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Questions and Answers
What is the primary function of carboxyl groups in biological molecules?
What is the primary function of carboxyl groups in biological molecules?
- They catalyze redox reactions.
- They facilitate hydrogen bonding.
- They contribute to the formation of peptide bonds. (correct)
- They enable nucleophilic attacks in enzymatic pockets. (correct)
Which functional group is primarily responsible for the formation of sulfur-sulfur bonds in proteins?
Which functional group is primarily responsible for the formation of sulfur-sulfur bonds in proteins?
- Thiol group (correct)
- Amino group
- Carbonyl group
- Hydroxyl group
What characteristic of the phosphate group makes it suitable for its role in redox reactions?
What characteristic of the phosphate group makes it suitable for its role in redox reactions?
- Its ability to form H-bonds
- Its polarity
- Its small size
- Its high electronegativity (correct)
Which of the following amino acids is likely to participate in maintaining the 3D structure of proteins through electrostatic interactions?
Which of the following amino acids is likely to participate in maintaining the 3D structure of proteins through electrostatic interactions?
How do carbonyl groups influence the reactivity of amino acids?
How do carbonyl groups influence the reactivity of amino acids?
What defines the chirality of amino acids?
What defines the chirality of amino acids?
In what form do amino acids typically exist when they are linked together?
In what form do amino acids typically exist when they are linked together?
Which of the following statements about peptide bonds is true?
Which of the following statements about peptide bonds is true?
Which statement accurately describes the tertiary structure of proteins?
Which statement accurately describes the tertiary structure of proteins?
Which functional groups increase the water solubility of molecules?
Which functional groups increase the water solubility of molecules?
What is a unique feature of glycine among amino acids?
What is a unique feature of glycine among amino acids?
What characterizes the quaternary structure of proteins?
What characterizes the quaternary structure of proteins?
Which of the following amino acids is an exception to the general structure of α-amino acids?
Which of the following amino acids is an exception to the general structure of α-amino acids?
Why are L-amino acids significant in biological systems?
Why are L-amino acids significant in biological systems?
What is the primary role of hydroxyl groups in biological molecules?
What is the primary role of hydroxyl groups in biological molecules?
What is the significance of chirality in amino acids?
What is the significance of chirality in amino acids?
Which D-amino acid characteristic is true regarding its occurrence in nature?
Which D-amino acid characteristic is true regarding its occurrence in nature?
Which group of amino acids is defined by having side chains that do not seek out polar interactions?
Which group of amino acids is defined by having side chains that do not seek out polar interactions?
What feature do zwitterions possess under physiological pH conditions?
What feature do zwitterions possess under physiological pH conditions?
Which property of an amino acid is primarily determined by its side chain (R group)?
Which property of an amino acid is primarily determined by its side chain (R group)?
How many amino acids are specifically utilized in mammalian proteins?
How many amino acids are specifically utilized in mammalian proteins?
Which types of amino acids can serve as buffers within peptide chains?
Which types of amino acids can serve as buffers within peptide chains?
What is the characteristic structural form of a zwitterion?
What is the characteristic structural form of a zwitterion?
How many basic groups can commonly classify amino acids based on their R substituents?
How many basic groups can commonly classify amino acids based on their R substituents?
What determines the ionization state of amino acids at different pH levels?
What determines the ionization state of amino acids at different pH levels?
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Study Notes
Functional Groups and Their Biological Importance
- Hydroxyl Group: Enhances water solubility through polarity and ability to form hydrogen bonds.
- Phosphate Group: Key structural component of nucleic acids and cell membranes; involved in redox reactions; influences protein 3D structure and enzymatic function.
- Carboxyl Group (Carboxylic Acid): Common in biology (e.g., amino acids, fatty acids); allows amino acids to link into proteins due to susceptibility to nucleophilic attack.
- Amino Group: Acts as a base by accepting protons; crucial for maintaining macromolecule structure via electrostatic interactions and hydrogen bonding.
- Thiol Group: Nucleophilic; engages in redox reactions; important for the structure of proteins, especially in cysteine, which forms disulfide bonds.
- Carbonyl Group: Characterized by a partial positive charge on carbon, making it a target for nucleophilic attack; crucial for peptide bond formation in amino acids.
Peptides and Protein Structure
- Peptides: Short chains of amino acids, smaller than proteins; many peptide-based drugs available.
- Secondary Structure: Determined by hydrogen bonds between nearby amino acids.
- Tertiary Structure: Formed by the folding of secondary structures into a 3D conformation through long-range interactions.
- Quaternary Structure: 3D arrangement of proteins with multiple subunits and their interactions.
Amino Acid Structure and Characteristics
- Common Structure: Alpha-carbon bonded to an acidic carboxyl group, a basic amino group, and a hydrogen atom; Proline is an exception with a cyclic structure.
- Chirality: All amino acids, except glycine, are chiral and exhibit L- and D- forms; only L-amino acids are integrated into proteins.
- D-Amino Acids: Rare in proteins but present in bacterial cell walls; potential links to human diseases.
Amino Acid Classification
- Presence: Over 300 amino acids exist, but mammalian proteins use only 20.
- Classification Groups:
- Nonpolar, aliphatic (7)
- Aromatic (3)
- Polar, uncharged (5)
- Positively charged (3)
- Negatively charged (2)
- Properties: Side chain chemical properties dictate bonding and interactions with other molecules; groupings illustrate functional roles and metabolic pathways.
Ionization of Amino Acids
- Buffering Capacity: Free and charged amino acids can act as buffers; possess at least two ionizable protons, each with a distinct pKa.
- Ionization Reactions:
- Carboxylic acid: COOH ↔ COO− + H+ (acidic pKa)
- Amino group: NH4+ ↔ NH3 + H+ (basic pKa)
Ionization State of Amino Acids
- Physiological pH Range (6.8-7.4): Amino acids exist as zwitterions, which are neutral molecules carrying both positive and negative charges.
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