Test SG

Microbial Metabolism

Glucose

• The most common carbohydrate used

  1. Glucose is converted to two pyruvic acid molecules

  2. Pyruvic acid gets converted to Acetyl-CoA

  3. Acetyl-CoA molecules enter the Krebs Cycle

Energy Investment Requires investing 2 ATP:

1. Energy Investment stage

2. Energy Comserving

   • You gain 4 ATP

   • After glucose you gained 2 ATP per glucose and 2 NADH

• 4 ATP molecules are produced (net gain of 2 ATP after accounting for the investment).

• 2 NADH molecules are generated, which carry electrons to the electron transport chain.

• End products: 2 pyruvic acid molecules, 2 ATP (net), 2 NADH.

Krebs Cycle (Citric Acid Cycle)

• Krebs cycle = TCA cycle = Citric Acid Cycle + tricarboxylic Acid Cycle

  The Krebs cycle products for one molecule of glucose are:

  • 2 molecules of ATP

  • 2 molecules of FADH

  • 6 molecules of NADH

  • 4 molecules of CO

Summary Table: ATP and Electron Carrier Yield

Pathway	ATP Produced	NADH Produced	FADH2 Produced	CO2 Produced
Glycolysis	2 (net)	2	0	0
Pyruvate Oxidation	0	2	0	2
Krebs Cycle (per glucose)	2	6	2	4

Key Terms and Concepts

• ATP (Adenosine Triphosphate): The primary energy currency of the cell.

• NAD(Nicotinamide Adenine Dinucleotide): An electron carrier involved in redox reactions.

• FAD (Flavin Adenine Dinucleotide): Another electron carrier involved in cellular respiration.

• Acetyl-CoA: A central metabolite that enters the Krebs cycle.

  Three Stages of Cellular Respiration

  1. Synthesis of acetyl-CoA

  2. Krebs cycle

  3. Final series of redox reactions (electron transport chain)

Electron Transport Chain

• 4 categories of carrier molecules that transfer electrons during the electron transport chain

  1. Flavoproteins

  2. Ubiquinoes

  3. Metal-containing proteins

  4. Cytochromes

• Aerobic respiration: oxygen serves as final electron acceptor

• Anaerobic respiration: molecule other than oxygen serves as final electron acceptor

• One side of the chain is more positively charged

Chemiosmosis

• use of electrochemical gradients

• cells use energy from reactions to build a proton gradient.

• Protons flow down this gradient through ATP synthases, which makes ATP

• This process is called oxidative phosphorylation because the proton gradient is created by the oxidation of ETC components

Energetics of the electron transport chain

• For every molecule of NADH- 3 ATP molecules are generated

• For every molecule of FADH2- 2 ATP molecules are generated

No Oxygen but need ATP?

• Glucose makes a little ATP, enough to get by

• Pretty soon yourun out of places to put the electrons

  • Your NAD gets completely filled and you need to find somewhere to dump the electrons

  • Need another molecule to put the electrons

  • We use lactate

Fermentation

• An alternative to respiration

• When cells can't completely oxidize glucose by cellular respiration, they will use fermentation

	Aerobic Respiration	Anaerobic Respiration	Fermentation
Oxygen Required	Yes	No	No
Type of Phosphorylation	Substrate-level and oxidative	Substrate-level and oxidative	Substrate level
Final Electron (hydrogen) Acceptor	Oxygen	externally acquired organic molecules	Cellular organic molecules
Potential Molecules of ATP produced per molecule of glucose	38 in prokaryotes, 38 in eukaryotes	2-36	2

What is microbial growth?

• Can be either the increase in cell size or the increase in cell number

• Mostly talking about an increase in number of cells

• 2 major areas of studies

  • growth of microorganisms in the lab

  • growth of microorganisms in the environment

Growth at the most fundamental level

• Using energy either from light or breaking chemical bonds to form bonds that are beneficial for the organism

How organsims grow

• They need energy, carbon, and electrons to grow

• They use a variety of nutrients to meet their energy needs

• Energy is

• To meet energy needs they must contain elements like carbon, oxygen, nitrogen, and hydrogen

• Microbes obtain nutrients from variety of sources

How to classify organism growth?

• Where organisms get their carbon, energy and electrons

• 2 groups

4 basic groups of organisms based on their Carbon and Energy sources

	Light (photo-)	Chemical compounds (chemo-)
carbon dioxide (auto-)	Photoautotrphs plants, algae, and cyanobacteria	Chemoautotrophes Hydrogen, sulfur, and nitrifying bacteria, some archaea
Organic compounds (hetero-)	Photoheterotrophs Green nonsulfur bacteria and purple nonsulfur bacteria, and some archaea	Chemoheterotrophs Aerobis: most animals, fungi, and protozoa and many bactera Anaerobic: some animals, protozoa, bacteria, and archaea Fermentation: some bacteria, yeasts and archaea