Membrane Structure and Lipid Bilayer

What are the plasma membrane's functions?

allows for communication with the outside world, transport of goods in and out of the cell, and expansion of the cytosol.

What distinguishes internal membranes in eukaryotic cells?

localization of functions and composition varies by organelle

What are the characteristics of membrane phospholipids?

amphipathic, heads face cytosol, move laterally and can form lipid rafts

Functions of inside & outside phospholipid layers?

inside: cell signaling

outside: chem rxns, cell recognition, cell communication

What are the main components of phospholipids?

a platform molecule (glycerol or sphingosine), one or more fatty acids, a phosphate, and sometimes an alcohol

How do double bonds in fatty acid tails affect their properties?

'cis' or 'trans'; cis double bonds create bends, trans are linear

What are phospholipids, cholesterol, and glycolipids (sphingolipids)?

membrane lipids that help with structure and function

How do membrane lipids differ structurally from storage lipids?

membrane lipids are amphipathic, triglycerides have 3 fatty acid tails + glycerol

What is the significance of membrane fluidity

lateral movement of lipids

What happens to lipids in water?

they form self-sealing bags (vesicles) because tail doesn't want to be exposed

What factors influence the fluidity of a lipid bilayer?

tail length (decrease) and unsaturation (increase)

What is the role of cholesterol in membrane fluidity?

slows lateral movement, thickens membranes + makes it rigid

What is lipid asymmetry in the lipid bilayer of the membrane?

uneven distribution of lipids, different compositions on the cytosolic and extracellular faces.

What are the types of membrane proteins and are they integral or peripheral?

Transmembrane (integral), monolayer-associated (integral), lipid-linked (integral), and protein-attached (peripheral).

What are the characteristics of each protein membrane? PLMT

transmembrane- inside & outside bilayer

monolayer- embedded- on cytosolic face, faces tails

protein-attached- linked to transmembrane, difficult to remove on outside

lipid-linked- proteins linked to lipids, inside or outside

How do polypeptide chains typically cross the lipid bilayer?

they form alpha helices, hydrophobic heads interact with tails on the outside

What are porins?

beta helices with hydrophilic side groups facing inward and tails outward, transports large molecules

What is the cell cortex and its function?

protein scaffolding that prevents lateral movement and creates barrier

How is the lateral movement of membrane proteins restricted?

tethering- attach to cortex & cytoskeleton

extracellular matrix- attaching to molecules

other cell proteins- attach to proteins of another cell

lipid rafts- more rigid, link together, break apart

diffusion- restricts proteins & phospholipids

What role do cell surface carbohydrates play?

cell recognition

what function do glycoslated lipids and proteins have?

they combine w/ ligasaccharides and form glycocalex, responsible for mucus, and cell signaling

What is the effect of temperature on membrane fluidity?

membrane fluidity changes with temperature

What enzymes are involved in moving lipids across the membrane?

flippase- outside to inside

floppase- inside to outside

scramblase- exchange 1 phospholipid

Lipid Production?

assembled by proteins & produced on cytosolic face, found on outside of the ER