Membrane structure and transport

Question 1

membranes functions

Answer 1

keep its molecules of life from dissipating awya (DNA and RNA)

keep out foreign molecules

Question 2

Selective permeability

Answer 2

amphipathic phospholipids are used to block certain molecules out of cell (polar, big molecules, ions)

Question 3

leaflets membrane

Answer 3

asymmetrical
glycolipids on extracellular leaflet so that the carbohydrate of the glycolipid protudes into extracellular medium

Question 4

lateral movements vs flipflop

Answer 4

lateral movement: occurs relatively often

Flipflop: rare, because does not occur spontaneously, needs energy imput

Question 5

ways to control membrane fluidity

Answer 5

lenght of FA:
Shorter leads to fewer stabilizing interactions leads to more fluid membrane

double bonds in acyl tail:
double bond makes a kink, prevents close packing of hydrocarbon tails and reduces hydrophobic interactions, so makes it more fluid

sterols through membrane:
cholesterol stabilizes membrane at low temperature (acts as spacer between FA) and keeps fluidity
at high temperature, hydroxyl group of cholesterol reacts with hydrophilic tails of phospholipids, makes it less fluid

Question 6

lipids raft

Answer 6

regions of phospholipids with enriches sterols and membrane protiens

play important role for signal transduction

Question 7

membrane protiens types

Answer 7

integral
covalent attachment of lipid to an amino acid within a protein, done post-translationally (after polypeptide is created)
transmembrane
goes through bilayer

Peripheral proteins
do not interact with the hydrophobic interior of the phospholipid bilayer
non-covenlantly bound to regions of integral membrane or to the polar head groups of phospholipids
typically bound to membrane by hydrogen or ionic bond

Question 8

membrane proteins functions

Answer 8

transport
enzymatic activity
signal transduction
cell-to-cell recognition
intercellular joining
attachement to cytoskeleton

Question 9

cell-cell junctions

Answer 9

anchoring junctions (anchor cells to cytoskeleton)

tight junctions (nothing gets through)

gap/communicating junctions (allows for commucation)

plasmodesmata (for plants because of cell wal)

Question 10

Extracellular matrix

Answer 10

main ingredients are glycoproteins secreted by cells

components:

fibers: made of glycoprotein collagen (looks like tubes)

proteoglycan: 95% carbohydrates (looks like filaments)

fibronectin: adhesive that attaches the ECM to the plasma membrane of the cell

integrins: bouds to the ECM on one side and to the microfilaments of the cytoskeleton on the other

Question 11

diffusion

Answer 11

molecules diffuse outwards from regions of high concentrations to lower ones

continues until homogenous

diffusion occurs when a system not at equilibrium

passive process (steeper the gradient (greater the different) high the net rate of solute movement)

larger the particle of solute, slower rate of diffusion

higher temperature faster rate of diffusion (since depends on kinetic energy)

increases entopy

Question 12

simple diffusion vs facilitated diffusionWAAS

Answer 12

simple diffusion: small, nonpolar molecules passes throigh lipid bilayer

facilitated diffusion: transport of hydrophilic molecules facilitated by proteins

Question 13

facilitated diffusion

Answer 13

done through:

polar protein channels (tunel), quick, usually for ions

carrier proteins: bonds to a specific solute and undergoes a series of conformational change (ex: uniport: moves 1 molecule)

is specific to only certain ions/moelcules

it saturates if all relevant carrier protiens are being used

still passive, uses gradient

Question 14

internal glucose

Answer 14

body keeps its internal glucose level by immideatly attaching phosphate (if not, by osmosis cell will explode) and then it becomes highly charged and cant pass though the membrane again

Question 15

gated channels

Answer 15

gated chanels: most channels have a gate to control its permeability ex Ligand-gated channels.

can also be done through intracellular protein that will activate the gate

some gates controled by reglatory proteins ex: phosphorylate gated chanel, chloride channels (openend by phosphorylation)

can also be volatge gated, response to electric gradient ex sodium and potassium nerve channels

can also me mechano sensitive (sensitive in changes in membrane tension) ex ability to hear depends on this

Question 16

active transport

Answer 16

require energy imput, goes against gradient
major factor of cell meintaining internal concentrations

primary: uses atp, ex sodium-potassium pump

secondary: uses energy in set up gradient to move something against the gradient, ex: high sodium concentration outside cell, will want to move inside but will have to be coupled with low concentration surcrose outside the cell to allow the trasnport to pass it through

symporter/cotransport (trasnports 2 molecules or more agaisnt gradient, same dirrection), antiporter (trasnports 2 or more molecules agaisnt gradient, different dirrection)

Question 17

sodium-potassium pump

Answer 17

3 sodium go out the cell, 2 potassion go in

universal in animal cells

maintaints voltage different accros nerve cell membranes

drives other transporters

Question 18

electrogenic pump

Answer 18

any pump which moves net electrical charges across membrane

sodium-potassium pump: as exchange not equal (3 Na+ leaving 2K+ coming), it creates a difference in the net charge accros the membrane surface called the membrane potential (interior is a bit negative)

Question 19

bulk transport

Answer 19

large molecules usually cross bilayer through bulk transport using vesicles

also requires energy

excosytosis: secretes out of cell, ex insulin

endocytosis: into cell
phagocytosis
pinocytosis
receptor-mediated endocytosis

exo-endo are likend and are in a sort of cycle to maintainsurface area and volume

Question 20

phagocytosis

Answer 20

cellular eating

cell wraps a peudopodia around it and packages it inside a sac

sometimes goes to lysosome to be destroyed

unspecific

Question 21

pinocytosis

Answer 21

cellular drinking

takes external fluid gulp, with all its solutes

unspecific

Question 22

receptor-mediated endocytosis

Answer 22

receptors activate intake

ex: LDL intake

Question 23

osmosis

Answer 23

water diffuses to where there is more solute throigh a semipermeable membrane (water gradient)

osmolarity: total solute concentration
depends on ions and dissasociation (NaCl=Na + CL so doule the osmolarity than initially)

iso-osmotic: same osmolarity
hyperosmotic: solution with a high osmolarity than another
hyposmotic: solution with a lowerosmolarity than another

osmotic pressure: indirredt measure of the pressure that must be exterted ona side of the selective permeanle membrane containing more solute to prevent diffusion of water from the side containg less solute
as osmotic pressure increases, osmolarity increases
as water concentration decreases, ormotic pressure increases

water will flow up an osmotic pressure gradient

Question 24

tonicity

Answer 24

measure of how a soluton affect cell colume

depends on solute concentration and solute permeability across semi permeable membrane

isotonic: solution does not alter cell volume
hypertonic: solution that causes cells to shrink (more concentrated outside)
hypotonic: solution that causes cells to swell (less concentrated outside)

Question 25

in plants tonicity

Answer 25

hypotonic: water vacule is full and cell is turgid (turgor pressure: force within the cell that pushes the plasma membrane against the cell wall)

isotonic: poper cell wall support, vacuole is not exterting too much pressure

hypertonic: water seeks to exit cell, vacuole empty, no rigidity in wall

Question 26

osmoregulation

Answer 26

urinary system and endrocrine system play major role in making sure we have good blood osmosis

paramecium are usually hypertonic relative to theur envritonment, so contractile vacuole will pump water out of cell