Cellular Mechanisms Of Hormone Action Flashcards
What does the endocrine system secrete? What differentiates it from the nervous system in terms of coordinating communication throughout the body?
Hormones. The endocrine system acts slower but has a long-lasting response. The nervous system conveys high speed electrical signals.
What are the 3 different methods of hormone signaling?
Endocrine
Paracrine
Autocrine
Give 3 actions of hormones that change the condition of the tissue/cell
- Altering plasma membrane permeability by opening or closing protein/ion channels
- Regulating expression of functional proteins (via gene activation of suppression)
- Moderating enzyme activity (activation or deactivation)
- Inducing or suppressing release of secretory products
- Stimulating mitosis and cell division
What are the factors influencing the degree of cellular response. Give 2 examples of each
Delivery of hormone:
- Rate of synthesis and secretion of hormone
- Proximity of target cell to hormone source
- Dissociation constants with transport proteins (for hydrophobic hormones)
- Rate of conversion from inactive to active forms
- Rate of clearance or elimination by liver/kidney
Receptor/Tissue status:
- Density and state of occupancy of receptors
- Affinity of receptors for hormone
- Desensitization of receptor
What are the classifications of hormones according to structure giving an example of each
Steroid Hormones: Derived from cholesterol. Testosterone and Estrogen
Amine Hormones: Amino acid derivatives. Epinephrine and thyroxine
Peptide Hormones: Short chain amino acids. Insulin and oxytocin
Protein Hormones: Long chain/complex proteins. Luteinizing hormone and TSH
Briefly describe Steroid hormones
- Derived from the lipid cholesterol
- Not soluble in water => hydrophobic
- Travels bound to a transport protein in the blood
Briefly describe Amine Hormones
- Derived from the modification of amino acids Tryptophan or Tyrosine
- Both hydrophilic and hydrophobic members
Briefly describe Peptide and Protein Hormones
- Consists of multiple amino acids that link to form an amino acid chain
- Peptide hormones consist of short chains of amino acids
- Protein hormones are longer polypeptides
How are hydrophobic and hydrophilic hormones transported in the blood?
Hydrophobic hormones bind to transporter proteins pr plasma proteins within the circulation
Hydrophilic hormones are transported readily in the blood
Are the receptors of hydrophobic and hydrophilic hormones different? If so, how are they different?
Hydrophobic hormones are complexed with the receptor intracellularly
Hydrophilic hormones bind to extracellular receptors including RTKs and GPCRs
Hydrophobic hormones are involved in intracellular signaling. Explain the steps involved in this process
- The hormone diffuses readily through the bilayer
- Hormone binds to specific receptors within the cell
- Activated receptor translocated to the nucleus
- Once in the nucleus, the activated receptor binds to hormone response elements (HRE) of DNA
- Binding drives changes in mRNA resulting in protein expression
Briefly describe Hormone Response Elements (HREs)
HREs are regions of DNA that contain a consensus sequence. They are typically found upstream or 5’ to the transcription initiation site.
HREs ALSO associate with nuclear receptor proteins or transcription factors which provide a further later of complexity and control.
What is the most common receptor that hydrophilic hormones tend to bind to?
GPCRs
State the mechanism of hydrophilic hormone signaling in GPCRs
- The hormone binds to GPCR receptors to carry signals across the membrane
- Activated G proteins in turn activate an enzyme called Adenylate cyclase which converts ATP to cAMP.
- cAMP is the second messenger and propagates the signal throughout the cell. It does so by targeting and activating protein kinase A within the cytosol
- PKA triggers selective phosphorylation of cellular proteins activating or inhibiting them.
What kind of feedback is associated with controlling cAMP signaling? How is cAMP deactivated?
cAMP signaling is controlled by negative feedback. PKA activates phosphodiesterase which deactivated cAMP. This turns the signal off until the next stimulus is received
Is the duration of a hormone signal short or long?
Duration of the hormone signal is short.
If you were thinking long, then you were probably thinking of the bigger picture (in the beginning of the powerpoint) where hormones circulate the blood for a long time.
What are the second messengers of hydrophilic hormones?
cAMP
Calcium
cGMP
Explain the process which involved Calcium as the second messenger including the role of calcium as a second messenger.
G-proteins activate the enzyme phospholipase C which cleaves membrane-bound phospholipids into DAG and IP3. DAG activates protein kinases which causes a phosphorylation cascade and IP3 increases intracellular calcium ions. It acts as a second messenger by influencing enzymatic and other cellular activities directly and by binding to the calcium-binding protein Calmodulin which is able to modulate protein kinase within the cell.
Explain the process which involves cGMP as the second messenger. Give an example that illustrates this process.
cGMP signaling is a GPCR independent mechanism that involves the conversion of GTP into cGMP. This is driver by the membrane-bound receptor Guanylate Cyclase.
Atrial Natriuretic Peptide (ANP): Increased blood pressure induces ANP release from the cardiac atria. The binding of ANP to its receptor causes the conversion of GTP to cGMP. cGMP activates a protein kinase G (PKG) and also directly regulates ion channels. This leads to a reduction in ECF volume by increasing renal sodium excretion.
Answer the following questions:
- In GPCR, cAMP activates what protein kinase?
- With Ca2+ as the second messenger, what activates protein kinases and what does it lead to?
- With cGMP as the second messenger, what is the receptor enzyme responsible?
- With regards to ANP (Atrial Natriuretic Peptide), what protein kinase is activated by cGMP
- Protein Kinase A
- DAG activates protein kinases leading to a phosphorylation cascade
- Guanylate Cyclase
- Protein Kinase G
What hormone receptor does insulin bind to? Briefly explain what happens when the hormone binds.
Insulin binds to an RTK (Receptor Tyrosine Kinase). The receptor is a tetramer. Once insulin binds, receptors aggregate and phosphorylate each other at specific tyrosine residues in a process called dimerisation and autophosphorylation. Then, the insulin response substrate (IRS-1) is phosphorylated and propagates signal transduction.
Is the Insulin receptor substrate phosphorylated when activated or deactivated
Activated
With regards to hydrophobic and hydrophilic hormones, associate each with their ultimate function.
- Gene Transcription
- Transporter channels
- Protein Translocation
- Protein Modification
- Hydrophobic
- Hydrophilic (sometimes hydrophobic but infrequent)
- Hydrophilic
- Hydrophilic
Can the cell respond to multiple hormones simultaneously?
Yep
