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Questions and Answers
What is the reason why cells are able to synthesize L-isomers of amino acids specifically?
What is the reason why cells are able to synthesize L-isomers of amino acids specifically?
- The active sites of enzymes are asymmetric (correct)
- The active sites of enzymes are neutral
- The active sites of enzymes are flexible
- The active sites of enzymes are symmetric
What is the pH at which the overall charge on an amino acid molecule is zero?
What is the pH at which the overall charge on an amino acid molecule is zero?
- pH 5
- Isoelectric point (correct)
- pH 7
- pH 3
What is the term for a molecule that can act as either an acid or a base?
What is the term for a molecule that can act as either an acid or a base?
- Ampholyte (correct)
- Ionizable
- Electrolyte
- Zwitterion
What is the term for a molecule that has both positive and negative charges, but is neutral overall?
What is the term for a molecule that has both positive and negative charges, but is neutral overall?
What is the term for a simple monoamino monocarboxylic α-amino acid, such as alanine, when fully protonated?
What is the term for a simple monoamino monocarboxylic α-amino acid, such as alanine, when fully protonated?
What happens to an amino acid at a pH more acidic than its isoelectric point?
What happens to an amino acid at a pH more acidic than its isoelectric point?
What is a characteristic of amino acids that enables them to resist changes in pH?
What is a characteristic of amino acids that enables them to resist changes in pH?
What determines the charge of an amino acid at a given pH?
What determines the charge of an amino acid at a given pH?
What determines the role of an amino acid?
What determines the role of an amino acid?
What is the main difference between amino acids in dietary proteins and structural proteins?
What is the main difference between amino acids in dietary proteins and structural proteins?
What is the main characteristic of nonpolar amino acids?
What is the main characteristic of nonpolar amino acids?
What is the function of the peptide bond in proteins?
What is the function of the peptide bond in proteins?
At physiological pH, what happens to the carboxyl group of amino acids?
At physiological pH, what happens to the carboxyl group of amino acids?
How are amino acids classified based on their R groups?
How are amino acids classified based on their R groups?
What is the effect of the hydrophobic effect on protein structure?
What is the effect of the hydrophobic effect on protein structure?
What is the simplest amino acid in terms of structure?
What is the simplest amino acid in terms of structure?
What is the significance of color reactions in amino acids?
What is the significance of color reactions in amino acids?
What is the result of condensation between two amino acid molecules?
What is the result of condensation between two amino acid molecules?
What is the term for a chain of many amino acids?
What is the term for a chain of many amino acids?
What is the linkage between amino acids in a peptide bond?
What is the linkage between amino acids in a peptide bond?
What is the direction of the amino acid chain in the figure?
What is the direction of the amino acid chain in the figure?
What is the role of ninhydrin in amino acid analysis?
What is the role of ninhydrin in amino acid analysis?
What is the term for a chain of a few amino acids?
What is the term for a chain of a few amino acids?
What is the orientation of the R groups in the peptide bond figure?
What is the orientation of the R groups in the peptide bond figure?
What is the significance of the peptide bond in protein structure?
What is the significance of the peptide bond in protein structure?
What is the term for the end of an amino acid chain with a free amino group?
What is the term for the end of an amino acid chain with a free amino group?
What is the role of disulfide bonds in protein structures?
What is the role of disulfide bonds in protein structures?
Which amino acid has a positively charged guanidinium group?
Which amino acid has a positively charged guanidinium group?
What is the role of histidine residues in enzyme-catalyzed reactions?
What is the role of histidine residues in enzyme-catalyzed reactions?
Which of the following amino acids has a net negative charge at pH 7.0?
Which of the following amino acids has a net negative charge at pH 7.0?
What is the function of γ-carboxyglutamate in proteins?
What is the function of γ-carboxyglutamate in proteins?
Which amino acid is a derivative of four lysine residues?
Which amino acid is a derivative of four lysine residues?
What is unique about selenocysteine and pyrrolysine?
What is unique about selenocysteine and pyrrolysine?
What is the role of basic amino acids in proteins?
What is the role of basic amino acids in proteins?
Which amino acid is essential in children but not in adults?
Which amino acid is essential in children but not in adults?
What is the common feature of glycogenic amino acids?
What is the common feature of glycogenic amino acids?
Which amino acid is converted to tyrosine?
Which amino acid is converted to tyrosine?
What is the number of glycogenic amino acids?
What is the number of glycogenic amino acids?
Which amino acid is not essential in humans?
Which amino acid is not essential in humans?
What is the common feature of ketogenic amino acids?
What is the common feature of ketogenic amino acids?
Which amino acid is converted to cysteine?
Which amino acid is converted to cysteine?
How many amino acids are essential in the human diet?
How many amino acids are essential in the human diet?
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Study Notes
Amino Acids
- Amino acids have various color reactions with the properties of their specific groups, which is important in recognizing amino acids and thus proteins.
- Ninhydrin is a color reaction specific to all amino acids.
Peptides and Polypeptides
- Two amino acid molecules can be covalently joined through a substituted amide linkage, termed a peptide bond, to yield a dipeptide.
- When a few amino acids are joined in this fashion, the structure is called an oligopeptide, and when many amino acids are joined, the product is called a polypeptide.
Polypeptide Chain
- A polypeptide chain consists of amino acids joined by peptide bonds.
- The amino terminal of amino acid has a free amino group (NH3+) and the carboxy terminal has a free carboxyl group (COO-).
Amino Acids as Acids and Bases
- Each amino acid has a particular pH called the isoelectric point at which the overall charge on an amino acid molecule is zero.
- At the isoelectric point, an amino acid exists as a zwitterion, with the carboxyl group donating a proton to the amino group.
Acid-Base Properties
- Amino acids can act as acids or bases, depending on their R groups.
- At a pH more acidic than the isoelectric point, the amino acid forms a positive ion, and at a pH more alkaline than the isoelectric point, the amino acid forms a negative ion.
Classification of Amino Acids
- Amino acids can be classified into five main classes based on the properties of their R groups:
- Nonpolar, aliphatic R groups (e.g., alanine, valine, leucine, isoleucine)
- Aromatic R groups (e.g., phenylalanine, tyrosine)
- Negatively charged (acidic) R groups (e.g., aspartate, glutamate)
- Positively charged (basic) R groups (e.g., lysine, arginine, histidine)
- Uncommon R groups (e.g., hydroxyproline, γ-carboxyglutamate)
Uncommon Amino Acids
- Uncommon amino acids include 4-hydroxyproline, γ-carboxyglutamate, desmosine, and others.
Essential Amino Acids
- Essential amino acids must be taken in through the diet, as humans do not have the enzymes to synthesize them.
- Essential amino acids for humans include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Glycogenic and Ketogenic Amino Acids
- Glycogenic amino acids are converted to pyruvate, α-ketoglutarate, oxaloacetate, fumarate, or succinyl CoA.
- Ketogenic amino acids are converted to acetyl CoA or acetoacetate.
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