Cells are the basic structural and functional units of all living organisms.

They perform essential life processes such as energy production, growth, communication, and reproduction.

Cells can be classified into two main types:

Prokaryotic cells – simple cells without a nucleus (e.g., bacteria).

Eukaryotic cells – complex cells with a nucleus and organelles (e.g., plant and animal cells).

Cells require energy to carry out their functions, including:

Active transport of molecules

Synthesis of proteins and nucleic acids

Muscle contraction

Cell division

The primary energy currency in cells is ATP (Adenosine Triphosphate).

ATP is a nucleotide composed of:

Adenine – nitrogenous base

Ribose – five-carbon sugar

Three phosphate groups – linked by high-energy bonds

Visual diagram (monospaced, ready for DokuWiki):

        Adenine
           |
          Ribose
           |
  +--------+--------+--------+
  |  Pα    |  Pβ    |  Pγ    |
  +--------+--------+--------+
     Low-E      High-E bond
                |
                +----> Energy released (ATP → ADP + Pi)

Legend:

Pα (alpha phosphate) – structural phosphate

Pβ (beta phosphate) – part of high-energy bond

Pγ (gamma phosphate) – terminal phosphate, bond cleavage releases energy

Optional color in DokuWiki (if HTML is supported):

<span style=“color:green”>Pα</span> - structural <span style=“color:yellow”>Pβ</span> - high-energy bond <span style=“color:red”>Pγ</span> - terminal phosphate

ATP hydrolysis releases energy:

ATP + H2O → ADP + Pi + Energy

Energy powers:

Muscle contraction

Active transport

Biosynthesis of macromolecules

Signal transduction

ATP regeneration:

ATP is recycled from ADP + Pi using energy from:

Glycolysis

Krebs cycle

Oxidative phosphorylation (mitochondria)

Photosynthesis (chloroplasts in plants)

     +--------------------------------+
     |  Energy from food / sunlight   |
     +--------------------------------+
                   |
                   v
        +----------------------+
        |       ADP + Pi       |
        +----------------------+
                   |
                   |  ATP Synthesis
                   |  (Glycolysis, Krebs Cycle,
                   |   Oxidative Phosphorylation,
                   |   Photosynthesis)
                   v
        +----------------------+
        |         ATP          |
        +----------------------+
                   |
                   |  ATP Hydrolysis
                   |  (Energy released for:
                   |   - Muscle contraction
                   |   - Active transport
                   |   - Biosynthesis
                   |   - Signal transduction)
                   v
        +----------------------+
        |  Cellular Work Done  |
        +----------------------+
                   |
                   +-----------------+
                                     |
                                     v
                               +-----------+
                               |  ADP + Pi |
                               +-----------+
                                     |
                                     v
                         (Cycle repeats continuously)

Optional color in DokuWiki:

<span style=“color:yellow”>ATP</span> <span style=“color:green”>ADP + Pi</span> <span style=“color:red”>Cellular Work Done</span>

Cytoplasm – powers glycolysis and cytosolic reactions.

Mitochondria – main ATP production via oxidative phosphorylation.

Chloroplasts (plants) – ATP produced during light-dependent photosynthesis.

ATP is essential for:

Muscle contraction

Active transport across membranes

Protein synthesis

Signal transduction and communication

ATP is the universal energy currency for cells.

Energy is stored in phosphate bonds and released during hydrolysis.

Continuous ATP regeneration is vital for sustaining all cellular processes.