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Biology > 2.5 biological membranes > Flashcards

2.5 biological membranes Flashcards

1
Q

Why is the fluid mosiac model called ‘fluid’?

A
  • phospholipids and proteins can move by diffusion
  • phospholipids move side to side
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2
Q

Why is the fluid mosiac model called ‘mosiac’?

A
  • scattered pattern produced by proteins within the phospholipid bilayer
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3
Q

Structure of a phospholipid

A
  • hydrophillic head
  • hydrophobic fatty acid tail (non-polar)
  • fatty acid tails face inwards creating a barrier against water soluable substances (polar substances)
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4
Q

Role of cholesterol in the fluid mosiac model

A

regulate fluidity and stability of the membrane
* stops it being too rigid at low temperatures and too fluid at high temperatures
* stops phospholipids packing too close together

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5
Q

Role of glycoproteins and glyolipids in the fluid mosiac model

A
  • forms hydrogen bonds with water to stabilise membrane
  • cell adhesion in tissue formation
  • receptors for cell signaling
  • antigens for cell recognition
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6
Q

Role of extrinsic proteins in the fluid mosiac model

A

partly embedded in the bi-layer
contain mainly hydrophillic R-groups

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7
Q

What are the key internal membrane functions

A
  1. isolation
  2. comparmentalisation
  3. control what enters and leaves the cell
  4. site of chemical reactions
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8
Q

Definition of bulk transport

A

a form of active transport that requires ATP but doen’t require a concentration gradient

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9
Q

Definition of endocytosis

A

bulk transport into cells
2 types: phagocytosis (solid) and pinocytosis (liquid)

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10
Q

Function of the phospholipids in the bi-layer

A

to create a partially permeable membrane

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11
Q

Defintion for exocytosis

A

bulk transport out of the cell

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12
Q

Process of exocytosis

A
  • transport out of the vesicles from the golgi appartus
  • move towards and fuse with the cell surface membrane
  • the contents are released outside of the cells
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13
Q

Process of endocytosis

A
  • cell membrane invaginates (bend inwards) when in contact with the substance to be transported
  • membrane enfolds until the membrane fuses to make a vesicle
  • this pinches off and moves to the cytoplasm for further transfer ( moved by cytoskeleton )
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14
Q

Role of the cytoskeleton

A
  • changes cell shape to engulf materials
  • movement of secertory vesicles
  • fusion with the cell membrane
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15
Q

Definition of cell signaling

A

communication between cells to trigger a reaction within the target cell

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16
Q

How do glycoproteins act as a receptor

A

specific shape which is complementary to the shape of the signalling molecule

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17
Q

Definition of diffusion

A

net movement of a substance from a region of high concentration to a region of low concentration
- caused by natural kinetic energy

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18
Q

What can pass through the PL bi-layer

A
  1. oxygen/carbon dioxide (small)
  2. lipid soluable molecules (alcohol, steriod hormones)
  3. water
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19
Q

What cannot pass through the PL bi-layer

A
  1. ions (charged - so they are repelled against non-polar fatty acid tails)
  2. polar/ large molecules (too large)
20
Q

Definition of faciliated diffusion

A

net movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via protein channels

21
Q

Functions of a channel protein

A

transport charged substances (ions)
acts as gates so part of the inside surface of the membrane can moves to close or open the pores

22
Q

Function of carrier proteins

A

can change between two shapes
creates a binding site to be open
the direction of movement depends of the concentrations

23
Q

Factors affecting diffusion

A
  1. concentration gradient
  2. temperature
  3. surface area
  4. distance
  5. membrane
  6. size of diffusing molecule
24
Q

How does the concentration gradient affect diffusion

A

the steeper the concentration gradient the faster the rate of diffusion

25
Q

How does temperature affect diffusion

A

the higher the temperature the more kinetic energy the particles will have to move around
it will occur faster

26
Q

How does surface are affect diffusion

A

the larger surface area : volume ratio of the membrane the more particles can diffuse at once
it will occur faster

26
Q

How does distance affect diffusion

A

the shorter the distance or the thinner the membrane the quicker the rate of diffusion

26
Q

How does membranes affect diffusion

A

the greater the number of protein channels or carrier proteins present the higehr the rate of diffusion

27
Q

How does the size of the diffusing molecule affect diffusion

A

the smaller the ions / molecule diffuses more rapidly than larger molecules

28
Q

Definition of active transport

A

net movement of substances against the concentration gradient ( low to high ) across a cell membrane, using ATP and carrier proteins

energy is from hydrolosis of ATP

29
Q

Defintion of osmosis

A

net movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane

30
Q

Definition of water potential

A

the pressure exerted by water molecules as they collide with the membrane

31
Q

What is the highest water potential

A

0

32
Q

Definition of isotonic

A

no overall net movement

33
Q

Definition of hypertonic

A

high solute concentration
low water concentration

34
Q

Definition of hypotonic

A

low solute concentration
high water concentration

35
Q

What happens in an animal cell if it is hypertonic

A

water leaves the cell so it crenates (shrivels)

36
Q

What happens to a plant cell if its hypertonic

A

water leaves and the cell membrane becomes detached
they are plasmolysed

37
Q

What happens to an animal cell if its isotonic

A

water goes in and out of the cell
becomes balanced (equilibrium)

38
Q

What happens in a plant cell if its isotonic

A

flaccid

39
Q

What happens in an animal cell if its hypotonic

A

it lyses (splits open) due to hydrostatic pressure (occurs in a closed system)

40
Q

What happens in a plant cell if its hypotonic

A

water goes in and the cell becomes turgid
the pressure potential prevents any further entry of water

41
Q

What is the water potential of a cell and why

A

negative water potential because it has dissolved solutes in their cytoplasm

42
Q

How does temperture affect the permeability of the PL bi-layer

A
  • PL are constantly moving
  • the PL gain more kinetic energy meaning the membrane becomes more fluid and gaps begin to form between the PL
  • if too fluid it will loose control of the entry and exit of substances and protein channels will denature
43
Q

How does solvents affect membrane permeability of the PL bi-layer

A

organic solvents (ethanol or acetone) dissolve the membrane as they are lipid soluable
this disrupts membrane permeability

Biology (12 decks)

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