Cell structure and function for microbiologists Prokaryotes Eukaryotes
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Transcript of Cell structure and function for microbiologists Prokaryotes Eukaryotes
Cell structure and function for microbiologists
Prokaryotes
Eukaryotes
Both have the same types of biological moleculesmetabolism, protein synthesis, ATP
Eukaryotes have organelles
• Much larger; more complex than prokaryotes• Processes compartmentalized into organelles
– Nucleus– Protein synthesis (ribosomes, RER, Golgi)– Mitochondria; chloroplasts– Lysosomes– Plasma membranes have different modifications– Cytoskeleton
Eukaryotes may be multicellular
• Cells may be variable within the organism– Tissues– Organs
– See table 3.7 on p. 72
Prokaryotes:Have no nucleus; genome is circular
No histones
No membrane-bound organelles
Cell wall usually contains peptidoglycan (cellwalls are more complex)
Divide by binary fission
Prokaryotes include eubacteria and archaea
How do you tell them apart? They’re all small!morphologychemical compositionnutritional and energy requirements
Typical shapes of bacteria
Most bacteria retain a particular shape; a feware pleiomorphic
Characteristic grouping (or not grouping)
Even in groups, bacteria tend to be single-celled in structure and behavior
Some have “colonial” traits
Well-studied example: myxobacteria“hunting” coloniesfruiting bodies
Etc.
Typical prokaryotic structures
Working from the outside in…
Extracellular components
Protectiondehydrationimmune mechanisms
Attachment
Glycocalyx- polysaccharide, proteincapsule if organizedslime layer if not
May contribute to virulence
Some bacteria are motile (due to flagella)
Bacteria vary in the way flagella are attached
How they move: running, tumbling, swarming
Can move toward or away from light orchemical stimuli
Flagellin protein is unique to prokaryotes
Peritrichous monotrichous(or amphi, or lophotrichous
Cocci do not have flagella
Pili- attachment; motility; conjugation
Cell membrane structure is similar in structureand function to that of eukaryotes
Phospholipid bilayer(everything moves through it, since thereare no organelles)
carrier proteins
generally involve proton motive force (i.e,require energy and moving against theconcentration gradient)
Cell wall- hallmark of prokaryotes
Their reaction with Gram stain allows bacteraito be divided into two groups
Positive-lots of peptidoglycan
Negative- thin layer, with an outer membraneand “periplasmic space” in betweenMany secreted proteins are found here
Structure of peptidoglycan
Gram-positive cell wall
Outer membrane is made of lipopolysaccharide(LPS)
Porins allow molecules to pass through outer membrane
LPS is protectivelipid A- strong inflammatory response(endotoxin)O-linked polysaccharide- antigenic
Significance of Gram-positive vs Gram-negativeantibiotic sensitivity
sensitivity to lysozyme
reaction with Gram reagentscrystal violetiodinealcoholsafranin
Mycoplasma do not have a cell wall
Lots of variety in archaea- but none havepeptidoglycan
Internal components
Nucleoid- with single, circular, supercoiledDNA molecule
Many bacteria have plasmidssmall, extrachromosomal, circularpiece of DNA
genes present are usually not requiredbut may be advantageous
(antibiotic resistance, resistance to metals)Now used for genetic engineering
Ribosomes
Involved in protein synthesis
Prokaryotic ribosomes are smaller thaneukaryotic (70S vs 80S)
Some antibiotics bind to the 70S ribosome
How does that affect bacteria?
No membrane-bound organelles
Some have storage granules
Some aquatic bacteria have gas vesicles
Some have endospores (soil bacteria) thatenable them to lie dormant under“unfavorable” conditions
NOT a reproductive structure
Summary• Eukaryotes have membrane-bound
organelles• Eukaryotes may be multicellular with
highly specialized cells• Prokaryotes have simple shapes and are
classified according to their morphology• Certain structures are unique to
prokaryotes