Download Chapter 9

How Cells Harvest Energy
Chapter 9
We EAT
sunlight energy
trapped in
arrangement
of atoms
CELLULAR RESPIRATION
why do we need oxygen?
energy
Breathing
by-product of photosynthesis?
• Cellular Energy Harvest
• Cellular Respiration
– Glycolysis
– Oxidation of Pyruvate
– Krebs Cycle
– Electron Transport Chain
• Catabolism of Protein and Fat
• Fermentation
• Evolution of Metabolism
burning fuel in the car
•Organic compounds + O2 -> CO2 + H2O + Energy
HEAT
•Catabolic pathways release energy
Autotrophs self feeders
use photosynthesis (usually) to make their own
food
produce organic molecules from CO2
ALSO source for all nonautotrophic food!
• Heterotrophs (us) consumers of
biosphere
– feed on
• plants and others
• dead organisms (feces, fallen leaves)
– dependent on photoautotrophs for:
– food
– oxygen
Cellular Respiration
• Cells harvest energy
• break chemical bonds and shift electrons
OXIDATION OF GLUCOSE
– GLUCOSE LOSES ELECTRONS (also protons ie
hydrogen)
– aerobic respiration - final electron acceptor is
oxygen
– anaerobic respiration - final electron acceptor is inorganic
molecule (not oxygen)
– fermentation - final electron acceptor is an organic
molecule
LIFE IS A LOT OF WORK!
•Carbohydrates, fats, and proteins - all fuel
•traditional - glucose
•C6H12O 6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)
•The catabolism of glucose is exergonic
•delta G = 686 Kcal per mole of glucose.
•positive or negative?
•WASTE PRODUCTS HAVE LESS ENERGY
• Remember Chemical reactions - exergonic or
endergonic - based on free energy
Do these products have more or less energy?
• SPONTANEOUS (less energy, releases heat)
Overall reaction:
glucose + oxygen -> carbon dioxide +
water + energy
C6H12O6 + 6O2
6CO2 + 6H2O + energy
how could this be measured in the lab?
ATP
• Adenosine Triphosphate
• energy currency
– drive movement
– drive endergonic reactions
• ATP Energy Currency :
• adenosine triphosphate
• nucleotide
– nitrogenous base (adenine)
– sugar (ribose)
– three phosphate groups
Figure 8.14a ATP
•phosphate bonds –covalent, but weak - each has negative charge
•repulsion contributes to instability
– Negatives repel – Phosphates are negative
– ATP (three phosphates), ADP (two phosphates)
– Linking them requires overcoming repulsion
Requires energy
– ATP from ADP and a third phosphate
requires energy
(endergonic)
– Releasing phosphate from ATP
generates energy
(exergonic)
• bonds between phosphate groups
broken by hydrolysis
– Hydrolysis forms adenosine
diphosphate
–
– [ATP -> ADP + Pi]
– releases 7.3 Kcal of energy per mole
of ATP
– delta G is -13 kcal/mol
Cell
membrane
•How IT WORKS IN
muscle cells
extracellular
Enzyme
Calcium
ions
–Calcium ions move to enzyme
ATP binding
site
Ca++
Ca++
–ATP splits -ADP and
phosphate
–energy transfers phosphate
onto protein
ATP
ADP
Ca++
Cytosol
intracellualr
P
P
–
–shape change drives calcium
across membrane
P
P
biochemical pathways
Ca++
•ATP: Important Energy Storage Molecule
energy stored as phosphate
bond in ATP
3rd phosphate group
added to ADP
using energy from food
energy
IN
p
p
p
p
energy released
when phosphate bond broken
ATP
energy
OUT
energy
hill
p
P+
p
ADP
p
P+
p
p
ADP
which is exergonic? enderogonic?
but we only have about .5 - 3 min worth of ATP stored!
Home runs and creatine? Creatine donates phosphate group!
creatine – natural amino acid (not protein)
C4H10N3 O5P
(liver, kidney)
Lots in muscle, cardiovascular tissues
increases phosphocreatine -> ATP
“reservoir” for ATP production
1 g diet; 1 g synthesized
high intensity exercise (baseball)
• transfer of phosphate group from ATP
phosphorylation
Substrate level phosphorylation
– changes shape - work
(transport, mechanical, or chemical)
–
returns to
alternate
shape
MUSCLE-RECYCLES 10 MILLION ATP/SEC
Also oxidative phosphyloration
• Uses proton gradient to produce ATP
• What are protons? H +
• Our cells do both
redox reactions
transfer electron(s) from one reactant to another
oxidation-reduction reactions
loss of electrons - oxidation
(degrades, catabolic – ENERGY OUT)
\addition of electrons – reduction
(energy IN, anabolic)
Hydrogen, electrons
NAD is a Cofactor (co enzyme, organic)
Na + Cl
Na+ Cl-
salt - redox reaction
*Na is oxidized -the reducing agent
*Cl is reduced – the oxidizing agent
(Cl
charge is reduced - drops from 0 to -1)
electron donor (sodium) - reducing agent
electron recipient (cloride) - oxidizing agent
need both donor and acceptor
Oxygen - potent oxidizing agent
(it is reduced!)
CH4 + 2O2
CO2 + 2H2O
*CH4 is oxidized
*O2 is reduced
*oxidation often involves the loss of H
Importance of electrons
*key role in atom’s reactivity
*CR - Transfer of e- through a
series of steps releases energy
the cell can use
WHY SMALL STEPS? - HEAT
cellular respiration – series of redox
• glucose is oxidized, releasing energy
(oxidation -loses electrons)
C6H12O6 + 6O2 -> 6CO2 + 6H2O +
energy (including heat)
• oxygen is reduced
(gains electrons)
Hypoxia
Shock
Altitude sickness
Blood loss
Sepsis
Systemic inflammation
Path of e- in cellular respiration:
food
NADH
e- transport chain
oxygen
Oxidation
C6H12O6 + 6O2
6CO2 + 6H2O + energy
Reduction
* happens over a series of steps that involve special molecules
called electron transporters
• Electron Carrier Molecules Shuttle Electrons
– Most important electron carrier is NAD+.
COFACTOR
NAD+ - oxidizing agent, accepts a
hydrogen atom and TWO electrons,
becoming NADH
– NADH can carry electrons down energy
hill on to another acceptor
(also FAD/FADH)
– Enzymes coordinate these transfers.
- -
NAD+
empty
NADH
loaded
+
NAD +
+ H
+
- H
H proton
NAD+
empty
NAD
oxidized
NAD
-
+
- - H
reduced
+
+
H
Electron loss accompanied by
protons
(hydrogen ion) “dehydrogenation”
-
-
4 stages of cellular respiration
1.Glycolysis
2.Pryuvate Oxidation
3.Krebs cycle
4.Electron transport chain
*net result of the 4 stages is about 36
ATP per glucose molecule
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cytoplasm
Glucose
NADH
Glycolysis
ATP
Pyruvate
Pyruvate
oxidation
AcetylCoA
NADH
NADH
Krebs
cycle
CO2
Intermembrane
space
Mitochondrial matrix
CO2
ATP
FADH2
H2 O
eMitochondrion
ATP
NAD+ and FAD
Electron
transport chain
Inner mitochondrial membrane
•cellular respiration uses oxygen as a
reactant to breakdown organic molecules
•Most occurs in “matrix” of
mitochondria
•BUT 1st step (glycolysis) occurs in
cytoplasm (before mitochondria)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
OVERVIEW OF GLYCOLYSIS
1
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
2
3
P
P
ENERGY IN!!!!!!
P
6-carbon sugar diphosphate
SOME
ENERGY OUT!
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
P
NADH
2 ATP
Priming reactions. Priming
reactions. Glycolysis begins with
the addition of energy. Two highenergy phosphates from two
molecules of ATP are added to the
six-carbon molecule glucose,
producing a six-carbon molecule
with two phosphates.
3-carbon
pyruvate
Cleavage reactions. Then, the
six-carbon molecule with two
phosphates is split in two, forming
two three-carbon sugar
phosphates.
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
2 ATP
3-carbon
pyruvate
Energy-harvesting reactions.
Finally, in a series of reactions, each
of the two three-carbon sugar
phosphates is converted to
pyruvate. In the process, an energyrich hydrogen is harvested as
NADH, and two ATP molecules are
formed.
glycolysis - steps
1. glucose (6 carbon-sugar) split into two, 3carbon sugars
2. sugars are oxidized and rearranged to form
2 molecules of pyruvate.
3. Each step catalyzed by specific enzyme
4. steps divided into 2 phases: an energy
investment phase and an energy payoff
phase.
*Most of the energy contained in glucose is
still stored in pyruvate, which goes into
the Krebs Cycle
Glycolysis yields 2 ATP and 2 pyruvates, 2 NADH
net yield of glycoloysis
2ATP, 2NADH, 2 pyruvates
Can it end here?
Copyright © The McGraw-Hill Companies, Inc. Permission equired for reproduction or display.
With oxygen
Pyruvate
H20
NAD+
O2
NADH
Acetyl-CoA
Without oxygen
CO2
NADH
NADH
NAD+
Lactate
Krebs
cycle
yeast
in absence of oxygen
(bread and wine)
dump electrons from
NADH onto acetaldehyde
(converted from pyruvic
acid by spewing off CO2))
reducing it to ethanol, and
regenerating NAD+.
Acetaldehyde
NAD+
Ethanol
• alcohol
fermentationpyruvate converted
to ethanol in 2 steps.
• lactic acid fermentation in animals in absence of
oxygen (muscle fatigue), pyruvate accepts electrons from NADH
and regenerates NAD+, but is converted into lactic acid (muscle
burn)
• Muscle cells switch from AR to fermentation
to generate ATP when O2 is scarce.
•
waste product,
lactate -muscle fatigue, but
ultimately converted back to
pyruvate in the liver
• used to make
cheese and yogurt
4 stages of cellular respiration
1.Glycolysis
2.Pryuvate Oxidation
3.Krebs cycle
4.Electron transport chain
*Pryuvate is “Fork in the road”
pyruvate must be converted to Acetyl CoA
Bridge between glycolysis and Krebs Cycle
pyruvate enters mitochondria using transport protein in
mitochondrial membrane, converted to Acetyl CoA
(cofactor) - also releases NADH
• Transition between Glycolysis and Krebs Cycle
–In the presence of oxygen, each of
the two pyruvic acids travels into the
mitochondria.
– Combine with coenzyme A to make acetyl
CoA, one NADH, and CO2
–Next - Krebs cycle
inner compartment of
mitochondria
Mitochondria
• outer and inner
phospholipid bilayer
membrane
• outer is smooth, inner
membrane is folded
crista (s) cristae(p)
-matrix –SOLUTION - high concentration of enzymes
REMEMBER mitochondrion?
For LAST stage -enzyme ATP synthase embedded in inner membrane
channel through which protons cross membrane
Protons move down concentration gradient
•


ATP synthesis - rotary motor
driven by a gradient of protons
4 stages of cellular respiration
1.Glycolysis
2.Pryuvate Oxidation
3.Krebs cycle
4.Electron transport chain
*Pryuvate is “Fork in the road”
4 stages of cellular respiration
3rd step - Krebs Cycle
*occurs in mitochondrial matrix
*gives off 2 CO2/turn (each)
*Yields 1 ATP, 3 NADH, & 1
FADH2 (each)
glycolysis
mitochondrion
pyruvic acid
cytosol
NAD+
coenzyme
A
NADH
to electron
transport
chain
CoA
CO2
inner
compartment
acetyl coenzyme A
Krebs
cycle
SUMMARY OF THE KREBS CYCLE
6 NADH
GLYCOLYSIS
2 FADH2
CoA
Krebs
cycle
acetyl coenzyme A
CO2
2 ATP
electron
transport
chain
oxaloacetic acid
NADH
1.
citric acid
NAD+
NAD+
6.
CO2
α-ketoglutaric acid
malic acid
FADH2
2.
NADH
3.
FAD+
5.
ADP
NAD+
note 1st product
citric acid
cycle
note CO2
CO2
NADH
4. α-ketoglutaric acid
derivative
succinic acid
ATP
Krebs Cycle
*8 reactions, 8 enzymes in the
matrix
*3 NADHs made for every
Acetyl CoA molecule
*1FADH2 for every Acetyl CoA
*1ATP for every Acetyl CoA
•cycle (aka citric acid cycle)
• Importance of Krebs Cycle
– Acetyl CoA broken down into CO2
– Only 1 ATP made for each acetyl CoA
that enters (total 2 ATP per glucose)
– But, most electrons have been
“captured” onto 6 NADH and 2 FADH2
(per glucose)
for last stage (electron transport chain)
4 stages of cellular respiration
1.Glycolysis
2.Pryuvate Oxidation
3.Krebs cycle
4.Electron transport chain
*Pryuvate is “Fork in the road”
4 stages of cellular respiration
finally - Payoff
Electron transport chain
*in inner mitochondria membrane
*yields CO2 and water
*AND Yields about 38 ATP!!
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Intermembrane +
H
+
space
H+ H+ H
+
+
H
H+ H H+
Rotor
Rod
Catalytic
head
ADP + Pi
ATP
Mitochondrial matrix
H+
chemiosmosis
• Coupling (linking)
• A) the movement of protons (Hydrogen minus
its electron)
• across a membrane (mitochondria)
• B) to the synthesis of ATP
inner
membrane
outer
membrane
H+
+
H
H+
H+
+
H
electron
transport
chain
Krebs
cycle
+
H
H+
H+
+
H
eO2
outer
compartment
H2O
inner compartment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Intermembrane space
H+
H+
H+
Inner
H+ mitochondrial
membrane
H+
ADP + Pi
NAD+
NADH
ATP
Proton pump
Mitochondrial matrix
H+
ATP synthase
• Electron Transport Chain
• NADH and FADH2 drop off electrons onto
molecules in inner membrane.
– Movement of electrons powers the movement of H+
ions against concentration gradient.
– pumps H+ from matrix into intermembrane space.
– now H+ move down gradient back into matrix
– energy is used to transfer phosphate onto ADP to
make ATP.
– Greatest amount made in this stage (28- 30
ATP /glucose)
– end of the chain O2 + 2 electrons + 2 H + = H 2O
– why we must breathe
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Intermembrane space
H+
H+
H+
Inner
H+ mitochondrial
membrane
H+
ADP + Pi
NAD+
NADH
ATP
Proton pump
H+
ATP synthase
Mitochondrial matrix
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Q
NADH e1. Electrons are harvested
and carried to the
Acetyl-CoA
transport system.
NADH
eKrebs
cycle
FADH2
CO2
2
ATP
Mitochondrial
matrix
2. Electrons
provide energy
to pump
protons across
the membrane.
H2O
e 3. Oxygen joins
1 O
with protons to
2 +2
form water.
2H+
H+
32 ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
Electron
transport
C system
H+
e-
O2
H+
ATP
synthase
electrochemical gradient
1) H+ ions pumped out of matrix
during the ETC
2) H+ flows through ATP
synthase
3) shape change allows ADP to
be phosphorylated
how do mitochondria use energy
released?
Chemiosmosis
- coupling energy
released in the ETC to synthesis of ATP
ATP production
ATP generation in ETC
oxidative phosphorylation
occurs as result of redox reactions
REMEMBER?
• transfer of phosphate group from ATP
phosphorylation
Substrate level phosphorylation
transfer of phosphate group from
ATP
phosphorylation
Substrate level
phosphorylation
uses enzymes
oxidative phosphorylation
Uses proton gradient to produce ATP
GLYCOLYSIS
ELECTRON
TRANSPORT
CHAIN
32
ATP
inner
membrane
inner compartment
H2 O
O2
outer
compartment
H+
H+
outer compartment
H+
H+
inner
membrane
mitochondrion
KREBS
CYCLE
H+
H+
H+
H+
ATP SYNTHESIS
H+
H+
H+
H+ H+
H+ H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+ H+
H+
H+ H+ H+
H+
H+
NADH
H+
NAD+
2 H+ + 1/2 O2
inner
compartment
ATP
synthesis
ADP + P
H2 O
ATP
ELECTRON TRANSPORT CHAIN
Duration of maximal exercise
Minutes
Seconds
10
30
60
2
4
10
30
60
120
Percent 90
anaerobic
80
70
50
35
15
5
2
1
Percent
aerobic
20
30
50
65
85
95
98
99
10
ATP Generation during Exercise
–What is greatest source of energy—aerobic or anaerobic
–HOW fast would we go without mitrochondria?
Feedback mechanisms control
cellular respiration
• Metabolic control of cellular
respiration - supply and demand
– If ATP levels drop, catabolism speeds up to
produce more ATP
– based on regulating activity of enzymes at
strategic points in the catabolic pathway
example: third step of
glycolysis
• catalyzed by
phosphofructokinase
(PKF)
• Allosteric regulation
of
phosphofructokinase
sets the pace of
respiration
Allosteric?
remote site
Without oxygen
• Fermentation
• ALSO carbon dioxide (Archaea)
• ALSO sulfur (bacteria)
• Carbohydrates,
fats, and
proteins
all catabolized
through the
same
pathways!!!!
a gram of fat
will generate
twice as much ATP
as a gram of carbohydrate
How did we get here?
Evolution
•
•
•
•
•
•
Break down carbon (store in ATP)
Glycolysis (series 2 billion years old)
Photosynthesis - no oxygen
Photosynthesis - forming oxygen
Nitrogen “fixation” before oxygen
Aerobic respiration
which is faster
enzyme activity lab
Or NEXT TIME
cellular respiration lab?
•Recall cellular respiration
•C6H12O6 + 6O2 -----> 6CO2 + 6H2O
+ Energy
•compare to photosynthesis :
6CO2 + 6H2O + light energy ----->
C6H12O6 + 6O2