MICR501 Week 3 – Bacteria and Archaea

Prokaryotic Structures

Cell wall, cytoplasmic membrane, ribosomes, nucleoid

Cell wall

Necessary for shape and rigidity; cytoplasmic membrane would rupture under turgor pressure

Prokaryote turgor pressure

~2 atmospheres

Bacterial cell wall

Formed largely of peptidoglycan

Peptidoglycan

Sugars connected by glycosidic bonds to form very strong chains

Gram positive bacteria

Thick, rough, single layer cell wall

Gram negative

Thin, smooth, multilayered cell wall

Archaeal cell wall

Relatively thick, composed of pseudopeptidoglycan

Pseudopeptidoglycan

Morphologically and functionally similar to peptidoglycan, differs in chemical structure

Cytoplasmic membrane

Consists of phospholipids

Bacterial cytoplasmic membrane

Lipid bilayer consisting of glycerol-ester lipids

Archaeal cytoplasmic membrane

lipid monolayer consisting of glycerol-ether lipids

Capsule

Tightly attached with definite boundaries, mostly composed to polysaccharide

Slime layer

Loosely associated, unorganised layer of extracellular material

Prokaryotic chromosome

Usually a covalently closed circular molecule

Bacteria origin of replication

Single original of replication

Archaea origin of replication

Often have multiple origins of replication

Can bacteria have plasmids?

Yes

Prokaryotic ribosomes

70S ribosomes, consisting of small 30S and large 50S subunit

Fimbriae

Short, thin, hair-like appendages found on many bacteria

Fimbriae function

Adhesion to surfaces, host tissues, other cells; Role in biofilm formation and colonisation

Pili

Longer, fewer in number compared to fimbriae

Pili function

Involvement in twitching motility and surface attachment; Important for pathogenicity in some bacteria

Binary fission steps

DNA replication from origin of replication, Cell elongation, Septum forms down middle of cell, Cell divides in two

Bacteria and Archaea similarities

Single-celled, no nucleus, have ribosomes, reproduce asexually, no membrane-bound organelles, can be autotrophs or heterotrophs

Recombination

Exchange of genetic material results in new gene/allele combinations in offspring

Mutation

Heritable change in base sequence of a nucleic acid genome of an organism

Spontaneous mutations

From errors during replication or natural mutagens

Induced mutations

From chemical and physical agents

Point mutations

Single nucleotide is changed

Frameshift mutations

Addition or deletion of nucleotides causing a shift in the reading frame

Silent mutation

Point mutation codes for same amino acid = no impact on protein

Nonsense mutation

Point mutation leads to RNA sequence terminating translation prematurely = truncated, incomplete, possibly nonfunctional protein

Missense mutation

Point mutation leads to different amino acid being encoded = likely faulty protein

Transformation

Foreign genetic material is taken up by a cell resulting in a stable genetic change within transformed cell

Transduction

A virus transfers genetic material from one bacterium to another

Conjugation

A bacterium passes genetic material to another via direct contact