Chapter 7 - Membrane Structure and Function Flashcards

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1
Q

what are state ingredients of membranes?

A

lipids and proteins - carbohydrates also important

lipids are the most abundant in the plasma membrane

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2
Q

what does amphipathic mean? what demonstrates this characteristic?

A

phospholipids form membranes - they are an amphipathic molecules meaning it has both a hydrophilic region and hydrophobic region

membrane proteins are also amphipathic - embed themselves in phospholipid bilayer

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3
Q

which part of the phospholipid faces water? inside?

A

hydrophobic tail faces inwards while hydrophilic heads face water

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4
Q

what is the fluid mosaic model?

A

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

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5
Q

where are lipids made?

where are membrane phospholipids made and the the assembly of the membrane take place?

A

smooth ER

membrane phospholipids and assembly of membrane + protein occurs in rough ER and golgi apparatus

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6
Q

phospholipid movement in the plasma membrane?

A

Most drift laterally (weak hydrophobic interaction)
Rarely does a lipid flip b/c it requires energy like ATP

proteins don’t usually move b/c larger but some can

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7
Q

which experiment showed that the plasma membrane isn’t static?

A

took two cells and labeled them with different colors and after an hour the proteins become equally distributed – this experiment shows that membrane isn’t static

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8
Q

phospholipid phase in relation to temperature

A

As temperature cools, membranes go from fluid to solid state b/c phospholipids pack together

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9
Q

what allows a membrane to stay fluid at lower temperatures?

A

membrane remains fluid to a lower temperature if it’s rich in phospholipids with unsaturated hydrocarbon tails - kinks in the tail b/c of double bond means they can’t pack closely together

different environments have different temperatures so you need a balance of sat/unsat to maintain fluidity

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10
Q

effects of cholesterol on the membrane

A

it’s a fluidity buffer

at high temperatures (body temp): cholesterol makes the membrane less fluid by restraining the phospholipid movement - gives structure to cell membrane

but at lower temperatures cholesterol also hinders the close packing of phospholipids and lowers the temperature required for the membrane to solidify

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11
Q

what determines most of the function of the plasma membrane?

A

the proteins

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12
Q

what are the two types membrane proteins?

A

1) integral proteins

2) peripheral proteins

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13
Q

what is an integral protein?

A

Integral protein is able to penetrate the hydrophobic interior of the lipid bilayer

the majority of integral proteins of transmembrane proteins - some only extend partway into the hydrophobic interior

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14
Q

what are trans-membrane proteins?

A

a type of integral proteins that span the membrane: a portion is inside and the other part is sticking outside

the hydrophobic regions of an integral protein consist of one or more stretches of non polar amino acids usually coiled into alpha helices

the hydrophilic regions are exposed to the aqueous solutions on either side of the membrane (extracellular and cytoplasmic side) - some proteins also have hydrophilic channels that allow passage through the membrane of hydrophilic substances

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15
Q

what are peripheral proteins?

A

peripheral proteins are not embedded in the lipid bilayer at all - they are appendages loosely bound to the surface of the membrane (often to exposed parts of integral proteins) or phospholipid head

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16
Q

how do membrane proteins attach?

A

on cytoplasmic side, some membrane proteins are held in place by attachment to the cytoskeleton

on extracellular side, they are attached to fibers of the ECM

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17
Q

what are the 6 major functions of membrane proteins?

A

1) Transport: if they’re too large or hydrophilic, proteins
help these molecules get across w/ channels

2) Enzyme activity: enzymes are embedded in the membrane which is useful because spatially you can keep chemical reactions close together
3) Signal transduction: may have a binding site with a specific shape that fits the shape of the chemical messenger (receptor) or the external messenger(signaling molecule) may cause protein shape to change to allow message to be relayed to the inside of the call
4) Cell-cell recognition: glycoproteins serve as ID tags
5) Intercellular joining: tight or gap junctions can form
6) Cytoskeleton and ECM attachment

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18
Q

how do cells recognize other cells?

A

cell recognize other cells by binding to molecules, that often contain carbohydrates, on the extracellular surface of the plasma membrane

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19
Q

membrane carbohydrates

A

usually short, branched, chains of fewer than 15 sugar units

some are covalently bonded to lipids forming glycolipids

most are covalently bonded to proteins which are glycoproteins

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20
Q

membrane sidedness and synthesis

A

o Distinct inside and outside faces
o The asymmetrical distribution of proteins, lipids, and associated carbohydrates is determined when the membrane is built by the ER and golgi

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21
Q

what are the components that make a cell’s membrane selectively permeable?

A

1) hydrophobic interior: polar molecules and ions can’t pass

2) specific transport proteins

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22
Q

what are transport proteins? what do they do?

A

transmembrane proteins that help hydrophilic substances pass through the lipid bilayer

channel proteins are a type of transport protein that have hydrophilic channels for certain molecules or atomic ions to use as a tunnel through the membrane

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23
Q

what are aquaporins?

A

channel proteins that facilitate the diffusion of water through the membrane

24
Q

what are some types of transport proteins?

A

channel proteins

carrier proteins

25
Q

what are carrier proteins

A

they are transport proteins that hold onto their passengers and change shape in a way that shuttles them across the membrane

26
Q

what is diffusion?

A

the movement of particles of any substance so that they speak out into the available space

spontaneous process, no work must be done to make it happen = no input of energy

27
Q

what is the rule of diffusion?

A

in the absence of other forces, a substance will diffuse from where it is more concentrate to where it is less concentrate

any substance will diffuse down its OWN concentration gradient!

28
Q

what is a concentration gradient?

A

the region along which the density of a chemical substance increases or decreases

concentration gradient represent potential energy and drive diffusion

29
Q

what is passive transport?

A

the diffusion of a substance across a biological membrane

passive because the cell doesn’t have to input energy

solute will diffuse down its concentration gradient

(random but directional)

30
Q

what is dynamic equilibrium?

A

Dynamic equilibrium: no gradient and molecules cross the barrier at the same rate

31
Q

how does water diffuse?

A

water diffuses across the membrane from the region of higher free water concentration/low solute contraction to that of lower free water concentration/higher solute concentration until the solute concentration on both sides of the membrane are more equal

WATER MOVES TO DILUTE

32
Q

what is osmosis?

A

diffusion of free water across a selectively permeable membrane

33
Q

isotonic solution

A

if a cell without a cell wall (like an animal cell) is immersed in an environment that is isotonic to the cell, there will be no net movement of water across the plasma membrane

water diffuses across membrane but at the same rate in both directions

34
Q

hypertonic solution

A

if a cell is in a solution that is hypertonic to the cell, the water will move out of the cell, shrivel, and probably die

35
Q

hypotonic solution

A

if a cell is in a solution that is hypotonic to the cell then water will enter the cell faster than it leaves and the cell will swell and burst

36
Q

what is osmoregulation?

A

the control of solute concentrations and water balance in cells that don’t have rigid cell walls

Ex. The protest paramecium which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump

37
Q

what does turgid mean? what’s it in reference to?

A

plant cells that have cell walls

when a plant cell swells as water enter by osmosis, the cell wall will only expand so much before it exerts a back pressure on the cell that opposes further water uptake and will become turgid = firm

38
Q

what is flaccid?

A

if a plant’s cells and their surrounding are isotonic and there’s no net tendency for water to enter/leave then the cells become flaccid = limp

39
Q

what is plasmolysis?

A

if a plant cell is in a hypertonic environment the cell will shrivel and its plasma membrane will pull away from the cell wall at multiple places –> causes plant to wilt and can lead to plant death

bacteria and fungi do the same thing

40
Q

what are ion channels?

A

facilitated diffusion

channel proteins that transport ions - electrochemical gradient

moves down electrochemical gradient - no energy

41
Q

what are gated channels?

A

ion channels that open or close in response to a stimulus

facilitated diffusion - no energy required

42
Q

what is active transport?

A

Proteins use energy to move solutes across a membrane against their concentration gradient

from low to high concentration of solute

ATP supplies energy for active transport

43
Q

what kind of proteins participate in active transport?

A

carrier proteins, no channel proteins

this is because when channel proteins are open they allow solutes to diffuse down their concentration gradients rather than picking them up and transporting them against their gradient

44
Q

what is the sodium-potassium pump?

A

active transport

exchanges Na+ for K+ across the plasma membrane of the animal cell

  • 3 Na+ ions move out of the cell for every 2 K+ ions that go in
  • a net of 1 positive charge is transferred from inside to out
  • the electrochemical gradient created helps cotransport other molecules (such as glucose and amino acids) into the cell and is used to conduct nerve impulses
  • Potassium pump changes shape depending on what it’s bound to
  • Outside of cell membrane becomes more positive with every pump
45
Q

what are types of passive transport?

A

1) diffusion (hydrophobic molecules and small uncharged polar molecules diffuse through lipid bilayer)
2) facilitated diffusion ( hydrophilic substances diffuse through membrane with assistance of transport proteins: channel/carrier down concentration gradient)

46
Q

what are the charges of the extracellular and cytoplasmic sides of the membrane?

A

cytoplasmic side of the membrane is negative in charge relative to the extracellular side because of uneven distribution of anions/cations

47
Q

what is the membrane potential?

A

the voltage across a membrane

48
Q

what is the electrochemical gradient?

A

two forces drive the diffusion of ions across the membrane:

1) a chemical force (ion’s concentration gradient)
2) electrical force (effect of membrane potential on ion
movement)

This determines the transport of ions: important in the transmission of nerve impulses

49
Q

what is cotransport?

A

a type of active diffusion - a transport protein (cotranporter) can couple the “downhill” diffusion of the solute to the “uphill” transport of a second substance against its own concentration gradient

ex. the carrier protein like sucrose-H+ cotransporter in a plant cell is able to use the diffusion of H+ down its electrochemical gradient into the cell to drive the uptake of sucrose

50
Q

how do larger molecules such as proteins and polysaccharides cross the membrane?

A

bulk transport!

the cross in bulk, packaged in vesicles = requires energy

51
Q

what is exocytosis?

A

the cell secretes certain molecules by the fusion of vesicles with the plasma membrane

transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell

ex. insulin

52
Q

what is endocytosis?

A

the cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane

almost like reverse exocytosis

53
Q

what are the three types of endocytosis?

A

1) phagocytosis
2) pinocytosis
3) receptor-mediated endocytosis (form of pinocytosis)

54
Q

what is a ligand?

A

a term for any molecule that binds specifically to a receptor site on another molecule

ex. iron, LDL

55
Q

what is phagocytosis?

A

cell engulfs a particle by extending pseudopodia around it and packaging it into food vacuole

macrophages use phagocytosis

56
Q

what is pinocytosis?

A

smaller solutes are brought it through pinching of membrane – molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles

57
Q

what is receptor-mediated endocytosis?

A

binding of ligands to receptors triggers vesicle formation