Prokaryotic cells structure and function
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features of prokaryotes that are different from eukaryotes
- do not have a membrane surrounding DNA
- Lack various internal structures
- are smaller
- 70s ribosomes
features of eukaryotes that are different from prokaryotes
- membrane bound nucleus
- have organelles such as the mitochondria and chloroplasts
- larger in size
- 80s ribosomes
how large are the 2 subunits of ribosomes for prokaryotes?
30s and 50s
how large are the 2 subunits of ribosomes for eukaryotes?
60s and 40s
what is s (svedberg units)?
- give a measure of sedimentation velocity (rate at which a particle sediments in a tube under centrifugal force)
- the faster a particle travels when centrifuged, the greater its svedberg value
what are the most common shapes of bacteria?
rods and cocci (spheres)
what is a tetrad?
4 cocci grouped together in the same plane
how big are nanobacteria?
less than .2micrometers
what is the average size of a bacteria?
- 1-2 micrometers in width
- 2-10 micrometers in height
what is a sarcinae?
8 cocci gouged together in a box shape
what is a bacilli?
a rod shape of bacteria
what is a spirilla?
rigid helices shape of bacteria
what is spirochetes?
flexible helices shape of bacteria
why might it be advantageous to have a small size for bacteria?
- may be protection mechanism from predation
- gives a larger surface area to volume ratio which is important for nutrient uptake
what are the functions of the plasma membrane?
- encompasses the cytoplasm
- selectively permeable barrier
- interacts with external environment (receptors, transport, metabolic processes)
what are the sterol like molecules in bacterial membranes?
what are growth factors?
organic compounds that must be provided by the environment if the cell is to survive and reproduce
what are the classes of growth factors?
- amino acids
- purines and prymidines
what is the use of amino acids for bacteria?
building blocks for protein synthesis
what is the use of purines and pyrimidines for bacteria?
building blocks for nucleic acid synthesis
what is the use of vitamins for bacteria?
function as enzyme cofactors
what is the use of heme in bacteria?
functions in cytochromes of electron transport chains
which transport mechanism is used in eukarya only?
what are the transport mechanisms used by microorganisms?
- facilitated diffusion
- active transport
- group translocation
what is the difference between facilitated diffusion and passive diffusion?
facilitated diffusion uses membrane bound carrier molecules
what sort of molecules are transported using facilitated diffusion?
glycerol, sugars, amino acids
what is active transport?
- energy dependent process to move molecules against the concentration gradient
- it involves carrier proteins
what is the mechanism of action of ABC transporters?
- solute binds to the solute-binding protein and approaches the ABC transporter
- the solute binding protein attaches to the ABC transporter
- hydrolysis of ATP drives movement of solute across membrane
what is group translocation?
energy dependent transport that chemically modifies molecule as it is brought into the cell
how do microorganisms uptake iron?
microorganisms secrete siderophores to complex with ferric ion and aid uptake
how are peptidoglycan chains strengthened?
by cross linking
where is the periplamic space of gram positive?
lies between the plasma membrane and the cell wall
what are exoenzymes?
enzymes secreted by gram positive bacteria that aid in the degradation of large nutrients
what is the structure of cell wall in gram positive bacteria?
- thick layer of peptidogycan
- periplamic space
- then cell wall
what is the structure of cell wall in gram negative bacteria?
- consists of a thin layer of peptidoglycan surrounded by and outer membrane
- outer membrane composed of lipids, lipoproteins and lipopolysaccharides
- no teichoic acids
what are the 3 parts of lipopolysaccharides?
- lipid A
- core polysaccharide
- O side chain
where is lipid A imbedded in the lipopolysaccharide?
embedded in the outer membrane
which parts of the lipopolysaccharide extend out from the cell?
the core polysaccharide and the O side chain
why is the LPS important?
- contribues to negaitve charge on cell surface
- helps to stabilize outer membrane structure
- may contribute to attachment to surfaces and biofilm formation
- creates a permeability barrier
- protection from host defenses (O antigen)
- can act as an endotoxin (Lipid A)
why is the outer membrane of gram negative more permeable than plasma membranes?
presence of porin proteins and transporter proteins
what is the gram reaction color for gram positive?
what is the gram reaction color for gram negative?
what is the effect of iodine on gram +?
dye trapped in wall
what is the effect of iodine on gram -?
nothing happens, purple dye stays on cell walls
what is the effect of alcohol on gram +?
crystals remain on cell wall
what is the effect of alcohol on gram -?
outer membrane is weakened and the wall loses the dye
what is the effect of the red dye (safranin) on the gram +?
red dye masked by violet
what is the effect of the red dye (safranin) on the gram -?
red dye stains the colorless cell
what is the outermost layer in the cell envelope made of?
- (capsules and slime layers/ s layers)
what does the glycocalyx do?
aid in the attachment to solid surfaces
what are the protective advantages of capsules?
- resistant to phagocytosis
- protect from desiccation
- exclude viruses and detergents
what are the function of S layers?
- protect from ion and pH fluctuations
- promotes adhesion to surfaces
- protects from host defenses
- potential use in nanotechnology b/c S layer spontaneously forms
what are the bacterial cytoplamic structures?
- nucleoid and plasmids
what is a plasmid?
extrachromosomal DNA that exist independently of chromosomes
how can plasmids be transferred between bacteria?
what are R plasmids?
genes that carry antibiotic resistance
what are fimbriae?
short thin hairlike appendages that can mediate attachment to surfaces for motility or DNA uptake
what is sex pili?
longer thicker and less numerous appendages that are required for conjugation
that are flagella
Threadlike, locomotor appendages extending outward from the plasma membrane and cell wall
what are the function of flagella?
- -motility and swarming behavior
- – attachment to surfaces
- – may be virulence factors
what are the 3 parts of the flagella and what do they do?
- 1. filament - extends from cell surface to the tip, made of hollo rigid cylinder of flagellin protein
- 2. hook - links filament to basal body
- 3. basal body - series of rings that drive flagellar motor
what is a bacterial endospore?
a complex dormant structure formed by some bacteria that is resistant to numerous environmental conditions
what makes an endospore resistant?
- calcium complexed with dipicolinic acid
- small acid soluble DNA binding proteins
- dehydrated core
- spore coat and exosporium protect it
when does sporulation occur?
normally commences when growth ceases because of pact of nutrients
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