Lecture 7: Cell Communication | General Principles Flashcards
What are the 5 types of cell to cell communication?
- contact dependent
- paracrine
- autocrine
- synaptic
- endocrine
Describe contact dependent communication
the cells are ______ to each other and there is a _________ ________ _________ molecule to allow interaction on the ____________ ___________
the cells are stuck to each other and there is a membrane bound signal molecule to allow interaction on the cell surface
Give an example of a contact dependent cell to cell communication
gap junctions (electrical synapses affecting their neighbour)
Describe paracrine cell to cell communication
the signalling cell secretes hormones into the local environment to have an effect on target cells in the local environment
Describe autocrine communication
the signalling cell secretes a local hormone which targets a receptor in the signalling cell so that this call can self regulate its own activity
Describe synaptic communication
a neurotransmitter is released from the axon terminal of a neuron into the synaptic cleft to act on receptors on the post-synaptic cell
Describe endocrine communication
an endocrine cell releases a hormone into the bloodstream and it is transported to a distant target cell to have an effect on the receptor
An endocrine cell secretes a hormone which circulates in the blood. What are four potential fates for this secreted hormone?
- it could be excreted into the urine or faeces
- it could be inactivated by metabolism
- it could be activated by metabolism (if it is inactive when secreted)
- it could bind to a receptor and produce a cellular response
Describe the process of synergy
When two hormones act together, they don’t have an added effect, they interact with one another to have an even bigger effect
Give an example of synergy occurring
Thyroid hormone and epinephrine both cause very small amounts of fatty acids to be released from lipocytes but when they are both used, they interact with each other and causes a really large amount of fatty acids being released.
What is the key thing about synergy?
the maximum combined response is bigger than the addition of the maximum individual responses
Describe the process of hormone targeting
A secretory cell releases a chemical messenger which is able to cause an effect on the cell which expresses the receptor for that specific messenger. However, the messenger just diffuses randomly and sometimes it reaches the right receptor
Explain why the target cell is self selecting
the secretory cell doesn’t chose the target cell, it just releases the chemical messenger which goes everywhere and the target cell choses to have receptors for that hormone
What does the sensitivity of a target cell depend on?
the number of receptors expressed
Why are receptors constantly degraded and synthesised?
to ensure efficiency
What is the process of upregulation?
this is when the synthesis of receptors on the cell surface exceeds the degradation which increases the number of receptors expressed
Does up regulation increase or decrease sensitivity?
it increases it
What is the process of down-regulation?
this is when the degradation of receptors exceeds the synthesis of receptors which decreases the number of receptors
Does down-regulation increase of decrease sensitivity?
decrease
Receptor up-regulation makes a target cell more sensitive to a hormone BECAUSE receptor up-regulation makes more of the hormone receptors available for hormone binding
both statements are true, and the second statement causes the first
What are the three chemical classifications of hormones?
- peptides
- amines
- steroids
Peptide hormones can be made from what?
from three amino acids to large protiens
Amino acid hormones are derivatives of what?
tyrosine
What are steriods synthesised from?
cholesterol
What can cholesterol be converted to?
androstenedione
androstenedione gets converted to what by dehydrogenase?
testosterone
Testosterone gets converted to estradiol by what enzyme?
aromatase
Where is testosterone secreted from?
the testes
Where is estradiol secreted from?
the ovaries
Explain how the expression of an enzyme determines what hormone is synthesised by giving an example
the synthesis of an hormone depends on the enzymes that are expressed in the cells
for example, if testosterone is in a cell that has aromatase then it will form estradiol
in the brain, there is a higher expression of aromatase so the _________ in the brain is converted to ________
testosterone
estradiol
Why can you not package steroids into vesicles?
because they are lipid soluble and therefore would just diffuse out of the vesicles
Steroids are synthesised and secreted by _________
diffusion across the membrane
What is the rate determining step in the synthesis and secretion of steroids?
the synthesis of them (the more you synthesise, the more you secrete because you can’t store it)
How does a steroid make it to the cell and get inside the cell?
because it is lipophilic, it needs to be carried through the bloodstream by a carrier protein
once it reaches the cells though, it can just diffuse across the membrane
What are the two things that steroids can do once inside the cell?
- they could bind to receptors in the cytoplasm and then act on the DNA in the nucleus
- bind to receptor already in the nucleus
What is the effect of steroids inside the cell?
they regulate gene transcription to either increase or decrease protein synthesis
The amine hormones are all derivatives of what?
tyrosine
What is the name of the enzyme that converts tyrosine into L-Dopa?
tyrosine hydroxylase
Dopa decarboxylase converts L-Dopa into what?
catecholamines which are packaged into vesicles
What are the three examples of catecholamines?
dopamine
norepinephrine
epinephrine
What does the further modification of dopamine to norepinephrine and epinephrine depend on?
the enzymes expressed in the cells (ie. if the cell had the right enzyme, it would go all the way to epinephrin)
Catecholamines are examples of what type of molecules?
signalling molecules
Where are peptide hormones synthesised and packaged?
they are synthesised in the rough endoplasmic reticulum and packaged in the golgi
What happens to the peptide hormones once they are packaged into vesicles in the golgi?
they bud off from the golgi and remain in the cell until the vesicle is needed
What causes the peptide hormones to be released?
a stimulus such as a depolarisation in neuron or hormone activating second messenger system which triggers increase in intracellular Ca2+ and the secretion of the signalling molecule (in this case, the peptide) by exocytosis
What is the mechanism by which lipophilic signal molecules interact with the intracellular invironment?
a nuclear receptor which causes something to happen
When a lipophilic signal molecule binds to the membrane receptor, what is usually activated?
a second messenger system
Where is the second messenger system activated?
inside the cell
Give an example of a second messenger inside the cell
intracellular signalling proteins
What is one advantage of having a second messenger system?
you can get multiple responses in the cell
As well as being able to get multiple responses inside the cell, one of the advantages of having a second messenger system it scaling. What is scaling?
This is when single first messenger ends up causing the activation of thousands or even millions of different molecules
Give an example to show the size of scaling
A single first messenger (signalling molecule) activates a few cAMP inside the cell. These are the second messengers and each of these can activate many cAMP-dependent protein kinases. Each of these can phosphorylate enzymes, which means that many enzymes become phosphorylated. Each of these enzymes can go onto activate up to 100 final products
As well as steroids, what else can alter gene transcription?
second messengers
Describe the process of second messenger transcription activation
A signalling molecule binds to a receptors which activates second messenger. In this case, the second messengers are proteins that function as transcription factors (immediate early genes). These enter the nucleus and cause the transcription of other transcription factors which then cause the synthesis of new proteins for particular functions
The activation of cAMP dependent protein kinases causes what to happen?
multiple things to happen in the cell
