cellular respiration in detail h. biology. the stages of cellular respiration respiration is a...
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Cellular Respiration in DETAIL
H. Biology
The Stages of Cellular Respiration
• Respiration is a cumulative process of 3 metabolic stages1. Glycolysis2. Kreb’s Cycle (The citric acid cycle)3. Electron Transport Chain (Oxidative phosphorylation)
Stage #1: Glycolysis Glycolysis produces energy by oxidizing glucose
pyruvateGlycolysis
Means “splitting of sugar”Breaks down glucose into pyruvateOccurs in the cytoplasm of the cell1 glucose breaks down 4 ATP made
+ 2 pyruvate molecules(net gain of 2 ATP…NOT 4 ATP)
GlycolysisMain Goal of Glycolysis is to turn glucose into two pyruvate: - Series of 10 steps - Produces a net gain of 2 ATP and 2 NADH (e- carriers) - From here it can go to the Krebs cycle (aerobic respiration) or to Fermentation (anaerobic) - Glycolysis is anaerobic - Occurs in the cytoplasm
Overall: Glucose → 2 Pyruvate; net gain 2 ATP and 2 NADH
Intermediate step
Pyruvate (made in the cytosol via glycolysis) diffuses into the mitochondria. As it diffuses is, it produces one molecule of CO2 loses a carbon (goes from 3C to 2C). This new 2C molecule is acetyl CoA. Acetyl CoA is what enters into the Krebs cycle.
Glycolysis
NET Glucose 2 pyruvate (pyruvic acid)
+ 2 H2O 4 ATP formed – 2 ATP used 2 ATP GAIN
substrate-level phosphorylation used 2 NAD+ + 4e- + 4H+ 2 NADH + 2H+
**Glycolysis can proceed WITHOUT O2
• Glycolysis consists of two major phases1. Energy
investment phase (endergonic= uses 2 ATP)
2. Energy payoff phase
(exogonic = makes 4 ATP)
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
1 Glucose
2 ADP + 2 P
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H +
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H + 2 NADH
+ 2 H+
Stage #2: The Kreb’s Cycle
• The citric acid cycle–Takes place in the matrix of the
mitochondrion
**NEEDS O2 TO PROCEED (unlike glycolysis)
• Stage #1 ½ : The Citric Acid Cycle• Before the citric acid cycle can begin– Pyruvate must first be converted to acetyl CoA, which links
the citric acid cycle to glycolysisCYTOSOL MITOCHONDRIO
N
NADH + H+NAD+
2
31
CO2
Coenzyme A
(a vitamin)Pyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
Uses active
transport
Diffuses out of cell
Acetyl group= unstable
The Kreb’s Cycle
• Also called the “Citric Acid cycle”
• NAD+ and FAD (both are coenzymes) = electron “carriers”; proton acceptors– They are reduced and carry e-’s from
Citric cycle to ETC–Dehydrogenase catalyzes hydrogen
transfer reaction
NAD+ and FAD
Oxidized Form Reduced Form NAD+ NADH (2 e-, 1 H)
FAD FADH2 (4 e-, 2 H)
THINK: FADH2 come into play in the 2nd stage of cellular respiration; it is also the 2nd electron carrier
An overview of the citric acid cycle
(this occurs for EACH pyruvate molecule)
ATP
2 CO2
3 NAD+
3 NADH+ 3 H+
ADP + P i
FAD
FADH2
Citricacidcycle
CoA
CoA Acetyle CoA
NADH+ 3 H+
CoA
CO2
Pyruvate (from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Citricacidcycle
Oxidativephosphorylation
Figure 9.11
Krebs/ citric acid cycleMain Function of the Krebs → to make electron carriers (NADH and FADH2) to send to the ETC
Series of 8 steps; Occurs in the mitochondrial matrix
So…1 glucose produces: 2 ATP6 NADH2 FADH2
(remember: 1 glucose = 2 pyruvates)
Acetyl CoA (2C) enters the Krebs and combines with another molecule (4C) to form citric acid (hence citric acid cycle)
Electron Carriers
Krebs →Makes 1 ATP, 3 NADH, and 1 FADH2 per turn
You do NOT need to memorize
this!
Figure 9.12
Acetyl CoA
NADH
Oxaloacetate
CitrateMalate
Fumarate
SuccinateSuccinyl
CoA
a-Ketoglutarate
Isocitrate
Citricacidcycle
S CoA
CoA SH
NADH
NADH
FADH2
FAD
GTP GDP
NAD+
ADP
P i
NAD+
CO2
CO2
CoA SH
CoA SH
CoAS
H2O
+ H+
+ H+ H2O
C
CH3
O
O C COO–
CH2
COO–
COO–
CH2
HO C COO–
CH2
COO–
COO–
COO–
CH2
HC COO–
HO CHCOO–
CH
CH2
COO–
HO
COO–
CH
HC
COO–
COO–
CH2
CH2
COO–
COO–
CH2
CH2
C O
COO–
CH2
CH2
C O
COO–
1
2
3
4
5
6
7
8
Glycolysis Oxidativephosphorylation
NAD+
+ H+
ATP
Citricacidcycle
Figure 9.12
Kreb’s Cycle Summary• pyruvate Acetyl-CoA + 1 NADH • Each turn of cycle uses 1 pyruvate–So… 1 glucose molecule produces 2 turns
of Kreb’s cycle• 1 turn of cycle yields 4 NADH, 1 ATP,
and 1 FADH2 and 3 CO2 (as waste product) Remember to multiply by 2…why?
Stage #3: Oxidative Phosphorylation (Electron Transport Chain (ETC) + Chemiosmosis)
• Chemiosmosis couples electron transport to ATP synthesis
• NADH and FADH2
–Donate e-s to ETC, which powers ATP synthesis using oxidative phosphorylation
**OCUURS IN CRISTAE (folds of inner membrane)
The Pathway of Electron Transport
• In the ETC…–e-s from NADH and FADH2 lose
energy in several steps**NEEDS O2 TO PROCEED
(unlike glycolysis)
Electron transport chain (ETC)
Occurs on the inner membrane of the mitochondria; Energy from NADH and FADH2 power ATP synthesis
The ETC is a series of proteins throughout the membrane; the electrons lose energy every time they get passed down the chain…
OXYGEN IS THE FINAL ELECTRON ACCEPTOR!!! → oxygen combines with the electrons and H+ to make WATER
Main Goal of the ETC → • It creates a proton gradient that powers chemiosmosis which creates ATP through ATP Synthase
•NADH and FADH2 drop off electrons to the ETC• As the electrons get passed down the chain, they lose energy•The ETC uses that energy (from the electrons) and pumps the protons OUT of the matrix into the intermembrane space• This creates a concentration gradientThe protons then diffuse back INTO the matrix through the ATP synthase (chemiosmosis)-This creates a TON of ATP either 32 or 34 ATPs
• Final e- acceptor after the electrons go down the ETC is OXYGEN (from the atmosphere)• It combines with e- and H+ to make the final product = WATER
Electron transport chain (ETC)
ETC Characteristics
• Lots of proteins (cytochromes) in cristae increases surface area– 1000’s (many) copies of ETC
• ETC carries e-’s from NADH/FADH2 O2
• O2 = pulls e-s “down” ETC due to electronegativity (high affinity for e-s)
• Chemiosmosis and the electron transport chain
Oxidativephosphorylation.
electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carriers
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis
Protin motive force is used!
• At the end of the chain– Electrons are passed to oxygen, forming water–O2 = final e- acceptor
• NAD delivers e- higher than FAD NAD provides 50% more ATP
What happens at the end of the ETC chain?
ETC is a Proton (H+) Pump• Uses the energy from “falling” e-s
(exergonic flow) to pump H+’s from matrix to outer compartment
• A H+ (proton) gradient forms inside mitochondria
• ETC does NOT make ATP directly but provides stage for CHEMIOSOMOSIS to occur
RECALL…Chemiosmosis
• Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work• Uses ATP synthase• Makes ~90% of ATP in Cell Resp. • Proposed by Peter Mitchell (1961)
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase– Is the enzyme
that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows past it down the H+
gradient.
A protein anchoredin the membraneholds the knobstationary.
A rod (or “stalk”)extending into the rotor/ knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP.
MITOCHONDRIAL MATRIXFigure 9.14
http://www.sigmaaldrich.com/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase.html
• There are three main processes in this metabolic enterprise
Electron shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose2
Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation
Maximum per glucose:
About36 or 38 ATP
+ 2 ATP + about 32 or 34 ATP
or
Figure 9.16
+ 2 ATP
• About 40% of the energy in a glucose molecule–Is transferred to ATP during
cellular respiration, making ~36- 38 ATP
Overall (Aerobic Respiration) FADH2 NADH CO2 ATP Total ATP
Gained
Glycolysis2 4 2 (net)
Pyruvate Acetyl-
CoA
2
Kreb’sCycle
2 6 6 2 2
ETC~32-34
ATP GRAND TOTAL = ~36-38 ATP per 1 GLUCOSE
Cellular Respiration overviewATP Summary →Glycolysis – 2 ATPKrebs – 2 ATPETC – 32/34 ATP