chapter 2 - microbial cell structure and functions Flashcards
What structures surrounds the cytoplasm and interacts with environment?
- cytoplasmic membrane
- surrounds cytoplasm and separates it from environment - cell wall
- confers structural strength to cells - outer membrane
- gram-negative bacteria - s-layers
- found in many bacteria and almost all archaea
What are the characteristics of the phospholipid bilayer membrane?
- phospholipid bilayer containing embedded proteins
- hydrophobic region made of tails
- hyrdophilic head exposed to environment
What are the different types of membrane proteins?
- integral membrane proteins: embedded in cytoplasmic membrane
- transmembrane proteins: integral membrane proteins that extend across the bilayer
- peripheral membrane proteins: loosely attached to the membrane
What is the archaeal cytoplasmic membrane composed of ?
ether linkage in phospholipids instead of ester linkage
lipids have isoprenes instead of fatty acids
What are the 3 functions of the cytoplasmic membrane?
- permeability barrier: polar and charged molecules are transported. prevents leakage.
- protein anchor: holds protein in place
- energy conservation: generation of proton motive force
What is the composition of bacterial cell wall?
- needs to maintain tugor pressure
- needs to maintain cell shape and rigidity
What are the differences between gram positive and gram negative bacterias?
- gram positive:
cytoplasmic membrane and thick cell wall
15 or more layers thick - gram negative:
cytoplasmic membrane, thin cell wall, outer membrane, periplasm
has lipoteichoic acids covalently bound to membrane lipids
Why is cell wall made of peptidoglycan?
- rigid plysaccharide layer that provides strength
- found in ALL bacterias with a cell wall
- contains a repeating unit of glycan tetrapeptide
What are the characteristics of archaeal cell envelope?
1- no peptidoglycan
2- lack outer membrane
3- have S-layer (rigid protein shell to prevent cell lysis)
What are the characteristics of pseudomurein cell wall?
- similar to peptidoglycan
- amino acids are L-steroisomers
- cant be hydrolyzed by lysosyme
What is the structure and ability of the lipopolysaccharide layer?
- made up of core polysaccharide
- lipid A portion is an endotoxin responsible for toxicity of pathogenic gram negative causing gas diarrhea and vomiting
- braun lipoprotein anchors outer membrane to the peptidoglycan
What are the characteristics of the periplasm?
located between cytoplasmic and outer membranes
porins are found in these periplasmic spaces as well as sensing proteins and transport proteins
What are porins?
channel proteins for the transport of small hydrophilic molecules
they can be specific to certain molecules or non specific water-filled pores
not permeable to large molecules and proteins
What is the composition of the S-layer?
- paracrystalline structure consisting of proteins and glycoproproteins
- always outermost layer if present
- fucntions:
1- strength
2- protection from lysis
3- facillitaing surface interactions
4- promoting adhesion
What are the sticky polysaccharides that coat outside of cell envelope?
- capsule: tight matrix tightly attached to cell envelope
- slime layer; loosely attached and easily deformed
What is the function of the sticky polysaccharides?
- assists in attachment to surface
- role in development and maintenance of biofilms
- contribute to infectivity
- prevent dehydration and desiccation
Describe the pili structure of bacteria
- thin filamentous protein structure
- produced by all gram negative and many gram positive
- facilitate genetic exchange between cells
- enable cells to stick to surface
- have fimbriae which is a short pili mediating attachment
What is hamus/hami?
similar to pili except for barbed termini
- assists in surface attachment and forming biofilms
Explain how cells form inclusions to store carbon polymers and minerals
- inclusion bodies: enclosed by thin protein membrane to reduce osmotic stress, for storage and special functions
- carbon storage polymers synthesize when carbon is in excess and break down to carbon for energy
What are floating cells?
bacteria that produce gas vesicles made of protein to control buoyancy in the water column.
What are magnetosomes?
acts as an internal magnet to orient within magnetic field, using earths magnetic field to move
allows cells to undergo magnetotaxis which is the migration along magnetic field lines
What is the function of endospores?
- specialized spores that have survival structures to endure unfavourable growth conditions
- dormant cells that are resistant to heat, radiation, chemical exposure, drying and lack of nutrient
Why is cell motility important?
microbes use motility to find food or run away from hostile environments. they do this with the use of flagella which allows them to glide along surfaces, propelled by secretion of polymers.
What are the characteristics of flagella?
long thin appendages that can be polar, amphitrichous, etc.
What are the different types of taxis?
- chemotaxi: response to chemicals
- phototaxi: response to light
- magnetotaxi: movement along magnetic field
- aerotaxi: movement towards optimal oxygen
- osmotaxi: movement towards environments of high ionic strength
6, hydrotaxi: movement towards water
What does taxi mean?
directed movement of bacteria and archaea in response to stimuli
What is the mechanism of chemoreceptors?
- absence of chemical gradient cells move randomly, run: counter clockwise rotation of flagella
tumble: clockwise rotation of flagella - presence of chemical gradient run becomes longer, tumble less frequent
How to measure chemotaxis?
1- insert capillary tube containing attractant or a repellent in a suspension of motile bacteria
2- chemical concentration decreases with distance from tip
3- chemotactic bacteria swarm toward attractant, increasing number of cells in capillary
4- screen nutrients for their preference by bacteria
