BIOC PART E

two membrane types of the cell?

function of membranes?

plasma membrane and organelle membrane

compartmentalize, communicate, convert energy and surface recognition

membrane composition is about 45% lipid, 50% protein and 5% carb, by surface area it is mostly _____

lipid

membrane phospholipids have hydrophillic and hydrophobic components making them _______

amphipathic

phosphoglycerides/glycerophospholipids

backbone made of ______

2 FA are in _____ link with glycerol

headgroup derived from _______

glycerol

ester

alcohol

most lipids in body are

phospholipids

what are 4 main head groups of phospholipids?

phosphatidic acid

phosphatidyl ethanolamine

phosphatidyl choline

phosphatidyl serine

phosphatidic acid

phosphatidyl ethanolamine

phosphatidyl choline

phosphatidyl serine

what net charges on each at pH=7?

(also draw out the structures of each group)

phosphatidic acid -2

phosphatidyl ethanolamine 0

phosphatidyl choline 0

phosphatidyl serine -1

Why is the net charge of phosphatidylethanolamine 0 when ethanolamine is +1?

Phosphatidylethanolamine has two charged groups

1. Ethanolamine group → protonated NH₃⁺ → +1 charge

2. Phosphate group → −1 charge

This makes phosphatidylethanolamine a zwitterion (both positive and negative charges but net 0).

sphingolipids

back bone made of ____
1 FA attached by _____ link

sphingosone

amine

sphingolipids have a net _____ charge

neutral

two types of sphingolipids are _______ and _______

ceramide and sphingomylein

ceramide and sphingomylein have what headgroups?

ceramide- none

sphingomylein- phosphocholine (phosphate considered part of head in sphingolipids unlike phosphoglycerides)

many sphingolipids have many complex _______

sugars

sphangolipids are structurally similar to phosphoglycerides but are _______ (smaller/larger)

smaller

many sphangolipids have carbohydrate head groups making them glycosphangolipids which in the body are commonly seen in _____

ABO blood type marking

ABO blood type markers include various carbohydrates taht show difference between blood types attaches to a _______ sphingolipid

ceramide

________ is the major animal sterol

cholesterol

describe cholesterol shape

• 4 fused rings termed the steroid nucleus (ABC hexagons and D pentagon)

• planar structure

• alkyl side chain (on D ring C17)

• polar head group -OH (on A ring C3)

two major classes of lipids are _____ and ______

storage and membrane

storage lipids include:

TAGs (glycerol attached to 3FA)

subcatagories of membrane lipids are ______ and _______

phsopholipids and glycolipids

glycolipids include

sphingolipids (sphingosine, FA and mono or oligiosaccharide)

sulpholipids (glycerol, 2FA, mono or disaccharide -SO4)

phospholipids include

sphingolipids (sphingosine, FA, PO4-choline)

glycerophospholipids (glycerol, 2FA, PO4-, OH)

plasma membrane composition is similar between cellular/organelle membranes (T/F)

F, membranes have unique compositions depending of function, however phophatidyl choline is a major component of them all.

note: minor lipid doesnt mean its unimportant just in smaller quantity

while found in other membranes, the plasma membrane specifically has relatively a lot of ______

cholesterol

4 common structures of phospholipid organization and description

monolayer- form at air whater interface, polar head in water, two tails extend to air.

micelles- single tails cause a wedge shape to form which assemble into curves, tails interact with eachother and polar heads interact with environment (common in detergents)

lipid bilayer- stable, 2 tails, thick (3nm), basic matrix of bio membranes, impermeable to ions and polar molecules

liposomes (vessicles)- most resemble cellular bilayer, aqueous centre, allow for study of biomembranes and transporters

functions of membrane proteins

-transporters and channels
- receptors
- structural components
- adhesion proteins
- surface antigens

two types of membrane proteins

1. Peripheral membrane proteins

2. Integral membrane proteins
   (a) covalently attached lipid anchor (kinda integral)
   (b) transmembrane domain (properly integral)

fluid mosaic model

components of a bilayer move around in leaflet

by weight are lipids or proteins heavier?

proteins

how are peripheral proteins attached to the membrane? how are they removed from the membrane?

periphreal protein has negative charge and so does the phospholipid membrane, so Ca2+ is the postive needed to hold them together.

if Ca2+ is removed by a change in pH or by a chelator or urea, carbonate, etc.. the attraction is gone and the periphreal protein disassociates from the membrane

if you need to use a detergent to remove a protein from the membrane, what type of protein is it?

integral membrane/ transmembrane protein

(hydrophillic domain coated with detergent, is pushed out of membrane)

GPI anchored proteins (lipid anchored) are removed from membrane by __________

phospholipase

peripheral proteins can be embedded in the membrane at different depths depending on _________________

electrostatic interactions, hydrogen bonds, interaction with head group of lipid bilayer

some membrane proteins are lipid anchored in class we talked about 4 lipids that attach to proteins by what AAs?

palmitoyl attaches ______

N-myristoyl attaches ______

Farnesyl attaches ______

GPI attaches ______

palmitoyl attaches Cys or Ser

N-myristoyl attaches N term of Gly

Farnesyl attaches C term Cys

GPI attaches C term (complex)

describe glycophorin A structure

huge transmembrane protein, cytosolic region glycosilated, type 2 protein (N term out, C term in)

where are the N term, C term (and do they use STA or SA- MCB content)

type 1

type 2

type 3

type 4

type 1- N lumen, C cyt, STA, (and signal sequence cleaved)

type 2- N cyt C lumen, SA

type 3- N lumen, C cyt, SA

type 4- varied, SA, STA, more than 2 TMDs

(also GPI N in C in, C phospholipid anchor)

a hydrophobicity plot helps you determine what about a protein?

how many hydrophobic (TMD) it has

how many hydrophobic residues in a row often indicates a TMD?

20+ (approx how many needed to span membrane)

on hydrophobicity graph what do peaks indcate above 0? below zero?

hydrophobicity, hydrophilicity

Bacteriorhodopsin, a GPCR protein type has how many TMD? is N term in or out?

why interest of drug companies?

7 , N term out, C term in

many drugs of interest target GPCRs

what is an annular lipid?

lipids that stay on a protein even when detergent used, detected as part of the proteins structure. often to remove an annular lipid you must break the protein structure. lipids look simiilar to bilayer with hydrophobic tails trying to stick near the hydrophobic protein regions.

all proteins with TMD are a-helixes (T/F)

F, some can be B barrels

where are beta barrel TMD proteins found?

bacterial and mitochondrial outer membranes

(examples in class FepA, OmpLA, maltopotin)

why cant beta barrel TMD always be detected on hydrophobicicity graph?

sometimes the residues are only 7 AA long (dont need to be 20+ like a helixes, because B barrel is a much more extended structure) so cant usually be sure

where are B barrel back bone hydrogen bonds?

between B strands (amine- carbonyl)

where are tyrosine and tryptophan residues concentrated in integral proteins? (Y and W)

where the polar head groups meath the acyl (FA) chains of the phsopholipids. this is because Y and W have both hydrophobic and hydrophillic regions

in beta barrels what is the general pattern of residues?

hydrophilic and hydrophobic AA alternate in sequence and point towards the prefered environment. (central hydrophillic, external hydrophobic bilayer)

where are Arg, Lys, Glu, Asp residues found?

hydrophillic areas (they are charged)

if a charged residue is in a hydrophobic area such as a TMD why might that be?

usually play a specific functional role

what are the two catagories of glycoproteins?

N linked and O linked

N linked glycoproteins sugars atttach by ______

O linked glycoproteins sugars attach by ______

N- attach by Asn side chain N (N-acetylglucosamine (GlcNAc))

O- attach by Ser/ Thr side chain OH (N-acetylgalactosamine (GalNAc))

what is the purpose of glycoproteins and glycolipids?

cell surface recognition, receptors

why is it important that a membrane is dynamic?

so shape can change without loss of integrity (leakage)

allow flip, flop, scramble

membranes usually bounce off eachother but can fuse with integrety loss

3 states of a membrane

gel- cold, motion constrained, paracrystaline, stiff tails, not a usual state

liquid ordered- physiological, motion of tails, and lateral movement of proteins

liquid disordered/ liquid fluid- constant aggregation and irregular motion

what do stearols such as cholesterol do?

act as buffer for fluidity of membrane

what type of FA can pack best in cell membrane? which type contribute to fluidity?

saturated fats pack tightly, unsaturated introduce a kink in the chain and pack less tight

cells can regulate fluidity (T/F)

T, cell may produce less saturated fats at a low temp for example

the behaviour of cholesterol in a membrane depends on temperature and composition, explain the effect of adding cholesterol in the following situations:

long chain saturated FA

unsaturated FA

high temp

low temp

long chain saturated FA- cholesterol interferes with acyl chain interactions and increases fluidity

unsaturated FA- cholesterol decreases fluidity by filling in the kinked regions for better packing

high temp- cholesterol helps to reduce fluidity as it is rigid and helps keep the flexible chains more straight in heat

low temp- cholesterol helps to increase fluidity by breaking up the straight chain acyl tails

(basically a buffer to bring membrane back to physiological in all situations)

uncatalyzed lateral diffusion happens very ________

transbilayer motion (flip flop) happens very _________

quickly

slowly (days)

why is transbilayer movement so slow?

hard for polar head to make it through hydrophoic bilayer

flipases, flopases and scramblases are transmembrane proteins that help facilitate transbilayer motion how?

act as an aqueous pore for the polar head of phospholipids to move through the hydrophobic membrane easier

flipases

flopases

scramblases

flipases- enzyme uses ATP, phosphoserine(-)/phosphatidylethanolamine, against gradient, outer→inner

flopases- enzyme uses ATP, ABC transporter, against gradient, inner→outer

scramblases- not an enzyme, moves lipids either direction with a gradient towards equilibrium (spontaneous)

lipids diffuse rapidly and freely often in a restricted region, and occassionally hop to a new restricted region (behave as if controlled by fences that they ocassionally escape) we know this by doing single particle tracking.

what keeps proteins confined to a small region

spectrin (part of cytoskeleton) and associated ankyrin

lipids are not randomly dispersed, rather often lipids of similar type can come together to form _________, which contain more _____ than surrounding membrane

lipid rafts (ex sphingolipid raft), more cholesterol

ions and small particles cross the membrane very slowly without help whereas _____ cross membrane very quickly

hydrophobic molecules and gasses(considered hydrophobic) such as steroids, O2, N2, CO2

Trp and Tyr are often in an inbetween zone due to hydrophobic and hydrophillic regions, often ______ are also there as they can serve as a link betwen hydrophillic and hydrophobic region

carbonyls

6 types of membrane transport

simple diffusion

facilitated

primary active transport

secondary active transport

ion channel

ionophore (down gradient)- not really gonna mention again

delta G is negative when molecule moves from ______ to _______ concentration

high to low

if log value is _____ than 1, then delta g is negative in ln (C2/C1)

smaller

when c1=c2 what occurs in diffusion?

ln(c2/c1)=ln1=0 therefor deltaG=0 and no net movement

to transport a hydrophillic solute across a membrane what do you need to do

with transporter

without transporter

with- low delta G, goes through aqueous channel (facillitated- down gradient)

without- need to expend energy to remove water from molecule, move through membrane, then put water back on in cytosol

what are the major differences between membrane channels and transporters?

channel- very fast rate of flux (only limited by rate of diffusion), regulated by gates, dont use ATP (like an open tunnel)

transporter- slower rate of flux (able to be saturated bc has binding sites), regulated by substrate avalibility, can use ATP or not (like a revolving door)

membrane channels are limited by _____

diffusion

are membrane channels saturable?

no

increasing _____ increases rate of diffusion of a channel

concentration of substrate

channels often transport ________

ions or water

what is the type of channel that water goes through?

aquaporin

aquaporins have 4 AA with specific functions, what are they and what function do they serve?

Arg195- electrostatic repulsion of H3O+ by its own pos charge

His180- prevents large molecules from going through channel (size exclusion)

Asn192, Asn76- H+ normally wants to jump around from H2O to H2O, these AA residues prevent this from happening by reorienting water molecules and excluding the H+ ions from bouncing around like a newtons cradle

all keep out OH-, H3O+ forms of water and allow H2O to pass (dont wanna fuck up cell pH by adding ions that are acidic or basic)

3 broad catagories of transporters

uniporters

co transporters: symporter (two things transported in same direction), aniporter (two things transported in oppisite direction)

passive transporters dont use _____ and go _____(with/against) concentration gradient

ATP, with

are transporters or channels more specific?

transporters- they are sterospecific (ex. a transporter can select for D glucose over L glucose)

passive transporters have a max rate (T/F)

T

passive glucose transporters include GLUT1 and GLUT2 what do each do differenty?

GLUT1- imports sugar (in erythrocytes)

GLUT2- exports glucose (in liver and intestine)

GLUT 1 is a: antiporter uniporter, or symporter? of L or D glucose? active or passive?

passive uniporter of D glucose (with gradient)

GLUT1 uniporter of D glucose (imports glucose into erythrocytes) has T1 and T2 states what are they?

T1- open to outside cell to bind glucose

T2- opens to cytoplasm to bring glucose into cell

active transporters use _____ to move molecules against their conentration gradient

ATP (many active transporters are atpases

in the sodium potassium transporter __Na+ are exported, __K+ are imported and __ ATP is used

3,2,1

(NOKIA 321- 3Na out, 2K in, 1ATO)

Vm=0 when transporter is at ____

equalibrium

ions can eaily pass through a membrane (T/F)

F (takes very long time if not facilitated or actively moved)

when an ion crosses the membrane a _____ imbalance results which causes membrane poteintial noted by delta psi ( trident lookin symbol)

charge

free energy of charges for a membrane equation

deltaG=zF delta psi

z- charge: electron (-) or proton (+)

F- faraday constant

delta psi- membrane potential

dela psi=

psi inside - psi outside

Class question: Given the transport equation:
ΔG = RT ln (c 2/c 1)
Which of the following about Na+ transport
across the cell membrane is true?
1) It will move down its concentration gradient
2) It will move up its concentration gradient
3) It will always be at equilibrium
4) None of the above

why?

the equation doesnt account for charge, it only accounts for concentration, to account for charge need to use the additive equation of delta G total that s concentration + charge

deltaG total = RT ln (c 2/c 1) + zF delta psi (know this equation he says)

typical plasma membrane has a charge of _____ inside

-60mV (cells neg inside normally pos outside)

about ¼ of your resting ATP is used for what process alone?

sodium potassium transporter (ATPase)- both ions move up (against) concentration gradient, requires a lot of energy

the Na+/K+ ATPase is a tertramer of a2B2, which subunits do the transporting?

a subunits

what are the main things that make the Na+/K+ transporter so important?

control cell volume
gradients maintained drive active transport of other species (ex. Na+/glucose symporter)
render nerve cells electrically excitable

in the Na+/K+ transporter teh phases of the cycle are

1. enz-I form of transporter binds ______ in cell

2. phosphorylation by ATP triggers P-enzII form

3. P-enzII form releases _______ to cytoplasm and picks up ______

4. dephoporylation triggers enz-I form

5. enz-I form releases ___ in cell

1. enz-I form of transporter binds 3Na+ in cell

2. phosphorylation by ATP triggers P-enzII form

3. P-enzII form releases 3Na+ out of cell and picks up 2K+

4. dephoporylation triggers enz-I form

5. enz-I form releases 2K+ in cell (and back to step 1)

primary vs secondary active transport

primary- ATP directly used to transport (ex. Na+/K+ transporter)

secondary- uses energy from ion gradient to move another substance against gradient (ex. Na+/glucose symporter)