cellular respiration: harvesting chemical energy -...
TRANSCRIPT
Life Is Work
• Living cells require energy from outside sources
• Plants E from ?
• Animals E from ?
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2 + H2O
Cellular respiration in mitochondria
Organic molecules
+ O2
ATP powers most cellular work
Heat energy
ATP
Energy flows into
ecosystem as light
Energy leaves as heat
ATP powers work
• Photosynthesis
– Organelle = ?
– Generates O2 and organic molecules
• Cellular respiration
– Organelle = ?
– Uses organic molecules to generate ATP
Catabolic Pathway review
• Organic molecules have potential (chemical) energy
• Exergonic rxns break down organic molecules energy (and heat)
Cellular Respiration
• Aerobic respiration – Uses O2
– ATP produced
Anaerobic respiration Does not use O2
ATP produced
Cellular respiration
1. Glycolysis Occurs in cytoplasm
Anaerobic
Glucose + 2NAD+ + 2ATP 2 pyruvate+ 2NADH + 4ATP
• 1 glucose 2 ATP and 2 pyruvate
• Glucose oxidized to pyruvate (loses electron)
• NAD+ reduced to NADH (gains electron)
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Glycolysis
CYTOSOL
Electron donor
mitochondrion
Glycolysis
1. Energy investment phase uses 2 ATP
2. Energy payoff phase
– 4 ATP produced
– 2NAD+ reduced to 2NADH
– 1 glucose split to 2 pyruvate
Glucose + 2NAD+ + 2ATP 2 pyruvate+ 2NADH + 4ATP
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed 4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2O Glucose
Net
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2. Citric acid cycle (Krebs cycle) • mt matrix
– Matrix is enclosed by the inner membrane
What’s in the matrix?
Enzymes (acetyl CoA)
mtDNA
Ribosomes
Citric acid cycle 2Pyruvate + NAD+ + FADH 2ATP + NADH + FADH2 + CO2 + H2O
Where did the pyruvate come from? How did it get into the mt matrix? # ATP generated? Waste product? Where does it go? NADH and FADH2 can donate electrons later What happened to the sugar? O2?
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
MITCHONDRION
citric acid cycle
1. Convert 2pyruvate to 2acetyl A (before cycle)
Acetyl CoA links
glycolysis to cycle
Pyruvate diffuses into mt matrix and is converted to acetyl CoA
Cellular Respiration: Bioflix animation
CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Pyruvate
Transport protein
CO2 Coenzyme A
Acetyl CoA
Pyruvate
NAD+
NADH
+ H+ Acetyl CoA
CO2
CoA
CoA
CoA
Citric acid cycle
FADH2
FAD
CO2 2
3
3 NAD+
+ 3 H+
ADP + P i
ATP
NADH
8 enzymatic steps
ATP:
For each pyruvate?
For each glucose?
For each turn of cycle?
Summary of citric acid cycle • Per molecule glucose =2 pyruvate
– NADH and FADH 2 electron donors
– 2 ATP (1 per turn) per glucose
• CO 2 produced (2 per turn) out
• mt matrix
Text Activity: The Citric Acid Cycle
BIO 231 TCA cycle animation: Acetyl CoA formation
3. oxidative phosphorylation in mt cristae Cristae compartmentalize mt inner membrane = more surface area
What happens?
NADH and FADH 2 donate electrons in the series of steps
Oxygen accepts electrons water
H+ proton gradient
ADP + P ATP
34 ATP produced
Add up the ATP yield per glucose:
Glycolysis + Citric acid cycle + Ox Phos =
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation
ATP
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Oxidative phosphorylation: 34 ATP
Stepwise Energy Harvest via Electron Transport Chain
1. Controlled rxns
(a) Uncontrolled reaction
H2 + 1/2 O2
Explosive release of heat and
light energy
(b) Cellular respiration
Controlled release of energy for synthesis
of ATP
2 H+ + 2 e–
2 H 1/2
O2 (from food via NADH)
1/2
O2
• 2. electron transport is a fall in energy during each step to control release of fuel energy
NADH
NAD+ 2
FADH2
2 FAD
Multiprotein
complexes FAD
Fe•S
FMN
Fe•S
Q
Fe•S
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
IV
50
40
30
20
10 2
(from NADH
or FADH2)
0 2 H+ + 1/2 O2
H2O
e–
e–
e–
powered by redox reactions
Electron Transport Chain
BIO 231 Electron transport animation Watch the electrons
Overview: Wiley
Electron Transport: Wiley
Watch the electrons
H+ gradient, a proton force • ET chain e- pumps H+ across mt membrane
• H+ gradient drives ATP production
• Interactive concepts
• Watch the H+ ions
• Mcgraw hill electron transport
• Watch the H+, no audio
• ATP synthase
– H+ ion enters for one turn
– ADP + P ATP
INTERMEMBRANE SPACE
Rotor
H+ Stator
Internal rod
Catalytic knob
ADP +
P ATP i
MITOCHONDRIAL MATRIX
Virtual Cell: Electron
Transport Chain animation
Protein complex of electron carriers
H+
H+ H+
Cyt c
Q
V
FADH2 FAD
NAD+
NADH
(carrying electrons from food)
Electron transport chain
2 H+ + 1/2O2 H2O
ADP + P i
Chemiosmosis
Oxidative phosphorylation
H+
H+
ATP
synthase
ATP
2 1
An Accounting of ATP Production by Cellular Respiration
• Most energy:
glucose NADH electron transport chain proton-motive force ATP
= ~38 ATP total
Maximum per glucose: About
36 or 38 ATP
+ 2 ATP +2ATP + about 32 or 34 ATP
Oxidative phosphorylation: electron transport
and chemiosmosis
Citric acid cycle
2 Acetyl CoA
Glycolysis
Glucose 2
Pyruvate
2 NADH 2 NADH 6 NADH 2 FADH2
2 FADH2
2 NADH CYTOSOL Electron shuttles span membrane
or
MITOCHONDRION
Glycolysis Citric Acid Cycle Ox. Phos.
Cytosol mt mt
Anaerobic respiration (cytoplasm) Prokaryotes
Eukaryotes
Generate ATP without O2
1. Glycolysis
2. Fermentation
Fermentation
No electron transport chain
NAD+ reused in glycolysis (way to keep generating ATP without O2)
2 ADP + 2 P i 2 ATP
Glucose Glycolysis
2 Pyruvate
2 NADH 2 NAD+
+ 2 H+ CO2
2 Acetaldehyde 2 Ethanol
(a) Alcohol fermentation
2
Lactic acid fermentation
Pyruvate + NADH lactate + NAD+
• Bacteria, fungi in cheese making
• Human muscle cells use lactic acid fermentation to generate Pyruvate + NADH lactate + NAD+
• ATP when O2 is low.
Glucose
2 ADP + 2 P i 2 ATP
Glycolysis
2 NAD+ 2 NADH
+ 2 H+ 2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Fermentation (no O2) vs. Aerobic Respiration
• Both use glycolysis to oxidize glucose (and other organic fuels ) to pyruvate
• ATP
– Cellular respiration 38 ATP per glucose
– Fermentation 2 ATP per glucose
• Obligate anaerobes – fermentation – cannot survive in the presence of O2
– Ex. clostridium botulinum
• Facultative anaerobes
– Yeast and many bacteria – can survive using either fermentation or cellular
respiration (pyruvate can be used either way) – Ex. E. coli, Streptococcus
Glucose
Glycolysis
Pyruvate
CYTOSOL
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Acetyl CoA Ethanol or
lactate Citric acid cycle
Facultative anaerobe
The Evolutionary Significance of Glycolysis
• Glycolysis occurs in nearly all organisms
• Glycolysis probably evolved in ancient prokaryotes before O2 on planet
The Versatility of Catabolism
• Glycolysis and fuel
– Carbohydrates – many accepted
– Proteins amino acids; glycolysis or the citric acid cycle
– Fats glycerol glycolysis
– Fatty acids acetyl CoA
– An oxidized gram of fat produces >2X ATP as oxidized gram of carbohydrate
Proteins Carbohydrates
Amino acids
Sugars
Fats
Glycerol Fatty acids
Glycolysis
Glucose
Glyceraldehyde-3-
Pyruvate
P
NH3
Acetyl CoA
Citric acid cycle
Oxidative phosphorylation
Fermentation and anaerobic respiration enable cells to produce ATP
without the use of oxygen
• Most cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP
Regulation of Cellular Respiration via Feedback Mechanisms
• Feedback inhibition is the most common mechanism for control
• If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
• Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway