BIO153 Lecture 8

Division Method:
- Bacteria replicates through binary fission.
- A parent cell divides into two new cells, resulting in exponential growth.
Exponential Growth Example:
- Escherichia coli divides every 20 minutes under optimal conditions.
  - After 1 hour: 1 cell ➔ 8 cells
  - After 6 hours: 1 cell ➔ 262,144 cells (0.26 million)
  - After 12 hours: 1 cell ➔ 68,719,476,736 cells (69 billion)
Growth Process:
- Cells divide in the middle, leading to separation.

The increased number of divisions leads to more DNA replication.
Higher chances for mutations to occur, which can lead to adaptations like antibiotic resistance.
Natural Selection:
- Some mutations allow bacteria to survive antibiotic treatment, leading to a population rich in resistant strains.

Growth requirements for bacteria include:
1. Energy Source
2. Carbon Source
3. Other elements (e.g., nitrogen)
Types of Bacteria:
- Photoautotrophs: Produce organic molecules using sunlight, water, and CO2.
- Chemoheterotrophs: Utilize organic molecules for energy and carbon (e.g., Escherichia coli).

Process:
- Glycolysis (glucose lysis) is the breakdown of glucose (a 6-carbon sugar).
- Initial cost: 2 ATP required to begin the reaction.
- End products include:
  - 2 pyruvate (3-carbon sugars)
  - 4 ATP total production (net gain of 2 ATP after two are utilized for further processes)
  - 4 electrons and protons (
  - NAD+ captures electrons to regenerate NADH.
NAD+ Limitation:
- Glycolysis cannot continue without regenerating NAD+.

Purpose:
- Regenerates NAD+ from pyruvate by transferring electrons from NADH to pyruvate.
- Results in byproducts such as alcohols or acids.
Efficiency:
- Fermentation yields only 2 ATP, as it does not utilize the stored energy in pyruvate, making it less efficient than aerobic respiration.

TCA Cycle:
- The citric acid cycle (Krebs cycle) extracts additional energy from pyruvate, producing 3 CO2 and generating more NADH and ATP.
- NADH feeds electrons into the Electron Transport Chain (ETC), regenerating NAD+ and producing energy.
- Oxygen acts as a terminal electron acceptor at the end of ETC, facilitating maximal energy production.
Energy Yield:
- Aerobic respiration can produce up to 38 ATP per glucose.

Utilizes other molecules as terminal electron acceptors (e.g., nitrate, sulfate).
Provides less energy compared to aerobic respiration but significantly more than fermentation.

Obligate Aerobes: Require oxygen for survival (e.g., Mycobacterium tuberculosis).
Facultative Anaerobes: Prefer oxygen but can survive through anaerobic respiration or fermentation (e.g., E. coli).
Obligate Anaerobes: Cannot survive in the presence of oxygen due to its toxicity.

Humans are obligate aerobes, primarily using O2 for aerobic respiration.
During intense aerobic activity, when O2 is depleted, fermentation converts pyruvate into lactic acid, leading to muscle fatigue.

Anaerobic fermentation using Lactobacillus bulgaricus and Streptococcus thermophilus.
These bacteria ferment lactose in milk into lactic acid, thickening the product and adding flavor.
Acidification helps suppress harmful bacteria like E. coli.

Yeast (Saccharomyces cerevisiae) utilized in alcohol production from starch.
Different starch sources contribute to the type of alcohol produced. Distillation is later necessary to increase alcohol content.

Gram-negative photoautotrophic bacteria capable of using sunlight to convert CO2 into glucose and O2.
Some cyanobacteria can fix nitrogen (N2 to NH3), essential for DNA and protein synthesis.
Challenges: Oxygen inhibits nitrogen fixation; heterocysts develop to block oxygen entry, allowing nitrogen fixation.

Filamentous cyanobacteria exhibit specialization: vegetative cells perform photosynthesis, while heterocysts specialize in nitrogen fixation. Heterocysts depend on neighboring cells for glucose and other nutrients.