Alice Clark/ATPsynthase

ATP synthase is shown here to the right in 3D with each protein shown in a different colour.

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Exploring the ATP synthase molecule

ATP synthase is a cellular molecular motor found in the mitochondrial membrane of humans, and also in other organisms. It has a role in the generation of ATP, the cells energy currency. This large molecule is built up of a number of different groups of proteins: the F0, the F1, and the stator - each group has an important role to play.

The contains α (alpha) (shown in light blue) and β (beta) (shown in dark blue), and making up the axel, the protein chain.

Q1: Describe how the protein chains are arranged to comprise the F1 region?

The F1 shown here has both adenosine diphosphate (ADP) and adenosine triphosphate (ATP) bound in the . See if you can zoom in on the ATP identify the phosphate atoms (orange), sugar and base. ==>

The three sites primarily located in the β subunits carry active ATP synthesis. The sites primarily located in the three α subunits are non-catalytic and exchange bound nucleotide very slowly, they are thought to be a carry over from evolution, and now play a more regulatory role.

Q2: How many phosphates atoms (orange) does ATP have, and how does this differ to ADP?

Q3: Between which atoms is the high energy bond formed, within the ATP (the bond that the ATP synthase catalyses within the β subunits)?

The rotates at 120° steps, putting the motor head into three different conformations, as the ADP and phosphate binds, the high energy bond is formed and the ATP is released.

Q4: What is the role of the axel, explain how it acts on the β subunits?

is a circular rotor that is formed of transmembrane α-helices that sit in the mitochondrial membrane. The hydrogen ions (protons) travel around the circular F0 motor, and turning the F0 rotor in the process, much like a waterwheel. Firstly, the hydrogen ion binds a negatively charged residue (amino acid) within the transmembrane α-helices, of the F0 motor. This action then allows the F0 to turn, as it can only turn in the hydrophobic membrane when a hydrogen ion is bound to these amino acids, as it neutralises the amino acid charge. Secondly, after a full rotation, the hydrogen is transferred to an amino acid and is passed to the opposite side of the membrane.

Q5: What is the location and role of the FO region?

Q6: Name two key amino acids, one acidic and one basic, that bind the hydrogen ions's within the the F0, during the ATP generation process?

Summary

The synthesis of ATP, the cells energy currency, involves a number of steps performed by a tiny molecular motor, found in the mitochondrial membrane, called ATP synthase.

1. Binding of ADP and phosphate to the ATP synthase beta domain located in the F1 domain

2. Formation of the new high energy phosphate-phosphate bond between the ADP and phosphate using energy, generated by the hydrogen ions moving the F0, then the movement is transmitted by the axel to the F1 region.

3. Releasing the newly made ATP from the F1 region

Key Terms

ATP = adenosine triphosphate (nucleotide)

ADP = adenosine diphosphate (nucleotide)

Aspartic acid = an acidic amino acid (negatively charged)

Glutamic acid = an acidic amino acid (negatively charged)

Arginine = a basic amino acid (negatively charged)

Transmembrane α-helices = membrane-spanning α-helices

ATP synthase - A molecular motor that generates ATP

Hydrogen ion = A hydrogen ion is created when a hydrogen atom loses or gains an electron. A positively charged hydrogen ion is also referred to as a proton

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