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?

What’s the point? The point is 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 CO 2 make energy & synthesize sugars through photosynthesis consumers producers

How are they connected? glucose + oxygen  carbon + water + energy dioxide C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ Heterotrophs + water + energy  glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Autotrophs making 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 H 2 S). 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 C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  + ++ CO 2 + H 2 O + heat fuel (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 CO 2 + H 2 O + ATP (+ heat) ATP glucose glucose + oxygen  energy + water + carbon dioxide respiration O2O2 O2O2 + heat enzymes ATP

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- ++ e-e- +– loses e-gains e-oxidizedreduced oxidationreduction redox e-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-oxidizedreduced oxidationreduction C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction H e-e-

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? – O 2  H 2 O = oxygen has been reduced – couple REDOX reactions & use the released energy to synthesize ATP C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction O2O2

Oxidation & reduction Oxidation – adding O – removing H – loss of electrons – releases energy – exergonic Reduction – removing O – adding H – gain of electrons – stores energy – endergonic C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction

Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around – NAD +  NADH (reduced) – FAD +2  FADH 2 (reduced) + H reduction oxidation P O–O– O–O– O –O–O P O–O– O–O– O –O–O C C O NH 2 N+N+ H adenine ribose sugar phosphates NAD + nicotinamide Vitamin B3 niacin P O–O– O–O– O –O–O P O–O– O–O– O –O–O C C O NH 2 N+N+ H NADH carries electrons as a reduced molecule reducing power! How efficient! Build once, use many ways H like $$ in the bank

Evolutionary perspective Order 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 (O 2 ) in atmosphere – energy had to be captured from organic molecules in absence of O 2 Prokaryotes that evolved glycolysis (first step of respiration) are ancestors of all modern life – ALL cells still utilize glycolysis (!) You mean we’re related? Do I have to invite them over for the holidays? Enzymes of 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?