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AS Biology > Chapter 4: Cell Membranes > Flashcards

Chapter 4: Cell Membranes Flashcards

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1
Q

What is osmosis

A

Net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane, as a result of random motion (diffusion).

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2
Q

What is water potential equation

A

Water p= Solute p + Pressure p

Symbol psi

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3
Q

What is water potential

A

Tendency of water to move out of a solution

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4
Q

Water potential depend on 2 factors :

A

Solute potential

Pressure potential

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5
Q

What is water potential of pure water at atmospheric pressure

A

0

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6
Q

What is solute potential

A

Contribution of concentration of solute to water potential. It is extent to which solute decreases water potential of solution.
The more the solute the lower the tendency of water to move out

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7
Q

Solute potential for pure water

A

0, and has negative value for a solution

Greater the solute concentration the more the negative value of solute potential

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8
Q

What is pressure potential

A

Contribution of pressure to water potential. Value always positive

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9
Q

Effect of isotonic solution on animal cell

A
  • amount of solute in sol=solute in cell
  • water potential in sol=water potential in cell
  • net movement of water is 0
  • no effect seen in cell
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10
Q

Effect of hypertonic solution on animal cell

A
  • amount of solute in sol> in cell
  • water potential of sol less than cell’s
  • net movement from cell to outside
  • cell shrinks
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11
Q

Effect of hypotonic solution on animal cell

A
  • amount of solute in sol less than that of cell
  • water potential of sol more than cell’s
  • net movement from sol to cell
  • cell swells and bursts
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12
Q

Effect of isotonic solution on a plant cell

A
  • solute concentration of solution= solute concentration of cell cytoplasm
  • water potential in and out is same
  • net movement of water=0
  • no effect on cell
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13
Q

Effect of hypotonic solution on plant cell

A
  • solute concentration of solution < solute conc in cell cytoplasm
  • water potential in sol > water potential in cell
  • net movement of water from sol to cell
  • cell becomes turgid, as cytoplasm increases in volume. Does not burst due to elastic cell wall. As cell wall swells exerts equal opposite wall pressure, little water needed to achieve this
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14
Q

Effect on hypertonic solution on plant cell

A
  • solute concentration of solution > solute conc in cell cytoplasm
  • water potential in sol < cells
  • net movement of water from plant cell to sol
  • cytoplasm shrinks and detaches from cell wall
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15
Q

Continued effect of hypertonic solution on plant cell

A

Cytoplasm shrinks and detaches from cell wall. Point cell membrane fully detached pressure potential (of cytoplasm of cell wall) is 0

W=Ws+Wp, Wp=0, Wn=Ws. WaterP=SoluteP

Water and solute from solution in cell both move through permeable cell wall. Hence external solution remains with shrinking protoplasm. As it shrinks pulls away from cell wall. Hypertonic sol occupies spaces
Called plasmolysis

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16
Q

What is protoplasm

A

Cell membrane+Interior

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17
Q

What is incipient plasmolysis

A

Point at which pressure potential has just reached 0 and plasmolysis is about to occur

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18
Q

What is diffusion

A

Net movement of molecules or ions from a region of higher concentration to region of lower concentration down a gradient as a result of random movement of particles

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19
Q

Factors affecting diffusion :

A 
Steepness of conc gradient 
Temperature 
Surface area 
Distance
Nature of molecule/ion
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20
Q

Steepness of conc gradient

A

Difference in conc os substance on 2 sides of the surface

Greater the difference in conc greater no of molecules passing in the 2 directions, hence faster rate of diffusion

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21
Q

Temperature affecting diffusion

A

Higher temp, molecules have more kinetic energy than at low temp. Move around faster and diffusion is faster

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22
Q

Surface area affecting diffusion (and to volume ratio)

A

Greater surface area faster diffusion

Larger the cell smaller the surface area in relation to volume

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23
Q

Example of structures that increase surface area

A

Microvilli are foldings in small intestine increase surface area

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24
Q

Distance affecting diffusion

A

Diffusion is inversely proportional to square of distance travelled
D α 1/d^2

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25
Q

Nature of molecule affecting diffusion

A
  • large ones need more energy to diffuse than small ones
  • non polar ones(glyercol,alcohol,steroids)diffuse more easily than polar through hydrophobic part of membrane
  • uncharged and nonpolar mols eg respiratory gases(O2, CO2)diffuse through membrane
  • water, being polar, rapidly diffuses across phospholipid bilayer because it’s small
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26
Q

What is active transport

A

Movement of substances from lower conc to higher conc using energy of ATP, using carrier proteins. It is specific

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27
Q

What is the Sodium-potassium ATP pump

A

Na+–K+ pump uses energy from ATP to pump 3Na from inside to outside and 2K from outside to inside

28
Q

3 instances of active transport

A
  • reabsorbtion of certain substances and ions in kidney into blood
  • loading sucrose from mesophyll cells to phloem
  • inroganic ions loaded into root hairs from soil
29
Q

What is facilitated diffusion

A

Diffusion of substances from higher to lower conc facilitated by transport proteins ie channel and carrier proteins

30
Q

What are channel proteins

A

Water filled pores that help in movement of ions and water

31
Q

What is non gated channel protein and eg

A

Open all the time

Aquaporin/porin

32
Q

What is gated channel protein and eg

A

Can move to open or close on the inside surface of membrane. Remain closed until receive chemical/electrical signal

Na+, K+ channel proteins found in nerve cell membrane helping in nerve impulse transmission

33
Q

Channel protein shape changes or is fixed?

A

Fixed

34
Q

Eg of a signalling molecule coming through gated channel protein

A

Acetyl choline (opens after binding)

35
Q

How carrier proteins work

A

Flip between 2 shapes
Do not have fixed shapes
Binding site is alternatively open to one side of membrane
Does not use ATP

36
Q

Rate of facilitated diffusion depends on which 2 factors :

A

No of channel/carrier proteins

In case of gated channel, whether it is open or closed

37
Q

Which ions from active transport can also move by facilitated diffusion

A

Na+

K+

38
Q

2 types of bulk transport

A

Endocytosis - engulfing material by cell surface membrane

Exocytosis - removal of material by cell membrane

39
Q

2 types of endocytosis

A

Phagocytosis - bulk uptake of solid material by cell into phagocytic vacuole
Pinocytosis - bulk uptake of liquid material by cell into vacuole/vesicle. If small vesicles called micropinocytosis

40
Q

Step by step process for phagocytosis

A

1) bacterium engulfed by cytoplasm fingers
2) bact engulfed by phagocytic vacuole
3) lysosomes with digestive hydrolytic enzymes fuse with vacuole
4) bact digested by enzyme
5) undigested remains removed by exocytosis

41
Q

Example if exocytosis

A

Secretory pathway

RER–>Protein–>Golgi complex (collect modify sort)–>*enzymes–>secretory vesicles–>cell membrane

42
Q

Structure of cell membrane

A

Phospholipid bilayer
With:
Hydrophilic heads outside with glycolipid attached, and hydrophobic tails inside

And within:
Smaller intrinsic/integral proteins attached with glycoprotein, and larger intrinsic protein(type) transmembrane protein spanning entire membrane (made of 1 or more α helical shape)

Outer:
Extrinsic protein

43
Q

Glycolipid is _ and glycoprotein is _

A

GL - carb chain attached to phospholipid

GP - carb chain attached to protein

44
Q

Function of proteins in cell membrane

A
  • Acts as tranport proteins for molecules and ions
  • Extrinsic proteins on the inside attached to cytoskeleton help maintain shape
  • in mitochondrial (respiration) and chloroplast (photosynthetic) membrane
45
Q

Function of glycolipid and glycoprotein in cell membrane

A
  • acts as receptor - nature:gl/gp - molecules eg cell signalling, endocytosis, cell adhesion
  • acts as cell mark/antigen(ABO blood grouping) help in cell wall recognition
  • helping in membrane stability by forming H bonds with H2O molecules
46
Q

Functions of cholesterol in cell membrane

A
  • mechanical stability prevent cell from break and burst
  • hydrophobic part prevents polar molecule passage
  • acts as buffer
47
Q

Where is it significant that cholesterol in membrane has hydrophobic part

A

ie in myelin sheet around nerve cell helps in fast impulse transmission (jump, lipid insulator)

48
Q

How does cholesterol in membrane act as buffer

A
  • at low temp it prevents close packing of phospholipid tails which prevents bilayer becoming rigid which restores fluidity to normal by decreasing it
  • at high temp cholesterol interacts/melts tails, stabilising bilayer, increasing fluidity and restoring it to normal
49
Q

Cholesterol amounts in organisms

A

Animal>plant>prokaryotes=0

50
Q

Function of phospholipids in cell membrane

A
  • act as signalling (extracellular) molecules that can move about in bilayers actigtaing other molecules such as enzymes
  • make cell membrane selectively permeable. Only uncharged non polar molecules can pass.
  • may be hydrolysed to release small water soluble glycerol related molecules that move through cytoplasm to bind to receptors (intracellular signalling)
51
Q

5 properties of phospholipids

A

1) Hphilic head, Hphobic tail making membrane have nonpolar interior (interacts cytoplasm) and polar exterior (aqueous surrounding)
2) tail can be saturated or unsaturated fatty acid
3) forms basis of membrane fluidity
4) micelles
5) liposomes

52
Q

Fluidity depends on 2 factors:

A

•Length of phospholipid tail
Longer fatty acid, more interaction, less fluid

•Proportion of unsaturated fatty acid chain
More proportion, more fluidity

53
Q

What are micelles

A

Single layer of phospholipid.

Hphilic head interacts with aq surrounding, Hphobic makes interior non polar.

54
Q

What are liposomes

A

Made up of phospholipid bilayer
Hphilic heads inside AND outside
(recall diagram)

55
Q

Types of receptors

A

Extracellular - on surface of cell

Intracellular - inside cell: 1)cytoplasmic 2)nuclear

56
Q

Types of signalling molecules

A
  • hydrophobic:bind to intracellular receptors, can cross cell membrane
  • hydrophilic:bind to extracellular recepto, can’t cross cell membrane
57
Q

Basic signal transduction pathway

A

Conversion of signal into transmitted message

stimulus/signal—>receptor—transmission—>target(effector)—>response

58
Q

Cell signalling mediated by membrane bound enzyme

A

Insulin binds outside cell to extracellular domain to it’s receptor and induces structural change that’s propagated across membrane to intracellular kinases domain inside cell that is responsible for activation of cell signalling cascade

59
Q

Cell signalling mediated by membrane bound protein

A

Signalling molecule eg acetyl choline neurotransmitter (transmit nerve impulse between neurons)
Binds to binding site of channel protein
Channel protein for Na+ opens
Causes Na+ to move inside cell
Depolarization- change in membrane potential

60
Q

Cell signalling involving a second messenger steps:

A

1) hydrophilic signal binds with specific shaped extracellular receptor which recognises it
2) signal brings change in shape of receptor that spans membrane so message is in effect passed to inside of cell (signal transduction). Changing receptor shape allows it to interact with next component so msg is transmitted.
3) activates G protein which releases second messenger. (Inactive G protein bound to GDP-> active G protein bound with GTP)

4) second messenger activates enzymes which further activates more enzymes eg adenylyl cyclase.
Amplification at each stage. Until an enzyme is produced which brings about required change in cell metabolism

5)Response towards original signal bound to extracellular receptor: secretion, trancsiption, movement, metabolic change/reaction

61
Q

About the second messenger

A

-Second messenger-small, double signalling molecules spread through cell greatly amplifying signal.
Intracellular and released by cell in response to exposure to extracellular signalling molecule

eg CAMP, IP3, CGMP

-Signal amplification: many second msngers made in response to 1 receptor being stimulated, ie original signal amplified.

62
Q

Intrinsic proteins stay in memvrane because

A

Hydrophobic region made of hydrophobic amino acids are next to hydrophobic fatty acid tails and repelled by watery environment either side of membrane

63
Q

Fluid mosaic model:

A

Described as such because phospholipids and proteins (layers) can move about by diffusion.
Mosaic is pattern produced by scattered protein in bilayers when membrane surface is viewed from above

Phospholipids move sideways mainly in own layers
Some protein molecules move about within phospholipid bilayer, others remain fixed to their structures inside/outside cell

64
Q

Why can polar molecules move through transport proteins

A

Their interiors are hydrophilic

65
Q

What forms a glycolipid or glycoprotein

A

Branched carbohydrate attached to lipid or protein

66
Q

Altered gene expression :

A
  • hydrophobic signal ie steroid hormones crosses cell membrane, binds to cytoplasmic receptor
  • this complex crosses nuclear membrane and binds with DNA, and alters it’s gene expression
  • DNA (bound with cytoplasmic receptor with hydrophobic signal) undergoes transcription to form altered mRNA and hence altered protein from translation which causes change in process
67
Q

How can phospholipids be modified to act as signalling molecules

A

Chemically modified
Move about in bilayers activating other molecules eg enzymes
Or
Be hydrolysed to release small water soluble glycerol related molecules, which diffuse through cytoplasm and bind to specific receptors

AS Biology (11 decks)

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