Unit 1: Cells And Proteins KA 1.4: communication and signalling Flashcards
The three examples of extracellular signal molecules
steroid hormones, peptide hormones, and neurotransmitters
what molecule are receptors made of?
Protein
suggest why cell may not respond to a signalling molecule
They don’t have complementary receptors
Describe how different tissues have tissue specific responses to the same signalling molecules
differences in the intracellular signalling molecules and pathways
What are examples of hydrophobic signalling molecules?
Steroid hormones such as oestrogen and testosterone
describe the term transcription factor
Transcription factors are proteins which can affect gene expression by binding to DNA and stimulating or inhibiting transcription of genes
do hydrophobic molecules pass through the membrane?
Yes
what does a hydrophobic signalling molecule binding to receptors make?
Hormone receptor complex
what happens after the hormone receptor complex is made in the stages of steroid hormones influencing transcription
The hormone receptor complex moves to the nucleus where it points to specific section of DNA called hormone response element
Hormone receptor complexes are a transcription factor so it influences the transcription/expression of lots of changes in the DNA. It can stimulate or inhibit it
example of hydrophilic molecules
Peptide hormones and neurotransmitters
What does transduced mean?
converted
explain G proteins in hydrophilic signalling
1) hydrophilic signalling molecules bind to the transmembrane extracellular receptor
2) this causes a conformational change in the receptor
3) the G protein is activated and relays the signal to a protein such as an ion channel or enzyme
explain the phosphorylation cascade in hydrophilic signalling
1) hydrophobic signalling molecules bind to the transmembrane extracellular receptor
2) this causes a conformational change in the receptor
3) this causes a phosphorylation cascade where one kinese activates the next and so on
Name an example of a peptide hormone
insulin
The phosphorylation cascade started by the binding of the insulin to receptors causes the recruitment of GLUT4 glucose transporters in the plasma membrane of what cells
fat and muscle cells
what does insulin binding to the extracellular receptor do in the recruitment of GLUT4 transporters?
causes a confirmational change and phosphorylation of the receptor which triggers an intracellular signalling Phosphorylation cascade
what do vehicles do in the recruitment of GLUT4 transporters?
vehicles move GLUT4 transporters to the membrane after the phosphorylation cascade
what is the purpose of GLUT4 transporters?
Glucose moves through the GLUT4 transporters down its concentration gradient into fat and muscle cells. This is an example of facilitated diffusion.
cause of type one diabetes and what it causes
genetic, failure to produce insulin
cause of type two diabetes and what it causes
Lifestyle choices, i.e. obesity and it causes loss to receptor function
Treatment of type one diabetes
Insulin injections
Treatment of type two diabetes
lifestyle changes, i.e. healthier diet and more exercise which triggers recruitment of GLUT4
explain why hydrophilic signal molecules do not pass through the membrane
They cannot pass through the hydrophobic region
Name two structures that can be activated by G proteins
enzymes an ion channels
by which process does glucose move into fat and muscle cells?
Facilitated diffusion
describe the meaning of the term resting membrane potential
when there is no net flow of ions across the membrane
what is membrane potential?
The electrical potential difference or voltage across the membrane
What maintains the electoral chemical gradient?
Sodium potassium pumps
what is action potential?
A wave of electrical excitation along the neurons plasma membrane
Explain depolarisation
when the cell becomes more positive due to the influx of positive sodium ions as a result of neurotransmitters binding at the synapse.
The neurotransmitter receptors are Ligand gated sodium ion channels
once a threshold is reached voltage gated sodium channels also open causing rapid further depolarisation, this triggers the adjacent voltage gated sodium channels depolarising the next section of membrane
Explain repolarisation/hyperpolarisation
after the wave of depolarisation passes, there has to be a process to re-establish the resting potential ready for the next impulse
Sodium channels close and voltage gated potassium channels open
this makes the positive potassium ions diffuse out of the neuron cell down the electrochemical gradient. This makes the inside of the cell more negative.
this can go too far in the cell becomes more negative than the resting membrane potential which is called hyperpolarisation
explain the restoration of the resting membrane potential
following repolarisation the sodium and potassium ion concentration gradient are reduced
The sodium potassium pump restores the sodium and potassium ions back to resting potential once resting potential has reached the potassium channel closes again
restoration of the resting membrane potential allows the inactive voltage gated sodium channels to return to a confirmation allows them to open again in response to the depolarisation of the membrane
what is the function of the photoreceptor rods?
functions in the dim light but does not allow colour perception
what is the function of the photoreceptor cones?
responsible for colour vision and only function in bright light
Where does light hit the eye and what are the structures of this area?
Retina made up a photoreceptors called Rod and corn cells
What kind of signal is the light being converted into in the eye?
Electrical
how many G proteins are activated by one photoexcited rhodopsin?
100s
how many PDE does each G protein activate?
1
how many cGMP molecules does each PDE breakdown?
1000s
how does cGMP cause a nerve impulse in retinal neurons?
decrease in the cGMP concentration causes sodium channels to close triggering a nerve impulse
Why can rod cells response to a low light level?
an effect of a single photon is amplified many times
what wavelength can cone cells be sensitive?
Red, green, blue and UV
