Module 3: Microbial Metabolism

Metabolism

the sum of all chemical reactions within a living organism

Catabolism

reactions that break down complex molecules into simpler ones and is exergonic → produces energy and building blocks for anabolism

Anabolsim

reactions that use energy and building blocks to make more complex biomolecules and is endergonic → involve dehydration reactions

ATP has ___ enegy bonds that enable energy to be released ____

high, quickly

Oxidation

removal of electrons

Reduciton

gain of electrons

Dehydrogenation Reactions

electrons and protons are removed simultaneously; equivalent of removing H atoms

Two forms and functions of the redox co-enzyme nicotinamide adenine dinucleotide

1. NAD+ → oxidized, accepts electons

2. NADH → reduced, electron donor

Steps of the NAD+/NADH Cycling and electron shuttle

1. enzyme I reacts with electron donor and NAD+

2. NADH and reaction product are formed

3. Enzyme II reacts with electron acceptor and reduced NADH

4. NAD+ is released

Generation of ATP

adenosine diphosphate (ADP) is phosphorylated by one of three methods:

1. Substrate level phosphorylation

2. Oxidative Phosphorylation

3. Photophosphorylation

Substrate level phosphorylation

ATP is generated when a high-level energy phosphate is directly transferred from a phosphorylated compound to ADP

Oxidative Phosphorylation

electrons are transferred from organic compounds to electron carriers. Those electrons are pass through the electron transport chain where it is passed to the final acceptor: O2 → the transfer of electrons generates ATP by chemiosmosis

Photophosphorylation

occurs in photosynthetic cells with light-trapping pigments: light energy convert to chemical energy in the form of ATP that involves the transfer of electrons (oxidation) from chlorophyll

Carbohydrate Catabolism is the primary means of producing ______ in most microbes

energy

the most common carbohydrate energy source is _____

glucose

Respiration

Fermentation

Two general processes for producing energy from glucose

1. cellular respiratoin

2. fermentation

Glycolysis

the oxidation of glucose to pyretic acid that is usually the first step in carbohydrate metabolism

Steps of Glycolysis

1. Preparatory stage → two ATP used and glucose is converted to two molecules of glyceraldehyde-3-phosphate (GP)

2. Energy-conserving stage → 2 Gps are oxidized to 2 pyretic acid molecules. 4 ATP, 2 NADH are produced

Glycolysis has a net gain of ______ for each molecule of glucose oxidized

2 ATP and 2 NADH

Net Reaction of Glycolysis

Glucose + 2ADP + 2Pi + 2NAD+ → 2 pyretic acid + 2 ATP + 2NADH + 2H+

Pentose Phosphate Pathway

• operate simultaneously with glycolysis; breaks down pentose (5C) sugars or glucose and produced NADPH

• provides building blocks for synthesis of nucleic acids and some amino acids

• Does not consume or produce ATP

Entner-Doudoroff Pathway

• operates independently of glycolysis; produced 2 NADPH and 1 ATP

  • found in Gram- bacteria

Transition Step

between glycolysis and the Krebs cycle; pyruvic acid is oxidized and decarboxylated (lost CO2) resulting in 2C compound attached to CoA to form acetyl-Coa and 1 NADH which will enter the krebs cycle

Krebs Cycle

the oxidation of acetyl CoA that generates 3NADH, 1FADH2, and 1ATP with CO2 being released as waste

Electron Transport Chain

located in the cytoplasmic membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes;

• series of carrier molecules that are capable of oxidation/reduction

• electrons enter the chain and are carried by NADH and FADH2 → as electrons pass through each carrier is reduced then oxidized

• ATP is generated by Chemiosmosis

aerobic respiration

when O2 is used (ex: ETC)

Chemiosmosis

as electrons pass along ETC, carriers pump H+ across the membrane creating a gradient. This gradient has potential energy - proton motive force

when H+ diffuse back across the membrane, the released energy is used to drive ATP synthesis from ADP (Oxidatie phosphorylation)

Anaerobic Respiratoin

cellular respiration where the final electron acceptor in the ETC is not O2: could be Nitrate, Sulfate, or Carbonate

• yields less ATP than aerobic

Fermentation

• a catabolic process that releases energy through the partial breakdown of a sugar

• uses ONLY glycolysis and does not require O2

• smaller amount of ATP produced via substrate-level phosphorylation

Fermentation ensures ________

a steady supply of NAD+ for glycolysis

In Fermentation an _____ molecule serves as the terminal electron acceptor

organic (eg. pyretic acid)

Lactic Acid Fermentation

glucose is oxidized to pyretic acid which is then reduced to lactic acid as the end product

Homolactic Fermentation

lactic acid is the only end product of fermentation

Heterolactic Fermentation

lactic acid & other compounds are produced as a result of fermentation

Alcohol Fermentation

Glucose is oxidized to pyretic acid, which is converted to acetaldehyde & CO2. The Acetaldehyde is reduced to ethanol

Alcohol fermentation equation

Glucose + 2ADP + 2Pi → 2 Ethanol + 2 CO2 + 2 ATP

Lactic Acid Fermentation Equation

Glucose + 2ADP + 2Pi => 2 Lactic acid + 2 ATP

Carbohydrate Catabolism

simple sugars are transported across cytoplasmic membrane and are broken down inside the cell → complex polysaccharides are too big to be transported and must be broken down outside the cell

Secreted Extracellular Enzymes

Complex polysaccharides are too big to be transported into the cell so these enzymes break them down

Types of Secreted Extracellular Enzymes for Carbohydrate Catabolism

• Cellulases: break down cellulose

• Pectinases: break down pectin

• Amylases: break down starch

Lipases

break down lipids extracellularly

Lipid and Protein Catabolism [!}

Amino Acid Decarboxylation Test

the growth medium contains pH indicator that turns purple due to decarboxylation of amino acids to identify the presence of bacteria based on presence of specific enzymes

If NO decarboxylation activity results in no colour change to yellow to acid production from glucose

Sugar Fermentaiton Test

the growth medium contains protein, a carbohydrate, and pH indicator.

The fermentation of sugar and acid production causes pH indicator to change to yellow.

Gas production is detected using an inverted Durham tube

The catabolism of protein results in no acid or gas production

Cyanobacteria carry out _________ while Purple and Green Bacteria carry out __________

oxygenic photosynthesis, an oxygenic photosynthesis

2 Stages of Photosynthesis

1. Photophosphorylation: Light-dependent light reactions

2. Carbon Fixatino: Light independent reactions

Oxygenic Photosynthesis Equation

6CO2 + 12H2O + light energy → glucose + 6H2O + 6 O2

Anoxygenic Photosynthesis

6CO2 + 12H2S + Light Energy → glucose + 6H2O + 12S

Photosynthesis

process by which light energy is converted to chemical energy

Photosystems

complexes that house light-absorbing pigments (chlorophylls or bacteriocholorphylls)

In Photophosphorylation; ATP is synthesized by _____ as electrons are passed along the ___

chemiosmosis, ETC

Cyclic Photophosphorylation

Only in Purple and Green Bacteria: uses only one photosystem wherein electrons are returned to bacteriochlorophyll in photosystem. → only produces ATP

Non-cyclic Photophosphorylation

Carried out by plants, algae, and cyanobacteria; uses photosystems I and II. Electons are released from chlorophyll in photosystems and are transferred to NADP+, the elections lost are replaced by elections from water. → former ATP, O2 (oxygenic) and NADPH

Calcin-Benson Cycle

anabolic pathway in which CO2 from air is used to synthesize sugars. The energy and electrons are supplied by light-dependent reactions

Calcin-Beson Cycle Equation

6CO2 + 18 ATP + 12H+ → 2GP + 18 ADP + 18Pi + 12NADP+

Heterotrophs

use organic compounds as a source of carbon

Autotroph

use an inorganic source of carbon (CO2) → aka primary producers that synthesize organic matter from inorganic C

Photoautotrophs

use light as primary energy source and CO2 as principal C source

Photoheterotrophs

use light as primary energy source and organic compounds as principal C source → carry out an oxygenic photosynthesis and do NOT fix CO2

Chemoautotrophs

use inorganic compounds (H2S, H2, NO2) as sources in redox reactions for energy production, and CO2 as C source → using Calvin-benson cycle

Chemoautotrophs

use organic compounds (glucose) as electron sources in redox reactions for energy production, AND as a source of C

Most bacteria, all fungi, protozoa, helminths are _______

chemoautotrophs