Transcript Ch. 9: Cellular Respiration

Ch. 9: Cellular Respiration
• The process by which cells break down
glucose (C6H12O6), or a nutrient that has
been converted to glucose or one of its
simpler products, into carbon dioxide
(CO2) and water (H2O).
• Potential energy stored in covalent bonds
is released (heat and ATP are produced).
ATP allows cells to do work.
TERMS TO KNOW
• Coenzyme: a nonprotein organic molecule that plays an
accessory role in enzyme-catalyzed reactions, often
acting as a donor or acceptor of electrons. NAD+ is a
coenzyme that becomes NADH when reduced (receives
H electrons)
• Endergonic reaction: a chemical reaction to which
energy from an outside source must be added before the
reaction can proceed (the reactants contain less energy
than the products)
• Exergonic reaction: energy-yielding and tends to
proceed spontaneously (reactants contain more energy
than the products and excess energy is released)
TERMS TO KNOW
• Activation energy: energy required to
destabilize chemical bonds to initiate a
chemical reaction
• Oxidation: loss of an electron by an atom
or molecule
• Reduction: gain of an electron by an atom
or molecule. Oxidation-reduction
reactions transfer energy in living systems.
Fig. 9.3
Fig. 9.4
Making ATP from Glucose
Catabolism
• Substrate level phosphorylation: a
phosphate is transferred directly to ADP
(glycolysis)
• Aerobic Respiration: Electrons (H+) are
harvested, transferred along the (Electron
Transport Chain) making ATP
(chemiosmosis) and finally donated to O2,
releasing H2O
Cellular Respiration
- Process that releases energy by breaking down
glucose and other food molecules in the presence of
oxygen.
6O2 + C6H12O6 -> 6CO2 +6H2O + ATP+heat
(reactants)
(products)
- Three Stages of Cellular Respiration:
1. glycolysis
2. Krebs Cycle (citric acid cycle)
3. Electron Transport
Fig. 9.6
Fig. 9.7
Cellular Respiration
• Glycolysis:
1. requires no oxygen (anaerobic)
2. occurs in the cytosol catalyzed by enzymes
3. 2 molecules of ATP are used to break one
molecule of glucose in 1/2, producing two
molecules of pyruvic acid (still containing most
of the energy of the original glucose molecule),
NADH (containing high energy electrons), and 4
molecules of ATP
Glycolysis cont.
• A small portion of the energy in the
glucose is released and some makes 4
molecules of ATP (substrate-level
phosphorylation)
• Remainder of small portion of energy
released (H+) are transferred to an energy
trransferring molecule(NAD+) which then
become NADH.
Pyruvate Pathways
•
•
Cells harvest energy from the electrons of covalents bonds of molecules.
The energy depleted electrons associated with a proton as a hydrogen atom
that are used to make ATP are donated to other molecules.
A) Aerobic Respiration: Pyruvate is oxidized into carbon dioxide (released)
and acetyl-CoA in the Krebs Cycle. Eventually, oxygen gas accepts the
high energy H atoms of NADH and FADH2 created in the rest of the Krebs
Cycle and water is created as a waste product (electron transport chain in
the membrane of the mitochondria)
B) Anaerobic Respiration: Pyruvate molecules are reduced to lactate and
NADH is oxidized to NAD+ to replenish the NAD+ for further glycolysis.
(some bacteria, fungi, and muscle cells). Used to make cheese and yogurt.
C) Fermentation: Pyruvate is reduced to ethanol alcohol and gives off 2
molecules of CO2 as well (bacteria and yeast) which is used in the bread,
beer and wine industries.
Fig. 9.9
Krebs Cycle
- Krebs Cycle (citric acid cycle)
1. requires oxygen (aerobic)
2. occurs in the inner membrane of mitochondria
3. pyruvic acid is oxidized into carbon dioxide (released) and acetylCoA.
4. Acetyl-CoA joins with a 4-carbon molecule and becomes citric acid
5. Citric acid is broken down, carbon dioxide is released, and 10
molecules of NADH and 2 molecules o FADH2 (both high
energy electron molecules) are produced
**If no oxygen is present, anaerobic respiration or fermentation
will occur instead of the Krebs Cycle. Pyruvate is oxidized and
becomes ethanol in grapes and bread dough and lactic acid in
muscles.
Cellular Respiration
- Krebs Cycle (citric acid cycle)
1. requires oxygen (aerobic)
2. occurs in the inner membrane of mitochondria (where necessary
enzymes are located)
3. pyruvic acid is oxidized into carbon dioxide (released) and acetylCoA. (co-enzyme)
4. Acetyl-CoA joins with a 4-carbon molecule and becomes citric acid
5. Citric acid is oxidized,more carbon dioxide is released, and 10
molecules of NADH and 2 FADH2 (high energy electron
molecules) are produced
6. These high energy molecules and their accompanying protons
move on to the ETC
Cellular Respiration
- Electron Transport:
1. The high energy electrons of NADH and FADH2 are
transferred to special energy accepting molecules
(Electron Transport System) within the cristae of the
inner mitochondria
2. As energized electrons leap from one of these
molecules to the next, their energy is used to pump their
accompanying protons from the inner chamber of the
mitochondria to the outer chamber. A concentration
gradient builds, and special carrier proteins bring (pump)
protons back in. The energy released from this pumping
is used to convert ADP and a phosphate into 34 more
ATP from each molecule of glucose (chemiosmosis)
ETC cont.
3. De-energized electrons are then accepted by oxygen
molecule and act as final electron acceptors
4. The electrons are reunited with their accompanying
protons (H+) and water is formed and released If this
final acceptor (O2) is not available, the electrons and
H+ ions will not move down the ETC and no additional
ATP will form in this step.
**36 molecules of ATP represents 38% of total energy
from glucose. Remaining 62% is given off as heat.
Fig. 9.16
Fig. 9.17
Fig. 9.18
Fig. 9.19
Fig. 9.10
Fig. 9.24a
Anaerobic Respiration
Alcohol Fermentation
Ex. Yeast activity in bread dough
1. Yeast break the sugar in the bread dough
into pyruvate and NADH. The pyruvate is
then broken down into acetaldehyde and
CO2 gas (bread rises)
2. The acetaldehyde becomes the electron
acceptor for NADH, and ethyl alcohol is
produced (up to 12%).
Fig. 9.24b
Anaerobic Respiration
Lactic Acid Fermentation
1. Muscle cells use NADH to convert
pyruvate into lactate (ionized form of
lactic acid)
2. Circulating blood removes excess
lactate, but if production exceeds
removal capability, lactic acid will build in
muscles and interfere with function (and
cause cramps)