BIOLOGY 1111
CHAPTER 8
ENERGY RELEASING PATHWAYS

Instructor Terry Wiseth

Northland College

PATHWAYS LEADING TO ATP FORMATION

1) Aerobic respiration

        requires oxygen

        most cells are able to perform

2) Anaerobic respiration

        does not require oxygen

        many bacteria and protists are able to perform

            a) Fermentation

            b) Electron Transport

All three types of respiration begin with glycolysis in the cell cytoplasm

Glucose is split and rearranged into two pyruvate molecules

AEROBIC RESPIRATION & FERMENTATION

Aerobic respiration

    Produces the most ATP for each glucose

    yields 36 ATP from 1 glucose

C₆H₁₂O₆ + 6 O₂            6 CO₂ + 6 H₂O + energy

Fermentation (anaerobic)

    yields only 2 ATP from 1 glucose

STAGES OF AEROBIC RESPIRATION

1) GLYCOLYSIS

    glucose-----> pyruvate

    occurs in the cytoplasm

2) KREB'S CYCLE

    pyruvate-----> CO₂ and H₂O

    occurs in the mitochondria

3) ELECTRON TRANSPORT PHOSPHORYLATION

    yields most of the ATP

    also occurs in the mitochondria

GLYCOLYSIS

6 carbon glucose molecule is broken down to a 3 carbon pyruvate

glycolysis process invests:

    1 glucose molecule

    2 ATP units

glycolysis process yields:

    4 ATP units

    2 NADH

    2 pyruvate molecules

KREB'S CYCLE

Named after Hans Adolf Kreb

Also called the Citric Acid Cycle

Takes place in the mitochondria

Functions:

    1) Load electrons and H⁺ onto the NAD⁺ and FAD molecules

            Forming NADH and FADH₂

    2) Produce 2 ATP units

    3) Rearrange intermediates into oxaloacetate to recycle the carbon chains

KREB'S CYCLE

1)  Hydrogen and electrons are transferred to NAD⁺ and FAD to form NADH and FADH₂

2)  2 ATP are produced©

3)  Intermediates are recycled

KREB'S CYCLE

Coenzymes are loaded up with hydrogen and electrons that are used in the electron transport stage

Involves preparatory steps:

    3 carbon Pyruvate is converted into 2 carbon Acetyl-CoA

    NADH is formed from NAD⁺ and electrons from the Pyruvate molecule

    CO₂ is produced by the addition of Coenzyme A

    Acetyl CoA (2 carbon) enters the cycle

KREB'S CYCLE

1) Coenzyme A is removed and recycled

        Resulting 2 carbon compound is attached to a 4 carbon Oxaloacetate

        Forms a 6 carbon Citrate

2) Citrate has a water molecule removed

        Forming 6 carbon Isocitrate

3) Electrons and hydrogens are given up to form an NADH molecule and one CO₂

 molecule

        Forms a 5 carbon alpha-Ketoglutarate

4) Electrons and hydrogens are removed from a ketoglutarate forming an NADH and one CO₂

5) Coenzyme A is added to the intermediate forming a 4 carbon Succinyl CoA

6) Coenzyme A and a phosphate are stripped from the Succinyl CoA

        Forms a molecule of ATP and recycles the Coenzyme A

        Results in the formation of a 4 carbon Succinate molecule

7) FAD removes hydrogens and electrons to form FADH₂

        Results in the formation of a 4 carbon Fumarate molecule

8) Water is removed from Fumarate to form Malate

9) Electrons and hydrogens are removed to form the 4 carbon Oxaloacetae and one NADH molecule

        Oxaloacetate is now available to pick up another pyruvate

ELECTRON TRANSPORT PHOSPHORYLATION

ATP production is the primary action

Produces about 32 ATP units from 1 glucose

This process occurs in the mitochondria

    Cristae define an inner compartment and an outer compartment

Mitochondrial membrane protein complexes transport electrons from high energy levels to lower energy levels

This releases energy which can be used to power proton (H⁺) pumps

The electrons are derived from the NADH and FADH₂ molecules

The release of electrons from the NADH and FADH₂ molecules also releases H⁺ ions into the inner compartments

H⁺ ions are carried to the outer compartment of the mitochondria

    this sets up an H⁺ concentration gradient as well as an electrical gradient