Lecture 23 Flashcards
standard reduction potential
- a measure of electron affinity (Eº)
- hydrogen electrode is used as a standard
- electrons can flow towards or away from reference cell
Postive Eº
- electrons flow from reference cell to wards the test cell
Negative Eº
- electrons flow from test cell towards the reference cell
the more negative a redox potential is the …
- 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
when electrons are passed down the ETC
the reduction potential increases with each transfarr
how to calculate E
G = -nFE
- n= number of electrons transferred
- F = faradays constant (96.5)
how do you know if a reaction is spontaneous
- G is negative and E is positive
What role do metals play
- 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
photosynthesis
- 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
chloroplasts
- specialized intracellular organelles where photosynthesis takes place
thylakoid membrane
- folds to form flattened sacs known as thylakoid which contain internal space known as the thylakoid space
- thylakoids can be stacked into grand
describe stage 1 and stage 2 of photosynthesis
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
chlorophyll
- 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
phtosystem
- 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
antenna complexes
- 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
What is charge separated state
- the special pair becomes positively charges while the electron carrier become negatively charges
What 2 systems does photosynthesis rely on
- photosystem 1 and 1
- they work together to produce products that will be used in stage 2 of photosynthesis
photosystem II
- 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
Photosystem I
- photosytem I absorbs light energy and transfers electrons to ferredoxin
- ferredoxin NADP reductase oxidized ferredoxin and reduces NADP+ to form NADPH in the stroma
In both photosystems I and II how do you obtain an electron to replace the special pair electron
- Photosystem II: from water
- photosystem I: from photosystem II
How does photosystem II replace the electron by using water
- 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
How does photosystem I replace the electron by photosystem II
- 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
