Intreacellular signalling Flashcards
(28 cards)
What happens when a hormone acts on a cell?
It initiates signalling events to trigger the nucleus to change the gene expression, e.g. muscle contraction
Where can signalling occur?
Internal or external
What are signalling processes facilitated by?
Protein kinases and protein phosphates, and secondary messengers acting after hormones
Protein kinase
Enzymes that can either attach or remove a phosphate to and from another protein
Where are these phosphates acquired?
ATP
Protein kinase + ATP =
Phosphorylated protein
Protein phosphotase
Removes phosphate from protein
What does phosphorylation do to a protein?
Switches a protein on or off by changing the structure of the polypeptide backbone
What can adding a phosphate to a protein also do?
Turns their charge negative, thus attracting other amino acids
- can make them more or less active
What does the phosphate replace in amino acids?
The -OH group
Serine/threonine kinase
Most protein kinases (A, B, C)
Tyrosine kinase
Growth factor and oncogenes
Explain the effect of hormones on phosphorylation.
- The hormones bind to the receptors and phosphorylate each other
- Receptors then make attract other proteins and become a docking site for other proteins = cascade of interactions
- this signals the cell but is very slow (can take minutes but last for hours)
How do Protein kinase cascades occur?
Mitogen-activated protein kinase (MAPK) used as an example.
Phosphorylation occurs through mitosis.
1. MAPK is doubly phosphorylated - it gets phosphorylated AND phosphorylates other proteins
2. MAPKinase switches on by acquiring 2 phosphates by MAPKinase kinase.
3. This process occurs twice, therefore a cascade
Why do protein kinase cascades occur?
Amplification
What are Second messengers?
Act secondary to hormones (primary messengers) to initiate signals within the cell. Secondary messengers must be created then destroyed to create this signal
How is Cyclic AMP made, as a secondary messenger?
Created by ATP in an agonist signal
2 phosphates removed and 1 remains attached to a ribose ring
Describe how agonists affect phosphorylation
- The agonist triggers receptors e.g. adrenaline
- This stimulates the enzyme, making Cyclic AMP from ATP
- GTP protein is also made (regulates signal duration)
Cyclic AMP binds to protein kinase A leads to
phosphorylation of different proteins e.g. glycogen breakdown
What is a benefit of protein kinase A?
PKA are small and thus diffuse faster = faster signals and response such as in fight-or-flight
What creates cAMP?
Adenyl cyclase + ATP = cAMP
What degrades cAMP?
cAMP + Phosphodiesterase = AMP
Protein kinase A (PKA)
made of 4 subunits - 2 catalytic subunits + 2 regulatory subunits
- when cAMP is added, R breaks from C and phosphorylate other proteins while C attaches to AMP
A lot of components in these processes have different isoforms. What does this mean?
The pathways may be slightly different and make different isoforms of the products
