Energy Processing Systems: An Overview

Big Questions

• How do living systems process energy?

• How do the energy processing systems of autotrophs and heterotrophs compare?

• What are the similarities between prokaryotic and eukaryotic energy processing systems?

2007-2008

What’s thepoint?

The pointis to make

ATP!

ATP

Energy needs of life• All life needs a constant input of energy

– Heterotrophs (Animals): capture free energy from carbon-based chemical compounds produced by other organisms

– eat food = other organisms = organic molecules• make energy through respiration

– Autotrophs (Plants) • capture free energy from the environment and store it

in carbon-based chemical compounds• build organic molecules (CHO) from CO2

• make energy & synthesize sugars through photosynthesis

consumers

producers

How are they connected?

glucose + oxygen carbon + water + energydioxide

C6H12O6 6O2 6CO2 6H2O ATP+ + +

Heterotrophs

+ water + energy glucose + oxygencarbondioxide

6CO2 6H2O C6H12O6 6O2light

energy + ++

Autotrophsmaking energy & organic molecules from light energy

making energy & organic molecules from ingesting organic molecules

Where’s the ATP?

oxidation = exergonic

reduction = endergonic

Autotrophs: A Bit Deeper

Two varieties:Photosynthetic- free energy comes from sunlight.

Requires oxygen.

Chemosynthetic- free energy comes from inorganic molecules (ex H2S).

No oxygen (or light) required.

Chemosynthetic Ecosystems

Heterotrophs: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

Harvesting stored energy• Glucose is the model

– catabolism of glucose to produce ATP

C6H12O6 6O2 ATP 6H2O 6CO2+ + +

CO2 + H2O + heatfuel(carbohydrates)

COMBUSTION = making a lot of heat energy by burning fuels in one step

RESPIRATION = making ATP (& some heat)by burning fuels in many small steps

CO2 + H2O + ATP (+ heat)

ATPglucose

glucose + oxygen energy + water + carbondioxide

resp

iratio

n

O2 O2

+ heat

enzymesATP

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

e-

+ +e-

+ –loses e- gains e- oxidized reduced

oxidation reduction

redox

e-

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• move H = move electrons p

e

+

H

+H

+ –loses e- gains e- oxidized reduced

oxidation reduction

C6H12O6 6O2 6CO2 6H2O ATP+ + +oxidation

reductionHe-

Coupling oxidation & reduction• REDOX reactions in respiration

– release energy (break C-C bonds in organics)• Strip electrons from C-H bonds: remove H atoms• electrons attracted to more electronegative atoms

– in biology, the most electronegative atom? –O2 H2O = oxygen has been reduced

– couple REDOX reactions & use the released energy to synthesize ATP

C6H12O6 6O2 6CO2 6H2O ATP+ + +oxidation

reduction

O2

Oxidation & reduction• Oxidation

– adding O– removing H – loss of electrons– releases energy– exergonic

• Reduction– removing O– adding H – gain of electrons– stores energy– endergonic

C6H12O6 6O2 6CO2 6H2O ATP+ + +oxidation

reduction

Moving electrons in respiration• Electron carriers move electrons by

shuttling H atoms around– NAD+ NADH (reduced)– FAD+2 FADH2 (reduced)

+ Hreduction

oxidation

PO–

O–

O–O

PO–

O–

O–O

CC

O

NH2

N+

H

adenine

ribose sugar

phosphates

NAD+

nicotinamideVitamin B3niacin

PO–

O–

O–O

PO–

O–

O–O

CC

O

NH2

N+

HNADH

carries electrons as a reduced molecule

reducing power!

How efficient!Build once,

use many ways

H

like $$in the bank

Evolutionary perspectiveOrder of things (for reasons that will be discussed soon):Anaerobic Heterotrophic Nutrition (“fermentation”) Photosynthetic Nutrition Aerobic Heterotrophic Nutrition (“aerobic respiration”)

Chemosythetic Nutrition (?)

Evolutionary perspective• Prokaryotes

– first cells had no organelles• Anaerobic atmosphere

– life on Earth first evolved without free oxygen (O2) in atmosphere

– energy had to be captured from organic molecules in absence of O2

• Prokaryotes that evolved glycolysis (first step of respiration) are ancestors of all modern life– ALL cells still utilize glycolysis (!)

You meanwe’re related?

Do I have to invitethem over for the holidays?

Enzymesof glycolysis are“well-conserved”

Is there anything DNA can’t do?

But I’m so much more

than a stowaway…

Any Questions?

Review Questions

1. What does a cell need in order to be able to accomplish each of the following:

– Heterotrophic nutrition– Autotrophic (photosynthetic)

nutrition

2. Provide three pieces of evidence that support the dominant hypothesis for the evolutionary order of energy processing systems in cells, and explain why each piece of evidence provides support:

Anaerobic Heterotrophic Nutrition (“fermentation”) Photosynthetic Nutrition Aerobic Heterotrophic Nutrition (“aerobic respiration”)

3. Why is it more difficult to establish the origin of chemosynthetic energy processing systems than it is to establish the evolution of non-chemosynthetic modes of energy processing?