Lecture 9 Flashcards
what is cell-cell communication in bacteria called?
quorum sensing
chemicals made and released to communicate
cell-cell signalling allows populations of cells to coordinate with one another and work like a team to accomplish tasks no single cell could carry out on its own.
how does bacteria coordinate a response?
when the concentration of an inducer molecule (autoinducer) made by the bacteria themselves reaches a certain level due to population density.
what are autoinducers?
molecules released from one cell and then read from another
what are certain responses to autoinducers?
- sporulation (protists and bacteria)= forming spores
- exchange of plasmid dna
- bioluminescence in symbiosis
- virulence (secretion of proteins that allow the bacteria to attack multicellular hosts and cause diseases
- production of biofilms (hard, polysaccharide-rich substances that encase the cells and attach them to a surface.
what do multicellular organisms do to communicate?
pheromones = chemicals released into the environment by certain organisms to communicate with others of their species
- a pheromone can indicate the location of a receptive partner or used to mark territories
why do plants release volatile compounds?
to protect and warn other plants of a disturbance or predator
example: catapillars have chemicals in their saliva that plant cells recognize - the plant recognizes this ans signals the plant to ekease pheromones that attract wasps ( these wasps lay their eggs in livings hosts therefore they negatively impact catepillars) = parasitic to the catapillars
what is local cell signaling?
- communication through cell junctions
- cell surface molecules
- paracrine signaling
- synaptic signaling
what is long distance cell signaling?
- communcation through endocrines (hormones)
how do cells communicate through cell junctions?
- signaling molecules through gap junctions between animal cells and between plasmodesmata between plant cells
next door neighbor signaling
how to cells communicate through cell-to-cell recognition?
- cell activity can be altered through the binding of a surface marker of one cell to the receptor of another
- important in embryonic development and the immune response
local signalling
what happens in paracrine signalling?
a secretory cell releases local regulator molecules that travel through the extracellular matrix to nearby cells where it will have an effect.
- numerous cells can simultaneously receive and respond to the molecules produced by a single cell in their vicinity.
target cells have receptors that recognizes the receptors and responds
local signalling
what happens in synaptic signalling?
- neurons communicate with other cells through the release of neurotransmitters
- these molecules act as chemical messengers, diffusing across the synapse; the functional junction between the nerve cell and its target cell
- neurotransmitters will affect the activity of nearby neurons or effector organs such as muscles or glands.
long-distance signalling
describe the endocrine tissues
- multicellular organisms are coordinated by hormomes
- hormones are usually present in minute concentrations, they may still have a large impact on the condition of the organism as a whole.
hormone specificity
what are target cells?
hormones only have an effect on cells that have specific receptors that they can bind to. These are called target cells.
- there are a variety of target cells that need specific receptors that are capable of binding to them.
Need to have the right receptor = receptor specificity
what are the stages of cell signaling?
1) reception
2) transduction
3) response
4) signal deactivation
Cell signaling
what happens during stage 1: reception?
- when the signalling molecule ( hormone ) binds to a receptor protein that is located at the target cell’s surface or inside the cell
- binding causes a change in the shape of the receptor protein which activates it and thus allows it to interact with molecules in the cytoplasm of the cell.
reception
what are the two types of signalling molecules?
1) water soluble:
- amino-acid based
- hydrophilic
- cannot diffuse through PMs of target cells
2) lipid soluble
- steroids and thyroid hormones
- hydrophobic
- can diffuse through PMs of target cells
what are the two different signalling MECHANISMS?
1) cell surface signalling
2) intracellular signalling
signaling mechanisms
describe the process of cell surface signaling?
- where water soluble signalling molecules cannot pass through the phospholipid bilayer and therefore bind to receptors on the surface of the cell.
- conversion of an extracelluar chemical signal into an intracellular response
e.g. peptide hormones such as insulin and glucagon
signalling mechanisms
describe the process of intracellular signalling
- where lipid soluble signalling molecules can pass through the phospholipid bilayer and bind to receptors in the cytoplasm or nucleus of the target cell
- directly involved in gene expression
- activates transcription factors
e.g. steroid hormones such as testosterone
cell-surface receptors
how do activated protein receptors affect the cell’s activity?
- by performing an enymatic function within the cytoplasm
- allowing passage of molecules into or out of the cell
- initiating a transfuction cascade
what are two major types of cell-surface receptors?
1) G protein-coupled receptors (GPCRs)
2) Receptor tyrosine kinases
what are G protein-coupled receptors?
- large family of receptors that are expressed in every type of cell in our body
- all GPCRs are composed of alpha-helices joined by intracellular andd extracellular loops
- different GPCRs bind to different ligands based on the specific conformation of their active site. Differences in their cytoplasmic conformations also confer them specificity for specific G proteins.
what are some functions in the body of GPCRs?
- embryonic development
- sensory reception
- autonomic nervous system transmission
- mood regulation
upon ligand binding, the GPCR will change conformation and activate a G protein which will initiate an intracellular signaling cascade
what are G proteins?
G proteins = family of transduction proteins with variability in their specific amino acid sequence.
- they are peripheral membrane proteins that act as an on and off switch depending on if GTP or GDP is bound to them
- GPCRs and G proteins work with enzymes
- upon GPCR activation (binding of its ligand) on the extracellular side, the receptor will undergo a conformational change. - this change allows its cytoplasmix portion to interact with a G protein and replace the GDP for a GTP, thus activating the G protein.
- activated G proteins dissociate from the GPCR and diffuse along the PM until they find an enzyme.
- once bound to the G protein, the enzyme becomes activated and can trigger the next step in signal transduction leading to a cellular response.
- G proteins are GTPase enzymes.
- they hydrolyze their GTP and GDP, inactivating themselves along with the targeted enzyme
- the GTPase activity of G proteins is a quick way to regulate the activity of certain enzymes in cells.
GDP= inactive
GTP = active
what are receptor tyrosine kinases (RTKs)?
they are receptors that also have enzymatic activities: they are kinase enzymes
- kinases catalyze the transfer of a phosphate group- the phosphate group is taken from ATP molecules
- they are specifc to tyrosine residues
- initiates more than one pathway at the same time = regulates and coordinated cell growth and cell reproduction at the same time
what is the key difference between RTKs and GPCRs?
RTKs initiate multiple signalling cascades from a single ligand-binding event.
what does the inactive RTK exist as?
exists as a monomer
describe the process of RTKs
1) RTKs are inserted into the plasma membrane by an alpha-helix domain. Their cytoplasmic domain contains multiple tyrosine amino acid residues
2) When a ligand binds the extracellular active site of a monomer, it gains a higher affinity for another monomer RTKs bound to a ligand and they dimerize ( the RTK are now in a dimer complex)
3) dimerization activates the tyrosine kinase region of each monomer. As a result, each RTK adds a phosphate group from an ATP molecule to a tyrosine on the tail of the other monomer
4) RTKs are recognized by specific proteins which bind to specific phosphorylated tyrosine residues. Binding alters the effector proteins conformation and each protein is now able to trigger a specific signal transduction pathway = cellular response
any enzyme ending in -ase has the job of grabbing the phosphate group
what happens when a defective receptor tyrosine kinase proteins cannot dimerize?
means that they can’t do the pathways/cannot facilitate any of the responses
what happens if a defective receptor tyrosin kinase proteins were always active?
this would deplet alot of ATP storage
- therefore you need to be able to turn off the receptors (balance)
what is intracellular signaling?
when lipid soluble hormones (steroids) can pass directly through the phospholipid bilayer of cells, and bind to a specific receptor in the cytoplasm or nucleus of the cell.
what do hormone-receptor complexes do?
they alter the gene expression levels in the cell
- genes can be upregulated ( more proteins made )
- genes can be down-regulated ( less proteins made )
step 3
what happens in transduction?
this is the stage that converts the signal form reception to a form that can bring about a specific cellular response.
- can occur in a single step but often requires a sequence of changes in a series of different molecules ( a signal transduction pathway)
tranduction
what are the molecules in the pathway of signal transduction called?
relay (effector) molecules
what does transduction do to the response?
amplifies the response - a chemical messenger binds to a receptor on the surface of the cell which activates it
- a long cascade of reactions will generally follow with amplification = this cascade involves the phosphorylation and/or dephosphorylation of intermediates
dont need to know the path but need to know the activations + main steps
transduction: cascade
what is phosphorylation?
the transfer of the terminal phosphate group from ATP to a protein molecule
- phosphorylation activates the protein through inducing conformational change.
ATP is high energy that contains 3 phosphate groups
transduction: second messengers
what are second messengers in transduction pathways?
when not all steps involve proteins you have second messengers that are small water-soluble molecules ( i.e. cAMP or Ca2+)
cAMP is made by removing two phosphate groups from ATP by an enzyme called adenyly cyclase - cAMP is a very common second messenger. - cAMP broadcasts the signal to the cytoplasm
transduction: second messengers
what converts cAMP to AMP
an enzyme called phosphodiesterase
transduction: second messengers
where are Ca2+ kept?
kept in high concentrations within the smooth ER and mitochondria of animal cells compared to the cytosol
- the receptions of a chemical messenger (neurotransmitter) can lead to the release of Ca2+ into the cytosol of the cell which stimulates cell response
Ca2+ are used as the main second messenger in muscle contractions
transduction
what happens when no receptor can bind?
no response can be processed by the cell
tranduction
what acts as a transcription factor for a specific gene when binding?
ligand-receptor complex
this binds to a specific gene affecting its transcription into mRNA and the subsequent production of a protein - having the right receptor is key
third step C
what is the third stage of cell signalling (what is triggered)?
the transduced signal triggers a specific cellular response
the response could be:
- catalysis by an enzyme
- rearrangement of the cytoskeleton
- activation of specific genes in the nucleus
what are the two general catagories of response to a cell-cell signal?
1) nuclear ( a change inwhich genes are expressed = slow )
2) cytoplasmic ( activate and deactivate target protein already in cell = fast )
what are the three intracellular targets and each of their cellular responses?
1) enzyme - altered metabolism or other cell functions
2) structural proteins - altered cell shape or movement
3) Transcription factor - altered gene expression which changes the types and the amounts of proteinsin the cell
what does the response of a signalling molecule depend on?
depends on the type of receptor and/or molecule involved in the cascade within the target cell
why does a cell have signal deactivation?
you do not want your cell to be constanly cell signalling as that takes alot of energy (ATP) therefore the cell deactivates through mechanisms that allow the cell to remain sensitive to changes in stimulus
signalling deactivation
what are three mechanisms that the cell undergoes as a signal to deactivate?
1) when the signal is no longer produces ( the body stopes making the orignal cell )
2) the removal from receptors ( physically removing the hormones from the receptor itself )
3) by protein deactivation ( permenately deactivating the protein )
summary review
summary review
cell signalling in animals
what are some important cell signalling processes in animal cells ?
a) apoptosis (cells death)
b) cell division
c) maintenance of homeostatsis
what is apoptosis?
programmed/controlled cell suicide
- essential in animal development and protection
abnormal cell signalling in apoptosis resulting in over activity or under activity implicated in human disorders and disease.
what can abnormal cell signalling in cell division cause?
cancer
what are the two possible pathways of abnormal cell signalling?
1) positive regulators (kinases) of the cell cycle may be overactivated ( become oncogenic )
2) negative regulators also called tumor suppressors may be inactivated
what are two system communications that maintain homeostasis?
nervous and endocrine systems act as control centers to maintain homeostasis
stimulate effector cells by neurotransmitters or hormones
- abnormal cell signalling can lead to disorders and diseases
review https://www.youtube.com/watch?v=VatdTJka3_M
