Cell Membranes

Question 1

Membranes are?

Answer 1

fluid mosaics or lipids and proteins; highly dynamic

Question 2

plasma membrane structure results in…

Answer 2

selective permeability

Question 3

selective permeability meaning

Answer 3

membranes allow some things to pass through more easily than others

Question 4

passive transport

Answer 4

(diffusion and osmosis) moves down a concentration gradient and doesn’t require energy

Question 5

facilitated transport

Answer 5

where trans-membrane channels speed up passive transport. Needs a carrier protein to move molecules

Question 6

active transport

Answer 6

uses energy to move solutes against their chemical gradients

Question 7

bulk transport

Answer 7

occurs via exocytosis and endocytosis

Question 8

movement of small polar, and nonpolar molecules through membrane

Answer 8

move across quickly

Question 9

movement of large polar molecules and ions through membrane

Answer 9

move slowly or not at all unless they receive help from membrane channels

Question 10

why does fatty acid saturation affect permeability?

Answer 10

because double-bonds introduce a kink in the fatty acid

Question 11

movement of lipids/proteins

Answer 11

can move laterally through membrane

Question 12

movement of phospholipids

Answer 12

move laterally within membranes but rarely flip sides

Question 13

movement of substances across membranes depends on…

Answer 13

1) selective permeability of lipid bilayer
2) transmembrane proteins that transport selected ions and molecules and facilitated diffusion and active transport

Question 14

why do some molecules move across lipid bilayers?

Answer 14

diffusion and osmosis. Small uncharged molecules can cross membranes readily and spontaneously without expenditure of energy

Question 15

channel protein function

Answer 15

allows ions and large polar solutes to diffuse rapidly down their concentration gradient

Question 16

why do ions move

Answer 16

they are charged so they move in response to a combined electrical and chemical gradient

Question 17

why are channels highly selective

Answer 17

due to the structure of the protein

Question 18

what can highly dynamic channels do

Answer 18

they can be gated (opened or closed)

Question 19

carrier proteins

Answer 19

change shape to move molecules across the membrane

Question 20

what powers the movement of molecules through transporters

Answer 20

diffusion

Question 21

what do voltage-gated ion channels do?

Answer 21

open and close in relation to changes in membrane potential

Question 22

change in membrane permeability can…

Answer 22

change very rapidly

Question 23

concentration of ions/molecules in the membrane

Answer 23

can be different across the membrane. Outside vs inside the cell due to selective permeability

Question 24

sodium-potassium pump exchange

Answer 24

3 Na+ out for 2 K+ in across the cell membrane.
requires ATP
involves a conformational change in the shape of the protein

Question 25

what does action potential equal?

Answer 25

an electrical signal

Question 26

A membrane potential is…

Answer 26

a voltage difference across a plasma membrane due to selective permeability and active transport

Question 27

ion concentration inside/outside neuron

Answer 27

high Na+ outside and high K+ inside

Question 28

how are ions’ movement affected

Answer 28

because of their charge, it is affected by the electrical gradient

Question 29

what is the type of equilibrium in the membrane?

Answer 29

there is a voltage difference

Question 30

at rest, a nerve cell has…

Answer 30

a resting membrane potential

Question 31

role of ion channels and Na+/K+ pumps

Answer 31

outward diffusion of K+ via open resting K channels.
little inward diffusion of Na+ due to few open resting Na channels.
Inside becomes negative due to loss of K+.

Question 32

how do Na+/K+ pump maintain concentration gradients

Answer 32

transporting 3 Na+ out for every 2 K+ in

Question 33

what happens when nerve cells become “excited”

Answer 33

there are rapid changes in membrane potential

Question 34

Action potential meaning

Answer 34

all or none response = constant strength and can regenerate along axon

Question 35

how does membrane permeability change to cause change in membrane permeability

Answer 35

voltage-gated ion channels open and close by changing shape in relation to changes in voltage difference

Question 36

when voltage-gated Na+ channels open

Answer 36

increase Na permeability -> Na+ will flow in down concentration gradient (depolarization)

Question 37

when K+ voltage-gated channels open

Answer 37

increase in K permeability -> K+ will flow out down concentration gradient (Hyper-polarization)

Question 38

voltage-gated ion channels change membrane permeability to…

Answer 38

generate an action potential (electrical signal)

Question 39

Step 1 resting state

Answer 39

voltage-gated Na+ and K+ ion channels are closed and non-gated channels maintain resting membrane potential

Question 40

step 2 depolarization

Answer 40

initial depolarization opens some voltage-gated Na channels allowing Na+ to diffuse in. Further depolarizes membrane, allowing even more Na+ in

Question 41

Step 3 rising phase

Answer 41

if depolarization reaches threshold then all voltage-gated Na channels open

Question 42

Step 4 hyperpolarization

Answer 42

voltage-gated Na channels rapidly close. “delayed” voltage-gated K channels open causing rapid K+ outflow

Question 43

what is the basis of electrical signalling in the nervous system

Answer 43

selective permeability and changes in permeability over time

Question 44

endocytosis

Answer 44

food particles, fluids, specific molecules being taken up in to the cell

Question 45

exocytosis

Answer 45

reverse process where proteins, hormomes, etc. are released from the cell into the extracellular space or into the circulation = secretion

Question 46

secretory vesicles function

Answer 46

fuse with cell membrane to release contents