1 - cell membrane physiology and cell communication

Question 1

what are the main components of a cell membrane?

Answer 1

• lipids
• carbohydrates
• proteins

Question 2

types of lipids that make up the cell membrane

Answer 2

• cholesterol
• phospholipids

Question 3

functions of cholesterol in the cell membrane

Answer 3

• stiffens the cell membrane
• controls membrane fluidity
• determines degree of membrane permeability
• decreases water solubility of the cell membrane

Question 4

describe the basic structure of phospholipids

Answer 4

hydrophilic polar heads and hydrophobic non-polar tails

Question 4

what is a glycocalyx?

Answer 4

‘sugar’ coating of the cell made up glycoproteins and glycolipids

Question 5

what are the functions of a glycocalyx?

Answer 5

• repels other negative objects as it has a negative charge
• enables cells to attach to one another
• holds on to water which decreases cell dehydration
• enables cells to differentiate betweem host amd foreign cell
• plays a roll in blood typing

Question 6

what are the functions of the cell membrane?

Answer 6

• acts as a ‘mechanical’ barrier
• controls what substances enter and leave the cell since it is selectively permeable
• enables communication between cells (gap junctions)

Question 7

name the types of cell membrane junctions

Answer 7

• tight junctions
• desmosomes
• gap junctions

Question 8

describe tight junctions and where they are found

Answer 8

they are impermeable junctions that join the lateral edges of epithelial cells near their luminal borders thus preventing movement of materials between the cells.

found in intestines

Question 9

describe desmosomes and where they are found

Answer 9

adhering junctions that spot-rivet cells, anchoring them together in tissues subject to considerable stretching.

found in skin, uterus and heart

Question 10

describe gap junctions and where they are found

Answer 10

communicating junctions made up of connexons, which form tunnels that permit movement of charge-carrying ions and small molecules between two adjacent cells.

found in cardiac and smooths muscle cells and embryonic cells.

Question 11

name the 2 types of passive membrane transport and briefly explain them

Answer 11

simple diffusion
* does’t use ATP
* no carriers
* transport is passive downhill

facilitated diffusion
* does’t use ATP
* uses carriers or channels
* transport is passive downhill

Question 12

state the different types of active membrane transport and briefly explain them

Answer 12

primary active transport - the transport of a substance down its concentration gradient and it requires a direct chemical energy source i.e. ATP. it makes use of ATPase enzyme

secondary active transport - the transport of one substance down its concentration gradient coupled with the transport of another substance against its concentration gradient

Question 13

what is co-transport?

Answer 13

transport facilitated by a symporter (a protein that transports 2 molecules simultaneously in the same direction)

Question 14

what is counter transport?

Answer 14

transport facilitated by an antiporter (a protein that transport 2 molecules simultaneously but in different directions)

Question 15

give examples of primary active transport

Answer 15

• Na+/K+ ATPase
• Ca++ ATPase
• H+ ATPase
• H+/K+ ATPase

Question 16

give examples of substances transported using secondary active transport

Answer 16

• glucose
• amino acids
• H+

Question 17

give examples of lipid soluble substances

Answer 17

• O2
• CO2
• alcohol
• steroid hormones
• small non-polar substances

Question 18

give examples of water soluble substances

Answer 18

• ions
• glucose
• urea
• large polar sunstances

Question 19

state the 9 categories of clinically important cell membrane proteins

Answer 19

1. ion pump
2. protein carriers
3. protein channels
4. enzymes
5. desmosomes (cadherins)
6. protein receptors
7. G-protein coupled receptors
8. interlocking junctional proteins
9. glycoproteins

Question 20

which clinically important cell membrane proteins are involved in membrane transport?

Answer 20

• membrane-bound enzymes
• protein receptors
• G-protein coupled receptors

Question 21

name the principal groups of excitable tissue

Answer 21

• muscle tissue
• nerve tissue

Question 22

state the broad categories of membrane potentials

Answer 22

• resting membrane potential
• graded potential
• action potential

Question 23

what is the physiological importance of membrane potentials?

Answer 23

• allows for conduction of nerve impulses
• trigger muscle cell contraction
• influences the secretion of some secretion of some secretory cells like insulin-secreting cells

Question 24

what is a resting membrane potential?

Answer 24

• the measured potential difference across a cell membrane in milivolts.
• intracellular potential relative to extracellular potential when cell is at rest

Question 25

which factors contribute to establishing a resting mebrane potential?

Answer 25

• K+ diffusion alone
• Na+ and K+ diffusion
• Na+/K+ ATPase pump

Question 26

how does K+ diffusion alone contribute to establishing a resting membrane potential?

Answer 26

• [K+] is greater inside cell than outside cell.
• This causes a large concentration gradient from outside to inside which results in the tendency of the ions to diffuse outside.
• As they move outside they carry positive charges outside thus creating electropositivity outside and electronegativity inside because of the negative ions that remain inside.
• The potential difference between the outside and inside becomes strong enough to block anymore diffusion of the ions out resulting in a net diffusion of 0.
• This leaves the exterior slightly positively charged and the interior slightly negatively charged.

Question 27

how does Na+ and K+ diffusion contribute to establishing a resting membrane potential?

Answer 27

• K+ channels are slightly permeable to Na+ ions
• Because the channels are more permeable to K+, they contribute more to establishing RMP as the influx of Na+ ions doesn’t compensate for the efflux of K+

Question 28

how does the Na+/K+ ATPase pump contribute to establishing a resting membrane potential?

Answer 28

The pump pumps out 3 Na+ ions and pumps in 2 K+ ions. The continual loss of positive charges inside creates on additional degree of negativity.

Question 29

what is an action potential?

Answer 29

a rapid change in membrane potential that spreads rapidly along the cell membrane

Question 30

give a synonym for action potential

Answer 30

spike potential

Question 31

name and explain the stages of an action potential

Answer 31

resting stage
* this is the resting membrane potential before an action potential begins. the membrane is polarised in this stage

depolarisation stage
* the membrane suddenly becomes permeable to Na+ ions allowing them to rapidly diffuse into the cell therby neutralising the normal polarised negative state

repolarisation stage
* Na+ channels begin to close and K+ channels open to a greater extend than normal, allowing K+ ions to rapidly diffuse out the cell. This establishes the normal negative resting membrane potential

Question 32

explain the process of activation of Na+ voltage-gated channels

Answer 32

when the membrane potential becomes less negative than during resting membrane potential, it reaches a voltage ( about -50mV) that causes a sudden conformational change in the activation gate, flipping it all the way to the open position. During this activated stage, Na+ ions can pour inward through the channel. [Depolarisation]

Question 33

explain the process of inactivation of Na+ voltage-gated channels

Answer 33

the same voltage increase that opens the activation gate also closes the inactivation gate. this means that the conformational change that flips the inactivation gate to the closed state is a slower process. Once closed, the Na+ ions can no longer pour into the cell. The membrane potential begins returning to resting membrane state. The inactivation gate will not reopen until membrane potential returns to or near the original RMP.

Question 34

explain the process of activation of K+ voltage-gated channels

Answer 34

during resting stage, channel is closed. As membrane potential increases, it causes a conformational opening of the gate and allows increased diffusion of K+ ions towards. There is slight delay in the opening so the gates open at about the same time as when the Na+ channels are beginning to close because of inactivation. [Repolarisation]

Question 35

what is an afterpotential?

Answer 35

after an action potential reaches the previous resting membrane potential, the tracing overshoots slightly in the hyperpolarisation direction to form a small but prolonged afterpotential. It lasts a few milliseconds after the action potential is over. It occurs because many K+ channels remain temporarily open after repolarisation is complete.

Question 36

Name some impermeable negatively charged ions inside cells

Answer 36

• anions of proteins molecules
• anions of phosphate compounds
• anions of sulfate compounds

Question 37

what is the physiological significance of the negatively charged ions inside cells?

Answer 37

they keep the ICF negative. It should be negative during RMP.