Download fermentation

Chapter 7
Section 1 Glycolysis and Fermentation
Objectives
• Identify the two major steps of cellular respiration.
• Describe the major events in glycolysis.
• Compare lactic acid fermentation with alcoholic
fermentation.
• Calculate the efficiency of glycolysis.
Chapter 7
Section 1 Glycolysis and Fermentation
Harvesting Chemical Energy
• Cellular respiration is the process by which cells break
down organic compounds (food) to produce ATP (energy)
• Organic compounds are needed to drive processes of cellular
respiration just like gasoline is used to create energy to drive the
processes for automobiles
• Both autotrophs and heterotrophs use cellular respiration to
make CO2 and water from organic compounds and O2.
• The products of cellular respiration are the reactants in
photosynthesis; conversely, the products of photosynthesis
are reactants in cellular respiration.
• Cellular respiration can be divided into two stages:
first comes glycolysis and then aerobic respiration.
Chapter 7
Section 1 Glycolysis and Fermentation
Overview of Cellular Respiration
• Glycolysis is the process of converting organic compounds
into three-carbon molecules of pyruvic acid, producing a
small amount of ATP and NADH (electron carrier molecule)
• Glycolysis is an anaerobic process because it doesn’t require
the presence of oxygen
• Aerobic Respiration takes place when oxygen is present in
the cell’s environment, pyruvic acid is broken down and
NADH is used to make a large amount of ATP
• The following equation summarizes cellular respiration:
C6H12O6 + 6O2 enzymes 6CO2 + 6H2O + energy (ATP)
Chapter 7
Section 1 Glycolysis and Fermentation
Photosynthesis-Cellular Respiration Cycle
Chapter 7
Section 1 Glycolysis and Fermentation
Glycolysis
• Cellular respiration begins with glycolysis, which
takes place in the cytosol of cells.
• During glycolysis, one six-carbon glucose molecule
is oxidized to form two three-carbon pyruvic acid
molecules.
• A net yield of two ATP molecules is produced for
every molecule of glucose that undergoes glycolysis.
Chapter 7
Section 1 Glycolysis and Fermentation
Glycolysis
When glycolysis occurs a molecule of glucose
is split, two molecules of pyruvic acid are
made and some ATP is produced
Chapter 7
Section 1 Glycolysis and Fermentation
Glycolysis
Click below to watch the Visual Concept.
Visual Concept
Chapter 7
Section 1 Glycolysis and Fermentation
Fermentation
• If oxygen is not present, some cells can convert
pyruvic acid into other compounds through additional
biochemical pathways that occur in the cytosol. The
combination of glycolysis and these additional
pathways is fermentation.
• Fermentation does not produce ATP, but it does
regenerate NAD+, which allows for the continued
production of ATP through glycolysis.
Chapter 7
Section 1 Glycolysis and Fermentation
Cellular Respiration Versus Fermentation
Chapter 7
Section 1 Glycolysis and Fermentation
Fermentation, continued
• Lactic Acid Fermentation
– In lactic acid fermentation, an enzyme converts
pyruvic acid into another three-carbon compound,
called lactic acid.
– When muscles are exercised excessively in the
absence of sufficient oxygen, lactic acid is
produced...this can cause cramping
– When not enough oxygen there will be excess or
extra lactic acid present
Chapter 7
Section 1 Glycolysis and Fermentation
Fermentation, continued
• Alcoholic Fermentation
– Some plants and unicellular organisms, such as
yeast, use a process called alcoholic
fermentation to convert pyruvic acid into ethyl
alcohol and CO2.
Chapter 7
Section 1 Glycolysis and Fermentation
Two Types of
Fermentation
Some cells engage in lactic
acid fermentation when
oxygen is absent. In this
process, pyruvic acid is
reduced to lactic acid and
NADH is oxidized to NAD+
Some cells engage in
alcoholic fermentation,
covering pyruvic acid into
ethyl alcohol. Again, NADH
is oxidized to NAD+
Figures 7-4 and 7-6
Pgs 134-135
Chapter 7
Section 1 Glycolysis and Fermentation
Comparing Aerobic and Anaerobic Respiration
Click below to watch the Visual Concept.
Visual Concept
Chapter 7
Section 1 Glycolysis and Fermentation
Efficiency of Glycolysis
• Through glycolysis, only about 2 percent of the
energy available from the oxidation of glucose is
captured as ATP.
• Much of the energy originally contained in glucose is
still held in pyruvic acid.
• Glycolysis alone or as part of fermentation is not very
efficient at transferring energy from glucose to ATP.
Chapter 7
Section 1 Glycolysis and Fermentation
Efficiency of Glycolysis cont.
• To figure efficiency of glycolysis use the following
equation:
– Eff. of glycolysis =
Energy required to make ATP
X 100
Energy released by oxidation of glucose
• Two ATP molecules are produced from every glucose molecule that is
broken down by glycolysis
• If the formation of a standard amount of ATP under certain
conditions requires 12 kcal of energy and the complete
oxidation of glucose yields 686 kcal of energy, how
efficient is glycolysis at extracting energy from glucose?
Chapter 7
Section 2 Aerobic Respiration
Objectives
• Relate aerobic respiration to the structure of a mitochondrion.
• Summarize the events of the Krebs cycle.
• Summarize the events of the electron transport chain and
chemiosmosis.
• Calculate the efficiency of aerobic respiration.
• Contrast the roles of glycolysis and aerobic respiration in
cellular respiration.
Chapter 7
Section 2 Aerobic Respiration
Overview of Aerobic Respiration
• In eukaryotic cells, the processes of aerobic
respiration occur in the mitochondria. Aerobic
respiration only occurs if oxygen is present in the cell.
– REMEMBER: Cellular Respiration begins in the cell’s
cytoplasm and ends in the mitochondria
• The Krebs cycle occurs in the mitochondrial matrix.
The electron transport chain (which is associated with
chemiosmosis) is located in the inner membrane.
Chapter 7
Section 2 Aerobic Respiration
The Krebs Cycle Quick Overview
• The Krebs Cycle is a biochemical pathway that breaks down
acetyl CoA, producing CO2, hydrogen atoms, and ATP.
• In the mitochondrial matrix, pyruvic acid produced in
glycolysis reacts with coenzyme A to form acetyl CoA. Then,
acetyl CoA enters the Krebs cycle.
• One glucose molecule is completely broken down in two
turns of the Krebs cycle. These two then produce four CO2
molecules, two ATP molecules, and hydrogen atoms that are
used to make six NADH and two FADH2 molecules.
• The bulk of the energy released by the oxidation of glucose
still has not been transferred to ATP.
Chapter 7
Section 2 Aerobic Respiration
The Krebs Cycle cont.
• Follow steps in your book, pgs 138-139
– In step 1, a two-carbon molecule of acetyl CoA combines
with a four-carbon compound, oxaloacetic acid, to produce
a six-carbon compound, citric acid
– In step 2, citric acid releases a CO2 molecule and a
hydrogen atom to form a five-carbon compound. The loss
of the hydrogen atom with its electron causes citric acid to
become oxidized. NAD+ becomes NADH.
– In step 3, the five-carbon compound formed in step 2 also
releases a CO2 molecule and a hydrogen atom, forming a
four-carbon compound, NAD+ is reduced to NADH, and a
molecule of ATP is synthesized from ADP.
Chapter 7
Section 2 Aerobic Respiration
The Krebs Cycle cont.
• Follow steps in your book, pgs 138-139
– In step 4, the four-carbon compound formed in step 3
releases a hydrogen atom to form another four-carbon
compound. In this step, the hydrogen atom is used to reduce
FAD to FADH2
• FAD is very similar to NAD+, FAD accepts electrons during redox reactions
– In step 5, the four-carbon compound formed in step 4
releases a hydrogen atom to regenerate oxaloacetic acid,
which keeps the Krebs cycle operating. The electron in the
hydrogen atom reduces NAD+ to NADH.
Chapter 7
Section 2 Aerobic Respiration
Electron Transport Chain and Chemiosmosis
• High-energy electrons in hydrogen atoms from NADH and
FADH2 are passed from molecule to molecule in the electron
transport chain along the inner mitochondrial membrane.
Electron transport and
chemiosmosis take
place along the inner
mitochondrial
membrane and
involve five steps
Figure 7-11, Page 140
Chapter 7
Section 2 Aerobic Respiration
Electron Transport Chain and
Chemiosmosis, continued
• Protons (hydrogen ions, H+) are also given up by NADH
and FADH2.
• As the electrons move through the electron transport
chain, they lose energy. This energy is used to pump
protons from the matrix into the space between the inner
and outer mitochondrial membranes.
• The resulting high concentration of protons creates a
concentration gradient of protons and a charge gradient
across the inner membrane.
Chapter 7
Section 2 Aerobic Respiration
Electron Transport Chain and
Chemiosmosis, continued
• As protons move through ATP synthase and down their
concentration and electrical gradients, ATP is produced.
Oxygen combines with the electrons and protons to form
water.
Chapter 7
Section 2 Aerobic Respiration
Electron Transport Chain and Chemiosmosis,
• The Importance of Oxygen
– ATP can be synthesized by chemiosmosis only if
electrons continue to move along the electron transport
chain.
– By accepting electrons from the last molecule in the
electron transport chain, oxygen allows additional
electrons to pass along the chain.
– As a result, ATP can continue to be made
through chemiosmosis.
– With oxygen present, the Krebs cycle and the electron
transport chain provide organisms an alternative to
glycolysis, produce most of the ATP needed for life, and
break down glucose to produce carbon dioxide, water,
and ATP.
Chapter 7
Section 2 Aerobic Respiration
Efficiency of Cellular Respiration
• Cellular respiration can produce up to 38 ATP
molecules from the oxidation of a single molecule of
glucose. Most eukaryotic cells produce about 36 ATP
molecules per molecule of glucose.
• Thus, cellular respiration is nearly 20 times more
efficient than glycolysis alone.
Chapter 7
Section 2 Aerobic Respiration
Efficiency of Cellular Respiration
• To figure efficiency of cellular respiration use the following
equation:
Energy required to make ATP
• Eff. of cellular respiration =
X 100
Energy released by oxidation of glucose
• If the formation of 38 molecules of ATP requires 266
kcal of energy and the complete oxidation of glucose
yields 686 kcal of energy, how efficient is cellular
respiration at extracting energy from glucose?
Chapter 7
Section 2 Aerobic Respiration
A Summary of Cellular Respiration
• Cellular respiration occurs in two stages
• Glycolysis – glucose is converted into pyruvic
acid, producing a small amount of ATP and
NADH, oxygen is not needed
• Aerobic respiration – pyruvic acid is converted to
CO2 and water in the presence of oxygen,
producing a large amount of ATP
• In cellular respiration, most energy is transferred
during the electron transport chain
Chapter 7
Section 2 Aerobic Respiration
A Summary of Cellular Respiration cont.
• Another Role of Cellular Respiration
– Providing cells with ATP is not the only important
function of cellular respiration.
– Molecules formed at different steps in glycolysis
and the Krebs cycle are often used by cells to
make compounds that are missing in food.
Chapter 7
Section 2 Aerobic Respiration
Summary of Cellular Respiration
Looking at this diagram we can see the steps of cellular respiration. Look closely at
the top dealing with the breakdown of different molecules that are broken down to
create ATP, when living cells break down molecules energy is stored as ATP, but it
also releases some heat.
The book gives the example (pg 143) that an automobile is only about 25 percent
efficient at extracting energy from gasoline, most of the 75% that is left is lost as
heat.