Photosynthesis and Pigments Quiz

Study Notes

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.

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.

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).

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).

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.

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.

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.