Lecture 6-7,9,11 + Textbook chap 15

Question 1

cell signaling

Answer 1

The process by which information from the extracellular molecules is translated to an internal cellular signal

Question 2

Cells usually communicate with one another through

Answer 2

extracellular messenger molecules

Question 3

Autocrine/paracrine signaling (2)

Answer 3

• the cell that is producing the messenger expresses receptors on its surface that can respond to that messenger. Consequently, cells releasing the message will stimulate (or inhibit) themselves
• messenger molecules travel only short distances through the extracellular space to cells that are in close proximity to the cell generating the message. Paracrine messenger molecules are usually limited in their ability to travel around the body because they are inherently unstable, or they are degraded by enzymes, or they bind to the extracellular matrix.

Question 4

endocrine signaling (2)

system+ sites

Answer 4

• messenger molecules reach their target cells via passage through the bloodstream
• Endocrine messengers, also called hormones, typically act on target cells located at distant sites in the body

Question 5

Juxtacrine signaling

Answer 5

Both the ligand and receptor are membrane bound (not secreted) and in close proximity

Question 6

second messenger

Answer 6

small non-protein molecules that typically activate (or inactivate) specific proteins to amplify the signal inside the cell

Question 7

Kinase vs phosphatases

Answer 7

kinase adds phosphates while phosphatases removes them

Question 8

signal transduction

Answer 8

information carried by extracellular messenger molecules is translated into changes that occur inside a cell

Question 9

Signals transmitted along such signaling pathways ultimately reach —— involved in basic cellular processes. Depending on the type of cell and message, the response initiated by the —— may involve a change in gene expression, an alteration of the activity of metabolic enzymes, a reconfiguration of the cytoskeleton, an increase or decrease in cell mobility, a change in ion permeability, activation of DNA synthesis, or even the death of the cell.

Answer 9

• target proteins

Question 10

Signal transduction pathway consisting of protein kinases and protein phosphatases

Answer 10

Signal transduction pathway consisting of protein kinases and protein phosphatases with catalytic actions that change the conformations, and thus the activities, of the proteins they modify. In the example depicted here, protein kinase 2 is activated by protein kinase 1. Once activated, protein kinase 2 phosphorylates protein kinase 3, activating that enzyme. Protein kinase 3 then phosphorylates a transcription factor, increasing its affinity for a site on the DNA. Binding of a transcription factor to the DNA affects the transcription of the gene in question. Each of these activation steps in the pathway is reversed by a phosphatase.

Question 11

Finally, signaling at the end of signaling transduction must be terminated. This is important because cells have to be responsive to additional messages that they may receive. The first order of business is to eliminate the extracellular messenger molecule. To do this……..

Answer 11

Certain cells produce extracellular enzymes that destroy specific extracellular messengers. In other cases, activated receptors are internalized. Once inside the cell, the receptor may be degraded along with its ligand, which can leave the cell with decreased sensitivity to subsequent stimuli.

Question 12

Control of signal transduction

Answer 12

• cell type specific expression of ligand-specific receptor
• timing of docking protein activation
• prescence/abscence of docking sites
• inhibitory proteins prevent certain signals

Question 13

Jack STAT pathway (7):

Answer 13

1. Prolactin binds to the prolactin receptor (cytokine receptor)
2. The two receptor chains dimerize upon prolactin binding
3. Jack will get active by autophosphorylation
4. Jack also phosphorylate the receptor chains
5. When Jack is active, it will activate STAT by phosphorylating STAT
6. STAT combine with another STAT (dimerization) with the phosphate group and phosphorylated tyrosine attached to each
7. STAT travel to the nucleus to increase transcription

Question 14

G protein-coupled receptors (GPCRs)

Answer 14

• ## These receptors translate the binding of extracellular signaling molecules into the activation of GTP-binding proteins.

Question 15

Receptor protein-tyrosine kinases (RTKs)

Answer 15

• Binding of a specific extracellular ligand to an RTK usually results in receptor dimerization followed by activation of the receptor’s protein kinase domain which is present within its cytoplasmic region.
• Upon activation, these protein kinases phosphorylate specific tyrosine residues of cytoplasmic substrate proteins, thereby altering their activity, their localization, or their ability to interact with other proteins within the cell.

Question 16

Steroid hormone receptors

Answer 16

• Steroid hormones diffuse across the plasma membrane and bind to their receptors, which are present in the cytoplasm.
• Hormone binding results in a conformational change that causes the hormone–receptor complex to move into the nucleus and bind to elements present in the promoters or enhancers of hormone-responsive genes
• This interaction gives rise to an increase or decrease in the rate of gene transcription.