MCB chapter 8 photosynthesis

during photosynthesis , the oxidation of water is linked with the reduction of what****

co2

atp synthase

synthesizes atp by using the movement of protons from the thylakoid lumen to the stroma

what happens to the electron in the molecule in a solution in the lab*****

the absorbed light energy is rapidly released, allowing the electron to return to its initial ground energy state. Most of the energy is converted into heat and a small amount is reemitted as flourescence light

what is an ideal source of electrons

water, because it is so abundant in cells which makes it always available to serve as an electron donor in photosynthesis

cyt

-this is where electrons pass between photosystem II to I

Which of these statements best explains why the result of rubisco oxygenase activity is called "photorespiration"? Question 4 choices Choice A., Photorespiration is cellular respiration that takes place in the light. Choice B., Photorespiration is the reverse of the photosynthetic process. Choice C., Photorespiration releases CO2 in the light.

Photorespiration releases CO2 in the light.

How does energy from sunlight become incorporated into chemical bonds?

The answer to this question arises from the fact that the synthesis of carbohydrates from CO2 and water is a reduction-oxidation, or redox, reaction - reduction reactions are reactions in which a molecule acquires electrons and gains energy, whereas oxidation reactions are reactions in which a molecule loses electrons and releases energy.

The enzyme rubisco is ___________BLANK because it adds O2 to _____________BLANK.

a oxygenase; RuBP

photosynthetic organisms are correctly described as

autotrophs because they can form carbohydrates from CO2, they also require a constant supply of ATP to meet each cell's energy requirements.

photsystem II***

suplies electrons to the beginning of the electron tansport chain. - when this system is oxidized, it is able to pull electrons from water. the enzyme that pulls e- from h2o is locaten on the lumen.

CR vs PS****

- like respiration PS uses redox reactions, uses e- carries but PS uses NADP (NADPH), - both have mitochondira. plants also have mitochondira in order to supply energy for other functions. the chloroplast is what supplies energy for the calvin cycle only. - CR generates ATP and carbohydrates are being oxidaized and giving e- to NAD but in PS e- are donated to carbohydrtaes by the e- carrier and in this process NADPH is oxidized - CR produces CO2 and h2o - photosyt produces O2 and glucose. (via chloroplas)

in the calvin cycle the reduction of 3-PGA involves teo steps

1) ATP donates a phosphate group to 3-PGA, (2) NADPH transfers two electrons plus one proton (H+) to the phosphorylated compound, which releases one phosphate group (Pi).

what is the byproduct that is produced when pulling electrons from water

O2. it diffuses readily away

Why does rubisco have such a low catalytic rate (that is, why is it so slow)?***

Rubisco faces a fundamental trade-off between selectivity and speed because it can use both CO2 and O2 as substrates. High selectivity of CO2 over O2 requires that the reaction have a high energy barrier, leading to a lower catalytic rate

photic zone

The surface layer of the ocean through which enough sunlight penetrates to enable photosynthesis.

The movement of electrons through the photosynthetic electron chain leads to the formation of

both NADPH and ATP

where are chlorophyll molecules bound to

bounded by their tail region to integral membrane proteins in the thylakoid membrane

what is chlorophyll structure of the molecule*****

the major photosynthetic pigment contained in the thylakoid membrane; it plays a key role in the chloroplast's ability to capture energy from sunlight. Chlorophyll appears green because it is poor at absorbing green wavelengths. - the molecule consists of a large, light absorbing "head" containgin a magnesium atom at its center and a long hydrocarbon tail. - The large number of alternating single and double bonds in the head region explains why chlorophyll is so efficient at absorbing visible light.******

A carboxylase reaction by rubisco consumes ______BLANK ATP, and an oxygenase reaction consumes ______BLANK ATP. Question 7 choices Choice A., 1; 1 Choice B., 1 ;0 Choice C., 0; 1 Choice D., 0; ½ Choice E., 1; ½

0; 1/2

what are carbs synthesized from during photosynthesis

CO2. to build carbs there needs to be an input of energy because carbs have more energy stored in their chemical bonds. that energy comes from sunlight -During photosynthesis, CO2 molecules are reduced to form higher-energy carbohydrate molecules. This requires both an input of energy from ATP and the transfer of electrons from an electron donor. In photosynthesis, energy from sunlight is used to produce ATP and electron donor molecules capable of reducing CO2

where is the phosynthetic electron transport chain located

In eukaryotic cells, photosynthesis takes place in chloroplasts. In the center of the chloroplast is the highly folded thylakoid membrane (Fig. 8.4). The photosynthetic electron transport chain is located in the thylakoid membrane.

are starch molecules soluble

no! which allows them to provide a means of CHO storage that doesn't lead to osmosis

z scheme*****

the overall energy trajectory has an up-down-up configuration resembling a "Z," the photosynthetic electron transport chain

The Calvin cycle consists of 15 chemical reactions are grouped into three main steps:

(1) carboxylation, in which CO2 is added to a 5-carbon molecule (ribulose- 1,5-bisphosphate (RuBP)). this step is catalized by the enzyme ribulose bisphosphate carboxylase oxygenase, AKA rubisco. Before rubisco can act as a carboxylase, RuBP and CO2 must diffuse into the rubisco's active site. Once the active site is occupied, the addition of CO2 to RuBP proceeds spontaneously in the sense that no addition of energy is required. The product is a 6-carbon compound that immediately breaks into two molecules of 3-phosphoglycerate (3-PGA). These 3-carbon molecules are the first stable products of the Calvin cycle. (2) reduction, in which energy and electrons are transferred to the compounds formed in step 1. Rubisco is responsible for the addition of the carbon atoms needed for the formation of carbohydrates, but by itself rubisco does not increase the amount of energy stored within the newly formed bonds. For this energy increase to take place, the carbon compounds formed by rubisco must be reduced. Nicotinamide adenine dinucleotide phosphate (NADPH) is the reducing agent used in the Calvin cycle. NADPH transfers the electrons that allow carbohydrates to be synthesized from CO (3) regeneration of the 5-carbon molecule needed for carboxylation

how do protins acculumalte in the thylakoid lumen****

- the odixation of h20 releases protons and 02 in the lumen - also the cty complex also with plastoquinone function together as a proton pump that is similiar to the proton pumping the electron transport chain of cellular respiration*****

triose phosphates

A 3-carbon carbohydrate molecule, produced by the Calvin cycle and exported from the chloroplast during photosynthesis

How many molecules of RuBP are oxygenated for each molecule of CO2 that is released by photorespiration? Question 5 choices Choice A., 1 Choice B., 2 Choice C., 3 Choice D., 4 Choice E., 5

2

what is present in photosynthetic cells that helps to reduce the issue that is caused when an o2 diffuses on the rubisco site instead of a co2

a metbolic pathway is present that recycles the 2-phosphoglycolate, this allows A portion of the carbon atoms in 2-phosphoglycolate are converted into 3-PGA, which can reenter the Calvin cycle. - some 2-phosphoglycolate is released as co2

when visible light is absorbed by chlorophyll, what happens to the electrons

one of the molecules electrons is elevated to a higher energy state

what does the photosynthesis proton pump involve

1) the transport of two electrons and two protons by the diffusion of plastoquinone from the stroma (outside of the membrane) side of photos II to the lumen side (inside) of the cyt complex 2) the transfer of e- within the cty to a different molecule of plastoquinone, which result in additional protons being picked up from the stroma and then released into the lumen

How many 3-carbon intermediates (3-PGA) enter the Calvin cycle for every CO2 that is released by photorespiration? Question 6 choices Choice A., 1 Choice B., 2 Choice C., 3 Choice D., 4 Choice E., 5

3

what is exported from chloroplats to the cytosol

Although ATP is produced within chloroplasts, only carbohydrates (and not ATP) are exported. - this is why cells that have chloroplasts also contain mitochondria. -In mitochondria, carbohydrates are broken down to generate ATP. Cellular respiration is therefore one of several features that heterotrophic organisms like ourselves share with photosynthetic organisms.

accessory pigment

a light absorbing pigment other than chlorophyll that is also found in the photosynthetic membrane ( thlakoid membrane + chlorophyll) - carotenoids are important accessory pigments - the presence of these allows photosynthetic cells to absorb a broader range of visible light than would be possible with just chlorophyll alone.

The reaction center****

- Antenna chlorophylls deliver absorbed light energy to the reaction center, allowing electrons to be transferred to an electron acceptor molecule. In this process the reaction center is being oxidized. Also known as photosytem II - the reduction of the reaction center is when an electron is gained because it is an electron acceptor - the reaction center is where light energy is converted into chemical energy as a result of the excited electron's transfer to an adjacent molecule. -the reaction center transfers an electron to an adjacent molecule that acts as an electron acceptor. When the transfer takes place, the reaction center becomes oxidized and the adjacent electron-acceptor molecule is reduced. The result is the conversion of light energy into a chemical form. This electron transfer initiates a light-driven chain of redox reactions that leads ultimately to the formation of NADPH. -Once the reaction center has lost an electron, it can no longer absorb light or contribute additional electrons. Thus, for the photosynthetic electron transport chain to continue, another electron must be delivered (electron donor) to take the place of the one that has entered the transport chain

how does the cold influence the calvin cycle

- it slows it down, but does not influence absorption. for example on a cold sunny day, more light energu is absorbed than can be used by the calvin cycle

calvin cycle

The process in which carbon dioxide is reduced to synthesize carbohydrates, with ATP and NADPH as the energy sources. - the biochemical pathway used in photosynthesis to synthesize carbohydrates from CO2

In photosynthesis, light energy absorbed by pigment molecules drives the flow of electrons through...

the photosynthetic electron transport chain.

what is photosynthesis***

the use of sunlight to get energy to make carbohydrates it also makes O2 6CO2+^H2O-> C6H12O6 + 6O2 - PS occurs in chlotoplasts through the leaves -CO2 enters through the stoma of the chlotoplasts -Thylakoid membrane= where the e- transport chain occurs. where light dependent reactions occur - stroma where the light independt occurs - requires both light dependent and light independent reactions

two major challeneges that photosynthesis faces

- if more light energy is absorbed than the calvin cycle can use, excess energy can damage the cell - If o2 instead of co2 diffuses into the active site of rubisco, the reaction can still proceed, but o2 is added to RuBp in place of CO2. When rubisco adds O2 instead of CO2 to RuBP, the result is one molecule with three carbon atoms (3-PGA) and one molecule with only two carbon atoms (2-phosphoglycolate). The production of 2-phosphoglycolate creates a serious problem because this molecule cannot be used by the Calvin cycle either to produce triose phosphate or to regenerate RuBP.

what are the major protein complexes of the photosynthetic electron transport chain - what are the small mobile compounds*****

- photosystem I and II - cytochrom-b6 f complex (cyt) - plastoquinone (pq)- a lipid soluble compound similiar in sturucture to coenzyme Q; it carries e- from photosystem II to the cyt by diffusing through its membrane. - plastocyanin (pc)- a h2o solbue protein that carries electrons from the cyt to photosystem I by diffusing through the thylakoid lumen of it.

The net result of a single rubisco-catalyzed oxygenase event is a ____BLANK -carbon intermediate that quickly converts to ___________BLANK molecules. Question 3 choices Choice A., 6; two 3-carbon Choice B., 6; one 2-carbon and one 4-carbon Choice C., 5; one 3-carbon and one 2-carbon Choice D., 5; two CO2 and one 3-carbon

5; one 3-carbon and one 2-carbon

what percentage of global photosynthesis is carred out by terrestrial organisms and what percentage is carried out in the ocean

60% and 40% - majority of orgamisms in marine environments are unicellular. about half is carried out by single celled marine eukaryotes while the other half is carried out by photosynthetic bacteria

How do antenna chlorophylls differ from reaction center chlorophylls?

Antenna chlorophyll molecules transfer absorbed energy from one antenna chlorophyll molecule to another, and ultimately to the reaction center. Reaction center chlorophylls transfer electrons to an electron acceptor, resulting in the oxidation of reaction center chlorophyll molecules.

How does cyclic electron transport lead to the production of ATP?

As the electrons from ferredoxin are picked up by plastoquinone, additional protons are transported from the stroma to the lumen. As a result, there are more protons in the lumen that can be used to drive the synthesis of ATP.

In what ways is photorespiration similar to cellular respiration (Chapter 7) and in what ways does it differ?****

Like cellular respiration, photorespiration consumes O2 and releases CO2. Unlike cellular respiration, it consumes rather than produces ATP.

chloroplast strucuture

- outer membrane - inner membrane - thylakoid membrane: A highly folded membrane in the center of the chloroplast that contains light-collecting pigments and that is the site of the photosynthetic electron transport chain. - grana: Interlinked structures that form the thylakoid membrane. look like stach of interlinked pancakes. Grana are connected to one another by membrane bridges in such as way that the thlakoid membrane encloses a single interconnect compartment called the LUMEN. -stroma: the region surrounding the thylakoid membrane. this is where CHO synthesis takes place

what happens to the electron in the molecule in the plant cell when the chlorophyll molecule is intact with the chloroplast

-energy can be transferred to an adjacent chlorophyll molecule instead of being lost as heat - when this happens, the energy released as an excited electron returns to its ground state raises the energy level of an electron in an adjacent chlolorphyll molecule. - this mode of energy transfer is extremely efficient in terms of there is little energy lost as heat. which allows the energy that is absorbed from sunlight to be transferred from one chlorophyll molecule to abother and then another.

The Calvin cycle requires both ATP and NADPH. Which of these molecules provides the major input of energy needed to synthesize carbohydrates?

NADPH supplies the major input of energy that is used to synthesize carbohydrates in the Calvin cycle.

challenges to PS: excess light (due to the limit of the calvin cycle) and solutions*****

1) excess light energy or e- can convert oxygen into ROS which can damage cells. This happens when the calvin cycle doesn't need to use these so there becomes a build up. solutions: 1) there are chemical that detoxify reactive oxygen species. these antioxidants exist in high concentration in chloroplasts 2) Xanthophylis are yellow organge pigments that slow the formation of ROS by reducing excess light energy. These pigments accept absorbed light energy directly from chloroophyll and then convert this energy to heat.

how many ATPs and NADPH is needed for one molecule of CO2 incorporated by rubisco

3 atp and 3 NADPH. ATP prepares 3-pga for the addition of energy and electrons from NADPH. NADPH procides most of the energy incorporated in the bonds of the CHO molecules produced by the calvin cycle

light independent (calvin cycle)**

CO2 is reduced. ATP is required and NADP is regerneated when it loses its electrons (oxized) supply adp +p + NADPH which gives the light depedendent the reaction the tools it needs to regenerate CALVIN CYCLE: -CO2 enter the calvin cycle 1. CO2 must become:Fixed CO2 (it undergoes a reaction that will allow it to be joined to a 5 carbon compound (RuBP)- this occurs due to the enzyme ribisco which attachs the CO2 to the 5 carbon compound (carboxylation ) it then becomes a 6 carbon molecule - the 6 carbon molecule gets broken down into 2 molecule of 3 PGA. this requires 2 ATP hydrolized and 2 NADPH to be oxizided 2. reduction: 3 PGA get modified which required energy (atp->ADP) and (reduction of NADP) these both supply the energy needed for this reaction to occur. this reaction makes triose phosphate. - some triose phosphate leave the calvin cycel to make complex sugar. but not all of them leave, for every 6 that are make 5 have to stay behind to regerate RuBP 3. Regeneration of RuBP: in this multistep process, 3 carbon compounds are reorganized and combined to produce RuBP the 5 carbon molecule Determine what you need in orde to make one glucose. if three CO2 are entering the calvin cycle and if only one CO2 entered 1. the name and number of molecule that enter the cycle: 1-it would have to turn 6 times into order to make one molecule of glucose because you need 6 CO2 to make 1 glucose. 3- it would take two turns 2. name and number of molecule that exit 1- 6 triose phosphate would exit if turned 6X 3- 2 triose phosphate would exit if 3 co2 entered 12 total are made since there are 6 total carbons, but only 10 stay because 5 total carbons are needed for each turn. 6x2=12-2 turns. 3. the number of atp used or synthesized 1- 18 atp used- because there are a total of 3 atp in the cycle 3- 6 atp used 4. the name and number of e- carried oxidixed or reduced 1- 12 NADPH would be prodcued since there are 2 NADPH per 1 CO2 3- 6 NADPH 1 CO2 everything is x6= 3ATP total, 2NADPH, 1 triose phospate leaves, 5 stay 3CO3 everything is x2

light dependent reactions***

H2O is oxidized prodcuing ATP and oxygen and NADP is reduced into NADPH. supply the calvin cycle with the atp and nadph - leaves contain chlorophlly which absorbes blue and orange, but not green. it reflects green, which is why the leaves are green. - ring strucutes= get excited when exposed to light which allows use to transfer energy to make nadph and atp. - the hydrocarbon determine where it sits. chlorophyll molecules are loctaed in the thylaokid membrane - when chlorophyll is excited in a plant molecule (in a test tube the energy is lost as heat) Photosystem II-the energy goes to an antenna chlorophyll and transmit it to other antenna molecules until it reaches the reaction center. in the reaction center gets an e- from the oxidation of H2O and energy is accepted then the e- gets donated (oxidation) to Photosystem I which then is the e- accepter becomes and becomes reduced. this then causes NADP to become reduced into NADPH - what is the point of light? becuase it excites the electrons which them prompts them to take the electrons from water which then allows those e- to be transferred to photosytem I. then they are ready to go to the calvin cycle

If you want to produce carbohydrates containing the heavy oxygen (18O) isotope, should you water your plants with H218O or inject C18O2 into the air?

You should label the oxygen in CO2 (that is, inject C18O2) because the entire CO2 molecule is used in synthesizing carbohydrates, whereas H2O donates only the electron needed for the reduction step of the Calvin cycle. The extraction of electrons from water releases O2 as a by-product.

oxygenase carboxylase****

an enzyme that adds o2 to another molecule - an enzyme that adds carbon to another molecule *remeber that rubisco has the ability to catalyze these two different reactions - The difficulty is that for rubisco to favor the addition of CO2 over O2 requires that the enzyme be highly selective, and the price of high selectivity is speed. CO2 and O2 are similar in size and chemical structure, and for this reason selectivity can only be achieved by rubisco binding more tightly with the transition state (Chapter 6) of the carboxylation reaction. As a result, the better rubisco is at discriminating between CO2 and O2, the slower its catalytic rate.

why do pigments look colored

because they reflect light enriched in the wavelenths that they do not absorb. So they absorb shorter wavelenghts (blue to purple) and longer wavelenths ( red to orange) quite well. But do not absorb green to yellow wavelenghts very well.

photosystem I***

energizes electrons with a second input of light energy so they can be used to reduce NADP into NADPH. NADPH is formed when e- passed form photsys I to a membrane associated protein called ferredoxin NADP+ + 2e- +H+-> NADPH

where are larger sugars such as glucose and sucrose assembled

from triose phosphates in the cytoplasm

if NADP is in short supply, what does the e- transport chain do

it "backs up" becuase nadp is needed to create NADPH. this increases the creation of reactive oxygen species which is a highly reactive form of oxygen. the ROS can be formed either by the transfer of absrobed light energy from antenna chlorophyll directly to O2 or by the transfer of an e- which would form O2.

becuase the calvin cycle doesn't use sunlight directly what is referred to as

light-independent or even dark reactions of photosynthesis. BUT- it does need NADPH and ATP which are both supplied by the photosynthetic electron transport chain (where light is captured and turned into energy) - In addition, several Calvin cycle enzymes are regulated by cofactors that must be activated by the photosynthetic electron transport chain. Thus, in a photosynthetic cell, the Calvin cycle occurs only in the light

photosystems

protein pigment complexes (containing the tail of the chlorophyll molecule and integral membrane proteins in the thylakoid membrane) are the functional and strucutural units that absorb light energy and use it to drive electron transport

what are pigments

they are molecules that absorb some wavelenght of visible light

cyclic e-transport

this is where electrons from photos I are redirected from ferredoxin back into the e- transport chain. - these e- reenter the photosyn e- transport chain by plastoquinon - this alternative pathway for e- during the calvin cycel increases the production of ATP - this pathway is needed because the transport of four electrons through the photosynthetic electron transport chain, needed to reduce two NADP+ molecules, does not transport enough protons into the lumen to produce the required three ATPs. An additional pathway for electrons is thus needed to increase the production of ATP.

leaves of plants efficiently absorb light across most of the...

visible spectrum

what is the major electron donor in photosynthesis

water. an electron donor is a molecule that loses electrons. - the oxidation of water results in the production of electrons, protons, and O2. - Thus, oxygen is formed in photosynthesis as a by-product of water's role as a source of electrons.

Of the 15 chemical reactions that make up the Calvin cycle, 12 occur in the last step, the regeneration of RuBP:

A large number of reactions is needed to rearrange the carbon atoms from five 3-carbon triose phosphate molecules into three 5-carbon RuBP molecules. ATP is required for the regeneration of RuBP, raising the Calvin cycle's total energy requirements to two molecules of NADPH and three molecules of ATP for each molecule of CO2 incorporated by rubisco.

photosynthetic electron transport chain****

A series of redox reactions in which light energy absorbed by chlorophyll is used to power the movement of electrons; in oxygenic photosynthesis, the electrons ultimately come from water and the terminal electron acceptor is NADP+. - The process begins with the absorption of sunlight by protein-pigment complexes. The absorbed sunlight provides the energy that drives electrons through the photosynthetic electron transport chain. In turn, the movement of electrons through this transport chain is used to produce ATP and NADPH. And finally, ATP and NADPH are the energy sources needed to synthesize carbohydrates using CO2 in a process called the Calvin cycle this is what happens during light dependent reactions in the chloroplast: - PSII-pq (shuffles e-)-cytocrom b6- pc-PSI-ferrdoxase-NADP reducatse(catalizes the reduction into NADPH) - atp synthtase- makes ATP. protons are in the lumen (the inside) due to the splitting of water and they are also getting pumped in via pc and cytocrom b6. this creates a electochemical gradient (think of the dam) and the onyl way out is through the ATP synthase (they go to the stroma the outside) which gives it the energy to make ATP. This is similiar to oxidation phospolation in CR. The ATP and NADPH then go to the calvin cycle The inner membrane is hydrophobic so they protons cant get through because they are charged.

what is an advantage of having two different photosystems in chloroplasts?*****

- since water it takes a great deal of energy to pull electrons from water, the two systems are able to capture enough energy from sunlight to pull the lectron from water and produce an electron donor capable of reducing NADP into NAPH - The energy supplied by the first photosystem (II) allows electrons to be pulled from water, and the energy supplied by the second photosystem (I) step allows electrons to be transferred to NADP+ - The key point here is that photosystem I when oxidized is not a sufficiently strong oxidant to split water, whereas photosystem II is not a strong enough reductant to form NADPH.

how many molecules of NADPH and atp are needed in the calvin cycle for each CO2

2-nadph 3-atp

an ezyme that adds CO2 to another molecule is called what

a carboxylase

he enzyme rubisco is ___________BLANK because it adds CO2 to _____________BLANK.

a carboxylase; RuBP

photorespiration****

a process in which rubisco acts as an oxygenase, reulting in a release of co2 and a net loss of energy. - it is the overall effect when there is a consumption of o2 and a release of co2 in the presence of light. this process consumes atp - atp drives the reactions that recycle 2-phosphoglycolate into 3-PGA. Thus, photorespiration represents a net energy drain on two accounts: First, it results in the oxidation and loss, in the form of CO2, of carbon atoms that had previously been incorporated and reduced by the Calvin cycle, and second, it consumes ATP. - input of O2 makes 3PGA and 2 phosphoglycolate. The 2 Phogly cant be used in the calvin cycle. this also result in a lower prodcution of 3 PGA, but the plant can convert 2 phogyl into 3 pga, but it has to use atp.

most of the chlorophyll molecules in the thylakoid membrane function an...****

antenna: energy is transferred between chlorophyll molecules until it is finally transferred to a specially configured pair of chlolorphyll molecules known as the reaction center

why is it that not every triose phosphate molecule produced by the calvin cycle is exported from the chloroplast

because RuBP could not be regenerated and the Calvin cycle would grind to a halt. In fact, most of the triose phosphate molecules must be used to regenerate RuBP. For every six triose phosphate molecules that are produced, only one can be withdrawn from the Calvin cycle

To use sunlight to power the Calvin cycle, the cell must be able to use light energy to produce...

both NADPH and ATP

how is atp synthesized in the chloroplasts***

by atp synthase (a transmembrane protein powered by a proton gradient)***

there is a ___ ___ of energy as electrons pass thorugh each of the two photosytems and along the photosynthetic electron transport there is a ___ __ in energy

large increase and a small decrease. - the decrease in energy indicates that these are exergonic reaction and thus explains why electrons move in one direction through the series of redox reactions. *to run these reactions in the opposite direction would require a lot of energy*