How energy transformed in living cell? 10-15-2013.

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; 1979Yeast 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).

Food

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Amino groups

Glycolysis Acetyl-CoA

KrebsCycle Electron

Transport

• Cellular respiration can “burn” other kinds of molecules besides glucose

Diverse types of sugar Fats Proteins

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.

Cantor J R , and Sabatini D M Cancer Discovery 2012;2:881-898

©2012 by American Association for Cancer Research

X

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

From David et al. 2010 Nature 463, 364-368

exon 9 is skipped

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 sourceSUN 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

Granum(stack ofthylakoids)

Cluster of pigmentmolecules embeddedin membrane

Thylakoid membrane

Photon

Electrontransfer

Primaryelectronacceptor

Reaction-centerchlorophyll a

Reactioncenter

Transfer of energy Photosystem

Antenna pigmentmolecules

• A photosystem

– Is an organized group of chlorophyll and other molecules

– Is a light-gathering antenna

Figure 7.9

Chloroplast

• The reactants and products of the reaction

The Overall Equation for Photosynthesis

Lightenergy

Carbondioxide

Water

Photo-synthesis Glucose Oxygen

gas

A Roadmap for PhotosynthesisEnergized e- added to CO2 to make glucose

Sunlight provides EIs a 2-step process

• Light reactions convert solar E to chemical E

• Calvin cycle makes sugar from CO2

Figure 7.4

Calvincycle

Light

Chloroplast

Lightreactions

NADP

ADP+ P

Calvincycle

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!

Light Light

To Calvin Cycle

Stroma

Thylakoidmembrane

Electron transport chainATP

synthase

Inside thylakoid

1/2

NADPADP + P

Figure 7.12

• The light reactions in the thylakoid membrane

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!

The structure of reaction center of photosynthetic bactreia

How is charge recombination prevented?

Electron acceptor 3

Electron donorPhoton absorber

Electron acceptor 2

Electron acceptor 1 +

-

Photon absorber

Electron acceptor 1

Electron acceptor 2

Electron donor

+

_

Source of electron!

Structure of reaction center

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)

The Calvin cycle

Calvin cycle

1

2

3

5C

3C6C

5C

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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