9 - Steroids Flashcards
What is included in the basic steroid template?
4 rings (sterane) and 2 methyl groups positioned at 10 and 13, but are labelled as C-18 and C-19 when both are present
What happens to 1,2-disubstituted cyclohexanes?
- Can be cis (same side) or trans (across from each other)
- Trans will be axial-axial or equatorial-equatorial
- Cis will be axial-equatorial
What is the relative configuration along the backbone of all biologically active steroids?
- a = alpha (below the plane); B = beta (above the plane)
- 5a-10B-9a-14a-13B
What is the geometry of all biologically active steroids?
- Trans-trans-trans geometry at ring junctions
- Anti-anti geometry for adjacent ring junctions
What is the ideal shape for a polycyclic steroid?
- Rigid “rod” shape is biologically active and more stable (alpha)
- Rigid “bent” shape is not active and less stable (beta)
What are the rules for nomenclature of double bonds of steroids?
- Give the position from which the double bond originates
- If the double bond points to any other position other than the next highest number, the atom where the bond terminates must be given
What are the 3 rules for steroid classes?
1) Carbon at C-17? (androstane and estane = no)
2) Methyl at C-10? (androstane = yes; estane = no)
3) If there is a carbon at C-17, is it a 2 carbon chain or 8 carbon chain? (pregnane = 2 C’s; cholestane = 8 C’s)
What are the main steroid hormone actions?
1) Follicle stimulating hormone and luteinizing hormone in ovaries or testes
2) Corticosteroids in adrenal cortex
How do steroids travel in blood?
Travel attached to protein carriers b/c don’t readily dissolve in blood plasma or water
Describe the mechanism of steroid hormone actions
1) Steroids are carried to the cell by protein carriers and dissociate near their target cells and bind to a steroid receptor
2) Steroid/receptor complex is carried to nucleus (translocation)
3) Binding of complex to DNA regulatory site
4) Instructs DNA to transcribe mRNA
5) mRNA then delivers its message to ribosomes in cytoplasm to increase protein synthesis (translation)
- OR steroid hormone can enter cell, directly enter nucleus, and bind to steroid receptor already in nucleus
Are estrogens, androgens, progestins, and adrenocorticoids needed in low or high concentrations to be effective?
Extremely low (less than 1 nM)
What do estrogens, androgens, progestins, and adrenocorticoids have high binding affinity for?
Intracellular hormone responsive elements (short DNA sequence)
What are the 2 main subtypes of adrenocorticoids?
Glucocorticoids and mineralocorticoids
___ serves as the starting point for all steroid hormones that are produced in the body
Cholesterol
What is cholesterol an essential component of?
- Animal cell membranes
- Acts as spacers to fill in the gaps to stabilize the membrane
What is glycocholate? Where is it stored? What is its function?
- Bile salt
- Stored in gallbladder
- Acts as emulsifier of fats in enterohepatic circulation; also a negative feedback control on 7 alpha-hydroxylase enzyme
What is the function of bile acids and phospholipids?
- Solubilize cholesterol in bile, preventing precipitation of cholesterol in gallbladder
- Act as emulsifying agents, rendering fats accessible to pancreatic lipases
- Facilitate intestinal absorption of fat-soluble vitamins/drugs
- Involved in the control of their own metabolism and transport via enterohepatic circulation
What is the function of vitamin D?
Induces P-glycoprotein transporters in GI tract, which enhance bile reabsorption to blood and liver
What is the role of the enterohepatic circulation w/ respect to recycling of steroids, lipids, and drugs?
- About 97% of cholesterol and steroid hormones are reabsorbed
- Uptake of dietary lipids and fat-soluble vitamins; all solubilized by bile salts in intestine
- Recycles most non-polar drugs/ metabolites and bilirubins
What is the enterohepatic circulation pathway?
Liver -> bile ducts -> gall bladder -> small intestine (reabsorption through GI wall to portal vein) -> liver
How much liver is absorbed and produced by the body daily?
- 300 mg absorbed from gut daily
- 800 mg produced by body
What are the 3 ways to lower cholesterol? What drugs are used for each mechanism?
1) Decrease production (statins)
2) Decrease absorption in small intestine (ezetimibe)
3) Decrease absorption in ileum (bile acid binding resins)
What are the main lipids in blood plasma? Can they be taken up into the cell via passive diffusion?
- Cholesterol and cholesterol esters
- Triglycerides
- Phospholipids
- Yes they can be taken up by passive diffusion b/c they are part of the cell wall
What is the difference between triglycerides and phospholipids w/ respect to function?
- Triglycerides = storage form of fatty acids
- Phospholipids = membrane lipids
Is cholesterol or a cholesterol ester more nonpolar?
Esterification w/ a fatty acid chain makes a molecule more nonpolar
How are plasma lipids transported in blood circulatory system?
Lipoproteins
- Spherical macromolecules consisting of carbs, phospholipid monolayer, triglycerides, and cholesterol and its esters
- Lipids are covalently and non-covalently bound to proteins and carbs
- These combinations prevent plasma lipids from forming insoluble aggregates
What is HDL called the “good cholesterol carrier”?
Has the highest protein content and lowest triglyceride content
Function of chylomicrons?
Transport fat to adipose
Function of LDL?
Transport cholesterol to extra-hepatic tissues
Function of HDL?
Removal of cholesterol from extra-hepatic tissues to LDL, IDL (intermediate density lipoproteins) /VLDL, and liver
How is cholesterol converted into an estrane?
1) C-17 side chain is reduced to a 2-carbon side chain and OH at C-3 is removed and double bond at C5,C6 is removed (forms pregnane)
2) 2-carbon side chain at C-17 is removed (forms androstane)
3) Methyl group at C-10 is removed (forms estrane)
