Bacterial CM transport Flashcards
what are teh two basic designs to a cell
- prokaryote ( no nuckeus)
- eukaryote (has nuceus)
- bacteria and archaea are collectively called prokaryotes
what is the cell structure like
- cell structure is highly ordered but flexible to maximize activity and function
prokaryote vs eukaryote
Prokaryote
- no nuclear membrane
- circiular chromosomes
- brinary fission (cell grows and dividdes into 2)
- no membrane bound organelles
- 70s ribosome
- rudimentary cytoskeleton
- complex cell walls
- simple appendages
Eukaryote
- Larger (10-100 micro m)
- mambrane bound organelles, nucleus and nucleolus
- linear DNA histones
- mitosis
- 80S ribosome
- mitochondia and chloroplast
- simple cell wall present, complex cytoskeleton
- complex appendages
model of ‘typical’ prokaryote cell
* much diversity amoung prokaryotes but ALL share these
- Cytoplasm: consists of a gel-like network
- Tightly coordinated cell functions
- Ribosomes (note: NO mitochondria!)
- Cytoplasmic membrane
- Nucleoid- region in the cytoplasm containing the single bacterial chromosome (not a nucleus!)
- Plasmid (1 or several) may be present
- Cell wall: most (not all) have a thick complex cell wall /envelope
- Flagellum: only motile bacteria
- May have additional cellular structures
what is the chemical composition of a bacterial cell
- water (70%)
- essential inorganic ions
- small organic molecules
- macromolecules (proteins, RNA, DNA, lipids, polycharides)
*cell composition varies with species, growth phase and environmental conditions, varieties of proteins will depend on physiological state of the cell
how are individual cell parts isolated for cell study
- Break open (lyse) the cell to release contents
- may be physical or chemical approach (must break open cell wall but not disintegrate complexes) - Centrifugation to separate the cellular components
- may require several fractionations (differential centrifuation) steps
*may need several fractionation steps to separate the diff components
* can learn more about composition like electrophoresis or mass spec
why do both prokaryotes and eukaryotes ahve ribosomes
- required for translation, allows information to flow
- ribosomes contain their own RNA
have a large and small unit (these untis are diff in prok and euk)
- not present in viruses
What are the different subunits in ribosomes
- ahve 2 subunits
- each unit made up of proteins and ribnucleic acid (RNA)
- ribosomes from prokaryotes have a smaller weight than eukaryotes
- weight is expressed in Svedburg units (s) or the centrigual velocity required to sediment the subunit
- prokaryotes have 70S ribosome and eukaryotes have an 80S
What are plasmids
- found in archaea, bacteria and some eukaryotic microbes
- extra chromosomal (not part of chromosome) DNA elements, usually circular that replicate autonomously
- typically much smaller than chromosomes
- copy number/cell varies widely
- contain additional/ advantageous genetic info (ex: genes encoding toxins, antibiotic resistance, activities that modify host proteins)
- can be gained, lost, traded between bacteria
How do bacteria exchange/share plasmids?
- Conjugation or bacterial sex
* direct cell-to-cell transfer thoguh a sex-pilli from a donor to a recipient cell - Transformation
* taking up bacterial DNA released from dead cells int he surrounding environment - Transduction: mediated by bacteriophages as they infect and replicate in bacterial cells then exit to infect another cell
what is the cytoplasmic membrane and its functions
- barrier that separates the internal cellular/cytoplasmic environment from the external environment
- protects and encloses the cytoplasma and its contents
- selectively facilitates transport in and OUT of the cell/cytoplasm
functions:
- Permeability barrier: prevents leakage and functions as a gatewar for transport of nutrients into and out of the cell
- Protein anchor: site of many proteins invovled in transport, bioenergetics and chemotaxis (proteins inv for making ATP embedded here, also chlorophyl)
- Energy Conservation: site of generation and use of the proton motive force
describe the fluid mosiac membrane
- at the atomic level the CM is a fluid mosaic membrane
- phospholipid bilayer with embedded proteins
- organized in leaflets (outer and inner), within it is proteins that perform functions of cytoplasmic membrane
- contains ATPase
- support matrix and exclusion functions
- the abundance, diversity, composition and arrangement of proteins and lipids vary greatly with growth conditions and between species
Bacteria and Eukaryote cells have phospholipids in their CM, describe them
- Phospholipids are amphipathic
- polar/charged head groups, naturally oriented towards aqueou environment
- hydrophobic tails naturally orient away from water and tail-to-tail in the membrane
- Phospholipid structure
- glycerol (3C) with two ester linked fatty acids and a phosphoryl head groups (neg charged and usually capped with a neutral or charged group like phosphatidylethanolamine)
how does the phospholipid bilayer act as a natural permeability barrier, how do diff phospholipids vary?
- Prevents free movement across CM of polar or charged molecules
- proteins facilitate transport (discussed later)
- vary with respect to: compositiona nd charge of phosphoryl head groups, abundance of specific phospholipids in response to env conditions, compositions (saturation) of the fatty acid side chains
How is membrane fluidity esential
- essential for CM stability and protein function
- membrane proteins are dynamic and require a certain level of membrane fluidity fo function
- membranes ahve regions of low and high fluidity (gel-fluid states)
- saturated lipids: melt at high temperatures: inc order/rigidity
- Unsaturated lipids: melt at lower temp: increase fluidity and disorder
CM of microbes that live at low temp have higher abundance of unsaturated lipids
what is the role of planar lipids molecules in the membrane?
- add strength
- membrane lipids also include planar molecules that fill gaps between hydrocarbon chains
- in eukaryotic membranes the reinforcing agents are sterols such as cholesterol
- in bacteria the same function is served by hopanoid
- bacteria regualte membrane fluidity & rigidity by varying the abundance of these different memrbane lipids
differences between Archaea and Bacteria/Eukarya membrane lipids
- Archaea have PHYTANYL chains NOT fatty acids
- archaea have ETHER linkages while bacteria/eukarya ahve ESTER linkages
*both have glycerol
describe the Archaea membrane lipids diversity
- archaea have the most extreme variations in side-chain structures
- Diethers: 2 chains of ether-linked to glycerol, form bilayers in membranes (like phospholipids)
- Tetraethers: 2 very long chains ester-linked at either end to a glycerol, form a monolayer (two chians attached to each glycerol right across the membrane
*advnatage in tetraether monolayer is no point of weakness, stays very stable under extreame conditions
describe simple diffusion
- small uncharged molecules such as O2 and CO2 easily permeate the membrane by passive/simple diffusion
- substrate moves down conc gradient directly across the CM (no facilitator proteins invovled)
- water diffuses across mem called osmosis
describe facilitated diffusion
- down a conc gradient (of the substrate) through a channel forming membrane protine
- the permease is a transmembrane/integral CM proteins
a) opens to bidn the substrate, then closes as the substrate is translocated through the channel
b? facilitated diffusion permeases can move substrate IN or OUT depending on the concentration gradient
*can move in or out depending on the conc gradient
What is the most common type of active transport and the 2 types of it
= requries energy
- coupled substrate transport system is most common
- export two diff substrates simultaneously
energy released by one sub is used to move the other substrate (the driving ion) moving DOWN its gradient is used to move a diff solube UP its gradient
Sympoters: move two mol in SAME direction
Antiporters: move two mol in opposite directions
what are the components of the ABC transporters?
- nutrient-binding/scavenging proteins located external to the CM
*high affinity for its nutreints
- transmembrane ATP-binding/hydrolysing permease
*has a site for interaction with permease, once it interacts with it ATP bidns to ytoplasmic site, is hydrolysed to release energy. this opens the channel, substrate is released into channel and then the channel closes
*for every 1 substrate an ATP is hydrolyzed
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