Photosynthesis and Pigments Quiz

ATP-ADP Cycle

• The ATP-ADP cycle is a crucial energy transfer process in cells.
• J. Willard Gibbs, a Yale professor (1878), proposed the idea of Gibbs free energy (represented by 'G'), which is a measure of the energy available in a system at constant temperature and pressure to do useful work.
• Free energy is the portion of a system's energy that can do work when temperature and pressure are constant; a notable example is a living cell.
• Exergonic reactions release energy, and ΔG is negative. In these reactions, energy is released spontaneously.
• Endergonic reactions require energy input. They have a positive ΔG and are nonspontaneous.
• Coupled reaction processes involve the transfer of energy from one side of a reaction to another by intermediates.
• ATP (adenosine triphosphate) is the key energy currency of a cell.

Work Involvement of ATP

• Chemical work involves pushing non-spontaneous endergonic reactions, like polymer synthesis from monomers.
• Transport work includes moving substances across membranes against the direction of spontaneous movement.
• Mechanical work includes processes like cilia whipping, muscle contraction, and chromosome movement.

Structure and Hydrolysis of ATP

• ATP consists of the sugar ribose, the nitrogenous base adenine, and a chain of three phosphate groups bonded to it.
• Hydrolysis is a reaction involving water.
• In ATP hydrolysis (breakdown), inorganic phosphate (Pi) is released from ATP. This results in ADP (adenosine diphosphate) and energy.
• The hydrolysis reaction of ATP to ADP is exergonic (ΔG = -7.3 kcal/mol or -30.5 kJ/mol).

Involvement of ATP in Cellular Work

• The cell's proteins have specific mechanisms to connect the energy from ATP hydrolysis to perform various cellular tasks.
• An example is the conversion of glutamic acid to glutamine, which requires energy and is an endergonic reaction (positive ΔG).

The ATP Cycle

• ATP synthesis primarily occurs in mitochondria and is catalyzed by ATP synthase.
• ATP is a renewable energy source.
• It regenerates through phosphorylation, which involves adding phosphate groups to ADP.
• ATP hydrolysis to ADP releases energy for cellular processes.

Importance of Chlorophyll and Other Pigments

• Chlorophyll, a green pigment, is found in the thylakoid membrane of chloroplasts, significantly impacting photosynthesis.
• Pigments absorb visible light.
• Different pigments (e.g., chlorophyll a, chlorophyll b, carotenoids) absorb different wavelengths of light. This process is essential to capture light energy for photosynthesis.

Types of Chlorophyll Pigments

• Chlorophyll a participates directly in the light reactions of photosynthesis.
• Chlorophyll b and carotenoids are considered accessory pigments, improving the range and efficiency of light absorption.
• Carotenoids are yellow/orange hydrocarbons protecting plants from light damage by absorbing and dispersing excess light energy.
• Chlorophyll a has a slightly different structure from chlorophyll b; this difference affects the wavelengths of light absorbed by each.