Unit 1- Communication within organisms Flashcards
What is a hormone?
Hormones are extracellular signaling molecules that are secreted by one tissue (such as an endocrine gland) into the blood. The hormone circulates in the bloodstream until it reaches the receptor protein of its target cell or until it is broken down.
Give examples of hydrophilic hormones?
Peptide hormones, ADH and Insulin
Give examples of hydrophobic hormones?
Steroid hormones and thyroxine
Describe hydrophobic signalling
Hydrophobic signalling molecules are lipid soluble and can therefore move by diffusion across the hydrophobic part of the plasma membrane. The receptor for these hormones is inside the cell in the nucleus. The receptor protein will be gene regulatory.
Describe how thyroxine works and the steroid hormones work
Thyroxine brings about the transcription of the gene for the Na/K ATPase pump. In the absence of the hormone, the thyroid receptor protein binds to the DNA and inhibits the transcription of the gene. When the hormone thyroxine binds to the receptor protein there is a conformational change which prevents the protein from inhibiting transcription allowing the Na/K ATPase to be transcribed increasing metabolic rate.
The steroid hormones bind to transcription factors so that only once the hormone binds to the receptor can the transcription factor bind to the gene regulatory sequences of DNA for transcription to occur.
Describe hydrophilic signalling
Hydrophilic molecules such as peptide hormones and neurotransmitters, are not lipid soluble. Hydrophilic signals cannot cross the hydrophobic part of the plasma membrane, they must instead bind to cell-surface receptor molecules. These transmembrane proteins change conformation when the signal ligand binds; causing the signal to be transduced across the membrane of the cell. This means that the behavior of the cell changes in response to the external binding of the signal molecule to the receptor molecule. Transduced hydrophilic signals often involve cascades activated by G-proteins or phosphorylation by kinase enzymes.
Describe how Insulin works
Once the signal binds, the signal is transduced and a series of phosphorylation events trigger the recruitment of GLUT4 glucose transporters to the cell membrane. These transporters allow glucose to enter these cells for further metabolism and the blood glucose level is controlled.
The effect of insulin on GLUT4 is reversible. Within an hour of insulin removal, GLUT4 is removed from the membrane and restored to intracellular vesicles ready to be re-recruited to the surface by insulin. Thus, glucose uptake by muscle and fat cells is regulated by modulating the number of GLUT4 glucose transporters on the membrane of cells.
Describe how ADH works
The binding of the peptide hormone ADH to its receptor in collecting duct cells of the kidney triggers the recruitment of the channel protein aquaporin 2 (AQP2). Aquaporin selectively conducts water molecules in and out of the cell, while preventing the passage of ions and other solutes. Aquaporins are integral transmembrane channel proteins. When a person’s water intake is low or when a lot of fluid is lost the body produces more ADH. This hormone triggers chemical reactions that ultimately recruit aquaporin 2 water channels into the membrane of collecting duct cells. These channels allow water to be reabsorbed into the bloodstream, which makes the urine more concentrated. When fluid intake is adequate, less ADH is produced. Without signals from ADH, aquaporin 2 water channels are removed from the membrane of collecting duct cells. At these times, less water is reabsorbed into the bloodstream and the urine is more dilute.
What can improve uptake of GLUT-4 and therefore improve uptake of glucose in type 2 diabetics?
Exercise
Why can different tissues respond differently to the same hormone?
Different tissues will have different signal transduction pathways
