Download LT AP BIO

Lecture #4
• Chapter 9~
A Musical Journey Through
Cellular Respiration
Objective:
How do organisms produce
energy for themselves to
do work?
Date _________
Principles of Energy Harvest
• Catabolic pathway –
breaking down molecules to
release energy
√ Fermentation
√Cellular Respiration
•
•
C6H12O6 + 6O2 ---> 6CO2 + 6H2O +
Energy (ATP + heat)
Products of photosynthesis are the reactants
of the cellular respiration
Why does ATP store energy?
O– O– O – O– O–
–O P –O
O– P –O
O––P
OO
P––O
O– P O–
O O O O O
• Each Pi group more difficult to add
– a lot of stored energy in each bond
• most stored in 3rd Pi
• ∆G = -7.3 kcal/mole
• Close packing of
negative Pi groups

spring-loaded
instability of its P bonds makes ATP an excellent energy donor
I think he’s
a bit
unstable…
don’t you?
How does ATP transfer energy?
O– O– O –
–O P –O
O– P –O
O– P O–
O O O
• Phosphorylation
– when ATP does work, it transfers
its 3rd Pi to other molecules
• ATP  ADP
• releases energy
– ∆G = -7.3 kcal/mole
• it destabilizes the other molecule
O–
–O P O – +
O
energy
Why is 3rd
phosphate
like a baaad
boyfriend?
Exergonic vs Endergonic Reactions
SPONTANEOUS
NON-SPONTANEOUS
What if endergonic reactions need to happen in our body?
ATP-coupled reactions
• The body couples ATP
hydrolysis to endergonic
processes by transferring a
P to another molecule
• The Phosphorylated
molecule is less stable
(more reactive)
• This turns an endergonic
reaction to an exergonic
(spontaneous) reaction
Using ATP to do work?
Can’t store ATP
 too unstable
 only used in cell
that produces it
 only short term
energy storage
 carbohydrates & fats
are long term
energy storage
Whoa!
Pass me
the glucose
& oxygen!
ATP
work
ADP + P
A working muscle recycles over
10 million ATPs per second
How do we create ATP?
• Cellular Respiration – systematic
breakdown of organic molecules (carbs,
lipids, proteins, etc.)
• Similar to the burning of gasoline in a car
Redox reactions – relocation of
electrons releases energy which is
then used to synthesize ATP
• Oxidation-reduction
• OIL RIG
(adding e- reduces +
charge)
• Oxidation is e- loss;
reduction is e- gain
• Reducing agent
(oxidized):
edonor
• Oxidizing agent (reduced):
• e- acceptor
Oxidizing agent in respiration
(electron carrier)
• NAD+ (nicotinamide
adenine dinucleotide)
• Removes electrons from
food (series of reactions)
• NAD+ is reduced to
NADH
• NADH carries high
energy electrons
• Oxygen is the eventual eacceptor
Electron transport chains
• Electron carrier molecules
(membrane proteins)
• Shuttles electrons that release
energy used to make ATP
• Sequence of reactions that
prevents energy release in 1
explosive step
• Electron route:
food---> NADH --->
electron transport chain --->
oxygen
Aerobic vs Anaerobic
Where does cellular respiration take
place?
Intermembrane
Space
Overview of cellular respiration
• 4 metabolic stages
– Anaerobic respiration
1. Glycolysis
– respiration without O2
– in cytosol
– Aerobic respiration
– respiration using O2
– in mitochondria
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
(+ heat)
Cellular respiration Overview
Glycolysis = Sugar + Break down
• 1 Glucose  2 pyruvate
• Energy investment phase: cell
uses ATP to phosphorylate fuel
– Glucose  G3P
• Energy payoff phase: ATP is
produced by substrate-level
phosphorylation and NAD+ is
reduced to NADH by food
oxidation
– G3P  Pyruvic acid
• Net energy yield per glucose
molecule: 2 ATP plus 2 NADH;
no CO2 is released; occurs
aerobically or anaerobically
Energy Investment Phase
ENZYMES
Energy Payoff Phase
Substrate-level phosphorylation
Oxidation of Pyruvic acid
• Each pyruvate is
converted into acetyl CoA
(begin w/ 2 pyruvate):
CO2 is released;
NAD+ ---> NADH;
• coenzyme A (from B
vitamin), makes molecule
very reactive
ACTIVE TRANSPORT = REQUIRES 2 ATP
Kreb’s Cycle
•
•
•
•
•
•
If molecular oxygen is present…….
From this point, each turn 2 C atoms
enter (acetyl CoA) and 2 exit (carbon
dioxide)
Acetyl CoA combines with
Oxaloacetate to form Citric acid (why it
is also called citric acid cycle)
Oxaloacetate is regenerated (the
“cycle”)
For each pyruvate that enters:
3 NAD+ reduced to NADH;
1 FAD+ reduced to FADH2
(riboflavin, B vitamin);
1 ATP molecule
Totals (2 pyruvates) = 6NADH,
2FADH2, 2 ATP’s, 4 CO2
Electron transport chain
•
•
•
•
NADH and FADH2 from
Glycolysis and Kreb’s are
transported to the ETC
Cytochromes carry electron carrier
molecules (NADH & FADH2)
down to oxygen
Chemiosmosis: energy coupling
mechanism
ATP synthase: produces ATP by
using the H+ gradient (protonmotive force) pumped into the inner
membrane space from the electron
transport chain; this enzyme
harnesses the flow of H+ back into
the matrix to phosphorylate ADP to
ATP (oxidative phosphorylation)
Review: Cellular Respiration
• Glycolysis:
2 ATP (substrate-level
phosphorylation)
• Kreb’s Cycle:
2 ATP (substrate-level
phosphorylation)
• Electron transport & oxidative
phosphorylation:
2 NADH (glycolysis) = 6ATP
2 NADH (acetyl CoA) = 6ATP
6 NADH (Kreb’s) = 18 ATP
2 FADH2 (Kreb’s) = 4 ATP
• 38 TOTAL ATP/glucose – 2 ATP’s used
in transporting NADH from glycolysis
to mitochondria
• Net Gain = 36 ATP’s
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Electron
transport
C system
Q
NADH
Acetyl-CoA
2. Electrons
provide energy
1. Electrons are harvested to pump protons
and carried to the transport
across the
system.
membrane.
-
NADH
Krebs
cycle
e-
e
FADH2
e-
3. Oxygen joins
with protons to
form water.
CO2
2
ATP
Mitochondrial
matrix
H2O
1 O
2 +2
2H+
H+
32 ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
e-
O2
H+
ATP
synthase
Related metabolic processes
• Fermentation:
alcohol~ pyruvate to ethanol
(also creates CO2) – useful
for bakers/brewers
lactic acid~ pyruvate to
lactate
• Both create 2 ATP’s
• Allow NAD+ to be recycled
to glycolysis
• Facultative anaerobes
(yeast/bacteria)