Lecture 11-14 Flashcards
All prokaryotes share the following traits (5)
- Cytoplasm
- Cytoplasmic membrane
- Nucleoid
- Cell wall
- Flagellum
pili
Small “hair”-like protein filaments used for attachment and/or exchange of genetic material
Fimbriae
shorter versions of pili; commonly used for adhesion
flagella
Long, helical appendages extending from cell membrane; used for motility (singular – flagellum)
Prokaryotic genetic material:
◦ 1-2 chromosomes; typically circular, haploid (unpaired);
◦ plasmids; extrachromosomal DNA; small, circular, double-stranded DNA molecules
Prokaryotic genomes
compact with very little non-coding DNA, ranges in size
Prokaryotic plasmids
- Extra-chromosomal DNA elements, usually circular, that replicate autonomously
- Contain additional/advantageous genetic
information, typically not required for “every day” survival (genes encoding antibiotic
resistance)
Horizontal gene transfer (HGT):
is the transfer of genes between organisms, outside of traditional reproduction
◦ Occurs almost exclusively in prokaryotes
Vertical gene transfer (VGT):
the transmission of genes from the parental generation to the offspring by asexual reproduction (binary fission)
Mechanisms of genetic diversification:
- Transformation
- Transduction
- Conjugation
Transformation
allows cells to uptake
DNA from the environment
Transduction
allows DNA to transfer
through bacteriophages (phage) that
infect bacteria
Conjugation
allows bacteria to directly
transfer DNA between cells via pili
hopanoids or hopes
fill gaps between hydrocarbon chains to control membrane structure
Archaeal lipid tails:
long isoprene chains with a methyl sidechain every 4 carbons.
Bacteria lipid tails:
straight chains of fatty acid without branches
Bond that joins the lipid tail to the glycerol Archaea:
glycerol-ether-lipids
bond that joins the lipid tail to the glycerol in bacteria:
glycerol-ester-lipids
Prokaryotic Cytoplasmic membrane function
- serves as site to anchor proteins
- Protects/encloses the cytoplasm and its
content - selectively facilitates transport in
and out of the cell/cytoplasm - site of proton motive force for energy conservation
Bacterial Cell Envelope
Includes at least one structural supporting layer and associated layers
◦ most common structural support for the cell
Bacterial Cell Walls are made from…
peptidoglycan sugar chains (murein) and cross-bridges
Peptidoglycan consists of:
alternating units of N-acetylglucosamine (NAG) and N- acetylmuramic acid (NAM)
N-acetylmuramic acid is bound to:
a short peptide (4-6 amino acids)
Peptidoglycan helps:
◦ cell shape
◦ withstand turgor pressure
Mycobacteria
bacteria with a complex, multilayered cell wall
Gram Positive bacteria
- Has multiple layers of peptidoglycan
- Threaded by teichoic acids (glycerol phosphate and carbohydrates) and lipoteichoic acids (bound to phospholipids) as reinforcements
Gram Negative Bacteria (2)
- Two membranes separated by periplasm (space between two membranes) that contains peptidoglycan
- Thin peptidoglycan layer consists of one or two sheets.
Lipopolysaccharide (LPS)
Used for classification of pathogens species called serotyping
Mycobacteria: Complex Cell Envelop (3)
- Consists of hydrophobic, waxy “mycomembrane”
- Rich in mycolic acids (contains 2 HC chains of different lengths) interleaved with sugar mycolates
- Mycolic acid layer and a peptidoglycan layer held together by arabinogalactan
Archaeal Cell Wall (3)
- Semi-rigid
- No peptidoglycan
- Most archaea contain a proteinaceous S-layer
considered a part of the call wall (unlike Bacteria)
Prokaryotic Cell Wall Add-ons: Capsule (2)
- Consists of a coat of polysaccharides and glycoproteins loosely bound to the cell envelope; form a hydration layer
- prevent phagocytosis
Specialized Structures: Thylakoid (2)
- only available for Gram-negative phototrophs
- Maximize photosynthetic capability of the cell
Specialized Structures: Carboxysomes (3)
- Found in Gram negatives
- polyhedral-shaped selectively permeable
protein shell containing CO 2–fixing enzymes - Found in all cyanobacteria
Specialized Structures: Gas Vesicles
allows microbes to float; aquatic phototrophs and some aquatic heterotrophs
Cyanobacterial Cell Structure
- Conduct photosynthesis in thylakoids
- Fix CO 2 in carboxysomes
- Maintain buoyancy using gas vesicles
- Many Cyanobacteria fix N2 in specialized cells called…
heterocysts
