by  Carla Huffman

This activity corresponds with the following National Science Education Standards: Content Standards A, C, and G;
Teaching Standard A; Assessment Standards A

• Recognize and analyze alternative explanations and models (A); developing student understanding including the cell and matter, energy, and organization in living systems (C); historical perspectives (G)
• Select science content and adapt and design curricula to meet the interests, knowledge, understanding, abilities, and experiences of students (A)
• Authentic assessment opportunities (A)

•  Cell respiration is a fundamental function of aerobic organisms.  The concepts of glycolysis, Krebs cycle and electron transport system (oxidative phosphorylation) are important yet challenging.  The example for role playing electron transport provides both the principles and chemical activities.

Students will be able to:

• identity the components of electron transport system through role play.
• explain the role of intermediate energy carriers to the production of ATP molecules.
• describe the relationship of electron transport system to Krebs Cycle and glycolysis as it relates to cellular respiration.
• anaylze the understanding of cellular respiration to other types of mechanisms for obtaining energy.

• Grades 9 - 12:  Biological courses

•  The use of biology coloring book illustrations are helpful when explaining or modeling the steps for cellular respiration.
• Another resource which reinforces the concepts of glycolysis, oxidative decarboxylation, Krebs cycle and electron transport  is the video series "Cellular Respiration".  Video tapes are in 10 minute segments to compliment instruction.  http://192.156.97.132/kn/itv/cellular.sht
• The diagram below is a suggested setup for the classroom to role play the electron transport system component:

Cell Respiration Overview

 http://www.whitman.edu/offices_departments/biology/classes/B111/Modules/Respiration/Comparison.html
Chart for the comparison of aerobic and anaerobic catabolism.

B.Anabolism - uses chemical energy (ATP) to recombine simple organic molecules into complex organic molecules
    1. Complex molecules such as: proteins, carbohydrates, lipids, DNA, etc.

Cell Respiration Steps

I. GLYCOLYSIS (occurs in cellular cytoplasm or cytosol)

Glucose + enzyme 1 --- >glucose 6-phosphate +enzyme 2 --- > fructose 6-phosphate (unstable and wants to revert)

(6 carbon)                                                                                      Reaction coupling - an ATP immediately enters

                                                                 to prevent fructose 6-phosphate from reverting to

                                                                                                      glucose 6-phosphate

 

+ enzyme 3 --- > fructose diphosphate + enzyme 4 --- >cleaves into DHAP + PGAL --- >the DHAP + enzyme 5--->

                                                                                   (3 carbon)

 forms another PGAL        (The 2 PGAL have a higher energy potential than the original 6-carbon glucose molecule. From this

                   (3 carbon)        point, every molecule is in duplicate.)

Next, the 2 PGAL + enzyme 6--- > 2 DPGA (diphosphoglycerate) + enzyme 7--->

                 (NADH₂ is an intermediate energy carrier which is used to generate ATP later in

                                                        the process.  The electron deficient NAD⁺ tends to snap up a pair of electrons plus

                                                        H⁺ from the oxidation of PGAL to DPGA.  Then, the NADH₂ goes to the ETS.)

2 3-PGA (3-phosphoglycerate) + enzyme 8   rearranges to>   2 2- PGA (2-phosphoglycerate) + enzyme 9 --->

  

2 PEP (phosphoenol pyruvate) + enzyme 10 --- > 2 pyruvate or pyruvic acid (3-C molecule)

 

Three ways that pyruvate can be possibly directed: 1) ethanol + CO₂ (fermentation), 2) lactic acid (anaerobic), or

3) cell respiration (aerobic).

INTERMEDIATE STEP - OXIDATIVE DECARBOXYLATION

(This process is the breakdown of pyruvate.  Pyruvate moves from the cytoplasm into the mitochondrial matrix.  The following is the AEROBIC pathway.)

2 pyruvate + enzyme 11 ---> 2 acetyl CoA (2 carbon)---> goes to the Krebs Cycle

 

II. KREBS CYCLE (or Citric Acid Cycle or TCA Cycle-Tricarboxylic Acid)

(Double the molecules made in this pathway)

Step 1: acetyl Co A (2 carbon) + oxyaloacetate (4 carbon) + enzyme --->

Step 2: citric acid + enzyme --->

Step 3: aconitate + water molecule + enzyme --->

Step 4: isocitrate + enzyme --->

 

Step 5: oxalosuccinate + enzyme --->

Step 6: ketoglutarate + enzyme + Coenzyme A-SH --->

 

Step 7: succinyl Co A + enzyme --->

Step 8: succinate + enzyme --->

        (Another kind of intermediate energy carrier which will make more ATP in ETS)

Step 9: fumarate + enzyme --->

Step 10: malate + enzyme --->

Then, back to oxaloacetate...

III. ELECTRON TRANSPORT SYSTEM (ETS or Oxidative Phosphorylation)

Background: There is an accumulation of 10 NADH₂ and 2 FADH₂ in the mitochondrial matrix from the previous steps. ETS occurs in the cristae membrane.

1. NADH₂ passes 2 H⁺ + 2 electrons to ETS.

a) 2 electrons make three trips through the cristae membrane dropping off 3 pairs of protons (H⁺) into the intermembrane space.

b) Each NADH₂ will produce 3 ATP's, ultimately.

3. At the end of the chain, the "spent" pair of electrons are accepted by 1 oxygen atom and 2 protons (H⁺) which are from dissociated water which will form a new water molecule.
a) Without oxygen (from breathing or ventilation), ETS would get backed up with electrons. Consequently, no more energy could be obtained from food via the cellular respiration pathway.

4. Energy is "stockpiled" in the form of a proton gradient found in the intermembrane space as potential energy.

5. As result of the energy from the proton gradient, a pair of protons moves back into the mitchondrial matrix through special protein channels that are connected to ATP synthase enzymes. (See attached C&EN article) The ATP synthase enzymes catalyze ADP + phosphate to form ATP.
a)ATP synthase + the proton gradient potential provide enough energy to join ADP + P.

ACCOUNTING
 

NET GAINS OF:	ATP	NADH2	FADH2
Glycolysis	2	2
Oxidative Decarboxylation		2 (makes only 2 ATP per NADH2 in ETS)
Krebs Cycle	2	6	2
Electron Transport System	32

        Three researchers received word last week from the Royal Swedish Academy of Sciences that they had won the world's most prestigious chemical honor---the 1997 Nobel Prize in Chemistry.
        One-half of this year's $1 million prize is being shared by emeritus professor of Biochemistry, Paul D. Boyer of the University of California. Los Angeles, and senior scientist John E. Walker of the Medical Research Council Laboratory of Molecular Biology, Cambridge, England. They are being honored for having elucidated the enzymatic mechanism by which ATP synthase (ATPase) catalyzes the synthesis of adenosine triphosphate (ATP), the energy currency of living cells.
        The other half of the prize goes to emeritus professor of biophysics Jens C. Skou of Aarhus University, Denmark, for his discovery, of the first molecular pump, an ion-transporting enzyme called Na^+-K⁺ ATPase.
        In the late 1970"s, Boyer proposed the "binding-change hypothesis," a detailed molecular mechanism for the ATPase-catalyzed synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate in animall mitochondria, plant chloroplasts, and bacterial cell membranes. Walker verified the mechanism by obtaining the amino acid sequence of ATPase in the eariv 1980's and the first high-resolution crystal structure of the enyzme's catalytic domain in 1994. "Walker's work complements Boyer's in a remarkable manner," savs the academy.
        Bover hypothesized that ATPase's three catalytic sites pass through "loose", "tight," and "open" conformational states in each of three catalytic cycles. In the first cycle, ATP synthesis involves binding of ADP and phosphate to an active site in the loose state, energy-driven conformational conversion of the site to the tight state, and subsequent synthesis of ATP.  ATP is actually released in the enzyme's second catalytic cycle, when the site converts from loose to open.  In the enzyme's third catalytic cyccle, the site reverts from open to loose, making it capable of binding substrate once again.
        Walker's crystal structure showed that at any one moment the conformations of each of ATPase's three catalytic sites were different, a finding consistent with Boyer's model. The structure also suggested a way that energy could be coupled to ATP synthesis by relative rotation of the enzyme's domains. This has been come out by subsequent research, including a recent study by a Japanese group in which an ingenious technique was used to visualize the rotation process.
        With his prize winnings, Walker said, "I was thinking I'd buy myself a new bicycle"-a gift in keeping with the theme of rotatory catalysis. Skou was honored for his discovery, in the late 1950's, of Na⁺-K⁺ATPase, the first enzyme found to promote directed transport through cell membranes. This specialized ATPase maintains the proper balance of sodium and potassium ions across membranes, consuming about one-third of all the ATP produced in the body in the process. The energy stored in the ion gradients is used to drive essential cell functions, such as nerve impulse transmission. Numerous enzymes have since been demonstrated to have related similar functions---including Ca²⁺ ATPase, which helps control muscle contraction, and Na⁺-K⁺ATPase, which plays a key role in digestion.
 
 

Introduction: Cellular Respiration is critical in aerobic organisms.  The process includes glycolysis, Kreb's cycle, and the electron transport system. The electron transport system is the aspect of the cellular respiration process that is the most dynamic in synthesizing ATP energy.

Purpose: The students will kinesthetically learn the electron transport system (ETS) process.

Procedure: The teacher will model the process with several students, initially.  Then, the students will "act out" ETS. It is recommended that students switch roles several times.

Observation: After the role play experience, each student will record their understanding of ETS.

Conclusions: Students can share their findings with the class in the more traditional fashion or using a cooperative learning strategy such as "Think-Pair-Share" or "JigSaw".  (Kagen)

• Each student or teams could summarize the ETS process in the form of a poem, song, or rap. Have students design a rubric appropriate to the task.
• Each student or teams could develop a game or three-dimensional (working, possibily) model of ETS.

References Including Web Addresses to top

 http://www.kagancooplearn.com/     Kagen Cooperative Learning resource site.
 http://www.fed.cuhk.edu.hk/~johnson/cmap/respir.html     Cellular respiration concept map.
 http://www.public.asu.edu/~dseeburg/teaching/bio181spring97/homeworks/homework08.html     Cellular respiration crossword puzzle.
 http://www.leeds.ac.uk/bionet/compend/bnt22pst.htm     Teaching aids on cellular respiration.
 http://www.kent.edu/microbiology/htm/cellular.htm         Cellular respiration terms.