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Amino Acid

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Amino acids are molecules containing an amine group, a carboxylic acid group, and a side-chain that is specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen. Amino acid is the building unit of protein , which have important role in our body because:

1-Amino acids used to compose antibodies which have role in immune system against microbial infection

2-Amino acids used to regulate cell growth and bio-synthesis of purine and pyrimidine ( this compounds have role in DNA synthesis)

H2NCHRCOOH

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Amino acid classification according to reactive group or R group

Aliphatic - Glycine, Alanine, Valine, Leucine, Isoleucine

Aromatic - Phenylalanine, Tyrosine, Tryptophan

OH- - Serine, Threonine Acidic - Aspartic Acid, Glutamic Acid Acid amide - Aspargine, Glutamine Basic - Arginine, Lysine, Histidine Sulphur - Cystine, Methionine Cyclic - Proline

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Non polar or Hydrophobic - Glycine, Alanine, Valine, Leucine, Isoleucine, Proline

Polar uncharged - Phenylalanine, Tryptophane, Tyrosine

Polar charged or Hydrophillic - Serine, Threonine (OH-), Cystine, Methionine (sulphur), Aspargine, Glutamine (acid amide)

Acidic or Positively charged - Aspartic Acid, Glutamic Acid

Basic or Negatively charged - Arginine, Lysine, Histidine

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Amino acid can be divided into the above 3 groups (non-polar, flexible and polar) and then subdivided by their chemical character.

Non-Polar -- 8 Amino Acids Hydrocarbon        Alanine, Valine, Leucine, Isoleucine, Proline Aromatic              Phenylalanine, Tryptophane Thiol Ether            Methionine Flexible -- 1 Amino Acids Glycine -- flexible because it has no side chain Polar -- 11 Amino Acids Alcohol        Serine, Threonine, Tyrosine Thiol            Cystine Amides        Aspargine, Glutamine Acids          Aspartic, Glutamic Bases          Lysine, Arginine, Histidine

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From Metabolic point of view, amino acid are divided into three groups:

Glycogenic Amino acid

i.e : Alanine, Glycine, Methionine etc Ketogenic Amino acid

i.e : Lysine and Leusine Glucogenic and Ketogenic Amino acid

i.e : Isoleusine, Tyrosine, Phenylalanine, Tryptophan

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They are classified according to the side chain into: 1- Aliphatic side chain

Alanine, Glycine, Isoleucine, Leucine, Proline and Valine.

2-Aromatic ringPhenyl alanine, Tryptophan and Tyrosine

3-Acidic side chainAspartic acid and Glutamic acid

4-Amidic ( contain amide group)Asparagine and Glutamine.

5-Sulphur containing Cysteine and Methionine

6-HydroxylicSerine, Threonine and Tyrosine

7-BasicArginine, Histidine and Lysine

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They are over 300 amino acids occur in nature but 20 amino acid occur only in protein ,they classified according to the synthesis by the body into:

Non essential amino acids which the body can synthesized

Alanine, Proline, Asparagine, Aspartic acid , Cysteine, Tyrosine, Serine, Glycine, Glutamine and Glutamic acid

Essential amino acids which the body can’t synthesized it.

i.e: Isoleucine , leucine, Lysine, Methionine, Valine, Phenyl alanine, Threonine,Tryptophan, Histidine and Arginine.

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In chemistry, a zwitterion is a neutral molecule with a positive and a negative electrical charge (n.b. not dipoles) at different locations within that molecule. Zwitterions are sometimes also called inner salts.

Fig - An amino acid contain both acidic (carboxylic acid fragment) and basic (amine fragment) centres. The isomer on the right is a zwitterion.

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Examples Amino acids are the best-known examples of

zwitterions. These compounds contain an ammonium and a carboxylate group, and can be viewed as arising via a kind of intramolecular acid-base reaction:

The amine group deprotonates the carboxylic acid.

NH2RCHCO2H NH3+RCHCO2

–

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A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged.Adding an alkali to an amino acid solutionIf you increase the pH of a solution of an amino acid by adding hydroxide ions, the hydrogen ion is removed from the -NH3

+ group. Then the amino acid now existed as a negative ion using electrophoresis.

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Adding an acid to an amino acid solutionIf you decrease the pH by adding an acid to a solution of an amino acid, the -COO- part of the zwitterion picks up a hydrogen ion. This time, during electrophoresis, the amino acid would move towards the cathode (the negative electrode).

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Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase (PAH), rendering it nonfunctional.This enzyme is necessary to metabolize the amino acid phenylalanine (Phe) to the amino acid tyrosine. When PAH activity is reduced, phenylalanine accumulates and is converted into phenylpyruvate (also known as phenylketone), which is detected in the urine.

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If PKU is diagnosed early enough, an affected newborn can grow up with normal brain development, but only by managing and controlling Phe levels through diet, or a combination of diet and medication. Optimal health ranges (or "target ranges") are between 120 and 360 µmol/L, and aimed to be achieved during at least the first 10 years.When Phe cannot be metabolized by the body, abnormally high levels accumulate in the blood and are toxic to the brain. When left untreated, complications of PKU include severe mental retardation, brain function abnormalities, microcephaly, mood disorders, irregular motor functioning, and behavioral problems such as attention deficit hyperactivity disorder.

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The isoelectric point (pI), sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge.

Amphoteric molecules called zwitterions contain both positive and negative charges depending on the functional groups present in the molecule. The net charge on the molecule is affected by pH of their surrounding environment and can become more positively or negatively charged due to the loss or gain of protons (H+). The pI is the pH value at which the molecule carries no electrical charge or the negative and positive charges are equal.

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For an amino acid with only one amine and one carboxyl group, the pI can be calculated from the mean of the pKas of this molecule. For amino acids with more than two ionizable groups, such as lysine, the same formula is used, but this time the two pKa's used are those of the two groups that lose and gain a charge from the neutral form of the amino acid.

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Lysine has a single carboxylic pKa and two amine pKa values (one of which is on the R-group), so fully protonated lysine has a +2 net charge. To get a neutral charge, we must deprotonate the lysine twice, and therefore use the R-group and amine pKa values (found at List of standard amino acids).

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1.General Features Nitrogen Balance & Metabolic Pools

2. Degradation Transamination & Glutamate

Dehydrogenases

3. Urea Cycle 4. Sulfur-containing amino

acids 5. Creatine & Creatinine

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In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are broken down if there is an excess of protein intake. The amino group is removed from the amino acid and converted to ammonia. The rest of the amino acid is made up of mostly carbon and hydrogen, and is recycled or oxidized for energy. Ammonia is toxic to the human system, and enzymes convert it to urea or uric acid by addition of carbon dioxide molecules (which is not considered a deamination process) in the urea cycle, which also takes place in the liver. Urea and uric acid can safely diffuse into the blood and then be excreted in urine.

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GuanineDeamination of guanine results in the

formation of xanthine. Xanthine, in a manner analogous to the enol tautomer of guanine, selectively base pairs with thymine instead of cytosine. This results in a post-replicative transition mutation, where the original G-C base pair transforms into an A-T base pair. Correction of this mutation involves the use of alkyladenine glycosylase during base excision repair.

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AdenineDeamination of adenine results in the

formation of hypoxanthine. Hypoxanthine, in a manner analogous to the imine tautomer of adenine, selectively base pairs with cytosine instead of thymine. This results in a post-replicative transition mutation, where the original A-T base pair transforms into a G-C base pair.

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Transamination as the name implies, refers to the transfer of an amine group from one molecule to another. This reaction is catalyzed by a family of enzymes called transaminases. Actually, the transamination reaction results in the exchange of an amine group on one acid with a ketone group on another acid. It is analogous to a double replacement reaction.

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The most usual and major keto acid involved with transamination reactions is alpha-ketoglutaric acid, an intermediate in the citric acid cycle. A specific example is the transamination of alanine to make pyruvic acid and glutamic acid. Lysine and threonine are the only two amino acids that do not always undergo transamination.

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Once the keto acids have been formed from the appropriate amino acids by transamination, they may be used for several purposes. The most obvious is the complete metabolism into carbon dioxide and water by the citric acid cycle.

However, if there are excess proteins in the diet those amino acids converted into pyruvic acid and acetyl CoA can be converted into lipids by the lipogenesis process. If carbohydrates are lacking in the diet or if glucose cannot get into the cells (as in diabetes), then those amino acids converted into pyruvic acid and oxaloacetic acids can be converted into glucose or glycogen.

The hormones cortisone and cortisol from the adrenal cortex stimulate the synthesis of glucose from amino acids in the liver and also function as antagonists to insulin.

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. Oxidative deamination is

a. the conversion of an amino acid to a keto acid plus ammonia

b. the conversion of an amino acid to a carboxylic acid plus ammonia

c. the transfer of an amino group from an amino acid to a keto acid

d. the transfer of an amino group from an amino acid to a carboxylic acid

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Transamination is

a. the conversion of an amino acid to a keto acid plus ammonia

b. the conversion of an amino acid to a carboxylic acid plus ammonia

c. the transfer of an amino group from an amino acid to a keto acid

d. the transfer of an amino group from an amino acid to a carboxylic acid

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