Unit 1 - Communication and Signalling Flashcards
What do multicellular organisms use to signal between cells?
Extracellular signalling molecules.
Give 3 examples of extracellular signalling molecules.
Steroid hormones, peptide hormones and neurotransmitters.
What are receptor molecules of target cells and how do they initiate a response within the cell?
They are proteins with a binding site for a specific signal molecule.
Binding changes the conformation of the receptor, which initiates a response within the cell.
Why might signalling molecules have different effects on different target cell types?
Due to differences in the intracellular signalling molecules and pathways that are involved.
What are hydrophobic molecules?
Molecules that are repelled by water. Also known as non-polar.
What type of signalling molecules can diffuse directly through phospholipid bilayers?
Hydrophobic signalling molecules.
What type of receptors do hydrophobic signalling molecules bind to?
Intracellular receptors called transcription factors.
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
Give 2 examples of hydrophobic signalling molecules.
Steroid hormones oestrogen and testosterone.
Where do steroid hormones bind to specific receptors?
In the cytosol or the nucleus.
What happens to a steroid hormone after it has bound to its specific receptor?
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression.
What are the specific sites on DNA that the steroid hormone-receptor complex binds to?
Specific DNA sequences called hormone response elements.
What does binding of a hormone-receptor complex to hormone response elements (HREs) affect?
Influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
What are hydrophilic molecules?
Molecules that are attracted to water and tends to be dissolved by water. Also known as polar molecules.
What type of receptors do hydrophilic signalling molecules bind to?
Transmembrane receptors.
Give 2 examples of hydrophilic extracellular signalling molecules.
Peptide hormones and neurotransmitters.
What happens when hydrophilic signalling molecules bind to transmembrane receptors?
Transmembrane receptors change conformation. The signal molecule does not enter the cell but the signal is transduced across the plasma membrane.
What is transduction?
Process by which a chemical or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response.
How do transmembrane proteins act as signal transducers?
By converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
What do transduced hydrophilic signals often involve?
G-proteins or cascades of phosphorylation by kinase enzymes.
What do G-proteins do?
Relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
How many intracellular signalling pathways do phosphorylation cascades allow to be activated?
More than one.
What do phosphorylation cascades involve?
A series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
What does binding of the peptide hormone insulin to its receptor result in?
Conformational change that triggers phosphorylation of the receptor. This starts a phosphorylation cascade inside the cell that triggers the recruitment of GLUT4 proteins to the cell membrane of fat and muscle cells.
What is type 1 diabetes mellitus caused by?
Failure to produce insulin.
What is type 2 diabetes mellitus caused by?
Loss of receptor function.
What is type 2 diabetes mellitus generally associated with?
Obesity.
Why can exercise help type 2 diabetes mellitus?
Exercise triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells.
What is a nerve impulse?
A signal transmitted across a nerve fibre.
What is the resting membrane potential?
State where there is no net flow of ions across the membrane.
What does the transmission of a nerve impulse require?
Changes in the membrane potential of the neuron’s plasma membrane.
What is an action potential?
A wave of electrical excitation along a neuron’s plasma membrane.
What are neurotransmitters?
Chemicals that transmit a signal across a synapse.
How do neurotransmitters initiate a response?
By binding to their receptors (ligand-gated ion channels) at a synapse.
What is depolarisation?
A sudden change in membrane potential (usually from a negative to positive internal charge).
What does depolarisation of the plasma membrane as a result of the entry of positive ions trigger?
Triggers the opening of voltage-gated sodium channels and further depolarisation occurs.
What restores the resting membrane potential?
Membrane repolarisation from the inactivation of the sodium channels and the opening of voltage-gated potassium channels.
What are neurotransmitter receptors?
Ligand-gated ion channels.
What must voltage/action potential reach to start membrane depolarisation?
A threshold value
What is hyperpolarisation?
A lowered membrane potential caused by the efflux of potassium ions and closing of the potassium channels.
What is membrane depolarisation caused by?
A rapid rise in membrane potential caused by opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions.
What does depolarisation of a patch of membrane cause neighbouring regions of membrane to do?
Depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened.
What happens when the action potential reaches the end of the neuron?
Vesicles containing neurotransmitter fuse with the membrane - this releases neurotransmitter which stimulates a response in a connecting cell.
How are ion concentration gradients re-established?
The sodium-potassium pump actively transports excess ions in and out of the cell.
What is the retina?
The area within the eye that detects light.
What are the two types of photoreceptor cells that retina contains?
Rods and cones.
What are rod cells?
Cells that function in dim light but do not allow colour perception.
What are cone cells?
Cells that are responsible for colour vision and only function in bright light.
What is the retinal-opsin complex called in rod cells?
Rhodopsin.
In animals, what is retinal combined with to form the photoreceptors of the eye?
Opsin.
What happens when retinal absorbs a photon of light?
Rhodopsin changes conformation to photoexcited rhodopsin and a cascade of proteins amplifies the signal.
What happens after rhodopsin becomes photoexcited rhodopsin?
Photoexcited rhodopsin activates a G-protein, called transducin, which activates the enzyme phosphodiesterase (PDE)
