Unit 1 - Communication and Signalling Flashcards
What are extracellular signalling molecules?
Cues ( growth factors, hormones, neurotransmitters etc) designed to transmit specific information to target cells
What are hydrophobic signalling molecules?
Signalling molecules that can diffuse through membranes, so their receptor molecules can be within the nucleus
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
They can enhance or block binding of RNA polymerase to specific genes, therefore controlling whether a gene is transcribed and expressed
When is the hormone-receptor complex formed?
When steroid hormones bind to specific receptors in the cytosol or the nucleus; they bind to specific sites on DNA and affect gene expression
What is a hormone response element?
A short sequence of DNA within the promoter of a gene that is able to bind to a specific hormone-receptor complex and therefore regulate transcription
What are hydrophilic signalling molecules?
Signalling molecules which are not able to pass through the membrane
What is signal transduction?
The conversion of extracellular signals into an intracellular response
What is a gene protein?
A family of proteins that act as molecular switches inside cells, they are involved in transmitting signals from a variety of stimuli outside a cell to its interior
What is a phosphorylation cascade?
A series in which one kinase activates the next one in a sequence, can result in the phosphorylation of many proteins as a result of the original signalling event
What is GLUT-4?
An insulin-regulated glucose transporter
What is the resting membrane potential?
The difference in ion concentration between the inside and outside the cell
What is an action potential?
A wave of electrical excitation along a neuron’s plasma membrane
What is depolarisation?
An electrical state in an excitable cell whereby the inside if the cell is made less negative relative to the outside than it is at the resting membrane potential.
What is the threshold value?
When the depolarisation reaches about -55mV
What is ion concentration gradient created by?
It is created by ion pump enzyme that transport ionic solutes across the membrane; energy is required to produce a gradient, so the gradient is a form of stored energy.
What is repolarisation?
The restoration of a membrane potential following depolarisation
What is a photon?
The basic unit of light
What are photoreceptor cells?
Cell found in the retina that are capable of phototransduction
What are rod cells?
Photoreceptor cells in the retina that function in dim light and respond to low light intensities; don’t allow colour perception
What are cone cells?
Photoreceptor cells responsible for colour vision, they only function in bright light
What is opsin?
A light-sensitive protein molecule
What is retinal?
A light-sensitive molecule within the eye that binds with opsin to form photoreceptors in the eye
What is rhodopsin?
The retinal-opsin complex in rod cells
What is transducin?
A protein naturally expressed in vertebrate retina rods and cones; important in vertebrate phototransduction
What is cGMP?
A second messenger for visual transduction; it is present in high concentrations in photoreceptor cells
What is phosphodiesterase?
The enzyme that catalyses the hydrolysis of cGMP
How do multicellular organisms signal between cells?
Extracellular signal molecules
What are example of extracellular signalling molecules?
Steroid hormones, peptide hormones, neurotransmitters
What does communication occur through in animals?
Nerve transmission and hormone secretion
What are receptor molecules?
Proteins with a binding site for a specific signal molecules
When a receptor binds to a signal molecule, what happens?
The receptor changes conformation which initiates a response
Why can hydrophobic signals bind to intracellular receptors?
Since they can diffuse directly through the phospholipid bilayer of membranes since the tails of phospholipid bilayers are also hydrophobic and allow molecules to pass across
What are the receptors for hydrophobic signalling molecules?
Transcription factors
Action of steroid hormones (hydrophobic signalling molecules) ?
- Steroid hormones bind to specific receptors in cytosol or nucleus, forms hormone-receptor complex
- Complex moves to nucleus, binds to specific sites on DNA called hormone response elements (HRE).
- Binding at these sites influences rate of transcription
What do hydrophilic signalling molecules do?
Bind to transmembrane receptors and do not enter the cytosol
Examples of hydrophilic signalling molecules
- Peptide hormones
- Neurotransmitters
Action of hydrophilic signalling molecules
- Ligand (hydrophilic signal molecules) binds to transmembrane receptor and receptor changes conformation.
- Signal is then transduced across the plasma membrane
- Transmembrane receptors act as signal transducers by converting extracellular ligand-binding event into intracellular signals
- This alters behaviour of cell
What is transduction?
Process where chemicals or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response
What do G-proteins do?
They relay signals from activated receptors to target proteins such as enzymes and ion channels. Enzymes then catalyse reactions within the cell, ion channels will either open or close to control ion movement
What is a phosphorylation cascade?
A series of events with one kinase activating the next in the sequence. Receptor becomes phosphorylated and in turn phosphorylates cytoplasmic molecules.
What does phosphorylation cascades allow?
Allows more than one intracellular signalling pathway to be activated
What are the 2 hormones involved in blood glucose regulation?
- Insulin
- Glucagon
Process when insulin binds to receptor
- Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor
- Starts a phosphorylation cascade inside cell
- This phosphorylation leads to GLUT-4 containing vesicles being transported to the cell membrane of fat and muscle cells
What is type-1 diabetes caused by and how can it be treated?
A failure to produce insulin in the pancreas.
Treated with regular injections of insulin throughout the day
What is type-2 diabetes caused by and how is it treated?
Caused by loss of insulin receptor function, associated with obesity.
Treated with medications to lower blood glucose levels along with lifestyle changes.
What does exercise trigger?
Recruitment of GLUT-4 so it can improve uptake of glucose to fat and muscle cells
When is there a resting membrane?
When there us no net flow of ions across the membrane
What is nerve transmission?
A depolarisation of the resting potential of a neuron
What does the transmission of a nerve impulse require?
Requires changes in the membrane potential of the neuron’s plasma membrane
When may an action potential be triggered?
If the change in membrane potential is big enough
What is an action potential?
A wave of electrical excitation along a neuron’s plasma membrane
Process of nerve transmission
- Neurotransmitters bind to receptors at synapse which triggers opening of ligand-gated ion channels at synapse
- Positive ion movement occurs and there is depolarisation of plasma membrane
- If sufficient ion movement occurs, and membrane is depolarised beyond threshold value, voltage-gated sodium channels open and sodium ions enter down their electrochemical gradient.
- This leads to rapid and large change in the membrane potential
- Shortly after, sodium channels become inactivated
- Voltage-gated potassium channels open to allow potassium ions to move out of the cell to restore resting membrane potential
What is a neurotransmitter receptor?
Ligand-gated ion channels
What happens when action potential reaches the end of the neuron?
Causes vesicles containing neurotransmitters to fuse with the membrane which releases neurotransmitters which stimulates a response in a connecting cell
What does restoration of the resting membrane potential allow?
Allows inactive voltage-gated sodium channels to return to a confirmation that allows them to open again in response to depolarisation of the membrane
How are ion concentration gradients re-established?
By the sodium-potassium pump, which actively transports excess ions and out of cell
What does the retina do?
Detects light and converts light into electrical energy
Process of retinal response to light
- Retinal absorbs a photon of light and rhodopsin changes conformation to photo excited rhodopsin
- Activates G-protein, transducin. (1 photo excited rhodopsin activates hundreds of G-protein)
- Transducin activates enzyme, phosphodiesterase ( 1 activated G-protein activates 1 PDE )
- PDE catalyses hydrolysis of cGMP, PDE breaks down thousands of cGMP per second
- This reduction in cGMP concentration affects function of ion channels in membrane of rod cells
- Ion channels close, inward leakage of positive ions (Na+) is halted so membrane potential increases
- Hyper-polarisation triggers nerve impulse in neurons in the retina
