Transcript How do cells do work?

…transferring a phosphate group to another molecule =
phosphorylation
-- use a little ATP to net a larger amount of kinetic E (work)
…have to make $ to spend $
How do cells
do work?
• ATP is involved
• What organelles are
responsible for energy
conversion?
• Converting E from sugar in
the presence of O2 =
cellular respiration
• …the cell captures E
released as ATP
Respiration vs. Breathing
• Exchange of gases… O2 in & CO2 out
• Aerobic energy harvesting = cellular
respiration
…more work
requires more O2
Energy extraction by cells…
• Glucose =
= C6H12O6 = potential E
• electrons (energy) transfer as carbon - hydrogen bonds
break
…hydrogen-oxygen bonds form as water
• Transfer of electrons from reactants to products side of
reaction = oxidation-reduction reaction (redox reaction)
3 main stages of cellular respiration
• Glycolysis
– Breaking glucose into
– a 3-carbon, pyruvate
• Citric acid cycle
– Modifies pyruvate
• Oxidative phosphorylation
– Uses the E from electron transport chain to
phosphorylate ADP
• Electrons are shuttled by NAD+
– an enzyme, nicotinamide adenine
dinucleotide, that gets reduced (gain of H) to
NADH
6.8 Pyruvate is chemically groomed for
the citric acid cycle
• The pyruvate formed in glycolysis is
transported to the mitochondria, where it is
prepared for entry into the citric acid cycle
– The first step is removal of a carboxyl group that
forms CO2
– The second is oxidization of the two-carbon
compound remaining
– Finally, coenzyme A binds to the two-carbon
fragment forming acetyl coenzyme A
Copyright © 2009 Pearson Education, Inc.
NADH  H+
NAD+
2
CoA
Pyruvate
Acetyl coenzyme A
1
3
CO2
Coenzyme A
6.10 Most ATP production occurs by oxidative
phosphorylation
• Oxidative phosphorylation involves electron
transport and chemiosmosis and requires an
adequate supply of oxygen
– NADH and FADH2 and the inner membrane of
the mitochondria are also involved
– A H+ ion gradient formed from all of the redox
reactions of glycolysis and the citric acid cycle
provide energy for the synthesis of ATP
Copyright © 2009 Pearson Education, Inc.
Intermembrane
space
Protein
complex
of electron
carriers
H+
H+
H+
H+
H+
H+
H+
Electron
carrier
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
Mitochondrial
matrix
FAD
NAD+
H+
1

2
O2 + 2 H+
H+
H+
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
ADP + P
ATP
H+
Chemiosmosis
Electron transport chain
• NADH delivers
electrons (e-) to a
cascade of reactions
…like a slinky moving down
a staircase…keeps
momentum resulting in a
net release of greater E
6.9 The citric acid cycle completes the oxidation of
organic molecules, generating many NADH and
FADH2 molecules
• With the help of CoA, the acetyl (twocarbon) compound enters the citric acid
cycle
– At this point, the acetyl group associates with a
four-carbon molecule forming a six-carbon
molecule
– The six-carbon molecule then passes through a
series of redox reactions that regenerate the
four-carbon molecule (thus the “cycle”
designation)
Copyright © 2009 Pearson Education, Inc.
Acetyl CoA
CoA
CoA
CITRIC ACID CYCLE
2 CO2
3 NAD+
FADH2
3 NADH
FAD
3 H+
ATP
ADP + P
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
CITRIC ACID CYCLE
Step 1
Acetyl CoA stokes the furnace.
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NAD+
2
NADH + H+
CITRIC ACID CYCLE
CO2 leaves cycle
ADP + P
ATP
Alpha-ketoglutarate
3
CO2 leaves cycle
NADH + H+
Step 1
Acetyl CoA stokes the furnace.
NAD+
Steps 2 – 3
NADH, ATP, and CO2 are generated
during redox reactions.
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NADH +
H+
NAD+
5
NAD+
2
NADH + H+
CITRIC ACID CYCLE
CO2 leaves cycle
Malate
ADP  P
FADH2
4
ATP
FAD
Alpha-ketoglutarate
3
CO2 leaves cycle
Succinate
NADH + H+
Step 1
Acetyl CoA stokes the furnace.
NAD+
Steps 2 – 3
NADH, ATP, and CO2 are generated
during redox reactions.
Steps 4 – 5
Redox reactions generate FADH2
and NADH.
How much energy or ATP is produced for
each glucose molecule?
Is this system efficient?
• 38 ATPs = 40% of the potential E in
glucose
• 60% escapes as heat
• Auto engine converts 25% E from fuel
• Muscle use 10,000,000 ATP per second
Fermentation (animal cells)
• Oxidize organic fuel & produce ATP without
oxygen
– Anaerobic alternative
– Relies on glycolysis (1st step of respiration)
• Only 2 ATPs
– Then…converts pyruvate to lactate
– muscle burn
– Lactate is recycled by liver
Fermentation (yeast)
• Oxidize organic fuel & produce ATP without
oxygen
– Anaerobic alternative
– Relies on glycolysis (1st step of respiration)
• Only 2 ATPs
– Then…converts pyruvate to ethanol and CO2
– Gas bubbles in beer & champhagne, dough to rise
– Alcohol is produced as yeast waste…eventually killing ‘em