46 Questions
A carboxyl group is deprotonated when it receives a hydrogen ion.
False
Amino acids have a three-letter abbreviation.
True
The structure of R influences the solubility of an amino acid in non-polar solvents.
False
Amino acids are soluble in non-polar solvents due to their ionic character.
False
The COO- group is a feature of amino acids.
True
A carboxyl group is basic when it receives a hydrogen ion.
False
Amino acids have only one type of abbreviation.
False
The R group of an amino acid influences its solubility.
True
Non-polar amino acids have hydrocarbon chains.
True
Polar amino acids are soluble in water.
True
Aromatic amino acids are bulky and have a negative charge.
False
Proline is an example of a polar amino acid.
False
Non-polar amino acids are usually found in the kinks of proteins.
True
Amino acids with an R-group containing sulfur are always charged.
False
Hydrophobic amino acids are capable of forming hydrogen bonds.
False
Hydrophilic amino acids are insoluble in water.
False
All non-polar amino acids have aliphatic R-groups.
False
Polar amino acids are always hydrophilic.
True
Glycine has a polar R-group.
True
Proline is likely to be found in kinks of a protein structure.
True
The pH of a solution is equal to 2.
True
The pH of a solution is directly proportional to the hydrogen ion concentration.
False
Cysteine's R-group is a hydrocarbon.
False
The R-group of methionine is easily polar.
False
A solution with a pH of 2 is basic.
False
Serine and threonine have similar R-groups.
True
The pH of a solution can be calculated as the square of the hydrogen ion concentration.
False
A solution with a pH of 11 is neutral.
False
Valine's R-group is small and non-polar.
True
Alanine is a polar amino acid.
False
The pH of a solution is a linear function of the hydrogen ion concentration.
False
A solution with a pH of 2 has a higher hydrogen ion concentration than a solution with a pH of 11.
True
Two cysteine molecules can form a disulfide bond.
True
The pH of a solution is always a whole number.
False
Isoleucine has a large R-group.
False
Phenylalanine's R-group contains oxygen.
False
The pH of a solution can be calculated using the formula pH = log[H+]
False
Weak acids and weak bases dissociate completely in water
False
The carboxyl group (-COOH) is basic
False
The pK1 of glycine is 9.6
False
The amino group (-NH3+) is acidic
False
At pH < 2.2, the carboxyl group (-COOH) is fully deprotonated
False
The reaction between an acid and its conjugate base is reversible
True
The pKR of an acid is equal to the pH at which the acid is fully dissociated
False
At pH > 9.4, the amino group (-NH3+) is fully protonated
False
The pH of a solution can be calculated using the formula pH = [OH-]
False
Study Notes
Amino Acids
- Carboxyl group is deprotonated, making it acidic, and receives an H+ to become basic
- Amino acids are soluble in polar solvents due to their ionic character, exemplified by the COO- and +NH3 groups
- Solubility is influenced by the structure of the R group
Types of Amino Acids
- Non-Polar Amino Acids: have hydrocarbon chains, are hydrophobic, neutral, and aliphatic
- Polar Amino Acids: dissolve in water, are hydrophilic, neutral, and form H-Bonds
- Aromatic Amino Acids: contain oxygen, are bulky, and have polarity dependent on the R group
Characteristics of Amino Acids
-
Some amino acids are found inside the protein, usually in the kinks of the protein
-
The R group has a charge, which affects solubility
-
Hydrogen bonds are not formed when the R group has no charge### Amino Acids
-
There are 20 standard amino acids, each with a unique R-group
-
Glycine (Gly) and Alanine (Ala) have small R-groups
-
Serine (Ser) and Threonine (Thr) have R-groups with a hydroxyl (-OH) group
-
Cysteine (Cys) has an R-group with a sulfur atom, which can form a disulfide bridge with another Cysteine
-
Tyrosine (Tyr) and Tryptophan (Trp) have large, rigid R-groups
-
Proline (Pro) has a unique, rigid structure that can cause kinks in protein chains
-
Valine (Val) and Isoleucine (Ile) have non-polar, hydrophobic R-groups
-
Asparagine (Asn) and Glutamine (Gln) have R-groups with an amide group
-
Methionine (Met) has a sulfide group in its R-group, making it easily soluble in water
-
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
-
Disulfide bridges can form between two Cysteine (Cys) residues, stabilizing protein structure
-
Hydrogen bonds and weak interactions between amino acids help stabilize protein structure
-
Proline (Pro) can cause kinks in protein chains due to its rigid structure### pH Scale and Acid-Base Properties
-
pH is a measure of the concentration of hydrogen ions (H+) in a solution, calculated as pH = -log[H+].
-
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 explores the acidic properties of carboxyl groups, including their deprotonation and acidic behaviors. Test your knowledge of carboxyl groups and their chemical properties.
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