Membrane Fusion, Membrane Potential, Acids/Bases

Question 1

What is a SNARE protein?

Answer 1

SNAREs catalyze the membrane fusion reaction in vesicular transport. Also provide an additional layer of specificity in the transport process

Question 2

What are the two main categories of SNAREs?

Answer 2

v-SNAREs (on vesicles) and t-SNAREs (on the target membranes)

Question 3

What is the specific name of the v-SNARE we talked about?

Answer 3

VAMP (or synaptobrevin?)

Question 4

What is the structure of VAMP? What does it contribute to the trans-SNARE complex?

Answer 4

It is a transmembrane protein and contributes 1 alpha helix to the complex

Question 5

What are the two types of t-SNAREs?

Answer 5

syntaxin and Snap25 (both found on the target membrane)

Question 6

What is the structure of syntaxin? What does it contribute to the trans-SNARE complex?

Answer 6

It is a transmembrane protein and contributes 1 alpha helix to the complex (just like VAMP)

Question 7

What is the structure of Snap25? What does it contribute to the trans-SNARE complex?

Answer 7

It is a peripheral membrane protein. Contributes 2 alpha helices to complex

Question 8

What is the trans-SNARE complex? What is it made of?

Answer 8

A stable four-helix bundle that locks the vesicle membrane and target membrane together. Brings them close enough to overcome all the barriers and fuse. 1 helix from VAMP; 1 from syntaxin; 2 from Snap25

Question 9

How do tetanus and botulism toxins work?

Answer 9

They are proteolytic neurotoxins that block synaptic transmissions (vesicles) by cleaving SNARE proteins in the nerve terminals.

Question 10

What does the NSF protein do?

Answer 10

Regulates the dissociation of SNAREs. Forms a kind of turning barrel around the SNARE complex and twists it apart with the help of a lot of ATP. Probably involved in regulating the availability of SNAREs so they are only used when needed

Question 11

What does Sec1 do?

Answer 11

After being unwound syntaxin becomes unfolded and Sec1 is needed to refold it properly

Question 12

What is the Nerst equation?

Answer 12

E (in mV) = (60/z) log (Co/Ci). E is the equilibrium potential; z is the valence of the ion in question; Co is the concentration outside; Ci is the concentration inside

Question 13

What does it mean if Vm is not the same as E?

Answer 13

Either a) the membrane is impermeable to the ion or b) the ion must be pumped across the membrane because it is not distributed at equilibrium

Question 14

What is the Donnan Rule?

Answer 14

[K+]o[Cl-]o = [K+]i[Cl-]i In words concentration of potassium times chloride outside equals concentration of potassium time chloride inside

Question 15

What 4 rules can we use to solve cell problems?

Answer 15

Osmotic balance (moles outside = moles inside). Charge neutrality (on each side; the + = -). Nernst Equation. Donnan Equilibrium

Question 16

What determines membrane potential in different cells?

Answer 16

Relative conductance (ie permeability) of Na and K

Question 17

What is the Henderson-Hasselbalch equation?

Answer 17

pH = pKa + log ([A-]/[HA]) OR pKa = pH - log([A-]/[HA])

Question 18

What do the relationships between pH and pKa mean?

Answer 18

If pH < pKa the solution is less than 50% deprotonated. If pH=pKa the solution is 50% deprotonated. If pH > pKa the solution is greater than 50% deprotonated

Question 19

How do you use the H-H equation to solve problems involving the bicarbonate buffer system?

Answer 19

pH = 6.1 + log ([HCO3-]/(.03 x PCO2 (mmHg))

Question 20

How to rearrange H-H equations to solve for [base]/[acid]

Answer 20

pH = pKa + log [base]/[acid]. Rearrange to give pH - pKa = log [base]/[acid] or 10 ^ (pH-pKa) = [base]/[acid]