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Nutritional Biochem 1 > Selenium > Flashcards

Selenium Flashcards

1
Q

Selenium is a nonmetal that exists in many oxidation states (Se2-, Se4+, Se6+) and has chemical properties similar to what element?

A

Sulfur

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2
Q

Selenium is in the same column as what element in the periodic table, and can therefore be substituted for this element in different amino acids…

A

Sulfur

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3
Q

What is the best source of selenium?

A

Seafood

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4
Q

Soil concentration of selenium is directly related to it’s concentration in plants, with this being true, where are cancer rates the highest?

A

Areas that have low soil Selenium concentrations

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5
Q

What kind of transporters do Selenomethionine and Selenocysteine use?

A

Amino acid transporters

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6
Q

What is the order of uptake efficiency from greatest to least?

A

Selenomethionine > selenocysteine > selenAte > selenIte > selenide

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7
Q

What are 4 substances that enhance selenium absorption? (Hint: 3 vitamins, antioxidant)

A

Vitamin A, C, E, and Glutathione

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8
Q

What are the inhibitors of selenium absorption, and how is it done? (Hint: 2 heavy metals, a cyclic acid)

A

Mercury, Cadmium, and Phytates (phytic acid) all do this through CHELATION

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9
Q

What carries 60% of the selenium into plasma?

A

Selenoprotein P as Selenocysteine

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10
Q

What carries another 30% of selenium into plasma?

A

Glutathione peroxidase 3 (GPX3)

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11
Q

The concentration of Selenoprotein P can be used as what?

A

An indicator of Selenium deficiency

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12
Q

What is the most important selenoprotein for cerebral function?

A

Selenoprotein P

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13
Q

What else does Selenoprotein P protect the human body from? (hint: related to cerebral functioning)

A

PRODUCTION OF FREE RADICALS, [note: slows the progression of the disease (significant cognitive decline is related to decrease selenium concentration)]

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14
Q

Selenide can be methylated and excreted in the urine as what?

A

Methyl selenide

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15
Q

Selenocysteine is synthesized with selenide and what two enzymes?

A

Selenophosphate synthetase, Selenocysteine synthase

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16
Q

Selenium is incorporated into selenoproteins as selenocysteine via…?

A

Selenocysteine tRNA

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17
Q

Selenocysteine tRNA reads this stop codon as an insertion site…

A

UGA stop codon

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18
Q

Selenocysteine is considered to be what in relation to amino acids?

A

The 21st AA

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19
Q

The unique recoding of the UGA codon requires 2 additional proteins to facilitate the recognition of the sec-tRNA by the UGA, what are they?

A
  1. SBP2 (selenocysteine insertion sequence binding protein)

2. EFsec (elongation factor for selenocysteine)

20
Q

SBP2 and EFsec are essential for the translational insertion of what?

A

Selenocysteine into selenoproteins

21
Q

If 1 or both of the proteins (SBP2 and EFsec) are absent, what will become of the codon?

A

The UGA is read as a stop codon

22
Q

How many selenoprotein genes have been identified in the human genome?

A

25 selenoprotein genes

23
Q

What are the 5 selenium containing isoenzymes?

A

GPX1, GPX2, GPX3, GPX4, GPX6

24
Q

What is the only isoenzyme found extracellularly?

A

GPX3

25
Q

GPX3 and Selenoprotein P account for what percentage of the selenium in the plasma?

A

90%

26
Q

In a proportional manner, what does the availability of Selenium affect? (hint: 3 things)

A
  1. GPX activity
  2. Concentrations of Se
  3. mRNA levels
27
Q

What enzyme converts thyroxine (t4) to triiodothyronine (T3)?

A

Iodothyronine 5’-deiodinase (mem cue?.. T3-T4 –> IT5D)

28
Q

What affect did Selenium supplementation have on patient with autoimmune thyroiditis? (2 things)

A

Decreased inflammation

Decreased thyroid autoantibody concentrations

29
Q

Thioredoxin reductase contains what at it’s active site?

A

Selenocysteine

30
Q

There are 4 functions of Thioredoxin reductase, what are they?

A
  1. Synthesis of deoxyribonucleotides for DNA synth
  2. Regeneration of antioxidants
  3. Intracellular maintenance of redox state
  4. Regulate gene expression by reducing transcription factors (ex. NFkB), affecting DNA binding
31
Q

What is the key component that is needed in the body to synthesize all the selenocysteine containing enzymes?

A

Selenophosphate [Selenophosphate synthetase 2 (SPS2)]

32
Q

What does SPS1 (selenophosphate synthetase 1) use instead of selenocysteine?

A

Cysteine

33
Q

What is the relationship between SPS1 and SPS2?

A

SPS1 catalyzes synth of selenophosphate for SPS2 – SPS2 will then catalyze the selenophosphate production from all other selenoproteins.

34
Q

Selenoprotein W is found where and what does it protect against?

A

Found in the cytosol of skeletal and cardiac muscle cells and protects against oxidative injury!

35
Q

Low plasma selenium is independently associated with what issue in the elderly?

A

Poor skeletal muscle strength

36
Q

Excretion of dimethylselenide has what kind of odor?

A

Garlicky odor

37
Q

Selenium deficiency can be seen in two different diseases, what are they and generally what do they involve? (hint: usually involves children)

A

Keshan disease - cardiomyopathy

Kashin-beck disease - osteoarthropathy (epiphyseal plate)

38
Q

A daily intake of 200 ug/day of Selenium may diminish the risk of what two diseases (hint: most common causes of death!)

A

Heart disease, Cancer

39
Q

If one was to increase their intake of selenium by 50%, what would that do to their risk of developing CHD?

A

Reduce the risk by 25%!

40
Q

Serum selenium concentrations have been seen to affect the incidence of some cancers such as prostate cancer, but only in men, why is this?

A

Women don’t have a prostate…. but what is the homologue? :)

41
Q

Suggested mechanisms of cancer prevention by Selenium include what? (hint: 3 ways)

A
  1. Inhibit cancer cell growth - causes cell cycle arrest
  2. Increase apoptosis
  3. Increased DNA repair
42
Q

Selenium has been shown to boost the immune system function by stimulating what cells?

A

Cytotoxic lymphocytes, NK cells, Macrophages

43
Q

Selenosis is the term used for…

A

Selenium toxicity

44
Q

What populations are seen to have Selenosis?

A

Miners and people who supplement with Selenium

45
Q

The tolerable upper intake level is set at how many ug/day?

A

400 ug/day

Nutritional Biochem 1 (6 decks)

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