Transcript 9.1 Catabolic pathways yield energy by oxidizing organic fuels

Ch. 9 Cellular Respiration
Harvesting Chemical Energy
9.1 Catabolic pathways
yield energy by oxidizing
organic fuels
Energy flows into an ecosystem as
sunlight and ultimately leaves as heat,
while the chemical elements essential to
life are recylcled.
The coupled reactions are what keeps
all life connected.
Photo:
6CO2 + 6H2O ------- C6 H12 O6 +6 O2
Cell Resp.
C6 H12 O6 + O2-----6CO2 +6H20+ATP
The products of one reaction become
the reactants of the next
9.1 The principle of Redox
Energy Must be transferred .
For every e- that is lost by one atom that
same e- must be gained by another
atom.
Redox Reactions
X is the reducing agent because it
donates the electron.
Y is the oxidixing agent because it
accepts the electron.
One cannot exist without the other.
9.1 NAD+ as an electron
shuttle
The Empty Bus. NAD+ will combine
with 2e- and 2H+ ( donated by food) to
create NADH (the loaded bus) and a
free H+
This energy rich molecule will shuttle eand H+ from glycolysis and the citric
acid cycle to oxidative phosphorylation..
9.1 An Introduction to
Electron Transport Chains
a.) Uncontrolled fall of electrons
Too muck energy at once, No control,
boom!
b.) Cell Respiration -Key differences :
1st - the H that reacts with O is derived
from food rather than H2.
2nd- Cell respiration uses the ETC to
break the fall of electrons into several
Energy releasing steps
c.) How it works: Electrons removed
from food are shuttled by NADH to the
“top” of the high energy end of the
chain. At the “bottom”, lower-energy
end oxygen captures these electrons
along with H+ , forming water.
9.1 The stages of Cellular
Respiration : A preview
2 ways to make ATP
1. substrate level phos. (not very
efficient) but makes a lot of loaded
buses.
2. Oxidative phos. Very efficient but
requires O2
9.1 Substrate Level
Phosphorylation
Happens in Glycolysis and the Kreb
Cycle
An enzyme acts on a substrate,
breaking off a phosphate and giving it
to ADP to make ATP.
9.2 Glycolysis harvest chemical
energy by oxidizing glucose to
pyruvate
10 step process takes place in the
cytosol
Net Product of 2 ATP. 4 ATP are formed
but 2 ATP are consumed.
2 NADH
2 H+
2 Pyruvate
2 H20
9.3 The citric acid cycle
completes the energy-yielding
oxidation of organic molecules
Note:
Pyruvate is the branching point:
No 02 = Fermentaion
O2 Present= Cell Respiration
Image:
The conversion of pyruvate to acetyl
CoA, the junction between glycolysis
and the cytric acid cycle.
9.3 On overview of the Citric
Acid Cycle
To calculate the inputs and the outputs
on a per-glucose basis, multiply by 2,
because each glucose molecule is split
during glycolysis into two pyruvate
molecules
AKA Kreb Cycle.
In Mitochondial Matrix
Produces Small amount of ATP (2)
Produces Large Amount of Electron
carriers, NADH (8) and FAD2 (2)
The Electron Transport
Chain
The controlled fall of Electrons
•1,000 of ETC are embedded in the
cristae of the inner mitochondrial
membrane.
•Most components are proteins.
•The ETC carriers shift between
reduced and oxidized states as the
donate and accept electrons.
• The Players: The e- are transferred
from NADH, Flavoprotein, Complex I,
to Q, to a series of cytochromes, and
finally to Oxygen. Which picks up to
H+ and forms water.
•It is hot potato with a finishing splash
of H20.\
•Note : FADH2 adds its electrons at a
lower level , thus FADH2 provides 1/3
less the energy to make ATP
Chemiosmosis couples the
ETC to ATP synthesis
ATP Synthase, a molecular mill:
•Protein uses the energy of the proton
(H +) Gradient to make ATP.
•The proton gradient is produced as
members of the ETC pass electrons,
while passing e- they also accept and
release H+.
•The concentration of H+ builds up in
the intermembrane space. This gradient
stores potential E referred to as the
“Protomovtive force”.
•The flow of H+ down the gradient
through the rotor and stator part of the
ATP synthase cause the rotor and
attached rod to rotate, activating the
catalytic sites on the knob portion
where ADP and iP join to form ATP.
•It’s the “Bump”
9.4 During oxidative
phosporylation, chemiosmosis
couples the electron transport
to ATP synthase
The proton gradient is produced as
members of the ETC pass electrons:
while passing e- they also accept and
pump H+ across the membrane into the
intermembrane space.
9.4 ATP yield per molecule of
glucose at each stage of the
cellular respiration
The Big Picture
Why 36 or 38 and not a discreet
number?
Because it depends on which shuttle
transports the e- from NADH in the
cytosol to the ETC.
If it is FADH2 =less ATP
If it is NADH= more ATP
9.5 Fermentation enables some
cells to produce ATP without
the use of oxygen as long as
there is enough NAD+ to accept e-’
a. Alcohol Fermentation
•
Consists of glycolysis plus reactions
that regenerate NAD+ by
transferring e-’s from the NADH
molecules to pyruvate.
•
When pyruvate picks up (accepts)
the 2 H+’s it becomes Ethanol.
b.
•
•
•
•
Lactic Acid Fermentation
Pyruvate is reduced by NADH with
no release of CO2.
Human muscle cells make ATP
this way when O2 is scarce.
This occurs during the early stages
of strenuous exercise when sugar
catabolism outpaces the muscles
supply of O2 from the blood.
The cells switch from aerobic
respiration to anaerobic. Lactate
builds up causes fatigue and pain.
But is carried to the liver to be
converted back to pyruvate.
9.5 The Evolutionary
Significance of Glycolysis
Pyruvate as the key junction in
catabolism.
•Glycolysis is common to Fermentation
and Cell Respiration.
•The product of Glycolysis, pyruvate,
represent the fork in catabolic pathways.
9.6 Glycolysis and the citric
acid cycle connect to many
other metabolic pathways
The catabolism of various molecules
from food:
“Love the one your with”
Any for these 3 macromolecules can be
used a fuel source to create ATP.
Proteins and Fats just need to be
altered first.
Proteins- to AA then AA are further
broken down in a process called
deamination when the – NH2 group is
broken off. This will increase the
nitrogenous waste.
Fats-great fuel source. 1 g. of fat
produces twice the amount of ATP than
1g. of Carb. But requires a lot of
intermediate steps. That’s why you have
to work so hard to lose weight. Longer
process to break down fats.
9.6 The Control of Cellular
Respiration
Feedback Inhibition controls the
anabolic and catabolic pathways.
•Phosphofructokinase- pace maker of
respiration. It is an allosteric enzymes
with Receptor sites fro AMP and ATP.
•ATP binds to Phospho. and
respiration is inhibited.
•AMP binds to Phospo. and the
respiration is stimulated.
•Cells are thrifty,expedient and
responsive to their metabolism.