Week 2 Forces acting across membranes

Question 1

Explain the composition of ICF and ECF

Answer 1

ICF

K in intracellular, protein and phosphates/sulphates in ECF

ECF na+, Cl-, HCO3- (bicarbonate).

Question 2

Volumes of fluid in ICF and ECF

Answer 2

plasma 3L

ISF - 11L

ICF 28L

Question 3

what can pass freely between all components?

ECF and ICF

how?

Answer 3

Water

presence of aquaporins channels - osmosis

Gases

across cell membrane etc 02, c02

Question 4

Where can Ions pass in ECF and ICF

Answer 4

readily between plasma and ISF

not as easily ICF - regulated - mainly impermeable

Question 5

7 important things on the cell membrane:

Answer 5

1. selective permeability

2 permeability can vary - various cell function e.g. transmission of nerve impulse

3. dynamic constantly formed, maintained, dismantled
4. thin double layer sheet of lipid (bilayer) hydrophilic and hydrophobic
5. membranes are very flexible due to fatty acid - if overstretched will rupture.
6. excellent insulators against movement of electrical charge.
7. embedded with proteins (and associated with carbohydrates)

Question 6

Explain membrane carbohydrates

Answer 6

Molecules may attach phospholipid or protein embedded ALL ARE extracellular

important role - if the cell is self vs non-self for recognition by the immune system.

Question 7

Function of membrane protein

integral protein

Answer 7

SPAN the hydrophobic core of lipic bilayer

Question 8

The function of membrane protein

peripheral protein

Answer 8

associated only with phosphate head (internal or external) of the lipid bilayer and does not penetrate hydrophobic core

Question 9

The function of membrane protein

5 function list

Answer 9

1. receptor

2 transport (transporter and channel protein)

3 enzyme

4 maintenance of cell structure (anchorage)

5 communication

Question 10

Role receptor

Answer 10

Integral to membrane structure - penetrace from ECF to ICF. allow communication of extracellular signal (LIGAND) e.g. neurotransmitter or hormone for cellular response.

Question 11

What is a Ligand?

Answer 11

ligand refers to substances that bind to receptors.

Question 12

receptor proteins specific?

Answer 12

yes cells will present receptors react certain chemicals e.g. gonads folicle stimulating hormone

Question 13

Are there any receptors inside cell?

Answer 13

YES

(intracellular receptors)

Question 14

Proteins

explain transporters

Answer 14

two forms

Channel protein - move ions across membranes

can be open (water) aquaporin or gated (ion) usually closed

transporters don’t create continuous pore from ECF to ICF - move larger molecules. open only one side at a time (ECF and ICF)

Question 15

Explain glucose transporters

Answer 15

permanently percent in the cell membrane

is INSULIN INDEPENDENT

e.g. nerve cells. insulin only requred for glucose reuptake in muscle and adipose tissue.

Question 16

Explain enzymes as membrane protein

Answer 16

membrane enzyme catalyse chemical reaction on cell membrane.

Enzymatic part may be on:

external side of membrane e.g. found small intestine break nutrients into smaller units

internal side converting signals carried from receptirs into an intracellular response

Question 17

Explain structural protein on the membrane

Answer 17

Anchor cell membrane to intracellular skeleton to extracellular matrix (collagen) or other cells. if dysfunctional cause disability - e,g, lack dystrophin protein in Duchennes Muscular Dystrophy.

Question 18

Explain protein-membrane communication

Answer 18

Can be within or out of cell

Glycoprotein act marker tell the immune system if self or non-self

carry hormone (or drug) to intracellular

Peripheral protein (inside) relay signal along membrane from integral receptor protein (span bilayer) to an integral enzyme protein.

Question 19

Explain how membrane differ in protein content

Answer 19

1. Myelin - specialist membrane insulator around myelinated nerves - low content protein (18%) major component is lipid.
2. plasma membrane have greater activity protein content (typically 50%)
3. membranes involved in energy transduction (inner membrane mitochondria) highest content - 75%

Question 20

What is an electrochamical gradient?

Answer 20

Ions creating concentration gradient are charged

as they move across membrane - creats electrical gradient.

drives direction of passive movement.

any movement against this gradient requires energy (active transport)

Question 21

What drives the direction of passive movement?

Answer 21

movement of ions down the electrochemical gradient

Question 22

What is active transport

Answer 22

any movement against the concentration gradient requires energy (active transport)

Question 23

Mechanism of movement across membranes

what is diffusion?

Answer 23

Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration down a gradient in concentration

Question 24

Mechanism of movement across membranes

what is passive diffusion

Answer 24

Directly through the lipid bilayer

The movement of substances in the direction of the concentration gradient without any energy input.

Question 25

Mechanism of movement across membranes what is facilitated diffusion

Answer 25

i) protein channels or; ii) protein transporters Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins.

Question 26

Mechanism of movement across membranes what is Active transport

Answer 26

movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient.

Question 27

What is endocytosis and exocytosis. what is the purpose?

Answer 27

Mechanisms for moving macromolecules across membranes without disrupting them

Question 28

Describe endocytosis

Answer 28

invagination of the cell membrane form a vesicle which disintegrates on the cytoplasmic (inside) surface of the membrane, releasing contents which then migrate within the cell to their destination

Question 29

Describe Exocytosis

Answer 29

involve the reverse of endocytosis **Proteins manufactured in the cell are released from those cells by exocytosis.** proteins packed in Golgi apparatus - travel up to membrane and then excreted

Question 30

LO: Define what is meant by diffusion list factos which favour diffusion through lipid bilayer define difference between passive diffusion and facilitated diffusion define difference between facilitated diffusion and active transport describe different typed of membran proteins and their functions explain what is meant by carrier mediated transport system (i,e transporters)

Question 31

Describe filtration

Answer 31

The movement of substance across the capillary wall

Question 32

The three types of passive transport are

Answer 32

Diffusion Osmosis Facilitated diffusion

Question 33

Active transport is different from passive transport because it allows .

Answer 33

molecules to be transported against the concentration gradient

Question 34

Passive transport is driven by the .

Answer 34

concentration gradient .

Question 35

(Primary/Secondary) active transporter proteins use the concentration gradient of one molecule to move a different molecule across the membrane against its concentration gradient.

Answer 35

**Secondary active** transporter proteins use the concentration gradient of one molecule to move a different molecule across the membrane against its concentration gradient.

Question 36

(Primary/Secondary) active transporter proteins use ATP directly to move molecules across the membrane against the concentration gradient.

Answer 36

**Primary active transporte**r proteins use ATP directly to move molecules across the membrane against the concentration gradient.

Question 37

In diffusion, if substances move from one compartment to another can it go back?

Answer 37

As long as the **membrane is permeable** to the **substance for both ways**, it allows it to come back. The net flux will move in the direction from high concentration to low, but some will come back.

Question 38

Are cell membranes permeable to intracellular proteins?

Answer 38

NO the membrane is effectively **impermeable** to intracellular proteins and organic anions. These cannot diffuse in any capacity and **stay inside** the cell.

Question 39

For smaller molecules passing membrane what is it important to distinguish?

Answer 39

Whether they are passing through the lipid bilayer (passive diffusion) or via proteins embedded in membrane (facilitated diffusion)

Question 40

An example of a substance that crosses via Passive diffusion

Answer 40

02 and c02 - needs to be lipophilic to diffuse across although c02 is not lipophilic it's small enough it still crosses

Question 41

An example of a substance hat crosses via facillitated diffusion

Answer 41

Glucose, ions can cross through ion channels

Question 42

Passive diffusion what do molecules need to be

Answer 42

_molecules need to be:_ **_1. small_** **_2. uncharged_** _3 ideally lipophilic (hydrophobic)_ _gases - small and uncharged. 02, c02, and nitrogen._ (large molecule e.g. glucose or small charged particles like ions do not cross membrane without assistance from membrane protein,, facilitated diffusion)

Question 43

Facilitated diffusion

Answer 43

ions (charged) nutrients e.g. glucose (large) slow movement na+ slower than c02 movement.

Question 44

name some membrane proteins to help transport proteins through facilitated diffusion

Answer 44

i) channel proteins ii) mediated transport proteins

Question 45

What are membrane channels

Answer 45

need to be in solution (water) to transport. water and ion molecules move together Na+, K⁺, Cl^-, Ca²⁺, H⁺ aquaporins (only allow water)

Question 46

What opens ion channels?

Answer 46

Ligand response trigger change through signal Electric charge signal

Question 47

How do ions cross the membrane

Answer 47

Using channels (usually GATED) remain closed until stimulus (chemical or electrical charge change) cause to open

Question 48

What channels open due to electrical potential., where are these found extensively

Answer 48

Voltage-gated channels extensively in muscle and nerve cells

Question 49

What channels open when chemical (neurotransmitter or hormone) channel?

Answer 49

Ligand-gated open bind chemical binding site to the channel protein. act transporter and receptor.

Question 50

What happens if there are conflicting electrical and concentration gradients?

Answer 50

both electrical charge and chemical concentrations cause a conformational change in channel protein to cause open or close. The direction of diffusion depends on concentration/electrical gradient (in charged particles) **Sometimes forces cooperate, sometimes they oppose. The net direction depends on the dominant force**

Question 51

How do molecules that are too big to move through channel proteins or lipid bilayer?

Answer 51

**facilitated diffusion through a carrier-mediated transport protein** molecules too big to move through channel proteins use carrier-mediated transport protein (transporters)

Question 52

Active transport

Answer 52

molecules being moved against electrochemical gradient.

Question 53

Example of active transporter (pump)

Answer 53

**Na⁺/K⁺ATPase** or **Na⁺/K⁺​​ pump**

Question 54

Na+/K+​​ pump purpose?

Answer 54

Help maintain different of Na+ outside cell and K+​​ inside. continuously purple 3 Na+ out cell and 2 K+​​ ions inside cell. Produces net movemen of positive charge **out** of the cell **electrogenic pump** creates charge difference across membrane 40% resting energy og body used by Na+/K+​​ ATPase

Question 55

Na+/K+​​ ATPase or Na+/K+​​ pump - distrubutes how much of Na+ and K+​​ to where?

Answer 55

**continuously pump 3 Na+ out cell and 2 K+​​ ions inside the cell.** Produces net movement of positive charge out of the cell electrogenic pump creates charge difference across the membrane 40% resting energy of body used by Na+/K+​​ ATPase

Question 56

The ratio of Na+ and K+​​ in/out of cell does what with charge across membrane

Answer 56

continuously pump 3 Na+ out cell and 2 K+​​ ions inside the cell. **Produces net movement of positive charge out of the cell electrogenic pump creates charge difference across the membrane** 40% resting energy of body used by Na+/K+​​ ATPase

Question 57

How much resting energy does the Na+ /K+​​ pump use

Answer 57

40% of resting energy

Question 58

What is osmosis?

Answer 58

Net movement of H₂O from regions of high concentration of H₂Oto regions of low concentration of H₂O

Question 59

difference osmosis and diffusion

Answer 59

Osmosis: Net movement of H2O from regions of high concentration of H2Oto regions of low concentration of H2O Diffusion: the net movement of **solute** from regions of high solute concentration to low concentration **water** can move freely between ICF and ECF body is osmotic equilibrium Not all solutes move freely

Question 60

How is H2O concentration related to concentration of solute

Answer 60

H2O is inversely related to solute concentration. more solute particles in solution, the more they will **displace** H2O molecules, lowering the concentration of H2O

Question 61

what is osmotic pressure

Answer 61

oppose increase of volume in pressure when cell is permeable to water but not solute on both sides.. this will mean ncrease unequal volume but equal water. so the pressure to oppose

Question 62

What will happen with osmosis with no diffusion

Answer 62

change in cel volume

Question 63

What is osmolarity describe it inclusing moles from a solute (e.g. NaCl)

Answer 63

1-mole substance dissolved in a litre mol/l a mole consists of 6/02x10²³ **molecules** **The number of** solute particles **not molecules which determine osmotic effect.** 1 mole glucose added to h20 - 1 mole/l 1 mole NaCL added to H20 - 2 mole/l as 1 molecule Na+ and 1 molecule Cl-

Question 64

Term osmolarity

Answer 64

measures concentration biological solution in units of OSMOLES - describe number particles/L of solution (use **_mili_**osmoles) NORMAL human plasma has osmolarity 285 mOsmol/l which is same within cells (often taken as 300 for ease)

Question 65

What is normal osmolarity in plasma

Answer 65

NORMAL human plasma has osmolarity 285 mOsmol/l which is same within cells (often taken as 300 for ease)

Question 66

For osmosis, the volume of the cell is dependant on the concentration of what on either side of the membrane?

Answer 66

Concentration of non-penetrating solutes

Question 67

What act as non- penetrating soluted in the ECF ICF

Answer 67

ECF - Na⁺ and Cl^- ICF - K⁺ and organic anions)

Question 68

Osmolarity described \_\_\_

Answer 68

total number of particles in solution including penetrating and non penetrating

Question 69

Tonicity describes\_\_

Answer 69

A number of the non-penetrating particles in solution.

Question 70

what does isoosmotic mean

Answer 70

same **TOTAL _number_** of solute particles.

Question 71

Hypo-Osmotic

Answer 71

Solutions with **fewer** total solute particles

Question 72

Hyper osmotic

Answer 72

Solutions with greater number of total solute particles

Question 73

Isotonic

Answer 73

Solution has same number of **nonpenetrating** particles as **normal ECF (plasma)**

Question 74

Hypotonic

Answer 74

solutions with **fewer** number of **nonpenetrating solute particles as normal ECF (PLASMA)**

Question 75

Hypertonic

Answer 75

Solutions with **greater** number of **nonpenetrating** solute particles as **ECF (plasma)**

Question 76

Non-penetrating particles determine \_\_\_ penetrating particles PLUS non penetrating particles determine \_\_\_\_ give examples

Answer 76

nonpenetrating particles (ions) determine tonicity. penetrating particles (e.g. urea) PLUS non-penetrating particle determine osmolarity

Question 77

What determines tonicity what determines osmolarity

Answer 77

nonpenetrating particles (ions) determine tonicity. penetrating particles (e.g. urea) PLUS non-penetrating particle determine osmolarity

Question 78

what happens to a cell when put in hypotonic solution

Answer 78

swell, maybe burst

Question 79

What happens to a cell when put in hypertonic solution

Answer 79

Shrink

Question 80

Why do we need to know a cell will swell in hypertonic solution

Answer 80

haemolysis which can kill

Question 81

what happens when cells have lysed (burst)

Answer 81

proteins will be introduces to interstitial fluid (ISF) increasing tonicity of extracellular fluid ECF in an uncontrolled manner making management very complicated

Question 82

what should you NEVER transfuse a patient with what are they usually transfused? what in rare occasions can a solution be prescribed?

Answer 82

Never transfuse with pure water Usually transfused an ISOTONIC solution of sodium chloride Nacl a hypotonic transfusion controlled in a drip. never injected

Question 83

If a solution is hypotonic it is ____ osmotic

Answer 83

Hypoosmotic

Question 84

If a solution is hyperosmotic it can be \_\_\_\_\_\_\_\_

Answer 84

Hypertonic, isotonic, hypotonic.

Question 85

if a solution is isoosmotic it can be \_\_\_\_\_\_

Answer 85

isotonic or hypotonic

Question 86

only changes in osmolarity/tonicity will change cell volume

Answer 86

tonicity

Question 87

what organ is most sensitive to changes in tonicity?

Answer 87

Brain