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as biology module 2 > 2.5 Cell Membranes > Flashcards

2.5 Cell Membranes Flashcards

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1
Q

Roles of membranes

A
  • Surface of cells (plasma membrane)

- within cells

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2
Q

Surface of cells (Plasma membrane)

A
  • barrier - control of substances entering and leaving- partially permeable
    (diffusion, osmosis, active transport)
  • Communication/ cell Signalling
  • recognition (immune system)
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3
Q

Within the cell

A
  • Compartmentalisation
  • Surface area for reactions
  • vesicles
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4
Q

Fluid Mosaic Model

A
  • Model of cell membrane structure
  • Lipid molecules give fluidity
  • Proteins give a mosaic appearance

-2 layers of phospholipids and easily flow over each other

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5
Q

Cell Signalling

A
  • Communication between cells using chemical messengers

- Drugs, hormones which travel to other cell and bind to receptor on cell membrane

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6
Q

Cell Membrane Receptors

A
  • Complementary shape to a messenger molecule binds with Receptor
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7
Q

Components of Cell Membranes

A
  • Phospholipids
  • Cholesterol
  • Proteins
  • Glycolipids
  • Glycoproteins
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8
Q

Phospholipid bilayer

A
  • form a barrier to dissolved substances
  • partially permeable
  • Rows of phospholipids naturally arrange themselves into a bilayer
  • head is hydrophilic- attracts water
  • tail is hydrophobic- it repels water
  • hydrophobic centre of bilayer- membrane
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9
Q

Cholesterol

A
  • gives membrane stability
  • between phospholipid bilayer
  • made of lipid
  • controls membrane fluidity
  • bind to hydrophobic tails of phospholipids
  • causing them to pack more closely together
  • making membrance less fluid
  • and more rigid
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10
Q

Proteins

A
  • channel and carrier proteins in membrane

- receptors on cell membrane

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11
Q

Channel proteins

A
  • ## form pores in the membrane for charged particles to diffuse through
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12
Q

Carrier proteins

A
  • move large molecules out of Cell
  • large molecule attaches to carrier protein in membrane
  • protein changes shape
  • releases molecule on opposite side of membrane
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13
Q

Receptors in proteins

A
  • receptors cell signalling

- when molecule binds to protein, chemical reaction takes place in cell

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14
Q

Glycolipids

A
  • carbohydrate on a lipid
  • stabilise membrane by forming hydrogen bonds with surrounding water molecules
  • sites where drugs, hormones and antibodies bind
  • receptors for cell signalling
  • antigens- involved in immune system
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15
Q

Glycoproteins

A
  • carbohydrate on a protein
  • stabilise membrane by forming hydrogen bonds with surrounding water molecules
  • sites where drugs, hormones and antibodies bind
  • receptors for cell signalling
  • antigens- involved in immune system
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16
Q

Temperature

A

Increasing temperature increases membrane fluidity

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17
Q
  1. Temperatures below 0°C
A
  • Phospholipids don’t have much energy so they can’t move much
  • Packed closely together and the membrane is rigid
  • Ice crystals form and pierce membrance making it highly permeable
  • Carrier and channel proteins deform increasing permeability
18
Q
  1. Temperatures between 0 and 45°C
A
  • Phospholipids can move and aren’t packed as tightly together
  • membrane is partially permeable
  • as temperature increases, phospholipids move more as they have more energy
  • increases permeability of membrane
19
Q
  1. Temperatures above 45°C
A
  • phospholipid bilayer starts to break down
  • membrane becomes more permeable
  • water inside the cell expands, putting pressure on the membrane
  • Channel and carrier proteins denature
  • increases permeability of membrane

-

20
Q

Types of transport across cell membranes

A
  • Diffusion
  • Osmosis
  • Active transport
  • Bulk transport
21
Q

Diffusion

A

1) the net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient

2) molecules diffuse both ways but net movement will be to area of lower concentration.
- This continues until particles are evenly distributed

  • Concentration gradient
  • passive
22
Q

What factors affects the Rate of Diffusion?

A

-temperature

-

23
Q

What factors affects the Rate of Diffusion?

A
  • Temperature
  • Concentration gradient
  • Movement
  • Surface area
  • Distance
24
Q

Temperature affecting rate of diffusion

A
  • the warmer
  • the faster rate of diffusion
  • particles have more kinetic energy so they move faster
25
Q

Temperature affecting rate of diffusion

A
  • as temperature increases
  • the faster rate of diffusion
  • particles have more kinetic energy
  • they move faster
26
Q

Surface area affecting rate of diffusion

A

-

27
Q

Surface area affecting rate of diffusion

A
  • larger surface area of membrane

- faster rate of diffusuon

28
Q

Distance affecting rate of diffusion

A
  • The thinner the exchange surface
  • The shorter the distance molecules have to travel
  • The faster the rate of reaction
29
Q

Facilitated diffusion

A
  • Diffuse through channel proteins or carrier proteins in cell membrane
  • Large molecules, ions and polar molecules don’t diffuse directly through phospholipid bilayer
  • Doesn’t use energy- passive
30
Q

Osmosis

Diffusion of water

A

-Movement of water from an area of high water potential to an area of low water potential down its water potential gradient

31
Q

Water potential c (negative)
(Ψ)
kiloPascals (kPa)

A

Measure of how much water there is

  • potential of water molecules to diffuse out of or into a solution
  • measure of the tendency of water molecules to diffuse from one region to another
32
Q

pure water

A
  • highest water potential
  • All solutions have a lower water potential than pure water
  • water potential of zero kPa
33
Q

Lower water potential

A
  • Large amount of solute dissolved

-

34
Q

Hypotonic

A
  • Solution with a higher water potential than the cell
  • Net movement of water molecules is into the cell
  • in Animal cell, cell bursts (lysis)
  • in Plant cell, vacuole swells
  • vacuole+cytoplasm push against cell wall
  • Cell becomes turgid (swollen)
35
Q

Isotonic

A
  • Solution with the same water potential as the cell
  • water molecules pass into and out of the cell in equal amounts
  • the cell stays the same
36
Q

Hypertonic

A
  • Solution with a lower water potential than the cell
  • Net movement of water molecules is out of the cell
  • in Animal cell, cell shrinks (shrivel)
  • in Plant cell, Cell becomes flaccid (limp)
  • cytoplasm and membrane move away from the cell wall
  • this is called plasmolysis
37
Q

Active transport

A
  • Against concentration gradient
  • Active - energy used from ATP
  • Use carrier and channel proteins
38
Q

Active transport process

A
  • molecule attaches to Carrier protein
  • Protein changes shape
  • moves molecule across Membrane
  • releasing it on the other side

-energy used to move Solute against Concentration gradient

39
Q

Bulk transport

A
  • Endocytosis- in
  • Exocytosis- out
  • Pinocytosis- liquid
  • Phagocytosis- solid
40
Q

Endocytosis

A

How large particles are brought into cell

Segment of plasma membrane surrounds and encloses particle

-brings it into the cell, enclosed in a vesicle

41
Q

Exocytosis

A
  • How large particles are exported out of cells
  • Substance to be exported out of cell is moved towards and fuses with plasma membrane
  • Fused site opens releasing contents of vesicle

as biology module 2 (13 decks)

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