Cellular Respiration: Harvesting Chemical Energy Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Quiz Define oxidation. Define reduction. List the four ways an enzyme reduces EA.

Quiz Define oxidation. Define reduction. The gain of an electron resulting in a reduced charge. Define reduction. The loss of an electron resulting in an increased charge. List the four ways an enzyme reduces EA. Orientating the substrate correctly. Stressing the bonds of the substrate Providing the correct chemical environment Covalently bonding to the substrate

Cells must work (use nrg) to live Figure 9.1

Review of nrg Cycle Energy Flows into an ecosystem as sunlight and leaves as heat. Our cells get nrg from the food we eat. Turn chemical nrg in food to ATP, CO2, and H2O

Overview of Cellular Respiration An overview of cellular respiration 3 Phases: Glycolysis* Citric Acid Cycle (AKA Krebs Cycle) Oxidative phosphorylation Each phase yields some ATP

Both glycolysis and the citric acid cycle Key Concepts Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

Substrate level phosphorylation Enzyme transfers a phosphate group from a substrate to an ADP. Substrate is an intermediary molecule in Glycolysis or the CAC. Makes only one ATP at a time.

The Breakers: A posse of enzymes and coenzymes The Players: The Victim: Glucose Gets broken down and has its e-’s stolen The Breakers: A posse of enzymes and coenzymes Will be introduced in each scene The Thieves: Electron Carriers NAD+, FAD Carry off electrons to the site of Oxidative Phosphorylation The motive: Make ATP

Inner Mitochondrial Membrane (Cristae) The scene: A dark stormy night, inside the cell. The action takes place in three areas: Cytosol Site of Glycolysis. Mitochondrial Matrix Site of the Citric Acid Cycle. Inner Mitochondrial Membrane (Cristae) Site of Oxidative phosphorylation.

An overview of Cellular respiration

9.2 Scene 1: The cytoplasm Glycolysis Means “splitting of sugar” Breaks down (oxidizes) glucose into pyruvate. 2 ATP 2 NAD+ 4 ADP

Glycolysis consists of two major phases Energy investment phase 5 steps Energy payoff phase

Special Note It is more important that you understand the overall process You will not be examined on the enzymes catalyzing each step of this or the intermediate conformations. However, it is advisable that you know them and are familiar with how the process occurs.

A closer look at the nrg investment phase 1 Glucose + 2 ATP = 2 Glyceraldehyde 3-Phosphate + 2 ADP Glucose gets phosphorylated 2 times. After 2nd phosphorylaton, Molecule gets split into 2 3-carbon molecules

A closer look at the nrg payoff phase 2 3-Carbon sugar + 2 NAD+ +2Pi = 2 Pyruvates + 2H2O +4 ATP + 2NADH + 2 H+ Pyruvates continue into CAC NADH+H+ goes to Oxidative phosphorylation. 4 ATP’s are generated 2 waters are generated

9.3- Scene 2: The mitochondrial Matrix Site of the Citric Acid Cycle Completes the energy-yielding oxidation (breakdown) of organic molecules Key Characters (names you should know): CoEnzyme A Acetyl CoA Oxaloacetate

Pyruvate must first be converted to acetyl CoA using Coenzyme A CYTOSOL MITOCHONDRION NADH + H+ NAD+ 2 3 1 CO2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH3 O Transport protein O– Figure 9.10

Overview of the Citric Acid Cycle (CAC) ATP 2 CO2 3 NAD+ 3 NADH + 3 H+ ADP + P i FAD FADH2 Citric acid cycle CoA Acetyle CoA NADH CO2 Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Oxidative phosphorylation Figure 9.11

A closer look at the CAC

A closer look at the CAC

A closer look at the CAC

A closer look at the CAC

Acetyl CoA + 3NAD+ + FAD + ADP + Pi  Summary CAC: Acetyl CoA + 3NAD+ + FAD + ADP + Pi  Oxaloacetate + 2CO2 + 3 NADH+3H+ + ATP + FADH2

Homework Review: 171 -176 (9.4-9.5)- Oxidative phosphorylation and fermentation Read and outline 176-178 (9.6) and 181-185 (overview-10.1 (Photosynthesis)) Exam C7-C10, Monday the 9th.

Quiz In CAC, what is the net yield, in terms of ATP and NADH, of one molecule of glucose? What is the molecule to which pyruvate is combined in the fist step of the Citric Acid Cycle? What are the two types of fermentation. Fermentation occurs under _____ conditions.

List the two types of fermentation. (2 pts) Quiz In CAC, what is the net yield, in terms of ATP and NADH, of one molecule of glucose? (2 points) 2 ATP and 6 NADH What is the molecule to which pyruvate is combined in the fist step of the Citric Acid Cycle? (2 points) Oxaloacetate List the two types of fermentation. (2 pts) Alcohol and lactic Acid Fermentation occurs under anaerobic conditions. (1 Point)

Chemiosmosis couples electron transport to ATP synthesis 9.4 Act 3 Inner mt Membrane Chemiosmosis couples electron transport to ATP synthesis NADH and FADH2 from glycolysis and CAC Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

The Pathway of Electron Transport E- gradually lose energy. (where does it go?) At the end of the chain Electrons are passed to oxygen, forming water

At certain steps along the electron transport chain Pumps H+ to the OUTSIDE of the inner membrane. Where actually is this, then, in the mt? What type of transport is this?

The resulting H+ gradient Stores energy Drives chemiosmosis in ATP synthase Is referred to as a proton-motive force

Chemiosmosis Is an energy-coupling mechanism that uses energy (H+ gradient) to drive cellular work. In this case, the H+ gradient is across the inner mt membrane, Work is making ATP

3 Processes in this metabolic enterprise

Chemiosmosis and the electron transport chain

Chemiosmosis: The Energy-Coupling Mechanism ATP synthase Is the enzyme that actually makes ATP

An Accounting of ATP Production by Cellular Respiration During respiration, most energy flows in this sequence Glucose to NADH to electron transport chain to proton-motive force to ATP

About 40% of the energy in a glucose molecule Is transferred to ATP during cellular respiration, making approximately 38 ATP

When electrons flow along the electron transport chains of mitochondria, which of the following changes occur? The pH of the matrix increases. ATP synthase pumps protons by active transport. The electrons gain free energy. The cytochromes of the chain phosphorylate ADP to form ATP. NAD+ is oxidized. Answer: a Source: Campbell/Reece - Biology, Sixth Edition, EOC Self-Quiz Question #6

In the 1940s, some physicians prescribed low doses of a drug called dinitrophenol (DNP) to help patients lose weight. This unsafe method was abandoned after a few patients died. DNP uncouples the chemiosmotic machinery by making the lipid bilayer of the inner mitochondrial membrane leaky to H+. What impact does this have on ATP production? * reduces substrate level phosphorylations increases substrate level phosphorylations reduces oxidative level phosphorylations increase oxidative level phosphorylations This would have no impact on ATP production. Answer: c Source: Campbell/Reece - Biology, Sixth Edition, EOC Process of Science Question Discussion Notes for the Instructor There are several questions which can be asked to guide the discussion of this question including: Which portion of the cellular respiration pathway involves hydrogen ions and the mitochondrial membrane? How do hydrogen ions cause ATP production? If the hydrogen ion concentration changes how does this impact ATP? Using these questions as an outline, discussion of the choices might look like this: Choice A, substrate level phosphorylations do not involve hydrogen ions. Choice B, substrate level phosphorylations do not involve hydrogen ions. Choice C, correct. Choice D, if there are fewer hydrogen ions to move through the ATP synthetase complexes less ATP will be produced. Choice E, hydrogen ion movement has a direct impact on ATP production.

Glucose, made from six radioactively labeled carbon atoms, is fed to yeast cells in the absence of oxygen. How many molecules of radioactive alcohol (C2H5OH) are formed from each molecule of glucose? 1 2 3 6 Answer: c Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #15

Cyanide is a poison that blocks the passage of electrons along the electron transport chain. Which of the following is a metabolic effect of this poison? The lower pH of the intermembrane space is much lower than normal. Electrons are passed directly to oxygen, causing cells to explode. Alcohol would build up in the cells. NADH supplies would be exhausted, and ATP synthesis would cease. No proton gradient would be produced, and ATP synthesis would cease. Answer: e Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #20

Which kind of metabolic poison would most directly interfere with glycolysis? an agent that reacts with oxygen and depletes its concentration in the cell an agent that binds to pyruvate and inactivates it an agent that closely mimics the structure of glucose but is not metabolized an agent that reacts with NADH and oxidizes it to NAD+ an agent that inhibits the formation of acetyl coenzyme A Answer: c Source: Barstow - Test Bank for Biology, Sixth Edition, Question #5

You have a friend who lost 15 pounds of fat on a diet. Where did the fat go (how was it lost)? * It was released as CO2 and H2O. Chemical energy was converted to heat and then released. It was converted to ATP, which weighs much less than fat. It was broken down to amino acids and eliminated from the body. It was converted to urine and eliminated from the body. Answer: a Source: Barstow - Test Bank for Biology, Sixth Edition, Question #63 Discussion Notes for the Instructor There are several questions which can be asked to guide the discussion of this question including: What are fats composed of and how does that relate to the answer choices? How are fats metabolized and what are the end products of this? Using these questions as an outline, discussion of the choices might look like this: Choice A, correct. The mass of a fat is in the atoms of the molecule. When fats are metabolized these atoms end up in CO2 and H20 Choice B, while this is somewhat true, energy has no mass and therefore cannot be the source of the weight loss. Choice C, When fats are metabolized the energy in them is used to make ATP, but the fats are not converted into ATP (a common misconception) Choice D, Fats are not composed of amino acids Choice E, Urine is generally the result of nitrogenous waste product, fats (i.e. Triglycerides contain little nitrogen if any and therefore do not result in urine production)