Download Biology 5.3 Cellular Respiration

Biology 5.3 Cellular Respiration
Cellular
Respiration
Key Concepts we will cover today. . .
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Respiration is the release of energy by combining oxygen with digested
food (glucose).
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Carbon dioxide and water are also produced as byproducts. They are the
waste products of respiration.
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Cellular respiration has two stages. First glucose is broken down to
pyruvate during glycolysis, making some ATP.
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The second stage involving the Krebs cycle is a series of reactions that
produce energy-storing molecules during anaerobic respiration.

During aerobic respiration, large amounts of ATP are made in an electron
transport chain.
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When oxygen is not present, fermentation follows glycolysis, regenerating
NAD+ needed for glycolysis to continue
Cellular Energy
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Most of the foods we eat
contain energy stored in
proteins, carbohydrates, and
fats.
Before our cells can use this
energy it must be transferred
to ATP within the cells.
Cells transfer the energy in
organic compounds to ATP
through a process called
cellular respiration.
Process cellular respiration
Cellular Energy
•
Oxygen in the air you breath makes
the production of ATP more
efficient. Some ATP is made
without this oxygen however.
1.
Metabolic processes that require
oxygen are called aerobic
processes.
2.
Metabolic processes that require
NO oxygen are called
anaerobic processes.
Cellular Energy: Respiration
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The energy-producing process in living
things is called respiration.
Respiration is the release of energy
by combining oxygen with digested
food (glucose).
Carbon dioxide and water are also
produced as byproducts. They are the
waste products of respiration.
A simple formula to show respiration
looks like this:
Glucose + oxygen  carbon dioxide (waste) + water (waste) + energy
Stages of Cellular Respiration
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Cellular respiration is the process cells
use to extract the energy in organic
compounds, particularly glucose.
Cellular respiration occurs in three major
stages
 Stage 1: glucose is converted to
pyruvate producing a small amount of
ATP and NADH
 Stage 2: Aerobic respiration occurs:
this is when oxygen is present,
pyruvate and NADH make more ATP.
 Stage 3: In an electron transfer
chain, continuing reactions
create a large amount of ATP
from the materials from stage
2.
Stage 1: Breakdown of Glucose
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The primary fuel for cellular
respiration is glucose which is
formed when carbohydrates
such as starch and sucrose are
broken down.
In the First stage of cellular
respiration, glucose is broken
down in the cytoplasm during a
process called glycolysis.
Glycolysis is an enzyme-assisted
anaerobic process that
 breaks down one six carbon
molecule of glucose
 to two three-carbon
pyruvate ions
1
Stage 1: Breakdown of Glucose: Glycolysis
Glycolysis can be
summarized in 4 steps
Step 1:
 in a series of three
reactions,
 phosphate groups from
two ATP molecules
 are transferred to a
glucose molecule
Stage 1: Breakdown of Glucose: Glycolysis
Glycolysis can be summarized
in 4 steps
Step 2:
 In two reactions,
 the resulting six-carbon
molecule is broken down to
 two three-carbon compounds,
 each with a phosphate group
Stage 1: Breakdown of Glucose: Glycolysis
Glycolysis can be
summarized in 4 steps
Step 3:
 Two NADH molecules are
produced,
 and one more phosphate
group is transferred
 to each three-carbon
compound.
Stage 1: Breakdown of Glucose: Glycolysis
Glycolysis can be summarized in 4
steps
Step 4:
In a series of 4 reactions,
 each three carbon
compound is converted to
 a three-carbon pyruvate,
 producing 4 ATP molecules
in the process

Stage 1: Breakdown of Glucose: Glycolysis
Summary: In this 4 step process:
1.
2.
3.
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Glycolysis uses two ATP molecules
but produces four ATP molecules
in return.
Thus, we gain two ATP molecules
for a gain ratio of 2 to 1.
Glycolysis is followed by another
set of reactions that uses the
energy temporarily stored in
NADH to make more ATP.
Stage 2: Production of ATP
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When oxygen is present,
pyruvate produced during
glycolysis enters a
mitochondrion and is converted
to a two-carbon compound.
This reaction produces one
carbon dioxide molecule, one
NADH molecule, and one twocarbon acetyl group
The acetyl group is attached to
a molecule called coenzyme A
forming a compound called
acetyl-CoA.
Stage 2: Production of ATP
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Acetyl-CoA enters a
series of enzyme-assisted
reactions called the Krebs
Cycle.
The Krebs Cycle has
several steps we will be
breaking down.
Stage 2: Production of ATP
Step 1:
Acetyl-CoA combines with
a 4 carbon compound,
forming a six carbon
compound and releasing
“coenzyme A”
Stage 2: Production of ATP
Step 2:
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Carbon Dioxide (CO2)
is released from the sixcarbon compound, forming
a five-carbon compound.
Electrons are transferred
to NAD+, making a
molecule of NADH.
Stage 2: Production of ATP
Step 3:
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Carbon dioxide is released
from the five-carbon
compound, resulting in a
four-carbon compound.
A molecule of ATP is
made, and a molecule of
NADH is produced.
Stage 2: Production of ATP
Step 4:
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The existing four-carbon
compound is then
converted to a new fourcarbon compound.
Electrons are
transferred to an
electron acceptor called
FAD, making a molecule of
FADH2.
FADH2 is another type
of electron carrier.
Stage 2: Production of ATP
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After the Krebs Cycle,
NADH and FADH2 now
contain much of the
energy that was
previously stored in
glucose and pyruvate.
When the Krebs Cycle is
completed, the fourcarbon compound that
began the cycle has been
recycled, and acetyl-CoA
can enter the cycle again.
Electron Transfer Chain
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In aerobic respiration, electrons donated by NADH and
FADH2 pass through an electron transport chain.
Step 1: The electron transfer chain pumps hydrogen ions
out of the inner compartment
Electron Transfer Chain
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Step 2: At the end of the chain, electrons and hydrogen
ions combine with oxygen, forming water (H2O).
Electron Transfer Chain
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Step 3: ATP is produced as hydrogen ions diffuse into the
inner compartment through a channel protein.
Electron Transfer Chain
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Hydrogen ions diffuse back into the inner compartment through
a carrier protein that adds a phosphate group to ADP, making
ATP.
At the end of the electron chain, hydrogen ions and spent
electrons combine with oxygen molecules (O2) forming water
molecules (H20)
Respiration in the Absence of Oxygen
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What happens when there is not enough
oxygen for aerobic respiration to occur?
When oxygen is not present, NAD+ is
recycled in another way
Under anaerobic conditions, electrons
carried by NADH are transferred to
pyruvate produced during glycolysis.
This process recycles NAD+ needed to
continue making ATP through glycolysis.
This recycling of NAD+ using an organic
hydrogen acceptor is called fermentation.
Respiration in the Absence of Oxygen
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Two important types of
fermentation are lactic acid
fermentation and alcoholic
fermentation.
Lactic acid fermentation by
some prokaryotes and fungi is
used in the production of
foods such as yogurt and some
cheeses.
Lactic Acid Fermentation
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Lactate is the ion of an organic acid
called lactic acid. For example, during
exercise, pyruvate in muscles is
converted to lactate when muscles must
operate without enough oxygen.
Fermentation enables glycolysis to
continue producing ATP in muscles as
long as the glucose supply lasts. Blood
removes excess lactate from muscles.
Lactate can build up in muscle cells if it
is not removed quickly enough,
sometimes causing muscle soreness.
Alcoholic Fermentation
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Alcoholic fermentation is a twostep process.
First, pyruvate is converted to
a two-carbon compound,
releasing carbon dioxide.
Second, electrons are
transferred from a molecule of
NADH to the two-carbon
compound, producing ethanol.
Alcoholic Fermentation
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Alcoholic fermentation by yeast, a
fungus, has been used in the
preparation of many foods and
beverages.
Wine and beer contain ethanol made
during alcoholic fermentation by yeast.
Carbon dioxide released by the yeast
causes the rising of bread dough and
the carbonation of some alcoholic
beverages, such as beer.
Ethanol is actually toxic to yeast. At a
concentration of about 12%, ethanol
kills yeast.
Thus, naturally fermented wine
contains about 12% ethanol.
Production of ATP: Summary
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The total amount of ATP that a cell is able to harvest from each
glucose molecule that enters glycolysis depends on the presence or
absence of oxygen.
Cells use energy most efficiently when oxygen is present.
In the first stage of cellular respiration, glucose is broken down to
pyruvate during glycolysis. Glycolysis is an anaerobic process (no oxygen
required), and it results in a gain of two ATP molecules.
In the second stage of cellular respiration, the pyruvate passes
through either aerobic respiration (requires oxygen) or fermentation.
When oxygen is not present, fermentation occurs instead.
Production of ATP: Summary
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Most of a cell’s ATP is made during aerobic respiration. (requiring
oxygen)
For each molecule of glucose that is broken down, as many as two
ATP molecules are made directly during the Krebs cycle,
and up to 34 ATP molecules are produced later by the electron
transport chain.
Key Concepts: Review . . .
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Cellular respiration has two stages. First glucose is broken
down to pyruvate during glycolysis, making some ATP.
The Krebs cycle is a series of reactions that produce
energy-storing molecules during anaerobic respiration
During aerobic respiration, large amounts of ATP are made
in an electron transport chain.
When oxygen is not present, fermentation follows
glycolysis, regenerating NAD+ needed for glycolysis to
continue
Computer Lab Activities
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Go to the following Web-based activities
and watch and complete both activities
including the quiz at the end of the
second site
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video 1 cellular respiration
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Aerobic respiration UK version
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Aerobic Respiration