Selenium Flashcards
Selenium shares chemical properties with what element?
Sulfur
How much selenium is needed
55 MICROgrams
What foods are high in Se?
Brazil nuts,
Why are brazil nuts high in Se?
It depends on the Se concentrations in soil
What are the Plan food forms of Se?
Selenomethionine and selenocysteine
What are the animal food forms of Se?
Selenocysteine
How are Organic forms of Se absorbed in the intestine?
Like AA via AA transporters
How are inorganic forms of Se absorbed?
Not known
Are selenomethionine and selenocysteine transported differently?
No
In Se deficiency what happens to absorption?
Nothing. Rate stays the same.
What is another name for Selenocytsteine?
The 21st Amino acid
Selenocysteine (Sec) occurs in how many proteins in the human proteome?
25 proteins
Conventional cysteine can do what that Sec can do?
fulfills a chemical function
What makes Sec different from other AA?
It is not coded for directly in the genetic code. It relies on independent SEC insertion machinery
What does SECIS stand for?
SelenoCysteine insertion sequence
What is SECIS?
A stemloop structure in the mRNA
How is sec put into proteins?
When an mRNA codes for UGA, the SECIS element binds to a SECIS binding protein which binds to elongation factors which is bound to a tRNA which will bring Sec in for UGA and keep moving.
The functions of the selenoproteins that we do know function in what?
antioxidant and anabolic processes
What is Selenoprotein P (SELP)?
Major Se transport protein
Accounts for 80% of plasma Se
Where SELP produced?
Liver
How many Se can SELP hold?
10 atoms/ molecule
What is a side function of SELP?
As an antioxidant for peroxynitrite radicals
What happens if you KO SELP?
Mice have neurological problems and trouble walking
What was the first selenoprotein identified in 1957?
Glutathione Peroxidase 1
Gluthione peroxidase 1 accounts for how much of total body Se?
more than 50%
What is glutathione peroxidase 1?
An antioxidant enzyme
What is Glutathione peroxidase 1 side function?
Function as a Se buffer
How does Glutathione peroxidase function as an antioxidant enzyme?
It converts hydrogen peroxide to water
Which GPx proteins work to detoxify H2O2?
GPx1 (cytosol), GPx2 (cytosol), GPx3 (plasma), GPx6 (cytosol).
What does GPx4 function as?
protects lipids from H2O2 mediated oxidation
What is thioredoxin reductase?
Enzyme that reduces thioredoxin
How does thioredoxin protein act as an antioxidant?
By acting as an electron donor (reducing agent)
What does thiredoxin reductase regenerate?
Thioredoxin
What is SelenoproteinW? (SELW)
Small selenoprotein found in muscle (implicated in white muscle disease that affects sheep)
How do you prevent white muscle disease?
Supplement soil with Se
How much Se can the body store?
30 mg
What tissue has the greatest concentration of Se?
The kidney
What tissue has the most Se?
Muscle
What form of excretion is important for maintaining homeostasis?
Urinary excretion
Pharmacologic doses of Se are released how?
Expired in the breath as diemthylselenide
What is the major form of Se in the urine?
Methylselenol
Se def rat
Visually smaller, leg weakness, rough hair coat, display muscle degeneration, reporoductive failure and liver necrosis if also Vit. E def
Se has been shown to correct what?
Liver necrosis cause by a lack of methionine, cysteine, or vitamin E
Human Se def was first reported where?
In China
What is Keshan Disease?
Human Se Def
Causes cardiomyopathy
What causes Keshan disease?
Low levels of Se in certain area and viral infection
What is Kashin-Beck disease?
Human Se def
Endemic disease of the cartilage
Due to low Se in soil (affects people in northern china and russia) and iodine def or toxic contamination may be involved.
Does Se supps cure Kashin-beck?
No.
What is Myxdematous Cretinism?
Disease characterized by thyroid enlargement and decreased intelligence
What contributes to Myxedematous cretinism?
Se and Iodine deficiency
Se status assessment
Intake indicators
- plasma/serum selenium: reflects recent diet
- red blood cell selenium: past 120 days
Where was Se toxicity first identified?
In livestock0 they consumed plants grown in high-se soil
Why are inorganic Se and amino acid forms toxic in excess?
Because they are highly bioavailable
What is Selenosis?
Chronic Se toxicity
What is commonly associated with selenosis?
Changes in nail structure, loss of nails, and hair
Continued ingestion of Se during Selenosis leads to:
- lesions of the skin and nervous system
- nausea
- weakness
- diarrhea
Symptoms of selenosis are present with what intake range?
3.2-6.7 mg /day
What causes acute Se toxicity?
Caused by ingestion of gram quantities of Se
What does acute Se toxicity cause?
GI and neurological disturbances
MI (Myocardial infarction)
Renal failure
Acute respiratory distress syndrome
How do you fix Se overdose?
There is no cure, it is fatal
What is Se strange? (LONG NOTECARD)
- Se is taken up form soil by the plants and incorporated into Sec. Neither Se or Sec are required for plants.
- Se takes the place of another atom (S) in cysteine and forming a new AA (Sec)
- Sec is not encoded for in the genomes; SECIS element is used
- Se absorption does not increase in deficiency
- Se def and toxicity are due to inadequate/excessive intake (which are directly caused by [Se] in soil)
