Cellular Respiration Flashcards
Describe the structure of the mitochondria
double membrane
inner membrane folds = cristae
matrix with small circular pieces of mitochondrial DNA
contains over 1000 different types of proteins
What are cristae? What purpose do they serve?
the inner membrane folds of the mitochondria expand the surface area
What is located in the matrix of the mitochondria?
small, circular pieces of mitochondrial DNA
How many proteins are found in the mitochondria?
over a thousand
What proteins does the mitochondrial matrix contain?
free enzymes that function in metabolic pathways (ex. pyruvate oxidation to acetyl-CoA, the CAC, the beta-oxidation of fatty acids)
What do the proteins in the inner mitochondrial membrane and cristae do?
enzymes are embedded there for the ETC and oxidative phosphorylation
What is the typical size of a mitochondria?
0.5-1 um
T or F: mitochondria are static and do not change shape or move
false! they are very dynamic
always moving, changing shape and size
how do mitochondria divide and fuse in relation to the cell they are located in?
independently
What process of cell division is mitochondrial division similar to?
binary fission
What form of mitochondria do some developing cells have?
tubular networks of mitochondria
What kind of cells have restricted space for mitochondria?
muscle fibres
sperm
What are mitochondria often associated with? what does this help with?
often associated with the cytoskeleton to determine their orientation and distribution in different cell types
motor proteins can help them travel up and down microtubules
What is a major distinction between the inner and outer mitochondrial membranes?
inner: selectively permeable membrane which many things require a transporter to pass through
outer: freely permeable to small molecules and some small proteins
What is the IMM most similar to?
bacterial plasma membrane
What is the OMM most similar to?
a membrane that lines the cell walls of some gram negative bacteria
What allows the OMM to be freely permeable?
its wide channels (porins)
What is the protein to lipid ratio of the IMM?
3: 1 protein: lipid
Why are there so many proteins in the IMM?
they are critical for cellular respiration and signalling
What major membrane component does the IMM not contain?
cholesterol
What is cardiolipin? Which mitochondrial membrane contains this and in what quantity?
a unique bacterial membrane phospholipid
inner membrane contains a large quantity
How many proteins are synthesized in the mitochondria? What synthesizes it?
13
its own DNA and its own ribosomes synthesize these
How and where are the other proteins for the mitochondria synthesized?
coded for in nuclear DNA
synthesized on cytosolic ribosomes
imported post-translation with a mitochondrial signal sequence
How do most proteins synthesized outside of the mitochondria enter the mitochondria?
they are translocated across both membranes by translocases
What does TOM stand for?
Translocase of the Outer Membrane
What does TIM stand for?
Translocase of the Inner Membrane
What do both TIM and TOM contain?
receptors that recognize and bind proteins as well as a translocation channel to move those proteins across the given membrane
How are new porins embedded within the OMM?
porins enter the intermembrane space through a TOM complex
chaperones in the IMM space prevent porins from aggregating there
the unfolded porin binds to a SAM complex which inserts them into the OMM and helps them fold properly
How do porins enter the intermembrane space?
through a TOM complex
What prevents porins from aggregating in the intermembrane space?
chaperones in the intermembrane space prevent porins from aggregating
What do the unfolded proteins bind to in the intermembrane space?
the SAM complex
What does the SAM complex do with the unfolded proteins that bind to them from the intermembrane space?
it inserts them into the OMM while helping them fold properly
How many different TIM channels are there in the IMM? What are they?
2
TIM22
TIM23
What is TIM22 for? Where is it located?
for inner membrane proteins
embedded in the IMM
What is TIM23 for? where is it located?
in the IMM
mostly for mitochondrial matrix proteins to pass through the IMM into the matrix
What is the targeting peptide that allows inner membrane proteins to move into the mitochondria?
an internal hydrophobic amino acid sequence
How does TIM22 function?
it opens laterally to anchor proteins in the IMM
What is the targeting peptide for TIM23?
an N-terminal positively charged amino acid sequence
How does TIM23 function?
mitochondrial chaperones aid the entry and folding while a matrix signal peptidase cleaves off the targeting sequence
What cleaves off the N-terminal positively charged amino acid sequence on mitochondrial matrix proteins using TIM23 to enter the mitochondria matrix?
signal peptidase
Where must a protein first translocate through to get to either TIM?
through TOM on the OMM
What two routes can integral proteins destined to be embedded in the IMM arrive at the IMM?
through TIM22 or TIM23
How does an integral protein destined for being embedded in the IMM moved through TIM23?
the same way a matrix protein does, but it will be inserted into the IMM by an OXA complex
What kind of integral membrane protein can move through TIM22?
a multi-pass integral membrane
Describe the steps of integral membrane proteins being embedded in the IMM via TIM22
- they enter the intermembrane space through TOM
- when in the intermembrane space they are bound by chaperones which take them to TIM22
- TIM22 recognizes the internal hydrophobic amino acid sequence in the protein
- TIM22 opens laterally to anchor the proteins in the IMM
Why is the hydrophobic amino acid sequence of multi-pass integral membranes not cleaved off once the protein is in the inner membrane?
because it’s in the middle of the protein so cleaving it would cut the protein in half
T or F: integral membrane proteins that enter through TIM23 use the same mechanism as the matrix proteins to enter the matrix
true
What happens to the integral membrane proteins once they reach the matrix?
their N-terminal signal sequence is cleaved to expose a second N-terminal hydrophobic signal sequence which targets them to the OXA complex
How are integral membrane proteins that enter through TIM23 targeted to the OXA complex?
when they enter the matrix, their N-terminal signal sequence is cleaved to expose their second N-terminal hydrophobic signal sequence which targets them to OXA
What is the function of the OXA complex?
it inserts the integral membrane protein which entered the matrix via TIM23 into the IMM
it also inserts membrane proteins that are synthesized on mitochondrial ribosomes
T or F: OXA only inserts integral membranes into the IMM that entered via TIM23
False. OXA also inserts integral membrane proteins that were synthesized on mitochondrial ribosomes
Which complexes are used when a porin needs to be embedded in the OMM?
TOM and SAM
Which complexes are used when a protein needs to be translocated to the matrix?
TOM and TIM23 (both are passed through together)
Which complexes are used when a multi-pass integral membrane protein from a nuclear gene needs to be embedded in the IMM?
TOM and TIM22 (carried between them in the IMS by chaperones)
Which complexes are used when a single pass integral membrane protein from a nuclear gene needs to be embedded in the IMM?
TOM and TIM23 (pass through both together) to get into the matrix and then a second signal to direct it to OXA
so TOM, TIM23, and OXA
Which complexes are used when a protein from a mitochondrial gene needs to be embedded in the IMM?
OXA
What does it mean to oxidize a sugar?
to REMOVE electrons from it
What’s a useful way to think of electrons in the context of cellular respiration?
as little packets of energy that can eventually be used to build ATP molecules
What is the goal of cellular respiration?
to remove as many electrons as possible from a sugar until the most oxidized/depleted remnant is left: CO2
Where do the electrons end up after they’ve been used to make ATP?
O2 which is converted into H2O
What is the overall reaction of cellular respiration?
C6H12O6 (glucose) + 6 O2 –> 6 CO2 + 6 H2O + ATP
What is the waste product of cellular respiration?
CO2
What does it mean to reduce something?
to add electrons
As each pair of electrons is stripped off a sugar, what temporarily holds them?
electron carrier molecules
Where do the carrier molecules eventually pass off the electrons to?
the ETC
T or F: electrons (And thus energy) is removed from sugars in one step
false!! it is done in small steps otherwise energy is not useful to a cell
How are electrons given to carrier molecules and eventually used to make ATP?
by extracting electrons (and thus energy) from sugar in small steps
When a carrier lacks the electrons from sugar, it is in the ____ form?
oxidized
When a carrier receives the electrons from sugar, it is in the _____ form
reduced
When a carrier donates the electrons to the ETC, it will be in the ____ form
oxidized
What else is pulled off when an electron is pulled off a sugar?
a hydrogen
Does the oxidized carrier have more or less hydrogens than the reduced carrier?
less hydrogens than the reduced carrier
Is NAD+ oxidized or reduced?
oxidized
Is NADH + H+ oxidized or reduced?
reduced
Is FAD+ oxidized or reduced?
oxidized
Is FADH2 oxidized or reduced?
reduced
What are the 3 metabolic activities?
glycolysis + fermentation
pyruvate decarboxylation + citric acid cycle
ETC/chemiosmosis
Where does glycolysis or fermentation occur?
in the cytosol
Where does pyruvate decarboxylation + the CAC occur?
in the mitochondrial matrix
Where does the ETC/chemiosmosis occur?
on the inner mitochondrial membrane
T or F: glycolysis and fermentation produce only a little ATP
true
T or F: glycolysis and fermentation can be done without oxygen
true
What process takes all the glucose carbons and releases them as individual CO2 molecules, fully oxidizing the sugar?
pyruvate decarboxylation to acetyl CoA and the CAC
What produces the proton gradient that produces ATP?
the ETC / chemiosmosis taking electrons from sugar
What is substrate-level phosphorylation?
the small amount of ATP produced by glycolysis and the CAC
How is most of the ATP generated in cellular respiration?
by oxidative phosphorylation
What are the 2 stages of oxidative phosphorylation?
the ETC uses energy from electrons to pump H+ into the intermembrane space
chemiosmosis uses ATP Synthase (F-type pump) in the IMM to move H+ back into the matrix while synthesizing ATP on the matrix side
How does chemiosmosis use ATP synthase?
uses ATP synthase in the IMM to move H+ back into the matrix while synthesizing ATP on the matrix side
What is the basic reaction in glycolysis?
glucose (6C) –> 2 pyruvate (3C each)
What are the 2 stages of glycolysis?
energy input stage
energy payoff stage
What does the energy input stage of glycolysis require?
ATP hydrolysis at 2 distinct steps
How many carbons are in glucose?
6
In the energy input phase, what does glycolysis convert glucose into?
6C glucose is converted into 2 identical 3C molecules called glyceraldehyde-3-phosphate
Why is it called the energy input phase?
because 2 ATPs need to be hydrolyzed for glycolysis to split glucose into 2 glyceraldehyde-3-phosphate molecules
In the energy payoff stage of glycolysis, what are the 2 glyceraldehyde-3-phosphates converted into?
Each glyceraldehyde-3-phosphate is converted into a pyruvate molecule
How many carbons does a single glyceraldehyde-3-phosphate have?
3
How many carbons does a single pyruvate molecule have?
3
During the energy payoff phase of glycolysis, how is ATP made?
by substrate-level phosphorylation
How much ATP and NADH is made for every 2 glyceraldehyde-3-phosphates (one glucose)?
4 ATP total
2 NADH
How many glyceraldehyde-3-phosphates and pyruvates are made per glucose molecule?
2 of each
Which electron carrier is produced in the energy payoff phase of glycolysis? Is it reduced or oxidized? How many are produced per G3P?
1 reduced electron carrier, NADH per G3P = total 2 per glucose
What is the reaction that reduces NAD+ to NADH?
NAD+ + 2e- + 2H+ = NADH + H+
T or F: CO2 is produced in glycolysis
FALSE FALSE FALSE
What are the NET products of glycolysis per glucose?
2 pyruvate + 2 H2O
2 ATP
2 NADH + 2H+
Why are only 2 ATP molecules produced per glucose molecule as a net product of glycolysis when 4 are produced during the energy payoff phase?
because the energy input phase requires the hydrolysis of 2 ATP per glucose molecule so
4 produced - 2 used = 2 net
At the end of glycolysis, are any carbons fully oxidized?
no
Where is most of the starting chemical energy of glucose stored after glycolysis?
in the 2 pyruvate molecules
Where is some of the chemical energy extracted during glycolysis?
when 2 NADH were produced
what is a key step in glycolysis?
fructose-6-phosphate getting a second phosphate to make fructose 1,6-bisphosphate
What helps in the phosphorylation of fructose-6-phosphate?
the enzyme phosphofructokinase converts fructose-6-phosphate into fructose 1,6-bisphosphate
Why is the phosphorylation of fructose-6-phosphate a key step in glycolysis?
because once it occurs, the carbons are irreversibly committed to glycolysis
Why is phosphofructokinase’s activity heavily regulated?
because once it phosphorylates fructose-6-phosphate, the carbons are committed to glycolysis
What are the basic steps of glycolysis?
- starts with one molecule of glucose
- molecules of ATP hydrolyzed
- fructose-6-phosphate is phosphorylated by fructophosphokinase
- glucose (6C) is cleaved into 2 molecules of G3P (3C)
- 4 ATP + 2 NADH produced
- 2 molecules of pyruvate (3C)
What is the basic reaction of pyruvate decarboxylation?
pyruvate –> acetyl-CoA + CO2
What happens to each pyruvate molecule if oxygen is present?
the pyruvate molecule crosses the outer mitochondrial membrane through the non-selective porin channels and the inner mitochondrial membrane through a transporter into the matrix
What are the 3 basic steps of pyruvate oxidative decarboxylation? Where do these occur?
in the mitochondrial matrix:
- pyruvate is broken into CO2 + acetate
- NAD+ is reduced to NADH
- acetate group is linked to Coenzyme A = Acetyl-CoA
What is each pyruvate broken down into?
CO2 + an acetate
What is coenzyme A?
a large molecule that includes an adenine base, ribose sugar, some phosphates, and a thioester functional group
What is the function of Coenzyme A?
it activates or primes the acetate group so that it can jump into the citric acid cycle
What happens to CoA after it helps the acetate group enter the CAC?
CoA is recycled
What is the overall reaction that occurs in the citric acid cycle?
Acetyl CoA –> 2 CO2
How many carbons are in acetyl-CoA?
2
How does acetyl-CoA enter the citric acid cycle?
it joins with oxaloacetate (4C) and CoA is removed
How many carbons does oxaloacetate have?
4
What is the product of oxaloacetate + acetyl-CoA?
the 6C citrate/citric acid
How many carbons does citrate/citric acid have?
6
Why is the citric acid cycle called a cycle?
because citrate is reconverted into oxaloacetate (ie., oxaloacetate is regenerated)
then a new acetyl-CoA can combine with oxaloacetate and enter the CAC
How many turns of the CAC occur per glucose? why?
2 turns because there’s 2 pyruvates per glucose and only one can enter at a time
What are the products of the CAC per turn?
2x CO2
3x NADH
FADH2
ATP (substrate level phosphorylation)
Why do 2 CO2s need to be produced for every turn of the CAC?
because citrate is 6 carbons and needs to be converted back into the 4C oxaloacetate so 2 carbons need to be released as CO2
What reactions does the cycle from citrate back to oxaloacetate include?
2 decarboxylations producing 2 CO2s
3 reductions of NAD+ to NADH
1 reduction of FAD to FADH2
1 addition of Pi to ADP to make ATP by substrate level phosphorylation
How is ATP produced in the CAC?
by substrate level phosphorylation when Pi is added to ADP
What has happened to all 6 of the carbons in the glucose by the end of 2 turns of the CAC?
they have all been fully oxidized to CO2
what’s another name for the CAC?
the Krebs cycle
How many pairs of electrons are given to the ETC from each cycle of the CAC? What carries these electrons to the ETC?
each cycle gives 4 pairs of electrons
3 carried by NADH
1 carried by FADH2
How many electrons are carried to the ETC from the CAC per molecule of glucose?
since one molecule of glucose requires two turns of the CAC,
there’s 6 NADH and 2 FADH2
How many electrons are ACTUALLY taken to the ETC from CAC, glycolysis and pyruvate decarboxylation?
glycolysis provides 2 NADH total
pyruvate decarboxylation provides 1 NADH per pyruvate = total 2 NADH
6 NADH from CAC per glucose
2 FADH2 from CAC per glucose
TOTAL = 10 NADH + 2 FADH2 PER GLUCOSE ENTER THE ETC
How many ATP molecules are given to the ETC from CAC and glycolysis (aka by substrate level phosphorylation)?
per glucose:
2 ATP from CAC + 2 ATP in glycolysis
= 4 ATP
How are the ATPs produced in the CAC and glycolysis made?
by substrate level phosphorylation
What are the two electron carriers that donate their electrons to the ETC? What happens to them once they donate their electrons?
reduced NADH and FADH2
they become re-oxidized NAD+ and FAD
What is the ETC?
Electron Transport Chain
a series of integral membrane protein complexes in the inner mitochondrial membrane
What are the integral membrane protein complexes of the ETC made of?
a collection of proteins and prosthetic groups tightly bound to them
What are prosthetic groups?
chemicals that are tightly bound to the collection of proteins that together make up an integral membrane complex in the ETC
What do prosthetic groups also carry?
electrons
What is a reduction potential?
the tendency to accept an electron and be reduced
How are the complexes of the ETC arranged in the IMM?
so that electrons will move from complexes with low reduction potential to complexes with high reduction potential
What would it mean for a complex to have a high reduction potential?
it has a higher tendency to accept electrons and wants to be more reduced
Where are most electron carriers of the ETC embedded?
in one of the four protein complexes
T or F: all the electron carriers within the ETC are embedded in one of the four protein complexes
false, some are mobile in them membrane and not embedded
Describe how electrons are moved through the ETC
they are passed from electron carrier to electron carrier with progressively higher reduction potentials until they are given to the terminal electron acceptor, O2
What is the terminal electron acceptor in the ETC? why is it the terminal one?
O2 because it has the highest reduction potential
What are the 5 types of electron carriers in the ETC?
flavoproteins
cytochromes
copper proteins
iron-sulfur proteins
ubiquinone
What are flavoproteins?
polypeptides bound to FAD or FMN (derivatives of vitamin B12)
a type of electron carrier
what are cytochromes?
proteins with bound heme groups, each has either Fe or Cu metal ions
a type of e- carrier
What are copper proteins?
a single protein complex that contains 3 copper atoms
alternates between Cu2+ and Cu3+
a type of e- carrier
What are iron-sulfur proteins?
proteins that contain iron atoms linked to the sulfur groups of cysteine residues
electron carriers
What is ubiquinone?
aka coenzyme Q
a lipid-soluble molecule that functions as a e- carrier
What is another name for ubiquinone?
coenzyme Q
What is the difference between the oxidized and reduced form of flavoproteins?
2 electrons and 2 H+
oxidized form has 2 e- + 2 H+ less
reduced has 2 e- + 2 H+ more
What is the difference between the oxidized and reduced forms of cytochromes?
the central iron ion is altered
1 e- removed = Fe3+ (oxidized)
1 e- added = Fe2+ (reduced)
Which cytochrome is not fixed within a protein complex?
cytochrome c
What does cytochrome c do?
it associates with the outer surface of the IMM through electrostatic interactions so that it can shuttle electrons between 2 protein complexes
How are the irons and sulfurs arranged in the iron-sulfur proteins? How are these e- carriers oxidized or reduced?
irons are linked to the sulfur atoms of the cysteine amino acids of the protein
the iron-sulfur (Fe-S) proteins accept and donate a SINGLE electron
How many electrons are accepted or donated by flavoproteins?
2
How many electrons are accepted or donated by cytochromes?
1 (by heme)
How many electrons are accepted or donated by Fe-S proteins?
1 by the iron atom
T or F: ubiquinone is a protein
FALSE, it’s a lipid-soluble molecule
What happens to ubiquinone when it is reduced?
it becomes even more lipid-soluble
What is the difference between the reduced and oxidized version of ubiquinone?
2 e- and 2H+
ubiquinone = oxidized
ubiquinol = reduced
How many electrons and protons does ubiquinone/ubiquinol donate or accept?
2 e- and 2 H+
How can ubiquinone be abbreviated when it is fully oxidized?
Q
How can ubiquinol be abbreviated when it’s fully reduced?
QH2
Is ubiquinone/ubiquinol embedded in the membrane or is it mobile?
it is mobile
Which two electron carriers are not embedded in protein complexes of the ETC?
coenzyme Q (ubiquinone) and cytochrome c
How does ubiquinone/ubiquinol move through the membrane to shuttle e- between complexes?
laterally in the membrane with its hydrophobic tail
Which electron carriers are embedded in protein complexes of the ETC?
flavoproteins
cytochromes (except C)
copper proteins
Fe-S proteins
Outline the basic steps of electron movement through the ETC
- entry of electrons into Complex I (NADH) or Complex II (FADH2)
- electrons passed to Coenzyme Q pool
- electrons moved to complex III
- electrons moved through intermembrane space by cytochrome c
- cytochrome c brings electrons to Complex IV
- from Complex IV, electrons added to O2 to form H2O
Is the passage of electrons from carrier to carrier exergonic or endogonic? why? What type of Gibbs free energy is this?
exergonic because energy is being released
negative gibbs free energy
How does the released energy from the electron transfer in the ETC relate to H+ concentration gradient?
the energy released by the electron transfer is used to drive protons against their concentration gradient from the matrix into the intermembrane space
What direction on their concentration gradient are protons moved and from where to where?
against their concentration gradient from the mito matrix to the intermembrane space
How is the release of energy along the ETC coupled with the movement of protons?
some of the proteins in the ETC complex are related to the Na+/H+ antiporters that move H+ against its gradient
the energy released from the ETC (exergonic) is used to move protons against their conc. gradient (endergonic)
Describe complex I
it is the largest (45 sub units)
contains FMN (flavoprotein) and Fe-S clusters
accepts electrons from NADH
Which electron carrier does complex I accept electrons from?
NADH
Where does the energy from the transfer of electrons from NADH to Complex I go?
it moves 4 H+ from the matrix into the intermembrane space
Which electron carrier does Complex II accept e- from?
FADH2
Describe complex II
contains FAD/FADH2 because it is also an enzyme in the CAC
also contains an Fe-S cluster
it completes the CAC step that produces FADH2 making it so the reduced carrier doesn’t have to travel anywhere
T or F: Complex II does not transport protons
true
Where do electrons go from Complex I or Complex II? How many electrons move?
Ubiquinone accepts 2 electrons from either complex and becomes ubiquinol (QH2)
How are electrons transferred from ubiquinol to complex III?
ubiquinol is mobile so it moves electrons laterally to complex III
WHat happens when ubiquinol donates the electrons to complex III?
it is re-oxidized to ubiquinone and returns back to complex I or complex II
What role does complex III play in the transfer of electrons from QH2 to cytochrome c?
complex III catalyzes the transfer of electrons between QH2 to cytochrome c (the electrons move from QH2 to the e- carriers in complex III then to cytochrome c)
Describe complex III
contains cytochromes and an Fe-S complex
how many electrons can cytochrome c pick up at a time?
1
What does the energy from the electron transfer from complex III to cytochrome c produce?
the movement of 4 H+ from the mito matrix to the intermembrane space
What role does complex IV play in the transfer of electrons from cytochrome c to oxygen?
it catalyzes the transfer (the e- move from cytochrome c to the electron carriers in complex IV to the O2)
Which electron carriers are found in complex IV?
cytochromes and copper proteins
What does the energy created from transferring electrons from cytochrome c to oxygen produce?
the movement of 2 H+ from the matrix to the intermembrane space
What is formed when cytochrome c passes electrons to oxygen?
water
What is the equation for forming water?
1/2 O2 + 2e- + 2H+ –> H2O
OR
O2 + 4e- + 4H+ –> 2 H2O
What is the proton motive force (PMF)?
the gradient of protons built up by the ETC as a source of energy
what does the PMF power?
the synthesis of ATP from ADP + Pi
What is chemiosmosis?
the process of producing ATP from a chemical gradient (the PMF)
What is oxidative phosphorylation?
ETC + chemiosmosis
What are the 2 components of the PMF?
charge and pH
What does the relative contribution of the charge and pH on the PMF depend on?
the permeability properties of the IMM
In mammals, how much of the PMF is from charge? from pH?
80% from charge
20% from pH
Once the gradient is established, what are the conditions like on the matrix side vs the intermembrane space?
intermembrane: low pH (high H+ concentration), positively charged
matrix: high pH (low H+ concentration), negatively charged
Describe the structure of ATP synthase
a multi-subunit complex consisting of 2 major structures:
F1 spheres and F0 channels
the spheres are connected to the channels by 2 stalks
What are the 2 stalks of ATP synthase?
a central stalk that rotates
a peripheral stalk that’s fixed and connects F1 and FO
Which of the ATP synthase stalks rotates?
central stalk
Which of the stalks of ATP synthase is fixed and connects F1 and FO?
peripheral stalk
In ATP synthase, how are the spheres connected to the channels?
by the two stalks: central + peripheral
Which domain of ATP synthase is catalytic (where ATP is synthesized)
the F1 sphere is where ATP is synthesized
What are the F1 subunits?
3x alpha 3x beta 1 gamma 1 delta 1 epsilon
Where are the catalytic sites on the F1 sphere of ATP Synthase?
on the 3 beta subunits
Where are the alpha subunits of the F1 sphere of ATP Synthase located?
in alternation with the beta subunits
Where is the gamma subunit of the F1 sphere of ATP Synthase located?
it is the central stalk
What is the delta subunit on the F1 sphere of ATP synthase?
it helps form the peripheral stalk
What is the purpose of the FO channel of ATP synthase?
it allows protons through to power ATP synthesis
What are the subunits of the FO channel of ATP synthase?
1a
2b
10-14c
What do the b subunits of FO channels of ATP synthase do?
they help make the peripheral stalk (with the delta subunit from the F1 sphere)
Describe the a subunit of the FO channel of ATP synthase
it contains the pore which is divided in half into the entry and exit channels (where H+ comes in and out)
Describe the 10-14c subunits of the FO channels in ATP synthase?
they form a ring in the IMM which rotates to move H+ through to the exit pore
How and where do ATP synthases exist?
as complexes in the mito cristae
Where is the ETC located? How does this support ATP synthase in its production of ATP?
ATP synthase is located in the cristae and the ETC is located nearby in the IMM so the protons that leave the ETC are nearby ATP synthase
Describe the movement of H+ protons through the subunits of the FO channel
a proton enters a half-channel in the a subunit on the IMS side
the proton binds to one of the c subunits in the ring and travels nearly 360 degrees as the c wheel spins to reach the exit half channel
the proton exits through the half channel into the matrix
Is the movement of H+ protons passive or active?
passive, they move down their gradients
What drives the rotation of the central gamma stalk?
the rotation of the c subunit ring
What drives ATP synthesis?
the gamma subunit of the stalk interacts with the beta subunits
What happens to the electrical energy of the proton gradient when the stalk rotates?
the energy becomes mechanical energy in the rotation of the stalk
How much ATP is produced per beta subunit? How much total?
1 360 degree turn of the gamma subunit results in 1 ATP per beta subunit
there’s 3 beta subunits in the F1 sphere, so total of 3 ATP produced
What happens as the gamma subunit rotates?
it makes contact with each different beta which induces a conformational change in each
Where is the gamma subunit relative to the alpha and beta subunits?
it projects into the central cavity between alpha and beta subunits
What determines the conformation of the beta subunits?
contact with the gamma subunit as gamma rotates
How many conformations does each beta subunit have?
3
how does each beta subunit move through the 3 conformations?
sequentially
What are the 3 conformations of beta? What is the difference between them
open
loose
tight
they each have different affinities for substrate and product
Describe the open conformation of beta subunit
there’s some affinity for ADP + Pi, low affinity for ATP (releases ATP)
Describe the loose conformation of beta subunit
high affinity for ADP + Pi (cannot be released)
Describe the tight conformation of beta subunit
spontaneous ATP formation occurs here
T or F: at any given time, more than one beta can be in the same conformation
FALSE, the 3 betas will always be in a different conformation to each other
How do the beta subunits move through their conformations?
sequentially and staggered to one another (ie., one will be tight, one will be open, one will be loose)
If a beta subunit currently has tight conformation, what will the following conformations be?
tight –> open –> loose
If a beta subunit currently has open conformation, what will the following conformations be?
open –> loose –> tight
If a beta subunit currently has loose conformation, what will the following conformations be?
loose –> tight –> open
Briefly outline the steps involved in ATP Synthesis
- proton from IMS enters ‘a’ subunit entry half channel
- proton binds to one c ring subunit
- c ring rotates and proton moves almost one full rotation and the energy in the proton gradient is converted into mechanical energy
- proton leaves subunit exit half channel into the matrix (down its gradient)
- gamma stalk is rotating with the c ring, meeting a new catalytic beta subunit every 120 degrees
- beta conformations are staggered
- each beta subunit forms a new ATP per rotation as it encounters the tight conformation
- 3 ATP formed per H+ and gamma stalk rotating 360 degrees
Which conformation of beta is ATP produced in?
tight
What does the entire process of cellular respiration (except for ATP synthase + generation of ATP) require?
an impermeable IMM
Describe uncoupling and what is does
uncoupling proteins can move protons across the IMM without going through ATP synthase which uncouples glucose oxidation and oxidative phosphorylation
What is the result of uncoupling?
the energy of the proton gradient is lost as heat instead of used to make ATP
What is an example of uncoupling?
thermogenin and brown fat
Describe uncoupling in relation to thermogenin and brown fat
thermogenin is an example of an uncoupling protein in brown adipose tissue (found in newborns and hibernating animals)
brown fat produces heat as glucose is oxidized to keep babies and hibernating animals warm
What type of mammals have brown fat?
hibernating animals and newborns
