Vitamin B Flashcards
(44 cards)
Name the B vitamins
Thiamin (B1)
Riboflavin (B2)
Niacin (B3)
Pantothenic Acid (B5)
Pyridoxine (B6)
Biotin (B7)
Folic Acid (B9)
Cobalamin (B12)
B vitamins are important in
Carbohydrate metabolism
Lipid metabolism
Protein Metabolism
B vitamins act as
a “coenzyme” in one/more of the chemical reactions necessary to generate energy from carbohydrate, fat, and protein.
Acts as carriers of electrons or atoms in metabolic reactions
Coenzyme form for Thiamin (B1)
Thiamine pyrophosphate (TPP)
Coenzyme form for Niacin (B3)
nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP)
Coenzyme form for Riboflavin (B2)
Flavin adenine dinucleotide (FAD), Flavin mononucleotide (FMN)
Coenzyme form for Panthothenic acid (B5)
Coenzyme Acetylation (CoA)
Explain the role of B vitamins in Pyruvate Dehydrogenase Reaction
- Vitamins B, specifically thiamin (B1), niacin (B3), riboflavin (B2), and pantothenic acid (B5), play crucial roles in the pyruvate dehydrogenase reaction as they are involved in the formation and function of coenzymes essential for this metabolic process.
- The pyruvate dehydrogenase complex requires these coenzymes to catalyze the conversion of pyruvate to acetyl-CoA.
- Thiamin is converted into thiamine pyrophosphate (TPP). TPP serves as a coenzyme in the decarboxylation step of pyruvate. In this step, TPP removes a carbon dioxide molecule from pyruvate, forming a temporary bond with the remaining two-carbon unit.
- Niacin, in the form of nicotinic acid or nicotinamide, is adenylated to form nicotinamide mononucleotide (NMN). NMN is adenylylated to form nicotinamide adenine dinucleotide (NAD). NAD serves as a coenzyme, accepting electrons during the oxidation step of the pyruvate dehydrogenase reaction. This oxidation step results in the conversion of the two-carbon unit in pyruvate to CO2 and the production of NADH.
- Riboflavin is converted into two coenzyme forms: Flavin Adenine Dinucleotide (FAD) and Flavin Mononucleotide (FMN). FAD and FMN serve as coenzymes in the pyruvate dehydrogenase complex. They participate in redox reactions, accepting and donating electrons during the conversion of pyruvate to acetyl-CoA.
- Pantothenic acid is phosphorylated and then converted into 4’-phosphopantetheine.
4’-phosphopantetheine is adenylated to form dephospho-CoA. Dephospho-CoA is phosphorylated to form coenzyme A (CoA), the active coenzyme form. CoA combines with the oxidized two-carbon unit (acetyl group) to form acetyl-CoA, involving the formation of a thioester bond. - Acetyl-CoA enters the TCA cycle, NADH is utilized within the TCA cycle for electron transport, and CO2 is released as a byproduct of the pyruvate dehydrogenase reaction.
Source of Thiamin (B1)
Abundant in germinating seeds and un-milled cereals
- Growing area of roots, leaves, and shoots
Animal products rich in thiamin
- Egg yolk, liver, kidney, lean meat
Also rich in whole grain foods, enriched cereal and soy milk
Thiamine pyrophosphate (TPP) acts as a coenzyme. What are the important reactions?
- Pyruvate dehydrogenase
-Conversion of Pyruvate to Acetyl CoA (enters TCA cycle) - Alpha-ketoglutarate dehydrogenase
- Within the TCA cycle
- Conversion of intermediate alpha-ketoglutarate to Succinyl CoA
Explain the role of Thiamine pyrophosphate (TPP) in Alpha-ketoglutarate dehydrogenase
The overall reaction catalyzed by the alpha-ketoglutarate dehydrogenase complex is:
Alpha-ketoglutarate + Coenzyme A + NAD → Succinyl CoA + NADH + CO2
Thiamine pyrophosphate (TPP), derived from thiamin (Vitamin B1), acts as a crucial coenzyme in the alpha-ketoglutarate dehydrogenase complex.
TPP facilitates the decarboxylation of alpha-ketoglutarate. During the reaction, TPP undergoes a series of changes in its redox state, enabling the removal of a carbon dioxide molecule from alpha-ketoglutarate.
The decarboxylation step results in the formation of a high-energy thiamin-bound intermediate, which then transfers the two-carbon unit to Coenzyme A, forming Succinyl CoA.
Succinyl CoA is a downstream intermediate in the TCA cycle and is further metabolized to produce ATP. As part of the reaction, NAD+ is reduced to NADH.
What is the name of Thiamin (B1) deficiency?
Beri beri
What does beri beri affect?
nervous and cardiovascular systems
What are the two main forms of beri beri?
dry beri beri and wet beri beri.
What are the symptoms of dry beri beri?
[mostly nervous system]
Fatigue and loss of appetite
Muscle weakness, cramps and loss of reflexes
Dysfunction of nervous system (paralysis of motor nerves)
Tacychardia (abnormally fast heart rate), heart failure (severe cases)
Explain the symptoms of dry beri beri
The neurological symptoms are due to thiamin’s role in maintaining the health of nerve tissues and its involvement in the synthesis of neurotransmitters.
Thiamin is involved in glucose metabolism, maintains the functions of the nerve membrane and supports the synthesis of myelin and several neurotransmitters, e.g., acetylcholine, serotonin, and amino acids (aspartate and glutamate)
Muscle weakness and cramps result from impaired energy metabolism, as thiamin is crucial for the conversion of pyruvate to acetyl-CoA in processes like the pyruvate dehydrogenase complex.
The heart is one of the most energy-demanding organs in the body, and thiamin is essential for the production of energy needed for the heart’s function
What are the symptoms of wet beri beri?
[Mostly cardiovasular system]
Severe edema in arms and legs
Enlargement of the heart (cardiomegaly)
Respiratory problems
Symptoms may last for years and then cardiac complications may develop and death occur quickly
Explain the symptoms of wet beri beri
The edema is a result of weakened heart function, leading to fluid retention in the extremities.
Enlargement of the heart and respiratory problems are indicative of severe cardiovascular involvement.
Wet beri beri often has a more acute and severe course, with potentially rapid progression to cardiac failure and life-threatening complications.
What is infantile beri beri?
A severe form of thiamin (Vitamin B1) deficiency that primarily affects infants. It is particularly prevalent in regions with a high prevalence of maternal thiamin deficiency.
Important cause of child mortality in south-east Asia
The condition arises when the mother has insufficient thiamin levels, resulting in thiamin deficient breast milk
Thiamin is crucial for the infant’s metabolic processes, growth, and the proper functioning of the cardiovascular and nervous systems.
Infantile Beri-Beri starts in first few months of life
What are the initial symptoms of infantile beri beri?
Anorexia (lack of appetite)
Vomiting
Abdominal distension (swelling or bloating of the abdomen)
Progression to edema
What are the signs of infantile beri beri as the deficiency worsens?
- Cardiovascular signs - become more prominent, these may include tachycardia and signs of heart failure
- Neurological signs
- may include irritability, difficulty sleeping, and changes in behaviour - Without intervention, infantile beri beri can lead to a critical stage.
- The infant may eventually experience coma due to severe neurological impairment
If left untreated, it can lead to death
What is the cause of Thiamin (B1) deficiency?
- Polished rice
- In many countries, especially in Asia, polished rice is the major staple.
- Brown rice has its bran and germ layer removed to produce white rice, a process known as polishing.
- Polished rice is lower in thiamin compared to its unpolished counterpart
- Alcoholism
- Alcoholism can contribute to thiamin deficiency due to several factors
- Impaired absorption: chronic alcohol consumption can lead to damage in the gastrointestinal tract, impairing the absorption of essential nutrients, including thiamin.
- Diminished utilization: alcohol can interfere with the body’s ability to use thiamin effectively in metabolic processes
- Alcohol-Induced Thiamin Excretion: Alcohol consumption can increase the excretion of thiamin by the kidneys, further contributing to thiamin deficiency.
- Diuretic effect: Alcohol is diuretic, leading to increased urine production and potential loss of water-soluble vitamins, including thiamin.
Which B vitamin functions as two conezymes: Flavin monoclueotide (FMN) and
Flavin adenine dinucleotide (FAD)?
Riboflavin (B2)
Coenzymes Flavin monoclueotide (FMN) and
Flavin adenine dinucleotide (FAD) are involved in oxidation reduction reactions including
- Electron transport
- Fatty acid synthesis and oxidation
