Download HOW CELLS HARVEST ENERGY

HOW CELLS HARVEST ENERGY
(AKA CELLULAR RESPIRATION)
CH 9
Energy is stored in the chemical bonds of organic molecules
carbs
proteins
fats
Breakdown of these large organic molecules releases ATP which is used for work
(primarily to drive endergonic reactions)
Energy stored in chemical bonds is potential energy
Energy released when those bonds are broken is kinetic energy
I.
Catabolism of glucose
Cellular respiration = catabolism of glucose to produce ATP
3 types of cellular respiration:
o Aerobic respiration (nearly all organisms)
o Anaerobic respiration (only a few types of bacteria)
o Fermentation (when aerobic can’t work)
A. Aerobic Respiration
Requires O2
Occurs in most organisms
In eukaryotes, most of it occurs in the mitochondria
Produces 36 ATP
Occurs in 4 stages:
Glycolysis
Oxidation of pyruvate
Kreb’s cycle
Electron transport chain and oxidative phosphorylation
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
1. Glycolysis
Occurs in ALL cells
Occurs in the cytoplasm
Breaks down glucose to 2 3-carbon molecules called pyruvate
Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
4 ATP
formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
RESULTS:
ATP production
2 ATP used
4 ATP made
Net yield = 2ATP
NADH production
2 NADH made which go to ETC to make ATP
Only 2 of the 36 ATP has been made
THE REST OF THE ENERGY STORED IN GLUCOSE IS
NOW IN THE PYRUVATES
http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html
2. Oxidation of pyruvate
Occurs in the mitochondria
Converts pyruvate to acetyl CoA
Produces NADH
NADH produced goes to ETC to make ATP
Fate of acetyl CoA:
o It enters into the Kreb’s cycle to continue aerobic
respiration
o If too much glucose is broken down in glycolysis, the excess
acetyl CoA is used to make fatty acids and triglycerides
(too much sugar makes you fat)
CYTOSOL
MITOCHONDRION
NAD+
NADH + H+
2
1
Pyruvate
3
CO2
Coenzyme A
Transport protein
3. Kreb’s cycle
Occurs in the mitochondrial matrix
Acetyl CoA
2 pyruvate
CO2
NAD+
Co
A
NADH
+ H+
2 Acetyl CoA
Co
A
Co
A
Citric
acid
cycle
2 CO2
6 NAD+
2 FADH2
6 NADH
+ 3 H+
2 FAD
2 ADP +
Pi
2 ATP
Yield:
For EACH glucose molecule
6 NADH
2 FADH2
2 ATP
NADH and FADH2 go on to ETC to make ATP
http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cy
cle_works__quiz_1_.html
4. Electron Transport Chain
Occurs on the inner membrane of the mitochondria
Uses energy in NADH and FADH2 to make 32 ATP
NADH and FADH2 donate e- to ETC
As e- is moved thru ETC, the energy in e- is used to actively
pump protons across the inner membrane
NRG from the e- is now stored in the proton gradient
As the protons diffuse down their concentration gradient, ATP
synthase uses the energy in the gradient to make 32ATP by
chemiosmotic phosphorylation
The e- that was hopping thru ETC goes to O2 which acts as final
acceptor of e4H+ +4e- + 202 →2H2O
+
H
+
H
+
H
+
H
Protein
complex
of electron
carriers
Cyt c
V
Q
ATP
synthase
+
FADH
2
NADH
(carrying
electrons
from food)
NAD
1
2 H + /2O2
H2O
FA
D
ADP + P i
+
ATP
+
H
1 Electron transport
chain
2 Chemiosmosi
s
Oxidative
phosphorylation
http://www.science.smith.edu/departments/Biology/Bio231/etc.html
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter9/
Aerobic respiration: the big picture
Electron shuttles
span membrane
CYTOSOL
2 NADH
6 NADH
2 NADH
Glycolysis
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2
Pyruvate
2
Acetyl
CoA
+ 2 ATP
Citric
acid
cycle
+ 2 ATP
Maximum per glucose:
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
About
36 or 38 ATP
B. Regulation of Aerobic Respiration
By feedback regulation
Glucose + ADP +NAD + FAD → ATP +NADH +FADH2
High ATP means cell has enuf ATP and ATP acts like allosteric
inhibitor to turn off 2nd enzyme in glycolysis (phosphofructokinase)
High NADH means too much glucose is being broken down and the
cell has enuf ATP it acts as allosteric inhibitor and inhibits oxidation of
pyruvate
High ADP means cell needs more ATP and ADP acts as allosteric
activator to activate phosphofructokinase
C. Aerobic respiration, small mammals and generation of heat
In the cold, many small mammals will allow the proton gradient
generated in the ETC to bypass ATP synthase
Thus instead of making ATP the energy in the proton gradient is
lost as heat to help maintain body temp
D. Aerobic respiration in prokaryotes
Almost identical to eukaryotes:
Glycolysis
Oxidation of pyruvate
Kreb’s cycle
ETC and chemiosmotic phosphorylation
HOWEVER:
Since they have no mitochondria, all of aerobic respiration takes
place in the cytoplasm, and the ETC occurs on the cell membrane
E. Anaerobic respiration
Occurs in certain bacteria
Has the same stages as aerobic respiration:
Glycolysis
Oxidation of pyruvate
Kreb’s cycle
ETC
However, O2 is NOT the final e- acceptor.
They use another molecule as the final e- acceptor
CO2
SO2
F. Fermentation
Occurs when not enuf O2 is available for aerobic respiration
Produces limited ATP (only 2) when compared to aerobic respiration
NADH produced in glycolysis is converted back to NAD to keep
glycolysis running
2 types: lactic acid fermentation and alcoholic fermentation
1. Lactic acid fermentation
Occurs in muscle cells when circulatory system can’t supply
enuf O2 for aerobic respiration
Produces lactic acid
2. Alcoholic fermentation
Occurs in yeast cells
Produces alcohol and CO2
The fate of pyruvates depends on the amount of oxygen:
II.
Catabolism of proteins and fats
Animals eat proteins fats and carbs
Within digestive tract proteins are digested to amino acids, starch and
sucrose are digested to glucose, and fats are digested to acetyl CoA
Amino acids, glucose and acetyl CoA diffuse out of small intestine to
blood
Circulatory system delivers these molecules to all cells and they enter
into aerobic respiration at various points
III.
How photosynthesis and respiration work together
Products of one are reactants of other
o Glucose and oxygen made in photosynthesis enter into aerobic
respiration
o The carbon dioxide from aerobic respiration enters into
photosynthesis