Download Harvesting stored energy

Harvesting stored energy
• Energy is stored in organic molecules
• carbohydrates, fats, proteins
• Heterotrophs eat these organic molecules  food
• digest organic molecules to get…
• raw materials for synthesis
• fuels for energy
• controlled release of energy
• “burning” fuels in a series of
step-by-step enzyme-controlled reactions
Figure 9.2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2  H2O
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
 O2
molecules
ATP powers
most cellular work
Living economy
• Fueling the body’s economy
• eat high energy organic molecules
• food = carbohydrates, lipids, proteins, nucleic acids
• break them down
• digest = catabolism
• capture released energy in a form the cell can use
• Need an energy currency
• a way to pass energy around
• need a short term energy
storage molecule
Whoa!
Hot stuff!
ATP
ATP
• Adenosine TriPhosphate
• modified nucleotide
• nucleotide =
adenine + ribose + Pi  AMP
• AMP + Pi  ADP
• ADP + Pi  ATP
• adding phosphates is endergonic
How efficient!
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high energy bonds
How does ATP store energy?
ADP
AMP
ATP
I think
he’s a bit
unstable…
don’t you?
O– O– O–
–O
– –O
–
OP
P –O
OP
OP
O–
O O O
• Each negative PO4 more difficult to add
• a lot of stored energy in each bond
• most energy stored in 3rd Pi
• 3rd Pi is hardest group to keep bonded to molecule
• Bonding of negative Pi groups is unstable
• spring-loaded
• Pi groups “pop” off easily & release energy
Instability of its P bonds makes ATP an excellent energy donor
How does ATP transfer energy?
O– O– O–
–OP –O
– –O
–
OP
OP
O–
O O O
ATP
ADP
O–
–OP O– +
O
• ATP  ADP
• releases energy
• ∆G = -7.3 kcal/mole
• Fuel other reactions
• Phosphorylation
• released Pi can transfer to other molecules
• destabilizing the other molecules
• enzyme that phosphorylates = “kinase”
7.3
energy
ATP / ADP cycle
Can’t store ATP
cellular
 good energy donor,
not good energy storage respiration
ATP
7.3
kcal/mole
 too reactive
 transfers Pi too easily
 only short term energy
ADP + Pi
storage
 carbohydrates & fats are A working muscle recycles over
long term energy storage 10 million ATPs per second
Whoa!
Pass me
the glucose
(and O2)!
How do we harvest energy from fuels?
• Digest large molecules into smaller ones
• break bonds & move electrons from one molecule to another
• as electrons move they “carry energy” with them
• that energy is stored in another bond,
released as heat or harvested to make ATP
loses e-
gains e-
+
oxidized
reduced
+
+
eoxidation
e-
–
ereduction
redox
Oxidation & reduction
• Oxidation
• Reduction
• adding O
• removing H
• loss of electrons
• releases energy
• exergonic
• removing O
• adding H
• gain of electrons
• stores energy
• endergonic
oxidation
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
reduction
Moving electrons in respiration
• Electron carriers move electrons by
shuttling H atoms around
• NAD+  NADH (reduced)
• FAD+2  FADH2 (reduced)
NAD+
nicotinamide
Vitamin B3
niacin
O–
O–P –O
O
phosphates
O–
O–P –O
O
NADH
O
H
C
N+
+
adenine
ribose sugar
H H
NH2
C
reduction
O–
–
–O
oxidation O P
O
O–
O–P –O
O
carries electrons as
H
O
a reduced molecule
N+
NH2
How efficient!
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Overview of cellular respiration
• 4 metabolic stages
• Anaerobic respiration
1. Glycolysis
• respiration without O2
• in cytosol
• Aerobic respiration
• respiration using O2
• in mitochondria
2. Pyruvate oxidation
3. Citric Acid (Krebs) cycle
4. Electron transport chain
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 (+ heat)
• Oxidative phosphorylation accounts for almost 90%
of the ATP generated by cellular respiration (Energy
stored in NADH and FADH2 is used to produce ATP)
© 2011 Pearson Education, Inc.
• A smaller amount of ATP is formed in glycolysis and
the citric acid cycle by substrate-level
phosphorylation
• For each molecule of glucose degraded to CO2 and
water by respiration, the cell makes up to 32
molecules of ATP
© 2011 Pearson Education, Inc.
Concept 9.2: Glycolysis harvests
chemical energy by oxidizing glucose to
pyruvate
• Glycolysis (“splitting of sugar”) breaks down glucose
into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two major
phases
• Energy investment phase
• Energy payoff phase
• Glycolysis occurs whether or not O2 is present
© 2011 Pearson Education, Inc.
Glycolysis
• Breaking down glucose
• “glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C
• ancient pathway which harvests energy
• where energy transfer first evolved
• transfer energy from organic molecules to ATP
• still is starting point for ALL cellular respiration
• but it’s inefficient
• generate only 2 ATP for every 1 glucose
• occurs in cytosol
That’s not enough
ATP for me!
In the
cytosol?
Why does
that make
evolutionary
sense?
Evolutionary perspective
• Prokaryotes
• first cells had no organelles
Enzymes
of glycolysis are
“well-conserved”
• Anaerobic atmosphere
• life on Earth first evolved without free oxygen (O2) in
atmosphere
• energy had to be captured from organic molecules in
absence of O2
• Prokaryotes that evolved glycolysis are ancestors of all
modern life
• ALL cells still utilize glycolysis
You mean
we’re related?
Do I have to invite
them over for
the holidays?
endergonic
invest some ATP
exergonic
harvest a little
ATP & a little NADH
net yield
2 ATP
2 NADH
If you get bored……but you don’t need to
know this!!!
Concept 9.3: After pyruvate is oxidized, the
citric acid cycle completes the energyyielding oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrion (in eukaryotic cells) where the oxidation
of glucose is completed
© 2011 Pearson Education, Inc.
The Citric Acid Cycle
• The citric acid cycle, also
called the Krebs cycle,
completes the break down of
pyruvate to CO2
• The cycle oxidizes organic
fuel derived from pyruvate,
generating 1 ATP, 3 NADH,
and 1 FADH2 per turn
© 2011 Pearson Education, Inc.
Figure 9.12-8
Acetyl CoA
CoA-SH
NADH
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2