Lecture 10b Flashcards
glycolysis review
Does glycolysis occur under aerobic or anaerobic conditions?
doesn’t matter, glycolysis will happen no matter what
glycolysis review
where are the enzymes of glycolysis located within the cell?
the cytoplasm
what occurs after glycolysis ?
pyruvate:
- as pyruvate is one of the end products of glycolysis, each pyruvate formed in glycolysis must enter a mitochondrion
- pyruvate molecules must pass through the inner and outer membranes of the mitochondrion into the matrix where the citric acid cycle occurs
what facilitates the passage of pyruvate through the outer membrane?
by facilitated diffusion
how does pyruvate move through the inner membrane into the matrix?
via a pyruvate/H+ symport carrier protein
symporter= transfers and carries the protein
example of secondary active transport
what happens when there is no O2 to accept the electrons at the end of the ETC?
this means there will be no H+ gradient thus the pyruvate cannot cross into the matrix
stage 1 of pyruvate oxidation
what happens in stage 1 of pyruvate oxidation?
the carboxyl group of pyruvate is removed and is given off as CO2 which then diffuses out of the cell into the blood for transport to the lungs
what happens in stage 2 of pyruvate oxidation?
the remaining fragment is oxidized into acetate where an enzyme tranfers the 2e- and a hydrogen from this oxidation to NAD+ storing energy is NADH
what happens in stage 3 of pyruvate oxidation?
the coenzyme A is attached to the acetate by an unstable bond, making the molecule very reactive. Acetyl CoA can now enter the citric acid cycle
in pyruvate oxidation, how many co2 and NADH does it yield per glucose molecule?
2 co2 per glucose molecule
2 NADH per glucose molecule
what is the reaction summary of pyruvate oxidation?
what occurs in the citric acid cycle?
the acetyl CoA moves on to the citric acid cycle
- has 8 steps where each is catalyzed by a specific enzyme
- most enzymes are located in the mitochondrial matrix
- each 2 carbons leaving the cycle are different from the 2 carbons entering the cycle
*1 ATP molecule for every 1 Acetyle CoA
what makes the citric acid cycle a cycle?
the regeneration of the first reactant (oxaloacetate) is what makes this pathway a cycle.
what are the goals of the citric acid cycle?
- complete breakdown of glucose
- store electron energy via oxidation ( NADH & FADH2)
- create ATP by Substrate-level phosphorylation
what is the most important step of the citric acid cycle?
STEP #1
what is the first step of the citric acid cycle?
where acetyl-CoA (2C) adds its carbons to oxaloacetate (4C) making citrate (6C)
citrate is the ionized form of citric acid ( where it got its name from )
what enzyme is used in the citric acid cycle?
citrate synthase
how much ATP, NADH, FADH2, CO2 is produced per glucose molecule in the citric acid cycle?
+2 ATP per glucose
+6 NADH per glucose
+2 FADH2 per glucose
+4 CO2 per glucose
how many CO2 molecules per glucose in glycolysis, pyruvate and the citric acid cycle?
glycolysis= none
pyruvate = 2 co2
citric acid cycle = 4 co2
how many ATP molecules do glycolysis and the krebs cycle produce together per glucose molecule?
krebs cycle= citric acid cycle
together they produce 4 ATP molecules per glucose molecule
what are the two processes of oxidative phosphorylation?
1) ETC:
- oxidizes NADH and FADH2
- creates H+ gradient across the inner mitochondrial membrane
2) Chemiosmosis:
- phosphorylation of ADP by ATP synthase enzyme
- energy provided by the H+ ion gradient
this process gives the human body MORE ATP than any other system seen so far
how many protein complexes does ETC have and how are they organized?
4 major protein complexes ordered in increasing electronegativity ( the electron tranfer is exergonic = releases energy
- these proteins contain prosthetic groups, non protein components essential for the catalytic functions of certain enzymes
ETC
the folding of the inner membrane is called what?
cristae
what does ETC transport?
electron carriers alternating between oxidized and reduced states that accept and then donate electrons
*electron transfer releases energy = exergonic
each component becomes reduced as it accepts electrons from its uphill neighbor ( reduction ) - has a lower affinity for electrons
each component becomes oxidized ( loses electrons ) when passing electrons downhill from its neighbor ( less electronegtative )
ETC
describe what happens in complex 1 of ETC
- the NADH product of glycolysis and krebs cycle enters the ETC at complex 1
- FMN is the first electron acceptor, followed by a series of proteins called sulfer-clusters (Fe-S centers)
- during this exchange of electrons 4H+ protrons are pumped across the inner mitcohondrial membrane
- ubiquinone ( coenzyme Q CoQ) is the last electron acceptor of complex 1 - not stuck in place thus travelled to complex 2
describe what happens in Complex 2 of ETC
- FADH2 of glycolysis and krebs cycle enters complex 2
- the electrons from FADH2 are accepted by Fe-S centers then are used to reduce a Heme (iron) molecule before reaching (CoQ)
- CoQ will travel through the inner membrane and reach complex 3
describe what happens in complex 3 and 4 of ETC
- complex 3 pumps 4H+ (picked up by oxygen to form water)
- complex 4 pumps 2 H+
- has cytochromes
- Cyt a3 ( a cytochrome at the end of the chain ) passes its electrons to O2 ( most electronegative electron acceptor in the chain.)
ETC
what are cytochromes?
proteins that are the remaining electron carriers between CoQ and O2
- proteins with a heme moiety as their prosthetic group
- what differentiates them is their electronegativity
the energy released in ETC is used for what?
to pump the protons (H+) from the matrix to the inter-membrane space
which out of the four complexes of ETC is NOT a pump?
complex 1,3,4 are pumps whereas complex 2 is NOT
how much H+ does 1 NADH pump across the membrane?
1 NADH release enough energy to pump 10 H+ across
how much H+ does FADH2 pump?
electrons from FADH2 release enough energy to pump 6 H+ across
what membrane transport mechanism allows oxygen to enter the mitochondria?
diffusion
what is the final electron acceptor in the ETC?
O2
- without O2 H+ ions cannot be pumped across the membrane since ETC would be blocked due to a lack of a final and renewable elctron acceptor at the end of the chain
- oxygen contributes to H+ gradient created by the ETC by taking H+ ions out of the mitochondrial matrix to form H20.
what is the total range of protrons transported across the inner mitochondrial membrane during 1 “run” of ETC?
6-10 protons
complex I = 4H+
complex II = 0 H+
complex III = 4 H+
complex IV = 2 H+
NADH = 10 H+ transported ( this pumps 100 protons )
FADH2 = 6 H+ transported
what does cyanide do that makes it dangerous?
cyanide binds to Cyt a3 in complex 4 of ETC preventing the release of electrons to oxygen and therefore stopping the whole ETC.
without a proton gradient chemiosmosis cannot occur, the cell will be depleted of ATP and it quickly dies.
what is chemiosmosis?
the process in which an ion concentration gradient across a membrane is used to drive cellular work
- this process couples the ETC to the creation of ATP
- needs the action of an embeded enzyme called ATP synthase
what does ATP synthase do?
ATP synthase uses the energy of an existing H+ gradient across the inner mitochondrial membrane to power ATP synthesis.
- works in both directions depending on the delta G of the reaction
what are the four main parts of ATP sythase?
1) rotor - where the membrane spins when H+ flows past down the H+ gradient
2) stator - anchored in the membrane where it holds the knob still
3) a rod ( or stalk ) - extends into the knob and spins, activating catalytic sites in the knob.
4) three catalytic sites ( static part ) in the knob that join inorganic phosphate to ADP to make ATP.
describe how ATP synthase works
- protons move one by one into the binding sites of the rotor, causing it to spin in a way that catalyzes ATP production from ADP and inorganic phosphate.
- the flow of protons behaves like a stream that turns a waterwheel
- ATP synthase is the smallest molecular rotary motor known in nature
how many active sites in the stationary knob catalyzes the phosphorylation of ADP into ATP?
3 active sites
- the rotation causes conformational changes in the stationary knob which activates the three catalytic sites in the knob sequentially and continually such that ADP and Pi combine to make ATP
How much ATP do NADH and FADH2 give?
in chemiosmosis
- we know that NADH results in 10 H+ being transported into the inner mitochondrial membrane
therefore somewhere between 3 and 4 H+ must re-enter via ATP synthase to generate 1 ATP.
1 NADH = 2.5 to 3.5 ATP = 3 ATP - FADH2 enters ETC through complex 2 and is responsible for the synthesis of 1.5 to 2 ATP
1 FADH2 = 2 ATP
what is the total number of ATP from the whole aerobic cellular respiration process?
total of 38 ATP
what process is this?
aerobic cellular respiration
how efficient is cellular respiration?
1 molecule of glucose = 686 kcal
energy in phosphate bonds = 7.6 kcal
7.6 x 36 or 7.6 x 38 = 274-289 kcal
8.274/686 or 289/686 = **40-42% efficient **
the remaining energy is lost as heat
review
https://www.youtube.com/watch?v=kN5MtqAB_Yc
