intercellular signalling Flashcards
Why do cells need to communicate?
cells need to be able to coordinate their behaviour
What are the types of molecules used as intercellular signals?
- proteins
- peptides
- small chemicals
- dissolved gases
What is the signalling molecule that binds to a receptor called?
a ligand
What conditions are necessary for a cell to respond to a signal?
- ligand must be present
- responding cell must have corresponding receptor
- receptor must be correctly coupled to intracellular signalling pathway
What are the 3 main categories of membrane receptors?
- receptors linked to ion channels
- G protein coupled receptors (GPCRs)
- receptors linked to enzymes
Which signal molecules can cross the cell membrane and bind directly to receptors inside?
- dissolved gas (e.g nitric oxide)
- hydrophobic molecules (e.g steroid hormone cortisol)
Where does adrenaline cause different reactions?
- contraction of smooth muscle cells in blood vessels supplying the gut
- relaxation of smooth muscle cells in blood vessels supplying skeletal muscles
How can adrenaline cause two different reactions?
- different adrenergic receptors
- alpha = contraction
- beta = relaxation
What are the types of signals?
- endocrine
- paracrine
- neuronal
- autocrine
- juxtacrine
Which signal is long range (meters)?
endocrine signals
Which signals are short range (micrometers)?
- paracrine
- neuronal
- autocrine
- juxtacrine
What is a cortisol and where is it released from?
- steroid hormone
- released by adrenal gland on kidneys
How does the stress response work?
- glucocorticoid receptor (GR) activates and suppresses gene expression
Give examples of endocrine signalling
- stress response
- insulin/glucagon
How do paracrine signals work?
signalling molecules released from one cell and diffuse locally to neighbouring cells
What are some examples of PROTEIN paracrine signals?
- cytokines (immune response)
- platelet-derived growth factor (cell proliferation)
Give an example of an amino acid derivative paracrine signal
histamine (local inflammation)
Give an example of a dissolved gas paracrine signal
nitric oxide (relaxes smooth muscle, dilates blood vessels)
What is nitric oxides target enzyme and where is it produced from?
- guanylate cyclase
- produced from arg when blood vessel wall endothelial cells are stimulated by acetylcholine
Describe the process of NO as a signal?
- binds do guanylyl cyclase, turns nucleotide GTP into cyclic GMP
- cyclic GMP causes smooth muscle cells to relax (increases blood flow)
- short lived effect, cyclic GMP quickly hydrolysed to GMP by phosphodiesterase
State a clinical use of nitric oxide?
- for angina
- administer nitroglycerin
- converts to NO in the body by mitochondrial aldehyde dehydrogenase (ALDH2), improving blood flow to coronary arteries
Describe neuronal signalling
neurotransmitters travel across synaptic gap to adjacent target cell
Give examples of neurotransmitters
- adrenaline
- acetylcholine
- serotonin
Describe autocrine signalling
cells secrete signalling molecules that bind to their own receptors to make change in their own behaviour
What is juxtacrine signalling
immediate neighbours signal to each other via membrane bound molecules
What are the two types of juxtacrine signalling
- gap junctions
- contact dependent receptor ligand binding
Describe gap junctions in juxtacrine signalling
channels form between cells allowing diffusion of small molecules such as ions, nucleotides and sugars
How are the gap junctions formed in juxtacrine signalling?
- by channels called connexons (consists of 6 protein subunits)
What are some synthetic hormones that activate the glucocorticoid receptor?
- hydrocortisone (cortisol)
- prednisolone
- dexamethasone
What does GTP stand for?
guanosine triphosphate
What does cGMP stand for?
cyclic guanosine monophosphate
How many types of connexon subunits exist?
20
How are gap junctions useful in the heart?
gap junctions between heart muscle cells allow waves of electrical excitation to pass
quickly through the tissue
How are gap junctions important in child birth?
appear in the myometrium of the uterus towards the end of pregnancy and help coordinate uterine contractions
