA
2 NAD
2 NADH2 P
2 PGA
2 ADP2 ATP
2 H2O
2 ADP2 ATP
PYRUVIC ACID
Kreb’s Cycle
Chemical energy from glucose is still stored in the pyruvate molecules.
Fate depends on presence or absence of oxygen
If O2 is present pyruvate enters the mitochondrion where it is completely oxidized
2. KREBS CYCLE• occurs in mitochondrial matrix• complete glucose oxidation by breaking down a pyruvate derivative (acetyl Co-A) into CO2 a small amount of ATP is
produced by substrate-level phosphorylation NADH formed by transfer of e- from substrate to NAD+
Formation of Acetyl-CoA
C=O
C=O
CH3
OH
C=O
S-CoA
CH3
CO2
NAD+
NADH+ H+
pyruvate
Acetyl CoA
A multienzyme complex catalyzes:• the removal of CO2 from the carboxyl group of pyruvate• the oxidation of the 2C fragment to acetate while reducing NAD+ to NADH• the attachment of coenzyme A to the acetyl group forming acetyl CoA
Krebs Cycle (Citric Acid Cycle)• oxidizes remaining acetyl
fragments of Acetyl-CoA to CO2For every turn of the Krebs cycle:
• 2 C enter in the acetyl fragment• 2 different C are oxidized and leave as CO2• coenyzymes are reduced
3 NADH and 1 FADH2• 1 ATP produced by s-l phosphorylation• oxaloacetate is regenerated
(6C)
(5C)
(4C)
(4C)
(4C)
ATP
H2O
It takes 2 turns of the Krebs cycle for complete oxidation of 1 glucose molecule.
GDP
GTP
P+
ADP ATP
CoA-SH
CH2
CH2
C=OS-CoA
COO-
succinyl CoA
CH2
CH2
COO-
COO-
succinate
3. ELECTRON TRANSPORT CHAIN• occurs at the inner
membrane of the mitochondrion• accepts energized e- from reduced coenzymes (NADH and FADH2) • O2 pulls the e- down the ETC to a lower energy state• couples the exergonic slide of e- to ATP synthesis (oxidative phosphorylation – makes 90% of all ATP)
FMN
CoQFeS
FeSCyt b
Cyt c
FeS
Cyt c3
Cyt aCyt a1
½ O2
NADH FADH2
Final e- acceptor(forms
water)
NADH=3 ATPFADH2=2 ATP
ETC does not make ATP directly.It generates a proton gradient across the inner mitochondrial membrane.
KREBS CYCLE net: (2 turns)• 2 ATP by s-l
phosphorylation• 6 NADH• 2 FADH2• 4 CO2
*** most energy found in NADH and FADH2 in high energy bonds
From glycolysis and Krebs
Process ATP by S-L
Phos.
Reduced Co-
Enzyme
ATP by Ox
Phos.
TOTAL
GlycolysisNet 2 ATP 2 NADH 4-6 ATP 6-8 ATP
Oxidation of
Pyruvate2 NADH 6 ATP 6 ATP
Krebs Cycle 2 ATP
6 NADH2 FADH2
18 ATP4 ATP 24 ATP
36-38 ATPTOTAL
* Prokaryotes usually get a better yield of 38 ATP because there is no membrane separating glycolysis from the ETC.* Eukaryotes usually only get 2 ATP per NADH in glycolysis.
Respiratory Poisons:Cyanide – blocks e- from cyt a3 to O2
Oligomycin (antibiotic) – inhibits ATP synthaseDinitrophenol (DNP) – uncouples the chemiosmotic reaction so protons leak across the membrane
Anaerobic Respiration:• occurs if O2 is not present there is no final
e- acceptor• used by plants, fungi (yeasts) and bacteria• occurs in the cytoplasm alongside glycolysis
2 PYRUVATE
2 ACETYLALDEHYDE
2 ETHANOL
2 CO2
2 NADH2 NAD+
2 PYRUVATE
2 LACTATE
2 NADH2 NAD+
ANAEROBIC RESPIRATION:• does not require O2• uses ETC to make ATP• uses a substance other than O2 as the final e- acceptorex. NO3 or SO4
-2
• produces ATP by oxidative phosphorylation
** occurs in only a few bacterial groups that exist in anaerobic environments
Strict (obligate) aerobes:organisms that require O2 for growth and as the final e- acceptor
Strict (obligate) anaerobes:organisms that only grow in the absence of O2, and are poisoned by it
FACULATIVE ANAEROBES:organisms can grow in either aerobic or anaerobic environmentsCells can make ATP by fermentation if O2 is not available or ATP by cellular respiration if O2 is available.PYRUVATE is common to both fermentation and respiration.
GLUCOSE
PYRUVATE
reduced to ethanol or lactate and NAD+ is recycled as NADH is oxidized
oxidized to acetyl CoA and oxidation continues into the Krebs cycle
no O2
O2
RESPIRATION CONTROLS:• Third step in glycolysis is catalyzed by the allosteric enzyme phosphofructokinase.• Ratio of ATP to ADP reflects energy status of the cell. PFK is sensitive to changes in this ratio.• Citrate and ATP are allosteric inhibitors of PFK.
When concentration rises, enzyme slows glycolysis.
• ADP is an allosteric activator of PFK
so when ADP rises, enzyme speeds up glycolysis