CHAPTER 9 CELLULAR RESPIRATION: HARVESTING CHEMICAL ENERGY Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: The Principles of Energy Harvest 1.Cellular respiration and fermentation are catabolic, energy-yielding pathways 2. Cells recycle the ATP they use for work 3. Redox reactions release energy when electrons move closer to electronegative atoms 4. Electrons “fall” from organic molecules to oxygen during cellular respiration 5. The “fall” of electrons during respiration is stepwise, via NAD + and an electron transport chain

I. Introduction to cellular respiration Living is work. A. Function of Cellular Resp? To produce ATP from glucose for cellular functions Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.1

Metabolic pathways that release the energy stored in complex organic molecules are catabolic (break down of complex mlcls) B. Types of catabolic pathways – 1. fermentation, anaerobic respiration (w/out oxygen) creates only a small amt of ATP, but purpose is to allow resp. to continue with limited O 2 a. alcohol - produced by bacteria & yeast & some plants b. lactic acid – produced by animals in low oxygen situation – removed from cells to liver (can then be removed from body or recycled back into glucose is enough ATP is present Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

2. A more efficient and widespread catabolic process, cellular respiration, uses oxygen as a reactant to complete the breakdown of a variety of organic molecules. Produces much ATP C. E flow in the ecosystem Light E > photosynthesis<> respiration> heat

D. Cellular Resp Equation (combustion rxn) – C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O + Energy (ATP + heat) – (can be other org cmpds besides glucose) Carbohydrates, fats, and proteins can all be used as the fuel, but it is traditional to start learning with glucose. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

An electron looses energy as it shifts from a less electronegative atom to a more electronegative one. A redox reaction that relocates electrons closer to oxygen releases chemical energy that can do work. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

E. The process of cellular respiration creates ATP molecules. They are created by the overal “fall” of electrons! In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy. Glucose is oxidized, oxygen is reduced, and electrons loose potential energy. that can be used elsewhere. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A. 3 metabolic stages of cell resp 1. glycolysis -- cytoplasm 2. the Krebs cycle– mitochondrial matrix 3. electron transport chain - ETC – mitochondrial cristae II. Where does cellular respiration occur? cytoplasm & mitochondria Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.6

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III. Mitochondria Review A. Mitochondria has 2 layers of membranes B. endosymbiotic theory – mito. (& chloroplasts) have their own DNA ergo they must have been prokaryotic endosymbionts (living w/in another organism) both (mito & cell) became dependent on each other ….evolution p

C. mitochondrial structure – 1. cristae – inner membrane foldings – 2. matrix – area enclosed by cristae

3. the inner membrane is highly folded to increase surface area 4. increased area allows for an ion gradient – a. ions (H + ) are pumped back & forth across the membrane to create ion gradients – these gradients are used to phosphorylate (add a phosphate to) ADP mlcls – (change ADP into ATP)

IV. Glycolysis – the 1 st step of cell resp A. Quick over view of glycolysis – 1. start with: glucose – 2. end with: 2 pyruvates

B. Glycolysis = sugar splitting 1. glucose starts as a 6-Carbon sugar 2. & is split into 2 3-Carbon sugars – a. the new sugars are oxidized (LEO goes GER) & rearranged to form 2 mlcls of pyruvate – in the process several e- are released an harvested by: 1)NAD+ = nicotinamide adenine dinucleotide– this gets electrons from food & is thus reduced to 2)NADH – oxidized from of NAD -- this is what carries the e- for the ETC – LEO goes GER = lose e - oxidized & gain e - reduced

3. 10 steps in glycolysis each w/it’s own enzyme 4. this phase of cell resp requires ATP (2 of them)

5. impt stuff produced during glycolysis – a. ATPs – 4 – b. NADHs – 2 – c. H 2 O (waste)- 2

6. oxygen not required (anaerobic) for glycolysis (this indicates this process probably evolved before the ETC & kreb’s cycle). However, if there is no oxygen present at all then the cell cannot go into the next stip of cell resp. – a. if no O2 --- process is fermentation (lactic acid production in animals) – b. at end of fermentation cell will produce alcohol or lactic acid

c. if oxygen is present 2 molecules of pyruvate move into the mitochondria & begin the Kreb’s cycle (the NADH mlcls will be saved for the ETC)

V. Krebs Cycle (aka citric acid cycle – because citrate is the 1 st product formed) A. O 2 must be present B. 2 pyruvate mlcls move into the mitochondrial matrix C. Krebs has 8 steps each w/ its own enzymes D. 2 pyruvates enter cycle & are rearranged

E. output of 1 turn of the Krebs cycle (remember there are 2 mlcls of pyruvate for each mlcl of glucose) – 1. CO 2 = 2 (x2) – 2. NADH = 3 (x2) – 3. ATP = 1 (x2) – 4. FADH 2 = 1 (x2) (flavin adenine dinucleotide – another e- carrier)

F. NADH & FADH 2 (stores the E from breaking down glucose so far) –will move into the 3 rd stage of cell resp.

VI. Electron Transport Chain A. found in cristae membrane of mito. B. It’s an actual chain of protein mlcls!!!! C. NADH will “drop off” its electrons to the 1 st mlcls in the chain FMN (flavin mononucleotide) – 1. e- is passed on from protein to protein – 2. it’s finally passed on to an oxygen which bonds toa couple of hydrogen ions to make water – 3. for every 1NADH you make 2 mlcls of water – 4. for every 1 NADH you make 3 mlcls of ATP

D. FADH – follows a similar pattern but drops its e- at a “lower” part of the chain thus transferring less energy (1/3 less) – 1. for every 1 FADH 2 you get 2 ATPs E. No ATP is made directly by the ETC – its job is to move electrons to oxygen slowly to release E in manageable amts

Remember, you’re basically carrying out a combustion rxn INSIDE of a cell --- the E has to be controlled so you don’t damage or kill the cell in the process!

F. Then how do we make ATP? chemiosmosis

VII. Chemiosmosis A. occurs during ETC!!! B. ATP synthase- enzyme used to catalyze ADP + P i ATP C. ATP synthase uses the E of an ion gradient to make ATP mlcls

D. How does the mitochondrial membrane generate & maintain a H+ gradient? – 1. function of the ETC a. as e- fall down the ETC, H+ ions are pumped into the space between the membranes (towards the outer membrane) of the mitochondria

b. the H+ ions naturally diffuse (osmosis) back to the matrix and the ONLY way back in is through the ATP synthase protein c. the ATP synthase can use the movement of H+ ions to fuel oxidative phosphorylation of ADP into ATP converting KE to PE (chemical energy)

d. the coupling of the ETC & oxidative phosphorylation is called chemiosmosis

2. In general, chemiosmosis is an energy- coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work 3. chemiosmosis occurs in other locations! – a. plants – photosynthesis – b. bacteria - fermentation