ATP-ADP Cycle Overview

Study Notes

Adenosine triphosphate (ATP) is the cell's energy currency, powering various cellular functions (mechanical work, transport, chemical reactions).
ATP consists of a ribose sugar, adenine, and three phosphate groups.
The last two phosphate bonds in ATP store high-energy bonds.
Hydrolysis of these bonds releases energy, breaking ATP into adenosine diphosphate (ADP) and inorganic phosphate (Pi).
The cell recycles ATP by phosphorylating ADP, using energy from catabolic processes.
ATP powers three main types of cellular work: chemical, transport, and mechanical work.

ATP hydrolysis breaks the phosphate bonds, releasing energy.
This energy is derived from the negative charge repulsion of phosphate groups, not from the bonds themselves.
Hydrolysis of ATP leads to a change in protein shape and ability to bind other molecules.
This shape change powers various cellular processes.

Catabolic (exergonic) reactions provide energy required for ATP regeneration from ADP and inorganic phosphate.
ATP regeneration is rapid; humans would need nearly their body weight in ATP daily without regeneration.

Pigments capture solar energy for photosynthesis.
Chlorophyll is the primary photosynthetic pigment in plants.
Chlorophyll absorbs blue and red light and reflects green light, resulting in plants appearing green.
Chlorophyll is found in thylakoid membranes inside chloroplasts.
Multiple chlorophyll types (e.g., chlorophyll a, chlorophyll b) capture more wavelengths of sunlight.

Chlorophyll molecules absorb photons of light.
This excites an electron to a higher energy level.
The excited electron returns to its original energy level, releasing energy as heat or light.
This process is crucial for transferring energy in photosynthesis.

Photosystems are protein complexes in thylakoid membranes that contain pigments and proteins.
They capture light energy and convert it to chemical energy.
Photosystem II and Photosystem I are the two main types of photosystems.