Download Cellular Respiration: Harvesting Chemical Energy

Chapter 9
 All
energy
ultimately comes
from the sun
 Energy flows into
an ecosystem as
sunlight and leaves
as heat
 Chemical
components are
recycled
 Energy


is released from the transfer of e-’s
Oxidation is a loss of (hydrogen) e-’s
Reduction is a gain of (hydrogen) e-’s


Reduce (+) charge of an atom by adding a (-) charge eLEO goes GER or OIL RIG
 Always
occur together
 Organic
molecules have high abundance of
hydrogen

Energy released as O2 oxidizes (accepts e-’s from)
H2
 e-’s
travel with a proton (hydrogen atom)
 PE lost as e-’s ‘fall’ down an energy gradient
(move towards more EN molecule)

Lower energy state from less complex molecules
 Enzymes
needed to facilitate in animals
because of energy of activation (EA)
 Glucose
(C6H12O6) is oxidized during cellular
respiration

Occurs in steps to effectively access and use energy
(avoids explosions)
 e-’s
transferred to an electron carrier, not
directly to O2


Coenzyme NAD+ as an oxidizing agent (e- acceptor)
Dehydrogenase removes a pair of hydrogen atoms (2
e-’s and 2 protons)


With no intermediates reaction = explosion
Little PE lost with e- transfer to NAD+


Each NADH stores energy for ‘fall’ to O2 (final e- acceptor)
Electron transport chain, proteins within inner
mitochondrial membrane, controls

Each carrier more EN than previous
3



metabolic stages
Glycolysis: in cytosol, breaks down glucose into
pyruvate
Citric acid cycle: in mitochondrial matrix, oxidizes
pyruvate to create CO2
Oxidative phosphorylation: mitochondrial matrix,
e-’s to O2 and H+ = H2O and synthesizes ATP
 Makes



36-38 ATP
Glucoses stores 686 kcal/mol of energy in bonds
ATP has 7.3 kcal/mol
Single, large unit of energy broken into smaller,
more usable forms
 Glucose
(6C)
2 pyruvate (3C)

No CO2 released
 Substrate-level
phosphorylation
 Can occur with or
without O2


O2 needed for citric
acid cycle
No O2 then
fermentation
 Pyruvate


(3C)
acetyl-CoA (2C)
High energy product so reacts exergonically
Decarboxylation is loss of CO2
 ‘Grooming’
for citric acid cycle
(2 C’s)
 Within mitochondria
Acetyl-CoA
ATP + 3 NADH + FADH2 + CO2
 Intermediate





2
steps
Acetyl-CoA becomes citrate
CO2 and NADH leave as
number of carbons reduces
to 4
FADH2 and an additional
NADH leave
Oxaloacetate joins 2nd
acetyl-CoA to reform
citrate
Cycle repeats
turns per 1 glucose
Oxaloacetate
(4C’s)
Citrate
(6 C’s)
(4 C)
molecule
2
processes = ETC and chemiosmosis within
inner mitochondrial membrane
 NADH and FADH2 store most energy till now
 Hydrogen concentration gradient setup
 Components are protein pumps
 NADH

and FADH2 bring e-’s to ETC complex
Oxidized when they lose e- to a lower neighbor (higher
EN)
 No
direct ATP, control of energy release from fuel
to oxygen (final acceptor)

Smaller, more manageable energy sources
 FADH2

adds to lower energy level
Produce third less energy for ATP synthesis
 Sets
up a H+ concentration gradient
 Energy
stored as H+ gradient across a
membrane drives cellular work
 H+ ions pumped out by ETC

Sets up the gradient to drives ATP synthesis
 ATP
synthase is a protein complex that
makes ATP from ADP and Pi
 Endergonic reaction of ATP synthesis is
coupled with exergonic ETC
C6H12O6 + 6O2
1 NADH = 3 ATP
1 FADH2 = 2 ATP
6H2O + 6CO2 + 36-38 ATP + heat
 Anaerobic

respiration
ETC, but O2 not final e- acceptor
 Fermentation

Primary purpose is to recycle NADH to NAD+ not
ATP production


Glycolysis


Pyruvate picks up e-’s (reduced)
Occurs because NAD+ is oxidizer, not O2
NAD+ recycling

NADH transfers e-’s to pyruvate to recycle NAD+
 Alcohol

Pyruvate to ethanol


Lose CO2 then reduced by NADH
In bacteria and yeast; makes bread, beer, and wine
 Lactic

fermentation
acid fermentation
Pyruvate directly by NADH to lactate


No CO2 released
To make cheese and yogurt