Unit 1: Key area 4 Communication and signalling Flashcards
How do multicellular organisms signal between cells
Multicellular organisms signal between cells using extracellular signalling molecules
Name examples of signalling molecules
Steroid hormones, peptide hormones, and neurotransmitters are examples of extracellular signalling molecules.
What are receptor molecules
Receptor molecules of target cells are proteins with a binding site for a specific signal molecule
What does the binding cause and what does this initiate
Binding changes the conformation of the receptor, which initiates a response within the cell
Describe how signalling molecules work
Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor
Why could signalling molecules have different effects on different target cells
Signalling molecules may have different effects on different target cell types due to differences in the intracellular signalling molecules and pathways that are involved
Remember this statement
In a multicellular organism, different cell
types may show a _________ to
the same signal
In a multicellular organism, different cell types may show a tissue-specific response to the same signal
Describe Hydrophobic signalling molecules
Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membranes, and so bind to intracellular receptors
The receptors for hydrophobic signalling molecules are transcription factors
Steroid hormones bind to specific receptors in the cytosol or the nucleus
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression
The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HREs). Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
What are transcription factors
Transcription factors are proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
What are examples of hydrophobic signalling molecules
The steroid hormones oestrogen and testosterone are examples of hydrophobic signalling molecules
Describe hydrophilic signalling molecules
Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol
Transmembrane receptors change conformation when the ligand binds to the extracellular face; the signal molecule does not enter the cell, but the signal is transduced across the plasma membrane
Name examples of hydrophilic extracellular
signalling molecules.
Peptide hormones and neurotransmitters are examples of hydrophilic extracellular signalling molecules.
Describe transduction
Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell
Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes
G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Describe the phosphorylation cascade
Phosphorylation cascades allow more than one intracellular signalling pathway to be activated
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.
Describe insulin and GLUT4
Binding of the peptide hormone insulin to its receptor results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells
Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor. This starts a phosphorylation cascade inside the cell,which eventually leads to GLUT4 containing vesicles being transported to the cell membrane.
What causes Diabetes mellitus
Diabetes mellitus can be caused by failure to produce insulin (type 1) or loss of receptor function (type 2)
Research health effects associated with type 2 diabetes and the success rate of treatment programmes.
What is type 2 diabetes generally associated with
Type 2 is generally associated with obesity
What triggers the recruitment of GLUT4
Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2
Describe the resting membrane potential
Resting membrane potential is a state where there is no net flow of ions across the membrane
What does the transmission of a nerve impulse require
The transmission of a nerve impulse requires changes in the membrane potential of the neuron’s plasma membrane
What is an action potential
An action potential is a wave of electrical excitation along a neuron’s plasma membrane
How do neurotransmitters initiate a response
Neurotransmitters initiate a response by binding to their receptors at a synapse
Describe the structure of neurotransmitters
Neurotransmitter receptors are ligand-gated ion channels.
What does depolarisation of the plasma membrane trigger
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
Explain how Inactivation of the sodium channels and the opening of potassium channels restores the resting membrane potential
Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse. Ion movement occurs and there is depolarisation of the plasma membrane. If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient.
This leads to a rapid and large change in the membrane potential. A short time after opening, the sodium channels become inactivated. Voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential.
What is depolarisation
Depolarisation is a change in the membrane potential to a less negative value inside
What does depolarisation of a patch of membrane cause
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
What happens when the action potential reaches the end of the neuron
When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitter to fuse with the membrane — this releases neurotransmitter, which stimulates a response in a connecting cell
What does the restoration of the resting membrane potential allow
Restoration of the resting membrane potential allows the inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane Ion concentration gradients are reestablished by the sodium-potassium pump, which actively transports excess ions in and out of the cell
What happens after repolarisation
Following repolarisation the sodium and potassium ion concentration gradients are reduced. The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels.
What is the function of the retina within the cell
The retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones
Describe the features/functions of rods and cones
Rods function in dim light but do not allow colour perception. Cones are responsible for colour vision and only function in bright light.
In animals what combined with the light-sensitive retinal and what is formed as a result
In animals the light-sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye
In rods what is the retinal-opsin complex called
In rod cells the retinal-opsin complex is called rhodopsin
What happens to the rhodopsin when Retinal absorbs a photon of light
Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin
What amplifies the signal
A cascade of proteins amplifies the signal
What happens when photoexcited rhodopsin activate. Describe the process
Photoexcited rhodopsin activates a Gprotein, called transducin, which activates the enzyme (PDE) single photoexcited rhodopsin activates hundreds of molecules of G-protein. Each activated G-protein activates one molecule of PDE.
What does PDE catalyse. Describe the process
PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)
Each active PDE molecule breaks down thousands of cGMP molecules per second.
The reduction in cGMP concentration as a result of its hydrolysis affects the function of ion channels in the membrane of rod cells.
After the reduction in cGMP concentration as a
result of its hydrolysis affects the function of
ion channels in the membrane of rod cells, what happens
This results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina
What does a very high degree of amplification result in
A very high degree of amplification results in rod cells being able to respond to low intensities of light
In cone cells, different forms of opsin
combine with retinal to give what?
In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV
