C2.1 Chemical Signalling (year 6) Flashcards
Describe the process of Quorum sensing using 1 example
Quorum sensing allows bacteria to alter group behavior based on population density.
Marine Bacterium Vibrio fischeri:
1. During their repro cycle, individual Vibrio fishceri produce AUTOINDUCER molcules which pass through their cell membrane and wall into the environment
2. As Vibrio fischeri are reproducing there is higher population density = higher conc. of autoinducer
3. When the no. of autoinducer reaches a certain threshold level they move into the bacteria cells and bind to the protein LuxR
4. LuxR binds to a DNA binding site called a lux box
5. the lux box produces luminescent protein called luciferase
Name the 4 functional ligands in animals
Hormones - e.g. oestrodiol
Neurotransmitters - released at synapses into the gap btwn junctions
Calcium ions - involved in hormone secretion, muscle contraction, cell signalling
Cytokines - Glycoproteins that act as messengers btwn cells
Diff btwn hormones and neurotransmitters
Hormones:
- Ligands carried in the bloodstream for a distant response
- have a general function of regulation
Neurotransmitteres:
- Signalling molecules that bind to nearby cells to create a localised response
- carry signals btwn neurons and from neurons to target cells
Reasons for chemical diversity in hormones and neurotransmitters
- these ligands must act on many different target cells = larger variety makes it easier to act on diff cells
- some ligands must travel long distances whereas some travel shorter distances
- diff ligands work diff ways on target cells
- some ligands create long-term/short-term effects
- to allow for specificity.
Name the 2 types of transmembrane receptors + the differences btwn them
Plasma membrane transmembrane receptor:
- embedded in the cell membrane
- hydrophillic ligands are unable to cross the cell membrane and bind to these
- have hydrophobic and hydrophillic domains
- have cytoplasmic and extracellular domains, where hydrophillic amino acids are found outside the membrane, vice versa for hydrophobic amino acids
Cytoplasm transmembrane receptor:
- floating in the cell cytoplasm
- hydrophobic ligands cross the cell membrane and bind to these
- have hydrophobic and hydrophillic domains
Describe the intiation of a signal transduction pathway
Ligand binds to a receptor with a complementary shape > produces a change in the receptor > signal transduction pathway initiated
Describe the 3 types of transmembrane receptors
Chemically gated ion channel receptors:
- Multipass protein with central pore
- has gates that open and close
Enzymatic receptor:
- Single pass protein
- Bind ligands extracellulary and activates enzymes intracellularly
G protein-coupled receptors:
- Multi-pass protein with intracellular binding site for G protein
- binds with ligands that activate the G protein
1 example of a chemically gated ion channel receptor
Acetylcholine receptor:
- Multi-pass protein as the domains thread back and forth the cell membrane multiple times
- The channel opens only when Acetylcholine binds to it
- acetycholine binds > ion channel opens > +ve charged ions diffuse into cell > voltage across cell membrane changes > cellular response
e.g. the acetycholine receptors in muscle cell membranes allow Na+ ions to pass into the cell, resulting in contraction
How do G protein-coupled receptors work + 1 example
- Ligand binds to G-protein coupled receptor, activting the receptor and the G protein
- The G protein binds to Guasonine Triphosphate (GTP) and activates, and GTP loses its 3rd phosphate by hydrolysis to become GDP.
- The effector protein is activated
- Cyclic AMP (cAMP) acts as a 2nd messenger in the action of EPINEPHRINE receptors.
- cAMP is produced when the enzyme Adenylyl cyclase acts on ATP.
- This continues the cascade involving multiple phosphorlations until the final effect is obtained.
The GPCR is located in the cell membrane, as the G protein is intracellular. When a ligand binds to GPCR outside the cell, the G protein is activated by phosphorylation, activating the specific intracellular interaction.
1 example of an enzymatic receptor + how it works
Tyrosine Kinase:
- made out of extracellular, transmembrane, intracellular membrane
1. 2 molecules of insulin bind to the extracellular domain of tyrosine kinase
2. the intracellular domain acts as a kinase (an enzyme which catalyses the transfer of a phosphate group from ATP to another molecule, phosphorylating it
3. In this case the receptors in the intracellular domain are phosphorylated in a process called autophosphorylation
4. this begins a signal cascade, in which several other proteins are phosphorylated in sequence.
5. the cascade sequence results in the activation of many Glut4 secretory vesicles which produce Glut4 glucose transporters.
6. The Glut4 transporters move towards the cell membrane and result in glucose being realeased into the bloodstream
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