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Questions and Answers
Which property allows amino acids to donate or accept a proton, making them regarded as ampholytes?
Which property allows amino acids to donate or accept a proton, making them regarded as ampholytes?
At what pH does an amino acid carry both positive and negative charges and exist as a zwitterion?
At what pH does an amino acid carry both positive and negative charges and exist as a zwitterion?
What property distinguishes amino acids from glycine in terms of optical isomers?
What property distinguishes amino acids from glycine in terms of optical isomers?
In strongly alkaline pH, how are amino acids charged?
In strongly alkaline pH, how are amino acids charged?
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What characteristic defines the isoelectric point (pI) of an amino acid?
What characteristic defines the isoelectric point (pI) of an amino acid?
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Which amino acid has a characteristic pH of 6.0 at which it carries both positive and negative charges and exists as a zwitterion?
Which amino acid has a characteristic pH of 6.0 at which it carries both positive and negative charges and exists as a zwitterion?
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What is the primary function of Bradykinin?
What is the primary function of Bradykinin?
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Which hormone controls blood pressure and acts as an antidiuretic?
Which hormone controls blood pressure and acts as an antidiuretic?
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What is the synthetic sweetener Spartame made of?
What is the synthetic sweetener Spartame made of?
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Which peptide hormone is involved in inducing labor in pregnant women?
Which peptide hormone is involved in inducing labor in pregnant women?
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What is the function of Glutathione in the body?
What is the function of Glutathione in the body?
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How much sweeter is Aspartame compared to sucrose?
How much sweeter is Aspartame compared to sucrose?
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What determines the ionic nature of amino acids?
What determines the ionic nature of amino acids?
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At the isoelectric pH, amino acids are found in which form?
At the isoelectric pH, amino acids are found in which form?
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How are amino acids joined together in peptides?
How are amino acids joined together in peptides?
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What is released during the formation of a peptide bond?
What is released during the formation of a peptide bond?
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What causes peptides to be rigid and planar?
What causes peptides to be rigid and planar?
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Which term refers to short chains of amino acids linked by peptide bonds?
Which term refers to short chains of amino acids linked by peptide bonds?
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Study Notes
Amino Acids Properties
- Amino acids generally have high melting points, often above 200°C.
- Amino acids can have different tastes, such as sweet (Gly, Ala, Val), tasteless (Leu), or bitter (Arg, Ile).
- All amino acids except glycine possess optical isomers due to the presence of an asymmetric carbon atom.
- Some amino acids have a second asymmetric carbon, e.g., isoleucine and threonine.
Amino Acids as Ampholytes
- Amino acids contain both acidic (COOH) and basic (-NH2) groups.
- Amino acids can donate or accept a proton, making them ampholytes.
- Amino acids rarely exist in a neutral form with free carboxylic and free amino groups.
- In strongly acidic pH, amino acids are positively charged (cation), while in strongly alkaline pH, they are negatively charged (anion).
- Each amino acid has a characteristic pH at which it carries both positive and negative charges and exists as a zwitterion (dipolar ion).
- The isoelectric point (pI) of an amino acid is the pH at which it has no net charge.
Peptides
- Peptides are short chains of 2-50 amino acids linked by peptide bonds.
- Chains of less than 10-15 amino acids are called oligopeptides (e.g., dipeptides, tripeptides, tetrapeptides).
- When a polypeptide contains more than approximately 50 amino acids, it is known as a protein.
- Peptides are formed by covalently linking amino acids through peptide bonds, which are amide linkages between the α-carboxyl group of one amino acid and the α-amino group of another.
- A water molecule is released during peptide bond formation.
Peptide Bond Characteristics
- Peptide bonds have partial double-bond character.
- Peptide bonds are rigid and planar.
- Peptide bonds have a trans configuration.
- Peptide bonds are uncharged but polar.
Interesting Peptides
- Enkephalins are pentapeptides that control pain by binding to receptors in certain brain cells.
- Bradykinin, vasopressin, and oxytocin are peptide hormones that are nonapeptides.
- Bradykinin inhibits tissue inflammation, vasopressin regulates blood pressure, and oxytocin induces labor and stimulates milk production.
- Gramicidin S is a cyclic decapeptide antibiotic produced by a strain of bacteria.
- Aspartame is a synthetic sweetener and a methyl ester of a dipeptide of L-aspartate and L-phenylalanine.
- Glutathione is a tripeptide that destroys harmful oxidizing agents in the body by reducing them.
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Description
Learn how to calculate the isoelectric point (pI) of amino acids by determining the average pKa values of ionizable groups. Explore an example with leucine, which forms a zwitterion at its pI. Understand how the pH of the medium influences the ionic nature of amino acids and peptides.
