lecture 2 - respiration

Question 1

what is the energy balance of cellular respiration?

Answer 1

During the breakdown of food most energy is harvested as electrons in NADH and FADH2 to be subsequently transformed to ATP during oxidative phosphorylation

Question 2

what is NADH used as?

Answer 2

an electron currency

Question 3

what is the redox potential?

Answer 3

The redox potential reflects the different affinity of atoms to incorporate or release electrons into/from their outer shell.

Differences in redox potential provide a source of energy.

Molecules with a negative redox potential have a lot of free energy.

Molecules with a positive redox potential have little free energy.

Relocating electrons from sugars to oxygen via NADH releases energy.

The enzymes in the ETC enable the redox reactions and use the released energy to build a pH gradient.

Question 4

what is the ETC, proton gradient and ATP synthase?

Answer 4

The electrons are delivered to the electron transport chain, which is a series of redox reactions in the inner membrane of the mitochondria. The ETC drives directional movement of protons into the inner membrane space and this pH gradient then drives ATP synthesis in the turbine-like enzyme ATP synthase.

Question 5

what are the most common redox groups?

Answer 5

-flavins
-quinones
-heme group
-iron sulfur clusters

Question 6

what is a mitochondria

Answer 6

versatile and dynamic organelles

Question 7

how is redox chemistry dangerous?

Answer 7

Unpaired electrons (free radicals) are dangerous. They are highly reactive and can destroy other molecules (e.g. DNA). Need to be avoided.

Enzyme complexes in the ETC safeguard the environment from radicals by holding them deep inside their structure.

Question 8

what is the Q cycle?

Answer 8

Electron transfer from reduced ubiquinone (QH2, carrying 2 e-) to cytochrome c (carrying 1 e-) requires a repetitive cycle in which a radical intermediate (semiquinone, Q*-) is held inside the enzyme.

Question 9

what is the sequence of redox complexes in the ETC?

Answer 9

Redox groups are ‘colored’:
they have distinct spectra in the visible light, which differ in the oxidized and reduced states.
By measuring these spectra we can follow the change in redox state of each component.