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Flashcards in Forces Acting Across Membranes Deck (28)
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1
Q

Describe the basic structures of membranes

A
  • cell membrane is made of phospholipid bilayer
  • freely permeable to some substances, permeability is selective
  • membranes provide binding sites for chemical recognition
  • dynamic - constantly formed and maintained or dismantled and metabolised depending on needs of cell
  • very flexible due to fatty acids
  • insulators
2
Q

What are the two classes of membrane proteins?

A
  • Integral

- Peripheral

3
Q

Describe integral membrane proteins

A
  • cannot be removed without disrupting membrane
  • amphipathic with the same orientation os the phospholipids
  • may span the membrane
4
Q

Give four examples of how an integral membrane protein might work

A

As

  • channels - through which ions can cross the membrane
  • carriers - to transport substances across i.e. pumps
  • enzymes - with binding sites at the surface
  • receptors - recognition sites for chemicals
5
Q

Describe peripheral membrane proteins

A
  • can be removed without major disruption of function
  • not amphipathic
  • contact IMPs on the intracellular side of the membrane and tend to have enzymatic function
  • important for cell shape and motility
6
Q

In what cells do membranes have very little protein content (18%) as they are mainly composed of lipid to provide insulation against electrical signals?

A

Schwann cells in nerves

7
Q

What organelles are very active and have a membrane protein content of around 75%?

A

Mitochondria

8
Q

What is diffusion across membranes in the body?

A

Diffusion occurs between compartments in the body, from a high concentration to a low concentration, provided the barrier between the two is permeable to the diffusing substance

9
Q

List the factors which favour diffusion through the membrane

A
  • a large surface area
  • high permeability
  • high concentration gradient
10
Q

To diffuse through the lipid bilayer, molecules need to be

A
  • small
  • uncharged
  • hydrophobic (lipophilic)
11
Q

Give four molecules which can diffuse through the lipid bilayer

A
  • O2
  • N2
  • CO2
  • urea
12
Q

What are protein channels?

A

Trans-membranous IMPs that act as an aqueous route for the diffusion of ions

  • H2O passes through aquaporins
  • some are always open while others are gated
13
Q

What are the two types of gated channels?

A
  • voltage gated

- ligand gated

14
Q

Describe voltage gated channels

A
  • changes in electrical potential act on the charged regions of the channel proteins producing a change in the configuration in their shape
  • this opens or closes the channel e.g. Na+ channels in nerve cells
15
Q

Describe ligand gated channels

A
  • when a certain chemical binds to the channel protein it produces a change in the configuration and opens or closes the channel
  • e.g. Acetylcholine receptors
16
Q

Define electrochemical gradients

A
  • for ion diffusion, electrical and concentration gradients need to be considered
  • separation of charges across most cell membranes
  • so inside of cell carries a relative negative charge in respect to outside
  • this membrane potential can affect the diffusion of ions across the membrane - electrochemical gradient
17
Q

What is carrier mediated transport?

A
  • carrier mediated transport proteins have binding sites for substances which cannot diffuse across or cross cell membranes via channels
  • they bind to solute and undergo a change in configuration which exposes the site on the other side of the membrane so solute can diffuse into the cell
  • protein returns to normal shape
18
Q

What are the two types of carrier mediated transport systems?

A
  • facilitated diffusion

- active transport

19
Q

What is facilitated diffusion?

A
  • transport of solutes down their conc gradient

- needs no direct energy source

20
Q

What is active transport?

A
  • requires energy to move substances against the gradient
  • energy comes from ATP so these pumps are known as ATPases
  • e.g. Na+/K+ ATPase is in all cells
21
Q

Define osmolarity

A

The measure of solute concentration - number of osmoles of solute per litre of solution

22
Q

Define osmolality

A

The measure of osmoles of solute per kilogram of solvent

23
Q

Tonicity is determined by the volume of the cells which depends on

A

the concentration of non-penetrating solutes on the two sides of the membrane

24
Q

If the ECF has a higher tonicity than the ICF, the solution is

A

hypertonic

- cell will shrink as water leaves via osmosis to compensate

25
Q

If the ECF has a lower tonicity than the ICF, the solution is

A

hypotonic

- cell will swell as water enters the cell

26
Q

What is an isosmotic solution?

A

A solution in which there is an equal number of both penetrating and non-penetrating solutes on either side of the cell membrane

27
Q

What is an isotonic solution?

A

One in which there is an equal number of non-penetrating solutes on either side of the cell membrane

28
Q

Describe the process of endocytosis

A

Invagination of the membrane to form a vesicle around the target substance

  • it eventually separates from the membrane on the cytoplasmic side and migrates within the cell to its destination
  • exocytosis is the reverse process