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How it Works Animations: “Role of B Vitamins in Metabolism” Transcript
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How it Works Animations: “Role of B Vitamins in Metabolism” Transcript
Speaker: Narrator
NARRATOR: The cell is the site of many metabolic processes. The B vitamins and the essential nutrient
choline are necessary for these reactions. There are eight B vitamins. These include thiamin, which is
vitamin B1; riboflavin, which is vitamin B2; niacin, or niacinomide, which is vitamin B3; pantothenic acid
which is vitamin B5; pyridoxine, pyridoxal, pyridoxamin, or pyridoxine hydrochloride are all names for
vitamin B6; biotin, which is vitamin B7; folic acid or folate, which is vitamin B9; cyanocobalamin, which is
vitamin B12.
Some B vitamins are commonly referred to by name, such as thiamin, riboflavin, niacin, pantothenic acid,
biotin, and folic acid or folate. Others are commonly referred to by their number designation, such as
vitamin B6 and vitamin B12.
Reactions occur in all parts of the cell including the nucleus, the mitochondrion, and cytosol.
DNA is synthesized in the nucleus. Folate is a vitamin that functions as a coenzyme in DNA synthesis.
Folate must be in the correct form before it can be used. Vitamin B12 is a coenzyme in the conversion of
folate to the active form.
Protein synthesis occurs in the cytosol. Thiamin, vitamin B6, and folate are involved in protein synthesis.
Amino acids found in the cytosol of the cell are part of the amino acid pool. The amino acid pool is
replenished by protein breakdown and by diet. Amino acids from the pool can be used to synthesize new
proteins, nonessential amino acids, glucose, or fatty acids.
Deamination or transamination reactions in the liver prepare amino acids for participation in these
pathways. Both reactions remove the amino group, NH2, from the amino acid. In deamination reactions,
the NH2 group is removed, leaving a carbon skeleton that can be used for a variety of purposes.
Several B vitamins including thiamin, riboflavin, niacin, B6, biotin, and pantothenic acid have roles in
amino acid metabolism. Deaminated amino acids can be used to synthesize glucose, produce energy,
synthesize fatty acids, or produce neurotransmitters. Vitamin B6 is involved in protein metabolism and
amino acid metabolism, including transamination and deamination reactions.
Biotin has a role in amino acid metabolism. Pantothenic acid is part of a coenzyme A, which is required
for the production of energy. Niacin coenzymes are needed for the breakdown of protein when it is used
to synthesize fatty acids and sterols. Thiamin, riboflavin, niacin, biotin, pantothenic acid, and vitamin B6
are needed to produce energy from protein.
Transamination reactions are used to synthesize nonessential amino acids. In transamination reactions,
an amino group from an essential amino acid is transferred from an amino acid to a carbon skeleton to
form a new nonessential amino acid. Vitamin B6 is needed for transamination reactions.
Amino acids also provide two carbon skeletons that can be used for the synthesis of acetyl-CoA, citric
acid cycle intermediates, or fatty acids.
Gluconeogenesis and glycolysis occur in the cytosol of the cell. Gluconeogenesis synthesizes glucose
from three carbon molecules. Vitamin B6 is involved in gluconeogenesis. Some deaminated amino acids
and the glycerol backbone from triglycerides enter the pathway for gluconeogenesis as pyruvate. Niacin
is involved in this process. Biotin is a coenzyme in glucose production.
How it Works Animations: “Role of B Vitamins in Metabolism” Transcript
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Energy can be derived from carbohydrates, proteins, and fats. Glucose undergoes glycolysis and enters
energy pathways as pyruvate. Amino acids, from the breakdown of protein, are deaminated and also
enter the pathways as pyruvate, as acetyl-CoA, or as citric acid cycle intermediates.
Fatty acids from beta oxidation, deaminated amino acids, and pyruvate can all enter the citric acid cycle
by first being converted to acetyl-CoA. The mitochondrion is the site of energy production.
Lipid metabolism involves fatty acid oxidation and synthesis. Riboflavin, niacin, biotin, and pantothenic
acid are required for lipid metabolism. Triglycerides split into fatty acids and glycerol in the cytosol to
prepare for entry into metabolic pathways. Riboflavin, B2, is a major cofactor in the reactions. Glycerol
from triglyceride breakdown can be used to synthesize pyruvate. Pyruvate can either be used to
synthesize glucose via gluconeogenesis or it can be converted to acetyl-CoA which enters the citric acid
cycle and produces ATP.
Fatty acids undergo beta oxidation in the mitochondrion which produces many two carbon acetyl-CoA
molecules. Niacin and pantothenic acid are required for these reactions. Acetyl-CoA can participate in
several metabolic pathways. In the cytosol, acetyl-CoA can be used to synthesize fatty acids. Fatty acids
are added to the glycerol backbone to complete triglyceride or fat synthesis. In the mitochondria, acetylCoA can participate in the citric acid cycle and generate energy in the form of ATP. Thiamin, riboflavin,
niacin, and pantothenic acid are involved in these processes.
Cellular respiration is a four-step process that begins in the cytosol with glycolysis and ends in the
mitochondrion with the electron transport chain. B vitamins are cofactors at several steps. Glycolysis
splits the six carbon glucose molecule into two three carbon pyruvate molecules in the cytosol. Niacin is a
coenzyme in this step. The reaction produces some energy in the form of ATP.
Pyruvate enters the mitochondrion, loses a carbon, and combines with coenzyme A to synthesize acetylCoA in step two of cellular respiration. Thiamin is a coenzyme in acetyl-CoA synthesis.
Acetyl-CoA enters the citric acid cycle in step three. Thiamin, riboflavin, niacin, and pantothenic acid are
also coenzymes in the citric acid cycle.
Generation of ATP in the electron transport chain is the final step. Riboflavin and niacin are coenzymes in
the electron transport chain. The electron transport chain traps energy from electrons and uses it to
generate ATP.
In summary, B vitamins are involved in each phase of cellular respiration. Niacin is important in glycolysis
and in the breakdown of pyruvate to acetyl-CoA. Thiamin is a part of this process. Acetyl-CoA participates
in the citric acid cycle with the help of riboflavin, niacin, and pantothenic acid. Energy is captured by the
electron transport chain with the help of riboflavin and niacin.
Nerves communicate by way of chemical neurotransmitters. Vitamin B6 and the chemical choline are
involved in neurotransmitter synthesis, important for nerve function. Aspects of healthy nerve function are
maintained by thiamin and vitamin B12.
Vitamin B6 and the chemical choline have roles in the synthesis of neurotransmitters. For example,
choline is part of the neurotransmitter acetyl choline. Nerves communicate by way of chemical
neurotransmitters. Hemoglobin is the molecule responsible for carrying oxygen throughout the body.
Vitamin B6 is necessary for synthesis of this molecule.
Cell membranes are made of several molecules including phospholipids, proteins, and cholesterol.
Choline is used to make phospholipids which are part of cell membranes. Choline is not a B vitamin but it
is an essential nutrient.
[End of Audio]
How it Works Animations: “Role of B Vitamins in Metabolism” Transcript
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From “How it Works Animations: ‘Role of B Vitamins in Metabolism,’" 2012. Adapted with permission from
Wiley.