How Cells Make ATP
by
PHOSPHORYLATION... adding a phosphate to ADP
ADP + P
------> ATP |
 |
a) substrate level phosphorylation...
where a substrate molecule (
X-p ) donates its P to ADP making
ATP
b) chemiosmosis - [Oxidative
Phosphorylation via Electron Transfer Chain]...
food substrates donate
e- & protons to
acceptor molecules [NADH], i.e., oxidation.
NADH gives up electrons &
protons are pumped out of mitochondria
(or
the chloroplasts in photosynthesis);
protons diffuse back into mito thru an enzyme -
ATP synthase,
the ATP synthase enzyme makes
ADP + P --> ATP figure
*
c) photophosphorylation....
e- of light energy, instead of food covalent bonds, are captured by
chlorophylls
to make a
proton gradient across the
chloroplast membranes...
figure*
protons move through a chloroplast ATP
synthase
enzyme
to make ATP |
Oxidative
Metabolism... (cell respiration)
occurs in
heterotrophic
organisms that consume foods
... we say organisms
oxidize (consume) foods (often
glucose) to make
energy
because they
remove & capture electrons...
... where is energy in foods?
it's in the covalent bonds (e-)
Thus - METABOLISM
is
cells capturing
e-
via REDOX reactions.
REDOX REACTION...
e-
passed from one molecule to another [PGAL -->
NAD+] in a chemical rx
energy is transferred into the new molecule
(a redox couple) by holding
e-
OXIDATION =
removal of electron &/or protons from food covalent bond
REDUCTION
= gaining electron &/or protons;
adds an electron to an acceptor molecule
a model redox reaction...
A-H + B-O
<---> A + B-O-H
donor
acceptor
(:H)
acceptor
donor
PGAL
NAD+
1,3-bisphosphoglycerate NADH
reducing
oxidizing
becomes becomes
agent
agent
oxidized reduced
Oxidation state*
and energy relationship --> the more reduced =
the more energy it holds
an example using
acceptor coenzyme (redox couple)
NAD+
<-->
NADH*
Thus :
metabolism becomes the stepwise
oxidation of foods
if aerobic - requires
oxygen as electron acceptor
if anaerobic - requires no oxygen (uses other e- acceptors)
Cell
RESPIRATION... is Concept
Activity 9.1 - Overview
of Cellular Respiration
Investigation
chapter 9.1 -
How
Rate of Respiration is Measured
1. oxidation of GLUCOSE --> CO2
+ H2O
&
2. reduction O2
to H2O
C6H12O6
+ 6O2 <----> 6
CO2 + 6
H20 +
e- ---> 36-38 ATP
DG = -686 Kc/mole
263Kc = 38%
called oxidation... because
e- are removed from glucose
called reduction... because
e- passed to O2 making water
&
3. phosphorylation of ADP
(thus oxidative phosphorylation)
a more complete definition of cell
respiration :
- series of enzyme rx's (in
a biochemical pathways)
in the cytoplasm & mitochondria that,
- removes e- (oxidation) from covalent bonds of substrates (as glucose),
and
- pass e- to
acceptor molecules [coenzymes] such as
NAD+
&
FAD*
which become reduced [
NADH & FADH2
]
- the reduced coenzymes [
NADH & FADH2 ] pass
e- to other acceptors...
a series of protein electron carriers called cytochromes,
- the electron carriers [cytochromes] pass
e- to
O2 --reduction-->
H2O
- cytochromes also
pump
protons [H+]
out of mitochondria into peri-mito
space,
- protons move back into mito thru a special enzyme (ATP
synthase*) & make ATP
overview
figure*
the
Enzyme Pathways* of Cell Respiration...
|
|
Glyco-lysis :
pathway converts 1 glucose (C6) to 2 pyruvate (C3)
produces : 2
molecules of pyruvate,
2
NADH, & 2 ATP (net)
occurs in :
cytoplasm [is anaerobic]
may include : alcoholic fermentation =
glucose --> alcohol
lactic acid fermentation = glucose -->
lactic acid
|
 |
KREBS Cycle :
oxidizes : 2 pyruvates to CO2 + H2O
produces :
8 NADH,
2 ATP, 2 FADH2
releases :
6 CO2
occurs in the mitochondria [is aerobic
= O2]
|
ETC
- Electron Transport Chain :
uses carrier proteins (including cytochromes, etc...) &
passes
e- & H+ from NADH &
FADH2 to O2 to make
H2O
generates a
proton gradient
(chemiosmosis) across the inner mitochondria
membrane
|
& ATP synthase :
the enzyme of the inner mitochondrial membrane
 that
passively carries
H+
back into mitoplasm & makes ATP directly |
Glycolysis... don't
memorize the
pathway, but learn the...
KEY REACTIONS of GLYCOLYSIS...
Concept Activity 9.2 -
Glycolysis
1.
substrate level phosphorylation*
[occurs twice in glycolysis]
2.
redox reaction
step 6* involving
NAD+
3.
reactions -->
investment phase* &
payoff phase* - Summary of glycolysis*
Quicktime movie animation of glycolysis*view
for homework
SUMMARY
GLYCOLYSIS
figure*
-
2 ATP to
initiate
-
2 substrate level phosphorylation steps = 4 ATP gross
thus Glycolysis makes:
what
goes in & come out*
2 ATP (net),
2 NADH, and
2 PYRUVATES
remember the role of the ... Fermentations &
Shuttles
the Glucose song
Heterotrophic Metabolism in Aerobic Organisms...
Krebs Cycle [Sir
Hans Krebs] the
Fate of Pyruvate*
PYRUVATE
DEHYDROGENASE Reaction... [
before Krebs cycle itself
]
in
mitoplasm
(Fig 9.10)*
oxidizes PYR -->
acetyl-CoA
a multienzyme
complex of 60 proteins and 5 coenzymes
involves
CoASH*
-----> acetyl coenzyme A [Fritz Lippman]
reactions:
1. decarboxylation
(-CO2),
2. reduction of NAD+
-->
NADH,
3. acylation & synthesis of
AcoA* |
 |
|
|
KEY Reactions of KREBS CYCLE
1. NAD+ is reduced
(NADH) and FAD is also reduced (FADH2)
2. substrate level
phosphorylation occurs (GTP <--> ATP)
3. decarboxylation
occurs [-COOH]
4.* an acylation
reaction via coenzyme-A (forms
Acetyl-coA)
SUMMARY Reactions: [Krebs
Cycle
Quicktime Movie*]
Summary
figure* full
cycle |
 --> how
many actual ATP
have we made so far?
Activity
9.3-
The Citric Acid (Krebs) Cycle |
OXIDATIVE PHOSPHORYLATION &
ELECTRON
TRANSFER CHAIN...
Concept Activity 9.4 -
Electron Transport*
the coupling of
oxidation
of substrates (-e) to the phosphorylation of
ADP to make ATP
µ remember, most of the energy of
glucose's bonds is now carried in NADH &
FADH2
e-
passed from NADH/FADH2
to O2 via "carrier
molecules"*
names*
these series of
electron carrier proteins occur in 4 membrane subunits
fig
9.16*
I) NADH Reductase,
II) Succinate Dehydrogenase
III) Cytochrome Reductase, IV) Cytochrome Oxidase
Virtual Cell - ETC animation*
CHEMIOSMOSIS
(fig
9.16*)
& ATP Synthase (fig
9.14* & EM)
creation of
a hydrogen ion gradient (H+)
by
e- flow thru the
ETC
- some
e- carriers release
protons to outside (into
perimitochondrial space)
-
bacteriorhodopsin*
provides experimental proof of H+
gradient making ATP
-
H+ diffuse
back into mitoplasm thru ATP synthase --->
ATP via a
molecular motor
-
Boyer
hypothesis* &
animation
of ATP synthase of mechanism by D. Nicholson*
ATP
synthase & H-ion Gradient synthesizes ATP*view@home
OVERVIEW of
Cell Respiration*...
µ A rule of thumb for amount of ATP
made per e- pair
(P/O ratio)* -->
NADH = 3 ATP FADH2 = 2 ATP
So How much
ATP is made per Glucose* ?
based on 3 ATP per NADH
& 2 ATP per FADH2
idealized = 36 to 38 ATP
What can serve as
substrates for aerobic metabolism?*
carbohydrates, proteins, lipds... can serve as
substrates
Aerobic metabolism intermediates are precursors for other molecules*
How is heterotrophic
metabolism regulated?
1. stiochiometric [substrate concentration] levels is a main control
mechanism
2. allosteric
controls include: +AMP/ADP stimulate enzymes & +ATP
inhibits enzymes
Key allosteric Enzyme :
PHOSPHOFRUCTOKINASE*
feedback inhibition
allosteric regulation
SUMMARY
- Heterotrophic Metabolism - Cell Respiration
1. Substrates
= sugars, amino acids acids, fatty acids
2. Glyco-lysis,
Krebs Cycle, ETC, &
ATP synthase are
Universal
to cells
3. Products = C02,
H20, and energy as
NADH,
FADH2, &
ATP
4. part of process is Anaerobic (doesn't
require -02
; GLYCO-LYSIS)
alcohol &
lactate fermentations (... anaerobic respiration)
& part is
Aerobic (requires +02 ;
glycolysis
& Krebs Cycle)
5. Reactions include:
oxidation,
reduction, substrate
level phosphorylation,
decarboxylation, acylation, &
hydrolysis (or dephosphorylation)
6. Energy capture is
via electron transfers,
gradients, proton
pumps, & ATP synthase*
7. Regulation is by:
feedback inhibition & allosteric modulation
of key enzyme: phosphofructokinase
8. Intracellular compartmentation:
glycolysis is in the cytoplasm
Krebs Cycle is mostly in the mitoplasm of mitochondria
ETC is in the cristae membranes of mitochondria
9. process is central
KEY* to all
metabolic pathways in cells
IUBMB-Nicholson Metabolic Pathways
Chart
next lecture*
- photosynthesis
 Key Concepts*
If you have comments or suggestions, email me at
cmallery@miami.edu
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copyright c2007,
Charles Mallery, Department of Biology, University of Miami, Coral Gables, FL 33124
Last Update -November 12, 2009
oxidative
phosphorylation animation
- Individual reaction steps
of glycolysis
|
