Signal Transduction Part 2

Lecture 22

all organisms

are able to detect and respond to some environmental variables, including light, temp, sound, touch, magnetic fields, gravitational fields, pH, and various chemicals

detection

involves the change in tertiary structure of a sensory receptor, which starts a cascade of events that lead to a response by the cell

cell-to-cell signaling

one cell produces a signal to be detected by another cell

a signal between cells

is produced by the signaling cell

conveys specific information

the recipient is the receiver or target cell

the goal is to elicit a response in the target cell

cell signaling

process that cells communicate with one another, receive and respond to external cues, and coordinate their actions

cell signaling

it involves the release of signaling molecules (such as hormones, growth factors, or neurotransmitters) from one cell

then bind to specific receptors on the surface of a target cell or inside it

response

the chemical signal (ligand) binds to its receptor and cascade of events (signal transduction) leads to a ______

juxtacrine signals

diffuse between cells through gap junctions and plasmodesmata

cell signaling requiring physical contact

vital in processes like immune responses

juxtacrine signals

cell signaling that requires physical contact

paracrine signals and autocrine signals

cell signaling on the local level

autocrine signals

bind to receptors on the same cell that secretes them

paracrine signals

bind to receptors on nearby cells

cell signaling on the local level

helps the activation of T cells

endocrine signals

cell signaling from a distance

cell signaling from a distance

growth, metabolism, and reproduction (chemical signal)

endocrine signals

are transported by the circulatory system and bind to receptors on distant cells

juxtacrine signaling

paracrine signaling

autocrine signaling

endocrine signaling

What are the four types of cell signaling

juxtacrine signaling

requires direct contact between the two cells

paracrine signals

diffuse to and affect nearby cells

autocrine signals

affect the same cells that release them

endocrine signaling

hormones are transported long distances by bulk flow

juxtacrine signaling

in this contact-dependent signaling pathway, a cell attaches to another cell to initiate the signaling pathway

juxtacrine signaling

What type of signaling fits this example

example: when leucocytes use this form of binding to “roll” through blood vessels prior to leaving the bloodstream at the site of an infection

paracrine signaling

a short-range signaling pathway where a cell secretes a signaling molecule that is picked up by target cells in the local vicinity

paracrine signaling

the ligand is released into the extracellular space, and it diffuses through the extracellular matrix to be picked up by nearby receptors

this occurs in what type of signaling

paracrine signaling

which type of signaling is this an example of:

the synaptic signaling and growth hormones used in development

autocrine signaling

the signal is released and received by the same cell

autocrine signaling

often used by the immune system in order to help it ramp up the immune response when activated (cancer cells)

autocrine signaling

sometimes a signal is released by a cell and is received by both itself and neighboring cells

endocrine signaling

a long-range signaling pathway where a cell secretes a signaling molecule that is picked up by target cells not in the local vicinity

considered to be slow

endocrine signaling

what type of signaling is this an example of?

most hormones, insulin, adrenaline, estrogen, growth hormones, etc

paracrine signaling

at the junction of two nerve cells, one of the cells secretes a neurotransmitter molecule that diffuses over to the neighboring cell, where it binds and stimulates an electrochemical response

endocrine signaling

to signal hunger, cells in the stomach secrete a peptide that circulates through the blood and binds to receptors on the cells in the hypothalamus in the brain

juxtacrine signaling

a cell in a developing embryo has a cell surface protein that directly contacts a receptor on a neighboring cell, causing it to change its gene expression pattern

signal transduction pathway

A signal activates a receptor

the location of receptor determines the type of ligand that binds to a receptor

signal transduction pathway

a signal arrives at a target cell

the signal molecule binds to a receptor protein on the cell surface or inside the cell

signal binding changes the three-dimensional shape of the receptor and exposes its active site

the activated receptor activates a signal transduction pathway

signal transduction pathway activates the cells response

ligand

transmits a signal or message by attaching to the receptor protein on a target cells surface or inside the cell

receptor-ligand interaction

is a fundamental part of cellular communication and cellular response or change in activity

they can be both!

are receptors intracellular or embedded in the membrane?

nonpolar signal

can diffuse directly across the lipid bilayer of the cell membrane to encounter its receptor in the cytosol or nucleus

polar signal or large signal

cannot diffuse through the cell membrane. its receptor is embedded in the membrane

by their location

How are receptors classified?

membrane receptors

located on the cell surface; ligands are large or polar and can’t cross the lipid bilayer. Also have a cytosolic region that initiates signal transduction

membrane receptors

intracellular receptors

What are the two types of signal molecule receptors?

intracellular receptors

located inside a cell; ligands are small or nonpolar and can diffuse across the cell membrane

polar signaling molecules

bind to membrane receptors-transmembrane proteins

GPCRs

protein kinase receptors

gated ion channel

What are the three examples of transmembrane proteins

cytosolic region

this region of a membrane receptor often functions as an enzyme, with its active site on the cytosolic side of the membrane

ligand

binds to the extracellular region and acts as an allosteric regulator, exposing the active site of the cytosolic region

a ligand interacting with a membrane receptor

the binding of adenosine to its receptor is an example of what?

adenosine receptors

are located on the cell membrane and belong to the G protein-coupled receptor (GPCR) family

membrane receptor

has both extracellular and cytosolic regions connected by a hydrophobic region

ligands

bind to receptors noncovalently and reversibly, and can be regulated

ligand-gated ion channels

these channels open or close in response to the binding of a specific molecule (ligand), such as neurotransmitter

when the ligand binds to the channel, it causes a conformational change in the channel protein, allowing ions to flow through

voltage-gated channels

these channels can also be called “voltage-gated ion channels”. They open or close in response to changes in the electrical potential (voltage) across the cell membrane

for example: when the membrane potential reaches a certain threshold, the channel changes its conformation, allowing ions to pass through

ligand-gated ion channels

voltage-gated channels

Types of ion channels found in cell membranes

ligand gated ion channel receptors

they change shape when a ligand binds

Ligand-gated ion channel

acetylcholine binds to two of the five AChR subunits, causing the channel to change shape and open

the channel is lined with negatively charged amino acids, allowing Na+ to flow into the cell

Na+ buildup in cells initiates events that lead to muscle contraction

voltage gated ion channel

are one type of gated ion channel that involves the membrane transport

they are transmembrane proteins

it opens up the channel across the membrane and ions enter or exit through the passage

it changes the conformation of the channel protein

What happens when the electrical potential is present near the voltage gated channel?

closed (resting) state

voltage gated ion channel

activation gate closed

inactivation gate open

(channel closed)

open (activated state)

voltage gated ion channel

activation gate open

inactivation gate open

(channel open)

inactivated (refractory) state

voltage gated ion channel

activation gate closed

inactivation gate closed

channel closed

voltage gated ion channel

resting—————→ activated——————————> inactivated

(closed) (open) (closed, refractory)

intracellular steroid hormone receptor

1. the receptor chaperone complex cannot enter the nucleus

2. cortisol enters the cytosol and binds to the receptor

3. causing the receptor to change shape and release the chaperone

4. which allows the receptor and cortisol ligand to enter the nucleus