Question

what is the role of oxygen in cellular respiration?

   AND

describe the structure and function of ATP synthase?

((this question is essential cell biology 4th edition chapter 14 )

Answer 1

NADH and FADH2 generated during glycolysis and krebs cycle of cellular respiration, carry electrons to the electron transport chain (ETC) on inner membrane of mitochondria. During transportation of electrons in ETC, protons are pumped across the inner mitochondrial membrane from the inner matrix to the intermembrane space, producing a strong hydrogen concentration gradient and both an electrical potential and a pH potential builds up across the membrane. The protein complex ATP synthase then makes use of this membrane potential to accomplish the phosphorylation of ADP to ATP. Once the electrons are used, they become depleted and must be removed from the body. Oxygen function as an electron acceptor, and used electrons bind with oxygen; these molecules eventually bind with hydrogen to form water.

ATP synthase consists of two protein entities: the F1, a soluble portion situated in the mitochondrial matrix, and the Fo, bound to the inner mitochondrial membrane. F1 is composed of three copies of each of subunits α and β, and one each of subunits γ, δ and ε. F1 subunits γ, δ and ε constitute the central stalk. Fo consists of a subunit c-ring (probably comprising eight copies and one copy each of subunits a, b, d, F6 and the oligomycin sensitivity-conferring protein (OSCP). Subunits b, d, F6 and OSCP form the peripheral stalk which lies to one side of the complex.

The function of ATP synthase is to synthesize ATP from ADP and inorganic phosphate (Pi) in the F1 portion. The proton gradient across the inner mitochondrial membrane establishes a proton-motive force. The energy is generated when protons pass through the Fo portion of the enzyme, down their electro-chemical gradient. The released energy causes rotation of two rotary motors: the ring of c subunits in Fo, along with subunits γ, δ and ε in F1, to which it is attached. Protons pass Fo via subunit a to the c-ring. Rotation of subunit γ within the F1 α3β3 hexamer provides energy for ATP synthesis. The catalytic sites, located in each of the three β subunits and each site switches cooperatively through conformations in which ADP and Pi bind, ATP is formed and then released.