Cell signalling

Question 1

Where does electrical impulse in neurone end

Answer 1

The electrical impulse in neurones end in the presynaptic terminal, where it is converted into a chemical signal

Question 2

What are the channels at the end of pre-synaptic axon terminals called

Answer 2

Voltage-gated calcium channels

Question 3

What effect does influx of calcium have at end of pre-synaptic axon terminal

Answer 3

In response to calcium influx, synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane to release their contents in synaptic cleft for neurotransmission

Question 4

What types of post-synaptic membrane receptors are there

Answer 4

Post-synaptic receptors can be G-protein coupled receptors, enzyme linked receptors or ionotropic receptors

Question 5

What is endocrine signalling and what are three examples

Answer 5

Endocrine signalling is signalling between distant cells in the body, often with signallig molecules transported by blood, for example glucagon secreted by pancreas stimulating the liver, adrenalin produced by adrenal gland acting on lungs and heart, insulin secreted by pancreas acting on liver, muscle cells and adipocytes

Question 6

What is paracrine signalling and what is are three examples

Answer 6

Paracrine signalling is signalling between adjacent cells within a tissue, for example insulin producing beta-cells inhibiting alpha-cells, vascular endothelial cells acting on neighbouring cells by nitric oxide and osteoclasts that are activated by growth factors secreted by adjacent osteoclasts

Question 7

What is signalling between membrane attached proteins and what are two examples

Answer 7

Cells on cell membrane can interact by membrane proteins to present substances or recognition proteins, for example with HIV binding to CD4 receptor on Th-cells and TLR reacting to bacterial cell wall substances

Question 8

Which protein does APC use to present pathogen molecules on membrane

Answer 8

Antigen presenting cells use MHCII-complexes to present antigens on membrane

Question 9

What is autocrine signalling and what are three examples

Answer 9

Autocrine signalling is signalling within a cell, for example T cells self-activating with IL-2, tumour cells producing and secreting TGF-beta which induces mitosis and motor nerves at NMJ where acetylcholine binds to muscarinic receptors presynaptic membrane

Question 10

What are ligands and second messengers

Answer 10

Ligands are molecules that bind to receptors inducing a response in the cell they bind to, second messengers are molecules that convey an intracellular signal from an extracellular ligand binding to a receptor

Question 11

What are the four reasons for signalling between cells

Answer 11

For processing internal and external information, for self-preservation and detecting danger, for voluntary movement and for homeostasis

Question 12

In what four distinct categories can receptors be divided

Answer 12

Ionotropic receptors, G-protein coupled receptors, enzyme linked receptors and intracellular receptors

Question 13

What happens to ionotropic receptor when ligand binds

Answer 13

When a ligand binds to a ionotropic receptor, the conformation of the receptor changes so that it creates a pore through which a specific ion can pass through

Question 14

What are the other names for G-protein coupled receptors

Answer 14

7-transmembrane receptor, G-protein linked receptor

Question 15

In inactive state how is G-protein coupled receptor configured

Answer 15

In the inactive state, the G protein is heterotrimeric and consists of an alpha unit, beta and gamma unit and a bound GDP which form a complex that sits near the transmembrane receptor

Question 16

What three regions does the G-protein consist of

Answer 16

G protein is heterotrimeric and conists of an alpha unit, beta unit gamma unit and is also bound to a GDP molecule

Question 17

What three categories of G-alpha subunits are there and what do they activate

Answer 17

Gaq/11 subunits which activate phospholipase C, Gas subunits which activates adenylyl cyclase and Gai/o which inhibits adenylyl cyclase

Question 18

When can GDP be changed into GTP in G-protein

Answer 18

When a ligand binds to the transmembrane receptor, a G-protein complex can bind and GDP can be exchanged for GTP

Question 19

What is the energy from GTP used for in G-protein

Answer 19

The energy of phosphorylation of GDP is used for Galpha subunit to dissociate from the betagamma subunit

Question 20

Which regions of G-protein bind to target protein in active state

Answer 20

The G-alpha subunit in active state binds to the target protein that induces a signalling cascade, the G-betagamma subunit can also induce a signalling pathway

Question 21

What effect can unbound Beta-gamma subunit of G protein have

Answer 21

This subunit complex can also induce another signalling cascade in the cell

Question 22

How does alpha-subunit become inactive again and what happens to it after that

Answer 22

It is dephosphorylated by internal GTPases and it then associates with a G-betagamma subunit again.

Question 23

How long is G-linked receptor active

Answer 23

G-linked receptor is activated as long as a ligand is bound to the receptor, which could mean that multiple G-proteins become activated by one activated receptor and this causes a signalling cascade

Question 24

What does membrane spanning receptor mean

Answer 24

A membrane spanning receptor has an external surface and internal surface components in the cell membrane that transduces an extracellular signal to inside the cell

Question 25

When do receptors cluster in enzyme-linked receptors

Answer 25

When a ligand binds to the receptor or both receptors, the receptors cluster

Question 26

What happens to clustered receptors to activate them

Answer 26

The clustered receptors become activated by phosphorylation of the cytoplasmic domain of the receptor by enzymes

Question 27

How is signal transmitted beyond activated enzyme-linked receptor

Answer 27

The phosphorylation of the receptor leads to the recruitment and binding of signalling proteins to the cytoplasmic domain and can then activate second messengers to induce signalling cascades within the cell

Question 28

How does enzyme-linked receptor become inactivated again

Answer 28

When phosphatases dephosphorylate the intracellular domain of the receptor, the signal is terminated

Question 29

In what two types can intracellular receptors be divided and what is the distinction

Answer 29

Type I and Type II receptors, which are respectively found in the cytoplasm and the nucleus of the cell. This means that type I receptors must pass nuclear membrane to have effect on gene transcription.

Question 30

What is bound to type I intracellular receptor in inactive state

Answer 30

In inactive state, a type I intracellular receptor is bound to a chaperone molecule called heat shock protein

Question 31

What happens to type I receptor when hormone binds to receptor

Answer 31

When a hormone binds to the type I receptor, the heat shock protein dissociates from the receptor and two hormone-receptor complexes form a homodimer that can enter the nucleus

Question 32

When can hormone-receptor complex enter nucleus

Answer 32

When two hormone-receptor complexes bind to form a dimer, they can be actively translocated into the nucleus where they exert their function

Question 33

What can this homodimer do in nucleus

Answer 33

The homodimer hormone-receptor complex can activate gene transcription by functioning as a transcription factor

Question 34

Where is type II receptor located and what happens after binding to hormone

Answer 34

Type II receptors are directly located within the nucleus bound to the DNA, normally bound to a corepressor, and when they form a hormone-receptor complex this complex functions as transcription factor by recruiting coactivators for gene transcription