lecture 14

Question 1

what can be used to pass along messages in signal transduction

Answer 1

The message can be passed on using proteins, chemical signals called second messengers, or
through sequential phosphorylation.

Question 1

what is signal transduction and what does It do

Answer 1

Signal transduction: when an active receptor starts a chain of events where messages are passed on through the cell.
Signal transduction often takes place over a multistep pathway as it provides opportunity to coordinate and regulate the cellular response.

Question 2

what can second messengers do and why

Answer 2

Second messengers can transmit signals from a receptor to other relay molecules because they are not attached to the membrane and are free to move in the cell.

Question 3

describe phosphorylation

Answer 3

Widespread mechanism for regulating protein activity where
protein kinases transfer phosphates from ATP to protein

Question 4

describe dephosphorylation

Answer 4

Protein phosphatases rapidly remove the phosphates from
proteins (dephosphorylation) to carefully control signal
transduction.

Question 5

what proteins are used in phosphorylation and dephosphorylation ?

Answer 5

protein kinases and protein phosphatases respectively

Question 6

how does the phosphorylation cascade work

Answer 6

In the cascade an agonist binds to the receptor, which activates a relay protein or adaptor protein, which goes onto active a kinase which then activates another kinase and so on.

Question 7

how do we regulate signal transduction in 3 ways

Answer 7

1. Ligand dissociation
2. Internalisation – receptor is
   removed from the cell surface
   through endocytosis so it can
   no longer respond to ligand
3. Phosphatases

Question 8

discuss signal transduction in GPCR generally

Answer 8

G protein-coupled receptors (GPCRs) use G proteins to
start signal transduction, hence their name.
* The GPCR activates the G protein, which communicates
with other proteins in the cell.
* There are different types of G proteins, which have
different effects.

Question 9

whats a G(alpha)s

Answer 9

Gαs = stimulatory G protein, which activates an enzyme called adenylate cyclase

Question 10

whats a Gαi

Answer 10

= inhibitory G protein, decreases
the activity of adenylate cyclase

Question 11

describe glucagon receptor signal transduction in the liver

Answer 11

Specific example is glucagon bindng to liver receptors, activating G proteins. The activation of the G protein stimulates activity of an enzyme called adenylate cyclase. The activation of Adenylate cyclase causes the release of cAMP. cAMP then works as a second messenger, diffusing within the cell and activating the kinase Protein kinase A. this then causes further signal transduction and more cell response. causing more glycogen breakdown

Question 12

insulin example of a GPCR

Answer 12

GLP-1 binds to GLP-1 receptors in the pancreatic beta cell membrane. Receptor activation causes G protein activation and further signal transduction events, leading to insulin secretion.

Question 13

describe the general path of signal transduction in RTK

Answer 13

• agonist ligand binds > receptor changes
  conformation and becomes activated > receptor
  autophosphorylation occurs > adaptor protein is
  phosphorylated

Question 14

how are RTK and GPCR different

Answer 14

Receptor tyrosine-kinases (RTKs) use
phosphorylation of so-called adaptor proteins
to start signal transduction. whereas GPCR act through the second messenger the G protein

Question 15

describe insulin RTK signalling in the muscle and adipose cells

Answer 15

Receptor activation causes phosphorylation of an
“adaptor” protein, and further signal transduction events, leading to GLUT-4 translocation. Glut-4 is a transport protein which allows glucose into the cell via the plasma membrane

Question 16

desribe RTK action on liver cells with insulin

Answer 16

In liver cells, receptor activation causes phosphorylation of an “adaptor” protein, and
further signal transduction events, this time leading to glycogen synthesis.

Question 17

what do agonists do to the ion gated channels

Answer 17

• An agonist ligand that binds causes a
  conformational change to activate the receptor.

Question 18

difference between ligand gated ion channels and RTK/GPCR

Answer 18

Instead of “relay” proteins like G proteins or
adaptors being used, ions directly flow through
the channel to produce effects.
* These receptors produce fast signalling,
compared to the slower signalling of GPCRs
and RTKs.