How energy transformed in living cell?
10-15-2013
+ Heat
Too large to be used!
Solution
• Dissecting glucose degradation into many steps.
• In some key steps, a relative constant amount
of energy will be released to generate one ATP
or one NADH.
• Transform the energy store in the structure of
glucose into common currency life can use.
Activation of glucose by ATP?
Why cells want to further convert pyruvate
into lactate when oxygen is insufficient?
If we want this pathway continue, what do we need?
For ADP:
ATP can be consumed by chemical reactions that need
energy to proceed inside the cell and regenerate ADP.
For NAD+:
In exhausted muscle:
Not enough oxygen!
When the supply of
glucose is OK, even in
the presence of
oxygen, yeast still do
fermentation:
S. cerevisiae has an unusual lifestyle: it
prefers to ferment rather than oxidize
glucose, even when oxygen is abundant.
(Metabolite suppression)
Mol. Cell. Biochem. 27, 139–146; 1979
Yeast 2, 221–228; 1986
• The most ancient metabolic pathway to extract
energy from organic molecules
Complete oxidation of one
mole of glucose will generate
686 kcal of heat or energy.
In the absence of oxygen,
glucose can only be degraded
into pyruvate (glycolysis).
One mole of glucose only
produce two mole of ATP
(7.3+7.3=14.6 kcal).
The efficiency of energy
preservation is only 2%.
Life evolve need more energy!
• Where the high energy (electric potential) stored in NADH
should be utilized?
• Where does the product of glycolysis (pyruvic acid) should be
utilized?
– It still contains a lot of energy and should be degraded further in order
to extract more energy .
Two new features for energy generation are
evolved: Krebs cycle and electron transport chain
Diversity of Life
.
• Glycolysis may be the most ancient model of life to
gain energy.
• If someone can only get energy from some rare
chemicals (born in a wrong place!).
• “He or She” should evolve a more efficient way to
extract energy from food obtained from the poor
environment.
Cooperation or Competition?
•
•
•
•
For the common resource: compete for surviving.
One’s waste is another one’s food: cooperation.
Cooperation through physical association.
Cooperation through fusing into one body.
– More efficient!
– Eliminate redundant setup to save energy and to gain
niche for competition.
– Absolute mutual dependent for surviving.
• A new species is emerging (Symbiosis).
• Cellular respiration can “burn” other
kinds of molecules besides glucose
Food
 Diverse types of sugar
 Fats
 Proteins
Polysaccharides
Sugars
Glycerol
Fats
Fatty acids
Proteins
Amino acids
Amino groups
Glycolysis
AcetylCoA
Krebs
Cycle
Electron
Transport
The degradation of
pyruvate through
Krebs cycle produces
large quantities of
higher energy electron
(NADH and FADH2).
How the reducing power such as NADH
generate ATP?
Evolvement of electron transport chain
• Electron donor: NADH or H2S or H2O.
• Stepwise release energy from electron to produce
ATP.
• High energy chemical intermediate (X) to receive energy
from NADH, then transfer energy to synthesis ATP.
– You need to identify chemical nature of this putative intermediate
– This intermediate has never been found!
• Electron acceptor: ferric ion, NAD+ to O2.
• The Chemiosmotic Theory.
The Chemiosmotic Theory (Nature 191, 144-148, 1961)
By Peter Mitchell who won Nobel Prize in Chemistry in 1978
How to capture energy (high energy electron) from NADH?
You need electron acceptor and energy converting machine!
A very ancient invention (3.6 BY?)
The net result of transporting
high energy electron along
electron transport chain is to
generate proton gradient
across the membrane (another
form of stored energy)!
14_41_01_develop_stages.jpg
Components needed for PMF Generation
• Impermeable membrane lipid bilayer
• Mechanism for generating a membrane potential
– redox chemistry
– photoic energy
– electron transport (vectorial H+ movement)
• Mechanism for harvesting the potential
– ATPase
– co-transport
Complete oxidation of one mole of glucose will generate 686 kcal.
Complete oxidation of one mole of glucose inside the cell produce 38 mole of
ATP (7.3x38=277 kcal). The efficiency of energy preservation is 40%.
Metabolism and Diseases
Warburg effect: cancer cells produce
lactic acid from glucose even under
non-hypoxic conditions.
1883-1970
The shortest grand proposal!
Why glucose does not go to TCA cycle
in cancer cells ?
Defect in mitochondria function or by
other mechanism?
Glucose and glutamine fuel proliferation.
X
Cantor J R , and Sabatini D M Cancer Discovery
2012;2:881-898
©2012 by American Association for Cancer Research
Pyruvate kinase
• tumour tissues exclusively express the embryonic M2
isoform (microarray analysis).
• four isoforms exist in mammals:
• the L and R isoforms are expressed in liver and red blood
cells;
• the M1 isoform is expressed in most adult tissues; and the
M2 is a splice variant of M1 expressed during embryonic
development
• M2 is a low activity enzyme, whereas M1 is a
constitutively active enzyme.
• the activity of the M2 isoform (but not the M1 isoform)
can be inhibited by tyrosine kinase signalling in tumour
cells
Myc enhances PKM splicing to
produce PKM2
exon 9 is skipped
From David et al. 2010 Nature 463, 364-368
The M2 splice isoform of pyruvate kinase is
important for cancer metabolism and tumour growth.
(Why?)
Nature 452: 230–233; 2008
Metabolism: resting versus proliferating cells.
Cantor J R , and Sabatini D M Cancer Discovery
2012;2:881-898
©2012 by American Association for Cancer Research
PKM2 may block flux of glycolysis and push reverse reaction
to pentose phosphate pathway to produce precursors for
biosynthesis of building block of cells.
The therapeutic target of cancer cell
Looking for alternative energy source
SUN LIGHT
1, source of energy：photon from sun light
2, who absorbs the energy: chlorophyll molecule！
3, how? Exciting electron of chlorophyll to higher energy level！
4, who is the electron acceptor？Electron transport chain！
5, who is the electron donor？
Water is abundant !
14_43_sulfur_bacteria.jpg
• A photosystem
– Is an organized group of chlorophyll and other
molecules
– Is a light-gathering antenna
Chloroplast
Cluster of pigment
molecules embedded
in membrane
Photon
Granum
(stack of
thylakoids)
Primary
electron
acceptor
Electron
transfer
Reaction
center
Reactioncenter
chlorophyll a
Thylakoid membrane
Antenna pigment
molecules
Transfer of energy
Photosystem
Figure 7.9
The Overall Equation for Photosynthesis
• The reactants and products of the reaction
Light
energy
Carbon
dioxide
Water
Photosynthesis
Glucose
Oxygen
gas
A Roadmap for Photosynthesis
Energized e- added to CO2 to make glucose
Sunlight provides E
Is a 2-step process
Light
Chloroplast
NADP
• Light reactions convert
solar E to chemical E
• Calvin cycle makes
sugar from CO2
ADP
+P
Light
reactions
Calvin
Calvin
cycle
cycle
Light absorption pigment in
thylakoid membrane
Take two electrons from water and
release one oxygen and two protons
Which one, PSII or PSI is more ancient ?
Why?
To increase surface area for light absorption!
• The light reactions in the thylakoid membrane
To Calvin Cycle
Light
Light
NADP
ADP + P
Stroma
Electron transport chain
Thylakoid
membrane
ATP
synthase
Inside thylakoid
1/
2
Figure 7.12
Chlorophyll: The most efficient
molecule on earth to absorb light!
Organization of
photosystems in the
thylakoid membrane:
How the energy
transfer is
unidirectional ？
What will the excited electrons go?
Return to the ground state and release the energy as heat or
transfer to another electron acceptors!
Photon absorber
Electron donor
Electron acceptor 1
+
Electron acceptor 2
-
Electron acceptor 3
The structure of reaction center of photosynthetic bactreia
How is charge recombination prevented?
Structure of reaction center
_
Electron acceptor 2
Electron acceptor 1
+
Photon absorber
Electron donor
Source of electron!
Photosynthesis
1. Light reactions: transform light
(sunlight) energy into ATP and
biosynthetic reducing power, NADPH.
2. Dark reactions (Calvin cycle): use ATP
and NADPH to reduce CO2 to hexose
CO2 Assimilation
• The assimilation of carbon dioxide occurs via a
cyclic process known as the Calvin cycle
• The key intermediate, ribulose 1,5-bisphosphate is
constantly regenerated using energy of ATP
• The key enzyme, ribulose 1,5-bisphosphate
carboxylase / oxygenase (Rubisco
• The net result is the reduction of CO2 with
NADPH that was generated in the light reactions
of photosynthesis
Net reaction of the Calvin cycle
6 CO2 + 18 ATP +12 NADPH +12 H2O 
C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ + 6 H+
Incorporation of one CO2 into hexose uses 3 ATP and 2
NADPH (from light reaction)
5C
The Calvin cycle
1
3
5C
Calvin cycle
2
6C
3C
Ribulose 1,5-bisphosphate carboxlase/oxygenase
(Rubisco): the most abundant protein on earth!
5C + 1C  2 x 3C
Structure of Rubisco.
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