Electron transport and oxidative phosphorylation Flashcards
What is oxidative phosphorylation?
Removal of electron from metabolic metabolic intermediates while simultaneously synthesising ATP from ADP
What is substrate level phosphorylation?
The formation of ATP via direct phosphorylation of ADP
Why does substrate level phosphorylation occur?
Occurs as some reactions have enough free energy to produce ATP directly and don’t require oxygen
Does substrate level phosphorylation require oxygen
NO
Name the reaction that generates all the energy we need for cellular processes?
Te hydrolysis of ATP
Other than providing energy what else does ATP act as?
Acts as a cofactor fro signal transduction reactions using a variety of kinases
What is the normal cellular ATP concentration maintains at
Maintained in the range of 1 to 10 mol/L
State the normal ratio of ATP/ADP
1000
What is the total quantity of ATP in an adult?
0.10 mol/L
Approx how much ATP do we require daily
100 to 150 mol/L of ATP are required daily
How many times a day is ATP recycled?
1000 to 1500 times per day
Where does the majority of respiration occur?
In the mitochondria
What is the mitochondria responsible for?
The generation of more than 95% of ATP
What does ATP stand for
adenosine triphosphate
Other than respiration what else is the mitochondria involved in?
- Intracellular signalling
2 Intracellular calcium regulation - Cellular differentiation and growth
- Cellular death pathways
Name the different structures of a mitochondrion
1. Outer membrane 2 Inner membrane 3. Cristae 4. Matrix 5. Intermembrena space
What is the Matrox pf the mitochondria bound to?
Bound with the intermembrane membrane
How does oxidative phosphorylation begin?
Begins with the electron entering the respiratory chain
The electron needed fro oxidative phosphorylation to start come from where?
They arise from the action of dehydrogenase from catabolic pathways (E.g. glycolysis)
What happens when NADH is oxidised?
Electrons are released
State the chemical equation for the oxidation of NADH
2NADH -> 2NAD+ + 2H+ +4e-
Describe the electrons that form due to the oxidation of NADH
They are high in energy so if the oxidation of NADH was to occur in on step too much energy would be released all at once
How do we overcome the fact that the oxidation of NADH all at once would produce to many high energy electrons?
The high energy electron are passed sequentially from one complex to another to ensure that too much energy is not released at once
What do electrons react with to release energy?
Oxygen
State the chemical equation for the reaction of electrons with oxygen
4e- +4H+ + O2 -> 2H2O
Where is the electron transfer chain found?
At the inner mitochondrial membrane
What makes up the electron transfer chain?
4 complexes found on on the inner mitochondrial membrane
3 carriers
What is the function of the complexes found on the inner mitochondrial membrane
- Their job is to accept electrons to be able to pass energy though the chain
- They use this energy to pump hydrogens into the inter-membrane space
What happens at complex I?
NaDH and FADH2 transfer electrons onto complex I
Energy obtained fro themeless electrons is used to pump out 4 electrons into the inter-membrane space
What does complex II do?
It accepts electrons from NADH and FADH2
The energy from these electrons is used to supercharge complex III
What happens at complex III
Complex III is super charged by complex II and releases 4 protons into the inter-membrane space
What does complex IIII do?
It releases 2 protons into the inter-membrane space
How are the elecron carriers of the electron transfer chain organised?
Organised into membranes
they are embedded supramolecular complexes that can be physically separated
Name the electron carriers present in the electron transfer chain
- Universal carriers NADH and FADH2
- Ubiquinone
- Cytochrome C
Name electron carrier 1
Flavin mononucleotide FMN
What does FMN do?
It oxidises NADH to NAD+ becoming reduced by accepting electron
Name complex I
NADH-Q oxireductase/ dehydrogenase
Describe the structure of FMN
It has a similar structure to FAD but just has a different R group
When does FMN bind to protons
FMN bonds to proton when they are reduced
How can FMN accept electrons
Can accept electrons via the semi-quinone intermediate
Give the chemical formula for the reduced forms of FMN
FMNH2
How is the energy from electrons harnessed in complex I
Harnessed through a series of Fe-S complexes
How does sulphur exist in the electron transport change
Exists in the amino acid cystine
Describe a Fe-S complex with only one iron atom
A single iron atom is tetrahedrally coordinated with 4 cystine-SH groups
Describe the journey of electrons starting at FMNH2 in the complex I
Electrons from FMNH2 cascade down a series of Fe-S complexes via direct transfer
Name electron carrier 3
Co enzyme Q
After the electrons have gone through the Fe-S cascade what needs to be done and how ?
The electrons need to be carried by co enzyme Q
Where is ubiquinone found?
In the inter membrane space of the mitochondria
Describe the structure of ubiquinone
Has a large hyrdrocarbon change attached to a benzene ring
It is uncharged and fully oxidised
What is another name for co enzyme Q?
ubiquinone
Wha is co enzyme Q
It is a hydrophobic quinone that diffuses rapidly within the inter mitochondrial membrane
What forms can ubiquinone be found in?
1, Semiqunione radical which is a semi reduced form
2, Ubiquinol (QH2) which is fully reduced
Summarise what happens in complex I
Complex I catalyses 2 simultaneous couples processes;
- The exorgonic transfer of hydride ion from NADH and a proton from the matrix (NADH + H+ +Q -> NAD+ +QH2)
- The exergonic transfer of 4 protons from the matrix into the inter membrane space
What is complex II called?
Succinate dehydrogenase
Describe Complex II
It is a membrane bound enzyme in the citric acid cycle
What does complex II contain?
- 2 Fe-2S centres
- A bound FAD
- Binding sire for the substrate succinate
In complex II how far do electrons have to travel from the succinate binding site to Q?
40A
Name Complex III
Cytochrome bc1
Wha does cytochrome bc do?
It couples the transfer of electrons from ubiquinol to cytochrome c with the transport of H+ from the matrix to the inner inter membrane space
State the overall chemical equation for the Q cycle
QH2 + 2cyrochrome C +2H -> Q + 2reduced cytochrome c + 4H+
What is complex 4 made up of?
2 heme groups and 2 copper centres
What is complex IV called?
Cytochrome c Oxidase
What happens at complex IV?
- The first copper centre accepts electrons from reduces cytochrome c and reduces he second copper centre
- A second reduced cytochrome c reduces the iron in
the second heme - This iron centre binds with oxygen. to form peroxide from the transfer of 2 electrons
- The bound oxygen bridges the iron and copper
- The third cytochrome c dumps ad electron which cleavers the O-O bond and takes a proton
- A 4th cytochrome c dumps an electron to facilitate the reduction of iron
- 2 protons are taken up allowing 2H2Os to be released
Summarise the electron transport chain
It is basically harnessing high energy electrons and then pushing them onto oxygen
Which molecule carries out the synthesis of ATP?
ATP synthase
Name the hypothesis that explains how ATP synthase makes ATP
chemiosmotic hypothesis
Talk through the chemiosmotic hypothesis
- Protons are pumped into the inte rmembreane space making it positively charged
- This creates an electric field with the mitochondrial matrix being negatively charged
- This gradient gives us the proton motive force
State the equation for the proton motive force
Proton motion force=
Chemical gradient + Charge gradient
