Biochemistry 🧪 Flashcards
what is the importance of intracellular communication?
Intracellular communication is very important to cell adaptation to the change in their internal or external environment
what are the types of intracellular communication?
direct & indirect
compare between Direct intracellular communication & Indirect intracellular communication
compare between endocrine system and nervous system according to:
- Types of chemical messenger
- Distance of action
- Speed of response
- Duration of action
- Major function
what is the definition of hormones?
are natural organic substances, secreted (released) from the ductless glands into the blood and alter the metabolism of target cell (act as chemical messengers)
what are target cells?
It is the cell that contains the specific receptors of the hormone.
in what manner does the hormone fit in its receptor?
hormone fits receptor on target cell like a lock and a key (Lock and key system)
what is the definition of hormone receptors?
They are cell-associated recognition molecules.
what is the nature of hormone receptors?
They are protein in nature.
what are the parts (functional sites) of hormone receptors?
Each receptor has two functional sites:
1) Recognition site: it binds the hormone specifically.
2) Signaling site:it couples hormone binding to intracellular effect.
what is the cellular location of hormone receptors?
Intracellular receptors: Located inside the cell either in the:
* In the cytosol: eg Steroid hormones.
* In the nucleus. eg. Thyroid hormones
Cell-membrane receptors: Located in the plasma membrane of the cell.
- Proteins, peptides, catecholamines.
what are hormones classified according to?
- Chemical Nature
- Solubility
what are types of hormones according to chemical nature?
- Steroid hormones
- Non steroid
what are steroid hormones derived from?
They are derived from cholesterol.
what are examples of steroid hormones?
- Glucocorticoids
- Mineralocorticoids.
- Sex hormones: Testosterone, Estrogen, and progesterone
compare between lipophilic hormones & Hydrophilic hormones according to:
- solubility
- transport in plasma
- penetraton of plasma membrane
- receptor
- mechanism of action
- response
- mediator
what is the mechanism of action of hormones which act via extracellular receptors (2nd messenger)?
- For Hydrophilic hormones (Proteins and peptide hormones, catecholamines)
- These hormones are water soluble → so, circulate mainly dissolved in the plasma→ reach to the target cells → but cannot penetrate the membrane as it is not fatsoluble → so, it binds to receptor proteins in the cell membrane.
- This hormone–receptor binding → activates an enzyme that catalyzes the synthesis of a second messenger (It is the signal produced because of hormone binding to its cell membrane receptor.
- This 2nd messenger activates other enzymes that catalyze a specific reaction in the cell to mediate the hormone action
what is the mechanism of action of CGMP as a second messenger?
- It is the 2nd messenger of Atrial natriuretic factor (ANF) that produced in cardiac atrial tissues.
- The hormone binds to its specific G protein coupled receptor→ activates the membrane bound form of guanylate cyclase → catalyzes the transformation of GTP to cGMP→ cGMP activates protein kinase G→protein phosphorylation→ mediate the effects of ANF ( smooth muscle relaxation, vasodilatation)
- After mediating its effects, cGMP is hydrolyzed by cGMP dependent phosphodiesterase enzyme 5’ GMP.
what is the mechanism of action calcium or phosphatidyl inositol as a second messenger?
- Some hormones like: GnRH, TRH, ADH utilize this 2nd messenger.
- Binding of the hormone (ligand) to its specific receptor →activates G protein (Gq) →activates the enzyme phospholipase C (PLC)→ The active PLC hydrolyses phosphatidyl inositol bi biphosphate (PIP2) to:
- Diacyl glycerol (DAG)→It activates protein kinase C→ phosphorylates of enzymes/protein → mediate the effects of the hormone.
- Inositol Triphosphate (IP3)→ couple Ca Channel→releases Ca2+ from intracellular storage sites (ER , Mitochondria) → Ca2+ binds to Ca binding protein (calmodulin) to form Ca2+/ calmodulin complex→phosphorylation of enzymes → mediate the effects of the hormone.
