Microbial Cell Structure and Function Flashcards
Cocci
spheres
Diplococci
pairs of spheres
Streptococci
chains of spheres
Staphylococci
grape-like clusters of spheres
Tetrads
4 cocci in a square
Sarcinae
cubic configuration of 8 cocci
Bacilli
rods
Coccobacilli
very short rods
Vibrios
resemble rods, comma shaped
Spirilla
rigid helices
Spirochetes
flexible helices
Filamentous
- mycelium (mat)
- network of long, multicellular filaments
Pleomorphic
- variable in shape
- may not have cell wall so their shape can depend on what they are against
- default shape is round
Unique shapes
star
Unique arrangements
palisades (picket-fence)
What is the size range for eukaryotes?
0.8 micrometers-hundreds of mircometers
What is the size range for bacteria/archaea?
0.2 micrometers-750 micrometers
What is the size range for viruses?
0.01 micrometers-2.3 micrometers
How does surface to volume ratio change with size?
smaller organisms have a larger surface to volume ratio
Why is being small an advantage?
- large surface to volume ratio
- faster binary fission
- more room for diffusion
- get nutrients in and wastes out faster
- get mutations faster which leads to natural selection
What is the cytoplasmic membrane?
a thin structure that separates the cytoplasm from the environment
What are the major functions of the cytoplasmic membrane?
- permeability barrier
- site of many proteins: transport systems, bioenergetics, chemotaxis
- energy conservation: proton motive force
What is the cytoplasmic membrane composed of?
- lipid bilayer composed of amphipathic phospholipids (polar heads and nonpolar tails)
- phospholipids can be saturated or unsaturated depending on the environment
- have hopanoids to add structural stability
- have integral and peripheral proteins
What are the saturation levels reflected by?
- the environment
- cold environment: unsaturated (to increase membrane fluidity)
- warm environment: saturated (to decrease membrane fluidity)
What are peripheral proteins?
- loosely connected to the membrane
- comprise 20-30% of the membrane proteins
What are integral proteins?
- embedded within the membrane (amphipathic)
- comprise 70-80% of the membrane proteins
- carry out important functions: transport, excretion and secretion, energy conservation
What is the difference between secretion and excretion?
- secretion is releasing for a purpose
- excretion is getting rid of waste
What is the bacterial cell wall?
- rigid structure that lies just outside the plasma membrane
- contains peptidoglycan (only in domain bacteria)
- component of most bacterial cells
What are the functions of the bacterial cell wall?
- provides shape to the cell (default shape is spherical without the cell wall)
- protects from osmotic lysis
- may contribute to pathogenicity (helps it cause disease by attaching to surfaces or keeping toxins or medicines out)
- protects from toxic substances
What does the gram-positive cell wall look like?
- thick layer of peptidoglycan over the plasma membrane
- no outer membrane
What does the gram-negative cell wall look like?
- thin layer of peptidoglycan over the plasma membrane
- has an outer membrane
What is the structure of peptidoglycan?
- mesh-like polymer
- two alternating sugars form the backbone:
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
- alternating D- and L- amino acids
What kind of linkage connects NAG and NAM?
Beta 1,4 bond
What is the structure of NAG and NAM?
- NAG has a shorter chain
- NAM has a longer chain with amino acids
What breaks the Beta 1,4 bond?
- lysozymes
- works well on gram positive, but not gram negative
What does penicillin do to peptidoglycan?
- causes a problem with the linking of amino acids (transpeptidation)
- if a bacterium is actively growing, it has to elongate and divide and it purposely puts holes in its cell membrane
- peptidoglycan precursors are put in the cytoplasm
- precursors are translocated to fill the holes
- normally, the amino acids would link, but penicillin prevents this
- then the precursor pieces to fill in the holes fall out, which causes lysing
What kind of linkage does E. coli have?
direct
What kind of linkage does S. aureus have?
indirect (has an interbridge)
What is the composition of gram-positive cell walls?
- composed primarily of peptidoglycan (90%)
- may also contain teichoic acids (negatively charged, reason why bacteria have a negative charge)
- lipetechoic acids
- some have a layer of proteins on surface of peptidoglycan
What do teichoic acids do?
- bind Ca2+ and Mg2+
- help maintain structure of cell wall
- protect from harmful substances
- role in pathogenesis
What is the composition of gram-negative cell walls?
- consist of a thin layer of peptidoglycan (10%) surrounded by an outer membrane
- periplasm (20-40%): contains hydrolytic enzymes, binding proteins, and chemoreceptors)
- outer membrane is composed of lipids, lipoproteins, and lipopolysaccharide (LPS)
- porins: channels that hydrophilic molecules can pass through
- does not have teichoic acids
What is LPS?
- made up of lipid A, core polysaccharide, and O-specific polysaccharide (O antigen)
- lipid embedded in the outer membrane
What is the role of LPS?
- contributes to negative charge on cell surface (core polysaccharide)
- helps stabilize outer membrane structure and can act as an endotoxin (lipid A)
- may mutate to protect from host defenses (O antigen)
- may contribute to attachment to surfaces and biofilm formation
- creates a permeability barrier
How does the cell wall protect from cell lysis?
- in hypotonic environments, the solute concentration outside of the cell is lower, so water rushes in
- the cell wall acts as a barrier to keep the cell from bursting
What is plasmolysis?
- happens in hypertonic environments (solute concentration outside the cell is higher)
- water rushes out of the cell
- cell shrivels up inside the cell wall
- hypertonic environments used for food preservation
What conditions do bacteria prefer to live in?
hypotonic environments
What evidence is there of the protective nature of the cell wall?
- lysozyme breaks bond between NAG and NAM in gram positive cells
- penicillin inhibits peptidoglycan synthesis (in actively growing cells)
- when cells are treated with either of these, they will lyse if put into a hypotonic solution
How do mycoplasma survive without a cell wall?
- don’t have peptidoglycan
- have hopanoids and sterols (like eukaryotes)
- plasma membrane is more resistant to osmotic pressure
- live in isotonic environments without a steep concentration gradient
What are gram positive cells without peptidoglycan called?
protoplasts
What are gram negative cells without peptidoglycan called?
spheroplasts
