Electron Transport Chain

What happens in the electron transport chain?

An electron transport chain (ETC) couples electron transfer between an electron donor (such as NADH) and an electron acceptor (such as O2) with the transfer of H+ ions (protons) across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate (ATP)

what happens to electrons as they progress through the electron transport chain?

they go to lower and lower energy states

Where is the electron transport chain located?

inner mitochondrial membrane

what are the four complexes of the electron transport chain

1) NADH dehydrogenase/NADH oxidoreductase

2) succinate reductase (contains succinate dehydrogenase)

3) cytochrome C reductase

4) cytochrome C oxidase

what is the function of Complex 1 of the electron transport chain

NADH dehydrogenase accepts electrons from NADH and transfers them to ubiquinone (Q)

it also pumps H+ into inter membrane space

what is the function of Complex 2 of the electron transport chain

accepts electrons from FADH2

what is the purpose of Complex3 of the electron transport chain

accepts electrons from ubiquinol and transferred them to cytochrome C

it also pumps H+ into the intermembrane space

what is the purpose of Complex4 of the electron transport chain

used electrons from cytochrome C to pump H+ into intermembrane space

is ubiquinone a protein?

no

where does cytochrome C bind

on the intermembrane side of complex 3/4

what is the path of an electron through NADH oxidoreductase (complex 1)

electrons move from NADH to FMN then move along a series of FeS groups creating an electric current (which is used to pump H+ out of matrix) then transferred onto ubiquinone

what is the path of an electron through succinate reductase (complex 2)

two electrons from FADH2 move through a series of FeS groups creating an electric current then transferred onto ubiquinone

what is the difference between ubiquinone, ubiquinol and semiquinone

ubiquinone is fully oxidized (has no electrons or H bound to it)

ubiquinol is fully reduces (has 2e- and 2H+ bound to it

semiquinone is the intermediate with only one electron and 0 H+ bound to it

what is the path of electrons in cytochrome C oxidoreductase (complex 3)

takes electrons from ubiquinol and and transferred them to cytochrome C through the Q cycle

what happens at the beginning of the Q cycle when ubiquinol (QH2) binds to complex 3

2 H+ are pumped into the intermembrase space and the 2e- follow two differenct paths

what is the first path that one electron follow in the Q cycle (the shorter one)

the electron moves onto iron groups of reiske centre and are then transferred to the heme group of cytochrome C1 then transferred onto cytochrome C

how many electrons can cytochrome C hold?

1

what is the second path that one electron follow in the Q cycle (the longer one)

the electrom moves to cytochrome B then is picked up by a new ubiquinone which is now partially reduced to semiquinone

how does the semiquinone become fully reduced?

another ubiqinol has to bind to complex 3 and again donate one e- to a cytochrome C and the second electron fully reduces the semiquinone to ubiquinol which can now start the Q cycle again

what are the three outcomes of the Q cycle

1) 2 QH2 oxidized to Q and release 4H+

2) one Q is reduced to QH2 (recycled)

3) 2 cytochrome C molecules are released (to intermembrane space)

What molecule is the final electron acceptor at the end of the Electron transport chain?

O2

what is the path of an electron through complex 4 (cytochrome C oxidase)

-2 reduces cytochrome Cs bind to complex 4 and bind to Cu(b) and hemeo3 reducing them

-reduced Cu(b) and hemeo3 bind with O2 to form a peroxide bridge

-2 more reduced cytochrome Cs bind to complex 4 donating 2e- and causing 2H+ from matrix to bind with peroxide bridge breaking it and releasing 2(H2O)

how many protons do complex 1, 2, 3, and 4 pump into the intermembrane space

complex 1 pumps 4 H+

complex 2 pumps 0 H+ (it is not a proton pump and doesn't span the inner mitochondrial membrane)

complex 3 pumps 4H+

complex 4 pumps 2H+

what is the function of ATP synthase

it is a protein that allows H+ ions to move through the thylakoid membrane (proton motive force) and rotates as they pass through allowing generation of ATP

what are the two general regions of ATP synthase?

F0 (proton pump)

F1 (catalytic unit)

where are the F0 and F1 regions loated

F0 located in the inner mitochondrial membrane

F1 located in the matrix

the F1 region has alpha, beta, gamma, epsilon, and delta subunits, which two make up the ring structure where ATP production takes place

alpha and beta (3 of each)

what is the function of the gamma and epsilon subunits

they combine to make the central stock that rotates

what is the function of the delta subunit

helps hold the alpha-beta ring in place

the F0 region is in the membrane is it hydrophobic or hydrophilic?

hydrophobic

what subunit makes up the proton channel?

10-14 c units

what are the function of the a and b subunits of region F0

helps connect F1 and F0

what are the two things that connect F1 and F0

the gamma epsilon stalk

the arm formed by 1a, 2b, and the delta subunits

ATP synthase has a rotating and stationary region, which subunits make up the rotating region

the c ring and the gamma epsilon stalk (the rest are stationary

the alpha beta ring is responsible for what three things (think of the states)

1) bind ADP and P

2) catalyze ATP sysnthesis

3) release ATP

do the alpha or beta subunits have a catalytic role?

the beta subunits, the alpha subunits can bind ATP but won't release it)

what are the three states of the beta subunit

1) open (formes ATP is released and ADP and P can bind)

2) loose (ADP and P become trapped and can't leave)

3) tense (ADP and P brought close and combined to form ATP)

what causes the beta subunits to change state

rotation of the stalk

what direction does the gamma epsilon stalk rotate?

counterclockwise (120 degrees each time)

what is the difference between oxidative phosphorylation and substrate level phosphorylation

oxidative phosphorylation is generation of ATP through the electron transport chain (ADP is being phosphorylated due to oxidization of electron carrier molecules) - uses H+ gradient

substrate level phosphorylation is enzyme facilitated, and for ATP production, ATP is directly produced

What is chemiosmosis?

the use of energy in a H+ gradient to drive cellular work

the inner mitochondrial membrane has may Christie, what are they, and what is their purpose

folds in the membrane to increase the surface area and allow for more oxidative phosphorylation

what are three common molecules that can be oxidized to reduce electron carrier molecules such as NAD and FAD

glucose

fatty acids

amino acids

what type of regulation does oxidative phosphorylation (ETC) have

it doesn't have a major regulation, no hormonal or allosteric regulation, rather if you increase reactants it pushed reaction forward and vice versa (le chatlieres)

what are the two most significant regulators of oxidative phosphorylation

ATP and ADP

what is the difference between necrosis and apoptosis

necrosis is uncontrolled cell death due to high cell stress

apoptosis is controlled, programmed cell death

what are five causes of apoptosis

1) development (create fingers)

2) DNA damage

3) infection

4) environmental stress

5) reactive oxygen species

what are the three methods of apoptosis

1) intrinsic pathway

2) extrinsic pathway

3) apoptosis inducing factor

what is the intrinsic apoptosis pathway

mitochondrial pathway

during the intrinsic pathway of apoptosis the mitochondrial membrane becomes more permeable, what molecule leaves intermembrane space?

cytochrome C enters the cytosol

in the cytosol cytochrome C activates the CASPASE -9 protein, what does CASPASE do?

breaks down polypeptides after aspartate residue using a cytosine residue

C-ASP-ASE

C = cytosine

ASP = aspartate

ASE = break down protein

what happens to the broken down units of the proteins?

phagocytksed by another cell

What is the extrinsic pathway of apoptosis?

signal molecules from outside cell bind to death receptors and release death activators which activate CASPASE-8

what is the apoptosis inducing factor method of initiating apoptosis

when al cell is damaged, apoptosis inducing factor is released from the intermembrane space of the mitochondria into the cytosol and eventually into the nucleus where it breaks down the DNA (neurons use this)

how many protons are pumped into the intermembrane space for NADH, for FADH2

NADH = 10 H+

FADH2 = 6H+

why is there a difference in number of protons pumped into the intermembrane space between NADH and FADH2

FADH2 enters the ETC later so it pumps fewer H+

if it takes about 4 H+ to make 1 ATP, how many ATP are produces for 1 NADH and for 1 FADH2

1 NADH = 2.5 ATP

1 FADH2 = 1.5 ATP

for one molecule of glucose, how much ATP is produced?

30-32 (max 38)

How many ATP, NADH, and FADH2 are created during glycolysis?

2 ATP and 2 NADH

(makes 5-7 ATP depending on shuttle)

glycolysis takes place in the cytosol, so the NADH needs to be transported into the mitochondria, what are two methods of doing this?

1) G3P shuttle onto complex 3 of ETC

2) malate-aspartate shuttle onto complex 1 of ETC

How many ATP, NADH, and FADH2 are created during the TCA cycle (for one molecule go glucose?

6 NADH

2 ATP (GTP)

2 FADH2

(makes 20 ATP)

How many ATP, NADH, and FADH2 are created during pyruvate decarboxylation?

2 NADH

(makes 5 ATP)