Energy in biosphere

Question 1

High energy chemicals for life produced by resp

Answer 1

ATP, NADH, NADPH

Question 2

How long ago did multicellular life form

Answer 2

1.5 giga years before now

Question 3

What does oxygenic photosynthesis involve

Answer 3

Water splitting

Question 4

How did photosynthesisers colonise the planet

Answer 4

By using water as a source of electrons

Question 5

How did O2 change the planet

Answer 5

1. World became aerobic 2. O2 converted to O3 (ozone) by UV in stratosphere - ozone screens out UV allowing life to come out from under the stones 3. Respiration to O2 evolves - more efficient than fermentation, glycolysis - energy becomes cheaper - multicellular life develops 4. Change in metal ion availability because of redox dependent solubility (Cu1+ insoluble but Cu2+ soluble) 5. Most species killed by O2 b/c it’s toxic

Question 6

Describe stability of O2

Answer 6

Thermodynamically unstable but kinetically stable

Question 7

Describe electron reduction of O2

Answer 7

1e- = thermo unfavourable. 2e- = thermo favourable (but slow and unlikely b/c requires another triplet state/ spin state change)

Question 8

What state is O2 in

Answer 8

Triplet state (2 unpaired electrons) - not as reactive as expected

Question 9

What is the stability of water

Answer 9

Very stable - requires lots of energy to oxidise it

Question 10

What is the most reactive oxygen intermediate

Answer 10

Hydroxyl radical (OH)

Question 11

What is the voltage difference between triplet O2 and singlet O2

Answer 11

Singlet O2 is one volt higher

Question 12

What are the two main enzymes that deal with H20 and O2 redox reactions

Answer 12

PSII and cytochrome oxidase

Question 13

Oxidation

Answer 13

Removal of electrons (associated with proton loss)

Question 14

Reduction

Answer 14

Gain of electrons (associated with proton gain)

Question 15

Redox couple

Answer 15

Reduced and oxidised form of one component in a redox reaction (Fe2+/ Fe3+)

Question 16

Redox potential

Answer 16

Measure of the tendency of redox couple to donate or accept an electron (relative to the standard: hydrogen electrode)

Question 17

Actual redox potential

Answer 17

Redox potential existing under function conditions (non-standard)

Question 18

Redox potentiometry

Answer 18

Measurement of Em values

Question 19

Key features of redox potentiometry

Answer 19

1. Needs to show reversibility 2. Needs anaerobicity to prevent side reactions with O2 3. Needs redox mediators: chemicals that carry e- between electrodes and redox cofactor buried in protein

Question 20

Em value

Answer 20

Conc of oxidised = conc of reduced

Question 21

Delta E

Answer 21

Difference in Eo’ values for the 2 redox couples involved in redox reactions (measurement of Gibbs energy available from reaction)

Question 22

+100 meV in joules

Answer 22

-9.6 kJmole-1

Question 23

What usually accompanies redox reactions

Answer 23

Colour change

Question 24

Positive delta E means..

Answer 24

Negative delta G

Question 25

How are half reactions written

Answer 25

As reductions

Question 26

Delta E

Answer 26

Eo acceptor - Eo donor

Question 27

How much energy does ATP synthesis require

Answer 27

50 kJ/mol

Question 28

Energy 1 H+ in a gradient across a membrane

Answer 28

-20kJ/mol = 200meV

Question 29

How many protons needed to cross membrane for ATP production

Answer 29

At least 2.5

Question 30

How much energy needed per H+ to make the proton gradient

Answer 30

At least 200 meV

Question 31

NADH/ NAD+

Answer 31

n =2, Em = -320mV

Question 32

O2/H20

Answer 32

n = 4, Em = +820mV

Question 33

How many protons can be translocated across the membrane per electron

Answer 33

Approx. 5

Question 34

What translocates protons across the membrane

Answer 34

Complex I, III, IV