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Transport across cell membranes Flashcards

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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

Study These Flashcards
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

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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

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A

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

25
Water potential unit
Trident thing
26
Units of pressure
kPa
27
Osmosis rules
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
Example of osmosis when left side of membrane has lower solute concentration
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
What happens if the water potential value is very low
More negative the value the lower the water potenial
30
Osmosis in animal cells
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
Active transport defintion
Movement of molecules into or out of a cell from low to high concentration using ATP and carrier proteins
32
What is ATP used for in active transport
Directly move molecules Co-transport (moving molecules using concentration gradient) thats been set up by direct active transport
33
Why is active transport different from passive forms
Metabolic energy in form of ATP Moved against concentration gradient Carrier protein molecules Very selective
34
How does direct active transport occur
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
Difference between facilitated diffusion and active transport
Facilitated = DOWN concentration gradient = DOESN’T need metabolic energy Active transport = AGAINST concentration gradient =NEEDS metabolic energy
36
What is Sodium-potassium pump an example of
More than one molecule moved in cell as one is removed
37
Explain sodium-potassium pump
Sodium ions removed actively as potassium ions are actively taken in
38
How to increase the rate of movement across membranes
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
Role of diffusion in absorption
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
Difference between carrier and channel proteins
Channel proteins = open and close, only charged substances diffuse Carrier = fixed specific shape (allowing one particular charged substance), diffuse down conc gradient
41
Two functions of membranes in cells
Regulate movement and exchange of substances Separate internal and external environment
42
Why do phospholipids form in an aqueous environment
Have a hydrophilic head and hydrophobic tail Molecules arranges themselves between tails and surrounding water is minimised
43
How do molecules move to the other side of a cell surface membrane if there are no carrier proteins
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
If the molecule is not lipid soluble how would it travel across the cell membrane
Facilitated diffusion Specific channel protein or carrier protein
45
When does facilitated vs simple diffusion occur
Simple = lipid soluble non polar doesnt need carrier Facilitated = not lipid soluble, polar needs carrier
46
Explain the appearance of cytoplsam under a microscope (not touching cell wall)
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
What would happen if you put a cheek cell in a test tube of pure water
Cheek cell has lower water potential than water so take water into cell by osmosis and swell and eventually burst
48
Onion cell placed in pure water waht would happen
Cell wall provides additional strength that can withstand pressure so does not burst
49
What is simple diffusion
Movement DOWN conc gradient Movement of O2 from plasma into red blood cell
50
What is facilitated diffusion
Movement of glucose from high to low conc Movement down conc gradient
51
What is cotransport vs facilitated diffusion
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
What is the purpose of using carrier proteins recycling atp
Maintains concentration gradient for sodium
53
Why is beetroot used in the experiment
Pigment is red Amount of pigment thtat leaves indicated permeability

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