Forces Acting Across Membranes

Question 1

What does the cell membrane do?

Answer 1

Separates ECF and ICf and is responsible for maintaining the differnce in composition

Question 2

What makes up the extracellular fluid?

Answer 2

Interstitial fluid and plasma

Question 3

What does not penetrate the cell membrane but passes freely across the capillary wall (so exchanges readily between plasma and ISF)?

Answer 3

Ions

Question 4

Where is [K+] high?

Answer 4

ICF

Question 5

Where is [K+] low?

Answer 5

ECF

Question 6

Where is [Na+] low?

Answer 6

ICF

Question 7

Where is [Na+] high?

Answer 7

ECF

Question 8

Where is there a high concentration of large anions and proteins?

Answer 8

ICF

Question 9

What is important about the permeability of the cell membrane?

Answer 9

Permeability can vary at different times which is important for different cell functions

Question 10

What is embedded in the cell membrane?

Answer 10

Receptors for chemical signals e.g. Hormones and neurotransmitters which regulate cellular activity

Question 11

What does it mean by saying a membrane is dynamic?

Answer 11

They are continually being formed and maintained or dismantled and metabolism depending on the needs of the cell

Question 12

What is the structure of the cell membrane?

Answer 12

Phospholipids with hydrophilic (lipophobic) phosphate head and a hydrophobic (lipophilic) fatty acid tail, embedded with proteins

Question 13

What are membranes insulators against?

Answer 13

Insulators against movement of electrical charge - prevents the passage of electrons

Question 14

What are the four general classe of membrane proteins?

Answer 14

1. Receptors
2. Transporters
3. Enzymes
4. Peripheral proteins

Question 15

What are the three membrane protein classes that make up the Integral Membrane Proteins (IMP)?

Answer 15

Receptors, transporters and enzymes

Question 16

What membrane protein class is not incorporated into the membrane itself?

Answer 16

Peripheral proteins

Question 17

What do membrane receptors do?

Answer 17

Allows communication of an extracellular signal to the intracellular space to create a cellular response

Question 18

What do membrane transporters do?

Answer 18

Proteins which allow movement of ions or molecules across the membrane

Question 19

What are the two types of transporter membranes?

Answer 19

Carrier and channels

Question 20

What do carrier proteins do?

Answer 20

Open to ECF, then ICF, but never at same time; move larger molecules than channels

Question 21

What do channel proteins do?

Answer 21

Create a pore through the membrane through which molecules flow - can be open or gated

Question 22

What do membrane enzymes do?

Answer 22

Membrane enzymes catalyse chemical reactions on the cell membrane

Question 23

What are the three main roles of peripheral membrane proteins?

Answer 23

1. Maintain structure of cells by anchoring membrane to intracellular cytoskeleton
2. Attach cells to the extracellular matrix
3. Perform signalling functions within cells

Question 24

What is the typical protein content of plasma membranes?

Answer 24

50%

Question 25

What is the typical protein content of membranes involved in energy transduction?

Answer 25

75%

Question 26

What are examples of membrane carbohydrates?

Answer 26

Glycoproteins and glycolipids

Question 27

What do membrane carbohydrates have an important role in?

Answer 27

Self vs non-self recognisition by the immune system

Question 28

What causes the concentration gradient across the cell membrane?

Answer 28

Ions which are charged particles

Question 29

What drives the direction of passive movement?

Answer 29

Electrochemical gradient

Question 30

What are some mechanisms of movement across the cell membrane?

Answer 30

Endocytosis and exocytosis, diffusion, mediated transport, osmosis and filtration

Question 31

What happens during endocytosis?

Answer 31

Invagination of the membrane to form a vesicle which eventually separates on the cytoplasmic surface of the membrane and migrates within the cell to its destination

Question 32

What is diffusion?

Answer 32

Process by which gas/substance in solution expands to fill all available volume; from high conc to low conc

Question 33

What is the permeability coefficient?

Answer 33

The ease with which a molecule can pass through a given membrane

Question 34

What are cell membranes inpermeable to?

Answer 34

Intracellular proteins and organic anions

Question 35

What three qualities do molecules need to have to pass through the lipid bilayer?

Answer 35

1. Small 2. Lipophilic (hydrophobic) 3. UNCHARGED

Question 36

What is THE most important quality for a molecule to have to pass easily through the lipid bilayer?

Answer 36

Uncharged

Question 37

How do mineral ions diffuse through channels?

Answer 37

Transmembrane IMPs that act as an aqueous route through the membrane for diffusion of ions

Question 38

What kind of channel does H2O pass through?

Answer 38

Aquaporins

Question 39

What do ions use to cross membranes at a faster rate than predicted by their lipid permeability?

Answer 39

Channels or mediated transport proteins

Question 40

What are channels made up of?

Answer 40

Individual protein subunits

Question 41

How does a gated channel work?

Answer 41

Remains closed until a stimulus (chemical or change in electrical charge) causes them to open

Question 42

How do voltage gated channels work?

Answer 42

Open/close in response to alterations in membrane electrical potential (muscle/nerve cells)

Question 43

How do ligand gated channels work?

Answer 43

Open/close when they bind a chemical (neurotransmitter/hormone) to a receptor binding site on the channel protein

Question 44

What is facilitated diffusion?

Answer 44

Movement of molecules through transport proteins down their electrochemical gradients

Question 45

What is active transport?

Answer 45

Movement of molecules through transport protiens AGAINST their electrochemical gradients requiring ATP

Question 46

What is an example of an active transporter?

Answer 46

Na+/K+ pump

Question 47

What doe s Na+/K+ATPase do?

Answer 47

Helps maintain this difference by continually pumping out 3 Na+ ions and pumping in 2 K+ ions for each molecule of ATP hydrolysed

Question 48

What is the electrogenic pump?

Answer 48

A net movement of positive charge out of the cell to create a charge difference across the membrane - as in the Na+/K+ pump

Question 49

How much of the body's resting energy is used by Na+/K+ATPase?

Answer 49

40%

Question 50

What is osmosis?

Answer 50

Net movement of H2O from high H2O region to low H2O region

Question 51

How is the H2O concentration related to the solute concentration?

Answer 51

Inversely proportional (the more solute particles, the more they will displace H2O molecules, lowing H2O conc)

Question 52

What happens if a solution of different conc is separated by a membrane permeable to H2O only?

Answer 52

After time will end up with: equal concentration either side of membrane but different volumes

Question 53

What is the osmotic pressure?

Answer 53

The pressure required to oppose an increase in volume/to prevent water movement

Question 54

What does a mole consist of?

Answer 54

6.02x10^23 molecules

Question 55

What determines the osmotic effect on [H2O]?

Answer 55

Number of solute particles

Question 56

What is the normal osmolarity of human plasma?

Answer 56

285 mOsmol/l