Chapter 9 Objectives: Cellular Respiration and Fermentation
Describe where pyruvate is oxidized to acetyl CoA, what molecules are produced, and how this process links glycolysis to the citric acid cycle.
2 molecules of pyruvate left over from glycolysis enter the mitochondrion if oxygen is present. From there, it can then be used by the Krebs Cycle. When it enters the mitochondrion, a multienzyme complex catalyzes these reactions. Pyruvate's carboxyl group is removed and is given off as carbon dioxide, leaving a two-carbon fragment. This fragment is oxidized to make acetate. The extracted electrons are moved to NAD+ to make NADH that stores energy. Then, coenzyme A attaches to the acetate by an unstable bond, which makes the acetate (acetyl group) very reactive. Pyruvate has now been converted into acetyl coenzyme A (acetyl CoA). Acetyl CoA's acetate can be used by the Krebs Cycle for more oxidation.
State the basic function of fermentation.
A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.
Distinguish between obligate and facultative anaerobes.
A facultative anaerobe does not require oxygen for respiration, but can function in the presence of oxygen. An obligate anaerobe does not require oxygen for respiration, and will cease to function if oxygen is present.
Describe the point at which glucose is completely oxidized during cellular respiration.
As electrons pass or slide down the electron transport chain energy is released. This is an exergonic reaction because energy is being released as electrons pass from carrier to carrier in the ETC. This energy is used by ATP synthase to create ATP. This is an endergonic reactions because it needs energy to take place. Energy is needed to produce ATP.
In general terms, explain how the exergonic "slide" of electrons down the electron transport chain is coupled to the endergonic production of ATP by chemiosmosis.
As electrons pass or slide down the electron transport chain energy is released. This is an exergonic reaction because energy is being released as electrons pass from carrier to carrier in the ETC. This energy is used by ATP synthase to create ATP. This is an endergonic reactions because it needs energy to take place. Energy is needed to produce ATP.
Identify the molecule that is generated from glucose by the end of the "payoff phase" in glycolysis. a. How many carbons make up glucose? How many carbons make up the molecule that is the end product of glycolysis? How many of the "end molecule" of glycolysis is made from 1 glucose?
By the end of the payoff phase in glycolysis, NAD+ reduces to NADH by electrons released from the oxidization of glucose. Glucose has six carbons which are split into two three carbon sugars. Four carbons are left as the end product of gylcolysis. 2 ATP and 2 NADH molecules are made per one glucose.
Describe how food molecules other than glucose can be oxidized to make ATP.
Each NADH and FADH2 molecule formed represents stored energy... contain high energy electrons from food molecules which are carried to an electron transport chain; Plants manufacture their own food by photosynthesis using energy from sunlight. Cells harvest the chemical energy stored in organic molecules and use it to regenerate ATP, the molecule that drives most cellular work. ADP + P + energy ATP
In general terms, distinguish between fermentation and cellular respiration.
Fermentation is the partial degradation of sugars or other organic fuels that occur without the use of oxygen. Cellular respiration involves both aerobic respiration and anaerobic respiration. Aerobic respiration involves the use of oxygen, consumed with organic fuels, while anaerobic respiration harvest chemical energy without oxygen.
Compare the processes of fermentation and cellular (aerobic and anaerobic) respiration. Which process is the most efficient ATP producer?
Fermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor, such as oxygen, via an electron transport chain Oxygen is a reactant in cellular respiration but not in fermentation. Also, fermentation produces ATP without the use of an electron transport chain
Describe anaerobic respiration. How does it relate to aerobic respiration?
Fermentation: Occurs without oxygen, is the partial degradation of sugars to release energy; A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid. Anaerobic respiration: The use of inorganic molecules other than oxygen to accept electrons at the "downhill" end of electron transport chains.
Name the three stages of cellular respiration and state the region of the eukaryotic cell where each stage occurs.
Glycolysis occurs in the cytosol. Pyruvate oxidation, the citric acid cycle, and oxidation phosphorylation also occurs in the mitochondrial matrix.
Although the numbers are inexact, summarize the approximate net ATP yield from the oxidation of a single glucose molecule.
Glycolysis--2 net ATP from substrate-level phosphorylation 2 NADH yields 6 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation;Transition Reaction--2 NADH yields 6 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation;Citric Acid Cycle--2 ATP from substrate-level phosphorylation 6 NADH yields 18 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation 2 FADH2 yields 4 ATP (assuming 2 ATP per FADH2) by oxidative phosphorylation Total Theoretical Maximum Number of ATP Generated per Glucose in Prokaryotes--38 ATP: 4 from substrate-level phosphorylation; 34 from oxidative phosphorylation; In eukaryotic cells, the theoretical maximum yield of ATP generated per glucose is 36 to 38, depending on how the 2 NADH generated in the cytoplasm during glycolysis enter the mitochondria and whether the resulting yield is 2 or 3 ATP per NAD
Compare the fate of pyruvate in alcohol fermentation and lactic acid fermentation.
In alcoholic fermentation, pyruvic acid is converted to ethanol. Carbon dioxide is released, and NADH is recycled into NAD+. In lactic acid fermentation, pyruvic acid is converted to lactic acid. NADH is recycled into NAD+
Define oxidation and reduction in terms of electrons and bonds.
Oxidation is the loss of one or more electrons and the loss of one or more bonds. Reduction is the gain of electrons and a the gain of one or more bonds.
Describe how the processes of photosynthesis and cellular respiration are related. Note: they are necessary not just in an ecosystem, but in each individual cell.
Photosynthesis generates oxygen and organic molecules used by the mitochondria of eukaryotes as fuel for cellular respiration, which breaks the fuel down to generate ATP.
Explain in general terms how redox reactions are involved in energy exchanges.
Redox reactions relocates electrons closer to oxygen, such as the burning of methane, releases chemical energy that can do work.
Review concept: ATP made is made by two processes - substrate level phosphorylation and oxidative phosphorylation. Describe the differences in ATP generation by these two methods. Which is more efficient at generating ATP?
Substrate-level phosphorylation is directly phosphorylating ADP with a phosphate and energy provided from a coupled reaction. Substrate level phosphorylation will only occur if there is a reaction that releases sufficient energy to allow the direct phosphorylation of ADP. Oxidative phosphorylation is when ATP is generated from the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons. That process generates an electrochemical gradient, which is required to power the ATP synthase. Substrate level phosphorylation yields 2 ATP molecules at the end of glycolysis. In oxidative phosphorylation, 34 ATP molecules are generated. Oxidative phosphorylation is more efficient when generating ATP molecules.
Explain why the citric acid cycle is called a cycle and define the roles of acetyl-coA, oxaloacetate, and citrate.
The citric acid cycle is called a cycle because every acetyl CoA that enters the cycle reacts with oxaloacatate and is recycled. Acetyl coA forms a bond with oxaloactetae to become citrate.
In general terms, explain the role of the electron transport chain in cellular respiration.
The electron transport chain in cellular respiration consists of a number of molecules (proteins) built into the inner membrane of the mitochondria of eukaryotic cells. Electrons cascade down the concentration gradient from one carrier to another, losing a small amount of energy with each step until they finally reach oxygen.
Explain where and how the respiratory electron transport chain creates a proton gradient. Explain why this gradient is described as a proton motive force.
The electron transport chain pumps protons from the matrix of the mitochondrion through the inner membrane and out to the intermembrane space (the interior of the cristae). The interior of the cristae becomes positively charged relative to the mitochondrion matrix, which creates a strong electrochemical gradient which favors the movement of protons back into the matrix.
Summarize the overall process of cellular respiration. Write the specific chemical equation for the degradation of glucose.
The process of cellular respiration occurs when we consume food which provides the fuel for respiration and the exhaust of carbon dioxide and oxygen. Chemical equation is as follows C6H12O6+6 O2+6 H2O+ Energy(ATP+ heat).
Describe the role of NAD+ in cellular respiration.
The role of NAD+ in cellular respiration is a suited electron carrier that is able to cycle easily between oxidized (NAD+) and reduced states (NADH). It functions as an oxidizing agent in the cellular respiration process. Also a co-enzyme.
Identify the molecule glucose is changed into at the end of energy "investment" phase of glycolysis. Explain why ATP is required for the preparatory steps of glycolysis.
Two molecules of ATP are consumed as glucose is split into two three-carbon sugars (glyceraldehyde 3-phosphate).The conversion of these molecules to pyruvate produces two NADH and four ATP by substrate-level phosphorylation.
Explain how ATP production is controlled by the cell. Describe the role that the allosteric enzyme phosphofructokinase plays in this feedback control.
When ATP levels are high in the cell, no metabolic energy production is needed. Phosphofructokinase (PFK) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose-6-phosphate: fructose-6-phosphate + ATP fructose-1,6-bisphosphate + ADP In part because of the irreversible nature of this step in glycolysis, PFK is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In this case, PFK's activity is inhibited by allosteric regulation by ATP itself, closing the valve on the flow of carbohydrates through glycolysis.
Explain why ATP synthase is considered a molecular rotary motor.
While the protons diffuse through it, it actually spins to make room for another proton to come through.
Does substrate-level phosphorylation and reduction of NAD+ occur in glycolysis? If so, how much ATP and NADH are produced per 1 molecule of glucose?
Yes, substrate level phosphorylation and reduction of NAD+ occurs in the payoff stage of glycolysis. It produces 2 ATP and 2 NADH molecules in one glucose.
