Overview
This lecture focuses on ATP (adenosine triphosphate)—its structure, function as an energy molecule, and the cycle by which it is used and regenerated in cells.
Structure of ATP
- ATP stands for adenosine triphosphate; writing "ATP" is sufficient in exams.
- ATP is a type of nucleotide composed of a ribose sugar, an adenine base, and three phosphate groups.
- Ribose is identified by an OH group on carbon 2.
- Adenine (a purine base) and ribose together are called adenosine.
- The presence of three phosphate groups is why it's called triphosphate.
- You may be asked to describe or draw ATP in exams.
Role of ATP in Cells
- ATP is the primary usable chemical energy source for cellular processes.
- Glucose also contains chemical energy, but cells cannot use it directly for work like moving cilia.
- ATP provides direct energy for activities such as muscle contraction, DNA replication, active transport, and protein synthesis.
- Glucose acts as an energy store; ATP is the energy currency—usable directly by the cell.
ATP vs. Glucose: Analogy and Relationship
- Glucose is like money (can’t be used directly for cellular work), ATP is like buying food with money (usable energy for the cell).
- Energy from glucose must be converted into ATP before use in cellular processes.
ATP Hydrolysis and Energy Release
- ATP provides energy when it is hydrolyzed (broken down using water), separating one phosphate to produce ADP (adenosine diphosphate) and inorganic phosphate (Pi).
- The released energy powers cellular work such as moving cilia or protein synthesis.
- In exams, write "ADP + Pi" to indicate ADP and inorganic phosphate; do not use "ADP + P".
Regeneration of ATP
- When ATP is hydrolyzed, its levels in the cell decrease.
- ATP can be regenerated from ADP and inorganic phosphate through condensation using energy from respiration.
- Respiration of organic molecules (like glucose) provides the energy for ATP synthesis.
- This use and regeneration of ATP forms a continuous cycle in cells.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — Energy-carrying molecule with adenine, ribose, and three phosphates.
- Hydrolysis — Chemical breakdown using water, e.g., ATP → ADP + Pi.
- ADP (Adenosine Diphosphate) — ATP after losing one phosphate; can be recycled to ATP.
- Inorganic Phosphate (Pi) — Free phosphate group released from ATP hydrolysis.
- Condensation — Joining ADP and Pi to regenerate ATP, requiring energy input.
- Energy Currency — A form of energy usable directly by the cell (ATP).
- Energy Store — A molecule storing potential energy, not directly usable (glucose).
Action Items / Next Steps
- Review ATP structure and practice drawing it.
- Remember to use "ADP + Pi" in exam answers.
- Study the process of ATP hydrolysis and regeneration through respiration.