Questions and Answers
What is a primary structural characteristic of proteins?
Which of the following functions is NOT performed by proteins?
Which type of protein acts as a signal carrier in the body?
What role do contractile proteins play in the body?
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In what way do proteins assist in the transport of substances in the body?
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Which protein is involved in the transport of oxygen in the blood?
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What is a function of cell adhesion molecules?
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Which protein is specifically associated with the deposition of calcium phosphate in bones?
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What is a primary protective function of proteins?
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What characteristic of alanine and branched chain amino acids primarily contributes to their clustering within proteins?
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How do branched chain amino acid side chains primarily interact within proteins?
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Which property of the side chain of proline impacts the structure of peptide backbones?
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What describes the state of free amino acids at physiologic pH (7.4)?
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What is significant about the side chains of aromatic amino acids?
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Which aspect of the side chains of branched chain amino acids contributes to their lipid-like characteristics?
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What functional role do the side chains of amino acids primarily dictate?
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Which of the following statements is true about glycine?
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What occurs due to the unique geometry of proline within proteins?
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Why can't the side chains of alanine and branched chain amino acids hydrogen bond with water?
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What is a characteristic of almost all carboxyl and amino groups in amino acids at physiological pH?
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Which classification does glycine belong to?
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What force is primarily responsible for the packing of branched chain amino acids in close proximity?
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What type of interaction do aromatic amino acid side chains engage in, dictated by their substituents?
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What is the predominant ionization state of the carboxyl group in free amino acids at pH 7.4?
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What effect do the bulky side chains of branched chain amino acids have on protein structure?
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What role does the structural feature of amino acid side chains influence in proteins?
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What characteristic of glycine allows its frequent occurrence in certain protein structures?
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Which property of amino acids aids in classifying them based on polarity?
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At physiological pH, what is the charge state of the amino group in free amino acids?
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What occurs to carboxylic acid groups as pH values decrease significantly below the pKa?
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At what pH do 50% of the molecules exist as carboxylate anions?
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Which amino acid side chains are categorized as basic?
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What happens to the carboxyl group of alanine at low pH?
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Which statement about the amine group (-NH3+) of amino acids is correct?
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How is isoelectric form represented for amino acids during titration?
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What is the primary role of methionine in metabolism?
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Which amino acid contains a sulfhydryl group that is important for forming disulfide bonds?
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At physiological pH, how is the side chain of aspartate typically charged?
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What characterizes the side chains of aspartate and glutamate?
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What is the significance of cystine in human physiology?
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What happens to cysteine's side chain at an alkaline pH?
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How can a cysteine molecule in solution affect other cysteine molecules?
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Which sulfur-containing amino acid is classified as nonpolar?
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What ionic interaction can aspartate and glutamate participate in?
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What is the pKa of cysteine's sulfhydryl group for dissociation of hydrogen?
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Study Notes
Overview of Proteins
- Proteins are the most abundant biomolecules essential for every life process.
- Composed of linear polymers formed by amino acids.
- Functions include:
- Hormonal signal transmission.
- Catalyzing biochemical reactions as enzymes.
- Transporting hydrophobic compounds (e.g., hemoglobin, plasma albumin).
- Cell adhesion to extracellular matrix.
- Forming ion channels in lipid membranes.
- Facilitating movement through contractile proteins (muscles).
- Providing framework for calcium phosphate deposition (collagen in bone).
- Immune protection through immunoglobulins.
Structure of Amino Acids
- 20 different amino acids.
- At physiological pH (7.4), amino acids exist as zwitterions:
- Carboxyl group loses a proton to become negatively charged.
- Amino group gains a proton, becoming positively charged.
- Most functional groups involved in peptide bonds are non-reactive aside from hydrogen bonding.
- The character of side chains determines the functional roles of amino acids in proteins.
Classification of Amino Acid Side Chains
- Amino acids classified based on polarity and structure.
Nonpolar, Aliphatic Amino Acids
- Glycine: Simplest amino acid, minimal steric hindrance; common in tight protein structures.
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Alanine & Branched Chain Amino Acids (Valine, Leucine, Isoleucine):
- These have bulky hydrophobic side chains, promoting hydrophobic core formation in proteins.
- Hydrophobic interactions are enhanced by van der Waals forces.
- Proline: Rigid structure causes kinks in peptide chains; crucial for collagen structure.
Aromatic Amino Acids
- Side chains contain aromatic rings that impact polarity.
- Aromatic structure consists of six-membered carbon-hydrogen rings with conjugated double bonds.
- Threonine: Contains hydroxyl group, serves as attachment site for oligosaccharides in glycoproteins.
Sulfur-Containing Amino Acids
- Methionine: Nonpolar, bulky with hydrophobic side chain, pivotal for metabolism due to methyl group transfer.
- Cysteine: Critical for enzyme active sites; features a thiol group enabling disulfide bond formation (cystine).
Acidic and Basic Amino Acids
-
Aspartate and Glutamate:
- Function as proton donors, fully ionized at neutral pH.
- Form ionic bonds with positively charged molecules (lysine, arginine, histidine).
- At low pH: Protonated carboxylic groups; at neutral pH: Mostly dissociated, negatively charged.
Amino Acids with Ionizable Groups
- Acidic: Aspartate and Glutamate.
- Basic: Histidine, Lysine, Arginine.
Titration of an Amino Acid
- Dissociation of carboxyl group (-COOH) explains protonation states at different pH.
- Applications of the Henderson-Hasselbalch equation for calculating pH and dissociation constants.
- The amino group (-NH3+) is a weaker acid compared to carboxyl groups.
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Description
Explore the essential role of proteins and amino acids in biological processes. This quiz covers the structural features of proteins, their functions, and their significance in metabolism. Test your knowledge about these vital molecules that support life.