17.2 ATP synthesis

why is ATP needed

• ATP molecules is used to drive essential metabolic processes - the production of ATP is therefore essential to all forms of life

chemiosmosis

• synthesises ATP in photosynthesis and respiration

• the diffusion of protons from a region of high concentration to low concentration through a partially permeable membrane

• the movement of the protons as they flow down the concentration gradient releases energy that is used in the attatchment of an inorganic phosphate to ADP forming ATP

• chemiosmosis depends on the creation of a protein concentration gradient. The energy to do this comes from excited electrons

how are electrons excited

• electrons present in pigment molecules are excited by absorbing light from the sun

• high energy electrons are released when chemical bonds are broken in respiratory substrate molecules

what happens during the electron transport chain

• an electron transport chain is made up of a series of electron carriers, each with progressively lower energy levels

• as high energy electrons move from one carrier in the chain to another, energy is released

• this is used to pump protons across a membrane, creating a concentration difference across the membrane and therfore a proton gradient

• the proton gradient is maintained as a result of the impermeability of the membrane to hydrogen atoms

• the only way the protons can move back through the membrane down the concentration gradient is through hydrophilic membrane channels linked to the enzyme ATP synthase. The flow of protons though these channels provides the energy used to synthesise ATP