ATP synthase is shown here to the right ==>
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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 F1 and Axle
The BRCA Protein contains an α (alpha) chain (shown in light blue) and a β (beta) chain (shown in dark blue). The axle, rotates (like the axle on a car), and is composed mainly of the γ (gamma) protein chain. The axle rotates with three 120° steps, putting the β chains into three different conformations, allowing the ADP and phosphate to bind, the high energy bond to form and the release of ATP.
Q1: Describe how the protein chains are arranged to comprise the F1 region?
Q2: What is the role of the axle, explain how it acts on the β subunits?
ADP and ATP are bound in the nucleotide binding sites
The F1 shown here has both adenosine diphosphate (ADP) and adenosine triphosphate (ATP) bound in the nucleotide binding sites. See if you can zoom in on the ATP identify the phosphate atoms (orange), sugar moiety and the base moiety. ==>
The three nucleotide binding sites, primarily located in the β subunits, carry out 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.
Q3: How many phosphates atoms (orange) does ATP have, and how does this differ to ADP?
Q4: Between which atoms is the high energy bond formed, and in which location in the ATP synthase does the catalysis occur (which chain)?
The F0 region
The F0 is a circular rotor that is formed of transmembrane α-helices located in the inner mitochondrial membrane. The positively charged 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 aspartic acid or glutamic acid 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 acids negative charge. Secondly, after a full rotation, the hydrogen is removed from the rotor by an arginine amino acid, into a charged pocket, and then is passed to the opposite side of the membrane.
Q5: What is the location and role of the F0 region. How many Transmembrane α-helices are there?
Q6: Name two key amino acids, one acidic and one basic, that influence the hydrogen ions's path within the the F0. Which one acts like a broom sweeping the protons off the rotor?
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.
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 (positively charged)
Transmembrane α-helices = Membrane-spanning α-helices
ATP synthase = A molecular motor that generates ATP
Hydrogen ion = A hydrogen atom that has lost (or gained) an electron. A positively charged hydrogen ion is also referred to as a proton
Moiety = A "part" or "functional group" of a molecule
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