Week 9 and 10 Flashcards
What is the difference between mandatory and voluntary fortification?
Mandatory
replacing nutrients lost by processing or where there is an obvious need
voluntary
manufacturers are allowed to add nutrients and decide which ones. this needs to fit in with regulations though.
Name all the B vitamins
B1: thiamin B2: riboflavin B3: niacin B5: pantothenic acid B6: pyridoxine B7: biotin B9: folic acid B12: cobalamin
Which vitamins are water soluble?
B vitamins
vitamin C
Choline
what is a coenzyme?
when the prosthetic group of an enzyme is an organic compound
what is a cofactor?
when the prosthetic group of an enzyme or another protein is a metal ion
what does coenzyme do?
enable the specific enzymes to function
What the Thiamin coenzyme called?
thiamin pyrophosphate (TPP)
Describe the absorption of Thiamin?
Small intestine, sodium-dependent active or passive absorption
Only free thiamin is absorbed
How is Thiamin transported?
Transported by red blood cells (RBCs) in the coenzyme form: thiamin pyrophosphate (TPP)
How is Thiamin stored?
Small amount stored in muscles and the liver
How is Thiamin excreted?
Excess rapidly filtered by kidneys and excreted via the urine
What are the functions of thiamin?
Assists enzymes involved in carbohydrate and branched chain amino acids metabolism
Thiamin is needed for normal function of nervous system
Required in decarboxyl at ion reactions
What are the diseases that are associated with thiamin deficiency?
Beriberi
Wernicke-Korsakoff syndrome
which foods contain thiaminase enzymes that destroy Thiamin?
raw fish, shellfish
which foods contain compounds that oxidize Thiamin?
Brussel sprouts, and beets
Which vitamin was Once called “yellow enzyme”?
riboflavin
how is riboflavin released and absorbed? how much is absorbed?
HCl in stomach releases riboflavin bound to dietary compounds (e.g. protein)
Free riboflavin absorbed via active transport or diffusion depending on concentration
60-65% absorbed
How is riboflavin trasported?
by carrier proteins in the blood
what is riboflavins coenzyme?
FAD FNM
where is riboflavin stored?
kidneys, liver and heart
where is riboflavin excreted?
when in excess through urine
you have bright yellow urine, which vitamin might cause this?
riboflavin
what are the 7 functions of riboflavin?
- Part of 2 key redox enzymes as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)
- Key roles in energy metabolism and in the CAC + ETC: FMN shuttles hydrogen atoms into ETC
- In beta-oxidation: conversion of fatty acids to acetyl CoA requires fatty-acyl dehydrogenase, which requires FAD
- The formation of niacin (vitamin B3) from tryptophan requires FAD
- Formation of the vitamin B6 coenzyme form (PLP) requires FMN
- Riboflavin participates in folate metabolism
- The synthesis of glutathione (part of cellular antioxidant enzyme glutathione peroxidase) requires the activity of a FAD-containing enzyme: glutathione reductase
who are at risk of riboflavin deficiency?
chronic alcoholism, malabsorption syndromes, use of contraceptive pill, high stress, elderlies
What are the two coezyme forms of riboflavin?
Flavin adenine dinucleotide (FAD) Flavin mononucleotide (FMN)
Where and how is niacin absorbed
Some absorbed in stomach, but mainly in small intestine
active transport and passive diffusion depending on concentration available
where is niacin first transported to
first transported in portal vein to liver
where is niacin stored?
liver
how is niacin excreted?
in urine
What are the functions of niacin
Required in oxidation-reduction reactions as NAD+ and NADP+
Pharmacological use to lower cholesterol
what are the four stages of niacin deficiency?
Dermatitis, diarrhea, dementia, death
How can niacin be synthesised other then dietary intake?
Niacin can be endogenously synthesised from tryptophan in dietary protein
how much and how is B5 absorped?
Only 40-60% of intake is bioavailable
Active transport and passive diffusion depending on concentration available
when is pantothenic acid formed?
CoA forms when pantothenic acid combines with a derivative of ADP and the amino acid cysteine in any cells requiring it.
How is pantothenic acid transported around the body?
Transported around the body freely and bound to RBCs
how is pantothenic acid excreted?
urine
what is the main function of pantothenic acid?
Essential as coenzyme A for the formation of acetyl CoA in all energy production pathways (entry into the CAC)
why is pantothenic acid deficiency rare?
it is found in a large variety of foods
what is the coenzyme form of pyridoxine?
pyridoxal phosphate (PLP)
where is pyridoxine stored?
muscle tissue
how is pyridoxine excreted?
urine
what happens if no B6 is available?
all amino acids become essential as you cannot synthesise them
what are the functions of pyridoxine?
- amino acid metabolism
- amino acid transamination for the synthesis of non-essential amino acids
- required in glycogenesis
- Gene expression regulation
- Modulation of effects of steroid hormones
- Immune function
- Requiredinthesynthesisofimportantmetabolic compounds
What are the effects of pyridoxine deficiency?
Oilydermatitis
Microcytic hypochromic anemia (small and pale RBC: due to reduced haeme and hemoglobin synthesis)
Convulsions, depression, confusion (due to altered neurotransmitters synthesis)
what does having toxic levels of pyridoxine risk?
permanate nerve damage
Describe how biotin might be absorbed?
in food as free biotin or biocytin (bound to lysine in protein)
then Biotinidase unbinds biotin for absorption then Free biotin absorbed by active transport (sodium dependent carrier)
What are the functions of biotin?
Required in carboxylation reactions: co-enzyme (as biotin) of carboxylase enzymes (add CO2 )
Carboxylation of acetyl-CoA to form malonyl CoA, the beginning of fatty acid synthesis
Required for metabolism of carbohydrates, fats and proteins, CAC intermediates
Catabolism of branched-chain amino acids: ketogenic BCAA used to make acetyl-CoA
Involved in DNA folding in the nucleus as it binds to proteins facilitating the folding: role in gene stability
Why might biotin deficiency occur?
Biotinidase enzyme deficiency (genetic polymorphism)
Excessive consumption of raw egg-white (>12 per day)
what is the difference between folate and folic acid?
folate: food source: 50-80% bioavailable
folic acid: synthetic source: 100% bioavailable
where does folate absorption occur?
small intestine
what is the main form of folate found in circulation
5-methyl THFA is the main form found in the circulation
where is folate stored?
liver
how is folate excreted?
urine or feaces
What are the functions of folate?
cell division, proliferation, and maintenance of new cells
DNA synthesis and repair
Amino acid metabolism
what are the folate deficiency signs and symptoms?
DNA synthesis and repair impaired
Affects especially the rapidly dividing cells: RBC and GIT cells
In bone marrow: precursor cells cannot form new DNA, affect blood cells:
GIT cells: poor absorption of nutrients, as cells are poorly replaced or formed
what are some causes of folate deficiency?
Methotrexate (anti-cancer-recurrence medication) is a folate antagonist: reduces the proliferation of cancer cells; but will affect healthy cells too
Poor intake or poor absorption (e.g due to polymorphism in folate conjugase: enzyme splitting poluglutamates to monoglutamate for absorption)
Polymorphism in dihydrofolate reductase (enzyme converting folate /folic acid to THFA, the active form of the vitamin)
Alcoholism: alcohol interferes with folate conjugase
Vitamin B12 deficiency (to recycle THFA)
Pregnancy increases needs due to increased cell division
what can folate deficiency in early pregnacy lead to?
neural tube defect: Spina Bifida
how much folate leads to toxicity?
1mg daily
What are the two coenzyme forms of cobalamin?
- methyl cobalamin
2. 5-deoxy-adenosyl-cobalamin
where does the conversion of cobalamin to coenzyme form occur?
in the liver
describe the absorption process of cobalamin
Cobalamin is bound to protein in food, e.g. meat
Cobalamin released by action of HCl and pepsin in the stomach
Free cobalamin binds to R-protein (from salivary cells + gastric cells)
In the small intestine, pancreatic proteases release cobalamin from R-protein
Free cobalamin binds to intrinsic factor (IF) (from parietal cells)
IF + B12 travel to and are absorbed in the terminal ileum by endocytosis
Absorption is increased with increased intake
where and how much cobalamin is stored in the body?
liver
enough for 2-3 years ~2500μg
where is cobalamin excreted?
urine
but most is recycled in enterohepatic recirculation
B12 is required as a coenzyme to which two enzymes?
- L- methylmalonyl-coenzyme A mutase
2. methionine synthase
what does a cobalamin deficiency lead to?
Pernicious anemia: megaloblastic and macrocytic: death within 2-5 years due to a lack of RBC
What are some of the possible causes for cobalamin deficiency?
Absence of R-protein (from stomach and saliva) Poor binding of the IF-B12 complex (receptor error) Presence of B12 consuming bacteria in the ilium
Anti-acid medications: reduced HCl production
Atrophic gastritis (with ageing, resulting in reduced HCl as parietal cells loose function)
Crohn’s and Coeliac‘s disease
Vegan /vegetarian diets without supplementing or using fortified products
Metformin (T2DM medication): interference with B12 absorption
where and how is choline absorbed?
small intestine via transport protein
where is choline transported in the body after absorption?
Circulates to the liver via the portal vein
From the liver, circulates to other tissues, uptake by diffusion and via carrier proteins such as in the blood-brain barrier
where is choline stored?
liver
How is choline excreted?
oxidized in the liver as betaine
Excess excreted via the urine
What are the functions of choline?
Is part of phospholipids, lipoproteins, cell membranes in all cells, sphingomyelin, phosphatidylcholine.
A precursor of acetylcholine: essential in brain function and muscle function
Decreases homocysteine: methyl donor in the conversion of homocysteine to dimethylglycine
what is the other name for vitamin C?
ascorbic acid
What form is vitamin C found in as food?
Dehydro-ascorbic acid: oxidized form that needs to be “regenerated”
Where is vitamin C absorbed?
is vitamin C absorbed differently between the two forms Ascorbic acid and Dehydroascorbic acid
Small intestine
Ascorbic acid: active transport
Dehydroascorbic acid: facilitated diffusion, then reduced to ascorbic acid
How is vitamin C transported?
As ascorbic acid in the blood
Where is vitamin C stored and how much is there in the body?
Pituitary gland, adrenal glands, WBC, eyes, brain
Body pool of 300 to 400mg
how is vitamin c excreted?
Excess filtered by kidneys and excreted via the urine
What are the functions of vitamin C?
- Electron donor
- Collagen synthesis
- Protects lipids from peroxidation
- Carnitine biosynthesis
- Assists in non-heme iron absorption (conversion to ferrous form)
- Synthesis of neurotransmitters, cholesterol, corticosteroids, bile acids, aldosterone, adiponectin
- Protects immune cells from destruction via antioxidant action
what disease occurs due to vitaminc C deficiency?
scurvy
