bacterial cell structures and functions Flashcards
Identify key structures, differentiate between cell types and explain functional roles.
definition of bacteria
unicellular prokaryotic organisms that lack a membrane bound nucleus and organelles.
shapes of bacteria
cocci (spherical), bacilli (rod-shaped), spirilla (spiral), vibrio (comma), pleomorphic (variable)
components of bacteria
cell envelope
- cell membrane
- cell wall
- outer membrane (gram
negative cells only)
cytoplasmic structures
- cytoplasm
- nucleoid
- plasmids
- ribosomes
external structures
- flagella
- pili and fimbriae
- capsule/slime layer
specialized structures
- endospores
bacteria plasma membrane
- phospholipid bilayer embedded with proteins
- phospholipids: hydrophilic head group (glycerophosphate, glycerol molecule bound to a phosphate) and hydrophobic tail group (fatty acid).
- the bond between glycerophosphate and lipid is an ESTER.
- fluid mosaic model
cytoplasmic membrane proteins
- integral or transmembrane proteins: span entire membrane.
- peripheral proteins: loosely attached to the membrane, can interact with external or internal environment. Important for cellular functions.
Archaea plasma membrane
- no fatty acids as part of the membrane
- isoprene units that can be linked together in chains
- bond between glycerophosphate and lipid is an ETHER
functions of plasma membrane
selective barrier: semi permeable membrane
- allows entry of nutrients
- facilitates exit of waste
- prevents harmful substances from entering
structural integrity
- anchores cell wall, shape and stability
site of energy generation
- ATP synthesis with electron transport chain through oxidative phosphorylation.
- maintains proton motive force driving ATP production, active transport and motility.
involved in transport
- passive (down concentration gradient) and active (against concentration gradient) transport.
- efflux pumps (export contributing to resistance in some bacteria)
bacterial transport in and out of the cell
- simple transport
- group translocation
- ABC transport system
Types of transport events
- uniporters: proteins that carry a substance unidirectionally
- antiporters: transport in and out of the cell simultaneously
- symporters: transfer of a molecule along with a second substance.
cell wall
- shape, structural support against osmotic pressure
- composed of peptidoglycan
- Peptidoglycan: two alternating sugar derivatives and a peptide chain of different AAs.
- NAG and NAM attached to each other by a glycosidic bond.
- peptide chain attached to carboxylic group of NAM (gram positive bacteria can replace DAP with L-Lysine)
Cross-Linking in Peptidoglycan Provides strength to the cell wall by linking peptidoglycan subunits.
Gram-negative bacteria:
Direct cross-links between D-alanine (D-ala) of one NAM and DAP of another NAM.
Gram-positive bacteria:
Use a peptide interbridge instead of a direct link.
The bridge connects D-alanine of one NAM to L-lysine of another NAM.
gram positive and gram negative envelopes
- gram positive: thick peptidoglycan cell wall, cytoplasmic membrane.
- teichoic acids in cell wall (carbohydrates chains in cell walls or membrane lipids)
- gram negative: envelope composed of outer membrane, cell wall and cytoplasmic membrane.
- cell wall is only one layer of peptidoglycan.
- periplasmic space like a gel matrix between cell wall and cytoplasmic membrane.
- outer membrane (second lipid bilayer)
- outer membrane attached to the peptidoglycan by murein lipoprotein.
- outer membrane contains LPS, highly toxic.
gram stain
- crystal violet
- iodine
- alcohol
- safranin
cytoplasmic structures
- cytoplasm
* gel with water, enzymes, nutrients, genetic material, metabolic processes - nucleoid
* region containing singular, circular DNA - plasmids
* small, circular, extra-chromosomal DNA for antibiotic resistance, horizontal gene transfer - ribosomes
* protein synthesis, two subunits
external structures
- flagella: appendage for motility, structure of filament (flagellin protein), hook and basal body (motor). Arrangements: monotrichous (single flagellum), lophotrichous (cluster at one pole), amphitricous (cluster at both poles, peritrichous (all over the surface)
- pili and fimbriae: short hair like projections, attachment to surfaces, conjugation.
- capsule/slime layer: outside cell wall, polysaccharides and polypeptides. protects against phagocytosis and desiccation, aids adhesion.
endospores
highly resistant structures (bacillus and clostridium)
contain DNA and essential components surrounded by protective coat
withstands extreme conditions
