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Cellular respiration
How do humans (and all living things) stay alive?
Aerobic Cellular Respiration
Glucose + O2 Æ CO2 + H2O + ATP
ƒ Specific organelle (Eukaryotes):
Mitochondrion
Aerobic Cellular Respiration
is an Enzyme pathway
A
EzA
B
EzB
Sequence of enzyme controlled reactions
C
EzC
D
EzD
EzE ATP
(cellular respiration)
E
ƒ Cellular respiration is catabolic pathway: breakdown of compounds (glucose)
Uses Electron Transport Chains (ETC)
ƒ In aerobic cellular respiration
ƒ e- (electrons) are transferred between special molecules named “electron carriers”
ƒ present in the inner membrane of both mitochondria and chloroplasts
ee-
e-
ƒ Inner membrane of
mitochondria
and…
e-
ee-
e-
Free electrons carrier molecules: coenzymes NAD+ & FAD
temporarily hold the high energy e- released in Glycolysis and Krebs, and the H+ originally
present in the glucose, and transfer the e- to the Electron Transport Chain (ETC)
NADH
FADH2
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Cellular respiration
Cellular Respiration
Burning the fuel of life (GLUCOSE)
2 types of cellular respiration…
Anaerobic: no molecular (O2) oxygen is used
Aerobic: molecular oxygen is required in the process
A) Aerobic Cellular Respiration
General equation for aerobic cellular respiration
C6H12O6 + 6O2 + 2ATP
6CO2 + 6H2O + ( Energy: Heat +38ATP)
Why ATP also as a reactant?
2 ATP molecules are needed to make the glucose unstable and ready to react
• Covalent bonds in the glucose and subsequent by-products are broken
down and e- (electrons) from H (hydrogen) atoms are used in etransport to produce ATP
1. Glycolysis
• Cytoplasmatic pathway
• Breakdown of glucose without the use of oxygen
• Energy (ATP) is needed to begin the reactions
Summary:
• 4 ATPs generated -2 ATPs used
= 2 final ATPs
• 2 NADHs
• 2 Pyruvic acids
1 Glucose (6 carbons)
ATP
Enzyme 1
GlucoseGlucose-P (6 carbons)
Enzyme 2
FructoseFructose-P (6 carbons)
ATP
Enzyme 3
FructoseFructose-1,6 biP (6 carbons)
Two sets of reactions:
1)
• Glucose is a very stable molecule
• Energy is needed to make it unstable and
easy to break down
• 2 ATP are used to initiate the process
• Each step requires a specific enzyme
2 Glyceraldehyde 33-P (3 carbons)
5 stages
Enzyme 4
2NADH
2ATP
2 ATP
Enzyme 9
2)
• Reactions are used to synthesize ATP and
capture hydrogens (H)
•The coenzyme NAD+ capture the H and eand is reduced to NADH
• Again, each step requires a specific enzyme
2 Pyruvic acid (3 carbons)
2
Cellular respiration
2. Krebs cycle
•Summary:
•Mitochondrion matrix pathway Æ Pyruvic acid enter
• 1 ATP is generated
the mitochondrion
• 6 CO2 are released
• Five pairs of H become attached
•When both Pyruvic acid molecules have
to NAD+(4) and FAD(1)
been processed:
(1) all the original C atoms from the
glucose have been converted to CO2 2 Pyruvic acid 3 carbons
Enzyme 1
(2) all the original H atoms from the
glucose have been transferred to NAD+
NADH CO 2 Acetyl CoA 2 carbons
or FAD coenzymes
2
Oxaloacetate
Enzyme 2
4 carbons
NADH
6 carbons
Enzyme 3
Enzyme 10
4 carbons
6 carbons
Krebs
cycle
Enzyme 9
Enzyme 4
5 carbons
Enzyme 5
4 carbons
Enzyme 8
FADH2
Enzyme 6
4 carbons
CO2
5 carbons
NADH
CO2
Enzyme 7
4 carbons
ATP
3. Electron Transport Chain (ETC)
Summary:
• 32 ATP are generated
• H2O is generated using O2
• NAD+ and FAD are
released to be used again
• Inner mitochondrion membrane pathway Æ etransported by NADH and FADH2 are released in
the inner membrane system
ƒ e- participate in the
ETC, this changes
the membrane
properties and
makes it permeable
to H+
(2)
ƒ H+ (protons) rush
across the membrane
(diffuse from high to
low)
(3) H+
H+
H+
H+
H+
H+
ADP+Pi
H+
(1) H Æ
e- +
H+
H+
H+
NADH
H+
O2
+4H+
ƒ (4) H+ return to the
original side using an
enzyme as an exit
ATPase (enzyme)
ATP
2H2O
+ +
H+ HH
ƒ (5)
ƒ e- come from H atoms that are converted to…
ƒ Protons = H+ accumulate in the inner space
The energy from the H+ flow is used
to make ATP, main product for cellular
respiration
ƒ Molecular O2 is used to receive the H+
and H2O is formed as a waste product
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Cellular respiration
B) Fermentation: Anaerobic cellular respiration
Lactic acid fermentation
ƒ Last H acceptor is converted to lactic acid
ƒ In bacteria, lactic acid eventually
interfere with metabolic processes and
the bacteria die
ƒ Used in dairy products (yogurt,
cheese, etc)
ƒ In humans: occurs in…
ƒ red blood cells (that lack
mitochondria)
ƒ muscle cells: in long periods
of exercise for example when
oxygen is unavailable Æ we
feel muscles tired because of
the accumulation of lactic acid
Æ cramping of muscles and
pain
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