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Questions and Answers
What determines the tertiary structure of a polypeptide chain?
What determines the tertiary structure of a polypeptide chain?
Why do glutamate, aspartate, histidine, lysine, or arginine disrupt the helix?
Why do glutamate, aspartate, histidine, lysine, or arginine disrupt the helix?
What is a characteristic of globular proteins in aqueous solutions?
What is a characteristic of globular proteins in aqueous solutions?
What is the fundamental functional and three-dimensional structural unit of a polypeptide?
What is the fundamental functional and three-dimensional structural unit of a polypeptide?
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What type of amino acids can interfere with the formation of the alpha helix?
What type of amino acids can interfere with the formation of the alpha helix?
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What is true about the length of polypeptide chains and their domains?
What is true about the length of polypeptide chains and their domains?
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What is the location of hydrophobic side chains in globular proteins?
What is the location of hydrophobic side chains in globular proteins?
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What is the characteristic structure of the beta conformation?
What is the characteristic structure of the beta conformation?
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How are beta sheets often visualized in illustrations of protein structure?
How are beta sheets often visualized in illustrations of protein structure?
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Why do hydrophilic groups in the interior of globular proteins form hydrogen bonds or electrostatic interactions?
Why do hydrophilic groups in the interior of globular proteins form hydrogen bonds or electrostatic interactions?
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What is the core of a protein domain built from?
What is the core of a protein domain built from?
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What is true about the folding of a peptide chain within a domain?
What is true about the folding of a peptide chain within a domain?
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What role do α-helix and β-sheet structures play in globular proteins?
What role do α-helix and β-sheet structures play in globular proteins?
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What is a key difference between alpha helices and beta sheets?
What is a key difference between alpha helices and beta sheets?
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What determines the unique three-dimensional structure of each polypeptide?
What determines the unique three-dimensional structure of each polypeptide?
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What is the result of maximal hydrogen bonding in globular proteins?
What is the result of maximal hydrogen bonding in globular proteins?
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In what ways can beta strands be arranged in a beta sheet?
In what ways can beta strands be arranged in a beta sheet?
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What are beta turns/loops typically found in?
What are beta turns/loops typically found in?
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What types of interactions cooperate in stabilizing the tertiary structures of globular proteins?
What types of interactions cooperate in stabilizing the tertiary structures of globular proteins?
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What is the function of beta turns/loops in proteins?
What is the function of beta turns/loops in proteins?
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What is the main characteristic of fibrous proteins?
What is the main characteristic of fibrous proteins?
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Which type of fibrous protein is characterized by being soft and flexible?
Which type of fibrous protein is characterized by being soft and flexible?
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What is the principal component of hair, nails, and wool?
What is the principal component of hair, nails, and wool?
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What is the structure of the α-keratin chain?
What is the structure of the α-keratin chain?
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What is the repeating pattern in each α-keratin chain?
What is the repeating pattern in each α-keratin chain?
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What is the characteristic of collagen molecules?
What is the characteristic of collagen molecules?
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What is the amino acid composition of collagen?
What is the amino acid composition of collagen?
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What is a consequence of abnormal collagen synthesis or structure?
What is a consequence of abnormal collagen synthesis or structure?
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What is the consequence of the accumulation of spontaneously aggregating proteins in neurodegenerative disorders?
What is the consequence of the accumulation of spontaneously aggregating proteins in neurodegenerative disorders?
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What is the role of the prion protein (PrP) in transmissible spongiform encephalopathies (TSEs)?
What is the role of the prion protein (PrP) in transmissible spongiform encephalopathies (TSEs)?
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What is the consequence of misfolding of transthyretin protein?
What is the consequence of misfolding of transthyretin protein?
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What is the function of transthyretin protein?
What is the function of transthyretin protein?
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What is the consequence of mutation in the gene coding for transthyretin?
What is the consequence of mutation in the gene coding for transthyretin?
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What percentage of African Americans are carriers of the Val42Ile variant?
What percentage of African Americans are carriers of the Val42Ile variant?
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What is the prevalence of Transthyretin Amyloidosis cardiomyopathy (ATTR-CM) in patients with heart failure?
What is the prevalence of Transthyretin Amyloidosis cardiomyopathy (ATTR-CM) in patients with heart failure?
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What is the characteristic of wild-type ATTR?
What is the characteristic of wild-type ATTR?
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Study Notes
Protein Structure
- The helix structure of a protein can be disrupted by certain amino acids, such as glutamate, aspartate, histidine, lysine, or arginine, which are charged and can form ionic bonds or repel each other electrostatically.
- Tryptophan, with its bulky side chains, or valine or isoleucine, which branch at the β-carbon, can also interfere with the formation of an α-helix if they are present in large numbers.
β-Sheet
- In the β conformation, the backbone of the polypeptide chain is extended into a zigzag rather than a helical structure.
- The zigzag polypeptide chains can be arranged side by side to form a structure resembling a series of pleats.
- Hydrogen bonds are formed between adjacent segments of the polypeptide chain.
- β-strands are often visualized as broad arrows in illustrations of protein structure.
- β-sheets are composed of two or more peptide chains (β-strands), or segments of polypeptide chains, which are almost fully extended.
- In β-sheets, the hydrogen bonds are perpendicular to the polypeptide backbone.
β-Bend/Turns
- β-bends/turns are normally present in globular proteins.
- Nearly 2/3 of the proteins in turns or loops are connecting elements that link successive runs of α-helix or β-conformation.
- β-turns connect the ends of two adjacent segments of an antiparallel β-sheet.
Fibrous Proteins
- Fibrous proteins are highly elongated protein molecules whose shapes are dominated by a single type of secondary structure.
- Examples of fibrous proteins include:
- Coiled coil: Keratin (durable, insoluble, unreactive)
- β sheet: Silk, fibroin of spider web (soft, flexible)
- Triple helix: Collagen (strong, high tensile strength)
Keratin
- Keratin is the principal component of hair, nails, wool, horns, hooves, scales, feathers, and shells.
- α-keratin is found in mammals, while β-keratin is found in birds and reptiles.
- The α-keratin chain is an α-helix, and pairs of α-keratin chains are inter-wound to form a two-chain coiled coil.
- Each α-keratin chain consists of ~310 residues having a 7-residue repeat, with residues a and d being nonpolar.
Collagen
- Collagen is a triple helix protein that contains three polypeptide chains.
- Each chain is a left-handed helix (3 residues/turn), and the three helical chains are twisted together in a right-handed manner to form a superhelical structure.
- Collagen has a distinctive amino acid composition, with 30% glycine and 15-30% proline or hydroxyproline.
Collagen Disorders
- Abnormal collagen synthesis or structure can cause diseases such as:
- Cardiovascular disorders (aortic and arterial aneurysms and heart valve malfunction)
- Bone disorders (fragility and easy fracturing)
- Skin disorders (poor healing and unusual distensibility)
- Joint disorders (hypermobility and arthritis)
- Eye disorders (dislocation of the lens)
- Examples of collagen disorders include:
- Scurvy (vitamin C deficiency)
Tertiary Structure of Globular Proteins
- The primary structure of a polypeptide chain determines its tertiary structure.
- Globular proteins have a compact, high-density structure with a high degree of close packing.
- Hydrophobic side chains are buried in the interior, while hydrophilic groups are generally found on the surface of the molecule.
- Hydrophilic groups in the interior of the polypeptide are involved in hydrogen bonds or electrostatic interactions.
Protein Domains
- Protein domains are the fundamental functional and three-dimensional structural units of a polypeptide.
- Domains are modular units that are built from combinations of super-secondary structural elements (motifs).
- Folding of the peptide chain within a domain usually occurs independently of folding in other domains.
- Each domain has the characteristics of a small, compact globular protein that is structurally independent of the other domains in the polypeptide chain.
Interactions Stabilizing Tertiary Structure
- The unique three-dimensional structure of each polypeptide is determined by its amino acid sequence.
- Interactions between the amino acid side chains guide the folding of the polypeptide to form a compact structure.
- Different types of interactions cooperate in stabilizing the tertiary structures of globular proteins, including:
- Covalent disulfide bonds
- Hydrophobic interactions
- Hydrogen bonds
- Ionic interactions
Protein Misfolding
- Deposits of misfolded proteins are associated with a number of diseases, including amyloidoses.
- The prion protein (PrP) has been implicated as the causative agent of transmissible spongiform encephalopathies (TSEs), including Creutzfeldt-Jakob disease in humans, scrapie in sheep, and bovine spongiform encephalopathy in cattle.
Transthyretin Amyloidosis (ATTR)
- ATTR occurs as a result of misfolding of the transthyretin protein produced by the liver.
- The misfolded protein produces amyloid fibrils that can deposit in various tissues, causing irreversible damage.
- Mutation in the gene coding for TTR can cause structural changes leading to misfolding (hATTR); normal aging process can render ATTR tetramer prone to misfolding (wATTR).
- ATTR cardiomyopathy (ATTR-CM) is a systemic amyloidosis caused by the accumulation of transthyretin fibrils in the myocardium.
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Description
This quiz covers the effects of different amino acids on protein structure, including those that disrupt the alpha-helix and those that interfere with beta-sheet formation.