Cellular Respiration Cell Respiration Step 1 Krebs Cycle

Cellular Respiration Cell Respiration Step 1 : Krebs Cycle Step 2: Electron Transport Chain (oxidative phosphorylation) *Much more energy is released than in fermentation so if an organism has a choice- will use cell respiration *Note: your book separates Krebs into 2 steps: “Pyruvate Processing” and “Krebs”. My lecture combines them as “Krebs” in attempt to simplify the steps.

Cellular Respiration Recall: Glycolysis left us with pyruvate If O 2 is present, pyruvate is converted to acetyl Co-A which enters the Krebs cycle CO 2 + NADH + Krebs Consequences of this oxidation rxn: 1 of the 3 C atoms in pyruvate converted to CO 2 The other 2 C atoms are converted to Acetyl Co. A Energy released from this rxn used to reduce NAD+ to NADH

Cellular Respiration acetyl Co-A (higher energy) Acetyl Co. A enters the Krebs Cycle: The Big Picture • Successive oxidation of 8 Carbon molecules • Enough energy released from this to generate ATP, NADH and FADH (similar role as NADH) (lower energy)

Cellular Respiration Krebs Cycle: The Big Picture 6 C 5 C 4 C Fig 9. 19 CO 2 also produced as a result of oxidizing C molecules (5 C sugar 4 C sugar + CO 2)

Cellular Respiration Krebs Cycle: The Big Picture (e-carriers/donors) Acetyl Co-A CO 2 + NADH + FADH + ATP ee- exhaled/ eused for ephotosynthesis O 2 Can immediately be used for energy (ATP ADP+ energy)H O 2 (e-acceptor) This happens in next step- electron transport chain

Cellular Respiration Where is this happening in the cell? Glycolysis and fermentation: cytosol Prokaryotes Respiration: mitochondria Eukaryotes Glycolysis, Fermentation, and respiration: cytosol

Cellular Respiration After glycolyis, pyruvate is transported into matrix of the mitochondria where the Krebs cycle occurs Where is this happening in the cell?

Cellular Respiration What happens to the Krebs Cycle Products? CO 2 gas released from cell (passes through mitochondria and cell membranes) Electron carriers (NADH & FADH) carry their electrons to the inner membrane where many molecules that make up the electron transport chain are embedded.

inner membrane outer membrane inner membrane space

Electron Transport Chain Big Picture (NADH or FADH) “chain” refers to a series of molecules that receive and then pass off electrons. ed leas gy re ased enegr y rele ener With each transfer, energy is released The final e- acceptor in the chain in O 2. The diff. in potential energy between NADH and O 2 is large. The difference is what is released. When O 2 receives (O 2) this is why e- it gets reduced to water. This is water O 2 needed H 2 O is a byproduct of respiration

Electron Transport and Chemiosmosis • Most of the ETC molecules are proteins containing chemical groups that facilitate redox reactions. All but one of these proteins are embedded in the inner mitochondrial membrane. – In contrast, the lipid-soluble ubiquinone (Q) can move throughout the membrane. • During electron transport, NADH donates electrons to a flavin-containing protein at the top of the chain, but FADH 2 donates electrons to an iron-sulfur protein that passes electrons directly to Q.

Unlike in Glycolysis and Krebs where ATP is directly generated from the change in free energy, there is another step between release of energy and ATP in the ETC: Oxidative Phosphorylation ATP *Released energy from ETC used to pump H+ into inner memb space (against gradient) where high [H+] accumulates (much potential energy in this space). As those H+ move down gradient through ATP synthase, the energy is release and that energy is used to make ATP from ADP

Glycolysis, Krebs Cycle and ETC (Cell Respiration) C 6 H 12 O 6 + 6 O 2 + CO 2 + 6 H 20 + ATP Gets converted to pyruvate (after many intermediate C molecules), then acetyl Co-A, then a series of more oxidized C molecules and eventually all the carbons in glucose become C in CO 2 (oxidized) used as the final electron acceptor in the electron transport chain, without it-- fermentation produced in Krebs cycle from reduction of O 2 in ETC 26 net/ glucose ENERGY!

Feedback Inhibition • Feedback inhibition occurs when an enzyme in a pathway is inhibited by the product of that pathway. – Cells that are able to stop glycolytic reactions when ATP is abundant can conserve their stores of glucose for times when ATP is scarce.

Regulation of Glycolysis ATP = product of glycolysis ATP inhibits glycolysis So if there is enough ATP, no glycolysis Remember, glycolysis does require some energy input. • Natural selection favors organisms that can conserve glucose when ATP is not needed. • •

Feedback Inhibition Regulates Glycolysis • During glycolysis, high levels of ATP inhibit the enzyme phosphofructokinase, which catalyzes one of the early reactions. • Phosphofructokinase has two binding sites for ATP: 1. The active site, where ATP phosphorylates fructose-6 phosphate, resulting in the synthesis of fructose-1, 6 bisphosphate 2. A regulatory site High ATP concentrations cause ATP to bind at the regulatory site, changing the enzyme’s shape and dramatically decreasing the reaction rate at the active site.

Regulation of Krebs cycle • The enzyme that converts acetyl Co. A to the first product in the Krebs cycle is inhibited directly by ATP. • There are other places where NADH or ATP directly inhibits the Krebs cycle.

Regulation of pyruvate (before entering Kreb (citric acid) cycle • High levels of ATP, acetyl Co. A, and NADH all inhibit PDH (pyruvate dehydrogenase). • High levels of NAD+, Co. A, or AMP (aka low ATP) speeds rxn

The cell can use other carbon compounds in these processes • Carbohydrates first, then fats, then proteins

Cellular Respiration What if there is an over-flow of pyruvate: (more made by glycolysis than is needed for cell respiration)? Converted to an stored as: Fats What if there is an over-flow of glucose (more glucose in the blood from glycolysis than is needed for cell respiration)? Converted to an stored as: glycogen

Anabolic Pathways Synthesize Key Molecules • Molecules found in carbohydrate metabolism are used to synthesize macromolecules such as RNA, DNA, glycogen or starch, amino acids, fatty acids, and other cell components.