Shared Flashcard Set

Details

Micronutrients 3: Cofactors
niacin, thiamin, riboflavin, B6, folate, B12, biotin, pantothenic acid
68
Nutrition
Undergraduate 2
03/31/2014

Additional Nutrition Flashcards

 


 

Cards

Term
Niacin is the general term for what?
Definition
nicotonic acid & nicotinamide
Term
True or False

Niacin can be produced in the liver from tryptophan in small amounts
Definition
True
Term
What is the active form of NADP? What is the active form of NAD?
Definition
NADPH is active (reduced NADP)
NAD+ is active (oxidized NAD)
Term
How many electrons are transferred between the oxidized and reduced forms of NADP & NAD?
Definition
2
Term
What are the main biological functions of niacin?
Definition

Enzymatic Cofactor -NAD+ accepts electrons in catabolic pathways -NADPH donates eletrons in anabolic pathways

 

Post Translational Modification -mono & poly (ADP) ribosylation

 

Intracellular calcium signaling molecules -cADPR & NAADP

Term
What condition(s) result from niacin deficiency?
Definition
Pellegra
-dermatitis, diarrhea, dementia, death
Term
True or False

A corn-based diet may lead to a niacin deficiency because it lacks tryptophan and the existing niacin is tightly bound to proteins
Definition
true
Term
Which classification of B vitamins is niacin?
Definition
B3
Term
Which classification of B vitamins is riboflavin?
Definition
B2
Term
What are some dietary sources of riboflavin?
Definition
food from animal sources
eg milk, meat
Term
How is protein-bound riboflavin absorbed?
Definition
HCl in stomach acid frees it for absorption
Term
How is FAD/FMN absorbed?
Definition
converted to free riboflavin
Term
How is cellular production of FAD/FMN regulated?
Definition
positive regulation by T3 hormone, which activates the enzyme flavokinase
Term
What effect will increased FAD/FMN production have on metabolic rate?
Definition
metabolic rate will increase
Term
How many electrons are exchange in reduction/oxidation of FMN & FAD?
Definition
2 electrons

FMN -> FMNH2
FAD -> FADH2
Term
What is the precursor of FMN & FAD?
Definition
riboflavin
Term
What biochemical pathways is riboflavin involved in?
Definition
B-oxidation
Kreb's Cycle
ETC
Term
Describe the function of FAD & FADH2 in the glutathione reductase reaction
Definition
1. NADPH passes 2 e- to FAD, NAD & FADH2 are produced 2. FADH2 passes 2 e- to GSSG, FAD & GSH are produced (glutathione)
Term
True or False

Riboflavin is continuously excreted in the urine
Definition
true
Term
What are some common symptoms of a riboflavin deficiency?
Definition
cracked & red lips
inflammation of the lining of the mouth & tongue
mouth ulcers
cracks @ corners of the mouth
Term
Which classification of B vitamins is thiamin?
Definition
B1
Term
True or False

Cooking foods in hot water will lead to a loss of thiamine
Definition
true
Term
What form of thiamin exists in plants? Animals?
Definition
Plants: free thiamin
Animals: thiamin pyrophosphate (TPP)
Term
How is TPP absorbed?
Definition
phosphate must be removed prior to absorption
Term
What disease results from a thiamin deficiency?
Definition
beriberi
Term
True or False

A diet of polished/white rice will likely lead to pellegra disease
Definition
False

Beriberi disease is characteristic of this type of diet
Term
What are the biological roles of thiamin?
Definition
-acts as TPP in pyruvate & a-ketoglutarate dehydrogenase reactions

-involved in transketolase pathway/hexose monophosphate shunt (NADPH production & ribose synthesis)

-oxidant defense

-TTP is plays a role in nervous transmission
Term
What enzymes are involved in the pyruvate dehydrogenase complex?
Definition
pyruvate carboxylase
transacetylase
dehydrogenase
Term
What are the symptoms of a thiamin deficiency?
Definition
Beriberi disease
wasting
neural dysfunction
irritability
edematous swelling in limbs
difficulty walking
risk of heart failure
Term
Where is the majority of pantothenic acid found in food?
Definition
as a part of coenzyme A
Term
What form is pantothenic acid found in the blood?
Definition
free form, in RBC
Term
What is the metabolic function of pantothenic acid?
Definition
assists in the formation of acetyl CoA
CoASH + pyruvate -> acetyl CoA, which is essential in the Krebs cycle
Term
What is the RDA for biotin?
Definition
there is none!
Term
What reactions are dependent on biotin?
Definition
1. conversion of pyruvate to oxaloacetate
2. acetyl coa -> Malonyl CoA (FA synthesis)
3. propionyl CoA -> succinyl CoA -> glucose
Term
What is the relationship of biotin & the enzyme pyruvate carboxylase?
Definition
biotin acts as a cofactor for this enzyme
Term
True or False

acetyl CoA supports glucose synthesis
Definition
False

acetyl CoA is strictly ketogenic
Term
What does pyruvate carboxylase do?
Definition
converts pyruvate to oxaloacetate for the krebs cycle, or for gluconeogenesis
Term
What does pyruvate dehydrogenase do?
Definition
converts pyruvate to acetyl CoA for the krebs cycle
Term
True or False

Folate & folic acid are interchangeable
Definition
False

Folate is the reduced form of Vit B12
Folic acid is the oxidized form of Vit B12
Term
Which is found naturally in foods, folate or folic acid?
Definition
folate
Term
What are the 3 components of folate?
Definition
pterin ring
PABA
glutamic acid
Term
How is folate aborbed?
Definition
folate is a polyglutamate, must be broken down to monoglutamtes for absorption
Term
How is folic acid absorbed?
Definition
folic acid is a monoglutamate and can be readily absorbed
Term
What might inhibit enzymes from breaking polyglutamate down into monoglutamates?
Definition
alcohols and enzyme inhibitors
Term
Compare the bioavailability of folic acid to that of folate
Definition
Folic acid: 100% bioavailable
Folate: 50% bioavailable
Term
What form of Vit B are cobalamins associated with?
Definition
B12
Term
True or False

It is easy to exceed the UL of folate
Definition
True
Term
How is Vit B12 produced?
Definition
by bacteria
Term
What is the best dietary source of Vit B12?
Definition
animal products
e.g. meat (esp. from ruminants) & milk
Term
What is required for effective absorption of B12?
Definition
secretion of an "intrinsic factor" binding protein which will chaperone B12 through the GIT & bring it to a receptor in the SI for absorption
Term
Is Vit B12 easily stored?
Definition
yes, can be stored in the liver up to 10 years
Term
What effects will be observed in a folate deficiency?
Definition
impaired DNA synthesis & DNA repair
uracil misincorporation
megaloblastic anemia
teratogenesis
Term
What are the effects of excess folate in the diet?
Definition
increased cancer cell growth
tumour progression
Term
What is the best indicator of a Vit B12 or folate deficiency?
Definition
megaloblastic anemia
Term
What is megoblastic anemia?
Definition
a condition where there are few large RBCs overstuffed with hemoglobin
-due to a folate deficiency
Term
Describe the absorption & utilization of folate, assuming Vit B12 is present
Definition
1. polyglutamate side chains are removed to form monoglutamates (in SI)
2. intestinal mucosal cells methylate folate to N5-methyl form & release into bloodstream
3. Vit B12 removes N5-methyl group when folate reaches target cells, releasing free folate (THF)
4. B12 transfers methyl groups to SAM cycle (imp. for metabolism)
5. THF is also reduced to N5-methyl form to feed SAM cycle
Term
Describe the absorption & utilization of folate when in a Vit B12-deficient state
Definition
1. polyglutamate side chains are removed to form monoglutamates (in SI)
2. intestinal mucosal cells methylate folate to N5-methyl form & release into bloodstream
3. B12 is not available, so folate is trapped in N5-methyl form
4. B12 deficiency leads to a functional folate deficiency
Term
What isomers of Vit B6 are found in foods?
Definition
all isomers are readily available, B6 deficiency is rare
Term
True or False

A B12 deficiency is sometimes mistaken for a folate deficiency
Definition
True
Term
True or False

Increasing folate intake can overcome all implications of a B12 deficiency
Definition
False

Megoblastic anemia can be cured, but neural degeneration & death will eventually occur
Term
How is vitamin B6 absorbed?
Definition
dephosphorylation must occur prior to absorption, followed by passive diffusion in the jejunum
Term
What is the metabolically active form of Vit B6?
Definition
pyridoxal phosphate
Term
What is the major storage site of PLP?
Definition
muscle
Term
True or False

As protein intake decreases, demand for B6 increases
Definition
False

as protein intake increases, demand for B6 increases
Term
What are the functions of Vit B6?
Definition
1. Transamination
2. 1st step in porphyrin synthesis
3. Synthesis of neuroactive amines
Term
What are the neuroactive amines synthesized by vit B6?
Definition
epinephrine, norepinephrine, serotonin, histamine, GABA
Term
What are some symptoms involved with a B6 deficiency?
Definition
- convulsive seizures
- microcytic anemia
- dermatitis
Term
What are some symptoms of Vit B6 toxicity?
Definition
- peripheral nerve damage
- numb feet/hands
- tingling
Supporting users have an ad free experience!