transport across cell membrane Flashcards

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1
Q

describe phospholipids

A

hydrophilic heads of both layers point to the outside of the CSM attracted to the water on both sides, hydrophobic tails of both layers point into the centre of the CSM, repelled by water on both sides

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2
Q

what are the functions of the CSM proteins?

A

provide support, act as carriers for substances, to help cells stick together, act as receptors

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3
Q

what are extrinsic proteins?

A

on the surface but only partly embedded, they give mechanical support to the cell/act as receptors for molecules such as hormones

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4
Q

what are intrinsic proteins?

A

completely span membrane, act as carriers to transport material across the CSM, others can be enzymes

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5
Q

what are glycolipids?

A

cell surface receptors for hormones and neurotransmitters, allow cell-cell recognition, helps cells attach to each other

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6
Q

what does cholesterol do?

A

adds strength/rigidity to the CSM by pulling the fatty acid tils of the phospholipids together, reduces membrane fluidity at high temps, prevents water leakage from the cell

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7
Q

why is the arrangement of the CSM referred to as the fluid mosaic model?

A

the phospholipids can move relative to one another, the proteins can vary in size and shape like the tiles in a mosaic

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8
Q

what factors affect diffusion?

A

concentration gradient, length of diffusion pathway, surface area, temperature

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9
Q

definition of diffusion

A

movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached

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10
Q

how to work out diffusion rate

A

surface area x concentration difference divide by lenth of diffusion pathway

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11
Q

what prevents molecules from passing through the CSM?

A

not lipid soluble, very large, polar

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12
Q

what is facilitated diffusion?

A

diffusion made easier by the use of channel and carrier proteins that span the CSM

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13
Q

what are protein channels?

A

protein pores that open or close to control the passage of selective ions e.g. sodium/potassium

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14
Q

what are carrier proteins?

A

take substances from one side of the membrane to the other

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15
Q

how does the number of proteins in the CSM limit the rate of diffusion?

A

proteins become saturated and can’t support any more molecules

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16
Q

what happens to the permeability of the CSM in very cold temperatures?

A

phospholipids don’t have much energy and can’t move much so they’re tightly packed together, making the membrane rigid. proteins denature, increasing permeability as proteins lose structure and function. ice crystals form, pierce through membrane making it highly permeable

17
Q

what happens to the permeability of the CSM in warm temperatures?

A

phospholipids can move around, not as tightly packed together - membrane is partially permeable. as temp increases the phospholipids move more as they have more energy, increases the permeability

18
Q

what happens to the permeability of the CSM in hot temperatures?

A

phospholipid bilayer starts to break down/melt and membrane becomes more permeable. water inside the cells expands, putting pressure on the membrane. proteins denature so can’t control what enters/leaves the cell - increases permeability

19
Q

definition of osmosis

A

water moves from an area of high water potential to low water potential across a semi-permeable membrane until equilibrium is reached

20
Q

water potential of pure water

A

zero

21
Q

what is water potential measured in?

A

kilo-pascals (KPa)

22
Q

what is water potential?

A

a measure of how easy it is for water to move

23
Q

what happens with animal cells are placed in a higher water potential?

A

red blood cells - absorb water by osmosis when placed in water as it has a higher water potential. has a very thin CSM that can’t stretch to a great extent, so CSM breaks, bursting the cell and releasing its contents…. HAEMOLYSIS

24
Q

how do animal cells stop haemolysis from happening?

A

they usually stay in a liquid which has the same WP as the cell

25
Q

what happens when a plant cell becomes turgid?

A

placed in pure water they absorb water by osmosis has it has a higher WP. protoplast swells and presses on cell wall - cell wall only capable of limited expansion so pressure builds up on it that resists the entry of more water.

26
Q

what happens with animal cells are placed in a lower water potential?

A

water leaves by osmosis and the cell shrinks, becoming shrivelled

27
Q

why does incipient plasmolysis happen in plant cells?

A

when it’s placed in a solution with equal/lower WP - water leaves cell by osmosis and the vol of the cell decreases. a stage is reached when the protoplast no longer presses on the cell wall and begins to pull away from it

28
Q

why does plasmolysis happen in plant cells?

A

when water leaves via osmosis, the further loss of water causes the cell contents to shrink further and the protoplast pulls even more (completely) away from the cell wall

29
Q

definition of active transport

A

when molecules move from an area of low concentration to an area of high concentration against the concentration gradient across a semi-permeable membrane - requires energy in the form of ATP

30
Q

how is ATP produced?

A

via aerobic respiration by mitochondria

31
Q

how does ATP help substances across the membrane?

A

with the release of energy from the ATP molecule, the shape of the channel protein changes to allow it through, it then goes back to normal and repeats again