Unit 1: KA4 - Communication and Signalling Flashcards
What does communication in multicellular organisms involve?
Producing extracellular signalling molecules.
What effect does binding with a receptor have?
A conformational change in the receptor, which initiates a response within the cell.
What must cells possess to detect a signal?
A specific receptor.
Describe the term ‘tissue-specific response’
In a multicellular organism, different cell types may respond differently to the same signal molecule.
How do Hydrophobic signals bind to receptors?
Hydrophobic signal molecules diffuse through the phospholipid bilayer and bind with specific receptors in the cytosol or the nucleus to form the hormone-receptor complex.
Name the receptors for a hydrophobic signalling molecule.
Transcription factors.
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
Name examples of hydrophobic signalling molecules.
Steroid hormones: Estrogen and Testosterone
What happens after the formation of the hormone-receptor complex?
It moves to the nucleus, where it binds to specific sites on DNA, influencing transcription.
What parts of DNA does the hormone-receptor complex bind to?
Hormone Response Elements (HREs)
How do hydrophilic signalling molecules bind to receptors?
Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol.
Name examples of hydrophilic signalling molecules.
Peptide hormones
Neurotransmitters.
What happens to receptors after binding with hydrophilic signalling molecules?
A conformational change in the transmembrane protein.
How do transmembrane receptors act as signal transducers?
Transmembrane receptors act as signal transducers by converting the extracellular ligandbinding event into intracellular signals, which alters the behaviour of the cell.
What do transduced hydrophilic signals often involve?
G proteins
Cascades of phosphorylation by kinase enzymes
What is the function of G-proteins?
To relay signals from activated receptors to target proteins.
What is the function of a phosphorylation cascade?
To allow more than one intracellular signalling pathway to be activated (amplified signal).
What is the function of the peptide hormone insulin?
To create an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter to the membrane of fat and muscle cells.
Describe the differences in diabetes types.
Type one is caused by the failure to produce insulin.
type two is caused by the loss of receptor function.
Which diabetes type is generally associated with obesity?
Type two
What does exercise do for those with type 2 diabetes?
Can trigger the recruitment of GLUT4, therefore improving glucose uptake in fat and muscle cells.
What is resting membrane potential?
Resting membrane potential is a state where there is no net flow of ions across the membrane.
What is required for the transmission of a nerve impulse?
Changes in the membrane potential of the neuron’s membrane.
Define the term action potential.
An action potential is a wave of electrical excitation along a neuron’s plasma membrane.
What happens between neurons transmitting a signal?
When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitters to fuse with the membrane — this releases neurotransmitters which stimulate a response in a connecting cell.
What is depolarisation?
The change in the membrane potential to a less negative value inside.
What is the result of depolarisation from the neurotransmitter?
Depolarisation of the plasma membrane as a result of the entry of positive ions triggers the opening of voltage-gated sodium channels, and further depolarisation occurs.
What does a neurotransmitter do?
It binds to a ligand gated channel causing it to open and allowing ions to enter, depolarising the membrane.
How does the signal travel along a neuron?
Depolarisation of a patch of membrane causes neighbouring regions of membrane to depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened.
How is the resting membrane potential restored?
The sodium channels are deactivated after a short time, and voltage gated potassium channels are opened and potassium ions move out of the neuron.
What does restoring the resting membrane potential allow?
This allows the inactivated sodium channels to return to a confirmation which allows them to be activated again.
How are ions gradients re-established after repolarisation?
Sodium potassium pump.
Which area of the eye detects light?
Retina
What type of cells does the retina contain?
Two types of photoreceptor cells:
- Rod Cells
- Cone Cells
What do Rod cells do?
- Sensitive to changes in light intensity
- Function in low light
What do Cone cells do?
- Only function in bright light
- Particularly sensitive to specific colours/wavelengths
What is retinal?
The light sensitive prosthetic group.
What are the photoreceptors of the eye made of?
Retinal is the prosthetic group covalently bonded to a membrane protein called opsin.
What is the photoreceptor in rod cells called?
rhodopsin
What happens once Retinal absorbs a photon of light?
Rhodopsin changes conformation to become ‘photoexcited rhodopsin’ and a cascade of G proteins amplify the signal.
What G proteins are activated by photoexcited rhodopsin?
Transducins
What enzyme does a single transducin activate?
Phosphodiesterase
What is Phosphodiesterase’s function?
PDE catalyses the hydrolysis of cyclic GMP molecules, resulting in the closure of ion channels, causing a nerve impulse.
What gives rod cells high sensitivity at low levels of light?
high degrees of amplification
In what way are cone cells different?
Retinal combines with different forms of opsin to give photoreceptor proteins for specific wavelengths of light
