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CELLULAR ENERGETICS Feb 12 - Darwin's BDay
read chapter
12/6e
Sep 25 - Thomas Hunt Morgan's BDay
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How Cells Make ATP |
via two fundamental
eukaryotic processes |
Autotrophic Metabolism
Photosynthesis
Photophosphorylation |
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Heterotrophic Metabolism
Cell Respiration ("Oxidation of Foods")
Aerobic & Anaerobic Respiration
Oxidative Phosphorylation
Substrate Level Phosphorylation
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...mainly by
phosphorylation of ADP |
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Primary Mechanisms of
Phosphorylation |
1.
Substrate Level
Phosphorylation |
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Pi |
see mcb
12.3*
steps 7 & 10
in glycolysis
page
482
or
ecb 13.1 |
2.
Chemiosomosis (Oxidative Phosphorylation)
subst-H
(glu) + NAD+
---> NADH + subst
(CO2 + H2O)
NADH
--e-transport --> H+ proton motive
force
--ATP synthase-->
ATP |
overview*
3.
Photosynthetic
Phosphorylation
Light
+ H2O +
NADP+ ----> NADPH
--e--->
H+
--ATP synthase-->
ATP |
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Cellular Respiration...
oxidation of food molecules
Evolution of aerobic metabolism was a major step
in the history of life on planet Earth...
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defined as: series cytoplasmic & mitochondrial...
- linked enzymatic pathways
-
catalyze stepwise OXIDATION of food molecules to make ATP
physiological view:
uptake of O2
& release of CO2
biochemical view:
O2
consumption & CO2
production
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3 Stages:
1.
Digestion of food polymers --> monomers
[CH2O]
2. Production of
AcoA (via
pyruvate)
-->
glycolysis
&/or FA-oxidation
3. Oxidation of
AcoA to CO2 & H2O
--> KC & ETC
ecb 13.2 pg 429* |
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4 Pathways of
cellular respiration: (glucose oxidation in
eukaryotes) |
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Glyco-lysis
[cytoplasm]
glucose --> pyruvate + NADH + ATP |
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Krebs Cycle
[mitochondria]
Acetyl-coenzymeA --> CO2 + NADH + GTP + FADH2 |
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Electron Transport Chain
(ETC)
[mitochondrial membrane]
passage of e's from NADH to O2 ---> H2O + H+ gradient |
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ATP synthase
[mitochondrial membrane]
mitochondrial membrane protein which
makes ATP as H+ move into
mitoplasm with
their chemical gradient |
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overview
mcb6e fig 12.5b* (overview
Karp fig 5.5*) |
GLYCO-LYSIS: Greek -glykos = "sweet" + "splitting"
 *text
description
Embden,
Meyerhof,
Parnas
Pathway
-
- 10 step enzymatic pathway
-
overview ecb 13.3
hexose (C6) --> 2 PYR (C3)
+ 4ATP (2 net) + 2NADH |
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- anaerobic = no requirement of oxygen,
but can occur in oxygen's presence
- cytoplasmic location (?
seems too structured for randomness
of aqueous solution
?)
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- energy investment phase (coupled Rx's)
phosphorylation of low energy intermediates
to high energy ones
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- energy capture phase...
2
key reactions types:
- redox reaction (glyceraldehyde3-PDH)
- substrate level phosphorylation
mcb6e
12.3 steps 6 & 7*
substrate-P + ADP ---> substrate +
ATP
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Karp fig 5.6
(pathway)µ &
mcb6e
12.3µ &
ecb panel 13.1 pg 432 |
GLYCO-LYSIS... Ancillary
Pathways
or how cells use its
products
Fates of
PYRUVATE...
if anaerobic –
1. lactic acid respiration -
via lactic acid dehydrogenase (mcb
12.5b muscle)*
2. alcoholic fermentation -
via alcohol dehydrogenase (mcb
12.5a ethanol)*
if
aerobic -
3.
Krebs Cycle -pyruvate
enters mitochondrial Krebs
NADH
SHUTTLES
*
text description
evolutionary advantage... moves the
e's from the cytoplasmic NADH's
into mitochondrial NADH or
FADH2
for use in the ETC...
glycerol-P shuttle* (Karp fig5.9) - skeletal muscle/brain
malate shuttle* (mcb
12.11) - liver, kidney, heart muscle
KEY REACTIONS of GLYCOLYSIS
substrate level phosphorylation (see
steps 7 &
10*)
redox reaction involving NAD+ (see
step 6* &
ecb panel 13.1 pg 432)
Summary of GLYCOLYSIS
(ecb
panel
13.1 pg 433*)
2 ATP to initiate pathway
2 substrate level phosphorylations
makes 2 ATP (net), 2 NADH, and 2 PYRUVATE
Fermentations (lactate & alcohol) &
the Shuttles
KREBS CYCLE
[Citric Acid Cycle
or Tricarboxylic Acid Cycle]
a cyclical biochemical pathway resulting in
aerobic oxidation of cellular fuels,
such
as CH2O, fatty acids, & amino acids, while making
CO2, H2O, &
ATP.
HISTORY
1910's - enzymatic nature learned -
dehydrogenases... (EC
1. - oxidoreductases)
1930's - substrates identified -
di-COOH's
experiments on minced flight muscle prep's
(NY city pigeons)
1937 -
Sir Hans Krebs
- citrate
synthetase...
(condensing enzyme)
acetyl-coA
[2C] + OAA
[4C] ---> citrate
[6C] +
coA-SH
1948 - cycle localized within the
mitochondria*
1961
-
Peter Mitchell
-
proposes Chemiosmosis...
[makes a proton
(H+) gradient]
Overall reaction:
acetyl-CoA + 3NAD +
E-FAD + GDP +
P + 2H2O ---->
--->
CoASH + 3NADH +
E-FADH2 + GTP + 2CO2
ENZYMES of KREBS CYCLE
mcb fig 12.10*
& overview
of aerobic respiration
5 dehydrogenases - ISDH, a KGDH, SDH, MDH, & PDH
2 hydrolyases - aconitatse & fumarase
1 thiokinase - succinyl thiokinase
1 synthetase - citrate synthatase
2 multi-enzyme complexes - each with 60 proteins & 5 coenzymes
each
1. pyruvate dehydrogenase
(figure*)
2.
alpha ketoglutarate dehydrogenase
µ
but prior to Krebs need to get pyruvate into mitochondria... figure*
Pyruvate
Dehydrogenase Complex...
catalyzes the Oxidative Decarboxylation
of an alpha-Keto
acid
(pyruvate)
3 enzymes :
60 proteins subunits (figure)*
A. pyruvate decarboxylase
12
dimers = 24
identical subunits
B.
lipoamide reductase transacetylase
(reductase)
8 trimers = 24 identical subunits, each 3 lipoates
C.
dihydrolipoyl dehydrogenase
6
dimers 12 subunits with FAD
Carbohydrates
vs. Fats as energy sources ?
FATTY ACID Metabolism
[ energy sources =
fats
vs. carbs
- fig 13.10* ]
oxidation Fatty Acids: triacylglycerol
=
mbc p491.Fatty Acids*
fat/lipid droplet &
fatty acid= figure &
ecb
2.4 pg 72
µ converts
free
fatty acids in blood into to Acetyl-CoA
in the mitochondria
3 Steps
of Fatty Acid Oxidation Cycle [beta
oxidation]
1. oxidation of
COOH end of free fatty acid & linking
FFA to
CoASH
2. transport of
fatty acyl-coA into
mitoplasm from cytoplasm
3. oxidation of fatty acyl-coA into 2 carbon fragments
of
Acetyl-CoA
4 enzymes of beta-oxidation cycle...
1.
fatty acyl-coA LIGASE (on outer mito.
membranes)
FA-COOH +
ATP +
CoASH <-->
FAcoA
+ AMP
+ PP
converts cyotplasmic FA to Fatty-acyl-coA
[c-c-c-c-ScoA]
2.
carnitine acyl-TRANSFERASE 1
(outer mito memb.)
FattyCoA
+ carnitine
<-> Fatty
acyl-carnitine
+ CoASH
transfers FAcoA to carnitine for transport
across mito
3.
carnitine acyl-TRANSFERASE 2
(in mitoplasm)
Fatty acyl-carnitine
+ CoASH <--> FAcoA
+ carnitine
releases
carnitine & leave FAcoA inside the mitoplasm
4.
fatty acyl-coA DEHYDROGENASE (in mitoplasm)
reduces FAD and
NAD+ in 4 steps
[my figure*] [another
figure]
Beta-Oxidation Cycle and the
fatty acyl-coA dehydrogenase
enzymes
four steps for this
mitochondrial dehydrogenase enzyme system...
a)
dehydrogenation w FAD --> FADH2
b)
hydration - addition of water
c)
dehydrogenation - NAD --> NADH.
d)
thiol clevage
with CoASH
mcb
12.12 FA oxidation
&
fig 13.9b
pg 438*
& Karp fig 5.8 pg191
release of a 2carbon fragment as
Acetyl-CoA
Net result: each turn of the cycle shortens a long chain fatty acid by
2 carbons
generating 1
AcoA, 1
NADH and 1
FADH2
for entry into Krebs cycle...
| Balance Sheet Aerobic Oxidation
6C- glucose vs.
6C- FFA |
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µ Rule of Thumb...
the P/O ratio (via mito &
ETC) 1 NADH = 3 ATP & 1 FADH2
= 2 ATP |
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Cell RESPIRATION
via glucose |
beta-OXIDATION
via 6C-FFA (c-c-c-c-c-c) |
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to start -
GLYCOLYSIS |
- 2 ATP |
@ LIGASE step |
-
1 ATP |
glyceraldehyde DH
PGA kinase (via SLP)
pyruvate kinase (via SLP) |
+ 2 NADH* + 6 ATP
+ 2 ATP
+ 2 ATP |
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KREBS Cycle per each
PYR |
per 2 cycles @
Fatty-AcoA-dehydrogenase |
|
PDH
-
2CO2 |
+ 2 NADH + 6 ATP |
+
3 AcoA*
+ 2 FADH2
+ 2 NADH |
+ 4 ATP
+ 6 ATP
+ 10 ATP |
ISDH
-
2CO2
αKGDH
- 2CO2
thiokinase
SDH
MDH |
+ 2 NADH + 6 ATP
+ 2 NADH + 6 ATP
+ 2 GTP + 2 ATP
+ 2 FADH2 + 4 ATP
+ 2 NADH + 6 ATP |
Totals
1 glucose --> 2 ATP + 2 pyruvate
--->
- 6 CO2 + 2 ATP + 10 NADH* + 2 FADH2 + 2 GTP |
Totals
6C-FFA via
beta-oxidation --> 10 ATP
& *Krebs cycle (3 AcoA)
-->
~
36 ATP |
*per
gly+Krebs+shuttles
total ATP = 36
to 38
ATP via 1 AcoA
alone =
12 |
total ATP = ~
46 ATP - 1 ATP =
~ 45 ATP
a gain of
~ 7
to 9
ATP |
Regulation of
Glucose Metabolism & Krebs Cycle...
substrate availability - mass action controls
flow of intermediates [out
& in] -
fig
13.23*
allosteric inhibition -
PFK-1&2*
&
classical feedback inhibition
models - fig 4.38 pg 152*
covalent modification - reversible phosphorylation...
protein kinases &
phosphoprotein phosphatases [Review]
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µ 4 key enzymes are involved in
Krebs regulation… |
| 1.
PDH
[arsenic
poisoning] |
+
SER-P by
kinase -
inactive |
| 2. citrate synthetase
|
+
ADP -
ATP/NADH/cit/AcoA |
| 3. isocitrate dehydrogenase
|
+
ADP/Ca+2
- ATP |
| 4. alpha-keto gluatarate dehydrogenase
|
+
Ca+2 - AcoA & NADH |
my figure*
[apply regulation to the
metabolic
charts
&
Nicholson ]
ENZYME REGULATION…
by
adjusting reaction rates of existing enzyme
via...
COVALENT MODIFICATION of
existing enzyme...
- addition of P to an
inactive enzyme --> activate enzyme via
P transfer
- reversible phosphorylation changes protein conformation
- done by
PROTEIN KINASES, which transfer P from
ATP
fig*
tyrosine kinases add P to TYR
residues of enzymes de/activating them
serine/theronine kinases add P to
SER or THR residues
- PROTEIN PHOSPHATASES... dephosphorylate,
thus inactivating
the Key metabolic reaction is a -->
REDOX Reaction...
AH + BO
< --- > A + BOH
C6H12O6
+ 6O2 < --- > 6CO2 + 6H2O + e's
recall...
the 3 steps in the Mitochondrial Oxidation of PYR
1. PYR --> CO2 + H2O
--> NADH/FADH2
Krebs
2. e- of NADH/FADH2 --> O2 to make H2O
ETC
3. ADP + P ---> ATP H+ transport via
Chemiosmosis
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