Lecture 2: Prokaryotes - Bacteria & Archaea

Characteristics of Prokaryotes

-mostly unicellular

-are microscopic

-thrive in multiple different environments

-typically smaller than eukaryotes

-lack nuclei & other organelles (e.g. mitochondria)

What are the two domains of prokaryotes?

Bacteria & Archaea

Cell wall of Bacteria

composed of peptidoglycan (network of sugar polymers cross-linked by polypeptides)

Cell wall of Archaea

lacks peptidoglycan

Cell wall of Eukaryote

made up of cellulose or chitin

Antibiotics

target peptidoglycan to damage cell walls of bacteria

Function of cell wall

-helps maintains shape

-provides protection

-prevents bursting in a hypotonic environment (fewer solutes [less in a solution] -> solvent [most in a solution] moves into a cell -> cell swells -> cell bursts

How many and what shapes do Prokaryotes come in?

comes in three shapes: spheres (coci), rods (bacilli), sprials

Frimbriae

hairlike appendages; helps cell adhere (stick to) other cells or substrate

Capsule

sticky layer of polysaccharide/protein that help cell adhere (stick to) & evade a host's immune system (capsule acts like shield -> makes it harder for the immune system to recognize it as "foreign")

Sex pilus

appendage that facilitates conjugation

Flagella

organs used by most mobile bacteria for propulsion/movement

Circular chromosome

NOT in a nucleus; small genome; tightly coiled into a supercoiled structure

Motile Prokaryotes

propel themselves by flagella

Taxis

ability to move toward or away from certain stimuli

In a heterogeneous environment (diversity of conditions)

bacteria exhibit taxis

negative taxis

movement away from a stimulus

positive taxis

movement toward a stimulus

Basal apparatus (part of flagellum)

motor; system of rings embedded in a cell wall & membrane; powered by a ATP driven proton pump

How do prokaryotes reproduce?

binary fission

Binary fission

a form of asexual reproduction in which one parent cell divides to form two identical daughter cells

How come prokaryotes can rapidly evolve?

Because prokaryotes divide quickly (1-3 hours), they have a growing population and more chances of mutation

What contributes to prokaryotic diversity?

1) rapid repoduction

2) mutation

3) genetic recombination (combining DNA from two sources)

Horizontal gene transfer

The transfer of genes from one genome to another

What are the three types of prokaryotic gene transfer?

1) Transformation

2) Conjugation

3) Transduction

Transformation

prokaryotic cell takes up & incorporates foreign DNA from its surrounding environment

Conjugation

genetic material or plasmids (small pieces of DNA) are transferred between two bacterial cells that are temporarily joined by the pilus

In conjugation, what does the pilus act as?

A connection point/bridge for two bacteria cells to exchange plasmids/genetic material

Transduction

movement of genes b/w bacteria by bacteriophages (viruses that affect bacteria)

Explain the steps of Transduction

1) The phage infects a host bacterial cell and injects its DNA

2) The host DNA is broken down/fragmented and the phage makes copies of its DNA and proteins

3) The phage might package a fragments of the host bacterial DNA into a phage capsid

4) The phage from the donor cell infects another cell and recombination occurs between the donor and recipient cell

5) Genotype of the recombinant cell differs (new genetic information) from the donor and recipient cells

Recombination

genetic material (DNA) is exchanged b/w different chromosomes or within the same chromosome, creating new combination of genes not found in the parents

in meiosis (egg and sperm formation) this happens through "crossing over" where homologous chromosomes swap segments

phototrophs

obtain energy from light

chemotrophs

obtain energy from chemicals, which can be from organic or inorganic compounds

Autotrophs

require CO2 as a carbon source; gets carbon from the atmosphere

Heterotrophs

requires an organic nutrient (contains carbon) as a carbon source to make organic compounds; cannot produce their own food & need to take nutrition from other sources

Heterocytes

nitrogen-fixing cells that convert N2 (from the atmosphere) -> NH3 (ammonia; usable nitrogen) through nitrogen fixation

In cyanobacteria Anabaena,

photosynthetic cells & nitrogen-fixing cells (heterocytes) exchange metabolic products

In some prokaryotes, metabolic cooperation occurs at

biofilms

What is metabolic cooperation?

Cooperation between prokaryotes that allows them to use environmental resources they could not use as individual cells

Biofilms

a surface coating colony of prokaryotic that engage in metabolic cooperation; makes new cells via binary fission

What are the roles prokaryotes in the biosphere?

1) recycle chemical elements b/w living and non-living components of the ecosystem

2) chemoheterotrophic prokaryotes are decomposers (break down corpses/dead vegetation/waste products

3) nitrogen-fixing prokaryotes add usable nitrogen to the environment for plants to use

Symbiosis

ecological relationship in which two species live in close contact/together

involves and host (larger) and symbiote (smaller)

Mutualism

both symbiotic organisms (host & symbiote) benefit

Commensalism

one organism benefits while NOT having/helping the other organism in a significant way

Parasitism

parasite harms but does NOT kill the its host

Pathogen

parasite that causes disease

Antibiotic-Resistance

Resistance evolving rapidly in many species of prokaryotes/bacteria due to overuse of antibiotics

How do pathogenic prokaryotes cause disease?

by releasing exotoxins or endotoxins

Exotoxins

secreted and cause disease even if the prokaryotes that produce them are not present; toxic substances that bacteria secrete into their environment

Endotoxin

a toxin that is present inside a bacterial cell & is ONLY released when the cell disintegrates/dies/cell walls break down

What are important aspects of prokaryotes?

1) digestive function in guts

2) immune system/disease prevention

3) bioremediation (removing pollutants from the soil & water)

4) prokaryotes are used to produce ethanol for vehicles

How do prokaryotes move?

flagella

How is the cell wall different in bacteria compared to archaea?

Bacteria have cell walls primarily made of peptidoglycan, network of sugar polymers cross-linked by polypeptides, while archaea lack peptidoglycan entirely

How are prokaryotes detrimental to humans?

1) kills human population through bacteria and human disease

2) threats human through sewers and lack of sanitation efforts