Questions and Answers
What type of protein structure is altered in sickle cell anemia?
What is the function of fibrous proteins in the body?
What type of bonds hold α chains together in collagen?
What is the function of vitamin C in collagen synthesis?
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What is the primary structure of collagen?
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What is the effect of the mutation in sickle cell anemia on hemoglobin?
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What is the function of proline and hydroxyproline in collagen?
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What is the structure of collagen fibrils?
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What primarily stabilizes the secondary structure of proteins?
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Which statement best describes a characteristic of tertiary protein structure?
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What role do hydrophobic interactions play in protein folding?
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Which factor is NOT typically involved in protein folding pathways?
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What is a defining feature of a protein domain?
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Which type of protein generally exhibits a quaternary structure?
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Which of the following amino acid types is characterized by its ability to form hydrogen bonds in secondary structures?
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In the context of protein interactions, what is typically the result of hydrophilic and hydrophobic side chain distributions?
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Which property must a protein possess to function correctly in its quaternary structure?
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What impact does abnormal protein structure typically have on cellular function?
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Which of the following statements accurately describes the role of hydrophobic interactions in tertiary protein structure?
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What is the primary difference between a super-secondary structure (motif) and a protein domain?
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Which of the following statements accurately describes the relationship between primary structure and tertiary structure?
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How do chaperone proteins contribute to protein folding?
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Which of the following statements accurately describes the role of disulfide bonds in tertiary structure?
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Why is protein folding a complex process that often requires chaperone proteins?
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Which of the following is NOT a common feature of protein domains?
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How do the R groups of amino acids contribute to the formation of beta-sheets?
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Which of the following statements accurately describes the concept of a "random coil" in protein structure?
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How does the tertiary structure of a protein contribute to its function?
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Study Notes
Protein Structure and Function
- Proteins have different levels of structure, including primary, secondary, tertiary, and quaternary structures, each stabilized by specific forces.
- Primary structure: the linear sequence of amino acid residues joined through peptide bonds, determining the 3D structure of a polypeptide.
- Peptide bonds: formed through condensation reactions between α-carboxylate and α-amino groups, with characteristics that affect protein structure, such as restricted rotation and resonance.
- Chemical nature of amino acids: classified into aliphatic, non-aromatic with hydroxyl R-groups, sulfur-containing, acidic, basic, aromatic, imino, and other groups.
Primary Structure
- Nonpolar (aliphatic) side groups: gly, ala, ile, leu, val, met, and pro.
- Side chains with basic groups: arg, lys, and his.
- Side chains with acidic groups: asp and glu.
- Polar but uncharged groups: amide derivatives of asp and glu (asn and gln), hydroxyl groups (ser, thr, and tyr), and sulfhydryl groups (cys).
- Other classifications: hydrophilic vs hydrophobic, optical properties, essential vs non-essential, and glucogenic vs ketogenic or ketogenic/glucogenic.
Secondary Structure
- H-bonding of peptide backbone causes amino acids to fold into a repeating pattern, forming common structures like α-helix and β-sheet.
- β-sheet: stabilized by hydrogen bonds co-planar with the β-pleat, with R groups alternating above and below the plane.
- Super secondary structures (motifs): combining secondary structural elements, such as the αβ motif, to form globular proteins.
Tertiary Structure
- Final folded state of a complete polypeptide in 3D conformation, stabilized by hydrophobic interactions, hydrogen bonding, ionic interactions, and disulfide bond formation.
- Creates specific and flexible binding sites for ligands and maintains an appropriate surface for the protein's cellular location.
- Folding can be affected by post-translational modifications of amino acids, such as phosphorylation, glycosylation, and acetylation.
Protein Domains
- Fundamental functional and three-dimensional structural unit(s) of a polypeptide, comprising one or more super-secondary structures.
- Folding of a domain usually occurs independently of folding in other domains.
- A domain is a conserved part of a given full-length protein sequence, with a defined tertiary structure that can evolve, function, and exist independently of the rest of the protein chain.
Protein Folding and Quaternary Structure
- Protein folding requires energy and is assisted by chaperone proteins, which protect and guide the proper folding of nascent polypeptide chains.
- Quaternary structure: multiple polypeptide chains (or subunits) assembled into a supramolecular complex, with a specific number of subunits designated by a prefix (e.g., dimeric, trimeric).
- May consist of identical (homopolymeric) or different (heteropolymeric) subunits.
Protein Misfolding and Function
- Protein misfolding alters normal function and interactions of proteins, as seen in sickle cell anemia, where a mutation in the β chain changes the quaternary structure of hemoglobin.
Fibrous Proteins
- Elongated, rigid proteins enriched in specific amino acids and unique secondary structures, serving structural functions in the body.
- Examples: collagen, which provides tensile strength, with a superfamily of extracellular matrix proteins.
Collagen
- Most abundant protein in the body, with a triple helix of three α-polypeptides wound around each other.
- Primary structure: polymer of (Gly-X-Y) repeats, where X is frequently proline and Y is often hydroxyproline (or hydroxylysine).
- Vitamin C is required as a cofactor for the hydroxylation of Pro and Lys.
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Description
Explore the different levels of protein structure, including primary, secondary, tertiary, and quaternary structures, and learn how they are stabilized by specific forces.
