Cellular Communication Flashcards
What are the two types of perception in cellular communication?
1) Perception of the environment
2) Perception of signals from other cells
Describe Perception of the environment
cells receive signals from the environment which cause a response appropriate to the environment
Examples of signals from the environment?
- single celled organisms – eg. Light, nutrients
- multicellular organisms – via specific sense organs
Describe Perception of signals from other cells
cells perceive signals from other cells – intercellular communication
Examples of signals from other cells?
- single celled organisms – reproduction
- multicellular organisms - development/homeostasis/cellular interaction
To accomplish mating yeast cells secrete …
…‘mating factors’
Yeast come in two…
… ‘sexes’, ‘a’ and ‘α’.
the two types of yeast cell (a and alpha) cause …
…protrusions which grow towards each other (a shmoo) and fuse.
Define a shmoo
protrusions which grow towards each other
How are the mating factors perceived and how do they make the yeast cells form the shmoo?
The a type secrete a protein called ‘a factor’ which attracts α cells.
Cells depend on …
…signals to survive
In complex organisms cells receive…
…multiple signals and in many cases these are required for continuing cell survival.
Signals ensure cells respond by:
1) Surviving
2) Growing/dividing
3) Differentiating
4) Dying (lack of signals)
5) Movement
In multicellular organisms signals act over a…
…range of distances.
Paracrine in this case may also include …
…‘autocrine’ where the cell signals to itself.
- e.g. T lymphocytes
If the cell does not recognise the other cell…
… it will kill it.
Where organisms are particularly complex they may …
…employ endocrine signals from special organs
Endocrine signals are…
…perceived by target cells
- e.g. insulin, adrenaline
Signals are perceived in two ways:
1) Signalling molecule binds at the cell surface
2) Signalling molecule binds an internal receptor
Signalling molecule binds at the cell surface and the signal is then …
…transmitted into the cell where the cell responds to the signal
Signalling molecule binds an internal receptor and transported to the …
… nucleus where it has its effect directly on gene expression
Nuclear receptors are found in …
…both the cytoplasm and the nucleus
Where receptors are in the cytoplasm …
…binding of ligand exposes Nuclear Localisation Sequence.
Exposure of Nuclear Localisation Sequence causes the receptor/ligand complex to …
…migrate to the nucleus where it acts directly on gene regulation.
Where receptors are in the nucleus, ligands …
…diffuse across the nuclear membrane and enter the nucleus where they bind and change the receptor to an active state.
Example of ligands?
Steroid hormones
Some signals are …
…non-proteins such as steroid hormones.
non protein signals such as steroid hormones circulate in the…
…blood in association with carrier proteins, dissociate and cross the plasma membrane directly.
Non-proteinaceous signals are common in …
…plants, such as phytohormones (auxin, gibberellin, abscisic acid, cytokinin, ethylene).
Auxin is taken up by…
…transporter proteins in the membrane and effect gene expression.
- Can have multiple effects in the plant.
Binding of steroid hormones to their receptor causes …
…a conformational change in the receptor protein.
define conformational change
a change in the shape of a molecule
binding of steroid hormone to its receptor opens up part of…
…the protein nuclear localisation sequence, NLS causing it to be transported to the nucleus.
The activated steroid hormone receptor then binds to …
…regulatory elements in the promoters of genes and activates or represses transcription.
The hormone can turn gene expression …
…on or off
Whether it gets turned on or off depends on…
… the hormone
On interaction between receptor and ligand there is a change in conformation of the receptor so that ions are …
…drawn into the cell through ion channels.
a change in conformation occurs in the receptor – G-protein coupled receptors interact with …
…membrane associated proteins.
Classically these are receptor kinases; on ligand/receptor interaction the …
…catalytic domain becomes activated
What happens when catalytic domain becomes activated?
signals to downstream proteins.
Classically signals are perceived at the …
…cell surface by receptor proteins.
Once signals are perceived at the cell surface by receptor proteins, the signal is then…
…transduced through the cell where it has an effect either on metabolic enzymes, cytoskeletal proteins or gene regulatory proteins
Signal transduction utilises …
…many different intermediate proteins.
Effector proteins are called effector proteins because …
…they are what cause the effect inside of the cell.
THE SIGNALS MAY BE …
…proteins
Many kinds of proteins that are secreted …
…outside of a cell and are perceived by ‘target cells’
Proteins as signals often called …
…ligands
ligands interact with…
…receptor molecules mostly on the cell surface.
insulin is secreted from β-cells in…
…the pancreas
insulin is secreted in response to…
…increased glucose
insulin travels in the…
…bloodstream
Insulin acts on…
…target cells
Insulin acts on target cells causing an increase in…
…glycogen synthesis
Insulin regulates…
…glucose because by creating glycogen, glucose is taken out of the bloodstream.
Remember the plasma membrane is a…
…phospholipid bilayer.
Proteins cross the membrane usually as an …
…alpha helix
The amino acids forming the transmembrane domain are …
…mostly hydrophobic
Amino acids/proteins fold into an alpha helix so that…
…H-bonds between peptide bonds form.
One of the most common forms of signal/receptor interactions in animals is via …
…G-protein coupled receptors (GPCRs)
G-protein coupled receptors (GPCRs) form a …
… large family of proteins
G-protein coupled receptors (GPCRs) are involved in…
…the perception of many different signals (e.g. polypeptide hormones, light, pheromones)
Whats a GPCR?
G-protein coupled receptors
GPCRs have in common …
…7 transmembrane helices and hence sit in the plasma membrane
Part of the G-protein faces the …
…outside of the cell and is available for ligands (e.g. adrenaline) to interact.
Part of the protein faces the inside of the cell and can…
…interact with proteins in the cytoplasm or other membrane associated proteins.
G-proteins are described as…
…heterotrimeric
What does heterotrimeric mean?
they contain α, β and γ subunits
α and γ subunits are anchored in the membrane via…
..lipids
ligand binding to GPCR causes …
…conformational change in GPCR
- causes conformational change in G-protein
GDP is exchanged for…
..GTP
exchanged GDP for GTP, this activates β/γ complex and α-subunit and regulates …
…target proteins
Both activated subunits of G-proteins can activate other proteins, these in turn can…
…relay the system on.
proteins interact with each other and change conformation – when they change their conformation…
… they can change their state from inactive to active and vice versa.
proteins interact with each other and change…
…conformation
Sometimes the interaction is just via …
…proteins binding
at other times it is the addition of molecules…
…cAMP, Ca2+ and most importantly phosphate groups (second messengers).
The process of GPCR signalling causes a…
…change in gene expression in the cell
What are secondary messengers?
molecules that are released on the perception of a signal which then bind to proteins activating them in specific ways
Examples of secondary messengers?
Apart from cAMP these include Ca2+ , cGMP, nitric oxide (NO) and various lipid molecules (e.g. inositol triphosphate – IP3)
Calcium (Ca2+ ) is one of the best characterized as its involved in …
…activation of many kinase enzymes (these phosphorylate other proteins so changing their activation state).
Norepinephrine acts as both a…
…stress hormone and neurotransmitter.
Norepinephrine is released from…
…the ends of sympathetic nerve fibres.
Norepinephrine acts to…
…increase the force of skeletal muscle contraction (rate and force of contraction of the heart).
Many of the signal transduction processes that effect changes in gene regulation depend upon …
…the activation or deactivation of proteins by the addition or removal of phosphate groups
addition of a phosphate to a protein will alter its …
…charge
Remember that addition of a phosphate to a protein will alter its charge and will therefore…
…affect its conformation.
Many of the proteins involved in signal transduction are:
- kinases – add phosphate groups
- phosphatases – remove phosphate groups
Mitogen-activated protein kinase (MAPK) is specific to the …
…amino acids serine and threonine.
What is MAPK?
Mitogen-activated protein kinase
Depending on their input, kinases can act as…
…central regulators modulating responses to different signals.
regulation of gene expression is controlled by …
…binding of activator or repressor proteins to regulatory elements in the promoters of genes.
What are activators?
These proteins bind to genes at sites known as enhancers. Activators help determine which genes will be switched on and they speed the rate of transcription.
What are repressors?
These proteins bind to selected sets of genes at sites known as silencers. They interfere with the functioning of activators and thus slow transcription.
What are coactivators?
These adapter molecules integrate signals from activators and perhaps repressors and relay the results to basal factors.
What are basal transcription factors?
In response to injunctions from activators, these factors position RNA polymerase at the start of the protein-coding region of a gene and send the enzyme its way.
Yeast mating depends on …
…perception by GPCRs and transduction of the signal via second messengers and a MAP kinase cascade – altered gene expression and movement.
