Cellular Respiration AP Biology Unit 4

Metabolic Pathways Metabolism = Totality of an organism’s chemical reactions Ex. Heme Synthesis Case Studies -- porphyria

Free Energy Changes Free Energy = G = energy in a system that can perform work –H = enthalpy = total energy –S = entropy –  G =  H - T  S –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 + H 2 O  ADP + P i –  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 Make ATPUse 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: C 6 H 12 O O 2  6 CO H 2 O + 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 H 2 0)

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 H 2 O 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

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 FADH 2 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 FADH 2 –4 CO 2 (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 FADH 2 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

O 2 as the Final Electron Acceptor At the end of the electron transport chain, the electron is transferred to O 2 along with some H + ions to produce H 2 O. This is why O 2 is required in cellular respiration  if O 2 is not present, then only the first step (glycolysis) will occur Cellular respiration is an aerobic process = requires O 2

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 FADH 2 generates enough H + force to synthesize 2 ATP

ATP Produced TOTAL = 38 ATP StageProductsATP Glycolysis2 NADH, 2 ATP2 Pyruvate Oxidation 2 NADH, 2 CO 2 0 Citric Acid Cycle 4 CO 2, 6 NADH, 2 FADH2, 2 ATP 2 Oxidative Phosphorylation 6 H 2 O, 34 ATP34

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