Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Bioinorganic Chemistry > Lecture 5 > Flashcards

Lecture 5 Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

How is energy y harvested from the sun?

A

Directly - photosynthesis

indirectly - using photosynthesising organisms as fuel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is energy in electrochemical terms?

A

a flow of electrons from fuel to oxidant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Examples of Fuels and Oxidants

A

Fuels - fats, sugars, H2

Oxidants - O2, nitrate and H+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Three types of proteins used to achieve electron flow

A
  • blue copper
  • iron- sulphur
  • cytochromes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do donors affect reduction potential?

A
  • Strong donors stabilise high oxidation states, and lower the reduction potential
  • Weak donors, pi acceptors and protons all stabilise low oxidation states and raise the reduction potential
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What other than donors affects reduction potential?

A
  • relative permittivity
  • media
  • hydrogen bonding interactions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is Marcus Theory?

A
  • explains rate of electron transfer

- the lower the reorganisation energy the faster the reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are Blue copper proteins? Give 2 examples

A
  • Small proteins bound to a single Cu atom and are so called due to their intense blue colour when oxidised
  • plastocyanins used in the photosynthetic pathway between Photosystem 1 and 2
  • Azurin found in bacteria, involved in electron transport between [NO3]- to N2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Structure of plastocyanin and azurin

A
  • Plastocyanin, Three closely bound donors (one Cys and 2 His) and a weaker Met donor
  • Azurin has an additional weak coordination from the Gly O atom
  • in both cases the Cu centre is protected from other molecules by the protien
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Geometry of Blue Copper Proteins

A
  • Rigid B-barrel structure, with fixed Cu coordination geometry
  • Coordination centre suits both Cu (I) and Cu (II) centres so there is rapid electron transfer
  • Bond lengths only increase by 5-10 pm on going from Cu (II) to Cu (I)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Distinctive Characteristics of type on blue copper Proteins

A
  • intense blue colour in the Cu (II) state at 600 nm
  • High but variable reduction potential (0.35 V)
  • EPR with small hyperfine coupling to the Cu nucleus in Cu(II)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What causes Blue Copper proteins intense colour?

A
  • Due to S(Cys) and Cu(II) LMCT

- high intensity means it can’t be a d-d transition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What causes hyperfine coupling?

A
  • Simple Cu(II) complexes have large EPR hyperfine coupling to the Cu (I = 3/2 for 65Cu and 67Cu).
  • Blue copper proteins have smaller coupling since the electron is delocalised onto the Cys S and “spends more time” away from the Cu centre.
  • 40% of the time on the S(Cys) leading to a highly covalent Cu- S(Cys) bond.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Iron-sulphur proteins

A
  • high spin Fe(III) and Fe(II) centres, tetrahedrally coordinated by sulphur ligands
  • classified by how many iron and sulphide atoms they contain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Rubredoxins vs Ferredoxins

A
  • Rubredoxins contain one iron centre

- Ferredoxins contain 2,3,4 iron centres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the biological function of Fe-S proteins?

A
  • essential in electron transfer processes such as photosynthesis and cell respiration
  • In nitrogen fixation
  • Catalytic sites in hydrogenases
17
Q

[1Fe-0S]

A
  • in some types of bacteria
  • contain a high spin Fe coordinated in a distorted tetrahedral fashion to four Cys residues
  • Single e- redox
  • redox potential is sensitive to the conformation of a protein chain
18
Q

[2Fe-2S]

A
  • mammals, plants and bacteria
  • two tetrahedral Fe with bridging S2- ions
  • extra iron centre allows a greater range of reduction potentials
  • negative R.P. means in their reduced form they are good reducing agents
  • e- is localised to one iron centre giving a high spin d6-d5 complex (S= 0.5)
  • In the oxidised form the two high spin d5 Fe atoms antiferromagnetically couple to give a diamagnetic complex (S=0)
19
Q

Rieske protein

A
  • important subset of [2Fe-2S]
  • 2 Cys and 2 His groups
  • carries out electron transfer in the photosynthetic pathway
  • Minor structural change causes change in reduction potential to + 0.29 V
20
Q

[4Fe-4S]

A
  • cubic
  • Fe and S- on alternate corners
  • Fe is often further coordinated by Cys or His
  • e- delocalised over all 4 iron centres
  • minimal bond length change on reduction
  • fast transfer due to low reorganisation energy
21
Q

3 Fe(III).Fe(II) [4Fe-4S]

A
  • Found in High potential protiens
  • used in anaerobic electron transfer
  • in photosynthetic bacteria
22
Q

[3Fe-4S]

A
  • cube with one missing corner
  • spin frustrated when reduced
  • E = +0. 1 to -0.4 V
  • Large range due to many arrangements
23
Q

Model Systems

A
  • hard to make due to redox and polymerisation reactions

- used to study metalloproteins simply

24
Q

Cytochrome structure

A
  • Haem proteins
  • Fe ox/red and low spin
  • 6 coordinate, 4 to Haem and 2 to amino acids
  • axial bonds are amino acids
  • very fast electron transfer
25
Q

Bonding in cytochromes

A
  • T2g non-bonding form a pi-overlap with the pi star anti bonding MO of the porphyrin ring
  • extends d orbitals, enhancing electron transfer and also reducing the distance the electron has to travel
26
Q

Mitochondrial cytochrome c

A
  • mitochondrial inter membrane space where it supplies electrons to cytochromes c oxidase at the end of the respiratory chain
  • the axial ligands are His and Met
  • Met is a neutral, soft donor which stabilises Fe(II) better than Fe(III) giving a high reduction potential of +0.26 V
  • The exposed edge of the porphyrin ring is the likely site for electrons to add or leave
  • Electrostatic interactions are important in allowing the protein to dock with the cytochrome c oxidase enzyme and transfer its electron

Bioinorganic Chemistry (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions