39 Questions
What happens to the carboxyl group?
It is deprotonated
Which of the following is a characteristic of the carboxyl group?
It is acidic
Why are carboxyl groups soluble in polar solvents?
Due to their ionic character
What is the charge of the carboxyl group after deprotonation?
Negative
What is the function of the R group in amino acids?
Determines the solubility of the amino acid
What is the significance of the +NH2 group in amino acids?
It is the basic group in amino acids
How are amino acids commonly referred to?
By their three-letter or one-letter abbreviation
What is the relationship between the R group and solubility?
The R group determines the solubility of amino acids
What is a characteristic of amino acids, except for Glycine?
They have two stereoisomers: L and D forms
What is the function of the amino group in amino acids?
To donate a hydrogen ion
What is a property of amino acids that allows them to neutralize acids and bases?
They are amphoteric
What is the name of the form of an amino acid that can donate a hydrogen ion?
Protonated form
What is the role of the R-group in amino acids?
It determines the amino acid's overall structure
What is unique about the amino acid Glycine?
It has only one stereoisomer
What happens when the amino group of an amino acid accepts a hydrogen ion?
It becomes protonated
Why are amino acids considered amphoteric?
Because they can act as both acids and bases
What determines the properties of an amino acid?
The R-group
What is the function of the acid group in amino acids?
To donate a hydrogen ion
Which amino acid is likely to be found in kinks?
Proline
What is the result of the bonding between two Cysteines?
A covalent bond
Which of the following amino acids is polar?
Serine
What is unique about the R-group of Glycine?
It is very small
Which amino acid has an R-group that is most likely to be found in the middle of a protein?
Glycine
Which of the following amino acids is non-polar?
Alanine
What happens to the polarity of an amino acid when it combines with another amino acid?
It becomes less polar
Which of the following amino acids is most likely to be found on the surface of a protein?
Methionine
What is the result of the bonding between a sulfur atom and an oxygen atom?
A covalent bond
Which of the following is a characteristic of Proline?
It has a rigid structure
What is the pH of a solution when the concentration of [H+] is high?
Less than 7
What is the process by which a weak acid dissociates in water?
Partially dissociates into ions
What is the pK1 of the amino acid glycine?
2.34
What is the ionization state of the amino group (-NH3+) at pH 9.4?
Fully deprotonated
What is the relationship between the forward and backward reaction rates at equilibrium?
The forward and backward rates are equal
What happens to the pH of a solution when a strong acid is added?
The pH decreases
What is the function of the carboxyl group (-COOH) in an amino acid?
It is acidic
What is the pH at which the amino acid glycine is fully protonated?
Exactly 2
What is the term for the mixture of an amino acid and its conjugate base?
Zwitterion
What is the relationship between the pKR and the gain of a proton?
The pKR is inversely proportional to the gain of a proton
Which one of these is the most correct?
This one
Study Notes
Amino Acid Properties
- Amino acids are amphoteric, meaning they can be both acidic and basic.
- Amino group is protonated (donates H+) and carboxyl group is deprotonated (receives H+) at certain pH levels.
- Overall, amino acids have a neutral charge.
Stereoisomers
- Except for glycine, all amino acids have two stereoisomers: L and D forms.
Solubility
- Amino acids are soluble in polar solvents due to their ionic character.
- The structure of the R group also influences solubility.
Amino Acid Representation
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Amino acids are referred to by three-letter or one-letter abbreviations.
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The R group is a key component of the amino acid structure.### Amino Acids
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There are 20 standard amino acids, each with a unique R-group
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Glycine (Gly) and Alanine (Ala) have small R-groups
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Serine (Ser) and Threonine (Thr) have R-groups with a hydroxyl (-OH) group
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Cysteine (Cys) has an R-group with a sulfur atom, which can form a disulfide bridge with another Cysteine
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Tyrosine (Tyr) and Tryptophan (Trp) have large, rigid R-groups
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Proline (Pro) has a unique, rigid structure that can cause kinks in protein chains
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Valine (Val) and Isoleucine (Ile) have non-polar, hydrophobic R-groups
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Asparagine (Asn) and Glutamine (Gln) have R-groups with an amide group
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Methionine (Met) has a sulfide group in its R-group, making it easily soluble in water
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Leucine (Leu) has a non-polar, hydrophobic R-group
Polarity of Amino Acids
- Amino acids can be classified as polar or non-polar based on their R-group
- Polar amino acids have R-groups with a hydroxyl (-OH) or amide group
- Non-polar amino acids have R-groups with hydrocarbon chains or sulfur atoms
- Glycine (Gly) and Serine (Ser) are polar amino acids
- Alanine (Ala) and Valine (Val) are non-polar amino acids
- Proline (Pro) is a non-polar amino acid, but its rigid structure makes it unique
Protein Structure
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Disulfide bridges can form between two Cysteine (Cys) residues, stabilizing protein structure
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Hydrogen bonds and weak interactions between amino acids help stabilize protein structure
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Proline (Pro) can cause kinks in protein chains due to its rigid structure### pH Scale and Acid-Base Properties
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pH is a measure of the concentration of hydrogen ions (H+) in a solution, calculated as pH = -log[H+].
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pH scale ranges from 0 to 14, with a pH below 7 being acidic, pH 7 being neutral, and pH above 7 being basic.
Weak Acids and Bases
- A weak acid is a molecule that partly dissociates in water, releasing H+ ions.
- Weak acids have a higher pKa (acid dissociation constant) than strong acids, indicating a lower tendency to donate a proton (H+).
- A weak base is a molecule that accepts H+ ions to form a conjugate acid.
Acid-Base Properties of Amino Acids
- Amino acids have both an acidic carboxyl (-COOH) and a basic amino (-NH2) group.
- The carboxyl group is protonated (acidic) at low pH and deprotonated (basic) at high pH.
- The amino group is deprotonated (basic) at low pH and protonated (acidic) at high pH.
Titration of Glycine
- Glycine, an amino acid, has two pKa values: pK1 (COOH) = 2.34 and pK2 (NH3+) = 9.6.
- At pH < 2.34, glycine is fully protonated (acidic).
- At pH > 9.6, glycine is fully deprotonated (basic).
- The zwitterion form of glycine, where the carboxyl group is deprotonated and the amino group is protonated, is most prevalent at pH around 6-7.
This quiz covers the properties and characteristics of various elements, including oxygen, nitrogen, and sulfur, as well as the structure of aromatic rings.
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