Unit 1.4 - Communication and Signalling Flashcards
What are receptor molecules?
Proteins with a binding site for a specific signal molecule
What response does binding create?
It changes the conformation of the receptor, which initiates a response within the cell
Why do only target cells respond to a specific signal?
Only target cells have receptor molecules for the signalling molecule
Describe a hydrophobic signalling molecule (lipid-soluble? passes through cell membrane? location? types of signals? examples?)
Lipid soluble - yes Passes through cell membrane - yes Location - cytosol Types of signals - steroid hormones Examples - oestrogen and testosterone
Describe a hydrophilic signalling molecule (lipid-soluble? passes through cell membrane? location? types of signals? examples?)
Lipid soluble - no Passes through cell membrane - no Location - extracellular membrane Types of signals - peptide hormones Examples - insulin
What is a hormone-receptor complex?
When a steroid hormone binds to a specific receptor
What is a hormone response element?
The DNA that the hormone-receptor complex binds to when it enters the nucleus
What protein is involved with transduced hydrophilic signals?
G-proteins
Describe the stages of signal transduction.
1 - Hydrophilic signalling molecule binds to the receptor. The signal is transduced.
2 - Binding of a ligand causes a conformational change, activating a G-protein. This can now bind to the target protein.
3 - Intracellular signalling pathway is now activated.
What is an action potential?
A wave of electrical excitation along a neurons plasma membrane
What are neurotransmitters?
Ligand-gated ion channels on synapses
How do neurotransmitters initiate a response and what does this cause?
1 - binding to their receptors
2 - changing conformation
3 - opening their channel and allowing Na+ ions through
This causes depolarisation of the resting potential
How can an actional potential take place?
If sufficient ion movement occurs the entry of positive ions triggers the opening of voltage-gated sodium channels, leading to depolarisation of neighbouring regions and so in, in a domino effect
What happens when the action potential reaches the end of the neuron?
Vesicles containing neurotransmitters fuse with the membrane, the neurotransmitter is released and stimulates a response in the connecting cell
How is the resting membrane potential restored?
When the voltage reaches a high level, the voltage-gated Na+ channels close and return to their original conformation. Voltage-gated K+ channels then open allowing K+ ions to diffuse out of the cell, restoring the resting membrane potential. Na+ channels are in their original conformation and can respond to further depolaisation
How are blood glucose levels maintained?
By a negative feedback system
How does glucose pass into the cells?
By travelling (facilitated diffusion) through transporter proteins called GLUT4 glucose transporters
What does the binding of insulin to its receptor cause?
A conformation changes that triggers phosphorylation of the receptor, this starts a cascade of kinase phosphorylation which eventually leads to GLUT4-containing vesicles to be transported to cell membranes
What effect does the extra GLUT4 transporters have on glucose levels?
It allows them to be controlled
Describe type 1 and 2 diabetes
Type 1 - caused by failure to produce insulin and is often genetic
Types 2 - caused by loss of receptor function and generally associated with lifestyle
What part of the eye is responsible for detecting light?
The retina
Describe the function of rods and cones in the eye
Rods - function in dim light but don’t allow colour perception
Cones - responsible for colour perception but require bright light to function
Where is rhodopsin embedded?
The membranes of rod cells
Why do rod cells have high sensitivity at low light intensities?
The protein cascade provides a high degree of amplification
Describe the process of rhodopsin and nerve impulse
1 - photon of light is absorbed by retinal, conformation change in rhodopsin
2 - changed rhodopsin activates hundreds of G-proteins (transducin) — each one actives a PDE
3 - Each activated PDE catalyses hydrolysis of cGMP so the Na+ channels close
4 - If there is a sufficient build up of the Na+, the membrane becomes hyperpolarised and a nerve impulse is generated
In cone cells, what gives a range of photoreceptor proteins? (each with a particular sensitivity to specific wavelengths)
Different forms of opsin.
