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Class Starter
Answer the following questions:
How are the products of photosynthesis and
respiration related?
• The products of photosynthesis are the starting
materials for respiration.
What kinds of organisms undergo cellular respiration?
• All organisms, including photosynthetic
organisms, undergo cellular respiration as long
as oxygen is available.
Objectives
• How does glycolysis produce ATP?
• How is ATP produced in aerobic respiration?
• Why is fermentation important?
Section 9.3:
Cellular Respiration
Glycolysis
• The cells of most organisms transfer energy found
in organic compounds, such as those in foods, to
ATP.
• The primary fuel for cellular respiration is glucose.
Fats can be broken down to make ATP.
• Proteins and nucleic acids can also be used to
make ATP, but they are usually used for building
important cell parts.
Glycolysis
• Glycolysis
– enzymes break down one six-carbon molecule of
glucose into two three-carbon pyruvate molecules.
• The breaking of a sugar molecule by glycolysis
results in a net gain of two ATP molecules.
• This process of glycolysis is anaerobic, or takes
place without oxygen.
Glycolysis
• Glycolysis is the only source of energy for some
prokaryotes.
• Other organisms use oxygen to release even
more energy from a glucose molecule. Metabolic
processes that require oxygen are aerobic.
• In aerobic respiration, the pyruvate product of
glycolysis undergoes another series of reactions
to produce more ATP molecules.
http://www.youtube.com/watch?v=O5eMW4b29rg
Checkpoint
• What is the primary fuel for ATP production? What
else is sometimes used?
• What is the name of the process that breaks down
sugars called?
– What is the end result of this process?
– How many ATP’s are produced?
– Is this an aerobic or anaerobic process? Explain.
• Which process produces more energy?
Fermentation
• To make ATP during glycolysis, NAD+ is converted
to NADH.
• Organisms must recycle NAD+ to continue making
ATP through glycolysis.
• The process in which carbohydrates are broken
down in the absence of oxygen is called
fermentation.
• Fermentation enables glycolysis to continue
supplying a cell with ATP in anaerobic conditions.
Fermentation
• lactic acid fermentation
– pyruvate is converted to lactic acid.
– During vigorous exercise, lactic acid fermentation also
occurs in the muscles of animals, including humans.
• alcoholic fermentation
– one enzyme removes carbon dioxide from pyruvate. A
second enzyme converts the remaining compound to
ethanol, recycling NAD+ in the process.
Checkpoint
• What is required in order for glycolysis to continue?
• What process occurs if oxygen is not present?
– Is this an aerobic or anaerobic process?
• What is the difference between lactic acid and
alcoholic fermentation?
– Which one takes place in us when we exercise?
Aerobic Respiration
• Organisms such as humans can use oxygen to
produce ATP efficiently through aerobic respiration.
• The first stage of aerobic respiration is the Krebs
cycle, a series of reactions that produce electron
carriers.
• The electron carriers enter an electron transport
chain, which powers ATP synthase.
• Up to 34 ATP molecules can be produced from one
glucose molecule in aerobic respiration.
Aerobic Respiration
Krebs Cycle
• Pyruvate (from glycolysis) is broken down and
combined with other carbon compounds.
• Each time the carbon-carbon bonds are
rearranged during the Krebs cycle, energy is
released.
• The total yield of energy-storing products from
one time through the Krebs cycle is one ATP,
three NADH, and one FADH2.
Aerobic Respiration
Electron Transport Chain
• The second stage of aerobic respiration takes place
in the inner membranes of mitochondria, where
ATP synthase enzymes are located.
• Electron carriers, produced during the Krebs cycle,
transfer energy through the electron transport
chain.
• Energy from the electrons is used to actively
transport hydrogen ions out of the inner
mitochondrial compartment.
Aerobic Respiration
Electron Transport Chain
• Hydrogen ions diffuse through ATP synthase, providing
energy to produce several ATP molecules from ADP.
• At the end of the electron transport chain, the electrons
combine with an oxygen atom and two hydrogen ions to
form two water molecules.
• If oxygen is not present, the electron transport chain
stops. The electron carriers are not recycled, so the
Krebs cycle also stops.
Checkpoint
• How many molecules of ATP can be produced from
1 glucose molecule?
• What is the first stage of aerobic respiration?
– How is energy released from this process?
– What is produced from this process?
• What is the second stage of aerobic respiration?
– The goal of this process is to produce what?
– What is formed at the end of this process as a result of
oxygen being present?
– What happens if oxygen isn’t present?
Fermentation
Efficiency of Cellular Respiration
• In the first stage of cellular respiration, glucose is
broken down to pyruvate during glycolysis, an
anaerobic process.
• Glycolysis results in a net gain of two ATP molecules for
each glucose molecule that is broken down.
• In the second stage, pyruvate either passes through the
Krebs cycle or undergoes fermentation.
– Fermentation recycles NAD+ but does not produce ATP.
Fermentation
Efficiency of Cellular Respiration
• Cells release energy most efficiently when oxygen
is present because they make most of their ATP
during aerobic respiration.
• For each glucose molecule that is broken down, as
many as two ATP molecules are made during the
Krebs cycle.
• The Krebs cycle feeds NADH and FADH2 to the
electron transport chain, which can produce up to
32 ATP molecules.
Checkpoint
• During glycolysis, __________ is broken
down into ___________ resulting in the
production of _____ ATP. This is an
__________ process.
• If oxygen is present pyruvate travels to
the________, producing ___ ATP. _____
and ____ also made are passed to the
_____________ where ___ ATP are
produced as well as _____.
Summary
• The breaking of a sugar molecule by
glycolysis results in a net gain of two ATP
molecules.
• The total yield of energy-storing products
from one time through the Krebs cycle is
one ATP, three NADH, and one FADH2.
Summary
• Electron carriers transfer energy through
the electron transport chain, which
ultimately powers ATP synthase.
• Fermentation enables glycolysis to
continue supplying a cell with ATP in
anaerobic conditions.