Molecular Neuroscience Flashcards
Why is the brain described as being a non-vital organ?
As if you are brain dead you can survive
Where does transcription and translation occur?
What have promotor studies shown?
- Identifies mouse mutants
- Identifies disease forming mutations in humans
Which of the following are regulated by nerve activity?
- Gene expression in DNA
- Maturation in RNA
- ALternate splicing in RNA
- protein function
All of them are regulated by nerve activity
For the following flow, what does each split into?
- DNA
- RNA
- Proteins
- Protein function
Whats required for Glutamate to turn into GABA?
Glutamate decarboxylase
Tell me about glutamate
- A naturally occuring AA, can get from diet
- The most abundant and excitatory AA in the brain
Tell me about GABA
- Has to be synthesised, not occuring naturally
- An inhibitory AA
What is the GAD gene recognised by? What is this to ensure?
GAD gene is recongised by transcription factors to ensure gene is selectivity expressed in GABA neurons
Whats the difference between enhancers and repressors?
Enhancers: increase the rate of transcription of genes
Repressors: Decrease the rate of transcription
What is cytoskeleton first born ?
Born as a non-neuronal cell mature and cells-develop processes
In the cytoskeleton; polarity of processes (tend to be ended)
What does the axon and dendrite form?
Axon: giving the presynaptic nerve terminal
Dendrite: Giving the postsynaptic nerve terminal
How does the cytoskeleton retain its shape?
Why is it important?
Retain this shape basic polarity static view but actually they are highly dynamic
Cytoskeleton is the important molecular component
What is the cytoskeleton made up of?
Microtubules
Actin filaments
Intermediate filaments
What dimers are the cytoskeleton made up of?
Alpha and beta dimers build the hollow tube giving a +ve and -ve end
What monomers make the F-actin filaments ?
G-actin monomers
How is the following arranged in a neuron?
- actin cytoskeleton
- Microtubules in axon and dendrite
- Neurofilament
What regulatory proteins are present?
- Dendrites use both orientations of microtubules
- Molecules define shape of neuron
- Associated protein found in sub compartments
What do kinesins and other motors do?
Move things around
What do kinesins bind to?
- cargo or proteins that need to be transported
- binds to microtubules
What do kinesins use?
ATP activity
What do kinesins walk along and where do they move proteins?
Kinesins move along the microtubule
They move proteins to extremities of the processes where the major signalling happens
Is kinesin a motor protein?
yes
What do Dyneins do?
They recognise mictotubules and move from +ve to -ve end (retrograde transport)
What does the Na+/K+ ATPase pump, pump?
3 Na+ out
2 K+ in
What are the levels (mM) of sodium inside and outside of the cell?
More sodium outside (142 mM) than inside (10mM)
What are the levels of potassium (mM) inside and outside of the cell?
More potassium inside (140mM) than outside (4mM)
What the major anion in the cell and what are its levels inside and outside of the cell?
Major negative ion chloride (Cl- is an anion) is higher outside (103mM) inside (4mM)
What is the minor ion in the cell and its levels (mM) inside and outside of the cell?
Minor ion Calcium outside (2mM) very low inside (100 nM)
What is the RMP set up by?
RMP is set up by a leak of K+ in the membrane, not by the ATPase ion pump
What two types of communication are used for intercellular communication?
- electrical communication
- chemical communication
What is the sodium channel made up of?
one protein sequence that contains 4 domains which are linked via a single polypeptide chain in order to make an ion channel
What does each domain of the sodium channel have?
a voltage sensor and 1/4 of the pore
For Na+ channels, whats the treshold for activation and inactivation?
Activation= -50mV
Inactivation= 0 mV
What are potassium channels made up of?
Made up of one protein sequence that contains 1 domain
made of isolated polypeptide chains
What does each potassium channel domain have?
A voltage sensor and 1/4 of the pore. Come together in a tetramer to make a functional channel
Whats the threshold for activation and inactivation in potassium channels?
Activation: 0 mV
Inactivation: -50 mV
Do K+ and Na+ open at the same RMP?
No
Tell me about how an action potential arises and the different voltages seen and what ion channels open/close?
- Voltage channels are closed and the Potassium (K+) leak channel and the sodium (Na+) pump maintain the resting membrane potential of -70 mV. The Sodium/Potassium Pump (ATPase) is responsible for maintaining the membrane potential at -70mv, the protein actively pumps three sodium ions out of the cell and pumps two potassium ions into the cell.
- The neurone becomes stimulated. The voltage gated sodium channels begin to open and the membrane potential begins to slowly depolarises and sodium enters the cell down its concentration gradient. All the voltage-gated Sodium channels open when the membrane potential reaches around -55 mV and there’s a large influx of Sodium, causing a sharp rise in voltage. As the potential nears +30mV, the rate of depolarisation slows down as the voltage-gated Sodium channels become saturated and inactivate, preventing further sodium ions from entering the cell.
- Voltage gated potassium channels open, and potassium leaves the cell down its concentration gradient. The depolarization of the cell stops and repolarisation can occur through these voltage-gated Potassium channels.
- Voltage gated sodium channels are completely deactivated and potassium floods out through the voltage gated potassium channels,
- Voltage gated potassium channels are slow to close, and therefore hyperpolarisation occurs. This is where the membrane potential drops below the resting potential of -70 mV as potassium continues to leave.
- Once the voltage gated potassium channels close, the resting state can be re-established through the Potassium leak channel and Sodium pump.
What is the speed of the ion channels opening/closing dependent on?
Speed is intrinsic to protein structure. The protein structure controls the speed in which the proteins react to membrane potential change
What are the two ways to bridge the synaptic gap?
What are the principles of chemical transmission?
What are the stages to chemical transmission?
- Stimulated neuron opens ion channels including those that allow Ca2+ into nerve terminal.
- Ca2+ is sensed. Recognized by a protein that binds Ca2+ and changes its conformation (Synaptotagmin).
- Change in conformation allows proteins SNARE proteins to promote fusion via a vesicle/plasmamembrane protein complex.
- Vesicle fuses with the plasma membrane, NT released and diffuses into the synaptic cleft.
- Receptors bind NT and these proteins are ion channels.
- NT binding opens (or is gates) receptor channel, allows ions to flow and change distribution across membrane.
- Excite by depolarizing the membranes {positive signal}.
- Inhibit by hyperpolarizing the membrane {negative signal}.
- Chemical signal is terminated by diffusion away or reuptake from the synaptic cleft
Initiating transmitter release by opening ion channels
How is transmitter release across the synapse initiated?
When an action potentail arrives at the synapse, it initiates the opening of calcium gates channels
What is Ca2+ couple to?
vesicle fusion
What is the calcium sensor in synapses and what does it do?
A protein called Synaptotagmin recognises Ca2+ and changes its conformation
What two things act as fusion promoting protein, making a vesicle/ plasma membrane complex
The vesicle (v) and target membrane (t) SNARE proteins
Tell me about Synaptotagmin and its role in the synapse?
Protein domains that bind Ca2+
Changes conformation when bound Ca2+
Allows vesicle to see the signal from Ca2+
Protein domains: Synaptotagmin contains two C2 domains, referred to as the C2A and C2B domains, that bind Ca2+ with similar properties and affinities
What does Ca2+ synaptotagmin promote?
Promotes vesicle SNAREs and plasmamembrane SNAREs to complex using complementary protein interaction domaines (i.e. coil-coil domains) this promotes fusion
Whats Synaptobrevin?
A protein complex which helps to drive fusion.
They are small integral membrane proteins of secretory vesicles, specialised secretory organelles that actively accumulate neurotransmitters and participate in their calcium-dependent release by exocytosis
Whats Syntaxin?
A family of membrane integrated Q-SNARE proteins participating in exocytosis
Whats SNAP-25?
Component of SNARE complex. Proposed to account for the specificity of membrane fusion by forming a tight complex that brings the synaptic vesicle and plasma membranes together
Tell me about the the stage of the action potential where the action potential is released, diffusion and reception
Tell me about receptor activation and transmitter action termination
How are receptors inhibited or excited during neurotransmitter release?
Inhibited by…
- hyperpolarised the membrane (negative ion Cl- influx)
Excited by…
- Depolarising the membranes (positive ions Na+ influx)
Where are the major excitatory synapses located?
Whats used as a transmitter?
On the dendrites
use Glutamate as the transmitter
Where are the major inhibitory synapses located?
Whats used as a neurotransmitter?
On cell body
Use GABA or glycine as the transmitter
What is a Axo-dendritic synapse and a Axo-somatic synapse?
Tell me whether the following synapses are often symmetric or asymmetric?
- Glutamatergic
- GABA/glycine
In a glutamatergic synapse
- What attaches to the stored glutamate?
- Tell me about the specialisation organiser
In a GABA/glycine synapse
What attaches to the stored glycine?
Tell me about the specialisation organiser
Tell me about the key features of glutamate receptors?
- Four subunits to make ion channel
- Glutamate binding site on outside
- Cation channel
- Bind to molecules like PSD-95 on inside
- Postsynaptic cell
Tell me about the key features of glycine/ GABA receptors?
- Five subunits to make ion channel
- Glycine binding site on outside
- Anion channel
- Bind to Gephyrin on the inside
- Postsynaptic cells
Key features on excitatory and inhibitory receptors
Organising molecules are multi-domain proteins and can help with segregation
Simple model as a primer for a complex synaptic glue
A real impact of molecular neurobiology in understanding and treating disease
Consider the following…
