Exam 2, niacin Flashcards
properties of niacin
stable to heat, light, acid, alkali, oxidation (REALLY STABLE)
niacin structure
basically a single hexose ring with
-COOH
riboflavin structure looks like
3 hexose in line then a chain sticking up
thiamin structure looks like
one hexose and one pentose together with methylene bridge
niacin coenzymes
NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate)
what is NAD’s job
removal and transfer of electrons from metabolic intermediates to ETC -> ATP
what is NADP’s job
reducing agent for biosynthetic pathways (fatty acid, cholesterol and steroid hormone synthesis)
digestion of niacin
-NAD and NADP are broken down in enterocyte to free nicotinamide
-nictotinamide and nicotinic acid absorbed in stomach and SI
-then nicotinamide enters blood and once in cells can be reverted to coenzyme form
toxicity of riboflavin
no known toxicity
what is the MAIN function of niacin
accepts + transfers H ions in ENERGY METABOLISM
what is one reason why niacin is essential in the body (popular)
> 400 enzymes require NAD and NADP as H donor/ acceptor
oxidative functions using NAD
-decarboxylation of pyruvate
-oxidation of Acetyl CoA in 3 places of krebs
-B oxidation of fatty acid
what other 3 “extra” pathways is NADPH used in
- glucose to monophosphate shunt
- regeneration of antioxidants
- oxidation of ethanol
NADPH works with FAD in the…
activation of glutathione reductase which restores glutathione (reducing it)
when people are going to drink they sometimes take?
B vitamins, they supposedly help with the metabolization of alcohol
main niacin defficiency- 4D’s (and how is one seen in dogs)
- dermatitis (pellagra and black tongue in dogs)
- diarrhea
- dementia
- death
Joseph Goldberger
-public health doctor, 1915
-worked with prisoners where corn was a staple with foods like cornbread for example
-changed their diet to healthier, more varied, more nutrients
-realized pellagra was not an infection, it was a deficiency
difference between cornbread = deficiency and corn tortillas not *
-in cornbread, niacin is bound to protein which means its not free to be absorbed
-in corn tortillas, the nixtamalization process leads to alkaline hydrolysis which cuts the bonds and frees niacin for absorption
photograph: person with spots on lower half o f face and tongue sticking out
pellagra: niacin deficiency
photograph: dry scaly skin in legs and elbows down
pellagra: niacin deficiency
photograph: scaly, even bleeding elbows
pellagra: niacin deficiency
photograph: skin affected only in collar
Casal’s collar, characteristic of pellagra: niacin deficiency, and occurs when affected skin is exposed to the sun so the dermatitis becomes more prevalent/visible in those areas
photograph: cracked feet before and after
pellagra : niacin deficiency
photograph: poultry that has it’s wings up (feather abnormalities/ behavior change)
dermatitis: niacin deficiency
photo: big chicken compared with little chicken of the same age
niacin deficiency
what is used to assess niacin status
urinary metabolites, serum/RBC NAD: NADP ratio
niacin toxicity symptoms
-liver dysfunction and damage
-blurred vision & edema of eyes
-glucose intolerance
-gout
-flushing
when does toxicity of niacin ocurr
UL: 35 mg/ day
photo: man before and after with skin normal and then red
flushing: niacin toxicity
what was niaicn supplementation used for in the past and why is it not anymore?
before statins existed it was used to lower LDL cholesterol levels and increase HDL, yet there was no proven decrease of heart disease
RDI niacin
M: 16 mg, F: 14 mg
main food source for niacin
chicken breast (all proteins in general)
why should niacin NOT be taken as a supplement *
-excess niacin is metabolized to 2PY and 4PY metabolites
-4PY activates inflammatory pathways
-explains heart thing, contraproducente
Explain and give examples of the differing roles of NAD and NADP as coenzymes in energy metabolism
and biosynthesis. *
NAD works as an electron carrier in metabolic pathways while NADP works in biosynthetic pathways (like fatty acid/ cholesterol/ steroid / antioxidant synthesis)
