Chapter 18: Electron Transport Chain

Question 1

How do you calculate deltaG^o’ for a reaction from the standard reduction potential?

Answer 1

deltaG= -nF(deltaE^o’)

F= 96,485 coul/mol

Question 2

Where in the cell does glycolysis occur?

Answer 2

In the cytosol/cytoplasm

Question 3

Where in the cell does the citric acid cycle occur?

Answer 3

In the mitochondrial matrix

Question 4

Where in the cell does oxidative phosphorylation occur?

Answer 4

In the inner membrane of the mitochondria

Question 5

What is the name of Complex 1?

Answer 5

NADH-Q oxidoreductase

Question 6

What is the name of Complex 2?

Answer 6

Succinate-Q reductase

Question 7

What is the name of Complex 3?

Answer 7

Q-Cytochrome C oxidoreductase

Question 8

What is the name of Complex 4?

Answer 8

Cytochrome C oxidase

Question 9

How do the electrons from NADH enter the ETC and does it generate a lot of energy?

Answer 9

NADH enters the chain through complex 1 and the protons are moved using a proton wire mechanism. (Be able to draw it). This results in quite a bit of energy since 4 H+ are pumped into the intermembrane space from the matrix and Q is reduced to QH2.

Question 10

How do electrons from FADH2 enter the ETC and does it generate a lot of energy?

Answer 10

FADH2 enters the chain through complex 2 where it is taken to form QH2. There is not a lot of energy generated from this because complex two does not pump protons while complex 1 does.

Question 11

How does the movement of electrons to QH2 create a proton gradient?

Draw the mechanism.

Answer 11

This is done in complex three when the QH2 molecules from complex one and two meet up at. The Q cycle is then started. (draw it.)

Question 12

How does the movement of electrons through a proton wire generate a proton gradient?

Draw the mechanism.

Answer 12

A H+ molecule is bouncing from inside the matrix to attach to an asp molecule and then a different asp molecule and then a third different asp molecule until the H+ is successfully moved from the matrix to the intermembrane space.

Question 13

Which complexes transport H+ into the inner mitochondrial membrane?

Answer 13

Complex 1,3, and 4

Question 14

How does Superoxide dismutase defend against reactive oxygen species? Give the reaction catalyzed, kinetic parameters and how it is regulated.

Answer 14

Superoxide dismutase defends against O2-. The reaction that proceeds is 2O2- +2H2 –> O2 + H2O2 .

The partial reduction of O2 can make this superoxide but it produced hydrogen peroxide which is also a ROS.

This enzyme can be upregulated by aerobic exercise. (more exercise causes more glycolysis, CAC and ETC which means more electrons to O2 which can cause more ROS to occur so you get more of this enzyme in response).

The catalytic efficiency (kcat/km) is very high and approaches the diffusion control limit. The slow step is the diffusion of the enzyme and substrate not the binding and reacting.

Question 15

How does Catalase defend against reactive oxygen species? Give the reaction catalyzed, kinetic parameters and how it is regulated.

Answer 15

Catalase is the enzyme that defends against hydrogen peroxide. The reaction catalyzed is 2H2O2 –> O2 + 2H2O .

This is also caused by partial reduction of O2 creating a ROS.

This enzyme can be upregulated by aerobic exercise. (more exercise causes more glycolysis, CAC and ETC which means more electrons to O2 which can cause more ROS to occur so you get more of this enzyme in response).

The catalytic efficiency (kcat/km) is very high and approaches the diffusion control limit. The slow step is the diffusion of the enzyme and substrate not the binding and reacting.

Question 16

How does the flow of electrons through the Fo subunit generate a rotary motion?

Answer 16

There is a matrix half channel where the pH in the matrix is high so the concentration of H+ is low whereas there is also a half channel in the cytosol where the pH is low and the concentration of H+ is high.

Fo is a C-ring with Asp acids. One hydrogen will enter the half channel on COO- in the cytosol and then rotate around clockwise. This movement causes a hydrogen to be put into the half channel connected to the high pH and low H+ concentration so it will move to deprotonate and restore COO- for the next protonation from a H+ in the cytosol half channel.

Question 17

Describe how rotary motion generates ATP in the F1 subunit (binding-change
mechanism).

Answer 17

F1 is attached to the C-ring Fo unit which is rotating by way of a stick like structure called gamma. The subunits DO NOT move; only gamma moves.

As gamma moves it switches and determines what conformation the alpha/beta subunits will be in.

The subunits:
-Open (O)–> doesnt bind anything
-Loose (L)–> binds ADP+Pi
-Tight (T)–> binds ATP

Question 18

What is the difference between the glycerol-3-phosphate shuttle and the malate-aspartate shuttle?

Answer 18

Glycerol-3-phosphate is a cycle used by skeletal muscle to ensure NAD+ is regenerated rapidly to use for glycolysis and in exchange it produces less energy. Malate Aspartate shuttle is used by liver and heart muscle to bring electrons into the matrix to form NADH but the process has a lot of steps so it is much slower than glycerol-3-phosphate.

Question 19

What tissues use glycerol-3-phosphate shuttle and why?

Answer 19

Skeletal tissue and because it is quick. Although it does not generate as much energy it is favorable because of how fast it goes to generate NAD+ for glycolysis.

Question 20

What tissues use malate-aspartate shuttle and why?

Answer 20

Heart and liver muscle use this because it generates more energy and in exchange the process goes slower.

Question 21

How is oxidative phosphorylation regulated?

Answer 21

Oxidative phosphorylation is regulated by ADP concentration.

A high ADP/ATP ratio (meaning we want to run oxidative phosphorylation).

It is also regulated by NAD+ and NADH.

A high NADH/NAD+ ratio means lots of NADH to put e- into the system so it will speed up oxidative phosphorylation.

Question 22

Explain how 2,4-dinitrophenol (DNP) functions as a weight loss chemical “poison”.

Answer 22

DNP is essentially a poison because it uncouples the electron transport chain from ATP synthase.

Question 23

Why does DNP have the symptoms of heavy breathing, being very hot and profuse sweating (why do you have so much water to sweat out)?

Answer 23

DNP does not allow hydrogens to flow in the correct way. It brings hydrogens into the matrix instead of out into the cytoplasm. This causes a temperature increase because pumping protons out and producing ATP are exothermic but if those cant happen then heat builds up and causes an increase in body temperature.

The lower ATP levels cause a response from glycolysis and the citric acid cycle to increase production to make ATP but this creates more CO2 (from the citric acid cycle). When the CO2 levels increase, it causes the levels of H2CO3 to increase which makes the blood pH more acidic. Because the blood pH controls the breathing rate (CO2 not O2), this acidic blood pH causes increased breathing rate.

DNP does not affect the ETC so as hydrogens are being pumped out by Complex 1,3, and 4, it causes the ETC to continue to run. This means that electrons are being brought to the final electron carrier O2 which then creates H2O. This influx of water causes an increase in profuse sweating.

Question 24

Which human tissues have the decoupler UCP-1?

Answer 24

Brown adipose tissues have this decoupler because it can be used to generate heat. Babies have this type of tissue for ‘non-shivering thermogenesis’.

-It is brown in color because there are a lot of mitochondria present in this tissue.

Question 25

How does ATP cross the inner mitochondrial membrane?

Answer 25

ATP crosses the inner mitochondrial membrane to be released into the cytoplasm. It uses ATP-ADP translocase to cross the membrane. (Has a -4 charge).

Question 26

How does ADP cross the inner mitochondrial membrane?

Answer 26

ADP crosses the inner mitochondrial membrane to be released in the matrix for use by ATP synthase. It uses ATP-ADP translocase. (Has a -3 charge).

Question 27

How does Pi cross the inner mitochondrial membrane?

Answer 27

Pi uses a phosphate carrier to cross the inner mitochondrial membrane. An OH- gradient powers the movement of Pi into the matrix. The matrix is more basic than the cytosol so there is abundant OH-.