Flashcards in Steroids and Fat Soluble Vitamins Deck (38):
1
vitamin D def
-prev in children is 9%, adults is 42%
-poor calclium absorption
-bone demineralization
-rickets in children
-osteomelacia in adults
-made synthetically from a precursor to cholesterol or from the diet in fatty fish, beef liver, cheese, egg yolks, some mushrooms
2
cholesterol
-membranes
-derivatives of this
-fits between phospholipids to reduce fluidity/permeability
-cholesterol rich rafts are important for membrane protein function and signalling
-bile salts, steroid hormones, vitamin D, coenzyme Q
3
cholesterol sources
-animal products in the diet
-we can not use plant sitosterols
-dietary cholesterol goes to liver as CE's in chylomicron remnants
-endogenouse synthesis by liver but also in skin intestines, and kidneys
4
what does cholesterol synthesis use
-acetyl CoA from citrate lyase path
-NADPH from PPS and NADPH linked malate dehydrogenase
5
cytoplasmic acetyl CoA is converted to
HMG-CoA
-this is essentially the same mechanism to make ketone bodies
6
HMG-CoA reductase
-the major regulated step in cholesterol synthesis
-produces melavonate, a key building block of chol, from HMG-CoA
-inhibited by: freee cholesterol, phospohrylation by AMPK, and statin drugs
-controlled by rate of synthesis and degradation (has a 3.5 hour half life and free cholesterol inhibits its transcription and activates its degradation)
7
statin drugs
-work by mimicking substrate of HMG-CoA reductase
-they are inhibitors
8
what happens to mevalonic acid in cholesterol synth
-it is activated to form IPP (5C) which is an isoprene unit
9
how is squalene formed
-condensation reaction of isoprene units
10
what can be attached to proteins to anchor them into the membrane
-farnesyl groups
11
squalene monooxygenase
squalene to squalene epoxide
12
other important isoprenoiids that IPP condensations yield
-dolichol: sugar carrier
-ubiquinone: a mitochondrial electron carrier (coQ)
13
what kind of enzyme makes acetyl CoA
-thiolase
14
HMG-CoA synthase
-synthesizes HMG-Coa from acetyl coa in the cytoplasm
15
squalene monooxygenase and cyclase form
-a 4x ring structure (lanosterol)
-some additional modifications form cholesterol
16
How our body gets cholesterol
-new synthesis (liver, skin, and intestine)
-uptake of LDL via LDL-R
17
where does our body send cholesterol
-membranes
-conversion to intracellular CE deposits by ACAT
-release of VLDL (liver) and vhylomicrons (liver and intestine)
-excess is removed by HDL and LCAT
-converts it into bile salts, steroidogenic tissues --> hormones
18
cholesterol regulation
-free cholesterol stimulates ACAT and downregulates LDL receptor levels and HMG-CoA reductase
19
LDL levels can be controlled by
-ensuring proper LDL uptake by LDL-R
-decreasing synthesis (HMG-CoA reductase inhibitors)
-decreasing dietary cholesterol
-promoting excretion of excess cholesterol as bile salts
20
conversion of cholesterol into a steroid hormone
-cholesterol to pregnenolone
-pregnenolone to progesterone
-progesterone to either cortisol, corticosterone, or testosterone
-corticosteron can be made into aldosterone
-testosterone can be made into estradiol
21
cortisol
-from the adrenal cortex
-CHO, protein and fat metabolism
-suppresses immune response and inflammation
22
aldosterone
-from adrenal cortex
-regulate electrolyte resorption in kidney
23
estradiol
-from ovary adn testes
-secondary sexual characteristics and reproductive cycle
24
difference between protein and steroid hormones
-proteins work through second messengers from the cell membrane
-steroids directly alter transcription in the nucleus
25
what can you make from farnesyl -PP
-dolichol
-haem A
-CoQ (ubiquinone)
-farnesylated proteins (Ras, lamin B)
26
the conversion of cholesterol to bile salts
-this happens in the liver and begins with 7-alpha-hydroxylase which adds an -OH to the 7th position
27
fat soluble vitamins
-they are isoprenoids that can not be synthesized de novo or for which de novo synthesis may not be efficient (Vit D)
-includes A, D, E, and K
-not excreted, great excess can be toxic
28
vitamin A
-light reception and hormone
29
vitamin D
-hormne controlling calcium absorption
-
30
vitamin E
-antioxidant
31
vitamin K
-important cofactor for blood clotting
32
fat soluble vitamins are usually transported by
-lipoproteins
33
the three faces of vitamin A
-all trans retinal
-retinol
-retinoic acid
-comes from animal products and cleavage of provitamin A, carotinoids
34
vitamin A functions
-retinoic acid
-retinal
-retinoic acid: hormone important for growth and differentiation. activates transcription factors of the steroid receptor class
-retinal: bound to opsin, forms rhodospsin. light induces a cis to trans isomerization, causing dissociation and the conformational change in opsin is the first signal in vision
35
vitamin D
-we can synthesize with sufficient UV exposure
-this is a penultimate intermediate in cholesterol biosynthesis
-maintains blood calcium levels
-activates a vitamin D dependent transcription factor that promotes intestinal Ca++ absorption
-bone resorption
36
vitamin E
-important antioxidant
-some dietary fat is needed for the absorption of vitamin E from the gastrointestinal tract
-terminates free radical oxidation of unsaturated FA's
37
vitamin K
-essential for blood clotting
-cofactorin gama carboxylation required for function of prothrombin and other clotting factors
-from plant sources and made by gut bacteria
-adult deficiencies are rare
-deficiency can cause hemorrhage in infants
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