ICPP Flashcards
What is the difference between homeostasis and heterostasis?
Homeostasis-the extracellular environment can be maintained so that there is a constant internal environment
Heterostasis-the intracellular environment is constantly changing in order for the cell to carry out specific functions
What is the difference error signal?
Set point- optimal set point for a physiological parameter
System output-sensor detects a physiological parameter and produced this signal related to the parameter
The system set point comparator produces a negative feedback signal proportional to set point - system output.
After what temperatures can the temperature control system no longer regulate itself by negative feedback so positive feedback occurs?
Above 40 and below 30
What is the difference between endogenous and exogenous signalling molecules?
Endogenous signalling molecules are signalling molecules in our body whereas exogenous molecules are drugs that aim to mimic or affect endogenous signalling molecules
What the three different types of endocrine signalling molecules?
Catecholamines, peptides to proteins, steroids
Order the 3 endocrine signalling molecules from fastest course of action and plasma half life to slowest
Catecholamines: Plasma half life-seconds, course of action-milliseconds to seconds
Peptides/proteins: Plasma half life-minutes, course of action-minutes to hours
Steroids: Plasma half life-hours, course of action- hours to days
What main processes are controlled by the endocrine system? (3)
Growth and development
Digestion
Sexual and stress behaviour
What are the 2 major types of paracrine signalling molecules?
Neurotransmitters
Local chemical mediators
What are the main types of neurotransmitters?
Amino acids (glutamate, glycine), monoamines (eg. Adrenaline, dopamine, seratonin), peptides, acetylcholine
What are the main types of local chemical mediators (2)
Cytokines
Eicosanoids
What happens when a signalling molecule binds to its receptor?
This causes a functional change that transduces the chemical signal into an alternative signal or performs a signal dependent task eg. Transport/synthesis
What are the signalling molecule targets?
Receptors- protein molecules whose function is to recognise and respond to endogenous signalling molecules
Kinase-linked receptors eg. Cytokine receptor
Ionotropic receptors (LGIC’s) eg. Nicotinic acetylcholine receptor
Nuclear receptors eg. Oestrogen receptor
G-protein coupled receptors: Gi, Gs, Gq
How do kinase-linked receptors work?
A ligand binds to the receptor and this stimulates a protein-kinase enzyme to phosphorylate certain groups. This causes increased or decreased transcription and protein production and can lead to growth, cell differentiation.
How many transmembrane domains to GPCR’s have and where is the N-terminal and C-terminal?
7 transmembrane domains
N-terminal outside cell and C-terminal inside cell
What is the essential property of all ligands that bind to nuclear receptors?
Lipid soluble
What is the intracellular effect of ligands binding to ionotropic receptors?
Depolarisation or hyperpolarisation
How is calcium involved in regulating metabolism?
Lipolysis
Glycogenolysis
Regulation of many metabolic enzymes eg. Krebs cycle
Bone metabolism
How is calcium involved in membrane-linked functions?
Excitation contraction coupling
Excitation secretion coupling eg. Release of neurotransmitters
Plasma membrane-vesicle fusion
What is basal intracellular calcium concentratio in nM?
1x10-7M
1x10-4mM
0.1microM
100nM
What is basal extracellular calcium in moles?
1x10-3 M
What is basal concentration of calcium in intracellular stores of SER/SR?
3x10-4M to 1x10-3M
How does Ca2+ leave across the plasma membrane?
PMCA- plasma membrane calcium ATPase
NCX- 3Na+ enters for 1 Ca2+ to leave by indirect active transport (antiport transporter)
How does Ca2+ enter across the plasma membrane?
NCX- 3Na+ leaves for 1Ca2+ to enter when cell membrane is depolarised
VOCC-activated by depolarisation
LGIC-activated by excitatory neurotransmitters binding
SOCC-activated when sensor protein detects low ca2+ reserves in SER/SR
How does Ca2+ enter SER/ER?
SERCA- SER Ca2+ ATPase, ca2+ enters by active transport
How does Ca2+ leave the SER/SR?
- Calcium induced calcium release stimulating RyR
- Gq activation stimulating ip3 receptor
If Ca2+ concentrations are high, which organelle other than the SER can take up Ca2+ and how?
Mitochondria through Ca2+ uniporter
What is the role of calcium buffers?
They bind to Ca2+ preventing rapid entry of Ca2+ into the cell and its compartments.
What is the role of Ca2+ sensors? Give an example.
Ca2+ causes a conformational change in these proteins so they can transduce Ca2+ signals to other proteins as Ca2+ would not be able to interact with these proteins alone. Eg. Calmodulin increases activity of PMCA
What is signal transduction?
Initial binding of a ligand to a receptor stimulates a cascade of reactions involving intracellular molecules to carry out a specific cellular response.
What does signal transduction allow?
Amplification. A small change in extracellular molecule can elicit a large change in intracellular molecules to create a response.
Explain three ways in which GPCR’s allow amplification.
- One activated receptor can change GDP to GTP on many G proteins.
- One activated G-protein can stimulate/inhibit many effectors.
- Effectors work in a catalytic manner. Each enzyme can catalyse the formation of many secondary messengers. Each open ion channel can allow many molecules inside.
What determines how long a G-proteins activity on the effector lasts for?
The intrinsic GTPase activity of the alpha subunit. This can be affected by proteins inside the cell that regulate its activity. It can also be affected by intracellular substrates required for its activity.
How does cholera occur?
CTx toxin systematically changes the Gs alpha subunit so that the GTP cannot be hydrolysed to GDP so they remain active. This allows the Gs alpha subunit to continuously stimulate adenlyl cyclase to form CAMP and hence PKA. PKA phosphorylates ion channels which remain open. Cl- floods out of gut epithelial cells and water follows.
How does the pertussis toxin work?
PTx systematically changes Gi alpha subunits by preventing GDP from being converted to GDP. The G protein remains in its heterotrimeric inactive form and adenlyl cyclase is not inhibited
How can ionotropy in the heart be increased?
Sympathetically released adrenaline
B1 adrenoreceptors in heart.
Adenylyl cyclase stimulated
PKA phosphorylates VOCC’s opening them. The alpha s-GTP subunit can directly interact with VOCC’s opening them so Ca2+ enters.
How can chronotropy of the heart be decreased?
Parasympathetically released Ach
M2 muscarinic receptors in heart
Adenlyl cyclase inhibited
Less VOCC’s phosphorylated. Gi alpha-GTP subunit directly binds to K+ ion channels so more K+ enters causing hyperpolarisation
How can bronchoconstriction occur
Acetylcholine
Binds to M3 receptors
Stimulated phospholipase C
Ip3 causes release of Ca2+ from SER and DAG stimulates phospholipase C that phosphorylates VOCC’s causing further increase in cytosol Ca2+
What regulates the amplification that GPCR’s cause?
Once a ligand has bound to its receptor and GDP has changed to GTP on a G protein, its bond with the ligand weakens
Once a G protein has had its GDP changed to GTP, protein kinases are likely to phosphorylate the GPCR so no more G proteins can bind
The GTPase activity of the alpha subunit is stimulated by substrates and proteins in the cytosol
The secondary messenger is metabolised by proteins to maintain basal levels
What is the permeability coefficient?
It tells you the speed at which a substance diffuses across a lipid bilayer. The greater the permeability, the higher the permeability coefficient.
Why is the speed at which water crosses lipid bilayers much higher than other polar molecules?
Water is a small polar molecule that exists as a gas so can pass between the phospholipids in the membranes.
What is passive diffusion directly proportional to?
Temperature and concentration gradient
What are the different types of proteins involved in facilitated diffusion?
Ping pong proteins (carriers) =change in conformation when ligand binds so it is released on to the other side Protein channels (pores) =certain stimuli causes the channel to remain open/closed eg. LGIC, VGIC, gap junction
What is an electrochemical gradient?
For an ion, there is a concentration gradient and a difference in charge across a membrane. If there are unequal concentrations, the ion moves from a region of higher concentration to a region of lower concentration. If there is unequal distribution of charge across a membrane, the electrical potential generates a force that drives ion diffusion until the charges are balanced.
What are the different types of transporters in a membrane?
Uniport= A solute molecule is transported from one side of the membrane to another Co-transport = A solute molecule is transported simultaneously with another molecule. Can be symport (transported in the same direction) or antiport (transported in opposite directions)
What is secondary active transport?
The transport of a substance depends on an electrochemical gradient of another substance via a co-transporter. The electrochemical gradient of this substance had been set up by active transport.
If the free energy change of the transport of a substance across a membrane is negative, will the process by which it is transported be active or passive?
Passive diffusion
If the free energy change for the movement of a substance across a membrane is positive, will the process by which it moves be passive or active?
Active transport
Which primary active transporters can be called pumps?
Those in the plasma membrane, in the membrane of organelles they are not called pumps
What is ischaemia?
Inadequate blood supply to part of the body. Tissues deprived of oxygen and nutrients.
Why does intracellular calcium increase during ischaemia?
Cells deprived of oxygen. Less ATP produced. Na+/K+ ATPase does not work.
Intracellular Na+ increases. NCX reverses. 3 Na+ is pumped out for 1 Ca2+ pumped in.
What is intracellular/extracellular Na+ and K+ concentrations?
Na+ i= 12mM o=155mM
K+ i=145mM o=4mM
Describe the structure of the sodium potassium pump.
Beta subunit anchors pump into plasma membrane
Alpha subunit is where Na+ K+, ATP and ouabain bind
List some functions of the Na+/K+ pump (6)
Creates a concentration gradient for Na+/K+
Drives secondary active transport processes for:
Ca2+ regulation
pH regulation
Cell volume regulation
Nutrient uptake
Which transporter is mainly responsible for removing Ca2+ from the cell
NCX
Why is high intracellular Ca2+ toxic?
Calcium phosphate forms causing ossification
Stimulates caspases involved in apoptosis
How do we stop acidification of cells?
Hydrogen ion extrusion by
NHE - Na+/H+ exchanger
Hydrogen ion extrusion and bicarbonate intrusion by
NBC - Na+/H+ HCO3-/CL- cotransporter
Bicarbonate intrusion by
3HCO3-/Na+ symporter
These are all secondary active transporters driven by the Na+ gradient set up by the Na+/K+ pump
How do we stop alkalisation of cells
Extrusion of bicarbonate
AE= HCO3-/Cl- exchanger
How do we stop cells from shrinking or bursting?
Opposing shrinking = Na+/K+/Cl- enter and 6 water molecules follow each
Opposing bursting = Na+/K+/Cl- leave and 6 water molecules follow each
How can we treat hypertension?
By blocking the protein transporters in the kidney that transport Na+ from the lumen of the tubules into the epithelial cells and thereafter the capillaries. This prevents water from following and re-entering the capillaries, decreasing blood pressure
In which area of the kidney is bicarbonate reabsorbed and why is bicarbonate reabsorption important?
The proximal tubule. Bicarbonate is the main buffer in the blood.
In which areas of the kidney is Na+ reabsorbed?
In the nephron
Thick ascending limb
Distal convoluted tubule
Cortical collecting duct
What is a membrane potential and what is it measured in?
Membrane potential is the magnitude of electrical charge across a plasma membrane and is always expressed relative to the extracellular solution. It is measured in millivolts.
How can membrane potential be measured?
Using a microelectrode. Voltmeter connected to 2 electrodes. One electrode in a beaker with solution. The other electrode is a fine glass pipette less than 1 micrometer which can penetrate the cell membrane without killing the cell. It is filled with a conducting solution of KCl.
What is the membrane potential of an erythrocyte and why is it this?
-9mV, virtually no selective permeability for K+ so Ek is close to 0
What is the membrane potential of skeletal muscle and why?
Around -90mV, very selectively permeable to K+ so very close to Ek.
What is membrane potential established by?
Asymmetrical distribution of ions across a plasma membrane
Selective ion channels in the membrane, especially K+, Na+ and Cl-
Why is resting potential negative?
High concentration of anions, negatively charged proteins and amino acids inside of the cell.
Most cells are very selectively permeable to K+ so membrane potential is close to Ek (the equillibrium potential when the electrical force and chemical force is balanced so there is no net movement across the membrane).
Membranes are not perfectly selectively permeable to K+ so other ion channels increase or decrease the size of the membrane potential.
If a membrane is very selectively permeable to K+, will this cause the membrane potential to become more negative or positive?
Negative
If a membrane is very selectively permeable to Na+, will this cause the membrane potential to become more negative or positive?
Positive
If a membrane is very selectively permeable to Cl-, will this cause the membrane potential to become more negative or positive?
Negative
Which equation allows you to work out the equilibrium potential of an ion?
The nernst equation
Which equation allows you to work out the membrane potential relative to permeabilities of different ions?
Goldman -Hodgkin-Katz equation
Why do ion channels contribute to establishing the membrane potential but transporters for ions do not?
Ion channels allow the rapid movement of ions down an electrochemical gradient in either direction. They are selective and open in response to certain stimuli.
Transporters allow very small movement of ions in one direction so do not contribute to membrane permeability.
What is the equillibrium potential of an ion measured in?
mV
Why does caffeine increase the efficacy of drugs?
Caffeine stimulates the RyR receptor on the SER of cardiomyocytes and smooth muscle cells so more Ca2+ enters by CICR. Therefore, there is increased force of contraction and stroke volume is increased. Vasoconstriction occurs and this causes hypertension. The increase in blood pressure means the blood flows faster and the drug is transported around the body faster. More of the drug reaches the target cells, increasing its efficacy.
When is the resting membrane potential changed? (3)
To generate an action potential in nerve and muscle cells
When converting a chemical signal in sensory cells to electrical signals
For the release of neurotransmitters or hormones
What are changes in membrane potential caused by?
Changes in ion channel activity and hence differential ion distribution across a membrane
Changes in the activity of electrogenic pumps
What are the different ways in which an ion channel can be controlled to change membrane potential?
LGIC
VOCC
Mechanical ion channels
Which types of ion channels are present in the hair cells of the inner ear that respond to sound?
Mechanical ion channels
Ca2+ open
K+ close
Give an example of an ion channel that is not perfectly selective for one type of ion.
Nicotinic acetyl choline receptor which is selective for Na+ and K+. Therefore when ACh binds a membrane potential intermediate to Ek and ENa is achieved.
How does the Na/K+ pump contribute to membrane potential?
It contributes a few mV to directly making the membrane potential negative as one positive charge is extruded from the cell.
However, it mainly contributes indirectly by maintaining the concentration gradient for K+ and Na+ by the active transport of these ions. These ionic gradients are responsible for resting membrane potential.
What is depolarisation? How are ions responsible for depolarisation?
Making membrane potential more positive so a decrease in size of membrane potential.
Na+ and Ca2+ channels open and enter the cell causing membrane potential to move towards ENa and ECa, making it more positive.
What is hyperpolarisation? How are ions responsible for this?
Hyperpolarisation is making the membrane potential more negative so an increase in the size of membrane potential.
K+ and Cl- ion channels open so K+ leaves the cell and Cl- enters the cell.
What occurs during synaptic transmission?
A neurotransmitter is released from the pre synaptic neurone and binds to a receptor on the post synaptic neurone. This causes ions to enter via an ion channel causing either hyperpolarisation or depolarisation.
What is involved in all fast synaptic transmission and give an example of one.
LGICS
Nicotinic ACh
What is summation?
Inhibitory synapses and excitatory synapses are present and the balance between the EPSP and IPSP determines whether an action potential is generated in the post synaptic neurone
What are the different methods of slow synaptic transmission?
Direct G protein gating
G protein gating via an intracellular messenger
What are the main differences between the two types of slow synaptic transmission?
Direct GPCR gating is localised in the plasma membrane and relatively quicker
Indirect GPCR gating via an intracellular messenger can be more widespread in the cell and is relatively slower
How do erythrocytes show that the Na+/K+ ATPase pump is not responsible for maintaining resting potential?
They have a resting membrane potential of -9mV.
If this was responsible it would be -90mV.
Erythrocytes have virtually no selective permeability for K+ channels demonstrating this is more important in maintains the resting potential.
How is membrane potential in the release of insulin from the beta cells of the islet of Langerhans?
Glucose enters
ATP conc increases
Binds to ATP-sensitive K+ channels which close
Membrane potential increases
VOCC’s open, Ca2+ enters
Exocytosis of insulin and vesicles fuse with membrane
How can membrane potential be exploited to treat type II diabetics?
Constantly depolarise the membrane so that VOCC’s are always open and insulin is continuously secreted by beta cells of islet of langerhans
Sulphonylurea activates K+ channels by binding to sulphonylurea receptors physically linked to them
What properties of cardiac ion channels enable the heart to be myogenic?
Selectivity-very specific to certain ions
VOCC- sensitive to small changes in membrane potential
Time dependent- close and open very quickly
Why do membrane potentials not equal to Ek?
They are not perfectly selective for K+. There are other ion channels present in the membrane.
What is the equillibrium potential of an ion?
The membrane potential when there is no net flow of ions.
Electrical gradient = concentration gradient
What are the properties of an action potential?
Change in membrane potential
Depends on ionic gradients and relative permeability
Depolarisation which must reach threshold at axon hillock
All or nothing
Propagated without loss of amplitude
What proves that Na+ is responsible for the rapid depolarisation that occurs during an action potential.
When we decrease Na+ extracellular conc, ENa decreases and becomes less positive.
When we decrease Na+ extracellular conc, the membrane potential at the peak of the action potential decreases in a manner proportional to the decrease in ENa.
How can we measure the flow of Na+ and K+ currents at a set membrane potential?
Voltage-clamp
How does a voltage clamp prove that Na+ channel inactivation occurs?
When a membrane potential is set to be depolarised, Na+ flows into the cell demonstration the voltage gated channels were open. However, this stops after a certain point, even if the membrane is continuously depolarised, demonstrating inactivation occurs.
What is conductance?
The number of channels for an ion that are open in a membrane
What happens when the conductance to a particular ion is increased?
The membrane potential moves towards the equillibrium potential of that ion
What is a major difference between the voltage gated sodium and potassium ions involved in an action potential?
Voltage gated sodium ions open rapidly and become inactivated when depolarisation is maintained
Voltage gated potassium ions open much more slowly but once opened, they stay open for the duration of depolarisation. Once resting membrane potential is established, they close slowly.
What proves that the sodium potassium pump is not important in repolarisation during an action potential?
There is only a small change in the intracellular concentration of Na+ during depolarisation, 40mM