Steroids Flashcards
features of steroids (facts)
- naturally occurring in animals and plants
- part of lipid family of molecules
- act as hormones (chemical messengers)
- other roles - increasing cell membrane rigidity/integrity and acting as surfactants
- they are highly specific and highly selective
- transported via bloodstream - usually protein bound
- easily enter cell membrane and can enter nucleus
synthetic steroids
they have been developed; most are steroids but some non-steroidal molecules can interact with steroid receptors because of similarity in shape.
the origin of steroids
(What are they derived from? made from what?)
-derived from triterpenoids
- their biosynthetic precursor is squalene which is made from 2 farnesyl pyrophosphate units (made from 3 isoprene units).
carbocation stability
stability increases from primary - tertiary
squalene to lanosterol
Steroid backbone rearrangement:
-4 consecutive 1,2-shifts
-followed by elimination
chair/boat conformations
- chair = newman project (stable)
- boat = (C-H) conds are eclipsed (close proximity)
anti-migration in groups.
each group that migrates is
-axial
-antiperiplanar
to the one before
lanosterol to cholesterol
-reduce alkene in one area and add alkene in other area
steroid’s structure
- four fused rings (3x6 membered cyclohexane) (1x5 membered cyclopentane)
-all ring junctions are trans except for rings A&B which may be cis or trans
-remarkably stable due to rigidness
beta and alpha bonds
beta faces up
alpha faces down
types of steroids
-sterols
-saponins
- cardioactive glycosides
- bile acids
-hormones (sex hormones, adrenocortical hormones/cortosteroids)
sterols
-steroids and alcohol
-transported via lipoprotiens in the blood
- found in cell membranes of all animal tissue
- ingested but also synthesised in body
- biosynthetic precursor to all steroid hormones
- may cause gallstone disease atherosclerosis
(chloestrol)
saponins
-of plant origin
- spiroketal at c-22
- sugar residues at 3 beta-oh
- acts as surfactants and soaps
- cause haemolysis - lysing of red blood cells
- mostly harmless
(diosgenin)
cardioactive glycosides
- of plant origin (digitais purpurea)
- cis-fused A/B and C/D rings
- 14beta-OH
- Unsaturated lactone at C-17b
-1-4 Sugar residues on 3b-OH - employed as arrow poisons and heart drugs
- treatment for cardiac arrhythmias, particularly atrial fibrillation
-sugar unit increases solubility and binding to heart muscle.
(digitoxigenin)
bile acids
-bile acids occur in salt form in bile
- bile acids secreted into gut to emulsify fats
- bile acids act as detergents
- Excreted as body’s main method for removing excess cholesterol
the inability to remove excess cholesterol through bile acids can…
causes atherosclerosis and gall stones which contain 70% cholesterol
hormones
secreted by specific glands
expert control over various body processes
2 main types of steroid hormone
- sex hormone
- adrenocortical
ADRENOCORTICAL HORMONES-CORTICOSTEROIDS
what are they produced by?
the adrenal cortex
what are the 2 main groups of corticosteroids?
- glucocorticoids
- mineralcorticoids
what do glucocorticoids control?
the synthesis of carbohydrates from protein and lipid, thereby controlling blood sugar levels.
inflammatory response
deposition of glycogen in the liver
what do minteralcorticoids control?
electrolyte balance in kidney
- retention of Na+/Cl-
- retention of water
- excretion of k+
physiochemical properties of steroids
- like dissolves like
- steroids are hydrocarbons
- fairly non-polar/lipophilic (hydrophobic)
-freely soluble in most organic solvents. - almost insoluble in water
-those carrying two or more hydroxy groups become more soluble in polar substances (methanol, water) - steroids with ionized groups (salts of carboxylic acids, sulfates) are generally soluble in water.
how are steroids transported?
because of their hydrophobicity, steroids must be made more water soluble to be transported around the body.
- attaching to a water compatible compound - large protein
-bonding to small compound such as sugar or salt (sulphate)
transport mechanism for steroids (must cross cell membrane)
- passive diffusion
- facilitated diffusion
- active transport
- pinocytosis
can steroids be transported in blood?
no, because of their lipophilicity.
what are the acceptations steroids can be transported through blood?
- they are bound to plasma carrier protiens
- steroids pass theough cell membrane as the free steroid
specific carrier protiens have
-high affinity
- high specificity
two types of specific carrier proteins
- sex hormone binding globulin (SHBG)
estradiol and testosterone, limits bioavaliability of these hormones. - corticosteroid-binding globulin (CBG/ transcortin)
hydrocortisone, aldosterone, progestrone
when bound is unavaliable to receptors
two types of specific carrier proteins
- sex hormone binding globulin (SHBG)
estradiol and testosterone, limits bioavaliability of these hormones. - corticosteroid-binding globulin (CBG/ transcortin)
hydrocortisone, aldosterone, progesterone
when bound is unavailable to receptors
