PM Part 1 (16) Flashcards by M B

what does the PM distinguish?

exterior & life

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what makes the PM dynamic?

capable of fusing without losing continuity

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external membrane

PM encloses the entire contents of the cell

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internal membrane

Nuclear envelope
Mitochondrial membranes 
Chloroplast membranes
Lysosomal membrane
ER

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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

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what is the membrane permeable to?

lipids

steroids

O2 & CO2 (gas)

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what is the membrane impermeable to?

water soluble compounds

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what do membranes consist of?

polar lipids in a bilayer

PROs

CARBs

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fluid mosaic model

fluid composition of lipids, carbs & PROs

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How do PROs appear in the fluid mosaic model?

discontinuous particles

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how do the interactions occur in the fluid mosaic model?

transient interactions

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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

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how do you fuse cells?

electric shock

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what lipids are found in the cell membrane?

o Phosphoglycerides
o Sphingolipids & Glycolipids
o Cholesterol

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diglyceride

one saturated & one unsaturated FA

straight chain

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3rd OH group is coupled to a phosphate plus either

Choline – phosphatidyl choline

Ethanolamine – phosphatidylethanolamine

Serine – phosphatidylserine

Inositol – phosphatidylinositol

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Sphingosine

amino alcohol with a long hydrocarbon chain

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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

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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

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what type of cells is cholesterol absent in?

bacteria

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What type of cholesterol is in plant cells?

phytosterol

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how does cholesterol effect lipids at high temp?

reduces membrane fluidity

Fills gaps b/w phospholipids preventing them from becoming too fluid

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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

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fluidity/viscosity

measure of freedom of movement within the membranes

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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