Steroids

Question 1

features of steroids (facts)

Answer 1

• 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

Question 2

synthetic steroids

Answer 2

they have been developed; most are steroids but some non-steroidal molecules can interact with steroid receptors because of similarity in shape.

Question 3

the origin of steroids
(What are they derived from? made from what?)

Answer 3

-derived from triterpenoids
- their biosynthetic precursor is squalene which is made from 2 farnesyl pyrophosphate units (made from 3 isoprene units).

Question 4

carbocation stability

Answer 4

stability increases from primary - tertiary

Question 5

squalene to lanosterol

Answer 5

Steroid backbone rearrangement:
-4 consecutive 1,2-shifts
-followed by elimination

Question 6

chair/boat conformations

Answer 6

• chair = newman project (stable)
• boat = (C-H) conds are eclipsed (close proximity)

Question 7

anti-migration in groups.

Answer 7

each group that migrates is
-axial
-antiperiplanar
to the one before

Question 8

lanosterol to cholesterol

Answer 8

-reduce alkene in one area and add alkene in other area

Question 9

steroid’s structure

Answer 9

• 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

Question 10

beta and alpha bonds

Answer 10

beta faces up
alpha faces down

Question 11

types of steroids

Answer 11

-sterols
-saponins
- cardioactive glycosides
- bile acids
-hormones (sex hormones, adrenocortical hormones/cortosteroids)

Question 12

sterols

Answer 12

-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)

Question 13

saponins

Answer 13

-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)

Question 14

cardioactive glycosides

Answer 14

• 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)

Question 15

bile acids

Answer 15

-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

Question 16

the inability to remove excess cholesterol through bile acids can…

Answer 16

causes atherosclerosis and gall stones which contain 70% cholesterol

Question 17

hormones

Answer 17

secreted by specific glands

expert control over various body processes

Question 18

2 main types of steroid hormone

Answer 18

• sex hormone
• adrenocortical

Question 19

ADRENOCORTICAL HORMONES-CORTICOSTEROIDS
what are they produced by?

Answer 19

the adrenal cortex

Question 20

what are the 2 main groups of corticosteroids?

Answer 20

• glucocorticoids
• mineralcorticoids

Question 21

what do glucocorticoids control?

Answer 21

the synthesis of carbohydrates from protein and lipid, thereby controlling blood sugar levels.

inflammatory response
deposition of glycogen in the liver

Question 22

what do minteralcorticoids control?

Answer 22

electrolyte balance in kidney
- retention of Na+/Cl-
- retention of water
- excretion of k+

Question 23

physiochemical properties of steroids

Answer 23

• 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.

Question 24

how are steroids transported?

Answer 24

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)

Question 25

transport mechanism for steroids (must cross cell membrane)

Answer 25

• passive diffusion
• facilitated diffusion
• active transport
• pinocytosis

Question 26

can steroids be transported in blood?

Answer 26

no, because of their lipophilicity.

Question 27

what are the acceptations steroids can be transported through blood?

Answer 27

• they are bound to plasma carrier protiens
• steroids pass theough cell membrane as the free steroid

Question 28

specific carrier protiens have

Answer 28

-high affinity
- high specificity

Question 29

two types of specific carrier proteins

Answer 29

• 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

Question 30

two types of specific carrier proteins

Answer 30

• 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