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Energy & Metabolic Pathways 1

Energy & Metabolic Pathways 1. ATP Redox Electron Carriers 2

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Energy & Metabolic Pathways

2

Energy & Metabolic Pathways

• ATP• Redox• Electron Carriers

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ATP

• What’s the Big Deal?• What is ATP?• How Do Cells “Run” on ATP?• How Do Cells Make ATP?

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ATP: What’s the Big Deal?

• Life = endergonic• Organisms …1. Require energy input• Plants—sunlight • Animals—food

2. Use this energy to maintain life• Build & repair• Reproduce

• Evidence?• Without sunlight (plants) or food

(animals), organisms die

P

R

EA

ΔGG

Time

Life

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ATP: What’s the Big Deal?

• Where does ATP fit into this? Analogy: Just as …• Vehicles run on Gasoline• Household appliances run on Electricity• Cells?

• How would this look on energy graph?• Conclusion:

Life

P

R

EA

ΔGG

Time

ATP ATP = general form of energy that cells use to maintain endergonic “lifestyle”

run on ATP

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ATP: What’s the Big Deal?

• Another analogy:• ATP = energy “currency” of

cell

• What does this mean?• $, Electricity, ATP = all easily

convertible• $ = wealth• Electricity = energy• ATP = energy for cells

• Food/Sunlight ATP Growth/Reproduction

• Work $ Make Purchases• Coal/Oil/Gas Electricity Run Machines

Energy FlowConvert … To … To …

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ATP: What’s the Big Deal?

• So … what’s the big deal?• ATP is fundamental to life• All cells run on ATP• Without ATP, there is no

life!

• OK, so ATP is important• What, exactly, is ATP?

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ATP

• What’s the Big Deal?• What is ATP?• How Do Cells “Run” on ATP?• How Do Cells Make ATP?

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ATP: What is ATP?

• What does ATP stand for?

• Biological molecule class:• Monomer:

• What is a Nucleotide?• Phosphate• 5-Carbon Sugar• Nitrogenous Base

• What is ATP?

NucleotideNucleic Acid

Adenosine Triphosphate

3 parts

Nucleotide

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ATP

• What’s the Big Deal?• What is ATP?• How Do Cells “Run” on ATP?• How Do Cells Make ATP?

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ATP: How Do Cells “Run” on ATP?• We know …

• Life = endergonic• ATP supplies energy to “run” endergonic “lifestyle”

• If ATP supplies energy, then ATP molecule must …• Contain energy• Transfer energy to endergonic reactions

• 3 questions:1. Where is energy in ATP molecule?2. How is energy in ATP released?3. How is energy transferred to endergonic reactions to

make them “run”?

Life

P

R

EA

ΔGG

Time

ATP

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ATP: How Do Cells “Run” on ATP?

Energy!

1. Where is energy in ATP molecule?• In bonds between phosphates

• How is energy stored here? (Hint: look at the 2 Pi below)• What do you notice?• Phosphates negative• How does this explain how energy stored?• 3 repel each other• To force 3 close together requires energy• Covalent bond between holding

these ions together contains this energy

PP

P P

( )P

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ATP: How Do Cells “Run” on ATP?2. How is energy in ATP released?• What do you notice?• Bonds between broken by hydrolysis• Energy released

ATP hydrolysis ADP + Pi + energy

PP

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ATP: How Do Cells “Run” on ATP?

• Can represent on energy graph …• Graph:• Include: axes labels, Reactants, Products,

EA, ΔG

• Reaction = endergonic / exergonic• ΔG = + / –• Reaction = spontaneous / not

spontaneous• On graph, what represents energy ATP

supplies to endergonic reaction to make it run?

ATP hydrolysis ADP + Pi + energy

ADP + Pi

ATPEA

ΔGG

Time

ΔG

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ATP: How Do Cells “Run” on ATP?• We know: • Can update our graph …

P

R

EA

ΔGG

Time

ADP + Pi

ATP

Life

P

R

EA

ΔGG

Time

ATP

ATP hydrolysis ADP + Pi + energy

Life

↓ energy

↑ energy

Energy transferred from ATP to R

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ATP: How Do Cells “Run” on ATP?

3. How is energy transferred to endergonic reactions to make them “run”?

• Use energy graphs …

2

3

4

5

1

G

Time

R

P+

• Couple Endergonic Reaction with ATP hydrolysis (= Exergonic)

• Overall reaction = Exergonic

ATP

ADP, Pi

Time

R, ATP P,

ADP, Pi

Time

P

R

EA

ΔGG

Time

ADP + Pi

ATP

Endergonic Reaction ATP Hydrolysis Coupled Reaction

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ATP: How Do Cells “Run” on ATP?• Example ATP making

endergonic reaction “run”

• Label concentrations• What process is

occurring?• How can you tell?

• Na+ & K+ moving up their gradients

• ATP supplying energy

↑[Na+]

↓[Na+]

↓[K+]

↑[K+]Active Transport

• What is actually happening? How is energy from ATP moving ions up their gradients?

Inside Cell

Outside Cell

↓ energy↑ energy

Transport protein

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ATP: How Do Cells “Run” on ATP?• What do you notice?• Na+ moves out, up gradient• K+ moves in, up gradient• ATP transfers Pi to transport

protein• Transport protein changes shape

• What can you conclude?• Energy in ATP transferred with Pi

• Energy causes protein to change shape• Shape change allows ions to move

up their gradients↑[Na+], ↓[K+]

↓[Na+], ↑[K+]

Transport Protein

OutsideCell

Membrane

InsideCell

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ATP

• What’s the Big Deal?• What is ATP?• How Do Cells “Run” on ATP?• How Do Cells Make ATP?

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ATP: How Do Cells Make ATP?• Average human

• Mass: 62 kg (62.000 g)• Amount of ATP: 51 g (0.08%)• Amount of ATP used per day: 100-150 kg

(100.000-150.000 g), about 2X body mass!

• What do you notice?• You have very little ATP but use a HUGE

amount every day

• How is this possible?• ATP recycled• Reverse reaction occurs also• ADP + Pi ATP

• We know …

ATP hydrolysis ADP + Pi + energy

ADP + Pi

ATPEA

ΔGG

Time

ADP + Pi

ATPEA

ΔGG

Time

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ATP: How Do Cells Make ATP?• Remember, we said …

• Life = endergonic• Organisms …1. Require energy input

• Plants—sunlight • Animals—food

2. Use this energy to maintain life• Build & repair• Reproduce

• Where does energy to make ATP come from?

• How would this look on the graph?

P

R

EA

ΔGG

Time

Life

Food or Sunlight

Food/ Sunlight

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ATP: How Do Cells Make ATP?• Consider food

• Burn food• Releases energy• Capture energy to make ATP

• Can represent on energy graph

• Conclusion:• Couple reactions so energy

Released from burning food added to ADP + Pi to synthesize ATP

• Overall reaction = exergonic

+ O2 CO2 + H2OFood (carbs,

fats)Energy

ADP + Pi ATP

+

Coupled Reaction

Time

ADP, Pi, Food,

O2

ATP, CO2, H2O

ATPADP,

Pi

Time

ATP Synthesis

Time

Food,O2

CO2, H2O

Burn Food

G2

3

4

5

1

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ATP: Overview

• Covered 2 reactions:• ATP ADP + Pi + energy• ADP + Pi + energy ATP

• Both reactions occur in cycle

• Here, emphasis on ATP• Shift focus to surrounding

reactions

ATP ADP + Pi

Energy released to drive endergonic reaction

Energy absorbed from food/sunlight to synthesize ATP

Exergonic

Endergonic

High Energy

Low Energy

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ATP: What’s the Big Deal?

• Another analogy:• ATP = energy “currency” of

cell

• Food/Sunlight ATP Growth/Reproduction

• Work $ Make Purchases• Coal/Oil/Gas Electricity Run Machines

Energy FlowConvert … To … To …

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ATP: Overview

• Energy output from catabolic reactions• Energy input to anabolic reactions• ATP connects reactions, shuttling

energy from catabolic to anabolic pathways

CO2, H2O

Food, O2

EA

G

Time

ΔG

P

R

EA

ΔG

Time

Catabolism:Exergonic Reactions

Anabolism:Endergonic Reactions

ADP + Pi

ATP

Food/Sunlight ATP Growth/ReproductionEnergy Flow

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• If ATP captures & holds energy, why don’t organisms use ATP for energy storage?• What molecules do cells use for energy storage?

• Carbohydrates (polysaccharides)• Lipids (fats)

• Why not use ATP?• Not stable• Only useful for short-term storage (immediate

energy transfer)

• How much ATP do you use per day?• Twice your mass!

ATP: Overview

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Energy & Metabolic Pathways

• ATP• Redox• Electron Carriers

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Redox: What is it?• Oxidation/Reduction• How to identify oxidation & reduction?• Oxidation• Loss of electrons• Often: gain of O / loss of H

• Reduction• Gain of electrons• Often: gain of H / loss of O

• How to remember oxidation & reduction?• OIL—Oxidation Is Loss (of electrons)• RIG—Reduction Is Gain (of electrons)

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Redox: How does it work?• Oxidation & Reduction = coupled reactions

• 1 atom loses an e- (= )• Another atom gains e- (= )

• NaCl = ionic compound• Define:

• But organisms made of covalent compounds• Define:

• Do redox reactions occur in covalent compounds?

oxidationreduction

Na Na+

Cl Cl-

e-

Na is gaining / losing e-

oxidized / reduced

Cl is gaining / losing e-

oxidized / reduced

ionic bond

Atoms gain/lose electrons= Redox Reaction

Atoms share electrons

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Redox: Does it occur in reactions with covalent compounds?

• Add electrons

• What do you notice?1. Bonds

• Reactants = nonpolar covalent• Products = polar covalent

2. Redox• C, H losing electrons = oxidation• O gaining electrons = reduction

• Conclusion:

Covalent compounds undergo redox reactions

nonpolar covalent bonds polar covalent bondsO gaining e- = reduction

H losing e- = oxidation

C losing e- = oxidation

Reactants Products

methane

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Redox: Is redox related to energy?• Burning methane releases energy• Energy release related to redox?

• What do you notice?• Nonpolar covalent bond = high energy

e-

• Polar covalent bond = low energy e-

• As e- transition from nonpolar to polar covalent bond• e- lose energy• Energy released• Energy lost from system

• How much energy released?

• Conclusion:

energy

C H C OTime

G

nonpolar covalent bond polar covalent bondhigh energy e- low energy e-

• = electron

Energy changes in reactions are related to redox

CH4 + 2O2 CO2 + 2H2O + energy

covalent bond

energy in bond

ΔG

ΔG

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Energy & Metabolic Pathways

• ATP• Redox• Electron Carriers

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Electron Carriers: What are they?

• Compounds that transfer (“carry”) e- from 1 compound to another compound

• Ex. NAD+ (nicotinamide adenine dinucleotide; main electron carrier in cellular respiration)• (Neither full name nor structure

required … whew!)

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Electron Carriers: How do they carry electrons?Equation: NAD+ NADH• How are electrons carried? Look at how

get from NAD+ to NADH• Add H, but H (or H2) not present, only H+;

Result?• But want NADH, not NADH2+; How to fix?• Add 2 e-; Result?• Overall reaction?

• Is NAD+ being oxidized or reduced? How do you know?• Gaining 2 e-/Gaining H, so reduced

• Which compound carrying electrons, NAD+ or NADH ?

• Another way to look at this reaction

NAD+ + H+ NADH2+ NADH + 2e- ( )

Summary: NAD+ + H+ + 2e- NADH

NAD+ NADH

H+ + 2 e-

H+ + 2 e-

oxidation

reduction

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Electron Carriers: How do they carry electrons?

• Let’s look at actual compound• Relevant portions shaded

• What do you notice when NAD+ NADH?• Added H+ & 2 e-

• New covalent bond (attached to H)

• Where are electrons “carried”? • In new covalent bond• (Remember: 1 covalent bond = 2 e-)

• Are these low or high energy electrons? How can you tell?

• High energy because 2 e- in nonpolar covalent bond

• Remember: vertices = C, so C—H bond

new covalent bond

Summary: NAD+ + H+ + 2e- NADH