Chapter 9 Objectives

Draw or describe or diagram how the H+ gradient is coupled with ATP synthesis. Understand the experiment (Fig. 9.17) that demonstrated how ATP synthesis is coupled to H+ gradients. (chemiosmotic, proton-motive force)

ATP synthase is a proton channel. A flow of protons through the Fo unit causes the rotor and shaft to spin. As the shaft spins within the F1 unit, it is thought to change the conformation of the F1 subunits in a way that catalyzes the phosphorylation of ADP to ATP. The H+ gradient is coupled with ATP synthesis because as H+ ions move down their concentration gradient the flow causes the rotor and shaft of ATP synthase to spin, and as the shaft spins within the F1 subunit, the subunits conformation changes in a way that catalyzes the phosphorylation of ADP to ATP

Describe or diagram how the electron transport chain creates a gradient. What proteins are involved and where are they located? How is energy stored in the gradient?

Draw Diagram- Energy comes from what is stored in the gradient forming ATP. Facilitated Diffusion and Active Transport occur through Complexes I, 2,3,4, Q (ubiquinone), the cytochrome and ATP synthase occurs with the help of phosphorilization. Book: The movement of electrons through the ETC actively transports protons from the matrix, across the inner membrane, and into the intemembrane space. Through redox reactions, Q shuttles electrons and protons from one side of the membrane to the other. The electrons proceed down the transport chain, and the protons contribute to an electrochemical gradient as they are released into the intermembrane space. Energy is carried by NADH and FADH2, much of which was originally present in glucose is now in the electrochemical gradient. The electron transport chain takes place in the inner membrane of the mitochondria. Electrons are passed from Complex I to Complex II to Complex III to Complex IV while NADH and FADH2 (DIAGRAM)

How do fats enter the respiration reactions (glycolysis, citric acid)?* How do proteins enter the respiration reactions?*

Fats enter cellular respiration when enzymes break down fats to release glycerol and convert the fatty acids into acetyl CoA molecules; glycerol can be further processed and enter glycolysis while acetyl CoA enter the citric acid cycle. Proteins can be broken down into their constituent amino acids, and enzyme-catalyzed reactions remove the amino groups. The remaining carbon compounds are converted to pyruvate, acetyl CoA, and other intermediates in glycolysis and the citric acid cycle

Following glycolysis, where do you find the energy that was initially stored in glucose? Where is most of the glucose energy stored? (ATP, NADH, pyruvate)

Following the 10 step sequence of reactions in glycolysis, the energy initially stored in glucose in transferred into ATP, NADH and finally, pyruvate. Phosphorylation along the way aids in the process of creating these forms of energy. The energy that was initially stored in glucose is divided into three product molecules. Some of the energy from glucose is stored in the two ATP produced during glycolysis, some of the energy is transferred as electrons in the reduction of NADH (eventually the electrons are donated to the electron transport chain which yield more ATP), but most of the energy initially from glucose will be stored in the two molecules of pyruvate

Where do glycolysis, the citric acid cycle and electron transport take place and what is the importance of location to each process? (cytoplasm, mitochondria, matrix, intermembrane space, compartmentalization)

Glycolysis - cytoplasm. Citric acid cycle (Krebs) - matrix of mitochondria. Electron transport chain - inner membrane of mitochondria. The separate compartmentalization of each process is important. The compartmentalization is due to the phosopholipid bilayer and allows the different processes to take place separately. Glycolysis takes place in the cytosol of the cell, the citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place in the inner membrane and cristae of the mitochondria. All three processes can take place at different locations in the cell and can all occur at the same times, increasing the efficiency of ATP production of the cell

Explain the mechanism of feedback inhibition of phosphofructokinase (ATP, allosteric). How does this regulation help the cell?

Phosphofructokinase-1 (PFK-1) is one of the most important regulatory enzymes (EC 2.7.1.11) of glycolysis. It is an allosteric enzyme made of 4 subunits and controlled by many activators and inhibitors. PFK-1 catalyzes the important "committed" step of glycolysis, the conversion of fructose 6-phosphate and ATP to fructose 1,6-bisphosphate and ADP. Because phosphofructokinase (PFK) catalyzes the ATP-dependent phosphorylation to convert fructose-6-phosphate into fructose 1,6-bisphosphate and ADP, it is one of the key regulatory and rate limiting steps of glycolysis. PFK is able to regulate glycolysis through allosteric inhibition, and in this way, the cell can increase or decrease the rate of glycolysis in response to the cell's energy requirements. For example high ratio of ATP to ADP will inhibit PFK and glycolysis. Feedback inhibition of phosphofructokinase occurs when the cell recognizes that it has an abundance of ATP, and since ATP serves as the substrate at the third step of glycolysis (in which ATP donates a phosphate group to form fructose-1,6-biphosphate, thus committing the sequence to glycolysis), when it exits in a high concentration, it will bind to the regulatory site of phosphofructokinase, changing the conformation of the enzyme in a way that dramatically lowers the reaction rate at the active site

Give one example of a kinase from glycolysis. What does this enzyme do? (ATP, substrate, high-energy phosphate bond)

Pyruvate is a kinase from glycolysis. It catalyzes the transfer of a phosphate to ATP to yield one molecule pyruvate and one molecule ATP. The phosphate group comes from a phosphorylate substrate to ADP, and then forms a high energy ATP bond. Phosphofructokinase transfers a phosphate from ATP to the opposite end of fructose-6-phosphate, increasing its potential energy and converting it to fructose-1,6-biphosphate

Draw the citric acid cycle focusing on steps where carbon is lost as CO2 and where energy is extracted in the form of reduced molecules. (Do not memorize chemical structures)

See pg 20 in booklet

ATP can be produced by oxidative phosphorylation and substrate-level phosphorylation. Give a specific example of each during cellular respiration.*

Substrate-level: metabolic reaction that results in ATP or GTP by donation of PO3 to ADP or GDP from a reactive intermediate (during glycolysis and krebs cycle) oxidative phosphorylation: takes place during cellular respiration NADH is oxidized to form NAD+, yielding 2.5 ATP and FADH2 yields 1.5 ATP during oxidation. Uses an electrochemical or chemiosmotic chemiosmosisgradient of protons (H+) across the inner mitochondrial membrane to generate ATP from ADP and a molecule of inorganic phosphate, which is a key difference from substrate-level phosphorylation Substrate-level phosphorylation occurs during glycolysis and the citric acid cycle and yields two ATP; it is the production of ATP by the transfer of a phosphate group from an intermediate substrate directly to ADP. Oxidative phosphorylation occurs during the electron transport chain and yields about 25 ATP; it is the production of ATP molecule by ATP synthase using the proton gradient established via redox reactions of an electron transport chain

How does NADH store the energy released during glycolysis? (reduction, oxidation, electron)

The NADH is oxidized to NAD during the process of oxidative phosphorylation which is ubiquitous in aerobic organisms. This oxidation of NADH is coupled to uptake of O2 with water as the final product. Energy is released during this process but this energy is captured in the form of ATP. Reduced NADH stores energy in the form of and extra H+ (proton) and then releases its extra electron before becoming NAD+ NADH does not specifically store the energy released during glycolysis; rather NAD+ accepts an electron and becomes reduced to NADH, and later donates its electrons to the ETC

Explain the regulation of the citric acid cycle. (ATP NADH, feedback inhibition)

The citric acid cycle can be turned off at multiple points, via several different mechanisms of feedback inhibition. Reaction rates are high when ATP is scarce; reaction rates are low when ATP is abundant. The cycle starts with the two-carbon acetyl molecule in the form of acetyl CoA and ends with the release of 2 CO2. Reactions occur in the mitochondial matrix, and the potential energy that is released is used to produce 3 NADH, 1 FADH2, and 1 ATP or GTP for each acetyl oxidized. The citric acid cycle can be inhibited at many points through several different mechanisms of feedback inhibition. In step 1, the enzyme that combines acetyl CoA and oxaloacetate to form citrate is shut down when ATP binds to it (feedback inhibition); in step 3, NADH interferes with the reaction by binding to the enzymes active site (competitive inhibition)

Describe and compare the roles of the inner and outer mitochondrial membranes. (H+ gradient,electron transport)*

The outer mitochondrial membrane separates glycolysis from the citric acid cycle and the electron transport chain, while the ETC is located in the inner membrane of the mitochondria, which is also responsible for the establishment of a proton gradient

Summarize the role of redox reactions in cellular respiration. (recuded carbon, oxidized carbon)

There's a lot of energy stored in the bonds between the carbon and hydrogen atoms in glucose. During cellular respiration, redox reactions basically transfer this bond energy in the form of electrons from glucose to molecules called electron carriers. So an electron carrier is basically a molecule that transports electrons during cellular respiration. By using electron carriers, energy harvested from glucose can be temporarily stored until the cell can convert the energy into ATP. Redox reactions are consistently occurring throughout cellular respiration and can be observed through the transfer of electrons and the oxidation of glucose and the reduction of molecules such as NAD+ to NADH and FAD+ to FADH2

What is the total number of ATPs produced by the breakdown of a glucose molecule with and without oxygen present?

With O2-30 ATP are produced without O2- 2 ATP are produced

In the absence of O2, how is NAD+ recovered? How does this process differ in fungi (yeast) and animals? (Fermentation, ethanol, lactic acid, CO2)

cells that don't use oxygen are anaerobic and tend to grow much slower than aerobic cells do. Fermentation is a metabolic pathway that regenerates NAD+ by oxidizing stockpiles of NADH. The electrons removed from NADH are transferred to pyruvate, or a molecule derived from pyruvate, instead of an electron transport chain. Allows glycolysis to continue producing ATP even when ETC is shut down, allowing cell to survive and grow in the absence of electron transport chains. Lactic acid fermentation regenerates NAD+ by forming a product molecule called lactate: a deprotonated form of lactic acid. Instead of depositing the electrons from NADH into pyruvate, the yeast first convert pyruvate to the two-carbon compound acetaldehyde-giving off CO2. Acetaldehyde then accepts electrons from NADH, forming the NAD+ required to continue glycolysis. The addition of electrons to acetaldehyde forms ethanol as a wast product. The yeast cells excrete ethanol as waste. In the absence of O2, NAD+ is recovered through fermentation; pyruvate, the product of glycolysis, (holds onto CO2 in lactic acid fermentation and releases CO2 in alcohol fermentation) accepts electrons from NADH which oxidizes it to NAD+ so that glycolysis can occur. Fungi (yeasts) can use alcohol fermentation while humans can use lactic acid fermentation

Every few seconds you inhale O2 and exhale CO2. What is the role of each of these molecules in cellular respiration? (aerobic respiration)

oxygen is the electron acceptor used by all eukaryotes and a wide diversity of bacteria and archaea-species that depend on oxygen as an e- acceptor use aerobic respiration and are called aerobic organisms. CO2 serves as an end product that is released from the body tissues (cells) after cellular respiration is used to release energy from an ATP molecule O2 is the final electron acceptor in the electron transport chain, and is the deciding factor in determining whether a cell will go through cellular respiration (aerobic respiration) or fermentation (anaerobic respiration). CO2 is a byproduct of the citric acid cycle, carbon atoms of the glucose molecules are released as CO2

Know all the steps of glycolysis that were covered in class. Your focus should be on steps that involve energy transfer from one molecule to the next.

see page 18 in booklet Glycolysis: a process that takes place in the cytosol of the cell and begins with the mobilization of sugar; fructose-1,6-biphosphate is cleaved to form 2 molecules of G3P (glyceraldehyde-3-phosphate); from there, sugar is oxidized until two molecules of pyruvate are produced

Chapter 9 focuses on glucose as an energy source for cells. However, we also eat proteins and fats. How do these molecules provide energy for the cell (glycolysis, glycerol, fatty acids, amino acids, pyruvate, acetyl CoA)*

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