Lecture 23

Question 1

standard reduction potential

Answer 1

• a measure of electron affinity (Eº)
• hydrogen electrode is used as a standard
• electrons can flow towards or away from reference cell

Question 2

Postive Eº

Answer 2

• electrons flow from reference cell to wards the test cell

Question 3

Negative Eº

Answer 3

• electrons flow from test cell towards the reference cell

Question 5

the more negative a redox potential is the …

Answer 5

• lower electron affinity it has (it is more likely to transfer electrons to something else)
• NADH is a good electron donor and O2 is a good electron acceptor

Question 6

when electrons are passed down the ETC

Answer 6

the reduction potential increases with each transfarr

Question 7

how to calculate E

Answer 7

G = -nFE
- n= number of electrons transferred
- F = faradays constant (96.5)

Question 8

how do you know if a reaction is spontaneous

Answer 8

• G is negative and E is positive

Question 9

What role do metals play

Answer 9

• metals are often found bound to a protein and function as an electron carrier
• Example: NADH dehydrogenase (complex 1) contains iron sulfur centres
  Example: cytochromes have iron containing heme group

Question 10

photosynthesis

Answer 10

• light driven reaction that creates organic molecules from atmospheric carbon dioxide.
• requires water and releases O2
• O2 produced made aerobic respiration widespread
• carried out in chloroplast

Question 11

chloroplasts

Answer 11

• specialized intracellular organelles where photosynthesis takes place

Question 12

thylakoid membrane

Answer 12

• folds to form flattened sacs known as thylakoid which contain internal space known as the thylakoid space
• thylakoids can be stacked into grand

Question 13

describe stage 1 and stage 2 of photosynthesis

Answer 13

stage 1 (light energy): protons are pumps into the thylakoid space driving the synthesis of atp
- NADP+ is reduced to NADHP
- light energy is required

stage 2 (dark reactions): ATP and NADPH are consumed to drive the manufacture of sugars from CO2

Question 14

chlorophyll

Answer 14

• light capturing pigments
• absorbs green light poorly because light is absorbed by electrons by porphyrin ring in blue
• contains a hydrophobic tail which holds the chlorophyll in the thylakoid membrane

Question 15

phtosystem

Answer 15

• is a multi protein complex containing chlorophyl that captures light energy and converts it into chemical energy
• contains a set of antenna complexes and a reaction centre

Question 16

antenna complexes

Answer 16

• contain chlorophyl that captures light energy and randomly transfer it from one chlorophyll to the next
• then the energy is eventually accepted by a chlorophyll dimer known as a special pari which is found within a reaction centre
• the special pair hold its electrons at a lower energy level than other chlorophyll molecule

Question 17

What is charge separated state

Answer 17

• the special pair becomes positively charges while the electron carrier become negatively charges

Question 18

What 2 systems does photosynthesis rely on

Answer 18

• photosystem 1 and 1
• they work together to produce products that will be used in stage 2 of photosynthesis

Question 19

photosystem II

Answer 19

• photosystem II absorbs light energy and transfers electron to platoquinone
• plastoquinone transfers its electron to a proton pump, pumping its electrons from the stroma to the thylakoid membrane generating a proton gradient
• the gradient is used to drive the synthesis of ATP by ATP synthase in the stroma

Question 20

Photosystem I

Answer 20

• photosytem I absorbs light energy and transfers electrons to ferredoxin
• ferredoxin NADP reductase oxidized ferredoxin and reduces NADP+ to form NADPH in the stroma

Question 21

In both photosystems I and II how do you obtain an electron to replace the special pair electron

Answer 21

• Photosystem II: from water
• photosystem I: from photosystem II

Question 22

How does photosystem II replace the electron by using water

Answer 22

• its uses a water-splitting molecule
• four electrons are removed from two water molecules and transferred and replaced electrons lost by four special pairs
• O2 was released
• important to make sure no partially oxidized water molecule is released

Question 23

How does photosystem I replace the electron by photosystem II

Answer 23

• the missing electron in photosystem I is re placed by an electron from photosystem II
• electrons are passed from cytochrome b6-7 complex to plastocyanin which replaces lost electrons from the special pair in photosystem I