2.1: Cell structure and function -The Cell Envelope Flashcards
(34 cards)
what does the bacterial cell envelope consist of? describe each component, what is the most important part
- Cytoplasmic membrane -thin structure that surrounds the cell, highly selective semi-permeable barrier that separates cytoplasm from outside environment.
- Cell wall -rigid layer that confers structural strength.
- Periplasm- space between the cytoplasmic membrane and the outside of the cell wall.
-most important: the cytoplasmic membrane, no such thing as cell without it.
what does the cytoplasmic membrane being highly selective and semi-permeable do?
-it enables concentration of specific metabolites (which can’t escape through membrane) and excretion of waste products (which can go through membrane).
describe the cytoplasmic membrane structure
- Composed of a phospholipid bilayer -phospholipids contain both hydrophobic (fatty acid tails), and hydrophillic (glycerol-phosphate) regions.
- Bacterial membranes contain ester phospholipids
which consist of:
-1 glycerol backbone
-2 fatty acid tails
-1 phosphate and a variable side chain (head group)
what does amphipathic mean?
how do phospholipids exhibit this?
Has both polar and non polar characteristics.
ex: due to amphipathic nature, phospholipids in water naturally aggregate to form bilayers.
-fatty acid tails point inward - form hydrophobic, non polar core.
-head groups remain exposed to water in outside environment -hydrophillic, polar.
what’s an ester bond? which organisms have it
- ester because fatty acid attached by carbon attached to O, and double bonded O.
- bacteria and eukarya have it
the phospholipid bilayer forms how many layers of _ to_ nm thick, visible using _
2 layers, 8-10 nm, thick, visible using TEM.
what’s a true unit membrane
- membrane that consists of two layers aka bilayer.
where are integral membrane proteins, what keeps them there?
- Firmly embedded in the membrane, amphipathic nature keeps it in place, takes no energy
where are peripheral membrane proteins located
- loosely associated with the membrane
peripheral membrane proteins may have a lipid portion called _
lipoproteins
peripheral membane proteins may interact with _
integral proteins
different membrane proteins often ….. to carry out a function
group together in clusters
describe the fluid mosaic model of the membrane
the cytoplasmic membrane exists in a semi-fluid state
-lipids in the outer leaflet are different from lipids in the inner leaflet ex: different head groups and fatty acid tails
-integral proteins can move laterally, but do not flip-flop sides (as polar hydrophillic ends do not want to move through hydrophobic middle region)
-overall composition may change to suit conditions
whats the difference in ETHER bonds compared to ester? what organisms have ether bonds?
- no double bonded O
- archaea have ether bonds
what’s are the differences in the tails of arachael phospholipids
- instead of fatty acid tails, they have hydrocarbon tails made of repeating units of isoprene
- some archael membranes are made of **glycerol diether ** phospholipids with long branched tails -phytanyl
- other archael membranes are made from diglycerol tetraether phospholipids
most archael tails are branched eukaryotes and bacteria’s are not
describe diglycerol tetraether phospholipids (which some archael membranes are made from)
- two phospholipids joined by the tails
- makes the inner and outer faces of the membrane
- forms a lipid mono-layer (since the tails connected all one)
in contrast to lipid bilayers, lipid monolayer membranes are _. so monolayers are commonly found in __ __.
extremely heat resistant
-commonly found in hyperthermophilic archaea (grow best in temps above 80 C
what are the 3 main membrane functions
- permability barrier - Nutrient and waste transport, small non-polar can diffuse across, large or polar must be moved by transport proteins
- protein anchor - holds proteins in place
- energy conservation -generation of PMF (gradient of protons across membrane) -since prokaryotes don’t have mitochondria or chloroplasts, membrane does this.
small non-polar molecules can cross membrane through __ __
passive diffusion (high to low conc)
can large polar and charged molecules need _ _ to cross membrane
they need transport proteins bc they cannot just diffuse across membrane.
how do integral membrane proteins work? (Facilitated diffusion)
what’s an example of one?
- allow specific molecules to diffuse across CM
- follow usual rules of diffusion:
-solutes move from high to low
-no extra energy is required - simply speeds up the rate of diffusion for molecules that would not easily cross the membrane otherwise.
- ex: E. coli’s aquaporin, allows H2O to diffuse into or out of the cell
describe how transport proteins work in active transport
Transport proteins work to accumulate solutes against a concentration gradient.
* requires input of energy
* moves solutes from area of low conc. (outside cell) to area of higher conc. (inside)
* allows solute conc. sufficient for biochemical processes
* highly specific -transport protein usually carries only a single kind of molecule
* subject to saturation effect
active transport is subject to the saturation effect, what is this
when the transporter is saturated already bringing in material as fast as it can, the rate of solute entry will level off at this point.
what are the 3 types of active transporters
- simple transporters - a single membrane spanning transport protein
- group translocation - a series of proteins carrying out the transportation event, and modifies the substrate, as it is brought into the cell (for accumulating solutes against concentration gradient).
- ABC transportation systems - use a substrate binding protein, a membrane transporter and an ATP hydrolyzing protein.
