metabolic processes review Flashcards

Question

Anaerobic Respiration

Answer 1

Some organisms live in anoxic environments and thus cannot use oxygen as their final electron acceptor. Instead, they use inorganic compounds such as sulfate, nitrate, or carbon dioxide as electron acceptors. They are said to carry out anaerobic respiration. In some organisms, anaerobic respiration is similar to aerobic respiration. For example, a few bacteria, including E. coli, carry out aerobic respiration when oxygen is available. When oxygen is not available but nitrate is, they synthesize an enzyme called nitrate reductase, which can accept electrons from the electron transport chain and pass them to nitrate according to the following equation: NO3-(aq) + 2e‒ + 2H+ → NO2‒(aq) + H2O(l) Other organisms, such as methanogens, have different metabolic pathways. However, they use electron transport chains and generate hydrogen ion gradients that provide energy for phosphorylation. They use hydrogen that is synthesized by other organisms as an energy source and carbon dioxide as an electron acceptor. The summary equation for their metabolism is: 4H2(aq) + CO2(aq) → CH4(g) + 2H2O() Some methanogens grow in swamps and marshes and are responsible for marsh gas, which is methane. Some of the prokaryotes that live in the stomachs of cows and other ruminants are methanogens, which are major sources of methane released into the environment.

Answer 2

Fermentation allows the production of a small amount of ATP without oxygen. If no oxygen is available, cells can obtain energy through the process of anaerobic respiration. A common anaerobic process is fermentation. Fermentation is not an efficient process and produces far fewer ATP molecules than aerobic respiration. Many single-celled organisms such as yeasts and some bacteria, use only glycolysis for energy. Multicellular organisms use glycolysis as the first step in aerobic metabolism. During intense exercise, however, oxygen cannot be delivered to muscle cells rapidly enough to supply the energy needs of the cells, so they rely on glycolysis for energy. The NADH that is reduced during glycolysis cannot be reoxidized by electron transport as fast as it is being reduced, and thus muscle cells will run out of oxidized NAD+ and glycolysis will cease unless another pathway is available. Different organisms and cell types have several different ways to reoxidize the reduced NADH, usually by reducing an organic molecule. These processes are called fermentation. Fermentation is much less efficient at supplying energy than aerobic respiration, because fermentation only produces the amount of ATP that is generated in glycolysis. Two common pathways are lactate fermentation and ethanol fermentation, There are two primary fermentation processes: Lactic Acid Fermentation and Alcohol Fermentation Occurs in the absence of O2 or insufficient O2. Requires NADH generated by glycolysis. Happens in the cytosol What does it do? - Yeasts convert sugar into carbon dioxide and ethanol (C6H12O6 🡪 2CO2 + 2CH3CH2OH) - Muscle cells produce lactic acid from reduction of pyruvate (CH3COCOO− + 2H🡪 C3H6O3) Only a few ATP are produced per glucose Lactic acid fermentation: occurs when oxygen is not available. Example: in muscle tissues during rapid and vigorous exercise, muscle cells may become depleted of oxygen. They then switch from respiration to fermentation. In muscle cells under low O2 conditions, pyruvic acid formed during glycolysis is broken down to lactic acid and NAD+, and energy is released to form ATP. Glucose → Pyruvic acid → Lactic acid + NAD+ + E (The pyruvate generated by glycolysis reacts with NADH to reoxidize it to NAD+. In the reaction, pyruvate is converted into lactic acid. The reoxidized NAD+ allows glycolysis to continue. The lactate that is formed in bacteria is secreted into the surrounding medium, causing it to become acidic. The lactate that is generated in muscles must be reoxidized to protect the tissues from the acidic environment. Oxygen is ultimately needed to allow the lactate to return to the oxidative pathways to be metabolized. The amount of oxygen required to eliminate the lactate is called the oxygen debt. The lactate produced in muscle cells is transported out of the cells into the bloodstream. there is evidence that the lactate is taken up by resting muscle cells. Some of the lactate is converted back into pyruvate and oxidized, while some is converted into glycogen, which is stored in the muscle. (as soon as u stop the strenuous activity adn rest your breathing and heart beat come back to normal and the oxygen demands can be met) Lactic acid fermentation temporarily replaces aerobic respiration so that the cell can have a continual source of energy, even in the absence of oxygen or low oxygen. This shift is only temporary because cells need oxygen for sustained activity. When sufficient oxygen levels return, aerobic respiration resumes and removes the lactic acid build-up. (reps and stuff gets easier after training is because u build up ur body to that point where u delay lactic acid fermentation or anaerobic respiration due to ur increased endurance). Lactic acid that builds up in tissue causes a burning, painful sensation. Alcohol Fermentation: occurs in yeasts and some bacteria, often even when oxygen is present (preferred method of metabolism). Pyruvic acid formed during glycolysis is broken down to alcohol, CO2, and energy, which is used to form ATP. Glucose → Pyruvic acid → alcohol + CO2+ energy (in form of atp) Yeast and some bacteria are able to function aerobically as well as anaerobically. These organisms are called facultative anaerobes. When they function anaerobically, they convert pyruvate to ethanol and carbon dioxide through ethanol fermentation. Fermentation by brewer’s yeast (Saccharomyces cerevisiae) is used in industry to manufacture baked goods and alcoholic beverages. When used in brewing, a variety of products can be made, depending on the substance being fermented, the variety of yeast used, and whether carbon dioxide is allowed to escape during the process. For example, yeast fermentation may be used to produce wine or champagne from grapes; a syrupy drink, called mead, from honey; or cider from apples. Beer is brewed by fermenting sugars in grain such as barley, rice, or corn. Fermentation has commercial uses --> () will ferment with other stuff to form certain products. ex. yogurt (lactobacillus)

Answer 3

Depending on the organism, fermentation can yield other substances besides lactate and ethanol. Two other examples of fermentation products, acetone and butanol, were essential during World War I. The British needed butanol to make artificial rubber for tires and machinery; acetone was needed to make a smokeless gunpowder called cordite. When war broke out in 1917, the demand for acetone was great. A swift and efficient means for producing the chemical was needed. In 1915, Chaim Weizmann, a chemist, had developed a fermentation process using the anaerobic bacterium Clostridium acetobutylicum. Through this process, Weizmann converted 100 tonnes of molasses or grain into 12 tonnes of acetone and 24 tonnes of butanol. For the war effort, Weizmann modified the technique for large-scale production. Today, both acetone and butanol are produced more economically from petrochemicals. Glucose is the main fuel for many organisms. However, much of the chemical energy of glucose remains in the compounds that form after glycolysis is complete. The process of fermentation does not remove much of this chemical energy. Therefore, the products of fermentation can still be used for fuel. In organisms that carry out ethanol fermentation, the ethanol they produce is released as a waste product. However, humans learned long ago that this “waste” can be burned. Ethanol was a common lamp fuel during the 1800s, and it was used for early internal combustion engines in cars and other machinery. Historically, because gasoline costs less to produce than ethanol, the use of ethanol was limited to small-scale, specialized applications. This situation changed in the late 1970s. At that time, rising oil prices, dwindling petroleum reserves, and environmental concerns caused some governments to invest in alternative energy resources such as ethanol fuels. When gas prices rise, some of these alternative resources become commercially viable sources of fuel. In cars, the use of a gasoline-ethanol fuel mixture has become common. Cars manufactured after 1980 can use this fuel mixture, called E-10, without any engine modification. Auto companies also design engines that can use fuels with ethanol percentages that are much higher than the 10 percent in gasohol. In Canada, the most common source of ethanol is the fermentation of corn and wheat. First the grain is ground into a meal. Then it is mixed with water to form a slurry called “mash.” Enzymes added to the mash convert the starches into glucose. The mash is heated to destroy any bacteria, then cooled and placed in fermenters. In the fermenters, yeast is added to the mash. The yeast grows on the glucose under anaerobic conditions and releases the end products, ethanol and carbon dioxide. When the fermentation is complete, the resulting product, called “beer,” is approximately 10 percent ethanol and 90 percent water. Distilling the “beer” to eliminate as much of the water as possible yields nearly pure ethanol. A small amount of gasoline is added to make the ethanol unfit for human consumption. The solid residues from the grain and yeast are dried to produce a vitamin- and protein-rich product called Distiller’s Dried Grains and Solubles (DDGS) used as livestock feed. Some single-celled organisms that live in conditions of very low oxygen can carry out anaerobic respiration by using an electron acceptor other than oxygen. Some single-celled organisms and, during extreme exertion, some muscle cells, use only glycolysis for energy in a process called fermentation. In lactate fermentation, pyruvate oxidizes NADH back to NAD+ and, in the process, is converted into lactate. In single-celled organisms, the lactate is released to the surroundings and in muscle cells, it is released into the bloodstream where it is carried to resting muscle cells and oxidized or converted to glycogen for storage. In ethanol fermentation, pyruvate is converted into a two-carbon compound, acetaldehyde, and carbon dioxide. The acetaldehyde reoxidizes the NADH back to NAD+ for reuse and becomes ethanol. Alcohol fermentation is a useful industrial process, used to generate ethanol for fuel. It is also the same process by which alcoholic beverages are produced.

Answer 4

Anaerobic respiration is a metabolic pathway in which an inorganic molecule other than o2 is used as a final electron acceptor during the chemiosmotic synthesis of ATP. It occurs in the cytosol of bacteria, yeast and animal cells in the process of fermentation. Fermentation is a form of anaerobic respiration. During anaerobic respiration, the final electron acceptor in bacteria can be nitrate or co2 but in fermentation NAD+ is regenerated by oxidizing NADH through an alternate method and there is no electron transport system involved. Fermentation is less sufficient at supplying energy compared to aerobic respiration as it produces much less ATP. Since the ETC is where most ATP is produced in aerobic respiration and fermentation skips/doesnt go to the ETC as there is no oxygen to drive it, less ATP is produced. In fermentation all the energy comes from glycolysis and glucose can't be completely oxidized. Building up anaerobic threshold: It's important to do this because when lactate fermentation occurs in the muscle cells, lactate acid will build up in the tissue which causes a buring and painful sensation which can last a while/ you need more time to recover and get the lactate acid out of the tissue. Anaerobic and glycolysis: Both require NAD+ as an oxidizing agent, include the production of pyruvate, and don’t require oxygen. Glycolysis stops at the production of pyruvate. Anaerobic processes regenerate NAD+ but glycolysis itself does not. Anaerobic processes use electron acceptor other than oxygen to generate NAD+. (glycolysis is needed to actually allow anaerobic respiration to occur)

Answer 5

If no oxygen is available, cells can obtain energy through the process of anaerobic respiration. A common anaerobic process is fermentation. Fermentation is not an efficient process and produces far fewer ATP molecules than aerobic respiration. There are two primary fermentation processes: Lactic Acid Fermentation & Alcohol Fermentation Fermentation allows the regeneration of NAD+ so that we can keep performing (NADH to NAD+). Start with glycolysis. Now we need the step to regenerate NAD+ (2 pyruvates will yield lactate) Lactate product - lactic acid Lactic Acid Fermentation: occurs when oxygen is not available. in muscle tissues during rapid and vigorous exercise, muscle cells may become depleted of oxygen. They then switch from respiration to fermentation. Pyruvic acid formed during glycolysis is broken down to lactic acid, and energy is released to form ATP. Glucose → Pyruvic acid → 2 Lactic acid + energy (+ 2 NAD). Lactic acid fermentation temporarily replaces aerobic respiration so that the cell can have a continual source of energy, even in the absence of oxygen. This shift is only temporary because cells need oxygen for sustained activity. Lactic acid that builds up in tissue causes a burning, painful sensation. Alcohol Fermentation: occurs in yeasts and some bacteria, often even when oxygen is present (preferred method of metabolism). Pyruvic acid formed during glycolysis is broken down to alcohol, CO2, and energy, which is used to form ATP. Glucose → Pyruvic acid → 2 alcohol + 2 CO2+ energy (+ 2NAD) ---- Anaerobic Pathways: - tends to be less efficient: produces less ATP. for organisms that live in environments where oxygen is low or absent. e.g. inside gut, deep underground or underwater, wetlands - found in some prokaryotes similar to aerobic cellular respiration. ETC takes place on specialized membranes. use another inorganic compound as a final electron acceptor instead of oxygen e.g. SO42-, NO3-, Fe3+ Fermentation: - eukaryotes and some bacteria cannot undergo anaerobic cellular respiration - can still undergo glycolysis: anaerobic - produce 2 ATP and 2 NADH - problem: will run out of NAD+ - solution: use fermentation after glycolysis to oxidize NADH back to NAD+ for use in glycolysis - two kinds: lactate fermentation & alcohol fermentation Lactate Fermentation: - found in some bacteria and some eukaryotes, including human muscle cells - pyruvate is reduced by NADH to create lactate (lactic acid) and NAD+ - lactate fermentation equation: 2 pyruvate + 2 NADH --> 2 lactate + 2 NAD+ - when oxygen is restored, the reaction is reversed: lactate is oxidized by NAD+ to recreate pyruvate and NADH Alcohol Fermentation: - found in some bacteria and yeasts - pyruvate is decarboxylated, producing acetaldehyde and CO2 - acetaldehyde is reduced by NADH to create ethanol (alcohol) and NAD+ - alcohol fermentation equation: 2 pyruvate + 2 NADH --> 2 ethanol + 2 CO2 + 2 NAD+ Thinking question: why does yeast create fluffy bread? (think of products of fermentation) --> How light the bread is is a function of how much gas is in the dough. It's the carbon dioxide that creates all the little bubbles that make the bread lighter and fluffier. Gas is created with the growth of the yeast. The more the yeast grows, the more gas in the dough

Answer 6

- Glycolysis: Uses glucose and enzymes to break it down --> 2 pyruvate molecules are produced and a little ATP (makes 2 ATP) - Krebs Cycle: Uses pyruvate to make a molecule of NADH and ATP--> makes ATP and NADH. CO2 is released as a waste product (makes 2 ATP) - ETC: NADH is used, e- move in the chain while H+ ions move into the intermembrane. e- leave the chain by reacting with oxygen gas and H+ ions to create water --> Water is produced - ATP Synthase: Hydrogen ions in the intermembrane space are used as they travel back to the matrix. They travel through ATP synthase and as it passes through it rotates and makes ATP --> ATP is made as the H+ passes through ATP synthase which rotates to make it. (makes 34 ATP) - 2-deoxyglucose: It's a poison that stops glycolysis. It attaches to the 1st enzyme in glycolysis. This stops glucose from being used by glycolysis so no pyruvate is made. - arsenic: It's a poison that stops the Krebs cycle. It attaches to the 1st enzyme in the Krebs cycle. This stops pyruvate from being used by the Krebs cycle so no NADH is made. - cyanide: It's a poison that stops the ETC. It attaches to the last enzyme in the ETC. This stops electrons from leaving the ETC, so new electrons cannot enter the ETC. Without new electrons, the ETC stops working and no H+ are moved into the intermembrane space. - oligomycin: It's a poison that stops ATP synthase. It attaches to the hole/pore in ATP synthase. This stops H+ from moving through ATP synthase and no ATP is made. Cyanide stops the ETC. If the ETC was stopped that means pyruvate is being used and produced at a regular amount and NADH is not being used as the ETC stops working. This matches with the results from Jareds muscle cells. Also the intermembrane H+ ion concentration is decreased which correlates to cyanide being the poison as if the ETC stops working no H+ are moved into the intermembrane space. Cyanide caused symptoms such as muscle weakness as it stopped the electron transport chain from working. This caused pyruvate to be produced and used normally, while there was an increase in NADH in the cells as it was not being used by the electron transport chain. Since the chain was not working this means the majority of the ATP that is made by cells was not being made therefore Jared had much less ATP/energy causing weakness in him. The antidote helps Jared cells make ATP as it changes the cyanide molecule to thiocyanate. This can be removed from Jareds body easily. Since the cyanide is now removed the ETC can start to continue working and electrons can leave the chain by reacting with oxygen gas. Now the H+ protons can move into the intermembrane space and create a H+ gradient so when H+ moves through ATP synthase, ATP will be produced

Answer 7

Anabolic: small molecules combine Endergonic: stores energy Requires carbon dioxide (CO2) → uses light energy, in the form of photons, and water (H2O) to produce glucose Takes place in plants plants are autotrophs, which means they make their own food (in the form of glucose) More specifically, photosynthesis takes place in the leaves: a. stoma: pores (which have guard cells for opening and closing) b. mesophyll cells (the chloroplasts here is where it happens) Stoma: The pores in a plant’s cuticle through which water vapour and gases (CO2 & O2) are exchanged between the plant and the atmosphere. Found on the underside of leaves Photosyntheis hpannes in mesophyll cells of leaf which included the cell wall, nucleus, central vacuole and chloroplast we have leaf → many different tissues → mesohpyll tissues have mysophyll cells which have chlorplasts → chrloplast has two membranes inner and outer → inside the inner memrbanes there are stroma in the stroma there are stacked discs celled grana → each disc called thylakoid → thylakoid has membrane and space (thylooikd in stac from a granum) → grana are connected together Plants are green because of chlorophyll which is located in thylakoid membrane. hlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue: 420 nm and red: 660 nm are most important). Plants are green because the green wavelength is reflected, not absorbed. In addition to the chlorophyll pigments, there are other pigments present. During the fall, the green chlorophyll pigments are greatly reduced due to shorter daylight hours, revealing other pigments. Carotenoids are pigments that are either red, orange, or yellow. CO2 is reduced to glucose (gains e-). Oxygen is produced through photolysis of water. photolysis is the splitting of water in the presence of light. the intended goal of photosynthesis is to produce glucose. Therefore, O2 is actually a waste product of photosynthesis Rxn: 2H2O → 4e- + 4H+ + O2 three external factors affect the rate of photosynthesis: - temperature - light intensity - carbon dioxide concentration the factor furthest from optimal level is the limiting factor (varies throughout day, season, year, etc.) Two reactions make up photosynthesis: - Light Reaction or Light-Dependent Reaction: Produces energy from solar power (photons) in the form of ATP and NADPH. - Calvin Cycle or Light-Independent Reaction: Also called Carbon Fixation. Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

Answer 8

Photosynthesis transforms the radiant energy of sunlight into the chemical energy of high-energy compounds. Photosynthesis enables plants to produce structural and metabolic substances that aid in their survival. 6CO2(g) + 6H2O(l) + energy → C6H12O6(s) + 6O2(g) numerous reactions occur between the substrates on the left side of the equation to produce the products on the right side. the process involves two sets of reactions. Photo refers to the reactions that capture light energy; synthesis refers to the reactions that produce a carbohydrate. The two sets of reactions that make up photosynthesis are called the light dependent reactions and the light independent reactions. In the light-dependent reactions, light energy is trapped and used to generate two high-energy compounds: ATP and NADPH. NADPH is similar in structure and function to NADH. In the light-independent reactions, the energy of ATP and the reducing power of NADPH are used to make a high-energy organic molecule. Water enters plants through the roots and is transported to the leaves through the veins. Carbon dioxide enters through openings, called stomata, in the leaves. The carbon dioxide and water diffuse into the cells and then enter the chloroplasts, where photosynthesis takes place. Thylakoids are central to photosynthesis, because the molecules that absorb the solar energy are embedded in the thylakoid membranes. Surrounding the grana in the chloroplasts is a fluid-filled interior called the stroma. The stroma contains the enzymes that catalyze the conversion of the carbon dioxide and water into carbohydrates. A compound that absorbs certain wavelengths of visible light is called a pigment. A photosynthetic pigment is a compound that traps light energy and passes it on to other compounds. When sunlight is available, pigments embedded in the thylakoid membranes absorb light energy, initiating the light-dependent reactions. Eventually, the energy is used to synthesize high-energy compounds. A chlorophyll solution absorbs red and blue light, and it transmits or reflects green light. An absorbance spectrum is a graph that shows the relative amounts of light of different wavelengths that a compound absorbs. The carotenoids absorb blue and green light, so they are yellow, orange, and red in colour. photosystem: one of two protein-based complexes composed of clusters of pigments that absorb light energy. Embedded in thylakoid membrane. when chlorophyll molecules are associated with different proteins in a photosystem, they can absorb light energy of various wavelengths. When any pigment molecule absorbs a photon, the molecule passes the energy to a unique pair of chlorophyll a molecules associated with a specific group of proteins. This pair of chlorophyll a molecules, in combination with these proteins, is called the reaction centre. The antenna complex includes all the surrounding pigment molecules that gather the light energy. The antenna complex transfers light energy to the reaction centre much as a funnel directs liquid into the mouth of a bottle. When a reaction centre has received the energy from the antenna complex, an electron in the reaction centre becomes “excited”—that is, the electron is raised to a higher energy level. The electron then has enough energy to be passed to an electron-accepting molecule. Since this electron acceptor has received an electron, it becomes reduced and is a higher energy level. The reaction centre pigment molecule of photosystem I is called P700, and the reaction centre pigment molecule of photosystem II is called P680, based on the wavelengths (in nanometres) of light these molecules absorb. Step 1: The P680 molecule in the reaction centre of photosystem II absorbs a light photon, exciting an electron. When the excited electron leaves P680 in photosystem II and goes to the electron acceptor, P680 is missing an electron. It is said to have a hole. The P680+, now positively charged, has a powerful attraction for electrons. Although water is very stable molecule, the attraction of P680+ pulls electrons from water. A water-splitting complex holds two water molecules in place as an enzyme strips four electrons from them, one at a time. P680+ accepts these electrons one at a time, and each is passed to another electron carrier. P680+ then absorbs another photon, becomes reduced, and passes on another electron. This process occurs a four times to form one oxygen molecule. The four hydrogen ions from the two water molecules remain in the thylakoid space. The oxygen atoms from the water molecules immediately form an oxygen molecule. This is the oxygen that is released by plants into the environment. Photosystem II can absorb photons, excite P680, and pass electrons to the electron acceptor more than 200 times a second. Step 2: From the electron acceptor, the energized electrons are transferred, one by one, along a series of electron-carrying molecules. Together, these molecules are referred to as an electron transport system. This photosynthetic electron transport system is similar to the electron transport system in mitochondria that is used in cellular respiration. With each transfer of electrons along the system, a small amount of energy is released. The released energy is used by a protein complex called the b6-f complex to pump hydrogen ions from the stroma, across the thylakoid membrane, and into the thylakoid space. Eventually, there are many more hydrogen ions in the thylakoid space than there are in the stroma. This pumping of electrons generates a hydrogen ion concentration gradient across the thylakoid membrane. This is similar to the formation of a hydrogen ion concentration gradient across the inner mitochondrial membrane during cellular respiration. Step 3: While the events of steps 1 and 2 are taking place, light energy is absorbed by photosystem I. This energy is transferred to the reaction centre P700 molecule, where electrons become excited. Once again, the excited electrons are passed to a high-energy electron acceptor. In photosystem I, the lost electrons are replaced by those that have reached the end of the electron transport system from photosystem II. Step 4: The electrons that were received by the electron acceptor from photosystem I are used by the enzyme NADP reductase to reduce NADP+ to form NADPH. The reducing power of NADPH will be used in the light-independent reactions. The movement of hydrogen ions is linked to the synthesis of ATP by chemiosmosis. Because the ultimate energy source is light photons, the process is called photophosphorylation. The hydrogen ions that are pumped from the stroma to the thylakoid space by the b6-f complex of the electron transport chain cannot diffuse back across the membrane, because the membrane is impermeable to these ions. As the hydrogen ions move down their concentration gradient through the ATP synthase molecule, the energy of the gradient is used to generate ATP molecules. The production of ATP by the passing of electrons through the Z scheme is often called noncyclic photophosphorylation. It is considered noncyclical because the flow of electrons is unidirectional—that is, the electrons are transferred from photosystem II to NADP+ to form NADPH. The passage of one electron pair through this system generates 1 NADPH and slightly more than 1 ATP. However, this ratio of ATP to NADPH is not sufficient for the light-independent reactions. These require three ATP molecules to two NADPH molecules. Chloroplasts are able to produce more ATP through cyclic photophosphorylation. excited electrons leave photosystem I and are passed to an electron acceptor. From the electron acceptor, they pass to the b6-f complex and back to photosystem I. The proton gradient is generated in the same manner as in noncyclic photophosphorylation, and ATP synthesis by chemiosmosis also occurs. Because the same electron that left the P700 chlorophyll molecule in photosystem I returns to fill the hole it left, the process is called cyclical. Notice, however, that neither NADPH nor oxygen is produced in cyclic photophosphorylation. SUMMARY: Photosynthesis includes two distinct sets of reactions: the light-dependent reactions and the light-independent reactions. Enzymes and electron carriers responsible for the light-dependent reactions are embedded in the thylakoid membranes of the chloroplasts. Pigment molecules absorb photons from the radiant energy of sunlight and use it to energize electrons. The energy of the electrons in noncyclic photophosphorylation is used partially to pump hydrogen ions into the thylakoid space and partially to reduce NADP+. In cyclic photophosphorylation, the energy of the electrons is used only to generate a hydrogen ion gradient across the thylakoid membranes. The energy stored in the hydrogen ion gradient is used to phosphorylate ADP.

Answer 9

Photosystems 1 and 2 are protein complexes of chlorophyll embedded in the thylakoid membranes of chloroplasts. they work together to capture photons and convert solar energy into chemical potential energy through “excitation” of electrons and electron transport. Photosystem II (PSII): Contains a reaction centre with a P680 molecule that absorbs light (~680nm) and “excites” electrons The electrons leave the reaction centre and go to an electron acceptor 🡪 plastoquinone (PQ) At the same time, H20 in the thylakoid space is split by a water-splitting enzyme to provide electrons that replace ones that have left Electrons that have left the reaction centre transport through electron carriers and other protein complexes in an electron transport system (similar to mitochondrial ETS) b6-f complex: The next “stop” for electrons after PSII Delivers electrons to photosystem I (PSI) via another electron carrier --> plastocyanin (PC) Pumps an H+ ion from the stroma into the thylakoid space across the thylakoid membrane (similar to the mitochondrial matrix, intermembrane space and inner mitochondrial membrane in mitochondrial ETS) Creates an electrochemical gradient in the thylakoid space (like in mitochondrial ETS) Photosystem I (PSI): Absorbs photons at the same time as PSII Reaction centre has a P700 molecule which absorbs light at ~700nm and re-excites electrons from PSII Electrons are passed to the final “stop” in the system via the electron acceptor called ferredoxin (FD) NADP Reductase: The final stop for electrons in the thylakoid ETS Reduces NADP+ to form NADPH, which is used to power light-independent reactions Chemiosmosis in Plants: Similar to chemiosmosis in aerobic cellular respiration H+ ions are pumped from the thylakoid space back into the stroma via ATP synthase Energy released(from movement of ions from thylakoid back to stroma) generates ATP from ADP Because photons are the energy source, this process is called photophosphorylation Noncyclic: Electron flow is unidirectional through Z scheme; transferred from PSII to NADP+ to form 1 NADPH, and slightly more than 1 ATP This ratio of ATP to NADPH is not sufficient to power light-independent reactions Cyclic: Electrons leaving PSI are passed to an electron acceptor and carried back to the b6-f complex, pumping more H+ ions into the thylakoid space This increases ATP production (photons supply energy and excite the e- that came from water molecule splitting by enzyme. the e- move to e- acceptor pq then to b6-f where h+ ions are pumped into thylakoid space. e- continue to PC carrier then to ps1 where they are excited by the photon and go to fd acceptor and to nadp reductase to form nadph which go into indepenct cycle/reactions. h+ ions move out into stroma through synthase creating atp) (chlorophyll in the photosystems abrosb the photons/light) The thylakoid membrane is composed of a phospholipid bilayer and photosystem I and photosystem II. The first and most important event in either system is the capturing of light energy by the pigments associated with each photosystem. Pigment 680 is associated with Photosystem II, and Pigment 700 is associated with Photosystem I. The numbers 680 and 700 refer to the wavelengths of light absorbed by the pigments. When a photon of light strikes the reaction center of Photosystem II, it “excites” an electron. Two water molecules bind to an enzyme that splits water into hydrogen ions (aka protons) and releases an oxygen atom. This process is called photolysis. Two electrons are released in this process, and these electrons can be traced through photosystem II and photosystem I. Two oxygen atoms will join together to create an oxygen molecule which is released from the plant as a byproduct of the entire reaction. The primary electron acceptor for the light-energized electrons leaving photosystem II is plastoquinone. The reduced plastoquinone passes the excited electrons to a proton pump embedded in the membrane called the b6-f complex. This proton pump moves protons (H+) atoms across the membrane against their concentration gradients, which eventually causes a build-up of protons in the thylakoid space. The thylakoid membrane is NOT permeable to protons, so they may only cross the membrane via transport proteins. The protons will exit the thylakoid space via a special channel provided by ATP Synthase. The protons move through the ATP synthase with the concentration gradient, which allows them to do work (namely, drive ATP synthesis). As protons pass through the ATP synthase, ADP is phosphorylated to ATP and released into the stroma. The process of making ATP is called photophosphorylation. This ATP is now on its way to the Calvin Cycle where it will be used to generate glucose. But wait, there's more! The electron that was used in Photosystem II is just sitting around, all de-energized but its story is not finished. A small protein called plastocyanin carries the electron to Photosystem I. Light absorbed by photosystem I energizes this electron and passes it to another primary electron acceptor called ferredoxin. The enzyme NADP Reductase transfers these electrons to NADP to form NADPH. The electron is now on its way to the Calvin Cycle as part of an NADPH molecule. Electrons lost from photosystem I are replaced by electrons generated from photosystem II.

Answer 10

Chloroplasts in plants contain enzymes in the stroma that, in conjunction with the energy supplied by ATP and NADPH, convert carbon dioxide to carbohydrates. Since the reactions can take place in the presence or absence of light, the more accurate terminology is light-independent reactions. The key initial step in the synthesis of carbohydrates in plants is conversion of carbon dioxide to organic compounds—a process called CO2 assimilation. The assimilation of carbon dioxide is carried out by a cyclical pathway that continually regenerates it's intermediates. This pathway is called the Calvin cycle. The Calvin cycle accomplishes the conversion of inorganic carbon, in the form of carbon dioxide from the atmosphere, into organic carbon, in the form of the three-carbon organic molecule glyceraldehyde-3- phosphate (G3P). This product of photosynthesis is then used as a starting substrate in many other metabolic pathways. The reactions of the Calvin cycle can be grouped into three phases. 1. Fixing Carbon Dioxide: The first phase is carbon dioxide fixation. The key to this is the chemical bonding of the carbon atom in carbon dioxide to a pre-existing molecule in the stroma. This molecule is a five-carbon compound called ribulose- 1,5-bisphosphate, or RuBP for short. The resulting six-carbon compound is unstable and immediately breaks down into two identical three-carbon compounds called 3-phosphoglycerate (PGA). Because these three-carbon compounds are the first stable products of the process, plants that use this method for photosynthesis are called C3 plants, and the process is called C3 photosynthesis. The reaction that leads to these three-carbon compounds can be summarized as: CO2 + RuBP → unstable C6 → 2 PGA. This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase, which is often called rubisco. Rubisco is possibly the most abundant protein on Earth. 2. Reduction: In the second phase, the newly formed three-carbon compounds are in a low-energy state. To convert them into a higher-energy state, they are first activated by ATP and then reduced by NADPH. The result of these reactions is two molecules of glyceraldehyde-3-phosphate (G3P). In their reduced (higher-energy) state, some of the G3P molecules leave the cycle and may be used to make glucose and other carbohydrates. The remaining G3P molecules move on to the third phase of the cycle, in which RuBP is replenished to keep the cycle going. 3. Regenerating RuBP: Most of the reduced G3P molecules are used to make more RuBP. Energy, supplied by ATP, is required to break and reform the chemical bonds to make the five-carbon RuBP from G3P. The Calvin cycle must be completed six times in order to synthesize one molecule of glucose. Of the 12 G3P molecules that are produced in six cycles, 10 are used to regenerate RuBP, and 2 are used to make one glucose molecule. The net equation for the Calvin cycle is: 6CO2 + 18 ATP + 12 NADPH + water → 2 G3P + 16 Pi + 18 ADP + 12 NADP+ The G3P that is produced can then be used for the synthesis of other molecules that plants require. A great deal of G3P is transported out of the chloroplasts and into the cytoplasm. There, G3P is used to produce a key sugar in plants, sucrose. In times of intensive photosynthesis, when G3P levels can rise quite high, the G3P is used to produce starch. G3P is also the starting substrate for cellulose. Plant oils such as corn oil, safflower oil, and olive oil are derived from G3P. As well, G3P and a source of nitrogen are used to synthesize the amino acids that are used to make proteins. Thus, G3P is a crucial molecule in plant metabolism. Rubisco is a critical enzyme in light-independent reactions. However, it has an undesirable property. Rubisco can use oxygen as a substrate as well as carbon dioxide. In fact, oxygen and carbon dioxide compete with each other for the same active site on the rubisco enzyme. When oxygen reacts with ribulose-1,5-bisphosphate in the process called photorespiration, the products are a two-carbon compound called phosphoglycolate and one of the three-carbon compound, 3-phosphoglycerate. As a result of photorespiration, all of the energy used to regenerate the ribulose-1,5-bisphosphate is wasted, thus reducing the efficiency of photosynthesis. Under normal conditions, when the temperature is near 25oC, C3 plants lose 20 percent of the energy used to fix one carbon dioxide molecule. Biologists estimate that the maximum possible efficiency of photosynthesis in C3 plants—assuming each photosystem absorbs the maximum amount of light—is 30 percent. Some laboratory-grown plants, raised under controlled conditions, have reached efficiencies of 25 percent. In nature, however, photosynthetic efficiency ranges from 0.1 percent to 3 percent. Atmospheric conditions influences the reduction of efficiency due to photorespiration. For example, under hot, dry conditions, leaves begin to lose water through the stomata. In response to these conditions, the stomata close to prevent further loss of water. With the stomata closed, the oxygen formed in the light-dependent reactions accumulates inside the leaves and carbon dioxide cannot enter. With the higher ratio of oxygen to carbon dioxide in the leaves, the amount of photorespiration increases significantly (which reduces the efficiency of photosynthesis). Some plants that are native to regions in which the climate is normally hot and dry, typically above 28oC, have evolved mechanisms to reduce the amount of photorespiration. These plants fit into two categories: C4 plants and CAM plants. Both use the Calvin cycle; however, they have developed different mechanisms for the uptake and storage of carbon dioxide that increase the ratio of carbon dioxide to oxygen for the Calvin cycle reactions. C4 plants have a structure that separates the initial uptake of carbon dioxide from the Calvin cycle into different types of cells. In the outer layer of mesophyll cells, carbon dioxide is fixed by addition to a three-carbon compound called phosphoenolpyruvate (PEP). The product is the four-carbon compound oxaloacetate, giving these plants the name C4. The oxaloacetate is converted to the four-carbon compound malate and transported into the bundle-sheath cells. There, the malate is decarboxylated. The resulting three-carbon compound, pyruvate, is transported back into the mesophyll cells and converted into PEP. The bundle-sheath cells are impermeable to carbon dioxide. As a result, carbon dioxide is concentrated in the bundle-sheath cells where the Calvin cycle takes place. This high CO2 concentration makes the Calvin cycle much more efficient than in C3 plants. CAM plants, which include succulent (water-storing) plants such as cacti and pineapples, use a biochemical pathway identical to the C4 plants, but the reactions take place in the same cell. Carbon dioxide fixation is separated from the Calvin cycle by time of day rather than by different cell types. Crassulaceae thrive in hot, arid desert conditions. To prevent water loss, their stomata remain closed during the day and open at night. Carbon dioxide is fixed at night while the stomata are open. The reactions proceed until malate is formed. It is then stored in a large vacuole until daytime, when the stomata close. When the light-dependent reactions have produced enough ATP and NADPH to support the Calvin cycle, the malate exists the vacuole and is decarboxylated, freeing the carbon dioxide which is then fixed again by rubisco and enters the Calvin cycle. The reactions that capture light energy and convert it to organic material are closely related to the reactions of aerobic respiration reactions. Both of these processes occur in plants and represent a plant cell’s energy cycle. The products of aerobic respiration, carbon dioxide and water, are the starting substrates for photosynthesis. The products of photosynthesis, oxygen and glucose, are the starting substrates for aerobic respiration. For plant cells, an outside source of carbon dioxide and water is needed to produce glucose, leaving oxygen as a by-product. For animal cells, which lack chloroplasts, an outside source of glucose and oxygen are needed to generate energy, leaving carbon dioxide and water as by-products. Respiration Photosynthesis Overall equation glucose glucose + 6O2 → energy*(ATP) + 6CO2+ 6H2O energy*(light) + 6CO2 + 6H2O → glucose 1 6O2 AEROBIC RESPIRATION (animal vs. plant): Cell location: Mitochondrion, Chloroplasts Starting substrates: Glucose and oxygen, Carbon dioxide and water products: Carbon dioxide and water, Glucose and oxygen Electron transport chain: yes, yes Electron carriers: NADH and FADH2 , NADPH ATP synthesis by chemiosmosis: yes, yes The light-independent reactions use the energy from ATP and NADPH from the light-dependent reactions to assimilate carbon dioxide and synthesize high-energy organic compounds in a series of reactions called the Calvin cycle. Plants that use only the Calvin cycle to assimilate carbon dioxide are called C3 plants. Due to photorespiration, C3 plants are extremely inefficient in hot, dry climates. Plants that thrive in these environments have evolved two mechanisms to increase their efficiency. C4 plants isolate carbon dioxide fixation from the Calvin cycle reactions by carrying out these reactions in two different cell types. CAM plants isolate dioxide fixation from the Calvin cycle reactions by fixing carbon dioxide at night and carrying out the Calvin cycle reactions in the daytime.

Answer 11

fixing co2 light-independent reactions RECALL: light-dependent reactions supply ATP and NADPH to drive light-independent reactions when light is not required - LIR are also called dark reactions, but this is a misnomer because the reactions can take place both with or without the presence of light - Ultimate goal of LIR: synthesize carbohydrates from CO2 RECALL: glyceraldehyde 3-phosphate (G3P) from glycolysis - The Calvin Cycle: light-independent cyclical pathway in the stroma that converts CO2 to G3P → used to make glucose and other sugars, or continue through the cycle to keep it going Carbon Fixation (light independent reaction) C3 plants (80% of plants on earth) Occurs in the stroma Uses ATP and NADPH from light reaction as energy to drive them Uses CO2 To produce glucose: it takes 6 turns and consumes 18 ATP and 12 NADPH. happens in stroma of chloroplast Start with co2 → one carbon bonds to RuBP which is a 5 carbon compound and this forms a 3 carbon pga (first into 6 6 carbon molecules then to 12 3 carbon molecules it's converted by rubisco an enzyme) → the pga become g3p but that produces adp since it consumes ATP and also uses NADPH which gets oxidized to NADP+ → the 12 G3P, 10 of them converted to RuBP while consuming 6atp to become that (10*3c is 30c which is equal to the 6*5c RuBP) while 2 become glucose and other sugars (2 since 2*3 c becomes 6 c for glucose) Does not porudce atp, it consumes atp but we produce glucose (stoarage molecule?) whihc is chemical potential enegry in the form of food, this glucose produces is used all over again to keep the plant alive This is carbon fixation pathway must happen 6 times to produce one molecule of glucose 6CO2 + 18ATP + 12NADPH + H2O --> 2G3P + 16Pi + 18ADP + 12NADP+

Answer 12

The enzymes for the Calvin cycle are located in the stroma, in the chloroplast of the mesophyll cells. The first step in which CO2 is assimilated into an organic compound is called carbon dioxide fixation reaction. It is catalyzed by rubisco. CO2 + RuBP → unstable C6 → 2 PGA The reducation phase of the calvin cycle is to convert the PGA into high energy states/levels by converting them into G3P molecules. Glycolysis will break down the glucose into 2 three carbon molecules producing one ATP and one NADPH so the first steps are to remove a phosphate group from ATP to form ADP and to oxidize an NADPH molecule to form NADP+. Photorespiration is the reaction of oxygen with RuBP in a process that reverses carbon fixation and reduces the efficiency of photosynthesis. All the enegry that was used to make the RuBP becomes wastes which is why there is a reduction in the efficiency of photosynthesis. In C3 plants when temperature increases the leaves lose water by evaporation through the stomata (opneing in the leaves) and to stop the water loss the stomata will close but as a result CO2 can not eneter the leaves as well as the oxygen produced by light dependent reactions remains in the cells and photorespiration will increase since the more oxygen is competing for sites on the rubisco enzyme. Since C4 plants live in hot and dry climate they have evolved mechanisms to reduce the amount of photorepriation that occurs. They still have the calvin cycle but there are different mechanisms for the uptake and storage of CO2 that increases the ratio of it compared to oxygen for the cycles reactions. C4 plants have a layer of cells called bundle sheath cells, which C3 plants do not have. The Calvin cycle happens only in the bundle sheath cells. In C4 mesophyll cells, carbon dioxide is fixed to a compound called PEP, producing a 4-carbon compound called oxaloacetate. Oxaloacetate is converted into malate, which is then transported into the bundle sheath cells. Once there, it is converted/decarboxylized to pyruvate, and carbon dioxide is released into the Calvin cycle. When the climate is hot and dry, carbon dioxide levels normally decrease due to the stomata closing, and so photorespiration becomes more likely. However, the malate is pumped into the bundle sheath cells and so the carbon dioxide concentration inside the cell stays high enough for RuBP to bind with CO2 rather than oxygen. This decreases the amount of photorespiration. (calvin cycle happens in bundle sheath cells instead of calvin cycle. CAM plants minimize photorespiration by separating carbon dioxide fixation from the Calvin cycle by time of day. At night, the stomata are open and carbon fixation happens, producing malate. It is then stored in a large vacuole. When the stomata are closed during the day, the carbon dioxide is removed from malate and enters the Calvin cycle. The candle burned out because the combustion reaction used up all the available oxygen in the bell jar. During the 27 days, the plant photosynthesized. It used the carbon dioxide in the jar, some of which was a product of the candle’s combustion reaction, to produce glucose. The glucose was then used in cellular respiration. The by-products of cellular respiration are carbon dioxide and water. Photosynthesis must have happened at a higher rate than cellular respiration, so that oxygen unused in cellular respiration was released into the bell jar through the leaves. Enough oxygen accumulated to keep the combustion reaction going when the candle was re-lit. Students will likely agree with the statement because the light-dependent reactions produce NADPH and ATP. The only source of these high-energy molecules are the light-dependent reactions. If the light-dependent reactions ceased to function, the light-independent reactions would also cease, once the NADPH and ATP were used up.

Answer 13

State when photosynthesis takes place: Photosynthesis takes place in the presence of light (needed for the dependent reactions) it's basically used to convert light energy into chemical energy. Explain the two reactions of photosynthesis (light dependent and independent): - When they happen → Light-dependent reactions will happen in the presence of light while independent happen in the presence or absence of light. - How they happen → Light dependent reactions use the light energy it receives in the forms of photons and water molecules to produce ATP and NADPH. It uses the e- from water and the light energy to excite it and pass it through the electron transport system where at the end it's passed to NADP+ reductase to form the NADPH and the H+ ion gradient that was formed by one of the complexes now produces ATP as the protons go through the synthase. The NADPH and ATP now go into the calvin cycle/independent reactions. The in the calvin cycle 6 CO2 will combine with RuBP by the use of the enzyme rubisco to form an unstable 6c compound which breaks into PGA. PGA will use up 12 atp to become 1,3 biphosphoglycerate and then use 12 NADPH to become 12 G3Ps two of which are used to become glucose and other sugars and 10 which use ATP to become the RuBP. The ADP and NADP+ are returned to the light reactions. - Where they happen → light dependent reactions happen in the thylakoid membrane while the independent reactions happen in the stroma. Both are technically in the chloroplasts of mesophyll cells. Overall reactions 6CO2 + 6H2O + energy → Glucose + 6O2 Two overall reactions in photosynthesis the light reactions which occur in the thylakoid membrane which involves the splitting of water into oxygen protons and e-. The protons and e- are transferred to the thylakoid membrane where they are used to create ATP and NADPH which go into the independent reactions. In there, co2 is converted into carbohydrates in the stroma. List some important applications of photosynthesis Photosynthesis fills our food requirements and needs for fibre (we eat the plants that use photosynthesis to create the high energy carbohydrates and when we eat it we use the glucose/starch to create energy). The energy in petroleum and natural gas comes from photosynthesis. Light reactions: * Are carried out by molecules in the thylakoid membranes * Convert light energy to the chemical energy of ATP and NADPH * Split H2O and release O2 to the atmosphere Calvin cycle reactions: * Take place in the stroma * Use ATP and NADPH to convert CO2 to the sugar G3P * Return ADP, inorganic phosphate, and NADP+ to the light reactions

Answer 14

C3 Photosynthesis: * Light reactions generate high energy molecules to run the dark reactions (Calvin cycle) * The first step of the Calvin cycle is the fixation of carbon by RUBISCO using carbon dioxide and ribulose 1,5 bisphosphate as substrates C2 Photosynthesis: * RUBISCO is an ancient enzyme, and evolved when oxygenation was insignificant * With oxygenic photosynthesis and higher O2 levels in the atmosphere, oxygenation by RUBISCO became significant Problem is→ 2-Phosphoglycolate is toxic to plants, it inhibits distinct reactions in the Calvin Cycle. It also represents a significant loss of energy to the plant and is therefore at some cost returned to the Calvin cycle. It takes energy to return 2- phosphoglycolate to the Calvin cycle The C4 and CAM pathways evolved to reduce the impact of oxidation by RUBISCO (photorespiration) * The C4 photosynthetic pathway concentrates CO2 in the vascular bundle sheath cells of leaves to significantly reduce competition with O2 for the active site on RUBISCO * The CAM photosynthetic pathway further separates absorption of CO2 in time from its incorporation in the Calvin cycle * C4 & CAM are more efficient than C3 at yielding energy above about 85 degrees F–Rubisco favors oxygenation the higher the temp because the concentration of CO2 in leaf tissue is less the higher the temp At 86° F C4 becomes more efficient than C3 due to photorespiration. The starch rich chloroplasts of the Kranz anatomy lack grana, the site of the light reactions. They differ from the chloroplasts of the outer bundle sheath (dimorphic chloroplasts). Some Grasses use the C3 photosynthetic pathway (cool season grasses) and some use the C4 pathway (warm season grasses) CAM Photosynthesis: In addition to being more efficient like C4 at higher temperatures, CAM conserves water by allowing stomata to be closed during the heat of the day “Since every CO2 molecule has to be fixed twice, first by 4-carbon organic acid and second by RuBisCO, the C4 pathway uses more energy than the C3 pathway. The C3 pathway requires 18 molecules of ATP for the synthesis of one molecule of glucose, whereas the C4 pathway requires 30 molecules of ATP. This energy debt is more than paid for by avoiding losing more than half of photosynthetic carbon in photorespiration as occurs in some tropical plants, making it an adaptive mechanism for minimizing the loss.”