Biochemistry Chapter 16 Photosynthesis

How many photooxidation events are required to oxidize 2 H2O molecules to 1 O2molecule?

4

The enzyme ribulose bisphosphate carboxylase/oxygenase, or rubisco, fixes carbon dioxide. The carbon dioxide is incorporated into a five-carbon compound, which is then hydrolyzed to yield two three-carbon compounds. Put the steps in order

1. Substrate 2. Rubisco removes a proton from C3 of ribulose-1,5-bisphosphate 3. An enediolate intermediate nucleophilically attacks CO2, incorporating it at C2 4. Water attacks C3 of the six-carbon β-keto acid, hydrating it 5. The six-carbon molecule splits, yielding two 3-phosphoglycerate molecules 6. Products

chloroplasts generate a proton gradient across the thylakoid membrane that is used to synthesize ATP in a process called photophosphorylation. There are three points during photosynthesis where protons are released into the lumen.

1. when plastoquinol is oxidized at the cytochrome bf complex 2. when water is oxidized at the manganese centers of the oxygen-evolving complex 3. when plastoquinol is oxidized in the second half of the Q cycle at the cytochrome bf complex

Which of the following shows the correct movement of electrons in the Z-scheme of photosynthesis?

H2O → P680 → plastoquinone → cytochrome b6f → plastocyanin → P700 → ferredoxin → NADP+

When a molecule absorbs a photon, it is said to be excited, or at a higher energy state. The excited molecule can then return to its ground state when the absorbed energy is dissipated through mechanisms. What are the mechanisms?

Heat, fluorescence, exciton transfer (resonance energy transfer), or photooxidation

Depending on conditions, plants convert the triose phosphates from the Calvin cycle into starch or sucrose. Where is starch and sucrose made?

Starch is made in the chloroplast while sucrose is made in the cytoplasm

What two substrates are needed to produce sucrose in plants?

UDP-glucose and fructose-6-phosphate

how do chlorophyll pigments absorb energy from light?

a photo excites an electron in the chlorophyll to a higher energy state

Production of ATP in chloroplasts

a proton gradient is generated by the transport of protons into the thylakoid lumen protons move from the thylakoid lumen to the stroma through ATP synthase, producing ATP

absorbed energy may be passed to another molecule in a process called

exciton transfer

Which of the following can happen when a photosynthetic pigment absorbs light? A) energy lost as heat B) energy given off by fluorescence C) exciton transfer D) photooxidation E) all of the above

all of the above

Which of the following occurs during cyclic electron flow? A) photosystem I absorbs light but not photosystem II B) protons are pumped into the lumen by cytochrome b6f C) electrons are transferred from photosystem I → ferredoxin→ cytochrome b6f → plastocyanin, then back to photosystem I D) there is no production of NADPH or oxygen E) all of the above

all of the above

in photosystem I, P700 transfers an electron to chlorophyll (A0) upon excitation by a photon. How is this electron replaced?

by electrons transferred from plastocyanin

in photosystem II, P680 transfers an electron to pheophytin upon excitation by a photon. How is this electron replaced?

by the splitting of water molecules at the manganese center of the oxygen-evolving complex

What organelle is responsible for photosynthesis?

cholorplast

Which of the following is NOT a part of the photosynthetic electron transport system? A) cytochrome b6f B) ferredoxin C) photosystem II D) photosystem I E) cytochrome c

cytochrome c

Z-scheme of photosynthesis

diagram representing the flow of electrons from water to NADP

The false statement about photophosphorylation is: A) electrons flow from NADPH to O2 B) electrons will flow spontaneously from reduced ferredoxin to NADP+ C) the major photoreceptor in green plants in chlorophyll a D) a proton concentration gradient is produced across the thylakoid membrane E) noncyclic photophosphorylation results in production of NADPH, oxidation of H2O, evolution of O2, and phosphorylation of ADP

electrons flow from NADPH to O2

What are the benefits of cyclic electron flow in photosynthesis?

energy is conserved in a proton gradient it promotes ATP synthesis by chemiosmosis

Energy from antenna pigments is transferred to the reaction center via

exciton transfer

The final carrier of electrons from photosystem I is _______________, which can then utilize electrons to produce either ATP or NADPH.

ferrodoxin

absorbed light given off as a lower-energy photo is

fluorescence

photosystem I

generates NADPH uses reduced ferredoxin to generate a biosynthetic reductant P700

photosystem II

generates electrons, protons (for setting up the proton gradient), and O2 oxidizes water P680

energy that has been converted to a potentially unusable form is lost as

heat

Calvin cycle

light-independent metabolic pathway converts carbon dioxide occurs in the stroma of the chloroplast

an excited molecule is oxidized and an acceptor molecule is reduced during

photooxidation

Rubisco, in stage I of the dark reactions, catalyzes the addition ("fixation") of CO2 to the following acceptor molecule:

ribulose-1,5-bisphosphate

Calvin cycle pathway

ribulose-1,5-bisphosphate -(CO2)-> 3-phosphoglycerate -(ATP->ADP)-> 1,3-biphosphoglycerate -(NADPH->NADP+ +Pi)-> glyceraldehyde-3-phosphate

The major sugar transported to non-photosynthesizing cells in plants is

sucrose

how are electrons moved from photosystem II to photosystem I in photosynthesis?

the cytochrome bf complex catalyzes the transfer of electrons from plastoquinol to plastocyanin

Chloroplasts

the stroma is analogous to the matrix of the mitochondria both the light-dependent (light) and carbon-fixation (dark) reactions occur in the chloroplasts the role of chloroplasts is to capture light energy thylakoids are usually arranged in stacks (grana)