1.4 communication and signalling Flashcards
Extracellular signalling molecules definition
Molecules that a multicellular organism uses to send messages between different cells, which are produced outside the cell.
Types of extracellular signalling molecules
Peptide hormones
Steroid hormones
Neurotransmitter
Nervous communication definition
The transport of electrical signals across neurones.
Hormonal communication definition
The transport of extracellular signalling molecules around the body.
Nervous communication nature of signal
Electrical impulses and neurotransmitter
Nervous communication transmission of signal
Across a neurone
Nervous communication target cell
Any cell with a connection to neurones
Nervous communication time for response to occur
Fast
Nervous communication duration for response
Shorter
Nervous communication extent of response
Localised
(specific)
Hormonal communication nature of signal
Extracellular signalling molecules
Transmission of hormonal communication
Through blood stream
Hormonal communication target cells
Any cell in body
Hormonal cells time for response to occur
Slower
Duration of hormonal communication
Longer
Extent of hormonal communication response
Widespread
Hydrophobic extracellular signalling molecules
Steroid hormones
Hydrophilic extracellular signalling molecules
Peptide hormones and neurotransmitters.
Receptor molecules definition
A molecule with a specific binding site for an extracellular signalling molecule, which changes conformation upon binding with the ligand.
How do receptors on the outside of cells work
A conformational change occurs which initiated a response inside the cell.
Characteristics of receptors
Different cell types produce different signalling molecules
Different receptors will bind to different signalling molecules
Different types of cell tissue with same receptor and signal molecule can trigger different metabolic pathways
Tissue specific response
Where a different cell tissue with the same signalling molecule and receptor will trigger a different intracellular pathway.
Steroid/ hydrophobic signalling molecule process
Leave endocrine gland and travel straight to the cell through bloodstream.
Travel through the plasma membrane.
Bind with receptor inside the cell forming a hormone receptor complex.
The transcription factor will bind with DNA in nucleus
This will then stimulate or inhibit the transcription of DNA.
This will increase or decrease the rate of specific protein production.
Hormone receptor complex
Where a hormone and a receptor bind together
Hormone response elements
Sites on DNA which hormone transcription factors will bind with which will alter the rate of transcription.
Transcription factors
Hormone receptor complexes which bind to DNA at transcription elements.
Steroid hormone examples
Testosterone and oestrogen
Where do steroid hormones bind to receptors
Cytosol or nucleus
Where do hydrophilic and peptide hormones bind to receptors
On the outside of the plasma membrane since they cannot travel through the plasma membrane
Hydrophilic peptide hormones process of communication
Peptide hormone will be released from endocrine gland and travel through blood stream to cell.
Peptide hormone binds to the receptor on outside of the plasma membrane
This will activate a G protein inside the cell converting GDP to GTP.
GTP will phosphorylate the protein and activate the protein.
The activated protein will start a phosphorylation cascade.
Transduction
Where a hydrophilic signalling molecule binds to a receptor and causes a change in the cell behaviour.
Examples of hydrophilic signalling molecules
Neurotransmitters and peptide hormones
Phosphorylation cascades
Where a protein activates another protein by phosphorylating the protein,
What type of proteins are G proteins
Kinases - since they add a phosphate to another molecule activating it.
Blood glucose level hormones
Insulin and glucagon
Blood sugar level decrease process
Blood glucose level is detected
Insulin produced by cells in pancreas.
Insulin binds as a ligand to the receptor molecules outside the plasma membrane.
This activates a G protein inside the cell.
This G protein phosphorylates GDP to GTP.
This GTP will then phosphorylate a protein causing a phosphorylation cascade.
This will recruit Glut 4 vesicles
Glut 4 vesicles will bind to the plasma membrane releasing Glut 4
Glut 4 will then transport glucose into the cell by facilitated diffusion.
Glut 4
A glucose transporter protein which transports glucose into the cell by facilitated diffusion.
Type 1 diabetes
Caused by failure to produce insulin
Type 2 diabetes
Caused by loss of insulin receptor sensitivity
What is type 2 diabetes caused by
Associated with obesity
Treatment for type 2 diabetes
Exercise since Glut 4 recruitment occurs in another metabolic pathway.
Process of a neurone firing
Neurotransmitters will travel across the synapse and bind to ligand gated ion channels on the dendrite’s plasma membrane. These ligand gated ion channels will open and allow for ions to undergo facilitated diffusion into the neurone. If many ligand gated ion channels open at once then the membrane potential will change from -70mv to -55mv, allowing for the threshold to be reached, and this will allow voltage gated Na+ channels to open and allow sodium ions to undergo facilitated diffusion into the cell. This will depolarise the cell, increasing the membrane potential to +40mv. When this occurs the voltage gated sodium channels will close and voltage gated potassium ion channels will open, allowing potassium to diffuse out of the cell (facilitated diffusion). This will allow for the cell to repolarise, which will decrease the cell membrane potential back down to -70mv and potassium channels will close, however the potassium channels will close too slowly and more potassium ions will leave the cell. Causing a hyper-polarisation. The sodium potassium pump will then activate and restore the membrane potential back to -70mv. The sodium potassium pump works by 3 sodium ions binding to an inwards facing high affinity binding site. ATP will then break down into ADP and Pi, which will then phosphorylate the sodium potassium pump, this will cause a conformational change releasing sodium out of the cell. Potassium will then bind to the new high affinity outwards facing binding site on the outside of the plasma membrane. The sodium potassium pump will dephosphorylate, which will allow for a conformational change to occur releasing 2 potassium ions into the cell and reverting the pump back to its original inwards confirmation. The process is then repeated. This depolarisation, depolarisation and hyper-polarisation will cause an electrical signal to travel down the axon to the presynaptic terminal.
Dendrite
The location on a neurone where the neurotransmitters bind to their ligand gated ion channels
Axon
The location in a neurone where an action potential will travel down.
Presynaptic terminal
The location in a neurone where the neurotramitters are released to travel across the synapse
Depolarisation
Where sodium ions will enter a cell through voltage gated ion channels increasing the membrane potential form -55 to +40
Repolarisation
Where potassium ions will travel out of a cell through voltage gated ion channels decreasing the membrane potential from +40 to -70
Hyperpolarisation
Where voltage gated ion channels in potassium will close to slowly - resulting in the membrane potential decreasing below -70 mv
How are ion gradients re established
Sodium potassium pump
Action potential
Where a neurone depolarises, repolarises and then hyperpolarises causing an electrical signal down the axon .
How does an action potential begin
With ions increasing the membrane potential to -55 mv
Types of ions in neurones
Inhibitory and excitatory ions
Inhibitory ions
Ions which decrease the membrane potential of a neurone away from the depolarisation threshold
Excitatory ions
Ions which increase the membrane potential towards the depolarisation threshold.
Area of the eye which detects light
Retina
Types of cells in the retina (photoreceptor cells)
Cone cells and rod cells
Rod cells function
Detect dim light without colour perception
Cone cells
Detect high intensity light with colour perception
Rhodopsin
A complex formed from a retinal prosthetic group and an opsin molecule
Different types of opsin
Cone cells have different types of opsin, rod cells have one type of opsin
Process of nervous impulse behind eye
Retinal group absorbs light and conformational change from rhodopsin to photoexcited rhodopsin occurs.
This activates the G protein transducin
This excites the enzyme PDE
PDE converts cGMP to GMP
cGMP concentration decrease is detected by sodium ion channels closing sodium ions channels to close.
This will cause a hyperpolarisation as the membrane potential decreases.
This will allow the neurones behind the eye to fire and send electrical impulses to other neurones.
Adaptation of cone cells for high light intensity
Have different forms of opsin to absorb different wavelengths of light at maximum intensity
Quantities for eye process
photo- excited rhodopsin will activate hundreds of G proteins.
1 G protein will excite 1 PDE
PDE will break down thousands of cGMP each second.
