Introduction to Cell Signalling Flashcards
(33 cards)
What makes a good signal
Specificity
Small – able to travel from the site of production to its effector
Whether intra or extra cellular signals need to be synthesised, mobilised or altered quickly
An enzyme that can be made/activated to create signal
Sequestered signals (vesicles) released
How are signals switched off after use
Internalisation of membrane receptors
Enzymatic degradation or modification
Sequestering (calcium is released and then removed from the cytoplasm)
What does the ligand-receptor interaction cause
receptor conformational change
which is detected inside the cell
What happens once the signal reaches its destination within the cell
-Metabolic enzyme
- Vesicle membrane protein
- Nuclear transcription factor
What responses does the cell mount
- Change in metabolism (glycolysis)
- Mobilisation of vesicle (exocytosis and hormone release)
- New protein transcribed
What does signal diversity refer to
Receptor-ligand interaction (specificity) in central signal perception and signal transduction pathway activation
What are the functions of an electrical signal
Electrical potential is generated across a cell membrane
Fast and efficient
Neurons – cover a long distance usually
Myelin sheath / nodes of Ranvier improves the signal speed
Synapses signal may be transmitted directly via a gap junction (electrical)
They can also be chemical (ligand/receptor)
What are the functions of chemical signals
Endocrine – long distance
Produced by a cell at one site and transported through the organism
This is done through the blood stream
They have an effect on cells at a distal site
Paracrine – short distance
Chemical produced by one cell which has a local effect on surrounding cells (inflammatory response)
Autocrine – like paracrine but effects the same cell that produced the signal (growth factors)
How do cells use different chemicals to communicate
Many signals (like hormones and paracrines) are soluble peptides
Soluble chemicals cannot diffuse through the cell membrane and require complementary membrane receptors in order to transmit the signal into the target cell
Steroid hormones are hydrophobic so can cross cell membranes
Therefore intracellular or intra-nuclear receptors are used over extracellular ones
What is the function of gap junctions
Small molecular hydrophilic signals (<1.2 kDa) can be transferred between cells directly using gap junctions
Nexus gap junctions connect the cytoplasm of 2 joining cells
Nexus gap junctions are “hemichannels” - each cell expresses one half on the cell surface
Gap junctions are made from connexion proteins In either homo or hetero-hexamer arrangements
What is the function of plasmodesmata
Many plant tissues also communicate directly through cell-to-cell connections – plasmodesmata
Cytosol is continuous with neighbouring cells
This is a membrane tube – desmotubule
Metabolites, proteins and mRNA have been shown to move through these junctions
How does cell-cell contact work
A cell surface molecule on one cell is the ligand for a cognate receptor on another cell
This is the basis for the immune response in the human body
What are important features of signal transduction
Ligand (primary signal)
Second messenger (amplification)
Kinase activation (amplification)
Target phosphorylation (amplification)
Enzyme activation (amplification)
What 2 features do pathways contain that improve their efficiency
Overlap and cross-talk
What are areas of homology in intracellular protein signalling components called
Domains and modules
What is an important feature of protein domains
They are conserved and identifiable across different proteins
What is Src homology (SH) domains
Src homology (SH) domain ; SH2 domains
SH2 domains are roughly 100 amino acids and have high affinity for phosphotyrosine residues
Src homology (SH) domains; SH3 domains
These domains conversely bind to the target sequence polypeptide that contains several proline amino acids
What are 14-3-3 proteins
14-3-3 proteins bind other proteins and act like “scaffolds” inside the cell (highly conserved central core)
14-3-3 proteins bind phosphorylated versions of proteins
In some cases, phosphorylation may not be sufficient to alter protein activity
If this is the case, further binding to 14-3-3 proteins is required
What do oncogenes do
Many ligand-binding events lead to the activation of signal transduction pathways which lead to cell proliferation
This can be caused by proto-oncogenes – similarly tumour suppressors lead to cell cycle arrest
If the proteins in this pathway become mutated this can lead to constrictive activation —> uncontrolled cell growth
What are the 4 classes of oncogenes
Class 1 – oncogenes that code for growth factors
Class 2 – oncogenes that code for growth factor receptors
Class 3 – G proteins and kinase genes (intracellular)
Class 4 – transcription factors
What is 1 of the principle ways cells communicate with each other
extracellular signals
Release and detection of extracellular signals is one of the main ways cells signal each other
What are the types of extracellular signals
Small water soluble molecules (adrenaline)
Peptides (cytokines,insulin)
Lipophilic (fat soluble)
Neurotransmitters
What is the function of cytokines
Small peptide molecules produced by the immune/epithelial which alter the growth/survival/function of the target cell
What are the types of cytokines
Interleukins (IL), interferons (IFN) and tumour necrosis factors (TNF)
