BIOSCI 108: Lecture 5 - Prokaryotes: Bacteria & Archaea

Prokaryotes

Cells that lack a membrane-bound nucleus to house their chromosomes and other membrane-bound organelles. This includes all bacteria and archaea.

Eukaryotes

Cells that contain a nucleus the surrounds their chromosomes and other membrane-bound organelles. Typically are a lot bigger.

Peptidoglycan Cell Walls

Most bacteria have a peptidoglycan cell wall that gives an extra layer of protection. It helps to determine the cell's shape as well as protect it from osmosis lysis (cell death related to water).

Bacteria are classified gram-positive if they have just one thick peptidoglycan cell wall layer. Or, gram-negative if they have a thing peptidoglycan cell wall sandiwched between two plasma membranes. These different cell walls can be dyed different colours for identification.

Plasma Membranes

Selectively permeable membranes made up of phospholipids that controls the entry and exit of specific molecules. It encompasses the cytoplasm and is typically a vital location of metabolic processes like respiration.

Differences Between Prokaryotes & Eukaryotes

The main differences would be:

• Eukaryotes having membrane-bound organelles and nuclei.
• Eukaryotes having linear DNA with lots of introns (non-coding DNA that help regulate transcription)

Differences between Archaea & Bacteria

The main differences would be:

• Bacteria having peptidoglycan cell walls. Archaea have cell walls using other molecules.
• Archaea can withstand extreme high temperatures (> 100°C)
• Bacter lack introns while archaea have some

Biofilm

A surface-coating of organised microbial communities encased in extracellular polymeric substances.

It gives the bacterial communities many benefits like:

• Facilitating cell-cell communication, acting like a multicellular community.
• Provides nutrional advantages where microbial communities may use each others metabolic waste as resources (syntrophy).
• Gives protection against predation, antimicrobials, UV, dessication, and other shear forces.
• It promotes HGT which then promotes genetic diversity.

Prokaryotic Modes of Life

Bacteria are associated with surface-associated life rather than a planktonic model of life.

They tend to make biofilms. Many bacteria also live in/on other organisms too, known as host-associated.

Bacterial Symbiotic Relationships

Bacteria tend to have symbiotic relationships with other organisms. Some examples are the gut bacteria in organisms that help break down extra tough carbs and glowing bacteria in glowing squids. In these cases, both species benefits in some way or another.

Quorum Sensing

The process by which bacterial cells communicate with each other using the density of signalling molecules.

It is density dependent and a phenotype is expressed/induced when enough bacteria cells are present to send out enough signalling molecules.

These molecules interact with repressor/inducer proteins to block/activate gene expression.

It gives bacteria cells multicellular characteristics.

We use quorum sensing against bacteria at times. Anti-QS theurapeutics (molecules that look similar to the signal molecules bacteria use) are used to inhibit quorum sensing in bacteria to prevent bacteria harm.

Vibrio fischeri & Glowing Squids

Vibrio fischeri is a symbiotic bacteria that glowing squids use to achieve their glow. Vibrio f. is able to present this glow with the use of quorum sensing.

At certain times of day, the glowing squid will open their sacs to allow Vibrio f. to enter and establish themselves. Then, as they grow, they use quorum sensing to determine whether or not there's enough bacteria to express their bioluminescent genes. Then, when the squid no longer needs the glow, it releases all the bacteria.