In Eukaryotic Cells, the reaction of Aerobic Respiration occur
Inside MITOCHONDRIA. The Krebs cycle takes place in the
Mitochondrial Matrix, and the Electron Transport Chain is located
in the Inner Membrane.

OVERVIEW DRAWING:

 

 

 

 

 

GLYCOLYSIS AND FERMENTATION

All cells break down complex organic compounds into simpler molecules.  Cells use some of the energy that is released in this process to make ATP.

HARVESTING CHEMICAL ENERGY

Autotrophs use photosynthesis to convert light energy from the Sun into Chemical energy.  Both Autotrophs and Heterotrophs depend on these Organic Compounds for the energy to Power Cellular Activities.

By Breaking Down Organic Molecules into simpler molecules, CELLS RELEASE ENERGY.

Some of the energy is used to make ATP from ADP and Phosphate.  ATP is the Main Energy Currency of Cells.

The Complex Process in which Cells Make ATP by Breaking Down Organic Molecules is known as CELLULAR RESPIRATION. OR THE PROCESS BY WHICH FOOD MOLECULES ARE BROKEN DOWN TO RELEASE ENERGY FOR WORK IS CALLED CELLULAR RESPIRATION.

PHOTOSYNTHESIS EQUATION:

        6CO2 +  6H2O + LIGHT ENERGY   C6H12O6  + 6O2
 

CELLULAR RESPIRATION EQUATION:

        C6H12O6 + 6O2    6CO2   +   6H2O +    ENERGY RELEASED (ATP)

Cellular Respiration takes place in TWO STAGES.

STAGE 1GLYCOLYSIS, that takes place in the Cells Cytosol, (requires no oxygen & yields little energy)

STAGE 2 - OXIDATIVE RESPIRATION, and follows Glycolysis.  It takes place in the  Mitochondria.  It consists of the Krebs Cycle and the electron transport chain.

THERE ARE TWO TYPES OF CELLULAR RESPIRATION:  AEROBIC (PRESENCE OF OXYGEN) AND ANAEROBIC (ABSENCE OF OXYGEN) RESPIRATION OR FERMENTATION. If OXYGEN is PRESENT, the products of Glycolysis ENTER the PATHWAYS of AEROBIC RESPIRATION.

Aerobic Respiration produces a much Larger Amount of ATP, UP TO 20 TIMES MORE ATP PRODUCED.
 

 

GLYCOLYSIS

 FOUR MAIN STEPS:   (Figure 7-2)

STEP 1 - TWO Phosphates are attached to Glucose, forming a NEW Six-Carbon Compound.  The Phosphate Groups come From TWO ATP, which are Converted to ADP.

    STEP 2 - The Six-Carbon Compound formed in Step 1 is SPLIT into TWO Three-Carbon Molecules of PGAL.

    STEP 3 - The TWO PGAL Molecules are Oxidized, and each Receives a Phosphate Group Forming Two NEW Three-Carbon Compounds.  The Phosphate Groups are provided by Two molecules of NAD+ forming NADH.

    STEP 4 - The Phosphate Groups added in Step 1 and Step 3 are Removed from the Three-Carbon Compounds.  This reaction produces Two molecules of Pyruvic Acid.  Each Phosphate Group is combines with a molecule of ADP to make a molecule of ATP.  Because a total of Four Phosphate Groups were Added, FOUR MOLECULES OF ATP ARE PRODUCED.

TWO ATP Molecules were used in Step 1, but FOUR are Produced in Step 4.   Therefore, Glycolysis has a NET YIELD of TWO ATP Molecules for every Molecule of Glucose that is converted into Pyruvic Acid.  What happens to the Pyruvic Acid depends on the Type of Cell and on whether Oxygen is present.
 

 

 

FERMENTATION

 

LACTIC ACID FERMENTATION IS THE PROCESS THAT PYRUVIC ACID IS CONVERTED TO LACTIC ACID.
 

Lactic Acid involves the Transfer of TWO Hydrogen atoms from NADH and H+ to Pyruvic Acid.  In the process, NADH is Oxidized to form NAD+ which is needed to Keep Glycolysis Operating. This occurs in food such as yogurt and cheese as well in certain animal cells. Specifically muscle cells which are missing O2.

 DURING EXERCISE, BREATHING CANNOT PROVIDE YOUR BODY WITH ALL THE OXYGEN IT NEEDS FOR AEROBIC RESPIRATION.  WHEN MUSCLES RUN OUT OF OXYGEN, THE CELLS SWITCH TO LACTIC ACID FERMENTATION.  The side effects of Lactic Acid Fermentation is Muscle Fatigue, Pain, Cramps, and you feel Soreness. Most Lactic Acid made in the muscles diffuse into the bloodstream, then to the LIVER, where it is converted back to PYRUVIC ACID When Oxygen becomes Available.

ALCOHOLIC FERMENTATION CONVERTS PYRUVIC ACID TO CARBON DIOXIDE AND ETHANOL (ETHYL ALCOHOL).

Bakers use Alcoholic Fermentation of YEAST to make Bread.  CO2 is produced and trapped in the dough, causing it to rise. When the dough is baked the Yeast Cells Die, and the Alcohol Evaporates, You cannot get drunk from eating bread! Alcoholic Fermentation is used to make wine, beer, and the ethanol added to gasoline to make gasohol.

ENERGY YIELD

 Energy is Measured in units of kilocalories (kcal).  One kilocalorie EQUALS 1,000 calories (cal). Scientist have calculated that the Complete Oxidation of a Standard Amount of Glucose releases 686 kcal. The kcal released from Glucose during Glycolysis only has the Efficiency of 3.5%.  Anaerobic Pathways are NOT Very Efficient in transferring Energy.

AEROBIC RESPIRATION

In most cells, the Pyruvic Acid that is produce in glycolysis does not undergo fermentation.  Instead, if Oxygen is available, Pyruvic Acid enters the pathway of Aerobic Respiration, or Cellular Respiration that requires Oxygen.  Aerobic Respiration produces nearly 20 times as much ATP as is produced by glycolysis alone.

OVERVIEW OF AEROBIC RESPIRATION

Aerobic Respiration has TWO Major STAGES:  THE KREBS CYCLE and the ELECTRON TRANSPORT CHAIN.

AEROBIC RESPIRATION TAKES PLACE INSIDE THE CELL'S MITOCHONDRIA ("POWER HOUSE").

THE KREBS CYCLE IS A BIOCHEMICAL PATHWAY THAT BREAKS DOWN acetyl CoA, producing   ATP, H, AND CARBON DIOXIDE.

INTERMEDIATE STEP

The Pyruvic Acid that is produced in glycolysis Diffuses across the Double Membrane of a Mitochondrion and enters the MITOCHONDRIAL MATRIX, the Space Inside the Inner Membrane of a Mitochondrion. 

When Pyruvic Acid enters the Mitochondrial Matrix, it Reacts with a molecule called COENZYME A to form ACETYL COENZYME A, abbreviated acetyl CoA. CO2, NADH, and H+ are produced in this reaction.

 DURING THE PROCESS FROM GLYCOLYSIS THROUGH THE KREBS CYCLE, ONE GLUCOSE MOLECULE YIELDS FOUR ATP, TEN NADH AND TWO FADH2.

THE KREBS CYCLE

The Krebs cycle is a biochemical pathway that breaks down Acetyl CoA, producing CO2, H+, NADH, FADH2, and ATP.  The reactions that make up the cycle were identified by Hans Krebs (1900-1980), a German-British biochemist.

The Krebs cycle has FIVE Main Steps. ALL Five Steps occur in the Mitochondrial Matrix.

    STEP 1 - A Two-Carbon Molecule of Acetyl CoA Combines with a Four-Carbon Compound, OXALOACETIC ACID (AHKS-uh-loh-SEET-ik), to Produce a Six-Carbon Compound CITRIC ACID.

    STEP 2 -  Citric Acid Releases a CO2 Molecule and a Hydrogen Atom to Form a Five-Carbon Compound.  By LOSING a Hydrogen Atom with its Electron, Citric Acid is OXIDIZED.  The Hydrogen atom is transferred to NAD+, REDUCING it to NADH.

    STEP 3 - The Five-Carbon Compound Releases a CO2 Molecule and a Hydrogen Atom, forming a Four-Carbon Compound.   NAD+ is reduced to NADH.  A Molecule of ATP is also Synthesized from ADP.

    STEP 4 -  The Four-Carbon Compound Releases a Hydrogen Atom to form another Four-Carbon Compound.  The Hydrogen is used to Reduce FAD (Flavin Adenine Dinucleotide) to FADH2, a Molecule similar to NAD+ that Accepts Electron during Redox Reactions.

    STEP 5 - The Four-Carbon Compound Releases a Hydrogen Atom to REGENERATE OXALOACETIC ACID, which keeps the Krebs cycle operating.  The Hydrogen Atom Reduces NAD+ to NADH.

In Glycolysis one Glucose Molecule produces TWO Pyruvic Acid Molecules, which can then form TWO Molecules of Acetyl CoA.  One Glucose Molecule causes TWO Turns of the Krebs cycle.  The Two Turns produce SIX NADH, TWO FADH2, TWO ATP, and FOUR CO2 Molecules (waste product - diffuses out of the cell).

Molecules of NADH and the 2 FADH2 Molecules from the Krebs cycle DRIVE the Next Stage of Aerobic Respiration - The Electron Transport Chain. 

ELECTRON TRANSPORT CHAIN

The ELECTRON TRANSPORT CHAIN makes up the Second Stage of Aerobic Respiration. It LINES the INNER MEMBRANE of the Mitochondrion, the inner membrane has many long  folds called CRISTAE.

ATP is produced by the Electron Transport Chain when NADH and FADH2 RELEASES Hydrogen Atoms, REGENERATING NAD+ and FAD, which return to the Krebs Cycle to be reused.  The electrons in the hydrogen atoms from NADH and FADH2 are at a High Energy Level. These High Energy Electron are PASSED Along a Series of Molecules. As the move from Molecule to Molecule, the Electrons LOSE some of their Energy.

The Energy they LOSE is used to PUMP Protons of the Hydrogen Atoms from the Mitochondrial Matrix to the other side of the Inner Mitochondrial Membrane.

The Pumping builds up a High Concentration (A Concentration Gradient) of Protons in the space Between the INNER and OUTER Mitochondrial Membranes. The Concentration Gradient of Protons Drives the Synthesis of ATP by Chemiosmosis.  ATP Synthase (enzyme) Molecules are located in the Inner Mitochondrial Membrane.  The ATP Synthase MAKES ATP from ADP as Protons move down their Concentration Gradient into the Mitochondrial Matrix.

THE ROLE OF OXYGEN

ATP can be synthesized by Chemiosmosis only if Electrons continue to move from molecule to molecule in the Electron Transport Chain.

Oxygen SERVES as the FINAL Acceptor of Electrons.  By Accepting Electrons from the last molecule in the Electron Transport Chain, Oxygen allows additional electrons to pass along the chain.  Allowing ATP to continue to be synthesized.  Oxygen also accepts Protons that were once part of the Hydrogen Atoms supplied by NADH and FADH2.  By combining with both Electrons and Protons, Oxygen forms WATER:

        O2  +   4E-  +  4H+  2H2O

ENERGY YIELD

1. Through Aerobic Respiration a Maximum Yield of 38 ATP Molecules can be PRODUCED.  (Figure 7-9)

    A.  2 - Glycolysis
    B.  2 - Krebs cycle
    C.  34 - Electron Transport Chain

2. The actual number of ATP Molecules generated through Aerobic Respiration varies from Cell to Cell. (36-38)

3. Most Eukaryotic Cells Produce only about 36 ATP Molecules per Glucose Molecule.

4. If a cell produces 38 ATP Molecules the Efficiency would be 66%.

 

 

COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION

  PHOTOSYNTHESIS RESPIRATION
FUNCTION  

 

 
LOCATION  

 

 
REACTANTS  

 

 
PRODUCTS  

 

 
EQUATION