Control and Movements within Cells Flashcards
Why do unicellular organisms need to communicate?
Allows communication amoung different cells types to envoke different reponses
The ability to communicate between cells not only involves sending signals but also responding to chemical signals from neighbouring cells
Why is cell signalling important
- Intergrate signals from neighbouring and distant cells
- Need to respond to changes in the environment
- Co-ordinate growth and development
What are the 4 forms of intercellular signalling
- Contact-dependent
- Paracrine
- Synaptic
- Endocrine
What is contact dependent signalling
Occurs between cells which are adjacent to another using a membrane-bound signal molecule
Allows rapid transfer of information
What is paracrine signalling
When a cell releases a signal molecule into its local environment either to influence different/same cell types
The signal carried by a local mediator does not travel very far as it is taken up by surrounding cells/enzymes released to break it down/parts of the extracellular matrix which bind to it
Hence the spread of this molecule is highly limited
Describe synaptic signalling
- A fast and highly specific
- Transports information over fairly long distances
- Depending on the type of cell, dispersal of neurotransmitter tends to be very localised but in high concentration (hence the transmitter have low affinity)
- This allow quick changes in signals
Describe endocrine signalling
This is a type of long-distance signalling but not highly specific or as fast
Where a cell will release a hormone (e.g. pancreas releasing glucagon or insulin) into the bloodstream, allowing movement of this message across a very wide distance
The hormone ends up being at a very low concentration and receptors for the hormone are highly specific and high affinity
What is a ligand/agonist
The molecule which binds to the receptor and activates it (often called the first messenger)
Some ligands can be interpreted differently by different cells
What are Antagonists?
These are compounds that are opposed to the action of the ligand, and they bind to the receptors/ligand itself - preventing the binding between the receptor and ligand, stopping the activation of signal processes
What are Second Messengers
These are intracellular molecules, often with short-life span, which are produced in response to a first messenger
When dealing with certain types of receptors, there is a signal tranduction
What is this?
A processes by which a signal is transmitted into a cell and then to produce a final response
Describe a simply signalling pathway
- The signal molecule binds to the receptor protein (generally plasma membrane)
- The receptor activates intracellular signalling proteins that initiate a signalling cascade (a series of intracellular signalling molecules that act sequentially)
- This signalling cascade influences a target protein, altering it and the behaviour of the cell
- Overall known as signal transduction
What are two different types of signalling you need to know about
- Signalling via phosphorylation
- Signalling via GTP binding proteins
How does phosphorylation cause signalling
On - A phosphorylation change the protein which is mandates by a set of enzymes (kinases that take a phosphate group off ATP and place it on the intracellular signalling protein)
This will lead to a change in the proteins structure and hence function
Off - Phosphatase turn the protein off
They are influenced by their own signalling pathway
How do GTP-binding proteins cause signalling
Instead of the phosphate group being added directly to the intracellular signalling protein, phosphate binds to GTP which binds to the protein allowing them to turn on
GTPase activity will breakdown GTP, turing the protein off
Name a benefit of having such a complicated signal transduction pathway
The ability to amplify signal and hence effect multiple targets
There are probably now more than 1500 different receptors (signal transduction pathways)
however they don’t all have their own separate signal pathways - why
There will be crossing-over and interacting between transduction pathways which allows convergence on a common target
This allows an enhanced response
Often components of signalling pathways can be kept separate from one another using scaffolding proteins (signalling complexes)
Extracellular signals can act slowly or rapidly in target cells how
Allosteric regulation of enzymes in the signalling pathways can have a really quick affect
Whereas changing gene transcription levels can take a lot longer
Ligands bind to specific receptors
Describe some key features of hydrophilic ligands
Hydrophilic ligand e.g. proteins (insulin, growth factors), small peptides
They are water soluble, membrane impermeable
Bind to cell surface receptors
Require signal transduction mechanisms
Ligands bind to specific receptors
Describe some key features of hydrophobic ligands
hydrophobic ligands e.g. steriod hormines (estrogen, testosterone, progesterone) Vitamin D, retinoids
Lipid soluble = membrane permeable
BInd the intracellular receptors to directly alter gene expression
What is the function of the Ion-channel-coupled receptors
- They bind to a ligand, causing them to open, which allows movement of ions across a membrane
- This rapidly changes the membrane potential (voltage) through changes in cytoplasmic ion concentration which elicits cell reponse
- They can be inhibitory/non-inhibitory and depolarise or hyperpolarise membranes
- Big example is neurones
Describe the function of G-protein-coupled receptors
- A cell-surface receptor which will bind to G proteins, which when activated will then go and influence behaviour of an enzyme or ion channel
- If an enzyme is influenced, lead to the creation of second messengers (e.g. cAMP)
Describe the function of Enzyme-coupled recepors
- A cell surface receptor which either acts as an enzyme itself or associate very closley with enzymes
- In many cases the ligand is often a dimer, and on binding to the receptor, dimerisation will occur allowing the receptor to activate
- This will then kick off the signal transduction pathway
How can Oestrogen affect transcription
The Oestrogen hormone will pass through the membrane and bind to the oestrogen receptor, resulting in dimerisation
The ligand will then move to the nucleus and kick off transcripition
How is compartmentalisation aid in early immunity
When Pathogen try and enter eukaryotic cells, they will cause the surface-membrane to pinch inwards and form a vesicle around the pathogen
When the pathogen then tries to leave this vesicle in the cytoplasm, glycans which are only ever contain on the outside of the cell are now exposed to the inside
These gylcans are then recognised by machinery that leads to the destruction of bacteria or using enzymes tag the pathogen with ubiquitin
How is Clathrin used in Vesicle assembly
- Starting off with a donor memebrane which recruits Clathrin (which has natural curvature)
- The Clathrin polymerises and starts to deform the membrane, the more the Clathrin moves in, the more the membrane buds at the donor budding site
- It is then cleaved and is transported elsewhere
