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Biochemistry MBS > Steroids and Fat Soluble Vitamins > Flashcards

Steroids and Fat Soluble Vitamins Flashcards

1
Q

vitamin D def

A
  • 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
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2
Q

cholesterol

  • membranes
  • derivatives of this
A
  • 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
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3
Q

cholesterol sources

A
  • 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
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4
Q

what does cholesterol synthesis use

A
  • acetyl CoA from citrate lyase path

- NADPH from PPS and NADPH linked malate dehydrogenase

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5
Q

cytoplasmic acetyl CoA is converted to

A

HMG-CoA

-this is essentially the same mechanism to make ketone bodies

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6
Q

HMG-CoA reductase

A
  • 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)
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7
Q

statin drugs

A
  • work by mimicking substrate of HMG-CoA reductase

- they are inhibitors

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8
Q

what happens to mevalonic acid in cholesterol synth

A

-it is activated to form IPP (5C) which is an isoprene unit

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9
Q

how is squalene formed

A

-condensation reaction of isoprene units

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10
Q

what can be attached to proteins to anchor them into the membrane

A

-farnesyl groups

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11
Q

squalene monooxygenase

A

squalene to squalene epoxide

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12
Q

other important isoprenoiids that IPP condensations yield

A
  • dolichol: sugar carrier

- ubiquinone: a mitochondrial electron carrier (coQ)

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13
Q

what kind of enzyme makes acetyl CoA

A

-thiolase

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14
Q

HMG-CoA synthase

A

-synthesizes HMG-Coa from acetyl coa in the cytoplasm

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15
Q

squalene monooxygenase and cyclase form

A
  • a 4x ring structure (lanosterol)

- some additional modifications form cholesterol

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16
Q

How our body gets cholesterol

A
  • new synthesis (liver, skin, and intestine)

- uptake of LDL via LDL-R

17
Q

where does our body send cholesterol

A
  • 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
Q

cholesterol regulation

A

-free cholesterol stimulates ACAT and downregulates LDL receptor levels and HMG-CoA reductase

19
Q

LDL levels can be controlled by

A
  • 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
Q

conversion of cholesterol into a steroid hormone

A
  • 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
Q

cortisol

A
  • from the adrenal cortex
  • CHO, protein and fat metabolism
  • suppresses immune response and inflammation
22
Q

aldosterone

A
  • from adrenal cortex

- regulate electrolyte resorption in kidney

23
Q

estradiol

A
  • from ovary adn testes

- secondary sexual characteristics and reproductive cycle

24
Q

difference between protein and steroid hormones

A
  • proteins work through second messengers from the cell membrane
  • steroids directly alter transcription in the nucleus
25
Q

what can you make from farnesyl -PP

A
  • dolichol
  • haem A
  • CoQ (ubiquinone)
  • farnesylated proteins (Ras, lamin B)
26
Q

the conversion of cholesterol to bile salts

A

-this happens in the liver and begins with 7-alpha-hydroxylase which adds an -OH to the 7th position

27
Q

fat soluble vitamins

A
  • 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
Q

vitamin A

A

-light reception and hormone

29
Q

vitamin D

A

-hormne controlling calcium absorption

-

30
Q

vitamin E

A

-antioxidant

31
Q

vitamin K

A

-important cofactor for blood clotting

32
Q

fat soluble vitamins are usually transported by

A

-lipoproteins

33
Q

the three faces of vitamin A

A
  • all trans retinal
  • retinol
  • retinoic acid
  • comes from animal products and cleavage of provitamin A, carotinoids
34
Q

vitamin A functions

  • retinoic acid
  • retinal
A
  • 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
Q

vitamin D

A
  • 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
Q

vitamin E

A
  • 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
Q

vitamin K

A

-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
-

38
Q

vitamin K epoxide reductase inhibitors

A
  • dicourmarins like warfarin and coumarol
  • cause uncontrolled bleeding
  • poison at high doses and low doses can treat thromboses

Biochemistry MBS (36 decks)

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