Principles of cellular physiology 4 Flashcards
State the difference between cell surface receptors and intracellular receptors
- CELL SURFACE Membrane receptors for: hydrophilic signalling molecules activate a wide variety of intracellular ‘signal transduction’ pathways e.g. gene regulation
- INTRACELLULAR: most receptors for hydrophobic signalling molecules act as transcription factors in nucleus to regulate gene transcription
What are hormones?
- First messengers and are classified as ‘steroid’ or ‘nonsteroid’
Describe steroid hormones.
- Lipid soluble - derived from cholesterol
- Relatively small so can pass through the plasma membrane
- Enter target cells and bind to intracellular receptor and activate genes that produce new proteins
- Slower acting than non steroid hormones
Describe non steroid hormones.
- Water soluble - derived from amino acid
- Binds to receptors on target cell membranes and activates signal transduction pathways that produces a chemical called a second messenger
- Work through intermediate mechanisms to activate existing enzymes; small amount of hormone can produce a significant cellular change
- Faster action than steroid hormones
Describe the hormone receptors pathway (steroid hormones)
Hormone - nuclear receptors - activate genes - synthesise new proteins or enzymes - cell responds
Describe the hormone receptors pathway (non steroid)
Hormone - membrane-bound receptors - receptors alter the activity of G proteins which opens or closes ion channels and activates existing enzymes - cell responds OR receptors alter the activity of intracellular enzymes which activates existing enzymes - cell responds
Name the ligands for intracellular-nuclear receptors
- Androgens, Oestrogens and progesterone - produced by gonads
- Corticosteroids, Glucocorticoids, Mineralocorticoids - produced by adrenal gland
- Thyroid hormone
- Vitamin D3
- Retinoic acid
Where are corticosteroids produced?
Adrenal gland
Where are glucocorticoids (GR) produced and what does it stimulate?
Adrenal gland
Act to stimulate glucose production
Where are mineralocorticoids (MR) produced and what does it act on?
Adrenal gland
Act on kidney to regulate salt and water balance
Where are thyroid (TR) hormones produced and state its role
Synthesised from tyrosine in thyroid gland
Has an important role in development and regulation of metabolism
Describe the role of vitamin D3
Regulated Ca2+ metabolism, bone growth
What is retinoic acid (RAR) synthesised from and what is its role?
- Synthesised from vitamin A
- Play important roles in vertebrate development
Where is the receptor GR localised?
cytoplasm
Where is the receptor MR localised?
Cytoplasm
Where is the receptor Estrogen localised?
Nuclear
Where is the receptor progesterone localised?
Nuclear
Where is the receptor TR localised?
Nuclear
Where is the receptor RAR localised?
Nuclear
Describe the structure of nuclear receptors.
- Transactivation domain (A/B & E)
- DNA-binding/dimerization domain (C)
- Nuclear localisation domain (D)
What is the role of transactivation domain (A/B & E)?
Contains the ligand binding domain (E) which causes a change of conformation to the DNA, initiating transcription
What is the role of DNA-binding/dimerisation domain (C)
Allows dimerisation of receptors and
binding to the DNA
What is the role of nuclear localisation domain (D)?
Allows the receptor to enter the nucleus or to maintain the nuclear localisation
Describe the mechanism of CYTOPLASMIC receptor activation.
- Receptor located in cytoplasm
- Ligand enters cell and causes receptor activation
- Ligand binding dislodges regulatory/repressor protein
- Ligand-Receptor complex enters nuclear and binds to specific DNA sequence (in promoter region)
- Gene transcribed and translated, protein produced
- Or gene expression inhibited
- Can have latent period of several hours due to production of mRNA and protein
