Niacin Flashcards
Two forms occur in foods (equal vitamin activity):
- Nicotinic acid
- Nicotinamide (also called niacinamide) (major form in blood)
Niacin in Plants
- present in food in ___ ____
- covalently bound to complex ___
- largely ________ in cereals eg maize
- is very _______ to heating and
oxidation
- water ______
- ______ available than animal sources
- free form
- CHO
- unavailable
- stable
- soluble
- less
Niacin in Animals
- mainly occurs as the _______
_______: _____ & _____
- nicotinamide, nucleotides: NAD+ & NADP+
Digestion & Absorption of Niacin
- NAD and NADP first need to be converted to _________ to enable absorption
- main site of f nicotinic acid and nicotinamide absorption - _____ _____
- _______ _______ with typical dietary intakes
- ________ _____ with pharmacological doses
- large intestine - ______ _____ absorbed by __-_______ high-affinity transporter
- nicotinamide
- small intestine
- Carrier facilitated
- Passive diffusion
- Nicotinic acid, Na-dependent
Transport & Storage of Niacin
In the blood:
- _______ transported in the blood _____
- _______ ____ can be bound to plasma ______
In the Tissue Cells:
* Readily enters most cells by _____ _____ (needs a transporter for kidney tubules & red blood cells)
* ________ used for the synthesis by all tissues of NAD+/NADH and NADP+/NADPH
* ______ ___ can also be used by the liver
Storage:
* ___ _____ ____ stores niacin
- Nicotinamide, freely
- Nicotinic acid, proteins
- simple diffusion
- Nicotinamide
- Nicotinic acid
- No single organ
Niacin Functions
* Component of ______ used in macronutrient & energy ______
* Role in reactions involved in _____ _____, __________ and ________
* Role in reactions involved in _______ ________
- coenzymes, metabolism
- DNA repair, replication and
transcription - calcium mobilisation
Redox Functions
* _________ is the _______ _____ of NAD+ and NADP+
* NAD+ and NADP+ are coenzymes in a wide variety of
_________ and _______ reactions in energy yielding
metabolism
* ~ _____ enzymes require NAD+ or NADP+
- Nicotinamide, reactive moiety
- oxidation and reduction
- 200
Functions of NAD+/NADH:
* NAD+ acts as an electron ______ in energy yielding metabolism
* The resultant NADH is _____ by the ______ electron transport chain
* Also participates in other oxidative reactions e.g. _______, _______ ___ ____ ___ in the citric acid cycle
→ Essential role in production of ____ & production of energy
- acceptor
- oxidised, mitochondrial
- glycolysis, oxidation of acetyl coA
- ATP
Functions of NADP+/NADPH
* _____ agent (donates hydrogen) in many biosynthetic pathways e.g. synthesis of ___, _______, ______ ______
- Reducing
- FAs, cholesterol, steroid hormones
Niacin Functions for Specific Nutrients
1. CHO metabolism
* ________ (anaerobic) requires _ dehydrogenase enzymes
* ____ _______ (aerobic) requires _ dehydrogenase enzymes
* electrons generated from NAD+ metabolism are then transported down the electron transport
chain with further release of ___; finally combined with molecular oxygen to form ______
- glycolysis, 2
- TCA cycle, 3
- ATP
- water
Niacin Functions for Specific Nutrients
2. FA metabolism
* ______ is required in reductive biosynthesis of fatty acids, cholesterol & steroid hormones from
acetyl CoA
- NADPH, reductive
Niacin Functions for Specific Nutrients
3. AA metabolism
* _____ is required with ______ dehydrogenase in oxidative ______ of glutamate (end
product of most AA __________) to _-_______ and _____ ions – recycled or excreted as urea
- NAD+, glutamate, deamination, transamination’s, a-ketoglutarate, NH4+
Niacin Functions for Specific Nutrients
4. Other functions:
* oxidation of _____
* activation of _____ (which is essential for all cell division)
* ______, ______ __ and ______ regeneration
- ethanol
- folate
- Glutathione, vitamin C and thioredoxin
DNA Repair & Ca Functions of Niacin
* NAD+ is a source of ___-_____ in transfer reactions
involved in ____ repair, replication and transcription
* NAD+ is the precursor of ___ second messengers that act
to _____ the release of _______ from intracellular stores
in response to ________
- ADP-ribose, DNA
- two, increase, calcium, hormones
Niacin Deficiency:
- ______
* characteristic red, scaly, itchy skin rash on areas exposed to sun
* ‘Casal’s collar’
* later skin becomes dark & rough, hence name
* pelle (‘skin’) agra (‘sour/rough’)
- __________
* + inflamed tongue (glossitis) & mouth, denuded lips, difficulty swallowing
- _______/_______ (severe cases)
* anxiety, depression, ‘burning feet’, hallucinations
* due to serotonin deficiency (see Kynurenine pathway)
- _____ (if untreated)
- Dermatitis
- Diarrhoea
- Delirium/Dementia
- Death
