Chapter 9: Cell Communication Flashcards
intercellular signalling
communication between cells
intracellular signalling
communication within a cell
signalling cell
cell that delivers signals to other cells
ligand
molecule that binds to another specific molecule
receptor
protein that can receive ligands from signalling cells
target cell
cell that has a receptor to receive ligands from signalling cells
What are the four categories of chemical signalling in multicellular organisms?
Paracrine signalling, endocrine signalling, autocrine signalling and direct signalling across gap junctions
paracrine signal
signalling between nearby cells
How do paracrine signals reach the target cell?
They diffuse through the extracellular matrix towards the target cell
What happens to a paracrine signal after it has reached its target cell?
It is degraded by enzymes or removed by neighbouring cells
Why do paracrine signals last a short time?
Removing the paracrine signal quickly reestablishes the concentration gradient so signals can travel freely again
synaptic signal
chemical signal that travels between nerve cells
neurotransmitter
ligand released by nerve cells
chemical synapse
small space between nerve cells
How are signals propagated through nerve cells?
They are propagated by electrical impulses
How are signals transferred from nerve cell to nerve cell?
Neurotransmitters are released from the signalling nerve cell to the target nerve cell
What happens to neurotransmitters after they have been received by the target cell?
They are destroyed by enzymes or are reabsorbed for further use
What type of chemical signalling is synaptic signalling?
Paracrine signalling
endocrine signal
signalling between cells that are very far away
endocrine cell
cells that secrete and send hormones in endocrine signalling
hormone
signalling molecules that are the ligands in endocrine signalling
How do hormones travel from the signalling cell to the target cell?
They travel through the bloodstream
How is endocrine and paracrine signalling different?
- Endocrine signalling is slower and longer lasting
2. Endocrine signalling ligands are found in lower concentrations
autocrine signal
when the signalling cell binds to the ligand that it produces
What cells are affected in autrocrine signalling?
The signalling cell and sometimes the neighbouring cells are affected
When does autocrine signalling usually occur?
During early development of an organism to ensure cells develop correctly
intracellular mediator
small molecule that transfers signals inside a cell
How can intracellular mediators diffuse to other cells?
Through gap junctions and plasmodesmata
internal receptor
receptors that are found in the cytoplasm of a cell
In what process are internal receptors often involved in?
They are used to regulate mRNA synthesis
How do internal receptors control DNA transcription?
When a ligand binds to an internal receptor, a DNA binding site is exposed on the receptor, which binds to DNA in the nucleus to promote transcription
cell-surface receptor
cell surface integral proteins that bind to external ligands
How much of the plasma membrane does a cell-surface receptor span?
They are all transmembrane receptors
What are the three components of a cell-surface receptor?
An extracellular, transmembrane and intracellular domain
What are the three types of cell-surface receptors?
Ion channel-linked receptors, G-protein-linked receptors and enzyme-linked receptors
ion channel-linked receptor
channel proteins that have a binding site for ligands to allow ions through
G-protein-linked receptor
receptor that activates G-proteins to transmit signals to membrane components
How many transmembrane domains does a G-protein-linked receptor have?
Seven
G-protein-coupled receptor
G-protein-linked receptor that has a G-protein bound to it
heterotrimeric G-protein
G-protein made up of an alpha, beta and gamma subunit
How are G-proteins activated?
An inactive G-protein binds to the receptor, and when a signalling molecule binds to the receptor, GDP in the alpha subunit is released and replaced with GTP, then the activated G-protein is split into an alpha and beta-gamma fragment to be used
How does an active G-protein become inactive?
The GTP in the alpha subunit is hydrolysed to GDP, and the alpha and beta-gamma fragments come back together to form an inactive G-protein
What are the main symptoms of cholera?
Dehydration and diarrhoea
What bacterium is responsible for cholera?
Vibrio cholerae
Which part of the body does Vibrio cholerae invade?
The small intestines
How does Vibrio cholerae invade the small intestines?
It produces a toxin called choleragen which modifies a G-protein to be constantly active and leads to water loss from the body
enzyme-linked receptor
receptors that have intracellular domains that interact directly with an enzyme or is an enzyme itself
What is the transmembrane domain of an enzyme-linked receptor like?
It is a single alpha-helical region spanning the membrane
How does an enzyme linked receptor work?
When a ligand binds to the extracellular domain, a signal is transferred through the membrane to activate the enzyme
receptor tyrosine kinase
enzyme-linked receptor that phosphorylates tyrosine residues to transmit a signal
How does a receptor tyrosine kinase work?
Ligands bind to two nearby receptor tyrosine kinases which are dimerised and the tyrosine residues are phosphorylated for a cellular response
What type of molecules are the main small hydrophobic ligands?
Steroid hormones
What is the main female sex hormone?
Estradiol
estrogen
group of steroid hormones in the female body
What is the main male sex hormone?
Testosterone
What is the precursor to all steroid hormones?
Cholesterol