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Questions and Answers
What mechanism allows an excited molecule to return to its ground state while dissipating energy?
What mechanism allows an excited molecule to return to its ground state while dissipating energy?
- Phosphorescence
- Radiative decay
- Intersystem crossing
- Internal conversion (correct)
What state does an excited molecule transition to during intersystem crossing?
What state does an excited molecule transition to during intersystem crossing?
- Non-radiative state
- Excited singlet state
- Excited triplet state (correct)
- Ground singlet state
Which of the following best describes the process of fluorescence?
Which of the following best describes the process of fluorescence?
- Emission of light at a longer wavelength after energy absorption (correct)
- A forbidden transition between two states
- An energy transfer to a neighboring molecule
- A change in electron spin state
What does 'PIB' refer to in the context of photosynthetic organisms?
What does 'PIB' refer to in the context of photosynthetic organisms?
When does CO2 exchange occur in a leaf placed in darkness?
When does CO2 exchange occur in a leaf placed in darkness?
What gas was likely absent in the atmosphere of early Earth, according to Haldane's proposal?
What gas was likely absent in the atmosphere of early Earth, according to Haldane's proposal?
Which type of bacteria are strictly anaerobic and produce methane?
Which type of bacteria are strictly anaerobic and produce methane?
What role do acetate and CO2 play in the metabolism of methanogens?
What role do acetate and CO2 play in the metabolism of methanogens?
Which of the following is a characteristic of Purple Sulphur Bacteria?
Which of the following is a characteristic of Purple Sulphur Bacteria?
What is the primary energy-generating process for methanogens?
What is the primary energy-generating process for methanogens?
How did early Earth conditions contribute to the evolution of life forms?
How did early Earth conditions contribute to the evolution of life forms?
What significant evolution occurred with cyanobacteria?
What significant evolution occurred with cyanobacteria?
What was the initial fate of oxygen produced by cyanobacteria in ancient environments?
What was the initial fate of oxygen produced by cyanobacteria in ancient environments?
What was the consequence of the prevention of an increase in atmospheric O2?
What was the consequence of the prevention of an increase in atmospheric O2?
What is a consequence of reactive oxygen species (ROS) in biological systems?
What is a consequence of reactive oxygen species (ROS) in biological systems?
How does high light intensity affect photosystems?
How does high light intensity affect photosystems?
What role does ascorbate peroxidase (APX) play in the detoxification process?
What role does ascorbate peroxidase (APX) play in the detoxification process?
What happens when a photon is absorbed by a ground singlet state molecule?
What happens when a photon is absorbed by a ground singlet state molecule?
What can happen to high energy electrons in the process of photosynthesis?
What can happen to high energy electrons in the process of photosynthesis?
Which of the following best describes reactive oxygen species (ROS) in terms of their lifespan?
Which of the following best describes reactive oxygen species (ROS) in terms of their lifespan?
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Study Notes
Excited Molecules and Energy Dissipation
- Excited molecules can dissipate energy via internal conversion (IC), fluorescence, or intersystem crossing (ISC).
- ISC involves a change in electron spin, resulting in an excited triplet state (T1).
- Excited singlet states (ESS) and excited triplet states (ETS) can transfer excitation energy to nearby molecules
Photosynthesis and Oxygen
- Early Earth's atmosphere was anaerobic and lacked oxygen, which was essential for the evolution of life.
- Methanogenic bacteria were the earliest life forms, thriving in an atmosphere rich in CO2 and H2.
- Cyanobacteria evolved oxygenic photosynthesis, which significantly impacted the Earth's atmosphere by introducing oxygen.
Oxygen Toxicity and Reactive Oxygen Species (ROS)
- Oxygen, while essential for life, is also toxic due to the formation of reactive oxygen species (ROS).
- ROS are short-lived but can extract electrons from other molecules, leading to oxidative damage.
Photorespiration and Rubisco
- Photorespiration is a process where Rubisco, a bi-functional enzyme, uses oxygen instead of carbon dioxide.
- Rubisco's oxygenation activity leads to the formation of glycolate, which is then processed by the glycolate pathway.
- The glycolate pathway is a complex and energy-consuming process that aims to recover carbon from photorespiration.
Glycine Decarboxylase (GDC) and Serine Hydroxymethyl Transferase (SHMT)
- GDC and SHMT are key enzymes involved in the glycolate pathway.
- GDC is particularly abundant in photosynthetic parts of plants, accounting for up to 30% of mitochondrial protein in some leaves.
Folate
- Folate is a crucial vitamin involved in various metabolic processes, including single-carbon metabolism.
- Folate deficiency can lead to anemia.
- Mitchell isolated folic acid from spinach leaves in 1941.
- The folate structure consists of a tripartite molecule with various oxidation levels.
- Folate is polyglutamylated in vivo and is photolabile.
Competition Between CO2 and O2
- Oxygen competes with carbon dioxide for the active site of Rubisco.
- This competition highlights the trade-off between photosynthesis and photorespiration.
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