Chapter 25 Notes
Metabolism

Backround Information

1. The end products of digestion of carbohydrates, lipids and proteins are glucose, glycerol, fatty acids, monoglycerides and amino acids.  The sum of their chemical reactions is Metabolism:

• CATABOLISM: further breakdown to produce ENERGY for:

- active transport
- DNA replication
- muscle contraction
- nerve impulses
- and anabolism

• ANABOLISM: synthesis of complex molecules such as proteins, hormones, glycogen uses energy
  
• ATP: the molecule that participates in energy exchanges

- ATP is synthesized by adding Energy to form the third high energy phosphate bond
- this is called phosphoryllation
- Glucose is the preferred source is glucose
- breaking the last phosphate bond is an immediate Energy source
- ATP online

• ATP Synthesis online
• GLUCOSE:  has high potential energy .

- because it contains many hydrogen atoms it is called "highly reduced"
- has more potential energy than oxidized compounds

• OXIDATION

- is the removal of H⁺ or electrons
- an energy producing reaction

• REDUCTION

- is the addition of H⁺ or electrons
- an energy storing reaction

• ENZYMES .

- PROTEINS, CATALYSTS, REUSABLE , SPECIFIC, FORMED by GENES
- not only used to hydrolyze foods but also for all metabolic reactions
- enzymes lock onto molecules, loosening their bonds
- enzymes cause a chemical reaction to occur
- molecules acted on are SUBSTRATES

• COENZYMES

- are helpers on enzymes that accept or donate atoms of a substrate
- metabolism uses two hydrogen carriers

1. NAD⁺ from niacin NADH + H⁺
2. FAD⁺ from riboflavin FADH₂

- NAD oxidized and reduced online
- as glucose is oxidized coenzymes pick up hydrogens and transfer them
   to other molecules in energy producing reactions

2. Oxidative phosphorylation is the process

• in this process glucose is stripped of its hydrogens (oxidized)
• hydrogen carriers (coenzymes) are reduced
• hydrogens from reduced coenzymes NAD⁺ and FAD⁺ are ionized to H⁺ and electrons
• online cellular respiration overview
• Fate of  Electrons
  - electrons are passed over an a chain of carriers
  - the series of carrier molecules that undergo oxidation reduction reactions
  - the energy released is used to form ATP by
  - a phosphate (Pi) is added to ADP  (phosphorylation)
  - the five carriers are

- Flavinmononucleotide
- Cytochromes
- Copper
- Iron bound to sulfur
- Coenzyme Q

• Fate of  H⁺ (Hydrogen ions)
  - the carriers listed above exist in three groups
  - each group pushes H⁺  across the membrane of the mitochondria
  - now we have an electrochemical gradient (lots of  H⁺ on one side)
  - proton channels allow the H⁺ to diffuse back
  - as H⁺ moves throught the channels ATP is produced
  - most of the ATP is synthesized this way

Carbohydrate Metabolism

3. Fate of digested glucose

1. oxidized to produce energy for ATP
2. converted to amino acid
3. glycogenesis in liver
4. stored as lipids in adipose tissue
5. excess spills into the urine

4. Oxidation of glucose

Step 1 Glycolysis

glucose
     |
PGAL
     |
2 pyruvic acid

• Summary of Glycolysis
  - net gain 2 ATP
  - end product is 2 molecules of pyruvic acid
  - reduction of 2 NAD to NADH + H⁺
  - this is an anaerobic reaction
  - 95% of the energy of glucose is still in pyruvic acid molecule
  - GLYCOGENESIS: glucose stored as glycogen
  - GLYCOGENOLYSIS: glycogen converted to glucose
• glycolysis animation online
• in depth glycolysis pathway

Step 2 Formation of Acetyl coenzyme A

pyruvic acid

        |                     CO2 is removed

Acetyl Coenzyme A     +       2NADH + H⁺

• Summary of formation of Acetyl CoA
  - a CO₂ is removed
  - reduction of a NAD⁺ to NADH + H⁺ for each pyruvic acid
  - Coenzyme A carries the acetyl group to the mitochondria
  - GLUCONEOGENESIS: fatty acids and amino acids enter metobolism here

Step 3 Krebs Cycle

   acetyl group

  oxaloacetic acid                                   citric acid
    NADH + H⁺

                        fumaric acid                                                              isocitric acid
                          FADH₂                                                                 CO₂ removed
                                                                                                         NADH + H⁺

succinic acid
CO₂ removed
NADH + H⁺

a ketoglutaric acid

 

• Summary of the Krebs cycle
  - CO₂ is removed via H⁺ + HCO₃^- (This is why you exhale!)
  - with each turn of the Krebs Cycle, 1 GTP (ATP) is produced
  - as glucose is oxidized hydrogens are passed to
  - 3 NADH + H⁺ and 1 FADH₂
  - these hydrogens carry most of the energy from the original glucose molecule
• Krebs Cycle online

Step 4 The Electron Transport Chain

A series of electron carriers in the mitochondria,

Flavomononucleotide

Cytochromes

Iron-sulfur complex

Copper

CoenxymeQ

These carriers are reduced as they pick-up electrons and are oxidized as they
release electrons to the next carrier, as electrons pass through  three clusters,
H ⁺ pass through an energy gradient in the mitochondrial membrane and 34 ATP
molecules are formed.

Online proton pump

Online animation of the electron transport chain

The spent electrons and H⁺ combine with OXYGEN to form water

• Summary of the electron transport chain
online

- the spent H⁺ and electrons combiner with the oxygen you inspire
- oxygen is the final molecule to be reduced
- 34 molecules of ATP are produced

• online review of reactions