1.4 Flashcards
How do multicellular organisms signal between cells?
Using extracellular signalling molecules
What are receptor molecules of target cells
Proteins with a binding site for a specific signalling molecule
What initiates a response in a cell
Binding causes a change in conformation of the receptor
Cells produce specific what?
Signals
When a cell produces a specific signal, how can it be detected and responded?
By a specific receptor
In a multicellular organism, different cell types show a what to the same signal?
Tissue specific response
What can hydrophobic signalling molecules do that allow them to bind to intracellular receptors?
They can diffuse straight through the phospholipid bilayer
Receptors for hydrophobic signally molecules are described to be what?
Transcription factors
What are examples of hydrophobic signally molecules?
Steroid hormones that are oestrogen and testosterone
Steroid hormones bind to receptors in the what?
Cytosol or nucleus
Whereas the hormone receptor complex moves to the nucleus what happens?
It binds to specific sites on DNA and affect gene expression
What do hydrophilic signally molecules bind to
Transmembrane receptors and DO NOT ENTER THE CTYOSOL
When do transmembrane receptors change conformation
When a ligand binds to extracellular face
What happens to the signal, when the ligand binds to the transmembrane receptors making a change in conformation, as it can not enter the cell?
Signal is Transduced across plasma membrane
What do transmembrane receptors act as?
Signal transducers
What do transduced hydrophilic signals involve?
G proteins or cascades of phosphorylation by kinase enzyme
What does phosphorylation cascades do ?
Allows more than one intracellular signalling pathway to be activated
Explain the insulin binding
Peptide hormone insulin binds to the receptor which makes a intracellular signalling cascade that triggers recruitment GLUT 4 glucose transporter to the membrane of fat and muscle cells
Describe type 1 diabetes
Diabetes mellitus can be caused by a failure to produce insulin
Describe type 2 diabetes
Loss of receptor function
What can exercise do to people with type 2 diabetes
Allow recruitment of GLUT 4 and improve uptake of glucose to fat and muscle cells
State the term for when there’s no net flow of ions across the membrane?
Resting
What does the transmission of a nerve impulse require?
A change in membrane potential of neurons plasma membrane
What is a action wave
A wave of electrical excitation along a neurons plasma membrane
How do neurotransmitters initiate a response
By binding to their receptors at the synapse
What causes a depolarisation of the plasma membrane
A entry of positive ions trigger a opening of voltage gated sodium channels and further depolarisation occurs
What restores the membrane potential?
The inactivation of sodium channels and opening of potassium channels
What makes a depolarisation of a patch of neighbouring regions of membrane to depolarise and go through the same cycle?
Opening of sodium channels
What happens when the action potential reaches the end of the neuron?
Vesicles containing nuerotransmitter fuse with the membrane and stimulates a reactors in the cell as it is released
What does the restoration of the resting membrane allow?
Allows inactive voltage gated sodium channels to return to a conformation which allows them to open again in response to a depolarisation
What does the sodium potassium pump do for nerve transmission
Re-establishes ion concentration gradients by actively transports excess ions in and out of cell
Where’s the bit in the eye that detects light
Retina
What type of photoreceptor cells does the retina contain
Rods and cones
What type of molecule is the retinal
Animal Light sensitive
What type of molecule is opsin
Membrane protein
What’s the rod cell molecule called when retinal and opsin combines
Rhodopsin
What happens when retinal absorbs a photon
Rhodopsin changes conformation to photo-excited rhodopsin
A cascade of protein does what
Amplifies the signal
What does photoexcited rhodopsin activate
G protein (transducin)
What does G protein (transducin) activate
PDE (phosphodiesterase)
PDE catalyses the hydrolysis of what molecule?
cGmp
What triggers a nerve impulse in neurons in the retina
Closure of ion channels in the membrane of rod cells
How can rod cells respond to low intensities to light
Very High degree of amplification
How are different photoreceptor proteins with maximal sensitivity to specific wavelengths created
In cone cells, different forms of opsin combine with retinal
