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Biology > Transport across cell membranes > Flashcards

Transport across cell membranes Flashcards

1
Q

Why are phospholipids important

A

HydrophIlic HEADS = attracted to water
HydrophObic TAILS = repelled by water

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2
Q

Functions of phospholipids

A

Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances entering and leaving
Make membrane flexible and self-sealing

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3
Q

Proteins in bilayer use

A

Never extend completely across surface of bilayer
Give mechanical support
Cell receptors

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4
Q

Functions of proteins in membrane

A

Structural support
Channels transporting water-soluble substances
Allow active transport
Form cell-surface receptors for identifying cells
Help cells adhere together
Receptors

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5
Q

Cholesterol molecules function

A

Add strength
Hydrophobic to prevent water loss and dissolved ions
Pull together fatty acid tails of phospholipid molecules, limiting movement

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6
Q

What are glycolipids made up of

A

Carbohydrate + lipid

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7
Q

Functions of glycolipids

A

Recognition sites
Maintain stability
Help cells attach to one another

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8
Q

What are Glycoproteins made up of

A

Carbohydrate chains on outer surface of of cell membrane

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9
Q

Function of glycoproteins

A

Recognition sites
Help cells attach to form tissues
Allow cells to recognise one another

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10
Q

Why molecules do not freely diffuse across permeable cell surface membrane

A

Not soluble in lipids
Too large
Same charge as charge on protein channels -> so repel
Polar so have difficultly passing through non-polar hydrophobic tails

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11
Q

Why is a fluid mosaic model of cell-surface membrane called fluid and mosaic

A

Fluid = phospholipid molecules can move relative to one another
Mosaic = Proteins vary in shape, size pattern (same way mosaics do)

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12
Q

What form of transport is diffusion

A

Passive

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13
Q

What occurs in all passive forms of transport

A

Particles constantly in motion due to kinetic energy they possess
Motion is random
Bounce off one another

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14
Q

What does passive transport mean

A

The energy comes from the natural, inbuilt motion of particles, rather than some external source

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15
Q

Diffusion definition

A

The net movement of molecules or ions
From an area of high concentration to an area of low concentration

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16
Q

Facilitated diffusion definition

A

Diffusion involving presence of protein carrier molecules to allow the passive movement of substances across plasma membranes

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17
Q

Two types of proteins involved in facilitated diffusion

A

Protein channels
Carrier proteins

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18
Q

Where does facilitated diffusion occur

A

Down a concentration gradient

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19
Q

Protein channels form

A

Water-filled hydrophilic channels across the membrane

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20
Q

What do protein channels allow

A

Specific water-soluble ions to pass through

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21
Q

How do protein channels work

A

Channels are selective, open in presence of specific ion and otherwise are closed

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22
Q

What happens as ions pass through protein channels

A

Ions bind to protein and change shape in way that closes it to one side of the membrane and opens is to the other side

23
Q

What to carrier proteins do

A

Span plasma membrane
Specific molecules bind with the protein
Change shape so molecule is released to inside of membrane
Go from area of high concentration to low so no external energy is needed

24
Q

Osmosis definition

A

Passage of water from high water potential to lower through a selectively permeable membrane

25
Q

Water potential unit

A

Trident thing

26
Q

Units of pressure

A

kPa

27
Q

Osmosis rules

A

More solute added lower water potential
Water + solute = water potential will always less than 0
Water moves from area of high -> low water potential

28
Q

Example of osmosis when left side of membrane has lower solute concentration

A

Solute and water move randomly by kinetic energy
Selectively permeable plasma membrane only allows water molecules to move across
Water molecules diffuse to right, where there is more solute and less water
Dynamic equilibrium established

29
Q

What happens if the water potential value is very low

A

More negative the value the lower the water potenial

30
Q

Osmosis in animal cells

A

Animal cells in liquid, blood plasma
So water potential in cells and outside is equal
Water potential outside cell higher = bursts, net movement enters cell
Water potential outside is lower = shrinks

31
Q

Active transport defintion

A

Movement of molecules into or out of a cell from low to high concentration using ATP and carrier proteins

32
Q

What is ATP used for in active transport

A

Directly move molecules
Co-transport (moving molecules using concentration gradient) thats been set up by direct active transport

33
Q

Why is active transport different from passive forms

A

Metabolic energy in form of ATP
Moved against concentration gradient
Carrier protein molecules
Very selective

34
Q

How does direct active transport occur

A

1) Carrier proteins span plasma membrane and bind to molecule to be transported to one side
2) Molecule binds to receptor sites
3) Inside of cell ATP binds to protein
4) ATP split into ADP + phosphate molecule
5) Protein molecules change shape and open to opposite side of membrane
6) Molecule released to other side of membrane
7) Phosphate molecule released from protein
8) Protein revert to original shape for repetition
9) Phosphate molecule recombines with ADP to form ATP

35
Q

Difference between facilitated diffusion and active transport

A

Facilitated = DOWN concentration gradient
= DOESN’T need metabolic energy

Active transport = AGAINST concentration gradient
=NEEDS metabolic energy

36
Q

What is Sodium-potassium pump an example of

A

More than one molecule moved in cell as one is removed

37
Q

Explain sodium-potassium pump

A

Sodium ions removed actively as potassium ions are actively taken in

38
Q

How to increase the rate of movement across membranes

A

Epithelial cells possess microvilli
- more SA for insertion of carrier proteins through diffusion and facilitated diffusion

Increase number of protein channels and carrier proteins

39
Q

Role of diffusion in absorption

A

Carbs and proteins digested
Greater concentration of glucose and amino acids in ileum than blood
Glucose moves by facilitated diffusion in ileum to blood
Continuously removed by cells
Maintains concentration gradient in ileum and blood

40
Q

Difference between carrier and channel proteins

A

Channel proteins = open and close, only charged substances diffuse
Carrier = fixed specific shape (allowing one particular charged substance), diffuse down conc gradient

41
Q

Two functions of membranes in cells

A

Regulate movement and exchange of substances
Separate internal and external environment

42
Q

Why do phospholipids form in an aqueous environment

A

Have a hydrophilic head and hydrophobic tail
Molecules arranges themselves between tails and surrounding water is minimised

43
Q

How do molecules move to the other side of a cell surface membrane if there are no carrier proteins

A

Move from outside of cell to inside directly in between phospholipids by simple diffusion
Because there is a higher conc of the molecules outside the cell than inside and diffusion takes place from high to low DOWN the conc gradient. Molecules are small and nonpolar so can move between the phospholipids
(Remember this can only happen if the molecule is non polar)

44
Q

If the molecule is not lipid soluble how would it travel across the cell membrane

A

Facilitated diffusion
Specific channel protein or carrier protein

45
Q

When does facilitated vs simple diffusion occur

A

Simple = lipid soluble non polar doesnt need carrier
Facilitated = not lipid soluble, polar needs carrier

46
Q

Explain the appearance of cytoplsam under a microscope (not touching cell wall)

A

Cell has been placed in solution with lower water potential
Water moves out by osmosis
Causing cytoplasm/ vacuole. Protoplast to shrink and decrease in volume

47
Q

What would happen if you put a cheek cell in a test tube of pure water

A

Cheek cell has lower water potential than water so take water into cell by osmosis and swell and eventually burst

48
Q

Onion cell placed in pure water waht would happen

A

Cell wall provides additional strength that can withstand pressure so does not burst

49
Q

What is simple diffusion

A

Movement DOWN conc gradient
Movement of O2 from plasma into red blood cell

50
Q

What is facilitated diffusion

A

Movement of glucose from high to low conc
Movement down conc gradient

51
Q

What is cotransport vs facilitated diffusion

A

Simple diffusion = no carrier proteins, go through phospholipid bilayer
Co transport = with carrier protein involving facilitated diffusion and active transprot. ATP
Facilitated diffusion = use channel and carrier proteins, transport polar and ions NO ATP

52
Q

What is the purpose of using carrier proteins recycling atp

A

Maintains concentration gradient for sodium

53
Q

Why is beetroot used in the experiment

A

Pigment is red
Amount of pigment thtat leaves indicated permeability

Biology (55 decks)

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