Phosphorylation - Biology Junction
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Cellular Respiration
Harvesting Chemical Energy
ATP
AP Biology
2006-2007
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
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
AP Biology
Harvesting stored energy
Glucose is the model
respiration
catabolism of glucose to produce ATP
glucose + oxygen energy + water + carbon
dioxide
C6H12O6 +
6O2
ATP + 6H2O + 6CO2 + heat
COMBUSTION = making a lot of heat energy
by burning fuels in one step
fuel
AP Biology
carbohydrates)
RESPIRATION = making ATP (& some heat)
by burning fuels in many small steps
ATP
enzymes
O2
ATP
O2
CO2 + H2O + ATP (+ heat)
glucose
CO2 + H2O + heat
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
AP Biology
e-
–
ereduction
redox
How do we move electrons in biology?
Moving electrons in living systems
electrons cannot move alone in cells
electrons move as part of H atom
e
p
move H = move electrons
loses e-
gains e-
oxidized
+
+
oxidation
reduced
+
–
H
reduction
H
oxidation
C6H12O6 +
AP Biology
H e-
6O2
6CO2 + 6H2O + ATP
reduction
Coupling oxidation & reduction
REDOX reactions in respiration
release energy as breakdown organic molecules
break C-C bonds
strip off electrons from C-H bonds by removing H atoms
C6H12O6 CO2 = the fuel has been oxidized
electrons attracted to more electronegative atoms
in biology, the most electronegative atom?
O2 H2O = oxygen has been reduced
O
couple REDOX reactions &
2
use the released energy to synthesize ATP
oxidation
C6H12O6 +
AP Biology
6O2
6CO2 + 6H2O + ATP
reduction
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
AP Biology
like $$
in the bank
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
AP Biology
H
reducing power!
NADH
O
H H
C NH2
N+
+
adenine
ribose sugar
C NH2
reduction
O–
–
–
oxidation O P O
O
O–
O – P –O
O
carries electrons as
H
O
a reduced molecule
N+
How efficient!
Build once,
use many ways
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. Krebs cycle
4. Electron transport chain
C H O6 +
AP Biology
6 12
6O2
ATP + 6H2O + 6CO2 (+ heat)
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
H+
And how do we do that?
H+
H+
H+
H+
H+
H+
H+
ATP synthase enzyme
H+ flows through it
conformational
changes
bond Pi to ADP to
make ATP
set up a H+ gradient
allow the H+ to flow
down concentration
gradient through ATP
synthase
ADP + Pi ATP
APBut…
Biology How
ADP + P
ATP
is the proton (H+) gradient formed?
H+
H+
Got to wait until
the sequel!
Got the Energy?
Ask Questions!
H+
H+
H+
H+
H+
H+
H+
ADP + P
ATP
AP Biology
H+
2006-2007
Cellular Respiration
Stage 2 & 3:
Oxidation of Pyruvate
Krebs Cycle
AP Biology
2006-2007
Overview
10 reactions
glucose
C-C-C-C-C-C
2 ATP
2 ADP
convert
fructose-1,6bP
glucose (6C) to
P-C-C-C-C-C-C-P
2 pyruvate (3C)
DHAP
G3P
produces:
4 ATP & 2 NADH P-C-C-C C-C-C-P
2H
consumes:
2Pi
2 ATP
net:
2Pi
2 ATP & 2 NADH
AP Biology
pyruvate
C-C-C
2 NAD+
2
4 ADP
4 ATP
Glycolysis is only the start
Glycolysis
glucose pyruvate
6C
2x 3C
Pyruvate has more energy to yield
3 more C to strip off (to oxidize)
if O2 is available, pyruvate enters mitochondria
enzymes of Krebs cycle complete the full
oxidation of sugar to CO2
pyruvate CO2
AP Biology
3C
1C
Cellular respiration
AP Biology
Mitochondria — Structure
Double membrane energy harvesting organelle
smooth outer membrane
highly folded inner membrane
cristae
intermembrane space
fluid-filled space between membranes
matrix
inner fluid-filled space
DNA, ribosomes
enzymes
free in matrix &
What cells would have
AP
Biology
a lot
of mitochondria?
outer
intermembrane
membrane
inner
membrane-bound space
membrane
cristae
matrix
mitochondrial
DNA
Mitochondria – Function
Oooooh!
Form fits
function!
Dividing mitochondria
Membrane-bound proteins
Who else divides like that? Enzymes & permeases
bacteria!
What does this tell us about
the evolution of eukaryotes?
Endosymbiosis!
AP Biology
Advantage of highly folded inner
membrane?
More surface area for membranebound enzymes & permeases
Oxidation of pyruvate
Pyruvate enters mitochondrial matrix
[
2x pyruvate acetyl CoA + CO2
3C
2C
1C
NAD
Where
does the
CO2 go?
Exhale!
3 step oxidation process
releases 2 CO2 (count the carbons!)
reduces 2 NAD 2 NADH (moves e )
produces 2 acetyl CoA
Acetyl CoA enters Krebs cycle
AP Biology
]
Pyruvate oxidized to Acetyl CoA
reduction
NAD+
Pyruvate
C-C-C
[
Coenzyme A
CO2
Acetyl CoA
C-C
oxidation
2 x Yield = 2C sugar + NADH + CO2
AP Biology
]
Krebs cycle
1937 | 1953
aka Citric Acid Cycle
in mitochondrial matrix
8 step pathway
Hans Krebs
each catalyzed by specific enzyme
1900-1981
step-wise catabolism of 6C citrate molecule
Evolved later than glycolysis
does that make evolutionary sense?
bacteria 3.5 billion years ago (glycolysis)
free O2 2.7 billion years ago (photosynthesis)
eukaryotes 1.5 billion years ago (aerobic
AP Biology
respiration = organelles mitochondria)
Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
4C
citrate
oxidation
of sugars
4C
6C
CO2
x2
4C
AP Biology
acetyl CoA
5C
4C
CO2
Count the electron carriers!
pyruvate
3C
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
4C
citrate
reduction
of electron
carriers
x2
4C
FADH2
4C
AP Biology
acetyl CoA
ATP
CO2
NADH
6C
CO2
NADH
5C
4C
CO2
NADH
Whassup?
So we fully
oxidized
glucose
C6H12O6
CO2
& ended up
with 4 ATP!
What’s the
point?
AP Biology
Electron Carriers = Hydrogen Carriers
H+
Krebs cycle
produces large
quantities of
electron carriers
NADH
FADH2
go to Electron
Transport Chain!
AP Biology
What’s so
important about
electron carriers?
H+
H+
H+
+
H+ H H+
H+
ADP
+ Pi
ATP
H+
Energy accounting of Krebs cycle
4 NAD + 1 FAD
4 NADH + 1 FADH2
2x pyruvate CO2
3C
3x 1C
1 ADP
1 ATP
ATP
Net gain = 2 ATP
= 8 NADH + 2 FADH2
AP Biology
Value of Krebs cycle?
If the yield is only 2 ATP then how was the
Krebs cycle an adaptation?
value of NADH & FADH2
electron carriers & H carriers
reduced molecules move electrons
reduced molecules move H+ ions
to be used in the Electron Transport Chain
like $$
in the
bank
AP Biology
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
H+
And how do we do that?
H+
H+
H+
H+
H+
H+
H+
ATP synthase
set up a H+ gradient
allow H+ to flow
through ATP synthase
powers bonding
of Pi to ADP
ADP + P
ADP + Pi ATP
ATP
H+
AP Biology
But…
Have we done that yet?
NO!
The final chapter
to my story is
next!
Any Questions?
AP Biology
2006-2007
Cellular Respiration
Stage 4:
Electron Transport Chain
AP Biology
2006-2007
Cellular respiration
AP Biology
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
ATP accounting so far…
Glycolysis 2 ATP
Kreb’s cycle 2 ATP
Life takes a lot of energy to run, need to
extract more energy than 4 ATP!
There’s got to be a better way!
I need a lot
more ATP!
AP Biology
A working muscle recycles over
10 million ATPs per second
There is a better way!
Electron Transport Chain
series of proteins built into
inner mitochondrial membrane
along cristae
transport proteins & enzymes
transport of electrons down ETC linked to
pumping of H+ to create H+ gradient
yields ~36 ATP from 1 glucose!
only in presence of O2 (aerobic respiration)
AP Biology
That
sounds more
like it!
O2
Mitochondria
Double membrane
outer membrane
inner membrane
highly folded cristae
enzymes & transport
proteins
intermembrane space
fluid-filled space
between membranes
AP Biology
Oooooh!
Form fits
function!
Electron Transport Chain
Inner
mitochondrial
membrane
Intermembrane space
C
Q
NADH
dehydrogenase
cytochrome
bc complex
Mitochondrial matrix
AP Biology
cytochrome c
oxidase complex
Remember the Electron Carriers?
Glycolysis
glucose
Krebs cycle
G3P
2 NADH
Time to
break open
the piggybank!
AP Biology
8 NADH
2 FADH2
Electron Transport Chain
Building proton gradient!
NADH NAD+ + H
e
p
intermembrane
space
H+
H+
H e- + H+
C
e–
NADH H
FADH2
NAD+
NADH
dehydrogenase
inner
mitochondrial
membrane
e–
Q
AP Biology
H+
e–
H
FAD
2H+ +
cytochrome
bc complex
1
2
O2
H2O
cytochrome c
oxidase complex
mitochondrial
matrix
What powers the proton (H+) pumps?…
Stripping H from Electron Carriers
Electron carriers pass electrons & H+ to ETC
H cleaved off NADH & FADH2
electrons stripped from H atoms H+ (protons)
electrons passed from one electron carrier to next in
mitochondrial membrane (ETC)
flowing electrons = energy to do work
transport proteins in membrane pump H+ (protons)
across inner membrane to intermembrane space
H+
TA-DA!!
Moving electrons
do the work!
+
H
H+
+
H
H+
H+
+
H+ H+ H
+
H+ H H+
C
e–
NADH
AP Biology
+
H
H+
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+
cytochrome
bc complex
+
1
2
O2
H2O
cytochrome c
oxidase complex
ADP
+ Pi
ATP
H+
But what “pulls” the
electrons down the ETC?
H 2O
O2
AP Biology
electrons
flow downhill
to O2
oxidative phosphorylation
Electrons flow downhill
Electrons move in steps from
carrier to carrier downhill to oxygen
each carrier more electronegative
controlled oxidation
controlled release of energy
make ATP
instead of
fire!
AP Biology
“proton-motive” force
We did it!
Set up a H+
H+
H+
H+
gradient
Allow the protons
to flow through
ATP synthase
Synthesizes ATP
ADP + Pi ATP
Are we
there yet?
AP Biology
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
Chemiosmosis
The diffusion of ions across a membrane
build up of proton gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Chemiosmosis
links the Electron
Transport Chain
to ATP synthesis
So that’s
the point!
AP Biology
1961 | 1978
Peter Mitchell
Proposed chemiosmotic hypothesis
revolutionary idea at the time
proton motive force
1920-1992
AP Biology
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Electron
transport
C system
Q
NADH
Acetyl-CoA
1. Electrons are harvested
and carried to the
transport system.
NADH
Krebs
cycle
e-
e-
FADH2
e-
2. Electrons
provide energy
to pump
protons across
the membrane.
e-
H2O
3. Oxygen joins
with protons to
form water.
1 O
2 +2
2H+
O2
H+
CO2
ATP
Mitochondrial
matrix
AP Biology
H+
ATP
ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
ATP
synthase
Cellular respiration
2 ATP
AP Biology
+
2 ATP
+
~36 ATP
Summary of cellular respiration
C6H12O6 + 6O2
6CO2 + 6H2O + ~40 ATP
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the ATP come from?
What else is produced that is not listed
in this equation?
Why do we breathe?
AP Biology
Taking it beyond…
What is the final electron acceptor in
H+
H+
H+
C
Electron Transport Chain?
e–
NADH
O2
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+ +
cytochrome
bc complex
1
2
O2
H2O
cytochrome c
oxidase complex
So what happens if O2 unavailable?
ETC backs up
nothing to pull electrons down chain
NADH & FADH2 can’t unload H
AP Biology
ATP production ceases
cells run out of energy
and you die!
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
Chapter 9.
Cellular Respiration
Other Metabolites &
Control of Respiration
AP Biology
2005-2006
Cellular respiration
AP Biology
2005-2006
Beyond glucose: Other carbohydrates
Glycolysis accepts a wide range of
carbohydrates fuels
polysaccharides glucose
hydrolysis
ex. starch, glycogen
other 6C sugars glucose
modified
ex. galactose, fructose
AP Biology
2005-2006
Beyond glucose: Proteins
Proteins
amino acids
hydrolysis
waste
H O
H
| ||
N —C— C—OH
|
H
R
amino group =
waste product
excreted as
ammonia, urea,
or uric acid
AP Biology
glycolysis
Krebs cycle
carbon skeleton =
enters glycolysis
or Krebs cycle at
different stages
2005-2006
Beyond glucose: Fats
Fats hydrolysis
glycerol & fatty acids
glycerol (3C) PGAL glycolysis
fatty acids 2C acetyl acetyl Krebs
groups
coA
cycle
glycerol
enters
glycolysis
as
AP PGAL
Biology
fatty acids
enter
Krebs cycle
as acetyl
2005-2006CoA
Carbohydrates vs. Fats
Fat generates 2x ATP vs. carbohydrate
more C in gram of fat
more O in gram of carbohydrate
so it’s already partly oxidized
fat
carbohydrate
AP Biology
2005-2006
Metabolism
Coordination of
digestion & synthesis
by regulating enzyme
Digestion
digestion of
carbohydrates, fats &
proteins
all catabolized through
same pathways
enter at different points
AP Biology
CO2
cell extracts energy
from every source
2005-2006
Metabolism
Coordination of digestion &
synthesis
by regulating enzyme
Synthesis
enough energy?
build stuff!
cell uses points in glycolysis &
Krebs cycle as links to
pathways for synthesis
run the pathways “backwards”
eat too much fuel, build fat
pyruvate
glucose
Krebs cycle
intermediaries
AP
Biology
acetyl
CoA
Cells are
versatile &
thrifty
amino
acids
fatty acids
2005-2006
Carbohydrate
Metabolism
The many
stops on the
Carbohydrate
Line
gluconeogenesis
AP Biology
2005-2006
Lipid Metabolism
The many stops
on the Lipid Line
AP Biology
2005-2006
Amino Acid
Metabolism
The many
stops on the
AA Line
AP Biology
2005-2006
Nucleotide
Metabolism
The many
stops on the
GATC Line
AP Biology
2005-2006
Control of
Respiration
Feedback
Control
AP Biology
2005-2006
Feedback Inhibition
Regulation & coordination of production
production is self-limiting
final product is inhibitor of earlier step
allosteric inhibitor of earlier enzyme
no unnecessary accumulation of product
ABCDEFG
1
2
3
4
5
6
X
enzyme enzyme enzyme enzyme enzyme enzyme
AP Biology
allosteric inhibitor of enzyme 12005-2006
Respond to cell’s needs
Key points of control
phosphofructokinase
allosteric regulation of
enzyme
“can’t turn back” step
before splitting glucose
AMP & ADP stimulate
ATP inhibits
citrate inhibits
Why is this regulation important?
Balancing act:
availability of raw materials vs.
energy
AP
Biologydemands vs. synthesis
2005-2006
A Metabolic economy
Basic principles of supply & demand regulate
metabolic economy
balance the supply of raw materials with the
products produced
these molecules become feedback regulators
they control enzymes at strategic points in
glycolysis & Krebs cycle
AMP, ADP, ATP
regulation by final products & raw materials
levels of intermediates compounds in the pathways
regulation of earlier steps in pathways
levels of other biomolecules in body
regulates rate of siphoning off to synthesis pathways
AP Biology
2005-2006
It’s a Balancing Act
Balancing synthesis
with availability of
both energy & raw
materials is essential
for survival!
AP Biology
do it well & you
survive longer
you survive longer &
you have more
offspring
you have more
offspring & you get
to “take over the
world”
Acetyl CoA is central to both
energy production & synthesis
make ATP or store it2005-2006
as fat
Any Questions??
AP Biology
2005-2006