cell structure and function unit 2

most integral membrane proteins have one or more ____ segments that span the lipid bilayer

hydrophobic

there fluid mosaic model

is thought to be a description of the structure of cell membranes, depicting a flexible matrix of lipids and proteins.

membranes are not

homogeneous - they randomly mix structures

membranes are ordered through dynamic micro domains called

lipids rafts

membrane lipids are important components of the ___ part of the fluid mosaic model

fluid

the different types of lipids that membranes contain

phospholipids, glycolipids, sterols

the most abundant lipids in membranes are

phospholipids

if you have a surface area of red blood cells and put them into a membrane how do you find the new surface area

multiply by two because bilayer

phospholipids have two diff types called

phosphglycerides (glycerol based) and sphingosine-based sphingolipids

phospholipid composition varies in

membranes from different sources

glycolipids are from by

the addition of carbohydrates to lipids

glycolipids are based with

glycerol or sphingosine

glycolipids are usually found on 

the outside of the membrane

the membranes of eukaryotes contain significant amounts of

sterols

the main sterol in animal cell membranes is

cholesterol

cholesterol is needed to 

stabilize and maintain membranes

membrane asymmetry is the difference between

the monolayers regarding the kind of lipids present and the degree of saturation of fatty acids in the phospholipids

most glycolipids in the plasma membrane of animal cells are in the

outer layer

membrane asymmetry is established

during the synthesis of the membrane

lipids move ___ within their monolayer

freely

rotation and lateral diffusion of lipids

are rapid and random

FRAP

fluorescent recovery after photobleaching

frap process

investigators label lipid molecules in a membrane with fluorescent dye

• a laser beam is used to bleach the dye in a small area creating a dark spot on the membrane

• the membrane is observed afterward to determine how long it takes for the dark spot to disappear, measure of how quickly new fluorescent lipids move in

example of FRAP

membrane asymmetry tends to be

maintained

transverse diffusion

also known as flip flop

• relatively rare

• requires hydrophilic head group to pass through the hydrophobic interior of the membrane

when transverse diffusion does occur

• phospholipid flip-flop does occur in natural membranes

• inn some membranes the smooth ER membrane have proteins that catalyze the flip flop of membrane lipids

the proteins in phospholipids that allow for transverses diffusion

phospholipid translocators, flippases

membranes fluidity must be

maintained

factors that regulate membrane fluidity 

• temperatyre, fatty acid structure, incorporation for sterols

how does temperature affect fluidity

temp increases and fluidity increases

fatty acid structure and fluidity

• saturation - unsaturated fatty acids increase membrane fluidity

• length of hydrocarbon tail, fluidity increases when hydrocarbon length decreases

incorporation of sterols and fluidity

• rigidity of sterol structure reduces membrane fluidity at higher temps

• rigidity of sterol structure also prevents phospholipids from 0packing too close together and reduces the tendency to gel at cooler temps 

membrane fluidity is characterized by tm value aka

temperature at which membrane changes from gel to fluid

lipids with saturated fatty acids pack

tight = less fluid

lipids with unsaturated fatty acids pack

loose = more fluid 

the number of double bonds has a ___ effect on membrane fluidity than hydrocarbon chain

much greater

cholesterol iso found on

• both inner and outer layers aka leaflets of plasma membrane

cholesterol acts as a ____ decreasing membrane fluidity at temperatures above the Tm and increasing fluidity when temperatures drop below the tm 

fluidity buffer 

sterols decrease ___

the permeability of the membrane

lipids rafts are

localized regions of membrane lipids that are involved in cell signaling

lipid rafts in the outer monolayer of animal cells have 

elevated levels of cholesterol and glycosphingolipids and are less fluid than the rest of the membrane 

lipid rafts bind to and concentrate

proteins at certain positions on the plasma membrane

the most prominent lipids in the animal cell membranes are

phospholipids

the mosaic part of the fluid mosaic model includes ____ however ___ are the main components

• lipid rafts and other lipid domains 

• membrane proteins

freeze fracture method

splits a membrane into its two layers, particles the size and shape of globular proteins can be seen

the protein/lipid ratio

varies among cell types

the classes of membrane proteins

integral membrane proteins, peripheral membrane proteins and lipid-anchored proteins.

integral membrane proteins

• embedded in the lipid bilayer because of their hydrophobic regions

peripheral membrane proteins are

hydrophilic and locate on the surface of the bilayer. they interact with integral membrane proteins and membrane through weak electrostatic interactions and hydrogen bonding

lipid anchored membrane proteins are

hydrophilic and attached to the bilayer by covalent attachments to lipid molecules embedded in the bilayer

lipid anchored membrane proteins require

covalent medication of the proteins

lipid anchored membrane protein anchor types

fatty acids, isoprenoid and GPI

membrane proteins are oriented ____ across the lipid bilayer

asymmetrically

onice in place in or on one of the monolayers proteins

cannot move across the membrane from one surface to the other

all the molecules of a particular protein are oriented in the ____ way in the membrane

same

many membrane proteins are _____

glycosylated

glycoproteins are

membrane proteins with carbohydrate chains covalently linked to amino acid side chains

the addition of a carbohydrate side chain to a protein is called

glycosylation

glycosylation occurs in ____

the er and Golgi compartments

glycosylation involves the linkage of the carbohydrate to

• the nitrogen atom of the amino group

  • n linked glycosylation ex. asparagine residue

• the oxygen group of an atom of a hydroxyl group

  • O-linked glycosylation of serine, threonine, or modified lysine or proline residue

the easiest membrane protein to dissociate from membranes

peripheral membrane proteins bc non covalent bonds

membrane proteins are more variable than lipids because of

ability to move freely within the membrane

some proteins can move freely whereas others are constrained because

they are anchored to protein complexes

reasons for restricted protein mobility in membranes

• anchoring cytoskeleton components (actin)

• anchoring to extracellular structures or neighboring cells

• large protein complexes that can only move sluggishly in the membrane

• incorporation into lipid rafts

Frye and Edidin fused human and mouse cells and used two _____ fluorescent antibodies each with differently colored dye linked to it 

fluorescent antibodies

the anti-mouse antibodies were linked to _____ a green dye

fluorescein

the antihuman antibodies were linked to _____, a red dye

rhodamine

frye and edidion expirements

cholesterol acts as a ____

fluidity buffer

fluidity buffer and cholesterol

decreasing membrane fluidity at temperatures above the Tm and increasing fluidity when temperatures drop below the Tm

sterols ____ the permeability of the membrane

decrease

How are proteins inserted into the

phospholipid bilayer?

through covalently attached lipids and through transmembrane domain made of hydrophobic amino acids 

sterols decrease the permeability of the membrane because

more rigid structure than other membrane lipids

passive transport

along a gradient - without net energy input

• passive diffusion, facilitated diffusion

active transport 

against the concentration gradient

important considerations for transport

• solute properties

• relative solute concentrations

• availability of specific transmembrane proteins

• availability of an appropriate energy source

The movement of a molecule that has no net charge

is determined by its

concentration gradient

simple diffusion and facilitated diffusion involve 

exergonic movement down the concentration gradient - negative delta G

active transport involves

endergonic movement up the concentration graduate - positive delta G

the movement of an ion is determined by ____

its electrochemical potential

electrochemical potential is

the combined effect of its concentration gradient and the charge gradient across the membrane

the active transport of ions across a membrane creates a charge gradient or _____ across the membrane

membrane potential

abbreviation for membrane potential

Vm

simple diffusion molecules

small polar - h2o, glycerol

small nonpolar - o2 co2

large nonpolar (oils, steroids)

facilitated diffusion

• small polar (h2o, glycerol)

• large polar, glucose

• ions (na, k , ca)

active transport molecules

large polar - glucose

9ions - na, k, ca2+

the best understood of all transport proteins

erythrocyte plasma membrane

the membrane potential is maintained by active transport of _______ inward and _____ outward 

potassium ions, sodium ions

special pores or channels allow ______ to enter or leave the cell as rapidly as needed

water and ions

Simple Diffusion

unassisted net movement of a solute from a high to low concentration

• only possible for gasses, nonpolar molecules, or small molecules such as water, glycerol, or ethanol

oxygen gas traverses the lipid bilayer readily by ____

simple diffusion

_____ take up oxygen in the lungs, where oxygen concentration is high and release it in the body tissues where oxygen concentration is low

erythrocytes

osmosis

the diffusion of water across a selectively permeable membrane.

water molecules are not affected by the membrane potential because

they are not charged + small

If two solutions are separated by a selectively permeable membrane, permeable to the water but not the solutes, the water will move toward

the region of higher solute concentration

osmolarity

relative concentration of solutes between cytoplasm and extracellular solution

an animal cell in an isotonic solution

water will be removed

if an animal cell is put into a hypotonic solution

the cell will be lysed as water goes inward