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cyclic and noncyclic photophosphorylation

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From Wikipedia

Light-dependent reactions

The light-dependent reactions, or light reactions, are the first stage of photosynthesis, the process by which plants capture and store energy from sunlight. In this process, light energy is converted into chemical energy, in the form of the energy-carrying molecules ATP and NADPH. In the light-independent reactions(also called dark reactions, by convention, as they are driven by products of light, ATP and NADPH-it should not be misunderstood that they occur in dark or they are independent of the need of light), the formedNADPH and ATP drive the reduction of CO2 to more useful organic compounds, such as glucose.

The light-dependent reactions take place on the thylakoid membrane inside a chloroplast. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane: Photosystem I (PSI), Photosystem II (PSII), Cytochrome c6f complex and ATP synthase. These four complexes work together to ultimately create the products ATP and NADPH.

The two photosystems absorb light energy through proteins containing pigments, such as chlorophyll. The light-dependent reactions begin in photosystem II. When a chlorophyll a molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI. In PSI the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor is water, creating oxygen as a waste product. Inanoxygenic photosynthesisvarious electron donors are used.

Cytochrome b6f and ATP synthase work together to create ATP. This process is called photophosphorylation, which occurs in two different ways. In non-cyclic photophosphorylation, cytochrome b6f uses the energy of electrons from PSII to pump protons from the stroma to the lumen. The proton gradient across the thylakoid membrane creates a proton-motive force, used by ATP synthase to form ATP. In cyclic photophosphorylation, cytochrome b6f uses the energy of electrons from not only PSII but also PSI to create more ATP and to stop the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions.

The net-reaction of all light-dependent reactions in oxygenic photosynthesis is:
2H2O + 2NADP+ + 3ADP + 3Pi→ O2 + 2NADPH + 3ATP

Light to chemical energy

The two photosystems are protein complexes that absorb photons and are able to use this energy to create an electron transport chain. Photosystem I and II are very similar in structure and function. They use special proteins, called light-harvesting complexes, to absorb the photons with very high effectiveness. If a special pigment molecule in a photosynthetic reaction center absorbs a photon, an electron in this pigment attains the excited state and then is transferred to another molecule in the reaction center. This reaction, called photoinduced charge separation, is the start of the electron flow and is unique because it transforms light energy into chemical forms.

The light-harvesting system

A common misconception is that photosynthesis relies only on chlorophyll pigments. The truth is that photosynthesis would be rather inefficient using only chlorophyll molecules. Chlorophyll molecules absorb light only at specific wavelengths (see image). A large gap is present in the middle of the visible regions between approximately 450 and 650 nm. This gap corresponds to the peak of the solar spectrum, so failure to collect this light would constitute a considerable lost opportunity. That's why photosynthesis organisms have developed a light-harvesti

Climate cycle

A climate cycle is a type of recurring climate pattern that involves natural cyclic variations in the Earth's surface temperature, as indicated by temperature proxies found in glacier ice, sea bed sediment, tree ring studies or otherwise.

One difficulty in detecting climate cycles is that the Earth's climate has been changing in non-cyclic ways over most scales of time. For instance, we are now in a period of global warming that seems to be anthropogenic. In a larger time frame, the Earth is emerging from the latest ice age, which means that climate has been changing over the last 15,000 years or so. And the Pleistocene period, dominated by repeated glaciations, has developed out of a more stable climate in the Miocene and Pliocene. All of these changes complicate the task of looking for cyclical behavior in the climate.

There are nevertheless several climate cycles which have been identified or hypothesized. These range from the cyclic behaviour of the Earth's orbital parameters (called Milankovich cycles) which are reflected in the long-term climatic record spanning several ice ages, through the Atlantic Multidecadal Oscillation, to short cycles such as:

The 11-year Sun spot cycle (the Hale cycle) may also be discernible in the climate record (see Solar variation).

Climate cycles are popular with media. One example is a 2003 study on the correlation between wheat prices and sunspot numbers..

There is also a 1,500-year climate cycle claimed from ice core samples, and used in the global warming controversy.

Other than the Milankovich cycles (and perhaps the Hale cycle), no climate cycle is found to be perfectly periodic and a Fourier analysis of the data does not give a sharp spectrum.



From Yahoo Answers

Question:The plant hormone abscisic acid (ABA) is involved in the regulation of photorespiration. Based on this information, ABA likely plays a role in A. the opening and closing of stomata. B. the photoelectric effect. C. cyclic photophosphorylation. D. noncyclic photophosphorylation.

Answers:definalty D

Question:10-cycle , where b represents beta . For which integers i between 2 and 10 is b^i also a 10-cycle ? (c) In S_3 , find elements a and b such that I a I = 2 , I b I = 2 , I ab I = 3 . Here a = alpha , b = beta .

Answers:Hi, a cyclic subgroup of order 4 will be generated by an element of order 4, such as (1, 2, 3, 4): your subgroup will then be <(1, 2, 3, 4)>. If you want to obtain a non-cyclic subgroup of order 4 instead, you will have to look for something like Z/2Z X Z/2Z inside S4. You will then need something generated by a couple of disjoint elements of order 2, like (1, 2) and (3, 4): your subgroup will then be <(1, 2), (3, 4)> = {id, (1, 2), (3, 4), (1, 2)(3, 4)}. For the second question I suppose you are no longer inside S4 (there you have no elements which are 10-cycles), but at least inside S10. The values for i you are looking for are the integers between 2 and 10 which are prime with 10: 3, 7 and 9. Finally, in S3 you have 3 good choices for a and b: (1, 2), (2, 3), (1, 3). If you take for example a = (1, 2) and b = (2, 3), you get ab = (1, 2, 3) whose order is 3. I hope this helped you...Bye!

Question:I just finished my H/W and i could not answer some of them, please help: 1)What is the only macromolecule whose monomer dont undergo dehydration to become polymers? 2)Which specific type of RNA includes the anti-codon loop and is bound to a specific amino acid? 3)Phosphatidylcholine is best describe as____? 4)DNA replication can be described as what type of process? 5)How is condensation reaction different from dehydration synthesis? 6)Which of the following is the main difference between cyclic and noncyclic photophosphorylation? a)they use different electron acceptor b)only photosystem I is used during cyclic process c) noncyclic photophosphorylation does not produce ATP 7)A sugar molecule deoxyribose is attached to one end of each _______. please help me, thanks in advance!!

Answers:1. DNA Molecules. The nucleotides are bonded together via hydrogen bonds. 2. tRNA 3. Phosphatidylcholine is the component of plasma membranes. 4. Unsure of what your teacher is trying to ask for certain, but it looks like the unwinding of a zipper. 5. Dehydration synthesis is the same as condensation except when the small molecule released in condensation is water. 6. Choice B. The cyclic photophosphorylation exists to fund the dark reactions with ATP. 7. Nucleotide pair

Question:Why is the general formula for a cyclic alkane CnH2n instead of CnH2n+2 as found in a noncyclic alkane?

Answers:Because two of the carbon molecules join to each other in a circle, rather than holding onto a hydrogen atom. Picture 6 people standing in a line, arms outspread, holding each others hands. The two on the ends are holding an apple in their single open hands. They have to put those two apples down in order to make a circle and hold each others hands. Those two apples (representing the hydrogren atoms) are the +2 that you lose when a straight-chain alkane becomes a cyclic alkane.

From Youtube

20.6.2 Geometric Isomerism in Alkenes IB Chemistry :20.6.2. Describe and explain geometrical isomerism in non-cyclic alkenes. Single covalent bonds have free rotation around the bond, but double bonds are "locked" in place (at least in IB chemistry) -- restricted rotation. A cis- prefix implies that the relevant branches are arranged in a U shape, a trans- prefix means that these branches are opposite from each other. Cis = same side Trans = across (eg transvestite, transcrainial, transport) showcase.unis.org