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Bio1MGC > Plasma membrane > Flashcards

Plasma membrane Flashcards

1
Q

what is selective permeability

A

allows some substances to cross the membrane more easily than others

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2
Q

what is an aquaporin?

A

membrane channel protein
one molecule of this protein enables billions of water molecules to pass through the membrane every second, many more than could cross on their own

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3
Q

what is an ion channel

A

transport protein embedded in plasma membrane

allows potassium ions to pass through the membrane

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4
Q

what are membranes made of?

A

lipids - mainly phospholipids
proteins
carbohydrates

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5
Q

what does amphipathic mean

A

has both a hydrophilic and hydrophobic region

most membrane lipids are amphipathic

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6
Q

describe the structure of a phospholipid bilayer

A

hydrophilic head exposed to water - made from choline and phosphate
hydrophobic tail - sheltered inside - made from gylcerol and fatty acids

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7
Q

what is the structure of membrane proteins

A

membrane proteins are amphipathic
have hydrophilic heads protruding and in contact with water in the cytosol and extracellular fluid
have hydrophobic parts are inside the membrane in a nonaqueous environment

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8
Q

what is the fluid membrane model

A

the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

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9
Q

how are proteins organised on the plasma membrane

A

not randomly distributed

groups of associated proteins in patches where they carry out common functions

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10
Q

How is the membrane fluid

A

bonds between molecules is weaker than covalent bonds
phospholipids shift sideways rapidly
proteins may also move

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11
Q

how does the temperature affect membrane fluidity

A

like fats at lower temperatures - phospholipids settle as the temperature decreases
as temp decreases they solidify
phospholipids with unsaturated hydrocarbon tails remain fluid to a lower temperature

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12
Q

what is a saturated lipid

A

all available carbons have a hydrogen attached

saturated with hydrogen

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13
Q

what does unsaturated mean

A

not every available carbon has a hydrogen

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14
Q

why do some phospholipids remain fluid in lower temperatures

A

phospholipids rich in unsaturated hydrocarbon tails remain fluid at lower temperatures
kinks in the tails where double bonds are located mean that hydrocarbons cannot pack together as closely as saturated hydrocarbon tails can

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15
Q

how does cholesterol work in membranes

A

cholesterol is wedged between phospholipids in the plasma membranes of animal cells
has different effects on membrane fluidity at different temperatures
at body temperature cholesterol makes the membrane less fluid by restraining phospholipid movement
at low temperatures hinders solidification by preventing phospholipids from packing
is a fluidity buffer

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16
Q

what cells have cholesterol

A

cholesterol is wedged between the phospholipid molecules in the plasma membrane of ANIMAL cells
compared to animals plants have very low levels of cholesterol but instead have steroid lipids buffer membrane fluidity

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17
Q

what are fluidity buffers in animal and plant cells

A

animals - cholesterol
plants - steroid lipids

buffers - resist changes in membrane fluidity brought about by changes in temperature

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18
Q

why do membranes need to be fluid

A

the fluidity of a membrane affects both permeability and the ability of membrane proteins to move to where their function is needed

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19
Q

what evolutionary adaptations occur in membrane lipid composition

A

variation in lipid composition depending on environment
some animals or plants that live in cold have high proportion of unsaturated hydrocarbon tails so phospholipids don’t solidify and remain fluid
bacteria and archaea that live in extreme temps have unusual lipids that prevent excessive fluidity

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20
Q

how are proteins arranged in the membrane

A

the membrane is a collage of different proteins often clustered together in groups, embedded in the fluid matrix of the bilayer
different types of cells have different sets of proteins
various membranes within a cell have a unique collection of proteins

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21
Q

what are the two types of membrane proteins

A

integral proteins and peripheral proteins

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22
Q

what is an integral protein

A

penetrate the hydrophobic interior of the lipid bilayer
majority are transmembrane proteins which span
others extend only part way into the hydrophobic interior

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23
Q

what are transmembrane proteins

A

proteins that span the membrane

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24
Q

what are peripheral proteins

A

not embedded into the lipid bilayer
loosely bound to the surface of the membrane
often bound to the exposed parts of integral proteins

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25
Q

what is the structure of an integral protein

A

hydrophobic region consists of one or more stretches of 20 - 30 non polar amino acids usually coiled into alpha helices
hydrophilic parts exposed to aqueous solutions

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26
Q

how do membrane proteins attach to the cell

A

cytoplasmic side - they attach to the cytoskeleton

extracellular - attach to materials outside the cell e.g. extra cellular matrix

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27
Q

what six functions are carried out by membrane proteins

A 
transport
enzymatic activity
signal transduction
cell to cell recognition
intercellular joining
attach to cytoskeleton and extra cellular matrix
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28
Q

how does a membrane protein function as transport

A

can be a channel protein - provide a hydrophilic channel selective for a particular solute
proteins may change shape to shuttle substance across the membrane
proteins may act as pumps

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29
Q

membrane proteins as enzymes

A

may be an enzyme with an active site where a reactant binds

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30
Q

membrane proteins that act as signal transductors

A

a membrane protein may act as a receptor for a signal
has a binding site that fits the shape of the chemical messenger
the messenger may cause the receptor to change shape allowing it to relay a message to the inside of the cell usually binding to a cytoplasmic protein

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31
Q

how do membrane proteins function in cell to cell recognition

A

some glycoproteins serve as identification tags specifically recognised by the membrane proteins of other cells (short lived)

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32
Q

how do membrane proteins function in intercellular joining

A

membrane proteins are involved in various kinds of cell junctions e.g. gap junctions / tight junctions

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33
Q

how does attachment to the cytoskeleton and extra cellular matrix benefit the cell

A

helps maintain cell shape
stabilises the location of certain membrane proteins
signal transduction - proteins that bind to ECM molecules like fibronectin / integrins can cause changes in the extracellular and intracellular environment

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34
Q

integrin

A

membrane proteins with two subunits - bind to the ECM outside the cell and to proteins attached to microfilaments on the inside
used to transmit signals between external environment and inside
the name integrin is based on integrate - integrins transmit signals between the ECM and the cytoskeleton and integrate changes occurring outside and inside the cell

35
Q

fibronectin

A

attaches the ECM to integrin embedded in the plasma membrane

36
Q

why is cell to cell recognition important

A

sorts cells into tissues and organs in an animal embryo

basis for the rejection of foreign cells by the immune system

37
Q

what types of membrane carbohydrates are there

A

glycolipids - carbohydrates covalently bonded to lipids
glycoproteins - carbohydrates covalently bonded to proteins

carbohydrates are usually short chains of fewer than 15 sugar units

38
Q

what molecules are involved in cell to cell recognition

A

carbohydrates - mainly glycoproteins and glycolipids

39
Q

where are membrane proteins and lipids synthesised

A

Endoplasmic reticulum

40
Q

process for making membrane glycoproteins and glycolipids

A

proteins and lipids synthesised in the ER
carbohydrates are added to transmembrane proteins making them glycoproteins in the ER
in the golgi glycoproteins undergo further modification
in the golgi lipids acquire carbs becoming glycolipids
transported in vesicles to plasma membrane
vesicle fuses with plasma membrane - positions glycoproteins and glycolipids on the outside face of the pm

41
Q

what types of substances can cross the plasma membrane easily

A 
non polar and hydrophobic molecules
hydrocarbons
carbon dioxide
oxygen
lipids

water can pass but slowly - aquaporins allow water to move at a much faster rate

42
Q

what types of substances cannot cross the plasma membrane without assistance

A 
polar and hydrophilic molecules
macromolecules
ions
amino acids
water
glucose and other sugars
charged atoms or molecules
43
Q

what are the different types of transport proteins

A

channel proteins - hydrophilic channel e.g. aquaporins
carrier proteins - hold on to passengers and change shape e.g. carrier protein in the plasma membrane of red blood cells transports glucose

44
Q

diffusion

A

the movement of particles of any substance so that they spread out into the available space
needs no input of energy - is a spontaneous process
called passive transport - cell does not have to expend energy

45
Q

concentration gradient

A

the region along which the density of a chemical substance increases or decreases
a substance will move up or down its concentration gradient
in diffusion a substance will move down its concentration gradient - no energy required

46
Q

in diffusion - what is dynamic equilibrium

A

substances will move down their concentration gradient until there is dynamic equilibrium - the solute molecules continue to cross the membrane but at roughly equal rates in both directions

47
Q

in diffusion - what happens when there are two solutes

A

each substance diffuses down its own concentration gradient - unaffected by the concentration gradient of other substances

48
Q

how does oxygen enter the cell

A

oxygen diffuses across the cell membrane during cellular respiration
dissolved oxygen diffuses into the cell across the plasma membrane. As long as cellular respiration consumes the oxygen as it enters, diffusion into the cell will continue

49
Q

what is passive transport

A

requires no energy

diffusion is passive transport because the concentration gradient (potential energy) drives the process

50
Q

what is osmosis

A

the diffusion of free water across a selectively permeable membrane
water diffuses across a membrane from the region of high free water concentration (lower solute) to low free water concentration
water follows solute
until the solute concentrations on both sides of the membrane was equal

51
Q

tonicity

A

the ability of the surrounding solution to cause a cell to gain or lose water

52
Q

how does tonicity work

A

water follows solute

if there is more solutes outside the cell - water will leave the cell and vice versa

53
Q

isotonic

A

the concentration of a solution is the same inside and outside the cell - equal
no net movement of water - water diffuses across the membrane but at the same rate in both directions
the volume of an animal cell is stable

54
Q

hypertonic

A

more solutes in the solution outside the cell
water follows solute - water will leave the cell
the cell will lose water, shrivel and probably die

55
Q

hypotonic

A

less solute in the water surrounding the cell / more solute inside the cell
water follows the solute
water will enter the cell faster than it leaves
cell will swell and lyse

56
Q

osmoregulation

A

in hypertonic or hypotonic environments organisms that lack rigid cell walls must have adaptations to survive
the control of solute concentration and water balance
e.g. paramecium - contractile vaccuole which acts to
pump out water

57
Q

turgor pressure

A

in cells with cell walls
cell walls help the cell maintain water balance
cell swells when water enters by osmosis
cell expands but when it reaches a certain level the cell wall will not let it expand any more - exerts turgor pressure - to oppose any further water uptake
the cell is turgid

58
Q

turgid

A

in plant cells that have a cell wall
cell is full water so that the cell wall exerts turgor pressure
turgid - very firm
plants that are not woody rely for structural support by cells kept turgid by surrounding in hypotonic solution - net tendency for water to enter the cell

59
Q

why do plants need to be in a hypotonic solution

A

more solute inside the cell
water follows solute and enters the cell
cell is turgid

60
Q

what happens when a plant is in an isotonic environment

A

no movement of water into the cell - less turgid / becomes flaccid

61
Q

what happens to a plant cell - with a cell wall - in a hypertonic environment

A

more solute outside the cell
water follows solute and moves out of cell - lose water to the environment and shrinks or shrivels
as the plant cell shrivels its plasma membrane pulls away from the cell wall - plasmolysis - causes plant to wilt

62
Q

plasmolysis

A

if a plant is in a hypertonic solution water will flow out of the cell and the cell will shrivel
as the plant shrivels the plasma membrane pulls away from the cell wall. This is called plasmolysis
plasmolysis causes the plant to wilt
plant cells / bacteria / fungi also plasmolyse in hypertonic environments

63
Q

facilitated transfusion

A

many molecules that can’t cross because of the lipid bilayer diffuse passively with the help of transport proteins that span the membrane e.g. acqaporins

64
Q

how does water enter cells

A

diffuse through aquaporins - water channel proteins
facilitate massive levels of diffusion of water in plant and animal cells
cells that need more water have more aquaporins

65
Q

ion channels

A

channel proteins that transport ions

many ion channels are gated channels

66
Q

gated channel

A

gated channels are ion channels that open and close in response to a stimulus e.g. electrical in nerve cells
other gated channels open or close when a specific substance other than the one to be transported binds to the channel

67
Q

ion channels and carrier proteins are forms of passive transport - why

A

ion channels and carrier proteins involve facilitated diffusion of a substance down the concentration gradient - no energy is required

68
Q

what is the difference between passive and active transport across a plasma membrane

A

passive transport relies on substances moving down their concentration gradient - no energy is required
active transport moves solutes against their concentration gradient from a side where they are less concentrated to a side where they are less concentrated
active transport needs energy

69
Q

what types of proteins are required for active transport

A

active transport is carried out by carrier proteins (not channel proteins)
they are transporting solutes against their concentration gradients

70
Q

give an example of active transport

A

sodium potassium pump - the cell has higher concentrations of potassium than its surroundings and a much lower concentration of sodium ions
the sodium potassium pump exchanges sodium for potassium across the plasma membrane of animal cells

71
Q

where does the cell get the energy required for active transport

A

ATP hydrolysis
e.g. ATP phosphate group transferred to the transport protein and changes its shape in a manner that translocates a solute bound to the protein across the membrane

72
Q

electrochemical gradients

A

there is a difference in charge across membranes
cytoplasmic side is negative / extracellular side is positive.
because the inside of the cell is negative and the outside is positive it effects ion movement
an ion diffuses down its electrochemical gradient (as well as concentration gradient)

73
Q

membrane potential

A

charge - inside the cell is negative and outside is positive
the voltage across the membrane is called the membrane potential

74
Q

electrogenic pump

A

ions usually diffuse down their concentration and electrochemical gradient
however sometimes the two are at odds - electrical forces due to membrane potential oppose simple diffusion - active transport is necessary
a transport protein that generates a voltage across a membrane is called an electrogenic ump

75
Q

give examples of an electrogenic pump

A

in animal cells - sodium potassium pump - moves three sodium out of the cell for every 2 potassium pumped in (against their concentration gradients)
in plants, bacteria and fungi - proton pump - actively transports protons (hydrogen ions) out of the cell creating a positive charge

76
Q

proton pump

A

a proton pump transports protons in the form of hydrogen ions out of the cell. This causes a charge /voltage which can be stored as energy that the cell can use
most proton pumps are powered by ATP hydrolysis
(remember proton pump in cellular respiration)

77
Q

cotransport

A

a transport protein (a cotransporter) can couple the downhill diffusion of a solute to the uphill transport of a second substance against its own concentration gradient e.g. H+/sucrose cotransporter in plants

78
Q

exocytosis

A

the process by which the cell secretes certain molecules by the fusion of vesicles with the plasma membrane
a transport vesicle that has budded from the golgi apparatus moves along microtubules of the cytoskeleton to the plasma membrane - the two membranes fuse and the contents of the vesicle spill out of the cell and the vesicle membrane becomes part of the plasma membrane

79
Q

give examples of cells that use exocytosis to export products

A

pancreas - insulin is secreted by exocytosis
nerve cells use exocytosis to release neurotransmitters
proteins needed to make plant cell walls are delivered through exocytosis

80
Q

endocytosis

A

cell takes in molecules and particles by forming new vesicles from the plasma membrane
three types - phagocytosis / pinocytosis / receptor mediated endocytosis

81
Q

phagocytosis

A

the cell engulfs a particle by extending pseudopodia around it and packaging it within a sac called a food vacuole. The particle will be digested after the food vacuole fuses with a lysosome containing hydrolytic enzymes e.g. amoeba engulfing a algal cell

82
Q

pinocytosis

A

cell continuously gulps droplets of extracellular fluid into tiny vesicles forming infoldings of the plasma membrane which pinch off.

83
Q

receptor mediated endocytosis

A

a specialised type of pinocytosis (endocytosis by pinching in) that enables the cell to acquire bulk quantities of specific substances even though those substances may not be very concentrated in the extracellular fluid
specific solutes bind to receptor proteins / the receptor proteins cluster in coated pits / each coated pit forms a vesicle
e.g. cholesterol

84
Q

what effect does exocytosis and endocytosis have on the plasma membrane

A

they provide mechanisms for rejuvenating and remodelling the plasma membrane
exocytosis adds new membrane / exocytosis subtracts
the amount of plasma membrane in a nongrowing cell remains fairly constant
the addition of membrane by one process appears to be offset by the other

Bio1MGC (11 decks)

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