acids as a part of their diet. Human beings also must include in their diet
adequate amounts of eight different amino acids, which they cannot
synthesize in their body. These are known as essential amino acids. The
eight essential amino acids are valine, leucine, isoleucine, phenylalanine,
tryptophan, threonine, methionine and lysine. Sometimes, arginine and
histidine are also included in the category of essential amino acids.
4.9.3 Glucogenic and ketogenic amino acids
The carbon skeletons of the amino acids can be used to produce metabolic
energy. Several amino acids can be classified as glucogenic and ketogenic
because of their degradation products.
Amino acids that are converted to glucose or glycogen are called
glucogenic amino acids. Alanine, arginine, asparagine, cysteine, glutamine,
glycine, histidine, hydroxyproline, methionine, proline, serine and valine are
glucogenic amino acids. Glucogenic amino acids give rise to a net production of pyruvate or TCA cycle, such as a-ketoglutarate or oxaloacetate, all
of which are precursors to glucose via gluconeogenesis.
Amino acids that give rise to ketone bodies (acetylCoA or acetoacetylCoA, neither of which can bring about net glucose production) are called
ketogenic amino acids. Leucine and lysine are ketogenic amino acids. Some
amino acids, e.g. threonine, isoleucine, phenylalanine, tyrosine and tryptophan, can be both ketogenic and glycogenic.
4.9.4 Amino acids in human body
All human tissues are capable of synthesizing the nonessential amino acids,
amino acid remodelling and conversion of non-amino-acid carbon skeletons
into amino acids and other derivatives that contain nitrogen. However, the
liver is the major site of metabolism of nitrogenous compounds in the body.
Dietary proteins are the primary source of essential amino acids (or
nitrogen). Digestion of dietary proteins produces amino acids, which are
absorbed through epithelial cells and enter the blood. Various cells take up
these amino acids that enter the cellular pools.
In our bodies, amino acids are used for the synthesis of proteins and other
nitrogen-containing compounds, or they are oxidized to produce energy.
Cellular proteins, hormones (thyroxine, epinephrine and insulin), neurotransmitters, creatine phosphate, the haem of haemoglobin, cytochrome,
melanin (skin pigment) and nucleic acid bases (purine and pyrimidine) are
examples of amino-acid-derived nitrogen-containing biologically important
group of compounds found in humans.
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CH4 ORGANIC FUNCTIONAL GROUPS
adequate amounts of eight different amino acids, which they cannot
synthesize in their body. These are known as essential amino acids. The
eight essential amino acids are valine, leucine, isoleucine, phenylalanine,
tryptophan, threonine, methionine and lysine. Sometimes, arginine and
histidine are also included in the category of essential amino acids.
4.9.3 Glucogenic and ketogenic amino acids
The carbon skeletons of the amino acids can be used to produce metabolic
energy. Several amino acids can be classified as glucogenic and ketogenic
because of their degradation products.
Amino acids that are converted to glucose or glycogen are called
glucogenic amino acids. Alanine, arginine, asparagine, cysteine, glutamine,
glycine, histidine, hydroxyproline, methionine, proline, serine and valine are
glucogenic amino acids. Glucogenic amino acids give rise to a net production of pyruvate or TCA cycle, such as a-ketoglutarate or oxaloacetate, all
of which are precursors to glucose via gluconeogenesis.
Amino acids that give rise to ketone bodies (acetylCoA or acetoacetylCoA, neither of which can bring about net glucose production) are called
ketogenic amino acids. Leucine and lysine are ketogenic amino acids. Some
amino acids, e.g. threonine, isoleucine, phenylalanine, tyrosine and tryptophan, can be both ketogenic and glycogenic.
4.9.4 Amino acids in human body
All human tissues are capable of synthesizing the nonessential amino acids,
amino acid remodelling and conversion of non-amino-acid carbon skeletons
into amino acids and other derivatives that contain nitrogen. However, the
liver is the major site of metabolism of nitrogenous compounds in the body.
Dietary proteins are the primary source of essential amino acids (or
nitrogen). Digestion of dietary proteins produces amino acids, which are
absorbed through epithelial cells and enter the blood. Various cells take up
these amino acids that enter the cellular pools.
In our bodies, amino acids are used for the synthesis of proteins and other
nitrogen-containing compounds, or they are oxidized to produce energy.
Cellular proteins, hormones (thyroxine, epinephrine and insulin), neurotransmitters, creatine phosphate, the haem of haemoglobin, cytochrome,
melanin (skin pigment) and nucleic acid bases (purine and pyrimidine) are
examples of amino-acid-derived nitrogen-containing biologically important
group of compounds found in humans.
182
CH4 ORGANIC FUNCTIONAL GROUPS