Cellular RespirationCellular Respiration

AP Biology Unit 4

Metabolic Pathways

• Metabolism = Totality of an organism’s chemical reactions

• Ex. Heme Synthesis Case Studies -- porphyria

succinyl CoA + Glycine

delta-aminolevulinic acid

delta-aminolevulinic acid

porphobilinogen uroporphyrinogen III

uroporphyrinogen I

coproporphyrinogen III

coproporphyrinogen I

coproporphyrinogen III

protoporphyrinogen IX

protoporphyrin IX

heme

1

23 4

4

5

6

7

mitochondria

cytoplasm

Free Energy Changes

• Free Energy = G = energy in a system that can perform work– H = enthalpy = total energy– S = entropy G = H - TS – If we know G for a

reaction, we know if it will supply energy for a cell to do its work.

What is the free energy used for?• Maintaining existing structures/processes

• Growth (adding biomass)

• Reproduction (if energy is available)

• Storage of energy

Metabolic rate vs. body size

• What do relationship do you see between body size and metabolic rate?

Free Energy (continued)

• Generally, the smaller the organism higher metabolic rate

• If not enough free energy is available (less than what’s needed) results in death

ATP as a Power Source

• ATP + H2O ADP + Pi G = -7.3 kcal/mol – Is this reaction endergonic

or exergonic?– Exergonic releases

energy

Why does ATP provide energy?• Contains many phosphate-phosphate bonds

• What is the charge on phosphates? – Negative

• It takes a lot of energy to put the phosphates together energetically favorable to break the bond (releases energy)

ATP as a Power Source

• Some reactions make ATP, others use it

ATP

ADP

+ Pi

Reactant 1 (Fuel)

Product 1

Product 2

Reactant 2

Make ATP Use ATP

Coupled Reactions

Random facts about ATP

• An active cell requires millions of ATP molecules per second to drive all of its activities

• An ATP molecule is typically consumed within a minute of its formation

• On average, a person at rest uses at least 40 kg of ATP a day.

Universal Currency

• Why have ATP as the main energy currency of the body?– Allows all enzymes that need it to recognize it

(don’t need as many “recognizers”)

Cellular Respiration

• The process used by cells to convert carbohydrates to a usable form of chemical energy (ATP)

• Requires oxygen

• Overall Equation:

C6H12O6 + 6 O2 6 CO2 + 6 H2O +

ENERGY

Oxidation

• Oxidation = loss of electrons (LEO)

• Reduction = gain of electrons (GER)

• Electrons release energy when they move from one atom to a more electronegative atom

• Glucose has many high energy bonds that release energy when the molecule is rearranged and broken down

Oxidation of glucose

• The energy is transferred in the form of 'high energy electrons' until it goes into making ATP (and the electrons are received by oxygen to make H20)

Process Occurs in Steps• Important Concept:

Cellular Respiration occurs in steps (not just one step)– Allows energy to be

harvested a little at a time (if all at once it would be too great)

– Allows for more points where the process can be regulated

Electron Carriers

• Molecules that electrons get transferred to and from (along with an H+)

• Intermediates that allow the energy to be transferred from glucose to ATP (eventually)

• NAD+ and FAD

Electron Carriers

• First steps involve transferring electrons from food (glucose) to NAD+ NADH

Electron Carriers

• After electrons are moved to NAD+, they are then (eventually) moved to oxygen to form H2O

• Where does all that energy (from electrons) go? It goes to make ATP!

Overview of Cellular Respiration

• In a eukaryotic cell

Question…

• How would cellular respiration be different in a prokaryote?

• Some processes would occur in different locations (no mitochondria in prokaryotes)

Glycolysis

• Occurs in the cytoplasm

• Series of 10 chemical reactions (each catalyzed by a different enzyme)

• Glucose 2 Pyruvates

O

CH2OH

HOOH

OH

OH

O

CH2OP

HOOH

OH

OH

O

CH2OP

HO

OH

OH

CH2OH

O

CH2OP

HO

OH

OH

CH2OP

O

CH2OH

C

CH2OP

OHC

CH2OP

H

OC

H

OHC

CH2OP

H

OC

OP

OHC

CH2OP

H

OC

O-

OPC

CH2OH

H

OC

O-

OPC

CH2

OC

O-

OC

CH3

OC

O-

ATP

ADP

ATP

ADP

GLUCOSE

PYRUVATE

2

2

2

2

2

2

2 NADH

2 Pi + 2 NAD+

2 ATP

2 ADP

2 ATP

2 ADP

Energy investing stage – use a little ATP(endergonic)

Energy harvesting (payoff) stage – make some ATP

(exergonic)

Glycolysis

• Net Yield Per Glucose:– 2 NADH – 2 ATP (made 4, used 2)

• All Carbohydrates can be broken down in glycolysis – converted to intermediates

• Enzymes in glycolysis can be regulated allosterically by ATP, activated by ADP

Pyruvate Oxidation• Second step in cellular

respiration• Energy is still in the

pyruvates (2)• If oxygen is present

pyruvates enter mitochondria (through active transport)

• Pyruvates converted into Acetyl CoA (2 Carbon)

waste product

Citric Acid Cycle

• Also called the TCA Cycle, Krebs Cycle

• Acetyl CoA enters the cycle lots of NADH and FADH2 is produced

• Takes place in the matrix of the mitochondria

• Cycle occurs 2 times per glucose (1 for each pyruvate)

Citric Acid Cycle

• Net Yield: (per glucose)– 6 NADH

– 2 FADH2

– 4 CO2 (waste)

– 2 ATP

Oxidative Phosphorylation

• Final step of cellular respiration “cashing in” to get all the ATP

• Occurs in the cristae (inner mitochondrial membrane)

• NADH and FADH2 produced in previous steps drop off their electrons energy from electrons used to make ATP

Electron transport chain (ETC)

• Series of proteins embedded in the innermembrane of mitochondria

• When the electrons are passed down ETC, it causes H+ ions to be pumped across the membrane into the intermembrane space

O2 as the Final Electron Acceptor

• At the end of the electron transport chain, the electron is transferred to O2 along with some H+ ions to produce H2O.

• This is why O2 is required in cellular respiration if O2 is not present, then only the first step (glycolysis) will occur

• Cellular respiration is an aerobic process = requires O2

H+ gradient

• Pumping H+ ions into the intermembrane space creates an imbalance in H+ on either side of cristae = gradient

• Gradient is both chemical and electrical – Chemical = More H+ = more acidic– Electrical = More + charges

ATP Synthase

• Because of the gradient, H+ ions diffuse back into the matrix through ATP Synthase

• ATP Synthase is an enzyme embedded in membrane

• As H+ passes through ATP Synthase, an ATP is produced

ATP Synthase

• 1 NADH generates enough H+ force to synthesize 3 ATP

• 1 FADH2 generates enough H+ force to

synthesize 2 ATP

ATP Produced

TOTAL = 38 ATP

Stage Products ATP

Glycolysis 2 NADH, 2 ATP 2

Pyruvate Oxidation

2 NADH, 2 CO2 0

Citric Acid Cycle

4 CO2, 6 NADH, 2

FADH2, 2 ATP

2

Oxidative Phosphorylation

6 H2O, 34 ATP 34

Wait! Almost…

• In eukaryotes, the 2 NADH produced in glycolysis requires 2 ATP (energy) to transport them into the mitochondria

• Net Yield of ATP =

38 ATP - 2 ATP = 36 ATP