L24: ETC & Oxphos

Question 1

What is substrate-level phosphorylation?

Answer 1

• Involves enzymes and substrates that phosphorylate ATP

Question 2

What is oxidative phosphorylation?

Answer 2

• Involves membrane-bound enzymes and proton gradient drives ATP phosphorylation.

Question 3

What is the first step of oxphos?

Answer 3

• Electrons are delivered by high energy intermediates NADH and FADH2
• NADH is being oxidized to NAD+ (giving up 2 electrons to complex 1)
• Same process for FADH2 for complex 2

Question 4

What is the ETC?

Answer 4

• The flow of electrons

Question 5

What is step 2 of oxphos?

Answer 5

• energy is captured by electrons passed along the ETC in a step-down process

Question 6

What does O2 have to do with oxphos?

Answer 6

• In aerobic cellular respiration: Oxygen is the terminal electron acceptor (TEA) & is reduced to water.

Question 7

Which direction are protons (H+) pumped?

Answer 7

• Matrix to the intermembrane space

Question 8

Step 3 of oxphos?

Answer 8

• Energy is needed to pump protons (H+) across the mitochondrial membrane.

Question 9

Where does the energy to do the H+ (proton) transport come from?

Answer 9

• From ETC. Energy is captured by electrons donated to the protein complexes.
• The energy is from the electron transfer is released in a series of redox reactions.

Question 10

Which direction do protons (H+) diffuse through the ATP synthase?

Answer 10

• Eukaryotic cells: Intermembrane space to the matrix

- Bacterial cells: Periplasm to the cytoplasm

Question 11

Step 4 of oxphos?

Answer 11

• Protons flow through the ATP synthase which results in INDIRECT synthesis of ATP

Question 12

ATP synthase transports H+ from the inter-membrane space to the matrix for ATP synthesis. what kind of transport is this?

Answer 12

• Facilitated diffusion

Question 13

the energy from the movement of electrons through the electron-transport chain is used to move protons H+ from the matrix to the intermembrane space by…

Answer 13

• Active transport

Question 14

In oxphos, ADP is phosphorylated with the aid of a proton (H+) gradient. this proton gradient provides…

Answer 14

• A source of energy to drive the ATP synthase

Question 15

How does the indirect synthesis of ATP occur?

Answer 15

• protons flow through (passively) the ATP synthase
• this is called the proton motive force or proton gradient
• ATP is synthesized i.e. ADP is phosphorylated to ATP

Question 16

What are the different depictions of ATP synthase?

Answer 16

• Lollipop shape (“Stem and head”)
• “Stem” proteins rotate as H+ diffuse through
• The flow protons provides the “head” proteins with energy to phosphorylate ADP to ATP

Question 17

Which side of the membrane accumulates H+?

Answer 17

• Intermembrane space

Question 18

Which side of the membrane synthesizes the ATP?

Answer 18

• Mitochondrial matrix

Question 19

What is DNP?

Answer 19

• An effective weight-loss agent (drug)

Question 20

What does DNP do?

Answer 20

• when the drug is added to mitochondria, the inner mitochondrial membrane becomes permeable (leaky) to protons

Question 21

What is the effect of DNP on the proton (H+) gradient across the membrane?

Answer 21

• Proton gradient is lost

Question 22

What is the effect of DNP on the ETC - will electron flow continue?

Answer 22

• yes, due to increased NADH

Question 23

What is the effect of DNP on ATP synthesis?

Answer 23

• slows initially then stops (no H+ gradient)

Question 24

What is the effect of DNP on energy - what happens to the energy generated from the proton motive force?

Answer 24

• It dissipates

Question 25

What is the effect of DNP on oxygen consumption - will oxygen continue to be reduced to H2O?

Answer 25

• It increased

Question 26

What is the effect of DNP on NADH/NAD+ ratio in the matrix

Answer 26

• remains the same (increase in total # of NADH due to increased catalysis of glucose)

Question 27

DNP diet pills result in weight loss because…

Answer 27

• rate of glucose (sugar) catabolism increases

Question 28

Oxidative phosphorylation general steps and principles.

Answer 28

• STEP 1: electrons are delivered by high energy intermediates NADH and FADH2
• STEP 2: energy is captured by electrons passed along the ETC in a step-down process
• STEP 3: this drives the energy needed to pump protons (H+) across the mitochondrial membrane
• STEP 4: protons flow through the ATP synthase results in INDIRECT synthesis of ATP