17.2 - ATP Synthesis

Question 1

What is chemiosmosis and how does it work (general process)?

Answer 1

Chemiosmosis: Creating a proton gradient through an ETC, the protons are used to synthesise ATP

1. Energy released from electrons travelling down ETC is used to pump protons from mitochondrial matrix into the intermembranal space
2. This creates a proton gradient (producing a pH gradient and a p.d. across the membrane)
3. The protons then will want to diffuse down the electrochemical gradient back into the mitochondrial matrix, the only way is through the hydrophilic channel protein ATP synthase
4. As protons flow through ATP synthase, the energy is used to condense ADP and Pi to make ATP

Question 2

How are electrons excited to higher energy levels?

Answer 2

• Electrons in pigments molecules (chlorophyll) excited by absorbing sunlight
• High energy electrons released when chemical bonds are broken in respiratory substrate molecules (glucose)

Excited electrons then pass into an electron transport chain, then used to generate a proton gradient

Question 3

What is the difference between chemiosmosis in animals and plants?

Answer 3

In plants, protons are pumped from the stroma, to the i_nner thylakoid space_, and then through ATP synthase back into the stroma

• Photophosphorylation in plants
• Oxidative phosphorylation in animals

The final stage of chemiosmosis in animals is, the protons in the mitochondrial matrix combine with electrons from the ETC and to oxygen (the terminal electron acceptor) to form water