Cell biology Theme 2 Flashcards
Why do cells need to communicate ?
To define their position , fate and growth
to function as a community
to respond to the environment
What is the generic cell signal pathway ?
An extracellular signal interacts with a receptor and recieves the signal
the signal is transduced
new intracellular signaling molecules are produced
this leads to a molecular change that alters the cell behaviour
Examples of cell signals ?
cholesterol based steriods peptide hormones fatty acid derivatives amino acids nucleotides
What is endocrine signaling ?
When endocrine cells release hormones that act on distant target cells.
Where are hormones produced ?
in endocrine organs such as the pancreas
How do the hormone molecules reach their target cells ?
`via the blood - a very public system
how do amino acid derivatives and peptide hormones act ?
via receptors on the plasma membrane to regulate metabolism
How do steroid hormones act ?
via intracellular receptors to regulate metabolism
What is endocrine signaling used for ?
respond to nutritional changes , inducing a wide range of changes and in changes to do with development
What is autocrine signaling ?
When a cell secretes a hormone or messenger that binds to autocrine receptors on the same cell that secreted it , leading to changes in that cell
How does autocrine signaling promote cancer ?
In cancer there is an over production of growth factors that lead to the formation of tumours. Due to a disfunctional autocrine signaling pathway
What is lidocaine and how does it work ?
An anaesthetic used to block pain , it moves to the inside of the cell and and binds to sodium channels blocking the influx of sodium ions. This stops nerve conductance and prevents further signals reaching the brain
Why is adrenaline used with lidocaine ?
adrenaline keeps the lidocaine local because lidocaine stimulates dilation of the blood vessels. increasing its absorption. Adrenaline constricts the blood vessels to counteract this
How do cells respond selectively to signals ?
because it depends which receptors the cells have and express
How do different cells respond to the same signal ?
in different ways
Cells having many different receptors allows for what ?
A small number of signaling molecules
Why do signals not act independently of one another ?
the presence of a signal can modify the responses to another signal
What do signals work in to regulate the behaviour of the cell ?
combinations
What can happen to a cell if it is deprived of signals ?
apoptosis
how can cells produce different responses to signals ?
by the interaction of intracellular systems
Why do some extracellular signals have a rapid effect ?
Because they have an effect on a proteins that are already present in the cell
Why do changes cell growth and cell division take hours to execute ?
the response requires changes in gene expression and production of new proteins
What is paracrine signaling ?
A form of cell to cell communication in which a cell produces a signal to induce changes in nearby cells altering the behavior of these cells.
What are common paracrine signaling molecules ?
cytokines and growth factors
What do paracrine signaling molecules act as ?
local mediators
What is the extent of paracrine signaling ?
it is restricted to a particular tissue and is localised eg. the immune response and wound healing
What is neuronal signaling ?
Delivering signals over long distances quickly and specifically to target cells through private lines (axons)
What to electrical signals at the axon terminal stimulate ?
the release of neurotransmitter which diffuses across the synapse eg. Acetylcholine
What do nerve cells communicate between ?
each other or muscle cells
What does acetylcholine do ?
binds to receptors on sodium channels and allows the influx of sodium ions to generate action potentials
What is contact dependent signaling ?
the signaling molecules are membrane bound and they bind to receptors embedded in the plasma membrane , direct physical contact is required
eg in the immune response/
What is delta notch signaling and how is in involved in development ?
Unspecialised epithelial cells form a sheet. An isolated epithelial cell develops into a neurone, inhibition of the rest of the cells must be initiated when the epithelial cell has delta molecules that bind to a notch. inhibiting development into a neuronal cell.
Molecules that are too large and hydrophilic bind to receptors where ?
on the plasma membrane
molecules that are hydrophobic bind to receptors where ?
in the cytosol or nucleus
What are nuclear receptors ?
they are activated by hormone binding which activates them allowing them to promote or inhibiut gene expressions as each hormone binds to different regulatory sets of DNA
The same hormone envokes what types of responses in different target cells ?
envolke different physiological responses
What is an intracellular signaling pathway ?
ann extracellular signal binds to receptors activating a series of intracellular actions that form a pathway
What is the primary step in intracellular signaling pathways ?
the receptor protein carries out signal transduction. the signal activates the receptor, recognises it and generates new intracellular signals in response
What do intracellular pathways usually end in ?
gene expression , enzyme action or cytoskeletal changes for shape change
What is the function of intracellular signaling pathways ?
the relay and transduce the signal
they amplify the signal
they integrate signals from other pathways
they distribute the signal to other intracellular targets
How are pathways subject to positive feedback ?
a downstream component acts on an earlier component to increase the response to the initial signal. this produces an all or none repsonse
How are pathways subject to negative feedback
a downstream component will inhibit an earlier component to diminish the response to the initial signal. this allows the response to oscillate between on and off
What are molecular switches ?
they receive signals which allows them to toggle between on/off
What are the 2 types of molecular switches ?
GTP binding proteins and proteins activated by phosphorylation
How do phosphorylated proteins work ?
Protein kinase adds a phosphate group amde available form ATP hydrolysis.
What does protein phosphatase do ?
removes the phosphate group
What does the activity of a phosphorylated protein depend on ?
the balance between the activities of protein kinase and protein phospohotase
what are phosphorylation cascades ?
when a protein kinase is phosphorylated causing another to be phosphorylated. and a chain reaction occurs. this amplifies the signal.
How do GTP binding proteins toggle between active or inactive ?
if GTP is bound - they are active
if GDP is bound- they are inactive
GTPase activity regulates this
What are the 3 types of extracellular receptors ?
ion channel linked receptors
g-protein linked receptors
enzyme-linked receptors
What do ion channel linked receptors do ?
they change the permeability of the plasma membrane to selected ions , altering the membrane potential.
What is the structure of a G protein coupled receptor ?
It is a single polypeptide chain that threads back and forth across the membrane 7 times, this is the seven-pass transmembrane structure.
What happens when an extracellular signal binds to a G-protein coupled receptor ?
when the signal binds to its receptor the altered receptor activates the G protein as the GDP is removed and the GTP is bound,
What do G-proteins often interact with ?
enzymes- adenylyl cyclase that produces cyclic AMP and phospholpiase which makes inositol triphosphate and diacylgylcerol.
What are cyclic ACP, IP^3 and DAG ?.
second messengers - they amplify and spread the signal
What are the consequences of GCPR activation ?
activation of membrane bound enzymes (adenylyl cyclase)
activation of phospholipase C ( makes DAG and IP^3)
regulation of ion channels (eg. potassium channels)
How do GPCR regulate ion channels ?
acetylcholine binds to receptor - this activates the G protein
This allows the potassium channels to open and membrane permeability increases
The G protein is inactivated as the GTP is hydrolysed
the potassium ion channel closes
What is the ‘flight or fight’ response ?
Adrenaline binds to the GPCR
this activates the adenylyl cyclase
the production of cAMP is amplified
this activates protein kinase A and leads to cascades
phosphorylation of phosphorylase kinase
this activates glycogen phosphorylase which breaks down glycogen into glucose
How can cAMP modify gene expression ?
a signal binds to a GCPR
this leads to an increase in the activation of adenylyl cyclase
this leads to an increase in cAMP which activates protein kinase A
this moves into the nucleus and phosphorylates specific transcription factors
How do enzyme coupled receptors work ?
an extracellular signal binds to the receptor and enzyme activity is activated within the cell
they are usually in pathways that control growth,development and differentiation.
slow responses as changes are required to gene expression.