Cell Signalling II Flashcards
What is hormone binding specificity?
Measure of the ability of a receptor to distinguish between closely related substances
What are the 2 main functions of receptors?
Binding the hormone with high affinity
Invoking signal inside the cell to initiate biological response
What kind of proteins are receptors usually?
High affinity binding proteins
What happens to receptor when it is bound by hormone?
Conformational changes in the receptor take place and those changes are detected by intracellular molecules
How does the filter assay for reecptor binding work?
Equilibrium binding takes place between labeled ligand and the receptor
Bound complex is radioactive and free receptor is not.
Free ligand can pass through filter but complex cannot pass
What are the steps to conduct a filter assay?
Membrane is isolated
Ligand added to membrane
Solution is passed through a filter and unbound ligand is washed off
Bound radioactivity is then measured which is proportional to amount of complex
What is a limitation to the filter assay?
Hydrophobic ligands are non-specifically incorporated into the membrane
How is the issue of nonspecific binding accounted for?
Total binding is measured
Nonspecific binding is measured after taking receptors out of the membrane
Total binding - NSB = specific binding
Specific binding data is then analyzed
What does Kd refer to?
The concentration of hormone at which half the maximal binding takes place
What is the slope of the [RL]/[L] vs [RL] graph?
-1/Kd
What are the methods of signalling through the cell membrane?
G protein coupled receptor activation
Receptor tyrosine kinase which activates transcription factor altering gene expression
Receptor guanylyl cyclase: Ligand binding to extracellular domain stimulates formation of cyclic GMP
Gated ion channels
Adhesion receptor (integrin) which binds molecules in extracellular matrix changes conformation thus altering interaction with cytoskeleton
Nuclear receptor allows receptor to regulate expression of specific genes
Which hormones bind to intracellular receptors?
Steroid hormones and thyroid hormones
What molecules are steroid hormones produced from?
Cholesterol via stepwise removal of carbon atoms and hydroxylation
Where are steroid hormones synthesized?
In the adrenal cortex (glucocorticoids and mineralocorticoids) and the gonads (estrogens, progesterone, and androgens)
What type of molecules are thyroid hormones? What does this allow them to do?
Small and hydrophobic, lipid soluble
Can diffuse through membrane of target cells
What happens after thyroid hormones bind to their target receptors?
Affects the ability to transcribe specific genes by interacting directly with the transcription factors they control
What hormone stimulates androgen production?
Luteinizing hormone
Which cells produce androgen hormones?
Leydig cells
What are the target cells of androgens?
Prostate
Bone
Muscle
The function is to maintain functional male reproductive system as well as male secondary characteristics and increasing muscle and skeletal size.
What are the main functional regions of a nuclear receptor?
Central DNA-binding domain which contacts the DNA
Ligand binding domain which binds specifically to hormone
Variable N terminal regions which contain one or more activation domains.
What happens to receptor that is unbound?
Inhibitory proteins bind to it and prevent transcription from taking place.
What happens to nuclear receptor when bound by ligand?
Conformational change releases inhibitory protein and a co-activator protein binds to it to induce gene transcription
Where are intracellular receptors located?
They can be in the cytosol and then travel to nucleus when ligand is bound.
Or they can be located in the nucleus.
What are nuclear receptor response elements?
Nucleotide binding sequence that interacts with nuclear receptors.
What do nuclear receptor response elements look like?
They lie adjacent to genes that the hormone regulates and consist of 6 base pair repeat sequences separated by 3 - 5 base pairs.
What do steroid hormones do to gene expression?
When they bind to their receptors the complexes promote activation of response element and in turn increase transcription and then translation.
Are there any intermediate molecules involved with nuclear receptors?
No, the receptor is the transcription factor which means there is less opportunity for regulation by other factors and pathways and thus there is limited amplification of signal
What domain structure is shared among all nuclear receptors?
Variable region DBD and LBD
Learning outcomes:
Understand that receptor/ligand interaction is very
specific
2. Understand how receptor ligand studies are
performed and be able to describe Kd and Bmax
represent
3. Understand the properties of small hydrophobic
signalling molecules
4. To describe the steroid hormone signal transduction
mechanism with particular reference to regulation of
gene TRANSCRIPTION
What is Kd?
The concentration of hormone at which half the maximal binding occurs
What does Bmax refer to?
The maximal binding which also means the total number of receptors available for binding
