Mitochondria and chloroplasts

Question 1

Proton electrochemical gradient

Answer 1

The proton electrochemical gradient across a membrane is generated by energy released as electrons travel down their electric potential gradient through the electron transport chain. This energy is eventually used to synthesize ATP

Question 2

Proton-motive force

Answer 2

The energy stored in the proton electrochemical gradient, used to power ATP synthesis

Question 3

ATP synthase

Answer 3

The ATP synthesizing enzyme. Used to move protons down their electrochemical gradient. As the protons move down their gradient, they release energy used to make ATP from ADP and Pi

Question 4

Aerobic respiration stage 1

Answer 4

Stage 1 is glycolysis, which occurs in the cytoplasm. One glucose molecule is used to produce 2 pyruvate molecules. 2 ATPs and some NADH are also produced

Question 5

Aerobic respiration stage 2

Answer 5

Stage 2 is the citric acid cycle, which occurs in the mitochondria. Pyruvate is oxidized to produce the necessary starting material (acetyl CoA). Produces carbon dioxide, ATP, and electron carriers NADH and FADH2, which store energy for later

Question 6

Aerobic respiration stage 3

Answer 6

Stage 3 is the electron transport chain. Electron carriers (NADH and FADH2 transfer their electrons to molecules near the beginning of the transport chain. As electrons are passed down the chain, they move from a higher to a lower energy level, releasing energy. Some of the energy is used to pump H+ ions, moving them out of the matrix and into the intermembrane space. This pumping establishes an electrochemical gradient. At the end of the electron transport chain, electrons are transferred to molecular oxygen, which splits in half and takes up H+ to form water.

Question 7

Aerobic respiration stage 4

Answer 7

Stage 4 is ATP synthesis. As H+ ions flow down their gradient and back into the matrix, they pass through an enzyme called ATP synthase, which harnesses the flow of protons to synthesize ATP.

Question 8

Stage 1 of photosynthesis

Answer 8

Occurs in the chloroplast- energy absorption by pigments and direct transfer to electrons. Chlorophyll absorbs the energy, entering an excited state. It donates an electron to the adjacent chlorophyll, which passes it down a chain of acceptor molecules. Quinone is the primary electron acceptor, similar to coenzyme Q in the mitochondria.

Question 9

Stage 2 of photosynthesis

Answer 9

Electron transport and proton motive force (H+ gradient). Electrons move from the high energy electron acceptor QH2 to a proton pump (the cytochrome bf complex).

Question 10

Plastocyanin

Answer 10

Plastocyanin is an electron carrier protein that transfers electrons from the cytochrome bf complex to a complex called photosystem I. The electrons are low energy after going through the proton pump.

Question 11

Stage 3 of photosynthesis

Answer 11

The proton gradient across the thylakoid membrane, which was generated by light, is used to synthesize ATP. Protons move down their concentration gradient from the thylakoid lumen to the stroma through the chloroplast F0F1 complex (ATP synthase).

Question 12

Stage 4 of photosynthesis

Answer 12

Carbon fixation. The NADH and ATP produced in stages 2 and 3 drive the synthesis of six-carbon sugars from water and carbon dioxide. Starch is synthesized in the stroma.

Question 13

Energy source for aerobic respiration

Answer 13

The chemical bonds of fuel molecules- sugars (primarily glucose) and fatty acids.

Question 14

Energy source for photosynthesis

Answer 14

Photons (sunlight)

Question 15

What is unique about Henneguya
salminicola?

Answer 15

It can survive without oxygen, which is changing the definition of what an animal can be. The 10 celled Henneguya
salminicola lives as a
parasite in salmon and is
related to jellyfish. It has lost its mitochondrial genome. Not sure how it survives but it probably steals nutrients from host.

Question 16

Super resolution microscopy of the mitochondria

Answer 16

The stacks of the cristae and their membranes can be visualized this way. The cristae are invaginations of the inner mitochondrial membrane and act to expand the surface area of that membrane. This is where ATP synthesis occurs.

Question 17

Microtubules and the mitochondria

Answer 17

Microtubules are essential for mitochondrial movement, as well as fission and fusion. While actin may not be a major highway for mitochondrial movement it may function as an entrance ramp, helping mitochondria get to the highway as needed. Microtubules can then move the selected mitochondria and regulate fission and fusion events. This model is similar to mitochondrial behavior in neurons. Neurons utilize the actin cytoskeleton to move mitochondria shorter distances and microtubules for long distance transport

Question 18

Internal structure of the mitochondria

Answer 18

There is a smooth outer membrane that forms the outside boundary of the mitochondria. The inner membrane is continuous and composed of 3 domains. The cristae are invaginations from the inner membrane to the center of the mitochondria. The intermembrane space is the fluid filled space between the inner and outer membranes. The matrix is the fluid filled space within the inner membrane, and it contains mtDNA, ribosomes, and granules.

Question 19

Transmission electron microscopy of the mitochondria

Answer 19

The mitochondrial membranes can be observed using this imaging technique. Crista junctions (that separate the crista membranes from the inner boundary membrane) can be seen.

Question 20

Mitochondrial microprotein

Answer 20

New “microprotein” (54 AA) called PIGBOS discovered on the outer mitochondrial membrane (green fluorescence). It communicates with the ER and regulates the UPR via
the ER protein CLCC1 at mitochondrial ER contact sites. Loss of PIGBOS increases UPR leading to
increased cell death

Question 21

Unfolded-protein response

Answer 21

Cells respond to the presence of unfolded proteins in the rough ER by increasing transcription of genes that encode ER chaperones and folding catalysts.

Question 22

Mitochondria associated membranes (MAMs)

Answer 22

Regions of direct contact between the ER membrane and the outer mitochondrial membrane. They affect mitochondrial structure and function. For example, in response to elevated IP3, calcium moves through the MAM into the mitochondrial matrix. Elevated calcium levels in the matrix increase ATP synthesis.

Question 23

The inner mitochondrial membrane (IMM)

Answer 23

The IMM contains the ETC and ATP synthase and an unusual four legged phospholipid called cardiolipin (CL)
which is now widely studied.

Question 24

Cardiolipin

Answer 24

Cardiolipin interacts with and is required for optimal activity of several IMM proteins, including the enzyme complexes of the electron transport chain (ETC) and ATP production and for their organization into supercomplexes. Acts like “glue” for the ETC. CL also plays an important role in mitochondrial membrane morphology, stability and dynamics, in mitochondrial biogenesis and protein import, in mitophagy, and in different mitochondrial steps of the apoptotic process

Question 25

Fusion and fission

Answer 25

The mitochondria undergo frequent fusions (merging) and fissions (breaking apart), which can generate tubular or branched networks. This could account for the variety in mitochondrial morphologies seen across cell types

Question 26

How is mitochondrial fusion regulated

Answer 26

Integral membrane proteins MFN1 and MFN2 mediate outer mitochondrial membrane fusion. This is followed by fusion of the inner mitochondrial membranes, which is mediated by integral membrane protein OPA1.

Question 27

How is fission regulated?

Answer 27

A GTPase called DRP1. Post-translational modifications of DRP1 regulate fission

Question 28

Tunneling nanotubes

Answer 28

Tunneling nanotubes are projections of the cell membrane that connect the cytoplasm of animal cells. They act like gap junctions by transferring chemical and electrical signals between the cells. In addition to intracellular movement, mitochondria and mtDNA have been found to be transferred from one cell to another via these membrane tubules

Question 29

Mitochondrial permeability transition pore

Answer 29

A transmembrane protein residing in the mitochondrial inner membrane. Normally closed, this large protein pore opens when stimulated by mitochondrial matrix Ca2+ accumulation, adenine nucleotide depletion, increased phosphate concentration or oxidative stress. Opening of the pore is linked to apoptosis.

Question 30

Why does mitochondrial fission occur? (2)

Answer 30

1. Distribute mitochondria into 2 daughter cells 2. Eliminate damaged parts of the mitochondria

Question 31

Intrinsic triggered apoptosis

Answer 31

Mitochondria can trigger cell death in response to intrinsic cell stress- increase in reactive oxygen species. Chemotherapy and radiation creates mutations in the nucleus so the cell is triggered to go into apoptosis

Question 32

What happens when the MPTP is opened? (4)

Answer 32

Triggers the mitochondrial apoptotic cascade 1. Cytochrome C is located in the ETC- triggers apoptosis when released 2. Next, cytochrome C is in the cytoplasm, binds to APAF1 3. APAF-1 now binds to procaspase 9- caspase 9 is inactive 4. Caspase 9 binds to procaspase 3- as a result we now have caspase 3 (executioner enzyme that kills the cell)

Question 33

Extrinsic apoptotic cascade

Answer 33

Linked via “cell death receptors”- activates caspase 8- then activates caspase 3.

Question 34

Bcl-2

Answer 34

Anti apoptotic protein (prevents the mitochondria from triggering apoptosis)- named because of discovery in B cell lymphoma. Overproduction of Bcl-2 is very common in many different cancers and can make them resistant to chemotherapy and radiation

Question 35

Treating Bcl-2 overexpressing cancers (2)

Answer 35

2 new drugs are being tested. 1. Genasense – Bcl2 antisense oligonucleotide targets Bcl2 mRNA 2. Obatoclax – Small molecule Bcl-2 inhibitor

Question 36

Venetoclax

Answer 36

Can now be used for a broader group of patients with chronic lymphocytic leukemia (CLL). Venetoclax was initially approved by the FDA in 2016 to treat people with CLL that has a specific genomic alteration, called deletion 17p. It targets BCL‑2 proteins and attaches to them. When Venetoclax is attached to these proteins, it helps to restore the process of apoptosis, allowing these cells to self‑destruct.

Question 37

Synta Pharmaceuticals

Answer 37

In preclinical trials with Elesclomol – a drug that triggers apoptosis through targeting the electron transport chain in cancer cell mitochondria. Fast Track Orphan Drug Status for metastatic melanoma. Mechanism- increases oxidative stress

Question 38

Reactive oxygen species

Answer 38

Highly reactive oxygen containing molecules. They are by products of the ETC and can be purposefully generated by WBCs to kill pathogens. ROS can react with and damage important biological molecules, such as lipids, proteins, and DNA

Question 39

Cyclosporin A

Answer 39

An immunosuppressant. Inhibits the MPTP and protects stem cells during storage and transport. It can stimulate hematopoietic stem cell growth.

Question 40

What technique is used to explore the UPR and MPTP pathways?

Answer 40

Western blot- used to detect proteins

Question 41

Mitochondria toxicity in drug development

Answer 41

Hepatocytes are used for mitochondrial in vitro toxicology. Cell type used was HEPG2- hepatoma cell line- have high glycolytic activity which could present a disadvantage. Some cells treated with a toxin in the presence of glucose will rely on glycolysis to meet their bioenergetic needs and will be unaffected by the toxin.

Question 42

Warburg effect

Answer 42

The Warburg effect is the observation that cancer cells metabolize glucose through aerobic glycolysis- glycolysis where pyruvate is fermented to lactic acid. Tumors have an anaerobic environment. Most normal cells only do this under conditions of limited oxygen, but cancer cells carry out this process even when they have enough oxygen. Cancer cells also produce increased levels of some metabolites such as GLUT1, PFK, and LDH that directly or indirectly alter patterns of gene expression

Question 43

Mitochondrial myopathies

Answer 43

Passed on through the mother. Mitochondrial myopathies are a group of neuromuscular diseases caused by damage to the mitochondria. Nerve cells and muscle cells require a large amount of energy, so they are most frequently affected. Symptoms include fatigue, muscle weakness, and muscle cramps. The prognosis ranges widely.

Question 44

Autism and mitochondrial DNA mutations

Answer 44

Research has shown that ASD is linked to mutations in mitochondrial DNA (mtDNA). ASD children had more than twice as many mtDNA mutations when compared to unaffected siblings. Inherited from mother as spontaneous mutations and more pronounced in children with lower IQ

Question 45

Ragged red fibers

Answer 45

Myoclonic epilepsy with ragged red fibers (MERRF) is a multisystem mitochondrial syndrome characterized by progressive myoclonus and seizures. Other features associated with MERRF include cerebellar ataxia, myopathy, cardiac arrhythmia, sensorineural hearing loss, optic atrophy, and dementia. MERRF occurs due to genetic mutations in the mitochondrial DNA (mtDNA)

Question 46

2 hypotheses for what causes Alzheimer's disease

Answer 46

1. Accumulation of amyloid beta protein 2. Mitochondrial dysfunction

Question 47

How is mitochondrial dysfunction related to Alzheimer's disease?

Answer 47

Defect in the TCA (Tricarboxylic Acid Cycle) precedes amyloid beta accumulation in C. elegans model

Question 48

Phosphofructokinase-1

Answer 48

The key regulatory enzyme in glycolysis. It is activated by AMP and fructose 2,6- bisphosphate , whose concentrations are elevated when the cell's energy stores are low. PFK-1 is inhibited by ATP and citrate- they are both elevated when energy stores are high (actively oxidizing glucose).

Question 49

The malate-aspartate shuttle

Answer 49

A cyclical series of reactions that transfers NADH in the cytosol across the inner mitochondrial membrane. The net result is the replacement of cytosolic NADH with NAD+ and matrix NAD+ with NADH. Because the IMM is impermeable to NADH, shuttles are used to allow electrons to be indirectly transferred from NADH to oxygen via the ETC.

Question 50

Peter Mitchell

Answer 50

Won the 1978 Nobel Prize for Chemiosmotic Model of Mitochondrial Function. He found that a burst of ATP synthesis accompanied the transmembrane movement of protons driven by a concentration gradient. Contrary to the dominant hypothesis of the time, it was found that protons actually move through ATP synthase as they cross the membrane.

Question 51

Inner mitochondrial membrane functions

Answer 51

The inner mitochondrial membrane is the functional barrier to the passage of small molecules between the cytosol and the matrix and maintains the proton gradient that drives oxidative phosphorylation. In contrast to the outer membrane, the IMM is not freely permeable to small molecules

Question 52

Cyanide

Answer 52

Poisons the electron transport chain due to its binding to the heme a3 prosthetic group in Complex IV (Cytochrome C oxidase). The shutdown of aerobic ATP generation is recognized as the primary mode of cyanide’s cytotoxic action in eukaryotes

Question 53

2,4 - Dinitrophenol (DNP)

Answer 53

A drug that causes weight loss, but it also has a very high rate of adverse events, including hyperthermia, tachycardia, diaphoresis and tachypnoea, and it can cause death at toxic levels. DNP acts as a chemical ionophore, stopping the final energy conversion and causing a shift in the proton electrochemical gradient then results in potential energy dissipating as heat, instead of being converted to ATP, with rapid consumption of calories. The heat production represents a failure in thermoregulatory homeostasis, leading to uncontrolled hyperthermia. It also uncouples oxidative phosphorylation.

Question 54

Thermogenin

Answer 54

Found in the inner mitochondrial membrane of brown adipose tissue of newborns. It is an uncoupling protein which supplies heat by allowing the dissipation of the proton gradient without ATP synthesis, similar to DNP. Generates heat by non-shivering thermogenesis

Question 55

Non-shivering thermogenesis

Answer 55

Cold-induced increase in heat production not associated with shivering activity. Babies do not shiver when they're cold due to thermogenin production

Question 56

Gramicidin and valinomycin

Answer 56

Two mitochondrial uncouplers - potassium ionophores that compromise the mitochondrial transmembrane voltage that is normally -200 mV. Valinomycin binds to potassium and carries it across the membrane in accordance with electric potential (moves toward the more negative side of the membrane).

Question 57

Ionophore

Answer 57

A small lipid soluble molecule that selectively binds a specific ion and carries it across otherwise impermeable membranes

Question 58

Oligomycin

Answer 58

Blocks the F0F1- this inhibits cellular respiration. It causes an accumulation of protons outside the mitochondrion because the proton pumping system is still intact, but the proton channel is blocked.

Question 59

Cycloheximide

Answer 59

Selectively blocks nuclear translation to selectively inhibit mitochondrial protein synthesis

Question 60

Chloramphenicol and tetracycline

Answer 60

Selectively blocks mitochondria-specific translation of proteins. Chloramphenicol can inhibit both bacterial and mitochondrial protein synthesis, causing mitochondrial stress and decreased ATP biosynthesis. Tetracyclines induce mitochondrial proteotoxic stress, leading to changes in nuclear gene expression and altered mitochondrial dynamics and function

Question 61

Chloroplasts in the laboratory

Answer 61

One experiment found that synthesis of ATP by ATP synthase depends on a pH gradient across the membrane. Isolated chloroplast thylakoid vesicles that contained ATP synthase were exposed to a buffer solution (pH= 4). The vesicles were then mixed with a solution of pH= 8 once the pH of the thylakoid lumen reached 4. A burst of ATP synthesis accompanied the movement of protons across the membrane, driven by the H+ concentration gradient

Question 62

Thylakoid membrane

Answer 62

Unlike mitochondria, chloroplasts contain a third membrane. It is the site where light-driven generation of ATP and NADH occurs. It contains integral membrane proteins that are bound to light absorbing pigments

Question 63

Mitochondria in the laboratory

Answer 63

The inner mitochondrial membrane was treated with ultrasonic vibrations to create inside out submitochondrial vesicles that were capable of both electron transport and ATP synthesis. Membrane vesicles and F1 particles could be combined to make reconstituted vesicles that were capable of both electron transport and ATP synthesis.

Question 64

Rhodamine 123

Answer 64

Rhodamine 123 is a popular green fluorescent mitochondrial dye that stains mitochondria in living cells in a membrane potential-dependent fashion. It is widely used in flow cytometry studies involving mitochondrial membrane potential. Discovered by Lan bo Chen.

Question 65

JC-1

Answer 65

JC-1 is a novel cationic carbocyanine dye that accumulates in mitochondria. It is a sensitive marker for mitochondrial membrane potential

Question 66

Mitochondrial transplantation

Answer 66

Researchers at UC Irvine have found that they can give cells a short term increase in energy through mitochondrial transplantation. This could be a future approach to treating cancer and metabolic, neurodegenerative, and cardiovascular diseases

Question 67

The act of white blood cells engulfing antigens and red blood cells is an example of which of the following?

Answer 67

Heterophagy

Question 68

Joseph Priestly

Answer 68

The first known person to do an experiment focused on photosynthesis by using a closed vessel containing a sprig of mint and a mouse. He showed that animals required something from plants released into the air that allowed them to survive longer when they were contained in a closed container.

Question 69

Spirogyra

Answer 69

Ribbon-like chloroplasts. Thomas Engelmann ran an experiment ( using a crystal prism. He found that Spirogyra algae produce oxygen mostly in the blue and red parts of the spectrum. This tells us that the key photosynthetic pigment should accept blue and red rays, and thus reflect green rays. Blue-green chlorophyll best fits this description.

Question 70

What was the turning point in the history of photosynthesis?

Answer 70

Purple sulfur bacteria

Question 71

Melvin Calvin

Answer 71

Dr. Melvin Calvin figured out the photosynthetic process at UC Berkeley. Green algae are aquatic organisms that use photosynthesis. Calvin placed the algae into a contraption he called “the lollipop.” Calvin shone light on the lollipop and used a radioactive form of carbon called carbon-14 to trace the path that carbon took through the algae’s chloroplast, the part of the cell where photosynthesis occurs. By this method, he discovered the steps plants use to make sugar out of carbon dioxide. The Calvin cycle is named after him.

Question 72

JCAP – Joint Center for Artificial Photosynthesis

Answer 72

JCAP researches artificial photosynthesis- wants to produce hydrogen and carbon based fuels using only water, sunlight, and carbon dioxide as inputs. Solar driven artificial photosynthesis is now producing formate at 10% efficiency

Question 73

Sun Catalytix

Answer 73

An MIT spinoff company that works on artificial photosynthesis, acquired by Lockheed Martin

Question 74

Cyanobacteria

Answer 74

In the future, there could be renewable energy from cyanobacteria- energy production optimization by metabolic pathway engineering

Question 75

Using photosynthesis to treat heart damage

Answer 75

New research from Stanford shows promising results using an unusual strategy-photosynthetic bacteria and light. Researchers found that by injecting cyanobacteria into the hearts of anesthestized rats with cardiac disease, then using light to trigger photosynthesis, they were able to increase the flow of oxygen and improve heart function. The bacteria dissipated within 24 hours, but the improved cardiac function continued for at least four weeks

Question 76

Cyanobacteria growth optimized for space

Answer 76

Leading space agencies are gearing up to send crewed missions to Mars. One of the many challenges of this mission is the production of food and other life-support consumables on site without having to import them from Earth. One study found that it is possible to grow Anabaena cyanobacteria under conditions that are a compromise between conditions on the Martian surface and optimal conditions for cyanobacterial productivity. They can be grown using local Martian gases, water, and other nutrients.

Question 77

Cyanobacteria and circadian clocks

Answer 77

Most if not all eukaryotic cells have circadian clocks that work using a similar set of molecular events. Cyanobacteria has served as a model system to study circadian clocks both as intact cells as well as a cell free system.

Question 78

Could large-scale artificial photosynthesis reverse climate change?

Answer 78

If CO2 emissions do not fall fast enough, then CO2 will have to be removed from the atmosphere to limit global warming. Not only could planting new forests and biomass contribute to this, but new technologies for artificial photosynthesis as well. Physicists have estimated how much surface area such solutions would require

Question 79

Neoplants

Answer 79

Paris-based Neoplants has used bioengineering and directed evolution to create plants with a purpose. Their first product – Neo P1 (cost $179) – is a houseplant that is designed to fight air pollution by capturing and recycling volatile organic compounds (VOCs) such as formaldehyde, benzene, toluene and xylene from indoor air

Question 80

Structure of chloroplasts

Answer 80

Similar to mitochondria, chloroplasts are bounded by two membranes separated by an intermembrane space. Photosynthesis occurs on a third membrane (the thylakoid membrane) which is surrounded by the inner membrane and forms a series of flattened vesicles (thylakoids) that enclose the lumen. The green color of plants to due to chlorophyll and carotenoids, both of which are located in the thylakoid membrane

Question 81

Granum

Answer 81

A stack of adjacent thylakoids

Question 82

Stroma

Answer 82

The space between the inner membrane and the thylakoids.

Question 83

Chloroplasts and Autofluorescence

Answer 83

Chloroplast, an organelle facilitating photosynthesis, exhibits strong autofluorescence, which is an undesired background signal that restricts imaging experiments with exogenous fluorophore in plants.

Question 84

Chlorophyll

Answer 84

The main light absorbing pigments in the chloroplasts- the first step in photosynthesis is light absorption by chlorophyll a. Like the heme component of cytochromes, chlorophylls have a porphyrin ring attached to a hydrocarbon chain. In contrast to the hemes, chlorophylls have a central magnesium ion (rather than iron) and an additional 5-member ring

Question 85

Light absorption in chloroplasts

Answer 85

Photosynthesis involves the interaction of two separate multiprotein (photosystems), each of which absorbs light at defined wavelengths (absorption spectrum). The action spectrum indicates the overall rate of photosynthesis at each wavelength of light

Question 86

How are deep ocean organisms different from land plants?

Answer 86

They can absorb green light if little blue or red wavelengths are available.

Question 87

Beta-carotene and cancer

Answer 87

Beta-carotene is an antioxidant that may have a role in preventing cancer. Antioxidants neutralize free radicals. It is currently in clinical trials (over 100 so far).

Question 88

Light harvesting complexes

Answer 88

Light is absorbed by light harvesting complexes in stage 1 of photosynthesis. LHCs transfer the absorbed energy to the reaction center of photosystem 2. At the PS2. it's used to generate high energy electrons and oxidize water to molecular oxygen.

Question 89

Resonance energy transfer

Answer 89

Photosystem core proteins and LHC proteins orient the pigment molecules in the precise orientations and positions that are optimal for light absorption and rapid energy transfer, or resonance energy transfer. Resonance energy transfer does not involve the transfer of an electron. Energy is transferred to the special-pair chlorophyll a molecules in a reaction center after being funneled through a bridging chlorophyll in each LHC.

Question 90

Cyclic electron flow

Answer 90

A process where electrons cycle among PSI, ferrodoxin, Q, and the cytochrome bf complex. They bypass the ferrodoxin-NADP+ reductase at PSI that normally generates NADPH. Therefore, during cyclic electron flow, proton pumping allows additional ATP synthesis, but no net NADPH is generated and there is no oxidation of water to produce oxygen.

Question 91

When does cyclic electron flow occur?

Answer 91

When cells are stressed by conditions like drought, high light intensity, or low carbon dioxide levels, plants have to generate greater amounts of ATP relative to NADPH than they can produce by linear electron flow. They can use cyclic electron flow to produce ATP photosynthetically without being accompanied by NADPH production

Question 92

Linear electron flow

Answer 92

Occurs during stage 2 of photosynthesis. NADPH is generated along with a proton gradient in order to synthesize ATP in the next stage

Question 93

Photoinhibition

Answer 93

A small amount of energy absorbed by chlorophyll can be converted to triplet chlorophyll, which transfers energy to oxygen and creates highly reactive triplet oxygen. Triplet oxygen will react with and damage nearby molecules like PS2 D1- the damage is called photoinhibition, and it can suppress thylakoid activity.

Question 94

How does the PS2 get uninhibited?

Answer 94

A chaperone protein called HSP 70-

Question 95

Photorespiration

Answer 95

A reaction pathway that competes with carbon fixation (calvin cycle) by consuming ATP and generating carbon dioxide. This reduces the efficiency of photosynthesis. Photorespiration is favored when carbon dioxide is low and oxygen is high

Question 96

C4 plants

Answer 96

plants which live in hot and/or dry conditions have evolved an alternative carbon fixation pathway to enhance the efficiency of rubisco so that they don’t have to keep their stomata open as much, and thus they reduce the risk of dying from dehydration. These plants are called C4 plants, because the first product of carbon fixation is a 4-carbon compound (instead of a 3-carbon compound as in C3 or “normal” plants). C4 plants use this 4-carbon compound to effectively “concentrate” CO2 around rubisco, so that rubisco is less likely re react with O2

Question 97

Rubisco

Answer 97

Ribulose 1,5-bisphosphate carboxylase- an enzyme that incorporates carbon dioxide into precursor molecules that will later be converted into carbohydrates. It is located in the stroma of the chloroplast.