Cellular
Respiration
Key Concepts we will cover today. . .

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.

Cellular respiration has two stages. First glucose is broken down to pyruvate
during glycolysis, making some ATP.

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.

When oxygen is not present, fermentation follows glycolysis, regenerating
NAD+ needed for glycolysis to continue
Cellular Energy

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

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

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

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.

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

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

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:

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:

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:

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

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 four-carbon
compound that began the
cycle has been recycled,
and acetyl-CoA can enter
the cycle again.
Electron Transfer Chain

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

Step 2: At the end of the chain, electrons and hydrogen ions
combine with oxygen, forming water (H2O).
Electron Transfer Chain

Step 3: ATP is produced as hydrogen ions diffuse into the
inner compartment through a channel protein.
Electron Transfer Chain

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

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

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

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

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

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

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

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 . . .

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 energystoring 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

Go to the following Web-based activities
and watch and complete both activities
including the quiz at the end of the second
site

video 1 cellular respiration

Aerobic respiration UK version

Aerobic Respiration