PM Part 1 (16) Flashcards
what does the PM distinguish?
exterior & life
what makes the PM dynamic?
capable of fusing without losing continuity
external membrane
PM encloses the entire contents of the cell
internal membrane
Nuclear envelope Mitochondrial membranes Chloroplast membranes Lysosomal membrane ER
what are functions of membranes?
Compartmentalization
Eukaryotes
Defines diff functions of the cell
Site of biochemical activities
Scaffolding of PROs
Chloroplasts –> photosynthesis facilitated by integral PROs
Selectively permeable membrane
Transporting solutes (proton pump) Creates gradients
Responding to external signals
Intercellular interaction
Cell-to-cell attachment & communication
E transduction
Ion gradients enable production of ATP
what is the membrane permeable to?
lipids
steroids
O2 & CO2 (gas)
what is the membrane impermeable to?
water soluble compounds
what do membranes consist of?
polar lipids in a bilayer
PROs
CARBs
fluid mosaic model
fluid composition of lipids, carbs & PROs
How do PROs appear in the fluid mosaic model?
discontinuous particles
how do the interactions occur in the fluid mosaic model?
transient interactions
what is the evidence of the fluid mosaic model?
2 cells with diff dye fused together
the combined cell had the dyes dispersed –> move freely
how do you fuse cells?
electric shock
what lipids are found in the cell membrane?
o Phosphoglycerides
o Sphingolipids & Glycolipids
o Cholesterol
diglyceride
one saturated & one unsaturated FA
straight chain
3rd OH group is coupled to a phosphate plus either
Choline – phosphatidyl choline
Ethanolamine – phosphatidylethanolamine
Serine – phosphatidylserine
Inositol – phosphatidylinositol
Sphingosine
amino alcohol with a long hydrocarbon chain
role of sphingolipids
membrane structure, decreases fluidity making it more gel-like –> provides resistance to stressors
signaling & cell membrane recognition with glycolipids
Tighter packing since only one FA chain is attached
glycolipids play a role in
Cell membrane recognition
Electrical conduction (ex: myelin around nerve cells)
Rigidity provides insulated properties
Myelin sheath acts as an insulator
Inter-cell communication
Binding bacterial toxins (ex: botulism) & some viruses permitting their entrance into the cell
Enable bacteria to target the glycolipid to infect us
what type of cells is cholesterol absent in?
bacteria
What type of cholesterol is in plant cells?
phytosterol
how does cholesterol effect lipids at high temp?
reduces membrane fluidity
Fills gaps b/w phospholipids preventing them from becoming too fluid
how does cholesterol effect lipids at low temp?
helps prevent membranes from freezing, increases fluidity
When lipids become too compact the cholesterol creates spaces b/w the molecules Lipids composition changes, creating more unsaturated bonds creating more bends in the chains not as compact
fluidity/viscosity
measure of freedom of movement within the membranes
why is fluidity important? & When is it relevant in cell processes?
mobility & organization (moving PROs)
cell growth
cell division
inter-cell junctions
endocytosis & vesicle traffic
heterogeneity
local patches of membrane may have unique fluidity
exs of heterogeneity
sphingolipid rich particles
cholesterol on lipid rafts
what is fluidity dependent on?
type of lipid & temperature
lipid rafts
region of the PM rich in sphingolipids & cholesterol
aggregates of PROs of the same function
what lipids aren’t amphipathic
glycolipids & cholesterol
desaturase
remodeling enzyme, alters FA chains, increases the number of double bonds
when does the cell increase the amount of desaturase?
cold conditions
acetyl transferase
moves FAs b/w glycerol & attaches them to a new spot
Used to alter PM triglycerides to maintain correct fluidity
phospholipase
splits FA from the glycerol backbone
Used to alter PM triglycerides to maintain correct fluidity
how is membrane fluidity altered?
Remodeling enzymes for short-term response when temperature changes
Increase the amount of desaturase (converts FA saturated chains to unsaturated chains)
Presence of double bonds = increase in kinks = increases fluidity
Shuffling of FAs on phospholipids
Phospholipase: splits FA from glycerol backbone
Acetyltransferase: moves FAs b/w glycerol & attaches them to a new spot
Saturated –> unsaturated to increase fluidity
what type of cells remodel their PMs?
prokaryotes & eukaryotes
what is an ex of an animal modifying its PM composition?
hibernating animals
increase fluidity of membranes
what maintains lipid composition on opp sides of the membrane?
Flippases & other PROS that move lipids from one side to the other
PROs that modify polar heads
lipid transport PROs that transport lipids through the cytoplasm
why is membrane lipid asymmetry important?
diff lipids provide durability on each side providing –> can withstand physical stresses better
which way to most carbs face on membranes?
outward into the extracellular space
what organelle’s membrane carbs don’t face outwards? & why
lysosomes
lipids point inwards protecting lumen from digestive enzymes
how are carbs assoc with the membrane?
glycoPROs
Glycolipids
glycoPROs
short, branched oligosaccharides
Play roles in cell interactions
Attached to the R-group of: Asparagine (N-linked) or Serine or Threonine (O-linked)
glycolipids roles
Provide tags to invaders (infectious diseases)
Identify cell types (ex: blood type)
What percentage do PROs, lipids & carbs have in the PM?
52% PRO
40% lipid
8% carb
glycocalyx
dense mass of glycoPROs on the cell surface protecting cells against abrasions & involved in cell signaling
what role does glycocalyx serve in the gut?
protective function against digestive enzymes
what role does glycocalyx serve in bacteria?
outer coating of the cell wall
what type of interactions does glycocalyx have?
receptor/ligand interactions
integral PRO
lipid soluble portion, cytosolic portion & exterior portion
peripheral PROs
inside or outside the membrane, assoc with non-covalent bonds
lipid anchored PROs
inside or outside, covalently linked to a lipid
what are the 3 classes of membrane PROs?
integral PROs
peripheral PROS
lipid-anchored PROs
what type of AAs are in the transmembrane portion of integral PROs? & what is its conformation?
hydrophobic or non-polar AAs
alpha helical
how do we determine what AAs are found in the transmembrane portion of an integral PRO?
hydrophobicity plot
how do peripheral membrane PROs attach to the membrane?
Bind to hydrophilic portion of phospholipids or
a hydrophilic portion of an integral PRO
what is the role of peripheral membrane PROs on the cytoplasmic side?
transmembrane signal transduction
what’s a major diff among lipid-anchored membrane PROs & peripheral membrane PRos?
lipid-anchored –> covalently bonded
peripheral –> non covalent
what are the types of lipid anchors?
Lipid + carb (ex: glycosol phosphatidyl linked PRO) in the outer leaflet
or
long hydrocarbon chain in the inner leaflet
what is the role of lipid-anchored membrane PROs?
cell signalling or adhesion
