Topic 8 - Cell communication Flashcards
How do yeast cells communicate?
mating factor
An example of contact-dependant signalling? deets
nerve cell differentiation in fruit fly
destined neuronal cell inhibits surrounding cells from also becoming neuronal cells
uses inhibitory signal (delta) & receptor protein (notch)
Know hormones in table 16.1 - 1 MCQ to be had!
also on slide 10
The cells response to a signal depends upon which 3 factors?
- receptor
- signal transduction proteins present in the target cell
- genetic programming of cell
T or F - The same signal molecule can induce different responses in different target cells eg.
true -
Heart muscle: ACh -> receptor1 -> decease HR & force
Salivary: ACh -> receptor1 -> ++secretion
Skeletal muscle: ACh -> receptor2 -> ++contraction
An animal cell depends on multiple extracellular signals. explain how eg?
different cells can have different receptors & in many combinations that trigger different responses
eg. survival signals (receptors) + division signals => cell grow & divide
no survival signal => apoptosis
Extracellular signals that involve gene expression take how long?
mins to hrs
Extracellular signals that involve modify existing proteins/enzymes take how long?
secs to mins
Nuclear receptors include…? why are they referred to as this?
both, cytosolic and nuclear receptors
Because, when activated by hormone binding, they act as transcription regulators in the nucleus
Name the intracellular signalling molecules
Which one crosses as the neutral -COOH/NH2 species?
steroids (& other small hydrophobic ones)
- cortisol
- estradiol
- testosterone
- thyroid hormones (thyroxine) - neutral
How do steroid hormones exert their intracellular effects? eg.
by binding and activating the nuclear receptor protein -> nucleus -> activate or repress transcription of specific genes
Some dissolved gasses can cross plasma membrane & activate intracellular enzymes directly. Name one & give example…
nitric oxide (NO - synthesised from arginine) -> released by endo cells of blood vessels upon ACh stimulation -> rapid diffusion of NO thru plasma membrane -> smooth muscle cells -> binds to guanylyl cyclase -> cGMP -> vessel relaxes -> dilate -> ++blood flow (5 - 10 secs)
example of NO synthetic drug that doe this?
viagra -> blocks CGMP phosphodiesterase -> ++cGMP
Which molecules cannot cross the plasma membrane & must bind to cell surface extracellular receptors?
proteins, peptides, small, highly water-soluble molecules
How can extracellular signals often activate intracellular signal transduction pathways? flow chart is good. figure 16-12 (slide 25)…
extracellular signalling molecule -> receptor protein (transmembrane receptor) -> intracellular signalling molecules (relay analogy) -> effector proteins (eg. metabolic enzyme or transcription regulator) -> cell responses (eg. altered metabolism & altered gene expression)
The components of these intracellular signaling pathways perform one or more crucial functions. List & describe them.
Relay - relay signal & help spread it thru cell
Transduce & amplify - make signal stronger (via 2nd messengers) so few extracellular signal -> large intracellular response
Integrate - receive signals from more than one intracellular signaling pathway & integrate them before passing ‘em on
Distribute - distribute the signal to more than one signaling pathway or effector protein
Some proteins can act as molecular switches. What are they? on/off triggers?
Phosphorylation: on via protein kinase, off via protein phosphotase
GTP-binding proteins: on GTP bound, off GDP bound
What are the 3 classes of membrane receptors?
- Ion-channel-coupled receptors
- G-protein-coupled receptors (GPCRs)
- Enzyme coupled receptors
Ion-channel-coupled receptors. 3 correct statements about ‘em…
- open or close in response to binding of ligand to the receptor
- Also called transmitter-gated ion channels
- Activation alters membrane potential → signal
What number % are human genes are GPCRs?
4% of human genes (>800 genes known)
GPCRs are coupled to …? subunits…?
a trimeric G-protein with 3 subunits: alpha, beta & gamma
Stimulation of GPCRs Activates G-Protein Subunits. Explain using diagram how it works. include activation & inactivation steps. all players involved…
Figure 16.17 & 16.18 (textbook)
movie 16.2 - must know these mechanisms well!
The G-protein switch demonstrates a general principle of cell signaling mentioned earlier: the mechanisms that shut a signal off are as important as the mechanisms that turn it on. Describe a condition that fucks this mechanism leading to pathology. (not super important but good to understand and fairly easy to remember)
Cholera - a bacterium that multiplies in the intestine, where it produces a protein called cholera toxin. This protein enters the cells that line the intestine and modifies the subunit of a particular G proteinin such a way that it can no longer hydrolyze its bound GTP. The altered subunit thus remains in the active state indefinitely, continuously transmitting a signal to its target proteins. In intestinal cells, this causes a prolonged and excessive outflow of Cl– and water into the gut, resulting in cata- strophic diarrhea and dehydration. The condition often leads to death unless urgent steps are taken to replace the lost water and ions
G-protein subunits can be … or … in the plasma membrane
G-protein subunits can be ENZYMES or ION CHANNELS in the plasma membrane
