NUTR 3210 Study Guide - Final Guide: Retinoic Acid Receptor, Basal Metabolic Rate, Vitamin K
28 Apr 2018
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Micronutrients 1
• What are characteristics for classification as a vitamin?
- Exogenous supply is required b/c body can’t produce it (or produce quickly)
- Needed in the amounts
- Distinct from sugars, fats, and proteins in regard to structure + function
- Performs at least 1 essential biochemical function in the body
- When lacking in diet, a characteristic deficiency disease develops
- Vitamins are organic
primary distinction from minerals
minerals = inorganic
• What are the functional groupings of micronutrients?
- Group 1: Micronutrients that control type II steroid hormone receptors ( TF) and
have major global health implications
Iodine – Vit.A – Vit.D – Calcium – Vit.K – Phosphorus – Fluoride
- Group 2: Micronutrients that work together in oxidant defense
Vit.E – Selenium – Vit.C – Niacin – Riboflavin – Copper – Zinc – Manganese
- Group 3: Micronutrients that act as enzyme cofactors
Thiamin – Niacin – Riboflavin – Vit.B6 – Folate – Vit.B12 – Biotin –
Pantothenic acid
- Group 4: Iron – Copper – Zinc-related divalent cations
• What’s up with Group 1?
- They are ligand-activated, something has to bind them
- Not all act directly on steroid hormone receptors (only vit.A, vit.D, and iodine)
vit.D = calcium = phosphorus = vit.K (involved bone metabolism)
- Vit.A consumed as retinol (animal based source) or beta carotene (plant), which
is eventually converted into retinoic acid = bioactive form that activates TF = the
ligand
- Vit.D precursors converted to calcitriol, which regulates calcium levels in the
body
- Iodine used to make T3 hormone = regulates synthesis of proteins that control
basal metabolic rate
find more resources at oneclass.com
find more resources at oneclass.com
• What are the 2 types of steriod hormone receptors?
- SHRs are intracellular protein receptors that bind ligands and become active
transcription factors
1) Receptors Cytosolic:
Respond to steroid hormones like estrogen, testosterone, glucocorticoids
2) Receptors Nuclear:
Respond to steroid and non-steroid ligands, like thyroid hormone, retinoic acid,
and calcitriol.
- TF in cytosol in inactive activates when ligand binds
- Not all ligands and derived from steroids
- SH transported bound to plasma carrier protein lipophilic ∴ move across
plasma membrane binds to cell cytoplasm receptor translocates as a
complex to nucleus binds to DNA (acts as a TF) stimulates gene
transcription protein produced response
• How is Iodine absorbed?
- Iodine is very H2O soluble
- Seafood has high concentrations
- Salt fortified with potassium iodide
- Typically found in the body in ionic form (I-); 70-80% located in thyroid gland.
- Dietary I can be bound to AA or found free
bound = rapidly convert to I- and absorb
most absorption in stomach
- In blood, free I- is found and can enter all tissues
most accumulate in thyroid gland, specially thyroid follicles
- Uptake in thyroid meditated by an active transport system known as (Na+/I-)
symporter (NIS) = allows uptake into follicles
find more resources at oneclass.com
find more resources at oneclass.com
• How iodide is transported and its functions?
- All tissues depend on THs T3+T4 rather than iodide (lipophilic)
- Once T3 + T4 made, they are secreted into blood and transported by specific
carrier proteins (albumin)
- 50x more T4 in plasma compared to T3, BUT T3 100x more potent b/c bioactive
T3 half-life < T4 ∴ more T4 b/c lasts longer
- T3 interacts with THR (thyroid hormone receptor)
- T3 + T4 production regulated by TSH (thyroid stimulating hormone)
- Dietary iodide GIT (I-) blood I- through NIS to thyroid to make T3 + T4
(storage + secretion) T4 to liver to convert to T3 by 5’ deiodinase enzyme
T3 in blood to regulate metabolic rate & growth by THR interaction brain
hypothalamus sense low levels of T3 signals to pituitary to release TSH.
• How does iodide make thyroid hormones?
- Follicles take up iodide from blood
- In the colloid, iodide is oxidized to from a free radical,
TPO helps attach it to a tyrosine residue in thyroglobulin
- THG peptide is made up the follicle cells with lots of Tyr chains on it (found in
colloid)
- Iodide is brought from the blood into follicular cell by NIS transporter. Then into
the colloid by a transporter called Pendrin
- Iodine Iodide by TPO and added to THG
- Iodide radical attacks Tyr residues in THG via 2 ways:
1 iodine on Tyr ring = monoiodotyrosine
2 iodines on Tyr ring = diiodotyrosine
- Tyrosine molecules joined = THs
T3 : MIT+DIT
T4 : DIT+DIT
- T3+T4 still attached to the THG, THG taken up by follicular cells, thyroid cell
proteases hydrolyze THG releasing (mostly) T4 and T3
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exogenous supply is required b/c body can"t produce it (or produce quickly) Distinct from sugars, fats, and proteins in regard to structure + function. Performs at least 1 essential biochemical function in the body. When lacking in diet, a characteristic deficiency disease develops. Group 1: micronutrients that control type ii steroid hormone receptors ( tf) and have major global health implications. Iodine vit. a vit. d calcium vit. k phosphorus fluoride. Group 2: micronutrients that work together in oxidant defense. Vit. e selenium vit. c niacin riboflavin copper zinc manganese. Group 3: micronutrients that act as enzyme cofactors. Thiamin niacin riboflavin vit. b6 folate vit. b12 biotin . They are ligand-activated, something has to bind them. Not all act directly on steroid hormone receptors (only vit. a, vit. d, and iodine) Vit. d = calcium = phosphorus = vit. k (involved bone metabolism) Vit. a consumed as retinol (animal based source) or beta carotene (plant), which is eventually converted into retinoic acid = bioactive form that activates tf = the ligand.
