Ion channels, receptors and signalling Flashcards Preview

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Flashcards in Ion channels, receptors and signalling Deck (30)
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1
Q

What is a receptor?

A

Sensing element in the complex system of chemical communication within the body

2
Q

What are receptors the target of?

A

Neurotransmitters
Hormones
Mediators such as growth factors, chemokines, cytokines
Therapeutic agents such as agonists, antagonists

3
Q

What is a autocrine response?

A

When the signalling molecule targets the signalling cell it was made in

4
Q

What is a paracrine response?

A

When the signalling molecule targets a neighboring cell called a target cell

5
Q

What is an endocrine response?

A

When the signalling molecule enters the circulation targeting cells all over the body

6
Q

What are the 4 types of receptor?

A

Ligand-gated ion channels
G-protein-coupled receptors
Kinase-linked
Nuclear

7
Q

Where are ligand gated ion channels located?

A

Plasma membrane and are therefore targets of hydrophilic signalling molecules e.g. neurotransmitters

8
Q

Where are G-protein-coupled receptors located?

A

Plasma membrane and therefore targeted by hydrophilic signalling molecules

9
Q

Where are kinase-linked receptors found?

A

Plasma membrane and so are targets of hydrophilic protein mediators such as insulin

10
Q

Where are nuclear receptors found?

A

In the nucleus and so are targeted mostly by hydrophobic signalling molecules such as steroid and thyroid hormones

11
Q

What are ion channels made from?

A

Transmembrane pores that are formed by glycoproteins that span the membrane to form an ion conducting pathway

12
Q

How are ion channels regulated?

A

By signals that cause the channel to cycle reversibly between a closed state and an open state known as gating

13
Q

How do open channels conduct ions?

A

The ions are passed passively down their electrochemical gradient at rapid rates

14
Q

What are examples of gates on ion channels?

A

Chemical signals e.g. ligand gated
Transmembrane voltage e.g. voltage gated
Physical stimuli e.g. thermal and mechanical energy

15
Q

What are the three types of ligand gated ion channels?

A

Trimeric
Tetrameric
Pentameric

16
Q

What is the function of ligand gated ion channels?

A

Consists of separate glycoprotein subunits that form a central ion conducting channel. Allows rapid changes in the permeability of the membrane to certain ions

17
Q

What is signalling via second messenger system?

A

The receptor activation modulates the activity of an effector that is generally an enzyme or ion channel

18
Q

What are many receptors linked to?

A

A cell membrane located effector by intermediary G proteins. The enzyme effector usually synthesizes second messenger molecules that will affect the activity of targets within the cytoplasm

19
Q

What is the pathway of signalling via second messengers?

A

Signal binds to receptor
This activates a G protein
Which in turn activates an effector enzyme or ion channel

20
Q

What is the basic structure of a G protein coupled receptor?

A

It is an integral membrane protein that is made up of a single polypeptide with extracellular NH2 and COOH terminals. It has 7 transmembrane spans that are joined together by 3 extracellular and 3 intracellular connecting loops. Many GRPRs function as dimers i.e. 2 receptors together

21
Q

What is the basic structure of a G protein?

A

Is a guanine nucleotide binding protein. It is a peripheral memrane that consists of 3 polypeptide subunits - alpha, beta and gamma
The alpha subunit has a guanine nucleotide binding site that can hold onto GTP/GDP

22
Q

How is a G protein activated?

A

Agonist binding to the GPCR to which they preferentially coupled

23
Q

What is the structure of a g protein when it is inactive?

A

The guanine nucleotide binding site of the alpha subunit is occupied by GDP

24
Q

How does the G protein stay attached to the plasma membrane?

A

Covalent bonds on the alpha and gamma subunits

25
Q

What does the alpha subunit contain?

A

A GTPase domain with Ras and AH sub-domains. Ras is the GTPase component whereas AH clamps the nucleotide in place

26
Q

What happens when the agonist binds to the GPCR?

A

The alpha subunit releases GDP to allow GTP to bind. This causes the G protein to seperate from the receptor and the beta/gamma dimer. This then results in an alpha unit and a beta/gamma diner

27
Q

What happens to the G-protein coupled receptor when there is no signalling present?

A

The receptor is unoccupied
G-protein alpha subunit is bound to GDP
Effector is not modulated

28
Q

What happens to the GPCR when it is activated?

A

Agonist binds and the G protein will bind to the receptor. GDP will dissociate from alpha subunit and GTP will bind. G protein dissociated into separate alpha and beta/gamma subunits

29
Q

How is the signal turned off?

A

The alpha subunit acts as an enzyme (GTPase) to hydrolyse GTP to GDP and Pi. The G-protein alpha subunit will then recombine with the beta/gamma subunit

30
Q

How does signalling via nuclear receptors work?

A

Steroid hormones can enter the cell and will combine with an intracellular receptor causing a conformational change that leads to receptor to move to the nucleus and form a dimer to bind to hormone response elements in DNA. The genes will then be switched off or on to alter mRNA levels and the rate of synthesis of mediator proteins