Alice Clark/ATPsynthase

ATP synthase is shown here to the right ==>

It is depicted 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 F1 and Axle

The contains an α (alpha) chain (shown in light blue) and a β (beta) chain (shown in dark blue). The , rotates (like the axle on a car), and is composed mainly of the 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 . 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

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 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 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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