Unit 1 KA4 Flashcards
(a)
How do multicellular organisms singal between cells?
Give examples too
They use extracellular signalling molecules
* steroid
* peptide
* neurotransmitters
(a)
What are receptor molecules of target cells?
Proteinds with a specific binding site for a specific signal molecule
(a)
What does binding do and what is the impact of it to a receptor
It changes conformation of receptor which initiates a response within the cell
(a)
What is the implication of different cells producing specific signals for a receptor?
They can only be detected and responded to by cells with the specific receptor attached
Signalling molecules may have different effects on different targets cell types due to differences in the intracellular signalling molecules and pathways involved
In response to the same signal what may different cell types show?
a tissue specific response to the same signal
(b)
How do hydrophobic signalling molecules bind to intracellular receptors?
Can diffuse directly through the phospholipid bilayers (as they are also hydrophobic)
(b)
Transcription factors
Definition
hydrophobic singalling molecules
proteins that when bound to DNA can either stimulate or inhibit initiation of transcription
(b)
Examples of hydrophobic signalling molecules
Oestrogen
Testosterone
(b)
Where to steroid hormones bind to specific receptors?
cytosol or nucleus
(b)
What happens to the hormone receptor complex when it moves to the nucleus?
It binds to specific sites on DNA (HREs) and affects gene expression
binding at these sites affects rate of transcription
steroid binding effects gene expression of many genes
(b)
What are HREs?
Hormone Response elements
(specific DNA sequences that hormone receptor complex binds to)
(c)
What do hydrophilic signalling molecules bind to and do not enter?
bind to transmembrane receptors
do not enter the cytosol
(c)
What are examples of hydrophobic extracellular signalling molecules?
Peptide hormones
Neurotransmitters
(c)
What happens to a transmembrane receptor when a ligand binds to extracellular face?
changes conformation
(c)
What happens after the ligand binds to extracellular face?
- signal molecule does not enter the cell
- signal is transduced across the plasma membrane
What do transmembrane receptors act as?
signal transducers by converting the extracellular ligand-binding event into intracellular signals which alters the behaviour of the cell
(c)
What do transduced hydrophillic signals often involve?
how do they give signals acroos the membrane
G-proteins or cascades of phosphorylation by kinase enzymes
(c)
What do G-proteins do?
relay signals from activated receptors (r are bound to a sig. mol.) to target proteins such as enzymes and ion channels
What do phosphorylation cascades allow?
allow more than one intracellular signalling pathway to be activated
(c)
What do phosphorylation cascades involve?
and what do they result in
- one kinase activates the next in the sequence
- can result in the phosphorylation of many proteins as a result of the original signalling event
(c)
What does the binding of the peptide hormone insulin result in?
- causes conformational change that triggers phosphorylation of receptor
- Intracellular signalling cascade that triggers recruitment of GLUT4 (glucose transporter proteins)
- Starts a cascade that leads to GLUT4 containing vesicles being transported to cell membrane
(c)
In relation to receptors
Type 1 Diabetes
Type 2 Diabetes
Type 1 - failure to produce insulin
Type 2- loss of receptor function
(c)
Type 2 diabetes
Association and What and why improves condition
- associated with obesity
- exercise triggers recruitment of GLUT4 can improve uptake of glucose to fat and muscle cells
(di)
What is 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
di)
What is action potential?
A wave of electrical excitation along a neuron’s plasma membrane
di
How do neurotransmitters initiate a response?
binding to their receptors at a synapse
di
What type of receptors are neurotransmitters?
Ligand-gated ion channels
di
How is the opening of voltage-gated sodium channels triggered?
Via depolarisation of the plasma membrane as a result of the entry of +ve ions
after the opening further depolarisation occurs
di
What is depolarisation?
a change in the membrane potential to a less negatie value inside
di
What restores the resting membrane potential?
Inactivation of the sodium channels and opening of potassium channels
di
What does the binding of a neurotransmitter trigger?
- the opening of ligand-gated ion channels at a synapse
- ion movement occurs
- depolarisation of plasma mem
- opening of sodium ions enter cell down electro chem gradient
- rapid and large change in membrane potenital
- quickly after Na channels inactivate
- Voltage gated K channels allow K+ to ove out
- restores membrane resting potential
di
What does depolarisation of a patch od membrane cause?
Causes neighbouring regios of membrane to depolarise and go through same cycle as adjacent voltage-gated Na channels are opened
di
What happens when the action potential reaches the end f the neuron?
causes vesicles containing neurotransmitter to fuse with the membrane
releases neurotransmitter which stimulates a response in a connecting cell
di
What does the restoration of the resting membrane potential allow?
Allows the inactive voltage gated Na channels to return to a conformation that allows them to open in response to depolarisation of the membrane
di
How are ion conc. gradients re-established?
By the Na-K pump which actively transports excess ions in and out of the cell
di
Following repolarisation what happens to the Na+ and K+ conc. gradient?
they are reduced
di
What restores the Na K ions back to resting potential?
The Na-K pump
dii
Retina
Area within the eye that detects light
contains 2 types of photoreceptor cells:rods and cones
dii
Rods
function
function in dim light
do not allow colour perception
dii
Cones
function
Responsible for colour vision
only function in bright light
dii
In animals what components form the photoreceptors of the eye
- light-sensitive molecule retinal
- membrane protein opsin
dii
Rhodopsin
In rod cells the retinal opsin complex is called this
dii
What does Retinal do wen it absorbs a photon of light?
- Rhodopsin changes conformation to photoexcited rhodopsin
- a cascade of protein amplifies the signal
- photoexcited rhodopsin activates a transducin (G-protein) (1r->100s G)
- activates PDE (1G->1PDE)
- PDE catalyses the hydrolysis of a molecule called cGMP (PDE —> 1000s cGMP/s)
- results in closure of ion channels in membrane of rod cells, triggers nerve impulses in neurons of retina
dii
What affects the function of ion channels in the membranes of rod cells?
Reduction in cGMP conc. (result of hydrolysis)
dii
What results in rod cells being able to respond to low intensities of light?
A very high degree of amplification
dii
Where do different forms of opsin combine with retinal to give different photoreceptor proteind a different max. sensitivity to specific wavelengths?
Cone cells
dii
what specific wavelengths do photoreceptor proteins have a max sensitivity for?
- Red
- Green
- Blue
- UV
