6.cellmembrane

Question 1

What disease develops against the cell membrane

Answer 1

Antiphospholipid syndrome

1. cause
   
   1. autoimmune disease with production of antibodies directed against specific phospholipids
      
      1. target varies between patients
2. symptoms
   
   1. formation of thrombosis
   2. mid-adulthood
3. incidence
   
   1. high
      
      1. 20% of stroke patients younger than 50 have APS which is the cause of the stroke

Question 2

describe the rigid component of the cell membrane.

Answer 2

cholesterol- no a phosphoipid, but intercalated with them

regulates membrane fluidity

brought into the cell, in LDL form, by clathrin-caveolin proteins that induce endocytosis.

Question 3

describe the cell membrane component involved with endocytosis

Answer 3

Lipid rafts are location on the cell with receptors for outside peptides. These receptors are usually in the fluid zone, until ligand binds than this lead to the formation of caveolin and clathrin pits, brought from the intracellular side.

LDL entry of cholesterol into the cell is carried by LDL-receptors. The receptors migrate to caveolae regions to induce endocytosis.

Question 4

discuss the three types of proteins in cell membrane. general category

Answer 4

proteins

1. integral
   
   1. transmembrane proteins
   2. hydrophobic aa interact with oil layer and hydrophilic aa interact with fluid layer, ECF and ICF
2. peripheral
   
   1. attached to ingetral proteins or are free floating on top
3. lipid-anchored
   
   1. covalently bound to lipid tails

Question 5

what moities are attached to proteins and lipids of cell membrane. Use the ABO blood groups as an example. what diseases are correlate with a and o?

Answer 5

glycolipids and glycoproteins-oligosaccharide branching chains composed of sugar

A,B,AB

A-N acetyl galactosamine

B-N acetyl glucosamine

disease risk

1. A = greater risk of stomach cancer
2. O =later risk of ulcers

Question 6

movement of water and solutes occrs which ways?

Answer 6

1. transcellular
   
   1. through the membrane
2. paracellular
   
   1. throuugh the spaces between the cells

Question 7

what are three determinants of diffusion across plasma membranes?

1. hydrophobicity
   
   1. 4 examples
2. surface area
3. thickness
   
   1. how thick

Answer 7

diffuusion across plasma membranes

1. prime determinant of diffusion rate across lipid bilayer
   
   1. hydrophobicity of molecule
      
      1. freely diffuse across
         
         1. steroid
         2. lipid
         3. small molecule
      2. water
         
         1. can diffuse because of its size, but it depends on the membrane being more permeable
         2. particuularly less cholesterol
   2. suurface area of membrane
   3. thickness
      
      1. usually between 7.5-10nM

Question 8

what is the measurment of diffusion?

what is not required?

Answer 8

ficks law-governs passive movement of substances accross cell membranes

1. J=Px(concentration difference)
2. flux is dependent on the permeability of the membrane and the concentration difference of the substance of interest across the membrane

no external energy

• means no ATP used

Question 9

what are the key components for transporting an ion across a membrane?

how can this assist overcoming limited flux?

Answer 9

Proteins-with selective proerties for what crosses

1. pores
2. gated channels
3. carriers

To overcome limited flux across membrane of some substances, integral proteins exist that transport them across. This is not a violation of ficks defenition of diffusion as long as energy is not being used.

Question 10

how does water pass through the membrane? 2 ways.

does ficks law apply?

Answer 10

water is small enough to diffuse if the [membrane] is not too rigid. Aquaporins exist to assitst osmosis-channel protein

1. their size and internal charge determines what can pass through

Ficks law DOES apply.

flux=(permebility of membrane) x (concentration difference)

Question 11

What are some gated channels (3)

how does this change ficks law?

Answer 11

gated channels

1. chemically gated
2. voltage gated
3. pressure

Ficks law

1. change diffusion by changing the permeability of the membrane
   
   1. open
      
      1. specific molecules move through w/o external energy
         
         1. this diffusion obeys ficks law

Question 12

Is their a carrier protein obey ficks law?

Answer 12

Carrier proteins which utilize facilitaed diffusion

1. never form a continuous pathway between ECF and ICF
2. the intrisic affinity for the ligand in question changes the conformation upon binding. Once the carrier is on the opposite side the affinity for the ligands cahnges. When L2 binds the carrier protein changes conformation and the process starts over again.

Ficks law

1. no external energy is required, obeys ficks law
2. flux is considerably lower compared to pores and gated channels

Question 13

give the examples of passive and active diffusion

Answer 13

1. passive
   
   1. pores
      
      1. aquaporins
   2. gated channels
      
      1. chemical
      2. voltage
      3. pressure
   3. carriers
2. active
   
   1. active carriers
      
      1. Na/K pump
   2. secondary active transport
      
      1. SGLT

Question 14

Is there an secondary active transport carrier that obeys ficks law?

give an amazing fact about this pump!

Answer 14

NO

Similar to facilitated carriers, but they use an energy source(ATP) to go against the gradient. using energu disobeys ficks law.

Na/K pump-electogenic pump

1. 50% of the calories during the day is to drive the Na/K pump
2. essential for life

Question 15

descrive processes of Na/K pump motion

Answer 15

Question 16

Why is it important to never eat limu-make-o-hana?

Answer 16

sea weed of death

1. produces
   
   1. palytoxin
2. action
   
   1. binds to Na/K pumps and converts it to a channel
3. consequence
   
   1. destrudtion of ion gradient across membrane

an intense vasocontrictor and one of the most poisonous peptides known

Question 17

What uses the gradient established by active transporters?

Answer 17

secondary active transporters-SGLT

1. uses the sodium gradient established by active transport to move glucose into the cell
2. types
   
   1. uniporters
   2. cotransporters
      
      1. symprter
      2. antiporter

Question 18

what are three important characteristics of carrier-mediated transporters?

How can these be controlled?

Answer 18

1. specificity
   
   1. transporters are specific for one molecule or chemically related ones
      
      1. shown is a transporter that recognizes galactose and glucose
2. competition
   
   1. if transporter is specific to a family of compounds, they will compete with each other for binding sites.
   2. this is frequently important in drug design.
   3. shown below the carrier becomes less effective when in a mixed solution of Glu and Gal
   4. probenecid acts as competative ligand for an anion transporter in the kidneys, allowing for uric acid to pass in the filtrate instead of being reabsorbed.
3. saturation
   
   1. as more and more binding sites are occupied the change in rate of transport slows down
   2. saturation of GLUTtransporters in kidneys when the blood plasma is higher than normal (diabetes) the carrier proteins that reabsorb the glucose be saturated and the glucose passes in the urine
4. control
   
   1. up and down regulation
      
      1. remove from membrane or active/inactive with phosphorylation

Question 19

how does probenecid work to cure gout?

Answer 19

Gout

1. cause
   
   1. increase in uric acid levels in plasma
2. treatment
   
   1. probenecid
      
      1. acts as a competitive ligand for anion transporters that reabsorb uric aid from filterate. competition with this carrier protein, decreaes the amount of uric acid reabsorbed.

Question 20

what could cause glucose to be seen in the urine?

Answer 20

over saturated glucose transporters in the kidneys

as fluid flows down nephrons, glucose is reabsorbed. In diabetes, the amount of glucose exceeds capacity of transporters and therefor some appears in the urine.