In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) in a reaction catalyzed by ATP synthase molecules tha
t are embedded in the thylakoid membrane. Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane?
1 answer:
Explanation:
<em>Complete Question:</em>
<em>A. Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid. </em>
<em>B. Increasing the proton concentration difference across the thylakoid membrane is not associated with a parallel increase in the rate of ATP synthesis. </em>
<em>C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane. </em>
<em>D. No ATP is synthesized while the Calvin cycle is synthesizing carbohydrates and using ATP and NADPH at a high rate. </em>
Correct: C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.
Photophosphorylation describes a process in which the H+ made in previous steps of photosynthesis, and free electrons are used to obtain energy stored as ATP; in the electron transport chain move down the chain the energy they release is used in pumping protons out of the thykaloid space.
The high concentration of H+ from photolysis, outside the leads to increased H+ concentration within the thykaloid space, due to its high permeability. This forms a gradient where there is a differential in the number of protons on either side of the membrane the protons flow into the stroma through the enzyme ATP synthase, which makes the energy storage molecules of ATP from the reduction of ADP and inorganic phosphate, Pi. NAD+ functions as the terminal electron acceptor and is reduced to NADPH.
Thus:
- a H+ concentration gradient is required for oxidative phosphorylation in the electron transport chain of the chloroplast, and thus the production of ATP
- the H+ ion gradient must favor the flow of electrons into the stroma
The free flow of H+ disrupts the gradient, and H+ cannot flow into ATP synthase to produce ATP.
Further Explanation:
Photosynthesis is a chemical pathway that’s integral to producing energy in plants and other primary producers. Energy in the form of molecules of glucose is produced from light, water and carbon dioxide while oxygen is released. This occurs in several complex steps, photosynthesis is a rate limited reaction, depends on several factors including carbon dioxide concentration, ambient temperature and light intensity; the energy is retrieved from photons, I.e. particles of light, and water is used as a reducing agent. This occurs in the thykaloids, where pigment molecules like chlorophyll reside.
The chloroplast is a membrane bound organelle found in plants. It contains several invaginations of a plasma membrane called the thylakoid membrane. This contains chlorophyll pigments, in stacks called granum, while the internal spaces of the organelle are called the lumen. Liquid surrounds the granum, forming the stroma.
During the light reaction:
- Light is absorbed by pigments in phosystem II (PSII). This energy is transferred among pigments til it gets to the reaction center, and is transferred to P680; this promotes an electron to a higher energy level where it then goes to an acceptor molecule.
- Water supplies the chlorophyll in plant cell with replacement electrons for the ones removed from photosystem II. Additionally, water (H2O) split by light during photolysis into H+ and OH- acts as a source of oxygen along with functioning as a reducing agent.
- the electron moves down an electron transport chain (to PS I)where it experiences continuous energy loss. This energy fuels the pumping of H+ from the stroma to thykaloid, leading to the formation of a gradient. The H+ move along their gradient and cross through ATP synthase, into the the stroma.
- ATP synthase converts ADP and Pi to the energy storage molecule ATP.
- The electron gets to photosystem I where it goes to pigments at P700. It absorbs light energy, the electron is promoted to a higher energy level, and passed to an electron acceptor. This leaves a space for another electron which is then replaced by one from photosystem II.
- in the ETC, the molecule NADP is reduced to NADPH by providing H+ ions. NADP and NADPH are integral to the Calvin cycle where monosaccharides or sugars like glucose are produced after the modification of several molecules.
Learn more about photosynthesis at brainly.com/question/4216541
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Answer:
- It is very likely that temperatures above 35°C will change the structural configuration of the enzyme, denaturing it and preventing it from performing its function.
- According to the information, the most probable consequences for this rice crop is that its starch content will be lower, compared to crops grown at optimal temperatures.
Explanation:
<u>The full question includes this statement</u>:
<em>A rice grain is a fruit that encloses a seed. Most of the dry mass of a rice grain is starch. In rice plants, starch is produced by hydrolyzing sucrose and then linking the released glucose molecules together into starch . The optimal temperature range for starch synthase activity in a particular strain of rice is 27°C - 30°C. The optimal temperature range for sucrose synthase in the strain is 30°C - 35°C.</em>
One of the factors affecting enzyme activity is temperature, according to which an enzyme can make a reaction faster, slower or inhibit the activity of that enzyme.
For a grain of rice to acquire its starch content, the activity of two enzymes is required, sucrose synthase - to obtain glucose from sucrose - and starch synthase, to polymerize glucose into starch (see image).
<h3>In this case, how temperatures above 35°C most likely affect the structure and function of the starch synthase?</h3>The temperature of 35°C is far above the optimum temperature required for the enzyme to act, so it is possible that a change in the structure of the enzyme will occur or that it will be denatured, preventing the starch synthase from performing its function. One consequence of this is a lower starch synthesis.
<h3>When the average temperature in the growing season is 33°C, what can be predicted about the consequences on the starch content in mature rice grains?</h3>A temperature of 33°C is outside the range of starch synthase activity -even though it is optimal for sucrose synthase- which would decrease starch synthesis and, because of this, the rice grains in this crop would have less starch content.
Learn more:
Relationship between the reaction of velocity of an enzyme and temperature brainly.com/question/14198802
