NAME:
SUBJECT: GENERAL BIOLOGY 1
WEEK 3
Module 3
SECTION:
Aerobic and Anaerobic Respiration
What I Need to Know
In module 2, you have learned about the patterns of electron flow through light reactions
events.
You also learned about the significant events of the Calvin cycle. In this module, you will learn how
to differentiate aerobic from anaerobic respiration. Glycolysis, Kreb’s cycle, and Electron Transport Chain (ETC) will also be
discussed as the sequence of cellular respiration. After going through this module, you are expected to:
1. Differentiate aerobic from anaerobic respiration, and (STEM_BIO11/12-IIa-j-6)
2. Explain the major features and sequence the chemical events of cellular respiration (STEM_BIO11/12-IIa-j-7).
Cellular respiration is a set of metabolic reactions and processes that takes place in the cells of an organisms to
convert chemical energy from oxygen molecules or nutrients into ATP and released waste product. There are two types of
respiration: the aerobic respiration and anaerobic respiration. While aerobic respiration is a process that requires oxygen,
on the other hand, anaerobic respiration, oxygen is not required. Aerobic and anaerobic respiration differ in terms of the
amount of energy that is produced. Anaerobic respiration produces less energy when compared with the process of aerobic
respiration.
We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to
harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate
(ATP). ATP a high energy molecule, is expended by working cells. Cellular respiration occurs in both eukaryotic and
prokaryotic cells. It has three main stages: glycolysis, the citric acid cycle, and electron transport
What’s New
Now that you have remembered about the two stages of photosynthesis which are the
light reaction and dark reaction which also known as Calvin Cycle. Perform the activity below.
Score: ___/ 10
ACTIVITY 1: Show me the Difference!
Directions: Fill in the table below with the correct answer in the column provided. Write the letter
only.
Aerobic
Anaerobic
1.
6.
2.
7.
3.
8.
4.
9.
5.
10.
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
Maximum yield of 36 to 38 ATP molecules per glucose
Rapid breakdown of glucose
Cause burning sensation in the muscle during strenuous exercise (in fermentation)
Brain cells in the human body can only live aerobically. They die if molecular oxygen is absent
Outputs are carbon dioxide, water and ATP
Electrons in NADH are transferred to electron transport chain
O2 is the final electron acceptor of the electron transport system
Single metabolic pathway (in fermentation
Pyruvate proceeds to acetyl formation in the mitochondrion
Cause burning sensation in the muscle during strenuous exercise (in fermentation)
What Is It
Aerobic respiration takes place in almost all living things. Some organisms can respire
in absence of air. There are a number of fermentations pathways that different cells used; yeast cells produced ethyl alcohol
by fermentation. Certain cells of our body, namely muscles cells, used lactic acid fermentation. Depending on the organism,
some of the other products of fermentation includes acetic acid, formic acid, acetone and isopropyl alcohol.
In plain language, anaerobic means where there is no air and thus anaerobic respiration is a term used for the
respiration that occurs without the use of oxygen. In this process, the molecules carry oxidation, when oxygen is absent.
This results in the production of energy or ATP. This type of respiration is also equivalent to fermentation when energy
production path (Glycolytic pathway) is functioning in one cell. There are two processes of this type of respiration alcoholic
fermentation, where the Glucose is broken down and produces Energy (ATP), Ethanol and Carbon Dioxide; Lactate
fermentation where Glucose breaks down into Energy and Lactic Acid (e.g. soreness of muscles after exercise).
AEROBIC RESPIRATION
ANAEROBIC RESPIRATION
How alike?
Both undergo glycolysis in the cytoplasm of the cell
Both undergo substrate-level phosphorylation and oxidative phosphorylation and chemiosmosis in producing ATP
molecules
Both split the 6-carbon glucose into two molecules of pyruvate, the three-carbon molecule
Both involve a series of enzyme-controlled reactions that take place in the cytoplasm
Both use NAD+ (nicotinamide adenine dinucleotide), a redox coenzyme that accepts two electrons plus a hydrogen
(H+) that becomes NADH
Both performed by eukaryotic and prokaryotic cells
AEROBIC RESPIRATION
ANAEROBIC RESPIRATION
How different?
Maximum yield of 36 to 38 ATP molecules
per glucose
maximum yield of 2 ATP molecules per glucose for obligate
anaerobes
Complete breakdown of glucose to carbon
dioxide and water with the
use of oxygen
Partial degradation of glucose without the use of oxygen
(obligate anaerobes)
Multiple metabolic pathways
Single metabolic pathway (in fermentation
Pyruvate proceeds to acetyl formation in the
mitochondrion
Pyruvate is broken down to ethanol and carbon dioxide or lactate (in
fermentation)
The presence of enough oxygen in the cell
makes the cell perform its job smoothly
without burning
sensation
Cause burning sensation in the muscle during strenuous exercise (in
fermentation)
More efficient in harvesting energy from
glucose with estimated 39% energy
efficiency (36-38 ATP) in eukaryotic
organisms but much
higher ATP production (38 to 40
ATP) in prokaryotic organisms
Less efficient in harvesting energy from glucose with 2% energy
efficiency (for obligate anaerobes)
Outputs are carbon dioxide, water and ATP
Outputs are lactate, alcohol and carbon dioxide (in fermentation); but
reduced inorganic compound in
anaerobic respiration
Products produce are for biochemical
cycling and for the
cellular processes that require
energy
Produce numerous products with economic and industrial importance
through fermentation
Slow glucose breakdown
Rapid breakdown of glucose
Electrons in NADH are transferred to
electron transport chain
Electrons in NADH are transferred to electron transport chain; but in
fermentation electrons in NADH are
transferred to organic molecule
fermentation electrons in NADH are
transferred to organic molecule
Mechanism of ATP synthesis is by
substrate-level and oxidative
phosphorylation/chemiosmosis
Mechanism of ATP synthesis is by substrate-level and oxidative
phosphorylation/chemiosmosis; but in fermentation substrate-level
phosphorylation only during
glycolysis
O2 is the final electron acceptor of the
electron transport system
In anaerobic respiration, inorganic substances like NO3- or SO42- are
the final acceptor of the electron transport
system; but in fermentation, there is no electron acceptor
because it has no electron transport system
Brain cells in the human body can only live
aerobically. They die if molecular oxygen is
absent
Some organisms like yeasts (eukaryotic), many bacteria (prokaryotic)
and the human muscle cells (eukaryotic) can make enough ATP to
survive in facultative anaerobes (can live in the absence or presence
of oxygen). But under anaerobic conditions lactic acid fermentation
occurs. A facultative anaerobe needs to consume the nutrient at a
much faster rate when doing the fermentation or anaerobic process.
The process of anaerobic respiration yields relatively less energy as compared to aerobic respiration. The process
of anaerobic respiration for production of energy can occur in either of the following: A.) alcoholic fermentation wherein
glucose is broken down to ATP, ethanol and carbon dioxide, B.) lactic acid fermentation wherein glucose is broken down to
ATP and lactic acid.
Alcoholic Fermentation
Types of Anaerobic Respiration
Lactic Acid Fermentation
Starts with Glycolysis
Starts with Glycolysis
Occurs in Yeast, plants and one-celled organism
Occurs in animal muscle cells and some onecelled
organisms
Produces 2 ATP and ethyl alcohol
Produces 2 ATP and lactic acid
Produces soreness when it builds In your muscles
Alcoholic Fermentation
enzymes
Glucose
Lactic Acid Fermentation
enzymes
Glucose
carbon dioxide + alcohol + energy
lactic acid + energy
Sequence of Cellular Respiration
Glycolysis
Glycolysis begins with the six-carbon ring-shaped structure of a single glucose molecule and ends with two molecules
of a three-carbon sugar called pyruvate. Glycolysis consists of two distinct phases. The first part of the glycolysis pathway
traps the glucose molecule in the cell and uses energy to modify it so that the six-carbon molecules. The second part of
glycolysis extracts energy for the molecules and stores it in the form of ATP and NADH, the reduced form of NAD +.
The breakdown of the six-carbon glucose into two molecules of the three-carbon pyruvate occurs in ten steps, the first five
of which constitute the preparatory phase (Fig. 1). Note that two molecules of ATP are invested before the cleavage of
glucose into two three-carbon pieces; later there will be a good return on this investment.
Step 1. The first step in glycolysis is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the
phosphorylation of six-carbon sugar. Hexokinase phosphorylates glucose uses ATP as the source of the phosphate, and
produces glucose-6-phosphate, a more reactive form of glucose.
Step 2. The enzyme isomerase converts glucose 6-phosphate into one of its isomers, fructose-6phosphate. An isomerase
catalyzes the conversion of molecule into one of its isomer.
Step 3. The third step is the phosphorylation of fructose-6-phosphate, catalyzes by the enzyme phosphofructokinase. A
second ATP molecule donates a high energy phosphate to fructos-6phosphate, producing fructose-1,6-biphosphate.
Step 4. The newly added high-energy phosphates further destabilize fructose-1,6-biphosphate. This step employs an
enzyme, aldolase, to cleave 1,6-biphosphate into three-carbon isomer: dihydroxyacetone-phosphate and glyceraldehyde-3phosphate.
Step 5. An isomerase transforms the dihydroxyacetone-phosphate into its isomer, glycerlaldehyde3-phosphate. Thus, the
pathway will continue with two molecules of a single isomer. At this point in the pathway, there is a net investment of energy
from two ATP molecules breakdown of one glucose molecule.
Image taken from
General
Biology
TG.
Pay Off
Stage
Figure 1. Stages of Glycolysis
So far, glycolysis has cost the cell two ATP molecules produced two small, three-carbon sugar molecules. Both of
these molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the
two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two
even higher-energy NADH molecules. The energy gain comes in the payoff phase of glycolysis.
Step 6. The sixth step in glycolysis oxidizes the sugar (glyceraldehyde-3-phosphate), extracting high energy electrons, which
are picked up by the electron carrier NAD+, producing NADH. The sugar is then phosphorylated by the addition of a second
phosphate group, producing 1,3biphosphoglycerate.
Step 7. In this seventh step, catalyzed by phosphoglycerate kinase, 1,3-biphosphoglycerate donates a high energy
phosphate to ADP, forming one molecule of ATP. A carbonyl group on the 1,3-biphosphoglycerate is oxidized to a carbonyl
group, and 3-phosphoglycerate is formed.
Step 8. The remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing
2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (isomerase).
Step 9. Enolase catalyzes the ninth step. This enzyme causes 2-phosphoglycerate to lose water from its structure; this is a
dehydration reaction, resulting int the formation of a double bond and produces phosphoenolpyruvate (PEP).
Step 10. The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the
reverse reaction of pyruvate’s conversion into PEP) and results in the production of a second ATP molecule by substrate
phosphorylation and the compound pyruvic acid (or its salt form, pyruvate).
Citric Acid Cycle or Krebs Cycle
If oxygen is available, aerobic respiration will go forward. In eukaryotic cells, the pyruvate molecules produced at
the end of glycolysis are transported into mitochondria, which are the next site for cellular respiration. There, pyruvate will
be transformed into an acetyl group that will be picked up and activated by a carrier compound called coenzyme A (CoA).
CoA is made from vitamin B5, pantothenic acid. Acetyl CoA can be used in a variety of ways by the cell, but its major function
is to deliver the acetyl group derived from pyruvate to the next stage of the pathway in glucose catabolism.
Like the conversion of pyruvate to acetyl CoA, the citric acid cycle or Krebs cycle takes place in the matrix of
mitochondria. Almost all of the enzymes of the citric acid cycle are soluble, with the single exception of the enzyme succinate
dehydrogenase, which is embedded in the inner membrane of the mitochondrion. Unlike glycolysis, the citric acid cycle is a
close loop. The last part of the pathway regenerates the compound used in the first step. The eight steps of the cycle are a
series of redox, dehydration, and decarboxylation reactions that produce two carbon dioxide molecules, one GTP/ATP and
reduce forms of NADH and FADH2.
Image taken from
Lehninger’s
Principle
of
Biochemistry
Figure 2. The Citric Acid Cycle or Kreb’s Cycle
Step 1. Prior to the start of the first step, a transitional phase occurs during which pyruvic acid is converted to acetyl CoA.
Then, the first step of the cycle begins. This is the condensations step, combining the two-carbon acetyl group with a fourcarbon oxoacetate molecule to form a six-carbon molecule of citrate. CoA is bound to a sulfhydryl group (-SH) and diffuses
away to eventually combine with another acetyl group. This step is irreversible because it is highly exergonic. The rate of
this reaction is controlled by negative feedback and the amount of the ATP available. If ATP levels increase, the rate of this
reaction decreases. If ATP is in short supply, the rate increases.
Step 2. The citrate loses one water molecule and gains another as citrate is converted into its isomer, isocitrate.
Step 3. The isocitrate is oxidized, producing a five-carbon molecule, a-ketoglutarate, together with a molecule of CO2 and
two electrons, which reduce NAD+ to NADH. This is the step is also regulated by negative feedback from ATP and NADH,
and a positive effect of ADP.
Step 3 and 4. These steps are both oxidation and decarboxylation steps, which release electrons that reduce NAD+ to
NADH and release carboxyl group that forms CO2 molecules. A-ketoglutarate is the products of step three, and a succinyl
CoA. The enzymes that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.
In step 5, a phosphate group is substituted for coenzyme A, and a high-energy bond is formed. This energy is used in
substrate-level phosphorylation to form either guanosine triphosphate (GTP) or ATP. There are two forms of the enzymes,
called isoenzyme, for this step, depending upon the type of animal tissue in which they are found.
Step 6. this is a dehydration process converts succinate into fumarate. Two hydrogen atoms are transferred to FAD,
producing FADH2. The energy contains in the electrons in these atoms are insufficient to reduce NAD+ but adequate to
reduce FAD. Unlike NADH, this carrier remains attached to the enzyme and transfers to the electrons of the electron
transport chain directly. This process is made possible by the localization of the enzyme catalyzing this step inside the inner
membrane of the mitochondrion.
Step 7. Water is added to fumarate during this step and malate is produced.
Step 8. The last step in the citric cycle regenerates oxaloacetate by oxidizing malate. Another molecule of NADH is
produced in the process.
Electron Transport Chain
The electron transport chain is the last component of aerobic respiration and is the only part of glucose metabolism that
uses atmospheric oxygen. Oxygen continuously diffuses into plants, in animals, it enters the body through the respiratory
system. Electron transport is a series of redox reaction that resembles a relay race or bucket brigade in that electrons are
passed rapidly from one component to the next, to the endpoint of the chain where the electrons reduce molecular oxygen,
producing water. The electron transport chain is present in multiple copies in the inner mitochondrial membrane of
eukaryotes and the plasma membrane of prokaryotes.
Image taken from
https://images.ap
p.goo.gl/1obFTZ2
WpHCec35t9
Figure 4. The Electron Transport Chain
Complex I
To start, two electrons are carried to the first complex aboard NADH. This complex called NADH dehydrogenase complex,
labeled I, is composed of flavin mononucleotide (FMN) and an ironsulfur (Fe-S)-containing protein. The enzyme in complex
I is NADH dehydrogenase ad is very large protein containing 45 polypeptide chains. Complex I accepts electrons from
NADH, passing them to ubiquinone via FMN and Fe-S centers. It can pump four hydrogen ions across the membrane from
the matrix into the intermembrane space, and it is in this way that the hydrogen ion gradient is established and maintained
between the two compartments separated by the inner mitochondrial membrane.
Q and Complex II
Complex II directly receives electrons from FADH2, which does not pass through complex I. The compound connecting the
first and second complexes to the third is ubiquinone (Q). Q receives the electrons derived from NADH from complex I and
the electrons derived from FADH2, from complex II, including succinate dehydrogenase. The number of ATP molecules
ultimately obtained is directly proportional to the number of protons pumped across the inner mitochondrial membrane.
Complex III
The third complex is composed of cytochrome b, another Fe-S protein, Rieske center (2Fe2S center), and cytochrome c
proteins; this complex also called cytochrome oxidoreductase (cytochrome b-c complex). This complex receives electrons
from ubiquinone (Q), passing them on to cytochrome c which carries electron to complex IV (cytochrome oxidase complex).
Complex III pumps proton through the membrane and passes its electrons to cytochrome c for transport to the fourth
complex of proteins and enzymes.
Complex IV
The fourth complex is composed of cytochrome proteins c, d, and a. This complex contains heme groups and three copper
ions. The cytochromes hold an oxygen molecule very tightly between the iron and copper ions until oxygen is completely
reduced. The reduced oxygen then picks up two hydrogen ions from the surrounding medium to make water. The removal
of hydrogen ions from the mitochondrial matrix contributes to the ion gradient used in the process of chemiosmosis.
Chemiosmosis
In chemiosmosis, the free energy from the series of redox reactions just described, is to used pump hydrogen ions
(protons) across the membrane. The uneven distribution of H+ ions across the inner mitochondrial membrane establishes
both concentration and electrical gradients (thus, an electrochemical gradient), owing to the hydrogen ions’ positive charge
and their aggregation on one side of the membrane. If the membrane were open to the diffusion by the hydrogen ions, the
ions would tend to diffuse back across into the intermembrane, driven by their electrochemical gradient. Chemiosmosis is
used to generate 90% of the ATP made during aerobic glucose catabolism; it is also the method used in the light reactions
of photosynthesis to harnessed the energy of sunlight in the process of phosphorylation. The production of ATP using the
process of chemiosmosis in mitochondria is called oxidative phosphorylation. The overall result of these reactions is the
production of ATP from the energy of the electrons removed from hydrogen atoms. These atoms were originally part of
glucose molecule. At the end of the pathway, the electrons are used to reduced an oxygen molecule to oxygen ions. The
extra electrons on the oxygen attract hydrogen ions (protons) from the surrounding medium, and water is formed.
Image taken from
p.goo.gl/Q7kx9V
https://images.ap
RJiQ69jPAj9
Figure 5. ATP
Synthase
What I Have Learned
ACTIVITY 2: Venn Diagram
Directions: Compare aerobic and anaerobic respiration by accomplishing the Venn diagram below. Write the letters
only.
.
A. Pyruvate proceeds to acetyl formation in the
mitochondrion
G. Cause burning sensation in the muscles during
strenuous exercise
B. Rapid breakdown of glucose
H. Both undergo glycolysis in the cytoplasm of the cell.
C. Outputs are lactate, alcohol and carbon dioxide.
I. Products produce are for biochemical cycling and for
the cellular processes that require energy.
D. Both performed by eukaryotic and prokaryotic cells.
J. Multiple metabolic pathways
E. Outputs are carbon dioxide, water and ATP
K. Produce numerous products for economic and
industrial importance through fermentation
F. Single metabolic pathway (in fermentation)
L. Both split the 6-carbon glucose into two molecules of
pyruvate, the three-carbon molecule.
PERFORMANCE ACTIVITY: Gas Production.
Fermentation is a metabolic process that convert sugar to acids, gasses, and or alcohol. It occurs in yeast, bacteria,
and other microorganism as well as oxygen starved muscle cells.
Directions: Perform the activity below to understand further the lesson on fermentation. Take a picture of
the steps as you perform the activity. Print the pictures and submit together with the module.
Objective: To be able to produce carbon dioxide.
Materials:
• 4 plastic/gas bottles
• 4 balloons
• Sugar
• Cup
• Yeast
• 1 tablespoon
Procedure:
1. Label the 4 bottles from 1 to 4.
2. Add 1 tablespoon of yeast in each bottles
3. Add no sugar in bottle 1, add ½ tablespoon of sugar in bottle 2, 1 tablespoon in bottle 3, and 1 ½ tablespoon
in bottle 4
4. Add 1 cup of warm water in each bottle
5. With all the ingredients in each bottle gently shake the mixtures.
6. Cover the bottles using the balloon and observe for few hours.
Guide Questions: Encircle only the letters
1. Which of the 4 bottles produced large amount of gas?
2. How do you know that this bottle produces large amount of gas?
3. What is your implication in doing the activity?
Assessment
Directions. Choose the letter of your choice and write it on the space provided.
___1. Which of the following organelles present in the cell is associated with cellular respiration?
A. Chloroplast
B. mitochondrion
C. endoplasmic reticulum
D. nucleus
___2. During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest
energy level?
A. NAD+
B. NADH
C. ATP
D. FADH2
___3. How many ATP molecules are used up during glycolysis?
A. 1
B. 2
C. 3
D. 4
___4. The primary role of oxygen in cellular respiration is to
A. yield energy in the form of ATP as it passed down the respiratory chain
B. Act as an acceptor for electrons and hydrogen, forming water
C. combine with carbon, forming CO2
D. combine with lactate, forming pyruvate
___5. Which metabolic pathway is common to both cellular respiration and fermentation?
A. the oxidation of pyruvate to acetyl CoA
B. the citric acid cycle C. oxidative phosphorylation D. glycolysis
___6. It is the first step in cellular respiration that begins releasing energy stored in glucose.
A. Glycolysis
B. Krebs Cycle
C. ETC
D. Chemiosmosis
___7. If oxygen is NOT present, glycolysis is followed by _____________________
A. Krebs cycle
B. ETC
C. Calvin cycle
C. Fermentation
___8. What is the products of glycolysis?
A. Carbon dioxide B. FAD and NAD C. Pyruvic acid
D. Lactate
___9. What are the products of Electron Transport Chain?
A. Glucose and oxygen
B. ATP and water
C. Lactic acid
D. Oxygen and ATP
___10. What types of respiration does not require oxygen?
A. Aerobic
B. Anaerobic
C. Glycolysis D. Krebs cycle
___11. Lactic acid fermentation occurs in your muscles after a workout because your cells are struggling to get
A. Glucose
B. Sunlight
C. Oxygen
D. Water
___12. which of the following is a reactant of Krebs cycle?
A. Oxygen
B. Carbon dioxide C. Glucose
D. Pyruvate
___13. When an organism is in a low oxygen situation, such as running sprints, cellular respiration ceases and the organisms
must use a different metabolic pathway for creating energy without oxygen. What do we call this process?
A. Acidification B. Hydrolysis C. Fermentation
D. Citric acid cycle
___14. What is the main difference between aerobic and anaerobic respiration?
A. Aerobic respiration needs oxygen to occur, while anaerobic does not
B. Anaerobic respiration needs oxygen to occur, while aerobic does not
C. Aerobic respiration needs carbon dioxide to occur, while anaerobic does not
D. Aerobic respiration creates oxygen, while anaerobic does not
___15. Which of the following types of fermentation can occur during anaerobic respiration?
A. Glycolysis and fermentation
B. Alcohol fermentation and lactic acid fermentation
C. Lactic acid and ethanol
D. Aerobic and anaerobic