Introduction to Receptors and Cell Signaling

What is signal transduction?

relaying a signal through a cell to produce a response

What are the main stages of signal transduction?

signal, reception, transduction, amplification, response and termination

Why is cell signalling important?

maintains homeostasis and is controlled by many medicines

What is a hormone?

extracellular signal secreted by endocrine glands

What is endocrine signalling?

hormone travels through blood to distant target organ

Give an example of endocrine signalling.

insulin

What is paracrine signalling?

cell releases a signal that acts on adjacent cells

Give an example of paracrine signalling.

ach released at neuromuscular junction

What is autocrine signalling?

signal acts on same cell type that released it

Give an example of autocrine signalling.

growth factors

What is signalling by plasma membrane-attached proteins?

direct cell-cell signalling using membrane attached proteins

Give an example of membrane-attached signalling.

t cell activation by proteins on antigen presenting cells

What is a receptor?

molecule that binds specific molecules and produces a cellular effect

What is a ligand?

molecule that binds to a receptor

What does the lock-and-key analogy explain?

ligand binds to specific receptor to activate signalling

What is a conformational change?

change in shape of a protein

How can a hormone signal cross the membrane without entering the cell?

binds to surface receptor, changes shape and triggers intracellular signalling

How can drugs affect receptors?

block receptors or mimic signalling molecules

What is an agonist?

ligand that produces the maximal response in a given tissue

What is a partial agonist?

ligand that produces a response below the maximum

What is an antagonist?

ligand that produces no visible response and blocks agonists

What are the three main cell-surface receptor classes?

g coupled protein receptors, receptor tyrosine kinases, ligand gated ion channels

What do G protein-coupled receptors use?

g proteins to help transmit signals

How do receptor tyrosine kinases signal?

attach phosphate groups to tyrosine residues

How do ligand-gated ion channels work?

ligand binding opens a channel, allows specific ions through

Where are intracellular receptors found?

cytoplasm or nucleus

Which signals can activate intracellular receptors?

small or hydrophobic messengers that cross the membrane, such as steroid or thyroid hormones

What is transduction?

relaying a signal from a receptor to target molecules inside the cell

What is a second messenger?

intracellular chemical signal that passes a message from a receptor to target molecules

What is the first messenger?

extracellular hormone or ligand that activates the receptor

What are the common second messengers?

camp, cgmp, ip3, calcium ions, dag

What is important about second messengers?

can diffuse inside cells and transmit signals from receptors to target molecules

Why can the same signal produce different responses in different cells?

cells contain different proteins and signalling pathways

What is pathway branching?

one signalling pathway produces multiple responses

What is cross-talk?

communication between two signalling pathways

How can a different receptor affect the cellular response?

can activate a different pathway, producing a different response

What is phosphorylation?

addition of a phosphate group to a protein

What is dephosphorylation?

removal of a phosphate group from a protein

What do protein kinases do?

transfer phosphate groups from atp to proteins

What do protein phosphatases do?

remove phosphate groups from protiens

What is a phosphorylation cascade?

sequence of phosphorylation events that activates proteins and leads to a cellular response

Which three amino acids can typically be phosphorylated?

tyrosine, serine, threonine

What is signal amplification?

each step activates more molecules, allowing a small initial signal to produce a large response

What are the main physiological functions of cell-surface receptors?

vision, taste, smell, neurotransmission, cell growth, development, heart rate control

Why must signalling be terminated?

stop the response so the cell can respond to new signals