BIOL 15 Exam III

What is cell signaling used for

Cells communicating with each other

Cells sensing things in their environment so they can respond

Phosphorylation

Adding a phosphate functional group to turn a protein/gene on

Dephosphorylation

Removing a phosphate functional group to turn off a protein/gene

Kinase

Enzyme that adds phosphate

Usually activates something

Phosphorylase

Removes/Takes off phosphates

Stops a signal

Ligand

Small molecule capable of sending signals in cell

Can be amino acids, polar/nonpolar

Autocrine Signaling

The cell that makes the signal receives it and responds to it

Juxtocrine Signaling

Cells are physically attached and pass signals back and forth through cytoplasms

Signal is sent between two adjacent cells

Gap Junctions

Specialized intercellular channels that directly connect the cytoplasm of adjacent animal cells

Paracrine Signaling

Signal sent through extracellular space

Cell makes neurotransmitter which is how the other cell receives it

Endocrine Signaling

Signal sent between different tissues through circulatory system

Relationship between distance and regulation

The longer distance a signal has to travel, the more regulation there is

Signal might not even make it to its destination

Steps of Cell Signaling

1. Receptor Acitivation

2. Signal Transduction

3. Response

4. Termination

Receptor Activation

Receptor binds to/associates with ligand

The stronger the IMF is the stronger the intensity/longevity of the signal

Can’t use covalent cause the ligand wouldn’t leave

Activation

Ligand binding with receptor

Signal Transduction

Receptor changes shape or activates or whatever then sends signals through the cell

Helps coordinate more powerful responses (amplifies signal)

#of downstream molecules : strength/speed of gene transcription turning on/off molecules

Response

Up/Down regulation of some gene

I.e. turn on/off transcription/translation of genes/proteins

Termination

Ligand Has to become unbound (must dissociate from receptor)

Receptor goes through structural reset to be ready to receive a new signal

Cell Surface Receptors

Respond to polar ligands that cannot pass through cell membrane

Which binding domain is on the extracellular side of the membrane

Ligand Binding

Which domain is on the cytoplasmic side of the membrane

Signal Transduction

What kind of residues should the extracellular ligand binding domain expect

Polar

What kind of residues should the cytoplasmic signal transduction domain expect

Polar residues

What residues should the trans membrane domain

Nonpolar

GPCR

G protein coupled receptor

Involved in senses, adrenogenic, and synapses

Structure of GPCR

7 transmembrane helices in a coordinate circle

G proteins (alpha, beta, and gamma)

Resets very quickly

Inactive state of GPCR

No ligand bound

G protein bound to GDP

G protein associated with main transmembrane protein

Active state of GPCR

Ligand binds

GDP is replaced with GTP at which point the alpha domain dissociated from the beta and gamma domain and transmembrane helix

Stimulatory

Stimulate a response

“Do something” “Activate something”

Inhibitory

“Stop doing something”

Phospholipids C Actibation

Histamine receptors

Specialized Sensory GCPRs

Signal very very quick responses to outside stimuli

RTK

Receptor Tyrosine Kinases

What type of receptors are RTKs

Cell surface/transmembrane receptors

Process of RTK Signaling

1. 2 Ligands bind to two inactive receptors at once

2. Dimenzation of receptors occurs → receptor can now autophosphorylate

3. Active receptor subunits phosphorylation each other

4. Phosphate groups are binding sites for intramolecular sign inhaling proteins

5. Signal is amplifies as other cytoplasmic proteins are phosphorylated

Ligand-Gated Ion Channels

Mainly composed of one polypeptide subunit with multiple transmembrane domains

Process of ligand-gated ion channels

1. Ligand binds to inactive protein channel (closed channel) @ extracellular protein sites

2. Channel opens

3. ions can float through causing an increase of ion concentration inside cell; Ions can pass through in direction of the membrane potential

4. Ligand releases and channel closes

Homodimer

Protein complex made up of two IDENTICAL subunits (monomers) that associate with each other

Heterodimer

Protein complex made of two NON-identical subunits or receptor monomers that associate to trigger signaling pathways

Which integrin subunit has a special feature? What is it?

The alpha subunit has a disulfide bond

When it becomes a dimmer it has quaternary structure as well

Where can integrins send signals

Both outside → inside cell and inside → outside cell

Unique to integrins

How do integrins bind to ligands

At a very low affinity (association) , meaning it needs a lot more ligands for the signal to start

integrins function

Bridge for cell-cell and cell-extracellular matrix interactions

Once bound, they recruit other adhesion molecules to an adhesion complex

Bound intergrins

Recruit adhesion molecules to an adhesion complex

Unbound integrins