Biology 1107: Chapter 7 & 8 Homework
The Calvin cycle has three phases:
1. Carbon fixation 2. Reduction 3. Regeneration of RuBP NOTE: - Read about the Calvin cycle and review the two stages of photosynthesis.
For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.
2 NOTE: - Each glucose produces two pyruvates, each of which is converted into acetyl CoA.
In glycolysis there is a net gain of _____ ATP.
2 NOTE: - It takes 2 ATP to produce 4 ATP.
How many NADH are produced by glycolysis?
2 NADH NOTE: - Two NADH molecules are produced by glycolysis.
In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules?
3
What process occurs within Box B?
Citric acid cycle NOTE: - The citric acid cycle transfers electrons to NADH and FADH2.
Which of these phosphorylates ADP to make ATP?
E NOTE: - ATP synthase phosphorylates ADP.
Where does the Calvin cycle occur?
E NOTE: - Where does the Calvin cycle occur?
Which of these is NOT a product of glycolysis? - ATP - NADH - Pyruvate - FADH2
FADH2 NOTE: - FADH2 is a product of the citric acid cycle.
True or false? The chemiosmotic hypothesis states that the synthesis of ATP generates a proton gradient that leads to electron flow through an electron transport chain.
False NOTE: - The chemiosmotic hypothesis states that the flow of electrons through an electron transport chain generates a proton gradient that leads to the synthesis of ATP.
True or false? The region of ATP synthase that catalyzes the production of ATP from ADP and inorganic phosphate spans the chloroplast membrane.
False NOTE: - The region of ATP synthase that catalyzes ATP production protrudes out of, but does not span, the chloroplast membrane; the region that spans the membrane is an ion channel through which protons can pass.
NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?
Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor.
What is the importance of the light-independent reactions in terms of carbon flow in the biosphere?
The light-independent reactions turn CO2, a gas, into usable carbon in the form of sugars. NOTE: - CO2 is unusable until plants have "fixed" this carbon into sugar.
Select the correct molecule that is the main product of the Calvin cycle.
G3P NOTE: - Glucose is discussed as the product of photosynthesis primarily for convenience. - In fact, very little free glucose is produced by or transported from photosynthetic cells. Read about the Calvin cycle.
What molecules belong in space A and B?
Glucose and oxygen NOTE: - Photosynthesis produces glucose and releases oxygen into the atmosphere. - CO2 + H2O = Sugar + O2
The four stages of cellular respiration do not function independently. Instead, they are coupled together because one or more outputs from one stage functions as an input to another stage. The coupling works in both directions, as indicated by the arrows in the diagram below. In this activity, you will identify the compounds that couple the stages of cellular respiration.
NOTE: - The main coupling among the stages of cellular respiration is accomplished by NAD+ and NADH. - In the first three stages, NAD+ accepts electrons from the oxidation of glucose, pyruvate, and acetyl CoA. - The NADH produced in these redox reactions then gets oxidized during oxidative phosphorylation, regenerating the NAD+ needed for the earlier stages.
In muscle cells, fermentation produces _____.
Lactate and NAD+ NOTE: - These are the products of fermentation as it occurs in muscle cells.
In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle.
Net Input: Acetyl CoA, NAD⁺, ADP Net Output: CO₂, Coenzyme A, NADH, ATP Not input or output: Pyruvate, Glucose, O₂ NOTE: - In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. - In addition, one molecule of ATP is produced.
From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis.
Net Input: Glucose, ADP, NAD⁺, Net Output: Pyruvate, ATP, NADH Not input or output: O₂, CO₂, coenzyme A and acetyl CoA NOTE: - In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. - There is no O2 uptake or CO2 release in glycolysis.
According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis?
Proton gradient NOTE: - A proton gradient across chloroplast and mitochondrial membranes drives ATP synthesis by the enzyme ATP synthase.
Which of the following particles can pass through the ATP synthase channel?
Protons NOTE: - The channels formed by ATP synthase are specific for protons.
Which term describes ATP production resulting from the capture of light energy by chlorophyll?
Photophosphorylation NOTE: - The excitation of chlorophyll by light energy initiates a chain of events that leads to ATP production.
Why are plants classified as producers?
Plants are classified as producers because they fix inorganic carbon into organic molecules. Submit NOTE: - Read about the fixation of carbon and the role of producers.
True or false? The light-dependent reactions of photosynthesis use water and produce oxygen.
True NOTE: - The water molecules are split to replenish electrons in photosystem II, leaving behind protons, which are used to generate a proton gradient for the formation of ATP, and oxygen, which is released as a by-product.
Which of the following reactions reduce(s) oxygen to form water?
cellular respiration only
The proximate (immediate) source of energy for oxidative phosphorylation is _____.
kinetic energy that is released as hydrogen ions diffuse down their concentration gradient NOTE: - Concentration gradients are a form of potential energy.
In fermentation _____ is reduced and _____ is oxidized.
pyruvate ... NADH NOTE: - The pyruvate from glycolysis is reduced to either lactate or ethanol, and NADH is oxidized to NAD+.
The light reactions of photosynthesis supply the Calvin cycle with __________.
ATP and NADPH
The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP. Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?
ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. Submit NOTE: - An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP. - Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. - It is the initial decrease in ATP levels that leads to an increase in ATP production.
Structure A is _____.
ATP synthase NOTE: - ATP synthase phosphorylates ADP.
Chemiosmotic Hypothesis:
ATP synthesis is powered by the potential energy stored in a gradient of protons across a membrane
Chloroplast membrane vesicles are equilibrated in a simple solution of pH 5 . The solution is then adjusted to pH 8 . Which of the following conclusions can be drawn from these experimental conditions?
ATP will not be produced because there is no ADP and inorganic phosphate in the solution. NOTE: - This statement is true; although the proton gradient is present, ADP and inorganic phosphate are required to make ATP and were not added to the reaction.
Which of these enters the citric acid cycle?
Acetyl CoA NOTE: - Acetyl CoA is a reactant in the citric acid cycle.
Which of these is NOT a product of the citric acid cycle? - ATP - acetyl CoA - NADH + H+ - FADH2 - CO2
Acetyl CoA NOTE: - Acetyl CoA enters the citric acid cycle.
Chemiosmosis
- During Photosynthesis, light energy fuels the production of ATP - Sunlight powers the transport of electrons through an electron transport chain - The energy released during electron transport drives the movement of protons across a membrane, forming a proton gradient - It is this gradient of protons across fuels the production of ATP - Chemiosmotic Hypothesis: ATP synthesis is powered by the potential energy stored in a gradient of protons across a membrane Example: - To prepare chloroplast membrane vesicles, ground up leaves into small fragments. - From these fragments, extract membrane material - The extracted material formed many tiny spherical vesicles. - Many of the vesicles were composed of pieces of chloroplast membranes - These vesicles contained the protein ATP synthase, found in chloroplast - Two main part of ATP synthase: 1. Channel (Spans the membrane and serves as a channel for ions) 2. Segment that protrudes out of the membrane (it contains the molecular machinery that joins ADP and inorganic phosphate to make ATP) -Next Step, prepare a solution of hydrogen ions or protons, adjusted to pH 4 - Place vesicles in solution - Allow vesicles to equilibrate for a long period of time -During that time, protons will slowly cross the membrane until the solution inside the vesicle is pH 4 - THEN, adjust the solution outside the vesicles to pH8 by greatly reducing concentration of protons - This created a concentration gradient across the membrane, with a high concentration of protons inside and a low concentration outside - During the pH change, ADP and inorganic phosphate were introduced into the solution - Under these conditions the scientist observed that ATP was produced Production of ATP - The channels of ATP synthase are selective for protons - Because the proton concentration was higher inside the vesicle than outside, protons entered the channels and diffused down their concentration gradient toward outside of the vesicle - At the same time, ADP and inorganic phosphate bound to the enzyme - These substances were converted to ATP as protons completed their journey through the ATP synthase channel
The Calvin Cycle
- During the light reaction, light energy has been stored in the chemical bonds of ATP and NADPH - In the Calvin cycle this stored energy is used to produce sugar molecule - The Calvin cycle is a complex series of chemical reactions carried out in the stroma - It begins with carbon fixation - Three molecules of carbon dioxide are added to 3 molecules of a five carbon sugar abbreviated RuBP - These molecules are then rearranged to form 6 molecules called 3 PGA (which have three carbon each) - In the next two reactions products from the light reactions are used to boost the energy of these three carbon molecules - First 6 ATP molecules contribute high-energy phosphate groups so that each 3 carbon molecule receives an additional phosphate group - 6 molecules of NADPH are oxidized providing electrons to six 3 carbon compounds - The electrons from NADPH reduce the 6 3 carbon compounds creating six high-energy G3P molecules - G3P (or glycerol with three phosphate) is a sugar - It is the final product of the Calvin cycle - One of the G3 molecules represents the three carbon dioxide molecules fixed - The other remaining five G3P are reshuffle to regenerate the original RuBP molecules - Summary: the Calvin cycle has used the energy from the light reactions to reduce 3 carbon dioxide molecules and produce one molecule of G3P. Three more carbon dioxide molecules are fixed to form G3p in this same complicated way. To make each G3P, the Calvin cycle consumes 9 ATP molecules and six NADPH molecules. These are regenerated in the light reactions, G3P is the actual final product of the Calvin cycle. The cell can combine two G3Ps to make glucose, which stores the energy that chlorophyll originally captured from the Sun.
Oxidative Phosphorylation: Electron Transport and Chemiosmosis
- Electron carries such as NADH deliver their electrons to an electron transport chain embedded in the inner membrane of the mitochondrion - The chain consists of a series of electron carriers - Most of them are proteins that exist in large complexes - Electrons are transferred from one electron carrier to the next in the electron transport chain - As electrons move along each step of the chain they give up a bit of energy - The oxygen you breath pulls electrons form the transport chain and water is formed as a byproduct -T he energy released by electrons is used to pump hydrogen ions across the inner membrane of the mitochondrion creating an area of high hydrogen ion concentration - Hydrogen ions flow back across the membrane through a turbine - Much like water through a damn the flow of hydrogen ions s spins he turbine which activates the production of ATP - These sinning turbines in your cell produce most of the ATP that is generated from the food you eat - Cellular respiration generated 10 million ATPs per second in just one cell NOTE: - Oxidative phosphorylation consists of two tightly linked processes - electron transport and ATP synthesis. - In electron transport, the NADH and FADH2 produced in the first three stages of cellular respiration are oxidized by O2O2 (the oxidative part of this stage). - These redox reactions also drive the pumping of protons across the inner mitochondrial membrane, creating a proton (H+) gradient. - This H+ gradient is used to power the chemiosmotic synthesis of ATP from ADP and Pi (the phosphorylation part of this stage).
Cellular respiration
- Example: As a mountain biker heads up a trail, the breakfast he ate that morning is being burned to power his bike ride. His breathing rate increases as his leg muscles demand more oxygen to burn more fuel. - Fuel is burned in the cells - Blood vessels delivers fuel and oxygen to a single muscle cell - In cellular respiration, energy in fuel is converted to ATP - Most ATP is made in the cell's mitochondria - ATP powers the work of the cell, such as contraction Glycolysis - ATP produced from a molecule of glucose (our fuel) - The first step (Glycolysis): It takes place outsidethe mitochondria - To begin the proces ssome energy has to be inveseted - NEXT, the moelcule is split in half - Now, the molecule NAD+ (an electron carrier) picks up electrons and hydrogen atoms from the carbon molecule, becoming NADH - Electron carriers play an important role by transporting electrons to reactions in the mitochondria - In the final steps of glycolysis, some ATP is produced, but not much - For every glucose molecule, only 2 net ATPs are produced outside the mitochondrion - However, glycolysis has produce pyruvic acid, which still has a lot of energy available Acetyl CoA Formation - The pyruvic acid molecule goes into a mitochondria - As the molecule enters the mitochondrion, one carbon is removed forming carbon dioxide as a by-products - Electrons are stripped forming NADH - Coenzyme A attaches to the 2-carbon fragment, forming acetyl CoA Citric Acid Cycle (Krebs Cycle) - Coenzymes A is removed and the remaining 2-carbon Skelton is attached to an existing 4-cabron molecule that serves as the starting point for the citric acid cycle - The new 6-cabron chain is partially broken down, releasing carbon dioxide - Several electrons are captured by electron carriers and more carbon dioxide is released - The carbon dioxide that you exhale comes form the reactions of cellular respiration - 2 ATPs are produced by the citric acid cycle for each molecule of glucose - At this point, only a small number of ATPs have been produced - However, more energy is availed in the electrons that are being transported by electron carriers Oxidative Phosphorylation: Electron Transport and Chemiosmosis - Electron carriers such as NADH deliver their electrons to an electron transport chain embedded in the inner membrane of the mitochondrion - The chain consists of a series of electron carriers, most of which are proteins that exist in large complexes - Electrons are transferred from one electron carrier to the next in the electron transport chain - As electrons move along each step of the chain, they give up a bit of energy - The oxygen you breathe pulls electrons from the transport chain and water is formed as a by product -The energy released by electrons is using to pump hydrogen ions across the inner membrane of the mitochondrion creating an area of high hydrogen ion concentration - Hydrogen ions flow back across the membrane through a turbine - Much like water through a dam, the flow of hydrogen ions spins the turbine which activates the production of ATP - These spinning turbines in your cells produce most of the ATP that is generated from the food you eat - Cellular respiration generates 10 million ATPS per second in just one cell - That ATP can power a biker up the trail or it can power your brain cells as you learn biology topics
Photosynthesis & the Calvin Cycle
- Inside the cell, carbon dioxide diffuses into the chloroplast, where photosynthesis takes place - Chloroplasts use energy from light to transform carbon dioxide and water into sugar and oxygen - The chloroplast contains thylakoids, here light energy is converted to chemical energy Photosynthesis - In the first phase of photosynthesis the light reactions occur in large complexes of proteins and chlorophyll that capture light energy an electron transport chain connects the two photosystems - There is a small mobile electron carrier that shuttle electrons from one large complex to another Light Reactions - The photosystem absorbs light energy exciting electrons that enter the electron transport - Electrons are replaced with electrons trip from water creating oxygen as a by-product - The energized electrons flow down the electron transport chain releasing energy that is used to pump hydrogen ions into the thylakoid - In the photosystem on the right, light energy excites electrons and this time the electrons are captured by an electron carrier molecule NADPH - The high concentration of hydrogen ions inside the thylakoid powers ATP synthase, producing ATPs - The light reactions in the thylakoid produce energy products (ATP and NADPH) that will power the production of sugar in the Calvin cycle Calvin cycle - The Calvin Cycle takes place outside the thylakoids in the stroma - At the beginning of the cycle carbon dioxide molecules combine with molecules called RuBP - The resulting molecules go through a series of reactions powered by ATP and NADPH forming the light reactions sugar molecules known as G3P - These are produced most of the G3Ps are rearranged the back into RuBP that will begin the Calvin cycle again - The important product of photosynthesis is the remaining G3P sugar - Some G3Ps is used to build glucose which can combine into starch or cellulose - Other G3Ps form sucrose and some of the sugar is broken down by cellular respiration using oxygen in the plant zone mitochondria generating ATP's that can power other work of the plant - Excess oxygen diffuses out of the leave through the pores while more carbon dioxide enters - With three simple ingredients (Carbon dioxide, water, and light) plants produce (sugar and oxygen) by photosynthesis powering plant metabolism and ultimately providing your fuel as well
Electron Transport
- Most of the energy harvested from organic molecules during glycolysis and the citric acid cycle is stored in NADH and FADH2 - These molecules give up their high-energy electrons in the third phase of cellular respiration - Oxidative phosphorylation, where most of the cell's ATP fuel is produced - The electron transport chain is an array of molecules, mostly proteins, built into the inner membrane of the mitochondrion - NADH gives up its high-energy electrons to the first complex in the electron transport chain - The electrons move from one membrane of the chain to the next giving up their energy as they are pulled from NADH toward highly electronegative oxygen - The energy given up by the flow of electrons is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space - Oxygen captures the electrons in the very last step in electron transport - The last complex adds a pair of electrons to an oxygen atom and two hydrogen ions, forming water - The electron transport chain ahs used the energy of moving electrons to pump hydrogen ions into the intermembrane space - This build up of hydrogen ions, like water behind a damn, stores the potential energy that was originally in the bonds of glucose molecules - The backed-up hydrogen ions give up their energy when they diffuse through a special protein in the membrane called ATP synthase - As hydrogen ions flow down their concentration gradient ATP synthase captures their energy to make ATP - This mode of TAP production is called oxidative phosphorylation because it is powered by the transfer of electrons to oxygen
Overview of Photosynthesis
- Photosynthesis converts light energy to the chemical energy of sugars and organic compounds - This process consists of a series of chemical reactions that require carbon dioxide (CO2) and water (H2O) and store chemical energy in the form of sugar - Light energy drives the reactions - Oxygen (O2) is a by-product of photosynthesis and is released into the atmosphere - Equation of photosynthesis: 6CO2 + 6H2O ➝ C6H12O6 + 6O2 - Photosynthesis transfers electrons from water to energy-poor CO2 molecules, forming energy-rich sugar molecules (C6H12O6) - This electron transfer is an example of an oxidation-reduction process - Oxidation-reduction process: The water is oxidized (loses electrons) and the CO2 is reduced (gains electrons) - Photosynthesis uses light energy to drive the electrons from water to their more energetic states in the sugar products, thus converting solar energy to chemical energy - In plants, photosynthesis occurs in chloroplasts, mainly in leaf cells - The light reactions occur along the thylakoid membrane within the chloroplasts, where pigments capture light energy - The sugar-making reactions of the Calvin cycle occur in the stroma (the fluid between the inner membrane of the chloroplast and the thylakoids) - In light reactions, light is absorbed by chlorophyll molecules, exciting their electrons. - The energy of excited electrons is then used to join ADP and phosphate to form ATP - NAD+ joins with excited electrons to form NADPH, which temporarily stores the energized electrons - In the process, water is split and oxygen is released - In the Calvin cycle, energy from ATP, electrons from NADPH, and carbon from carbon dioxide (CO2) are combined to produce sugar molecules
Citric Acid Cycle
- The oxidation of glucose continues in the citric acid cycle - Pyruvate molecules formed during glycosis are transported from the cytosol in the mitochondria - pyruvate itself does not enter the citric acid cycle - A reaction occurs that removes a carbon atom releasing it in carbon dioxide - Electrons are transferred to a NADH molecule, storing energy - Coenzyme A (CoA) joins with the 2-carbon fragment, forming acetyl CoA - One molecule of acetyl CoA enter the citric acid cycle - The 2-carbon fragment of acetyl CoA attaches to the 4-carbon molecule oxaloacetate in the first reaction of the cycle - This forms citrate - In a series of steps, bonds break and reform - Two carbons are released, one at a time, in molecules of carbon dioxide - Electrons are carried off by molecules of NADH and FADH2 - One step produces an ATP molecule by substrate-level phosphorylation - A 4-carbon oxaloacetate molecule is regenerated - Since two acetyl CoA molecules are produced for each glucose molecule broken down a second acetyl CoA enters the citric acid cycle - The same series of reactions occurs, releasing carbon dioxide and producing more NADH, FADH2, and ATP - The cell has gained 2 ATPs that can be used to direct it - However, most of the energy contained in the bonds of glucose is now carried by the NADH and FADH2 molecules
Fermentation
- The synthesis ATP via the process of glycolysis - In many cells, if oxygen is not present, pyruvate (pyruvic acid) is metabolized in a process called fermentation - By oxidizing the NADH produced in glycolysis, fermentation regenerates NAD+, which can take part in glycolysis to produces more ATP - The net energy gained in fermentation is two ATP molecules per molecule of glucose - 1 Glucose = 2 ATP - Fermentation compliments glycolysis and makes it possible for a ATP to be continually produced in the absence of oxygen - Two common types of fermentation 1. Alchol fermentation 2. Lactic acid fermentation Alchol Fermentation - Alcohol fermentation occurs in yeast, resulting in the production of ethanol and carbon dioxide lactic - Acid fermentation occurs in muscles, resulting in the production of lactate lactic acid - Glycolysis produces NADH, ATP, and pyruvate (pyruvic acid) - If oxygen is not present NADH cannot be oxidized in the electron transport chain - Without fermentation the cell would run out of NAD+ bringing glycolysis to a halt in alcohol fermentation the pyruvate (pyruvic acid) from glycolysis loses one carbon in the form of carbon dioxide (CO2) and the product is then reduced to ethanol by NADH - With the formation of ethanol, NADH is oxidized and becomes NAD+ - With a continuous supply of NAD+ glycolysis can continue producing more ATP during fermentation - The NADH produced by glycolysis is oxidized ensuring a continuous supply of NAD+ for glycolysis - Example: Alcohol fermentation occurs in yeast cells - Glycolysis produces NADH, ATP and pyruvate pyruvic acid - If oxygen is not present NADH cannot be used in the electron transport chain without fermentation - The cell would run out of NAD+ bringing glycolysis to a halt Lactic acid Fermentation - In lactic acid fermentation, the pyruvate (pyruvic acid) from glycolysis is reduced to lactate (lactic acid) by NADH - With the formation of lactate (lactic acid), NADH is oxidized and becomes NAD+ - With a continuous supply of NAD+, glycolysis can continue producing more ATP - Fermentation the NADH produced by glycolysis is oxidized ensuring a continuous supply of NAD+ for glycolysis lactic acid fermentation occurs in muscle cells
Match each product of pyruvate metabolism with the condition under which it is produced. 1) Lactate 2) Ethanol 3) Acetyl CoA
1) Fermentation in human muscle 2) Fermentation in yeast and bacteria 3) Aerobic oxidation NOTE: - In the presence of oxygen, human cells carry out aerobic respiration, which yields acetyl CoA. - In the absence of oxygen, human cells can carry out lactic acid fermentation, which yields lactate. - Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobic conditions, and produces ethanol.
For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.
6 NOTE - 3 NADH + H+ are produced per each acetyl CoA that enters the citric acid cycle.
How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose?
6 NOTE: - Six carbon dioxide molecules are required to produce two G3P molecules, which can be combined to make one glucose molecule.
Which of these equations best summarizes photosynthesis?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
To synthesize one glucose molecule, the Calvin cycle uses ______ molecules of CO2, ______ molecules of ATPATP, and ______ molecules of NADPHNADPH.
6; 18; 12
_____ splits water into 1/2 O2, H+, and e- .
A NOTE: - Photosystem II splits water into 1/2 O2, H+, and e- .
Chlorophyll can be found in _____.
A and C NOTE: - The photosystems contain chlorophyll.
In glycolysis, what starts the process of glucose oxidation?
ATP NOTE: - Some ATP energy is used to start the process of glucose oxidation.
_____ releases energy that is used to pump hydrogen ions from the stroma into the thylakoid compartment.
B NOTE: - The energy released as electrons are passed along the electron transport chain is used to pump protons into the thylakoid compartment.
How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)
Both electron transport and ATP synthesis would stop. NOTE: - Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. - Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. - In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.
Energized electrons from ____ are used to reduce NADP+.
C NOTE: - Energized electrons from photosystem I are used to reduce NADP+.
What is the basic role of CO2 in photosynthesis?
CO2 is fixed or incorporated into organic molecules. NOTE: - Read about the fixation of CO2 in the Calvin cycle.
4. The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce ______ to ______.
CO2; G3P NOTE: - The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P), which then exits the Calvin cycle.
What molecules belong in spaces E and F?
Carbon dioxide and water NOTE: - Carbon dioxide and water are by-products of cellular respiration.
Select the correct statement about cellular respiration.
Cellular respiration and breathing differ in that cellular respiration is at the cellular level, whereas breathing is at the organismal level. Submit NOTE: - Read about the distinction between cellular and organismal respiration. - Both plants and animals perform cellular respiration
In the citric acid cycle, ATP molecules are produced by _____.
Substrate-level phosphorylation NOTE: - A phosphate group is transferred from GTP to ADP.
Under anaerobic conditions (a lack of oxygen), glycolysis continues in most cells despite the fact that oxidative phosphorylation stops, and its production of NAD+ (which is needed as an input to glycolysis) also stops. The diagram illustrates the process of fermentation, which is used by many cells in the absence of oxygen. In fermentation, the NADH produced by glycolysis is used to reduce the pyruvate produced by glycolysis to either lactate or ethanol. Fermentation results in a net production of 2 ATP per glucose molecule. During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?
Glucose utilization would increase a lot NOTE: - ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. - To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.
Glycolysis
Glycolysis occurs in the cytosol.
Which of the following sequences correctly represents the flow of electrons during photosynthesis?
H2O → NADPH → Calvin cycle
1. In the light reactions, light energy is used to oxidize ______ to ______.
H2O; O2 NOTE: - In the light reactions, light energy is used to remove electrons from (oxidize) water, producing O2 gas
Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops.
In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. NOTE: - NAD+ couples oxidative phosphorylation to acetyl CoA formation. - The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. - Without O2, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.
From the following choices, identify those that are the inputs and outputs of the Calvin cycle.
Input: - ATP - NADPH - CO2 Output: - ADP - NADP+ - G3P Not input or output: - Light - Glucose - O2 NOTE: - In the Calvin cycle, the energy outputs from the light reactions (ATP and NADPH) are used to power the conversion of CO2 into the sugar G3P. - As ATP and NADPH are used, they produce ADP and NADP+, respectively, which are returned to the light reactions so that more ATP and NADPH can be formed.
From the following choices, identify those that are the inputs and outputs of the light reactions. (Recall that inputs to chemical reactions are modified over the course of the reaction as they are converted into products. In other words, if something is required for a reaction to occur, and it does not remain in its original form when the reaction is complete, it is an input.)
Input: - Light - Water - NADP+ - ADP Output: - O2 - ATP - NADPH Not input or output: - CO2 - Glucose - G3P NOTE: - In the light reactions, the energy of sunlight is used to oxidize water (the electron donor) to O2 and pass these electrons to NADP+, producing NADPH. - Some light energy is used to convert ADP to ATP. - The NADPH and ATP produced are subsequently used to power the sugar-producing Calvin cycle.
Stage of Cellular Respiration:: Glycolysis
Location: Cytosol NOTE: - Cellular respiration begins with glycolysis in the cytosol. - Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes.
Stage of Cellular Respiration: Oxidative Phosphorylation
Location: Inner mitochondrial membrane NOTE: - The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
Stage of Cellular Respiration: Citric Acid Cycle
Location: Mitochondrial Matrix
Stage of Cellular Respiration: Acetyl CoA Formation
Location: Mitochondrial Matrix NOTE: - Both acetyl CoA formation and the citric acid cycle take place in the matrix. - The NADH and FADH2 produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane.
The overall function of the Calvin cycle is __________.
Making sugar NOTE: - Using the ATP and NADPH made during the light reactions, carbon is reduced in the Calvin cycle, and sugar is made.
In glycolysis, ATP molecules are produced by _____.
Substrate-level phosphorylation NOTE: - A phosphate group is transferred from glyceraldehyde phosphate to ADP.
What organelle is indicated by the letter C?
Mitochondrion NOTE: - Mitochondria are the sites of cellular respiration.
During electron transport, energy from _____ is used to pump hydrogen ions into the _____.
NADH and FADH2 ... intermembrane space NOTE: - The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and used to pump hydrogen ions into the intermembrane space.
2. The electrons derived from this oxidation reaction in the light reactions are used to reduce ______ to ______.
NADP+; NADPH NOTE: - These electrons are ultimately used to reduce NADP+ to NADPH.
After 3-PGA is phosphorylated, it is reduced by _____.
NADPH NOTE: - NADPH supplies the electrons that reduce the phosphorylated 3-PGA.
Which of the following molecules is the primary product of photosystem I?
NADPH NOTE: - The NADPH produced by photosystem I is used to supply energy for the production of sugars during photosynthesis.
3. The Calvin cycle oxidizes the light-reactions product ______ to ______.
NADPH; NADP+ NOTE: - In the Calvin cycle, NADPH is oxidized back to NADP+ (which returns to the light reactions).
In eukaryotes, all the reactions of photosynthesis occur in various membranes and compartments of the chloroplast.
NOTE: - The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. - Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions. - Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. - Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.
In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation.
Net Input: NADH, ADP, O₂ Net Output: NAD⁺, ATP, and Water Not input or output: Pyruvate, Glucose, Acetyl CoA, Coenzyme A and CO₂. NOTE: - In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. - The electron transport reactions supply the energy to drive most of a cell's ATP production.
In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation.
Net Input: Pyruvate, NAD⁺, coenzyme A Net Output: Acetyl CoA, NADH, CO₂ Not input or output: O₂, ADP, glucose and ATP NOTE: - In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.
The final electron acceptor of cellular respiration is _____.
Oxygen NOTE: - Oxygen is combined with electrons and hydrogen to form water.
What molecule is indicated by the letter D?
Oxygen NOTE: - Oxygen is the final electron acceptor of cellular respiration.
What process occurs in structure H?
Photosynthesis NOTE: - Chloroplasts are the sites of photosynthesis.
Which process produces oxygen?
Photosynthesis NOTE: - Oxygen is a by-product of the photosynthetic process.
Overview of Photosynthesis
Photosynthesis: - The ultimate source of energy for most life on Earth Is the Sun - Plants use the process of photosynthesis to capture the Sun's energy and put it to work - Cells derive the energy for life by respiration, using compounds that were originally created by photosynthesis - Cellular respiration and photosynthesis are complementary processes - In photosynthesis, plants use carbon dioxide, water, and light energy to produce sugar and other complex molecules - Oxygen is released as a by-product - The complementary process of cellular respiration converts oxygen and sugar into carbon dioxide and water - In the process, some energy is released to make ATP, and the rest is lost as heat Outside view of process: - Photosynthesis can be broken down into sets of reactions: Light-dependent Light independent - The light-dependent reactions transform the energy in sunlight to chemical energy in the form of electrons with high potential energy - These reactions result in the production of oxygen from water Inside the thylakoid: - The light-independent reactions use ATP and NADPH to reduce carbon dioxide front the atmosphere to sugar, through a set of reactions called the Calvin cycle - The carbohydrates produced by the Calvin cycle are sued in cellular respiration to make ATP for the cell - The light-dependent fractions of photosynthesis occur within the thylakoid membranes inside the chloroplast - The thylakoid membranes contain an array of proteins as well as chlorophyll and other pigments - This complex, called a photosystem, absorbs light and initiates the reactions of photosynthesis - Light-dependent fractions have two photosystems - In photosystem I, excited electrons are used to producing NADPH - In photosystem II, they are used to produce ATP - A photosystem absorbs photons of light, which bump electrons from chlorophyll molecules to electron acceptors within the photosystem - The chlorophyll molecules are left oxidized - Photosystem II transfers the energized electrons to a molecule called plastoquinone via an electron transport chain - The transfer releases enough energy to transport protons across the thylakoid membrane - A proton gradient forms, with a higher concentration inside the thylakoid than outside - The proton gradient is important because it represents the potential energy that the cell uses to produce ATP - Missing electrons in Photosystem II are replenished by stripping electrons from water, leaving behind protons and oxygen - Meanwhile, the electrons transferred to plastoquinone pass next to a cytochrome complex and then to a molecule called plantacyanin - Photosystem I also absorbs photons, which boost electrons from chlorophyll molecules to an electron acceptor within the photosystem - The energized electrons are passed to a molecule called ferredoxin, then to an enzyme that passes two electrons and a proton to a molecule of NADP+ - This reaction produces, NADPH, an electron carrier that donates its energy to the-light independent reactions of photosynthesis - Photosystem I is now oxidized (it has lost electrons) - These electrons are replenished by electrons originating from photosystem II - The result of these light-dependent reactions is the production of NADPH, a proton gradient that fuels ATP production, and the release of oxygen gas into the environment - When electrons are transferred along the thylakoid membrane, they have different energy levels - The electrons transferred from water to chlorophyll are relatively low in energy Energy Levels: - Electrons have differing energy levels as they transfer along the thylakoid membrane - Photons boost them to a much higher energy level, where they are captured by the electron acceptor, called pheophytin, in photosystem II - The electrons are then gradually stepped down in potential energy through a series of redox reactions, releasing energy that is used indirectly to make ATP - Light again energizes the electrons, which are ultimately captured in NADPH - In this system, light increases the energy level of electrons, allowing them to fuel the production of ATP and NADPH - One function of the electron transport chain of photosystem II is to pump protons into the interior of the thylakoid - The accumulated protons, or hydrogen ions, represent a form of potential energy - The enzyme ATP synthase taps this energy - The hydrogen ions have a tendency to flow down their electrochemical gradient - As they flow through a pore in the ATP enzyme, they make the enzyme spin - This conformational change in the enzyme drives the phosphorylation of ADP to make ATP - The chemiosmotic synthesis of ATP occurs in both chloroplasts and mitochondria - The light-dependent reactions occur in the thylakoid membranes and require light to produce NADPH and ATP - These molecules fuel the next series of reactions, which occur in the stroma - The light-independent reactions, also known as the Calvin Cycle, can occur with or without light Calvin Cycle: - light-independent reaction - It can occur with our without light - The Calvin cycle consists of three phases; 1. Fixation phase 2. Reduction Phase 3. Regeneration phase Fixation phase: - In the fixation phase, carbon dioxide from the atmosphere, combines with a 5-carbon molecule called ribulose-bis-phosphate, or RuBP - This process, in which carbon dioxide is made useable to life by incorporating it into an organic molecule, is called carbon fixation - The product of the initial reaction is an unstable 6-carbon compound that splits to yield two 3-carbon molecules of 3-phosphoglycerate Reduction phase: - The reduction phase begins when 3-phosphoglycerate is phosphorylation by ATP and concludes when it has been reduced by electrons from NADPH - The product is the phosphorylated sugar glyceraldehyde-3-phosphate (G3P) - Two G3P molecules are used to manufacture glucose Regeneration phase: - If the Calvin cycle didn't go through a regeneration phase, the chloroplast would run out of the RuBP molecules required to make glucose - To make a single molecule of glucose and to regenerate RuBP, the cycle must run six times - The Calvin cycle allows plants to use carbon dioxide from the air to form the sugar molecules required by all organisms - (NOTE how much ATP -> ADP; RuBP (w/ carbon atoms) is needed depending on the amount of CO2 inserted into the Calvin Cycle)
Which of the following does NOT occur during the Calvin cycle? - carbon fixation - oxidation of NADPH - release of oxygen - regeneration of the CO2 acceptor
release of oxygen
Sort the following items according to whether they are reactants or products in the anaerobic reduction of pyruvate during lactic acid fermentation. Reactant: Pyruvate Reactant: NADH
Reactant: Lactate Product: NAD+ NOTE: - When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate - In the process, NADH is oxidized to NAD+ - This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP
When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the various processes involved in cellular respiration and oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.)
Remains the same - Rate of oxygen update - Electron transport rate Decreases (or goes to zero) - Rate of ATP synthesis - Size of the proton gradient NOTE: - Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. - However, the leakiness of the membrane has no effect on the ability of electrons to move along the electron transport chain. - Thus, the rates of electron transport and oxygen uptake remain unchanged.
Carbon fixation involves the addition of carbon dioxide to _____.
RuBP NOTE: - In the Calvin cycle, carbon dioxide is added to RuBP.
Which molecule is regenerated in the regeneration phase of the Calvin cycle? Without regeneration of this molecule, the Calvin cycle would stop.
RuBP NOTE: - The regeneration of RuBP ensures that the Calvin cycle can proceed indefinitely, since RuBP fixes carbon dioxide into an organic molecule that is used to produce sugar.
In cellular respiration, a series of molecules forming an electron transport chain alternately accepts and then donates electrons. What is the advantage of such an electron transport chain?
The advantage of an electron transport chain is that a small amount of energy is released with the transfer of an electron between each pair of intermediates. NOTE: - As the electrons "fall" down the electron transport chain, the energy released is used to actively transport protons into the inner-membrane space. - (Read about the respiratory electron transport chain).
Which of the following statements best represents the relationships between the light reactions and the Calvin cycle?
The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns ADP, Pi, and NADP+ to the light reactions.
Which set of reactions uses H2O and produces O2?
The light-dependent reactions NOTE: - The light-dependent reactions use H2O and produce O2.
Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis?
The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions. NOTE: - Light energy drives the formation of ATP and NADPH during the light-dependent reactions; these energy molecules are then used during the light-independent reactions to form sugars.
What is the biological significance of the light-independent reactions of photosynthesis?
They convert carbon dioxide to sugar. NOTE: - All organisms use the sugars produced by photosynthesis to generate energy.
In mitochondrial electron transport, what is the direct role of O2?
To function as the final electron acceptor in the electron transport chain NOTE: - The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor. - Oxygen's high affinity for electrons ensures its success in this role. - Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.
In cellular respiration, most ATP molecules are produced by _____.
oxidative phosphorylation NOTE: - This process utilizes energy released by electron transport.
The light reactions of photosynthesis use _____ and produce _____.
water ... NADPH Submit NOTE: - NADPH is a reactant in the Calvin cycle.
