S B I 4 U BY S A RA AV E N T

AEROBIC CELLULAR RESPIRATION

AGENDA

• Overview• Lab investigations• Redox reactions and free energy• Glycolysis• Pyruvate Oxidation• The Krebs Cycle• Electron Transport and Chemiosmosis• Oxidative ATP Synthesis• Energy efficiency

CURRICULUM EXPECTATIONS

Overall Expectations• C2. investigate the products of metabolic processes such as

cellular respiration and photosynthesis;• C3. demonstrate an understanding of the chemical changes

and energy conversions that occur in metabolic processes.

Specific Expectations• C2.1: use appropriate terminology related to metabolism,

including, but not limited to: energy carriers, glycolysis, Krebs cycle, electron transport chain, ATP synthase, oxidative phosphorylation, chemiosmosis, proton pump.

• C2.2: conduct a laboratory investigation into the process of cellular respiration to identify the products of the process, interpret the qualitative observations, and display them in an appropriate format.

• C3.1: explain the chemical changes and energy conversions associated with the processes of aerobic and anaerobic cellular respiration (e.g., in aerobic cellular respiration, glucose and oxygen react to produce carbon dioxide, water, and energy in the form of heat and ATP).

• C3.4: describe, compare, and illustrate (e.g., using flow charts) the matter and energy transformations that occur during the processes of cellular respiration (aerobic and anaerobic) and photosynthesis, including the roles of oxygen and organelles such as mitochondria and chloroplasts.

CURRICULUM EXPECTATIONS (CONT’D)

INVESTIGATION

• Using Pasco CO2 gas sensor students can observe real-time evidence germinating seeds are engaged in cellular respiration.

• CO2 gas increases inside the flask with germinating seeds – proof that cellular respiration is occurring as the seeds germinate.

AEROBIC CELLULAR RESPIRATION OVERVIEW

• All organisms (except chemoautotrophs) use glucose as a primary source of energy.• Through a series of enzyme-controlled redox reactions, the bonds are broken, and the molecule is rearranged into more stable configurations, and energy is released.

C6H12O6 (aq) + 6O2(g) 6CO2 (g) + 6H2O (l) + heat + ATP

oxidized

reduced

REDOX REACTIONS AND ENERGY

C6H12O6 (aq) + 6O2(g) 6CO2 (g) + 6H2O (l) + heat + ATP

C H

O H

More ordered

Less ordered

Is this oxidation or reduction?

WHAT ABOUT THE REST?

C6H12O6 (aq) + 6O2(g) 6CO2 (g) + 6H2O (l) + heat + ATP

O O

O C

More ordered

Less ordered

Release of Free Energy!

Is this oxidation or reduction?

VISUALISING ENERGY

http://www.youtube.com/watch?v=6YWGnfnEmgM

REDOX REACTIONS AND NICOTINAMIDE ADENINE DINUCLEOTIDE

ENERGY TRANSFER

• The ultimate goal of cellular respiration is to capture as much of the available free energy in the form of ATP. • Substrate-level phosphorylation:

HOW MUCH ENERGY IS RELEASED?

• ΔG = -2870 kJ/mol glucose• When glucose is burned

in a test tube CO2, H2O are formed and heat and light are given off.• Cells have evolved

methods to trap this energy (ATP) to power endergonic processes in cell.

IN A LIVING CELL THINGS GET COMPLICATED

• Oxygen won’t just bump into glucose and react in the environment.• What would happen if it

could?• Solution: activation energy • How does a cell control this

process?• Enzymes catalyze and control.

CELLULAR RESPIRATION PROCESS

Stage 1

Stage 4

Stage 2

Stage 3

STAGE 1: GLYCOLYSIS

• 6-carbon glucose two 3-carbon pyruvates• Glyco = “sugar”; lysis = “split”• Cytoplasm

• This is a complicated process, but don’t worry – students only need to identify and understand the important parts.

• So what’s important?• The points

in the pathway where things are made or used.

• 2 ATP are used in step 1 and 3.• Phosphate groups

are added to the glucose molecule

• In step 4 & 5 the molecule is split into DHAP and G3P. An enzyme converts DHAP to G3P. This produces two molecules of G3P.

• Step 6 produces two NADH (one from each G3P).

• In step 7, two ATP molecules are produced by substrate-level phosphorylation.• The ATP debt is

paid.

• In step 10, two ATP molecules are produced by substrate-level phosphorylation and pyruvate is formed.

ENERGY YIELD FOR GLYCOLYSIS

4 ATP produced2 ATP used

2 ATP produced net 2 NADH produced

2 mol ATP x 31 kJ/mol ATP = 62 kJ

Total free energy in 1 mol of glucose = 2870 kJ

Energy conversion efficiency = 62 kJ x 100% =

2.2% 2870 kJ

STAGE 2: PYRUVATE OXIDATION

• Two pyruvate molecules are transported through the mitochondrial membrane into the matrix and acetyl-CoA is formed.

PYRUVATE OXIDATION

1. Carboxyl group is removed as CO2.2. The remaining two-carbon portion is oxidized by NAD+ and

forms an acetyl group.3. Coenzyme A attaches to the acetyl and forms acetyl-CoA.

PRODUCTS OF PYRUVATE OXIDATION

2 Acetyl-CoA 2 NADH

2 CO2 2 H+

2 pyruvate + 2NAD+ + 2CoA 2acetyl-CoA + 2NADH + 2H+ + 2CO2

STAGE 3: THE KREBS CYCLE

• Discovered in 1937 by Sir Hans Krebs.• In 1953, Krebs and

Fritz Albert Lipmann shared the Nobel Prize for their discoveries.• Krebs cycle is a cyclic

series of reactions that transfers energy from organic molecules to ATP, NADH, FADH2 and removes carbon atoms as CO2. Retrieved from: http://www.nndb.com/people/619/000129232/

• Two molecules of acetyl-CoA form for every molecule of glucose: the Krebs Cycle occurs twice for each molecule of glucose.

• CoA is recycled.

• Energy is harvested in steps 3, 4, 5, 6, 8.

• NAD+ is reduced to NADH in steps 3, 4, 8.

• Step 5 produces ATP by substrate-level phosphorylation.

• In step 6 energy is harvested. FAD is reduced to FADH2.

• The C atoms from the glucose molecule exit the process as CO2 in steps 3 and 4.

• FADH2 carries less energy than NADH.

BY THE END OF THE KREBS CYCLE

6 carbons from glucose

CO2

2 ATPglycolysis

2 ATP Krebs

2 NADHglycolysis

2 NADHpyruvate oxidation

6 NADHKrebs

2 FADH2

Krebs

STAGE 4: ELECTRON TRANSPORT AND CHEMIOSMOSIS

• NADH and FADH2 transfer the hydrogen atom electrons to a series of proteins in the inner mitochondrial membrane called the electron transport chain.

1. The first protein complex picks up the hydrogen atom from NADH and Q strips the electrons which causes the protein complex to let go of the proton.

2. Q shuttles the electrons to the next complex. The first protein complex is oxidized and the second is reduced.

3. The electrons become more stable as they move along the chain and free energy is released. This energy moves H+ across the membrane.

4. At the final complex, oxygen oxidizes the cytochrome oxidase complex and forms water.

5. The whole process is highly exergonic and the free energy produced pumps H+ across the membrane and creates a proton gradient.

NADH VS. FADH2

• NADH can pass its electrons to the first protein complex in the ETC.• FADH2 transfers its electrons first to Q

(ubiquinone).• NADH can pump 3 protons • FADH2 can only pump 2 protons.

• As a result, NADH forms 3 ATP molecules and FADH2 forms 2 ATP molecules.

• NADH produced by glycolysis in the cytoplasm is brought into the matrix by a glycerol-phosphate shuttle and converts it to FADH2.

FINALLY: CHEMIOSMOSIS AND OXIDATIVE ATP SYNTHESIS

• Remember: there is now an electrochemical gradient that is storing free energy.• Electrical component: higher positive

charge in the intermembrane space than the matrix.

• Chemical component: higher concentration of protons in the intermembrane space than the matrix.

• This gradient creates a voltage across the membrane much like a battery.

• The protons are unable to pass through the phospholipid bilayer unaided.

1. Protons cannot diffuse across the membrane alone. They travel through proton channels associated with ATPase.

2. Proton-motive force (PMF) moves the protons through the ATPase.

3. The free energy from protons moving through the ATPase drives the synthesis of ATP from ADP and Pi in the matrix.

Peter Mitchell won the Nobel Prize in Chemistry in 1978 for discovering

this ATP generating mechanism.

STUDENT ACTIVITY: MODEL MAKING & VIDEOS

• http://www.youtube.com/watch?v=3rO26W1xG9U

WHAT NEXT?

• ATP molecules are transported through the mitochondrial membranes by facilitated diffusion into the cytoplasm of the cell where they can drive endergonic processes like movement, active transport, and synthesis reactions in the cell.

EFFICIENCY

• Aerobic respiration captures 32% of the available free energy of one molecule of glucose.• Using the actual yield of 30 ATP per glucose

molecule:• Efficiency = 30 mol ATP x 31 kJ/mol ATP / 2870 kJ x 100%

= 32%

• This is much more efficient than glycolysis!• In comparison, the energy efficiency of a car is

approximately 25%.