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Questions and Answers
What is the primary factor that stabilizes the unique shape of a protein chain?
What is the primary factor that stabilizes the unique shape of a protein chain?
Which of the following peptides is known for its role as an antioxidant?
Which of the following peptides is known for its role as an antioxidant?
The classification of amino acids based on polarity of side chains includes which of the following?
The classification of amino acids based on polarity of side chains includes which of the following?
Which amino acids are classified based on their nutritional value?
Which amino acids are classified based on their nutritional value?
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What structural feature is essential for a protein to function efficiently?
What structural feature is essential for a protein to function efficiently?
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Which hormone is linked to the contraction of smooth muscles in the uterus?
Which hormone is linked to the contraction of smooth muscles in the uterus?
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Which amino acids are commonly classified based on their structure?
Which amino acids are commonly classified based on their structure?
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What is the composition of hemoglobin?
What is the composition of hemoglobin?
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What is a common chemical modification that affects protein localization?
What is a common chemical modification that affects protein localization?
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Which amino acid residues undergo phosphorylation?
Which amino acid residues undergo phosphorylation?
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What occurs to nonacetylated proteins within cells?
What occurs to nonacetylated proteins within cells?
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What type of protein structure does collagen represent?
What type of protein structure does collagen represent?
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What primarily determines the rigidity of fibrous proteins like keratins?
What primarily determines the rigidity of fibrous proteins like keratins?
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Which amino acid is known to introduce a 'kink' in the α-helix structure?
Which amino acid is known to introduce a 'kink' in the α-helix structure?
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What defines the primary structure of a protein?
What defines the primary structure of a protein?
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What type of bonding stabilizes the β-pleated sheet structure in proteins?
What type of bonding stabilizes the β-pleated sheet structure in proteins?
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In terms of alignment, which type of β-strands have all N-terminal ends aligned together?
In terms of alignment, which type of β-strands have all N-terminal ends aligned together?
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Which bond is primarily responsible for stabilizing the secondary structure of proteins?
Which bond is primarily responsible for stabilizing the secondary structure of proteins?
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Which amino acid can disrupt the α-helix structure due to its bulky side chain?
Which amino acid can disrupt the α-helix structure due to its bulky side chain?
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What would likely happen if the primary structure of a protein is altered?
What would likely happen if the primary structure of a protein is altered?
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Which type of secondary structure is characterized by a rod-like shape with side chains extending outward?
Which type of secondary structure is characterized by a rod-like shape with side chains extending outward?
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Which type of hydrogen bonds can be formed in the same polypeptide chain?
Which type of hydrogen bonds can be formed in the same polypeptide chain?
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What component is primarily absent in fibrous proteins compared to globular proteins?
What component is primarily absent in fibrous proteins compared to globular proteins?
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What is a significant consequence of a mutation affecting the primary structure of a protein?
What is a significant consequence of a mutation affecting the primary structure of a protein?
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In globular proteins, how do β-sheets usually appear when viewed along the polypeptide backbone?
In globular proteins, how do β-sheets usually appear when viewed along the polypeptide backbone?
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What is the role of hydrogen bonds in the α-helix structure?
What is the role of hydrogen bonds in the α-helix structure?
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Which structural level of protein complexity involves folding and coiling of the polypeptide chain?
Which structural level of protein complexity involves folding and coiling of the polypeptide chain?
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What is a common characteristic of charged amino acids in relation to α-helix formation?
What is a common characteristic of charged amino acids in relation to α-helix formation?
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Which of the following sequences correctly describes the components involved in forming β-pleated sheets?
Which of the following sequences correctly describes the components involved in forming β-pleated sheets?
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Which statement regarding molecular weight (MW) of proteins is true?
Which statement regarding molecular weight (MW) of proteins is true?
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What type of secondary structure involves regions arranged in folds that resemble an accordion?
What type of secondary structure involves regions arranged in folds that resemble an accordion?
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What type of proteins are characterized by a roughly spherical shape and consist of coils with no regular structure?
What type of proteins are characterized by a roughly spherical shape and consist of coils with no regular structure?
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Which of the following contributes to the stability of a protein's 3D shape?
Which of the following contributes to the stability of a protein's 3D shape?
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What type of protein structure refers to the arrangement and interaction of multiple polypeptide chains?
What type of protein structure refers to the arrangement and interaction of multiple polypeptide chains?
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In the context of protein folding, what is a domain?
In the context of protein folding, what is a domain?
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Which of the following is NOT a type of bond stabilizing the quaternary structure of proteins?
Which of the following is NOT a type of bond stabilizing the quaternary structure of proteins?
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Which characteristic is typical of fibrous proteins?
Which characteristic is typical of fibrous proteins?
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What interaction is important for bringing cysteine residues into proximity in protein structure?
What interaction is important for bringing cysteine residues into proximity in protein structure?
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How do changes in polypeptide chain folding impact domains?
How do changes in polypeptide chain folding impact domains?
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What can increase the likelihood of a protein becoming denatured in an extracellular environment?
What can increase the likelihood of a protein becoming denatured in an extracellular environment?
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In a heterodimer, what is true about the subunits?
In a heterodimer, what is true about the subunits?
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Study Notes
Lecture 3: Proteins
- The lecture was presented by Randa A. Zaghloul, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt.
- The course is Biochemistry-1.
Recap
- The lecture covered the following topics: What is Biochemistry 1 about, carbohydrates, proteins, and amino acids.
Learning Objectives
- The objectives were to learn about the level of folding of proteins and post-translational modification.
Classification of Amino Acids
- Nutritional value: Glycine, Alanine
- Biological value: Valine, leucine, isoleucine, threonine, serine, cysteine, methionine, proline
- Polarity of side chains: Phenylalanine, tyrosine, tryptophan, arginine, lysine, histidine, glutamate, aspartate, glutamine, asparagine
Biologically Active Oligopeptides:
- Glutathione : A tripeptide (γ-Glutamyl-cysteinyl glycine), functions as an antioxidant.
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Oxytocin and Vasopressin: Nona peptides secreted by the posterior lobe of the pituitary gland.
- Oxytocin: Uterine contraction, induction of labor.
- Vasopressin (ADH): Peripheral blood vessel constriction, increases blood pressure.
Levels of Protein Structure
- Figure 2: Illustrates the primary, secondary, tertiary, and quaternary levels of protein structure visually.
Hierarchical Structure of Proteins
- Protein chains fold into unique shapes stabilized by non-covalent interactions.
- The 3D shape is crucial for function.
- Protein structure is complex, involving four organizational levels.
Primary Structure
- Definition: The sequence of amino acids in a protein.
- Importance: Many genetic diseases are caused by abnormal amino acid sequences, affecting protein folding and function.
- Bonds: Amino acids are joined covalently by peptide bonds.
- Molecular Weight: Protein size is reported as mass in daltons or molecular weight (MW).
Secondary Structure
- Definition: Regularly repeating structures.
- Importance: Without secondary structure, proteins would form long, spaghetti-like molecules. Secondary coils and folds are formed due to H-bonds between backbone constituents.
- Bonds: H- bonds.
- Types: α-helix, β-pleated sheet, β-turns.
Protein Structure
- α-helix: Rod-like structure; side chains extend outward from the central axis; hydrogen bonds stabilize the helical structure.
- β-pleated sheets: Polypeptide chains line up side-by-side to from sheets; stabilized by hydrogen bonds; found in globular proteins and often form a core.
Tertiary Structure
- Definition: The overall 3D shape of the entire protein molecule.
- Importance: Formation and arrangement of domains within the protein.
- Bonds: Interactions between R groups, rather than backbone constituents.
Hydrophobic interactions, covalent cross-linkages:
- Non-polar side chains fold to protein interior; polar/charged side chains tend to be on the surface of the molecule.
- Disulphide bonds are covalent bonds between the (-SH) of two cysteine residues; formation of cystine; may be separated by many amino acids in the primary structure; may be on different polypeptide chains.
Types of proteins
- Globular proteins: Roughly spherical shape, varying coils with no regular structure.
- Fibrous proteins: Straight chain, with a regular structure. In tissues like hair and skin.
Domain
- Functional and 3D structural units.
- Polypeptide chains > 200 amino acids consist of two or more domains.
Quaternary Structure
- Formed from multiple polypeptide chains (subunits).
- Subunits can be the same or different.
- Interactions between subunits form larger aggregates.
- Stabilized by H-bonds, disulfide bridges, and salt bridges.
- Examples: Collagen (three coiled polypeptides) and Hemoglobin (four polypeptides: two alpha and two beta).
Post-translational Modifications
- Modifications occur after protein synthesis on ribosomes; altering function, lifespan, and location.
- Examples:
- Acetylation: Adding an acetyl group to the N-terminal residue (common and influences lifespan of the protein by degradation).
- Long lipid-like groups added to proteins, anchor to the lipid bilayer.
- Phosphorylation of serine, threonine, tyrosine, and histidine residues, regulating protein activity through reversible phosphorylation/dephosphorylation.
- Glycosylation (attachment of carbohydrates) to asparagine, serine, and threonine residues; facilitating protein folding, stabilizing structure, and facilitating cell-to-cell adhesion.
- Hydroxylation of proline and lysine residues in collagen (for triple helix formation and stabilization)
- Methylation of histidine residues in membrane receptors.
- Y-carboxylation of glutamate in prothrombin (essential blood-clotting factor)
Ubiquitin Marks Cytosolic Proteins for Degradation in Proteasomes
- Intracellular protein lifespan varies.
- Proteins are marked for degradation through modifications of lysine side chains by adding ubiquitin.
- This process leads to protein breakdown by a specialized proteolytic machine. Subsequent ubiquitin molecules are added, forming a polyubiquitin chain.
- Proteasome recognizes the chains and degrades the protein.
- The process involves ATP.
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Description
Test your knowledge on the structural features of proteins and the classification of amino acids with this engaging quiz. Explore topics such as protein shape stabilization, nutritional values of amino acids, and the functions of various protein types. Perfect for students of biochemistry and molecular biology!
