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Chapter 9
Cellular Respiration
Cellular Respiration Overview
Goals:
• Explain where organisms get energy for life processes
• Define cellular respiration
• Compare photosynthesis and cellular respiration
Chemical Energy and Food
• Organisms get their energy from
food
• Autotrophs make food (glucose)
• Heterotrophs consume food
Chemical Energy and Food (cont.)
• Energy is released when chemical bonds are broken
• Recall a calorie is the amount of energy required to raise the temperature of 1 g
of water 1 oC
• There are 1000 calories in 1 food Calorie (capital C)
• 1g of glucose can release 3,811 calories of heat energy if burned in the
presence of oxygen (combustion)
Cellular Respiration to the Rescue!
• Cellular respiration is the process that releases energy from food in
the presence of oxygen
• Happens through a series of controlled chemical reactions that can be
summarized as:
Stages of Cellular Respiration
Glycolysis is considered an
ANAEROBIC process because it
does not require oxygen
The Krebs Cycle (indirectly) and
the Electron Transport Chain
(directly) use oxygen and so are
considered AEROBIC processes
Notice that each stage captures some of the energy
available in food and uses it to produce energy (ATP)
Step 1: Glycolysis “split sweets”- glucose
undergoes a series of chemical reactions in
the cytoplasm to form 2 molecules of
pyruvic acid
Summary
Don’t forget mini-step!
Step 2: Krebs Cycle- 2 pyruvic acid
molecules from glycolysis undergo a
series of chemical reactions in the
mitochondrial matrix
Products formed:
C
I
K
S
S
F
M
O
I digress…
• You're not alone.
Summary
Step 2: Krebs Cycle
Takes place in the matrix of
mitochondria
Process in aerobic
CO2 is released
Net gain:
2 ATP
8 NADH
2 FADH2
• Why twice as many as the diagram?
• Because there are 2 pyruvic acids, so two
Acetyl CoA enter the Krebs Cycle for each
glucose molecule.
Step 3: Electron Transport Chainenergy from electrons carried by
NADH and FADH2 to the inner
mitochondrial membrane is used
to make ATP.
As e- move down the etc, energy
“spillover” is used to pump H+
into inner membrane space.
H+ diffuse back through ATP
synthase which adds phosphates
onto ADP molecules to form ATP.
Lots of it!
Energy Totals
Glycolysis
2 ATP
2 NADH*
Krebs
2 ATP
8 NADH
2 FADH2
2 ATP
4 ATP (traveling from cytoplasm)
2 ATP
24 ATP
4 ATP
total ~36 ATP
3 ATP per NADH and 2 ATP per FADH2, but *only 2 ATP for NADH in glycolysis
Summary
Step 3: ETC
Takes place in along the
inner mitochondrial
membrane
Process in aerobic
O2 is the final e- acceptor in
the etc
Net gain:
~30 ATP (on average 3 ATP
per electron carrier NADH
and FADH2)
1
CR Review
1. Name process
a. Where does it take place?
b. Aerobic or anaerobic?
c. Reactants/products
2
2. Name process
a. Where does it take place?
b. Aerobic or anaerobic?
c. Reactants/products
3
3. Name process
a. Where does it take place?
b. Aerobic or anaerobic?
c. Reactants/products
Fermentation
• How do organisms generate energy when oxygen is not available?
• In the absence of oxygen, fermentation releases energy from food
molecules by producing ATP.
Fermentation
Fermentation is a process by which energy
can be released from food molecules in the
absence of oxygen. Fermentation occurs in
the cytoplasm of cells.
Fermentation
•
Under anaerobic conditions, fermentation
follows glycolysis. During fermentation,
cells convert NADH produced by
glycolysis back into the electron carrier
NAD+, which allows glycolysis to continue
producing ATP.
Alcoholic Fermentation
Yeast and a few other microorganisms use alcoholic
fermentation that produces ethyl alcohol and carbon
dioxide.
• This process is used to produce alcoholic beverages
and causes bread dough to rise.
Alcoholic Fermentation
•
Chemical equation:
Pyruvic acid + NADH  Alcohol + CO2 + NAD+
Lactic Acid Fermentation
•
•
Most organisms, including humans, carry out fermentation using a
chemical reaction that converts pyruvic acid to lactic acid.
Chemical equation:
Pyruvic acid + NADH  Lactic acid + NAD+
Energy and Exercise
• How does the body produce ATP during different stages of exercise?
• For short, quick bursts of energy, the body uses ATP already in
muscles as well as ATP made by lactic acid fermentation.
• For exercise longer than about 90 seconds, cellular respiration is the
only way to continue generating a supply of ATP.
Quick Energy
•
Cells normally contain small amounts of ATP
produced during cellular respiration, enough for a few
seconds of intense activity.
•
Lactic acid fermentation can supply enough ATP to
last about 90 seconds. However, extra oxygen is
required to get rid of the lactic acid produced. Following
intense exercise, a person will huff and puff for several
minutes in order to pay back the built-up “oxygen debt”
and clear the lactic acid from the body.
Long-Term Energy
•
For intense exercise lasting longer than 90 seconds,
cellular respiration is required to continue production of
ATP.
•
Cellular respiration releases energy more slowly than
fermentation does.
•
The body stores energy in the form of the
carbohydrate glycogen. These glycogen stores are
enough to last for 15 to 20 minutes of activity. After that,
the body begins to break down other stored molecules,
including fats, for energy.
Long-Term Energy
•
Hibernating animals like this brown bear rely on
stored fat for energy when they sleep through the
winter.