11 Cell Communication Flashcards
List three forms signals that are received by cells take?
They take light, touch, and most commonly, chemical
Define a signal transduction pathway
A series of steps in which a signal is converted to a response
What property do bacterial populations have that allows them to coordinate their activities to maximum efficiency and productivity?
Quorum sensing, the ability of bacteria to monitor the local density of cells. Example is formation of biofilm
List two ways communication by direct contact can take place in the cell
- Cell junctions: signalling mlcls dissolved in the cytosol pass through either gap junctions (animals) or plasmodesmata
- Cell-to-cell recognition: animal cells may interact by interaction between mlcls protruding from their surfaces
Define local regulator; give an example.
A local regulator is a signalling molecule released by the signalling cell that travels short distances; example is a growth factor or neurotransmitter
List two types of local signalling
a) Paracrine signalling - secreting cell acts on numerous nearby cells by discharging local regulators
b) Synaptic signalling - a nerve cell releases neurotransmitter mlcls into synapse (gap bw nerve cells), stimulating it
List one type of long-distance signalling
Endocrine/hormonal signalling
Define hormone. Two examples of hormones that vary greatly by size and type would be:
It is a chemical used by plants and animals for long distance signalling
A gaseous plant hormone, ethylene, that promotes ripening
Insulin, a mammalian hormone that regulates glucose levels
When glycogen & glycogen phosphorylase are mixed in a test tube, is glucose phosphate generated?
No it is not, becuase the generation requires an intact cell with an intact receptor in the membrane and intact signal transduction pathway
Define ligand. What is the effects of ligand binding?
a mlcl that specifically binds to another larger one.
Ligand binding causes a change in shape for the receptor protein, which activates it and enables it to interact with other cellular mlcls.
Give two examples of a plasma membrane receptor. Explain how it works.
A G protein-coupled receptor. The GCPR is integrated in membrane while the G-protein, acting as a switch, is attached loosely to cytoplasmic side.
When the GCPR is activated (by a signalling mlcl attaching to extracellular site) it changes shape and its cytoplasmic side binds to inactive G-p, and GTP displaces GDP
The activated protein then dissociates from the receptor and binds to a membrane enzyme, activating it which then sends a cellulor response.
The G-protein hydorlzes GTP to GDP releasing Pi group, becomes inactive and leaves enzyme
Receptor Tyrosine kinases
What is a G protein?
A protein that binds to the energy-rich GTP, or guanosine triphosphate. When GDP binds to it, it is inactive.
Abnormal functioning of RTKs is associated with:
many types of cancer
What is a kinase?
A kinase is an enzyme that catalyses the transfer of phosphate groups
A tyrosine kinase catalyses the transfer of P groups specifically from ATP to amino acid tyrosine
What is an ligand-gated ion channel?
It is a membrane receptor. The ion channel receptor remains closed until a ligand binds to it on its extracellular side, at which specific ions can flow through it and affect ion concentration of specific ions like Na+ or Ca^2+
Where are intramembrane receptor proteins found?
Either in cytoplasm or nucleus of target cells. This is why chemical messengers have to be hydrophobic and small to be able to pass through.
Give a specific example of an intramembrane receptor, and explain its journey
Testerone, a steroid hormone passes through plasma membrane, binds to receptor protein cytoplasm and activates it. Then the hormone-receptor complex enters nucleus and binds to specific genes.
What is a protein kinase?
It’s an enzyme that transfers P groups from ATP to protein
Explain a phosphorylation cascade
It is a cascade of protein phosphorylation with each bringing a shape change
How would the abnormal acitvity of a kinase cause cancer?
Because some kinases regulate proteins that in turn regulate cell reproduction
Why are protein phosphatases important in the phosphorylation cascade?
Becuase they are enzymes that can rapidly remove Phosphate groups from proteins, a process called dephsophorylation
Also because hey make protein kinases available for reuse
What are the components of a signal transduction pathway? What are second messengers?
Either proteins or second messangers. The latter are small water-soluble mlcls or ions
Give two popular examples of second messangers
Cyclic adenosine monophosphate (cAMP) is a compound that activates teh serine/threonine kinase or protein kinase A.
Calcium ions and inositol triphosphates (IP3)
What is adenylyl cyclase?
It is an enzyme embedded in the plasma membrane that coverts ATP to cAMP when it receives an extracellular signal.
