Microbial Metabolism

Chapter 5

Metabolism - all of the chemical reactions within a living organism

1. Catabolism ( Catabolic )• breakdown of complex organic molecules into

simpler compounds• releases ENERGY

2. Anabolism ( Anabolic )• the building of complex organic molecules

from simpler ones• requires ENERGY

Enzymes - catalysts that speed up and direct chemical reactions

A. Enzymes are substrate specific• Lipases Lipids• Sucrases Sucrose• Ureases Urea• Proteases Proteins• DNases DNA

Enzyme Specificity can be explained by the Lock and Key Theory

E + S -----> ES ------> E + P

Naming of Enzymes - most are named by adding “ase” to the substrate

Sucrose Sucrase Lipids Lipase DNA DNase Proteins Protease removes a Hydrogen Dehydrogenase removes a phosphate phosphotase

Naming of Enzymes

Grouped based on type of reaction they catalyze

1. Oxidoreductases oxidation & reduction

2. Hydrolases hydrolysis

3. Ligases synthesis

Enzyme Components

2 Parts

1. Apoenzyme - protein portion

2. Coenzyme (cofactor) - non-protein

Holoenzyme - whole enzyme

Coenzymes

Many are derived from vitamins

1. Niacin• NAD (Nicotinamide adenine dinucleotide)

2. Riboflavin• FAD (Flavin adenine dinucleotide)

3. Pantothenic Acid• CoEnzyme A

Factors that Influence Enzymatic Activity

Denaturation of an Active Protein

Inhibitors can effect enzymatic activity

1. Competitive Inhibitors

2. Noncompetitive Inhibitors

Competitive Inhibitors -compete for the active site

1. Penicillin • competes for the active site on the enzyme involved in

the synthesis of the pentaglycine crossbridge 2. Sulfanilamide (Sulfa Drugs)

• competes for the active site on the enzyme that converts PABA into Folic Acid

• Folic Acid - required for the synthesis of DNA and RNA

Selective Toxicity

Non-competitive Inhibitors - attach to an allosteric site

Energy Production

1. Oxidation• refers to the loss of Hydrogens and or electrons

2. Reduction• the gain of Hydrogens and or electrons

NAD Cycle

Carbohydrate Catabolism

Microorganisms oxidize carbohydrates as their primary source of energy

Glucose - most common energy source Energy obtained from Glucose by:

• Respiration• Fermentation

Aerobic Cellular Respiration

Electrons released by oxidation are passed down an Electron Transport System with oxygen being the Final Electron Acceptor

General Equation:

Glucose + oxygen----> Carbon dioxide + water ATP

Chemical Equation

C6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O

38 ADP + 38 P 38 ATP

Aerobic Cellular Respiration

4 subpathways

1. Glycolysis 2. Transition Reaction 3. Kreb’s Cycle 4. Electron Transport System

1. Glycolysis (splitting of sugar)

Oxidation of Glucose into 2 molecules of Pyruvic acid

Embden-Meyerhof Pathway

End Products of Glycolysis:• 2 Pyruvic acid• 2 NADH2

• 2 ATP

2. Transition Reaction

Connects Glycolysis to Krebs Cycle

End Products:• 2 Acetyl CoEnzyme A

• 2 CO2

• 2 NADH2

3. Krebs Cycle (Citric Acid Cycle)

Series of chemical reactions that begin and end with citric acid

Products:• 2 ATP

• 6 NADH2

• 2 FADH2

• 4 CO2

4. Electron Transport System

Occurs within the cell membrane of Bacteria

Chemiosomotic Model of Mitchell• 34 ATP

How 34 ATP from E.T.S. ?3 ATP for each NADH2

2 ATP for each FADH2

NADH2

Glycolysis 2 T. R. 2 Krebs Cycle 6

Total 10

10 x 3 = 30 ATP

FADH2

Glycolysis 0 T.R. 0 Krebs Cycle 2

Total 2

2 x 2 = 4 ATP

Total ATP production for the complete oxidation of 1 molecule of glucose in Aerobic Respiration ATP Glycolysis 2 Transition Reaction 0 Krebs Cycle 2 E.T.S. 34

Total 38 ATP

Anaerobic Respiration

Electrons released by oxidation are passed down an E.T.S., but oxygen is not the final electron acceptor

Nitrate (NO3-) ----> Nitrite (NO2-)

Sulfate (SO24-) ----> Hydrogen Sulfide (H2S)

Carbonate (CO24-) -----> Methane (CH4)

Fermentation

Anaerobic process that does not use the E.T.S. Usually involves the incomplete oxidation of a carbohydrate which then becomes the final electron acceptor.

Glycolysis - plus an additional step

Fermentation may result in numerous end products

1. Type of organism

2. Original substrate

3. Enzymes that are present and active

1. Lactic Acid Fermenation Only 2 ATP End Product - Lactic Acid Food Spoilage Food Production

• Yogurt - Milk• Pickles - Cucumbers• Sauerkraut - Cabbage

2 Genera:• Streptococcus• Lactobacillus

2. Alcohol Fermentation

Only 2 ATP End products:

• alcohol

• CO2

Alcoholic Beverages Bread dough to rise

Saccharomyces cerevisiae (Yeast)

3. Mixed - Acid Fermentation

Only 2 ATP End products - “FALSE”

Escherichia coli and other enterics

Propionic Acid Fermentation

Only 2 ATP End Products:

• Propionic acid

• CO2

Propionibacterium sp.

Fermentation End Products

Lipid Catabolism

Protein Catabolism

Photosynthesis - conversion of light energy from the sun into chemical energy

Chemical energy is used to reduce CO2 to sugar (CH2O)

Carbon Fixation - recycling of carbon in the environment (Life as we known is dependant on this)

Photosynthesis• Green Plants

• Algae

• Cyanobacteria

Chemical Equation

6 CO2 + 6 H2O + sunlight -----> C6H12O6 + 6 O2

2 Parts:• 1. Light Reaction• 2. Dark Reaction

Light Reaction

Non-Cyclic Photophosphorylation• O2

• ATP

• NADPH2

Light Reaction (simplified)

2. Dark Reaction