Chapter 8: Microbial Metabolism

Metabolism

The sum of all chemical reactions in an organism

Catabolism

Large molecules are broken down into smaller one, releasing energy

Anabolism

Small molecules are assembled into larger ones, using energy

Autotrophs

Use CO2 (inorganic sources) as a sole source of carbon

Heterotrophs

Must obtain carbon in an organic form made by other living organisms.

Phototrophs

Uses light as an energy source; photosynthesis

Chemotroph

gain energy from compounds (chemicals)

Chemoautotrophs

Energy Source: Chemical

Carbon Source: Inorganic

Ex: Hydrogen-, sulfur-, iron-, nitrogen-, and carbon monoxide-oxidizing bacteria.

Chemoheterotrophs

Energy Source: Chemical

Carbon Source: Organic Compounds

Ex: All animals, most fungi, protozoa, and bacteria.

Photoautotrophs

Energy Source: Light

Carbon Source: Inorganic

Ex: All plants, algae, cyanobacteria, and green and purple sulfur bacteria.

Photoheterotrophs

Energy Source: Light

Carbon Source: Organic Compounds

Ex: Green and purple nonsulfur bacteria, heliobacteria.

Reduction

Gain of electrons/Gain of hydrogen

Oxidation

Removal of electrons/Removal of hydrogen

Redox Reaction

An oxidation reaction paired with a reduction reaction

Energy (electron) carriers

Repeatedly accept and release electrons (and hydrogen) to facilitate the transfer of redox energy

• Most carriers are coenzymes:

  • NAD+, NADP+, FAD, Coenzyme A.

ATP

“Energy currency'“ of the cells

• Removal of terminal phosphate releases energy

• Utilization and replenishment is a constant cycle in active cells

Endergonic Reaction

chemical reaction that requires energy beyond activation energy to occur

Exergonic Reaction

chemical reaction that does not require energy beyond activation energy to proceed; releases energy when the reaction occurs.

• Drives an energy requiring reaction

Substrate-level Phosphorylation

Transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP.

• Formation of ATP

Oxidative Phosphorylation

Series of redox reactions occurring during respiratory pathway.

• Formation of ATP

Photophosphorylation

ATP is formed utilizing the energy of sunlight.

Enzymes

• Biological catalysts

• Increase reaction rate by lowering the activation energy

• Highly specific

• Not used up/Not permanently changed by the reaction

• Greatly affected by temperature & pH.

Holoenzymes

enzyme with a bound cofactor or coenzyme

• Protein + nonprotein

Apoenzyme

enzyme without its cofactor or coenzyme

• Protein portion

Cofactors

inorganic ion that helps stabilize enzyme conformation and function

• nonprotein portion

Coenzymes

organic molecule required for proper enzyme function that is not consumed and is reusable

Enzyme Characteristics

• Composed mostly of protein; may require nonprotein cofactors for proper functioning.

• Increase reaction rate without being used.

• Lowers the activation energy of the reaction.

• Reusable

• Specific

• Sensitive to pH, temperature, substrate concentration, etc.

Denaturation

the process of altering the structure of proteins or nucleic acids, causing them to unfold or break apart

Enzyme Activity

Factors influencing ______ ______

• Temperature

• pH

• Substrate Concentration

• Inhibition/Inhibitors

Competitive Inhibition

phenomenon in which a substrate molecule is prevented from binding to the active site of an enzyme by a molecule that is very similar in structure to the substrate

Noncompetitive Inhibition

a type of enzyme inhibition where an inhibitor binds to an enzyme at a site other than the active site, reducing the enzyme's activity

Allosteric Site

location within an enzyme, other than the active site, to which molecules can bind, regulating enzyme activity

Cytosol and Mitochondria

Enzymes for glucose oxidation are in found in both…

cellular respiration

Three main stages of _____ ______.

• Glycolysis (Cytosol - Anaerobic)

• Transition Reaction (Cytosol - Anaerobic)

• TCA/Citric Acid Cycle (Mitochondria - Aerobic)

• Electron Transport System (Mitochondria - Aerobic)

Glycolysis

first step in the breakdown of glucose, the most common example of which is the Embden-Meyerhoff-Parnas pathway, producing two pyruvates, two NADH molecules, and two (net yield) ATP per starting glucose molecule.

• Happens in both prokaryotes and eukaryotes

• Occurs in the cytosol

• Theoretical Maximum Yield of ATP Molecules: 2

Transition Reaction

reaction linking glycolysis to the Krebs cycle, during which each pyruvate is decarboxylated and oxidized (forming NADH), and the resulting two-carbon acetyl group is attached to a large carrier molecule called coenzyme A, resulting in the formation of acetyl-CoA, Carbon Dioxide, and NADH; also called the bridge reaction

• Occurs in the cytoplasm in Prokaryotes

• Occurs in the mitochondria of Eukaryotes

• Theoretical Maximum Yield of ATP Molecules: 0

Krebs Cycle

cyclic pathway during which each two-carbon unit entering the cycle is further oxidized, producing three NADH, one FADH2, and one ATP by substrate-level phosphorylation, releasing two CO2 molecules and regenerating the molecule used in the first step; also called the citric acid cycle or the tricarboxylic acid cycle.

• Occurs in the cytoplasm in Prokaryotes

• Occurs in the mitochondria in Eukaryotes

• Theoretical Maximum Yield of ATP Molecules: 2

Single Cycle (Krebs)

2 x CO2 : 1 x ATP : 1 x FADH2 : 3 x NADH + H+

Two Cycles (Kreb)

4 x CO2 : 2 x ATP : 2 x FADH2 : 6 x NADH + H+

Electron Transport System

A series of carrier molecules that are, in turn, oxidized are reduced as electrons are passed down the chain.

• Energy release can be used to produce ATP by chemiosmosis.

• Oxidative Phosphorylation

• Oxygen is the final electron acceptor

• 24 ATP

• Occurs in Cell Membrane in Prokaryotes

• Occurs in Mitochondrial Membrane in Eukaryotes