Block 2 Lecture 25

Question 1

what causes a change in the rate of reaction

Answer 1

either the maximum velocity (Jmax) or the affinity of the protein for its substrate (Kt) or both

Question 2

when would Jmax change

Answer 2

when the number of transporters change but can also sometimes be caused by changing the turnover number

Question 3

what would cause Jmax to increase

Answer 3

if more proteins are synthesized

Question 4

what is the turnover number of proteins

Answer 4

how rapidly proteins undergo the conformational changes associates with moving substrate across the membrane

Question 5

what causes a change in Kt

Answer 5

affinity of an enzyme for its substrate changing or the protein structure changing

Question 6

what happens when transport proteins are occupied at a low concentration of substrate

Answer 6

the transport protein has a high affinity for the substrate

Question 7

what are the two basic strategies for responding to a change in the environment

Answer 7

1. a long term response-involves making more or less of the proteins required to deal with the change (hours to days)
2. a short term response- modifying the activity of an existing protein to make them go faster or slower (seconds to minutes)

Question 8

what do cells use in short term responses

Answer 8

post translational modification (PTM)

Question 9

what are the 2 basic PTM strategies

Answer 9

1. modify the structure of a protein- influencing how well it works under current conditions of the cell
2. change the location of the protein- exposing it to more or less of the reactant with which its supposed to work

Question 10

What does modifying the structure in PTM entail

Answer 10

non-covalent binding of a protein to something (Ca2+, GTP, or another protein), or addition/ removal of a phosphate group, or removing a portion of the proteins amino acid sequence

Question 11

what happens with Ca2+ binding in PTM

Answer 11

• under normal physiological conditions, PMCA mediated Ca2+ efflux occurs at a low rate because Ca2+ is low and because Kt for Ca2+ is high (affinity is low)
• when Ca2+ rises, PMCA cannot bring [Ca2+] back to normal by itself. calmodulin is a calcium binding protein that binds to Ca2+ and changes its conformation and permits it to bind to PMCA. the PMCA/Calmodulin complex has a higher affinity for Ca2+ than PMCA does by itself so efflux of Ca2+ increases

Question 12

what happens in the phosphatidylinositol signal pathway in PTM strategy 1

Answer 12

1. secretagogues bind to GPCR
2. that protein activates phospholipase C which converts a membrane phospholipid to DAG and IP3
3. DAG binds to and activates PKC
4. PKC phosphorylates proteins including Rab (involved in SSC)
5. Rab activates v-SNAREs and t-SNAREs that result in release of zymogens
6. IP3 binds to and activates a Ca2+ channel in the ER reeleasing Ca2+ into cytoplasm which binds to proteins like synaptotagmin which stimulates v-SNAREs and t-SNAREs that stimulates release of zymogens

Question 13

what are examples of PTM strategy 2 (change in location)

Answer 13

• GLUT4 transporter that transport glucose from blood, Rab proteins place the fully competent transporters into a location where they can do their job
• endocytic receptor down regulation- the conformational change that certain receptors undergo following binding of a ligand results in aggregation in the membrane and internalization via endocytosis which makes the receptor inactive

Question 14

what happens in PDZ based regulation

Answer 14

-PDZ adapter proteins have 2 or more PDZ domains where a PDZ ligand can bind. it brings proteins close together the influence each others activity with much greater efficiency than if the proteins were to come in contact by facilitated diffusion

Question 15

where are PDZ ligands found

Answer 15

at the c-terminal end of many transport proteins

Question 16

where does NHERF1 bind

Answer 16

one PDZ domain binds to the PDZ ligand at the C-terminus end of CFTR and the other domain binds to the ligand found at the c-terminus end of the Cl/HCO3 exchanger

Question 17

what is the CL/HCO3 exchanger also called

Answer 17

SLC26A6

Question 18

how does NHERF1 tether proteins next to one another

Answer 18

through the interaction of globular amino acid element found near the c-terminus of SLC26A6

Question 19

what does NHERF1 stimulate

Answer 19

CFTR mediated Cl- channel activity

Question 20

what is the globular amino acid element also called

Answer 20

the STAS element

Question 21

how can Cl- flux be supported

Answer 21

by CFTR coexpressed with SLC26A6 protein or the globular STAS element

Question 22

what does NHERF1 do in general

Answer 22

increases the efficiency of SLC26A6’s stimulation of CFTR

Question 23

what do PDZ based networks do in general

Answer 23

they are a common strategy to regulate protein-protein interactions which influences the movement and activity of many proteins