Lecture 14: ACTIVATION AND INHIBITION OF PROTEINS (PART 2) Flashcards
What does an active receptor start?
A chain of events where messages are passed on through the cell via a process called signal transduction
What is signal transduction often?
Multi-step pathways that provide opportunities for coordination and regulation of the cellular response
What can relay molecules be?
Proteins or chemical signals called second messengers
What can second messengers do?
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
What do GPCR’s use to start signal transduction?
G proteins
What does the GPCR do?
Activates the G protein, which communicates with other proteins in the cell
What are the different types of G proteins?
Stimulatory G protein (G alpha s) and Inhibitory G protein (G alpha i)
What does stimulatory G protein do?
Activates an enzyme called adenylate cyclase
What does adenylate cyclase do?
Produce cAMP (a second messenger)
What does cAMP do?
Activate kinase
What does inhibitory G protein do?
Decreases the activity of adenylate cyclase
What do RTK’s use to start signal transduction?
Phosphorylation of adaptor proteins
What do adaptor proteins do?
Communicate with other proteins in the cell
What do the different types of adaptor proteins have?
Different effects
What do phosphorylation and dephosphorylation events do?
Turn activity on and off or up and down as required
What is phosphorylation?
A widespread mechanism for regulating protein activity where protein kinases transfer phosphates from ATP to protein (phosphorylation)
What do protein phosphates do?
Rapidly remove the phosphates from proteins (dephosphorylation) to carefully control signal transduction
What activates ligand gated ion channels?
An agonist ligand that binds and causes a conformational change
What happens when a ligand gated ion channel is activated?
Instead of relay molecules being activated, ions directly flow through the channel into the cell to produce effects
Whaat receptors produce fast signalling?
Ligand gated ion channels
What can responses be controlled by?
Where receptors are expressed
What do different cells have?
Different collections of receptors and relay molecules, allowing cells to detect and respond differently to different ligands
What can the same ligand receptor pairing have?
Different effects in different cells because they use different combinations of relay molecules for signal transduction
What can further help the cell coordinate signals from incoming ligands?
Pathway branching and cross talk
What happens in pathway branching?
The first protein activated further activates two proteins which each have individual cellular responses
What happens in cross talk?
Two individual receptors each activate a protein and then the activated proteins act together to activate another protein
What are insulin, glucagon and GLP-1 examples of?
Endogenous peptide ligands (hormones)
What happens with insulin in muscle and adipose cells?
RTK receptor activation causes phosphorylation of an adaptor protein, and further signal transduction events, leading to GLUT-4 translocation
What is GLUT-4?
A glucose transporter
What is done with GLUT-4?
It is transported to the cell membrane to allow glucose to enter
What happens with insulin in liver cells?
RTK receptor activation causes phosphorylation of an adaptor protein and further signal transduction events, leading to glycogen synthesis
What happens with glucagon in the liver cells?
Receptor activation causes stimulatory G-protein activation and further signal transduction events, leading to glycogen breakdown
Where is GLP-1 produced?
In the gut
What does GLP-1 act on?
Pancreatic beta cells when we eat a meal
What does GLP-1 receptor activation cause?
Stimulatory G protein activation and further signal transduction events, leading to insulin secretion
