Download Cellular Respiration Review

Cellular Respiration
 Respiration= obtaining O2 and releasing CO2; aerobic break down of food
molecules to yield ATP.
 Releasing ATP= main function of cellular respiration.
 Equation for cellular respiration:
6O2 + C6H12O6  6CO2+ 6H20 +36ATP
 Glucose= most commonly shown as the representative food molecule for
cellular respiration; free glucose molecules are not common in our diet.
 Cellular respiration also occurs from the breakdown of lipids, proteins,
sucrose, starch, etc.
 When a cell breaks down glucose, it can only capture 40% of glucose’s
energy into ATP molecules; the rest is lost as heat.
 Cellular respiration may be inefficient, but yeast cell harvest energy from
glucose in an anaerobic (no O2) environment (fermentation) where only 2%
of glucose’s energy is converted to ATP/ 2 ATP from fermentation.
 Cellular respiration breaks down glucose (the covalent bonds) in a series of steps and taps into the energy carried by
electrons.
 Respiration shuttles these electrons via a series of energy-releasing reactions.
 The energy gets released in small amounts and the cell stores some of it as ATP.
 OIL RIG (Oxidation Is Losing; Reduction Is Gaining)
 Redox reaction: movement of electrons from one molecule to another.
 Since an electron transfer requires both a donor and an acceptor of electrons, oxidation and reduction always go together.
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 Dehydrogenase pulls off hydrogen from a molecule (oxidation).
 NAD+ is a coenzyme that cells make from vitamins and is used to carry
electrons.
 NADH delivers its electron load to an electron carrier molecule.
 Electron carrier molecules: proteins that take the electrons from NADH
and use that electron to make ATP energy.
 Oxygen is the final electron acceptor; it has the greatest affinity for
electrons.
The redox reactions release energy in small amounts to
be used by the cell.
Energy is trapped in the bond between the phosphates in
ATP.
When either of the last 2 phosphates bonds is broken,
energy is released.
Spent ATP molecules are continuously recycledphosphates reattached.
Aerobic Respiration: with oxygen, consists of 4 stages:
1. Glycolysis
2. Formation of acetyl CoA
3. Kreb’s cycle
4. ETC & chemiosmosis.
 Keep track of the carbons and ATP and
energy carriers like NADH & FADH2.
Glycolysis:
 Splitting/ “lysis” of glucose glycol
 Usually consists of 10 steps to break down
glucose to pyruvate, each one catalyzed by
an enzyme.
 Glucose= 6 carbon sugar that gets broken
down into 2 pyruvates/pyruvic acids (3carbon molecules)
 2 ATP’s are needed in intermediate steps,
but 4 ATP’s are made during glycolysis.
 Thus, due to our investment of 2 ATP’s, there is a NET GAIN of 2 ATP’s from glycolysis
 2nd product of glycolysis is NADH, which resulted from the transfer of H+ to the hydrogen/electron carrier NAD+
 Reaction: C6H12O6 + 2NAD+ +2ATP 2 pyruvate +2NADH +4 ATP
 Occurs in the cytosol of the cell and not in the mitochondria!
 Is an anaerobic process (no O2)
 ATP is made by substrate level phosphorylation
 Formation of Acetyl CoA:
 When O2 is present, pyruivic acid moves to the
fluid matrix of the mitochondria
 2 pyruvic acids combine with 2 coenzyme A to
form 2 acetyl CoA—2 carbon molecule
 Forms 2 NADH & 2CO2 molecules
 Reaction: 2 pyruvate + 2 coenzyme A + 2 NAD+ 
2 acetyl CoA + 2CO2 + 2NADH
 Kreb’s Cycle:
 Also called citric acid since it is the first product in
the cycle
 Each of the 2 acetyl CoA molecules enter the
Kreb’s cycle ONE AT A TIME and all the carbons
will ultimately be converted to CO2.
 Occurs in the fluid matrix of the mitochondria
 Each molecule of acetyl CoA combines with oxaloacetate (4-carbon molecule) to form citric acid/citrate (6-carbon
molecule).
 Since the cycle begins with the 4 carbon molecule oxaloacetate,
it also has to end with this molecule to maintain the cycle.
 2 CO2 molecules are made each cycle for a sum of 4 CO2
molecules since the cycle makes 2 turns-one for each acetyl CoA
 CO2 produced here in the mitochondrial fluid matrix during the
formation of acetyl CoA and during the Kreb’s cycle, is the CO2
animals exhale
 With one turn of the cycle, molecules are produced:
a. 1 ATP
b. 3 NADH molecules
c. 1 FADH2 (coenzyme similar to NADH)
d. 2 CO2
 DOUBLE the products to figure out the total # of
products/molecule of glucose
 For a sum total of 12 hydrogen carriers altogether are made thus
far.
 Electron Transport Chain (ETC):
 Hydrogen carriers NAHD & FADH2 store energy in their
hydrogen atoms; they can carry the hydrogens to the
phospholipids bilayer of the inner mitochondrial
membrane/cristae, where they enter the ETC
 In ETC, hydrogens of NADH & FADH2 are split into H+ and e H2 2H+ + 2e High energy electrons from NADH and FADH2 are passed
down a series of carrier molecules
 Some of these are iron-containing protein carriers called
cytochromes
 Each carrier molecule hands down electrons to the next
molecules until reach the final electron acceptor, O2 that
combines with hydrogen to form H2O a lot of potential
energy is created.
 ^explains the “aerobic” in aerobic respiration
 If O2 weren’t available to accept electrons, the last carrier in
the chain would be “stuck” with them, shutting down the whole process of ATP production.
 This is the cell’s main mechanism for the production of ATP.
 Oxidative Phosphorylation:
 The potential energy released from
ETC is used to pump hydrogen (H+)
across the inner mitochondrial
membrane/cristae to the
intermembrane space
 Proton pump pumps hydrogen
ions creates H+ gradient or
proton gradient
 This gradient is equivalent to a pH
gradient or an electrical gradient
with lots of potential energy
 These hydrogen ions eventually
want to come back across the
inner membrane but can do so
only by passing via a special
protein channel called ATP
synthase
 ADP +Pi are sitting on the other side of ATP synthase
 Flow of protons via these channels yields even more ATP
 This process is called oxidative phosphorylation since it is aerobic and we are attaching a phosphate group to the ADP.
 ETC and oxidative phosphorylation that produce the most ATP molecules
 NADH= 3 ATP’s
 FADH2= 2ATP’s
 Total # of ATP’s produced by the ETC/chemiosmosis= 32 ATP’s
Step in Respiration
Glycosis
Split to acetyl CoA
Krebs cycle
ETC/OP
Takes place in the…
Cytosol
Fluid matrix
fluid matrix
inner membrane/cristae
Net result
2 ATP 2NADH
-2NADH
2 ATP 6NADH & 2FADH2
32 ATP
Net: 36 ATP
 Some organisms can’t do aerobic respiration since they are
anaerobic; they can’t use O2 to make ATP.
 They use glycolysis to make a net of 2 ATP from this stage, as well
as reduce 2NAD+ to 2NADH and form 2 pyruvate molecules.
 Instead of carrying out the other stages of aerobic respiration,
these organisms carry out fermentation.
 Alcoholic fermentation:
 Occurs in bacteria, fungi (yeast), and plants
 Yeast do anaerobic and aerobic respiration if O2 is available
 Each pyruvate molecule gets converted 1st to acetaldehyde and releases
CO2
 CO2 formed is the source of bubbles in fermented drinks like beer and
champagne
 Then the acetaldehyde is converted into ethanol
 NADH=the energy to drive this part of the reaction, releasing NAD+
 For each acetaldehyde, 1 ethanol/ethyl alcohol is produced and 1 NADH
is oxidized.
 NAD+ then enters glycolysis where it gets reduced and recycled.
10 NADH*3= 30 ATP
2 FADH2 *2= 4 ATP
34 ATP
34 ATP- 2ATP= 32 ATP
(it takes 2ATP to move pyruvate
into fluid matrix)
 Ethanol is energy-rich, unlike H2O & CO2. Ethanol is toxic to organism. Yeast can die if their surroundings become too
concentrated with alcohol.
 Its goal is not to make ethanol; main goal= to release some NADH which can be recycled and used in glycolysis.
 Reward= 2 ATP for glycolysis.
 Lactic acid fermentation:
 Only one step in lactic acid/lactate fermentation: the conversion of 2
pyruvate molecules from glycolysis into 2 lactates.
 Like alcoholic fermentation, NADH gives up its hydrogen to form
NAD+ which can be recycled and used in glycolysis.
 It occurs in many types of cells, including bacteria & human muscle
cells.
 To make cheese and yogurt
 With humans, lactic acid fermentation occurs when O2 is unavailable,
which can occur during strenuous exercise.
 Although humans are aerobic organisms, fermentation is carried out
not only in the cytoplasm of glycolysis but also in the cytosol of
muscle cells with lactic acid fermentation.
 Cramp during exercise= anaerobic respiration and the buildup of lactic acid in muscle cells.
 Lactic acid causes muscle cells to ache and needs to be converted back to pyruvate with the aid of liver for the cramp to
go away.