Lecture 5: Domain Archaea

Carl Woese

came up with the idea to use a small subunit of the ribosome to characterize organisms (mainly prokaryotes)

based on the sequence data - proposed a complete change in our understanding of the relationship between organisms

True/False: Archaea has peptidoglycan present in cell wall

false

Archaea: S-layer

most common

proteins or glycoproteins

Archaea: S-layer + external layer

the external layer is either a protein sheath or a polysaccharide

Archaea: S-layer + pseudomurein

PG-like

N-acetyltalosaminuronic (NAT) instead of NAM

beta-1,3 glycoside links between NAT and NAM

L-AA crosslinks

Pseudomurein are

resistant to lysozyme and antibiotics that target bacterial cell wall (PG)

Archaea: complex polysaccharide

single thick layer

no s-layer

Archaea: Glycocalyx

not a cell wall rather a slime layer

Archaea: Outer membrane

not a cell wall

Plasma membrane of archaea

differs slightly from both bacteria and eukarya

Archaea PM contains

hydrocarbons of repeating isoprene units

Isoprene units of archaea are attached to ___ by ____

glycerol; ether linkages

Two major types of archaeal lipids

glycerol diether and diglycerol tetraether

Glycerol diether

2 hydrocarbons attached to the glycerol

each usually 20 C in length

Diglycerol tetraether

2 glycerol linked by two hydrocarbons that are 40 C in length

True/False: Archaea has both hopanoids and sterols

False

Archaea chromosome are ___ and reside in ____

circular dsDNA; nucleoid

archaea genomes compared to bacteria are

smaller

Genetic material in archaea are associated with

histones

Histones

proteins used to condense DNA/packaging

Archaeal flagella structure

filament

motor complex

rotation

Filament

not hollow and proteins are added to the base for growth

Motor complex

proteins are in the PM

Rotation

ATP hydrolysis, directions of cells are either forward or reverse

there are no runs/tumbles

Archaea typically lives in

extreme environments (extremophiles)

Halophiles

thrive in high [salt]

Psychrophiles

0-20 celcius

Thermophiles

50-80 celcius

Hyperthermophiles

>80 celcius

Barophiles

pressure > 1 atm

Acidophiles

low pH

Methanogens

produce methane

Thermophiles proteins stability

AA composition similar to heat-labile bacteria

highly hydrophobic cores and ionic interaction on surfaced, creating a low tendency to unfold

have heat-shock proteins

Heat-shock proteins

synthesis increases with stress of excessive heat

refolds partially denatured proteins before protease recognize improper folding and destroys

DNA stability by _____ allows for the survival of thermophiles

Potassium cyclic 2,3-diphosphate (salt)

reverse DNA gyrase

proteins

Potassium cyclic 2,3-diphosphate (salt)

associates with DNA and increases stability of bases

Reverse DNA gyrase

unique form of DNA topoisomerase

introduced positive supercoils into DNA, which increases stability and prevents heat denaturation

Proteins in thermophiles

maintain the integrity of DNA

Sac7

small heat-stable DNA binding protein

binds to small grooves of DNA, increases melting point by 40 celsius

Monolayer archaea _____ tendency of heat to pull it apart

resist

Bilayer archaea are _____ stable with high temps

less, higher temps pull the two layers apart

Halophiles

have a very high salt requirement, thus inhibiting a highly saline environment

Halobacterium

the glycoprotein cell wall is high in aspartate and glutamate concentration that repels each other, thus requiring Na⁺ to bind to surfaces and shield negative charges

High [Na⁺] outside of the cell results in

water moving out of the cell causing plasmolysis

To prevent plasmolysis due to [Na⁺]

K⁺ is pumped into the cell in large amounts thus water inside and outside of the cell is maintained

Acidophiles have

the optimal environment of 0-5.5 pH, but an internal neutral pH

Sulfolobus Acidocaldrius

inhabits hot springs

allows K⁺to enter cells to reduce the member potential

highly impermeable PM

active H+ export by transporter

has secondary transporters, chemicals that bind and sequester H, DNA and RNA repair systems and degradation of organic acids

Impermeable PM of Sulfolobus Acidocaldrius is due to

tetraethers and calditol

Tetraethers

resist dissociations, ether links are less sensitve to acid hydrolysis

Calditol

unique to archaeal lipid head groups