Steroids and Fat Soluble Vitamins Flashcards Preview

Biochemistry MBS > Steroids and Fat Soluble Vitamins > Flashcards

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
-

38

vitamin K epoxide reductase inhibitors

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