Ch4 Biochem Bashar Khatib
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Questions and Answers
- 1.
The disulfide bonds -S-S can be formed in primary structure of proteins by :
- A.
IsoleucineÂ
- B.
Glutamic acid
- C.
Valine
- D.
CysteinsÂ
Correct Answer
D. CysteinsÂExplanation
Cysteins can form disulfide bonds in the primary structure of proteins. Disulfide bonds are covalent bonds formed between two cysteine residues, where the sulfur atoms from each cysteine are oxidized and joined together. These bonds play a crucial role in stabilizing the protein's structure and can contribute to its overall function. Isoleucine, glutamic acid, and valine do not have the necessary sulfur atoms to form disulfide bonds.Rate this question:
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- 2.
One of the following is incorrect about Collagen :
- A.
Collagen is considered a fibrous protein
- B.
30% of the amino acids in the collagen are Pro and Hyp
- C.
Every second position in the sequence of amino acids in collagen fiber must be Gly
- D.
Each polypeptide chain in collagen fiber is a helix
Correct Answer
C. Every second position in the sequence of amino acids in collagen fiber must be GlyExplanation
Collagen is a fibrous protein that is found in connective tissues such as tendons, ligaments, and skin. It provides strength and structure to these tissues. One of the unique characteristics of collagen is that every third position in the sequence of amino acids must be glycine (Gly), not every second position as stated in the incorrect option. This glycine repetition allows collagen fibers to form a tightly packed, triple-helix structure, which gives collagen its strength and stability. Additionally, about 30% of the amino acids in collagen are proline (Pro) and hydroxyproline (Hyp), which contribute to its unique structure.Rate this question:
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- 3.
Protein folding required that peptide backbone structures be able to change its direction and conformation :
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
Protein folding is a complex process that involves the rearrangement of peptide backbone structures. These structures consist of a chain of amino acids connected by peptide bonds. In order for a protein to fold into its functional three-dimensional shape, the peptide backbone must be able to change its direction and conformation. This flexibility allows the protein to adopt different secondary structures such as alpha helices and beta sheets, which are essential for its proper functioning. Therefore, the statement that protein folding requires the ability of peptide backbone structures to change direction and conformation is true.Rate this question:
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- 4.
A repetitive of super secondary structures and give information about folding :
- A.
Domain
- B.
Modules
- C.
Reverse turn
- D.
Electrostatic interaction
Correct Answer
B. ModulesExplanation
Modules are repetitive super secondary structures that provide information about folding. They are distinct units within a protein that can fold independently and often have specific functions. These modules can be repeated multiple times within a protein, contributing to its overall structure and function. The presence and arrangement of modules can influence the folding process of a protein, as well as its stability and interactions with other molecules. Therefore, modules play a crucial role in understanding the folding of proteins.Rate this question:
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- 5.
In disturbing of alpha-helix, the proximity of several side chains of like charge lead to :
- A.
Strong electrostatic repulsion
- B.
Crowding
- C.
Presence of proline amino acid
- D.
Steric repulsion
Correct Answer
A. Strong electrostatic repulsionExplanation
The correct answer is strong electrostatic repulsion. In the alpha-helix structure, the proximity of several side chains with like charges creates a repulsive force between them. This repulsion can disrupt the stability of the alpha-helix and cause it to unfold or distort. Strong electrostatic repulsion refers to the strong repulsive forces between charged particles, in this case, the side chains with like charges.Rate this question:
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- 6.
Non-covalent bonds that occur between the non-polar side residues in the interior of proteins :
- A.
Hydrophobic bonds
- B.
Metal ion interactionsÂ
- C.
H-bonds
- D.
Electrostatic bonds
Correct Answer
A. HydropHobic bondsExplanation
Hydrophobic bonds occur between non-polar side residues in the interior of proteins. These bonds are formed due to the hydrophobic effect, where non-polar molecules or groups tend to cluster together in order to minimize their contact with water. In proteins, hydrophobic residues are typically found in the interior, away from the aqueous environment. The hydrophobic bonds help stabilize the protein structure by bringing these non-polar residues closer together, reducing their exposure to water and increasing the overall stability of the protein.Rate this question:
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- 7.
The 4-pyrole rings of the Protoporphyrin in heme group connected to each other by :
- A.
Imidazole
- B.
Methine bridges
- C.
Ferrous iron
- D.
His F8
Correct Answer
B. Methine bridgesExplanation
The correct answer is "Methine bridges." Methine bridges are the connections between the 4-pyrole rings of the Protoporphyrin in the heme group. These bridges help to stabilize the structure of the heme group and are important for its function in binding oxygen and other molecules.Rate this question:
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- 8.
Which way of proteins denaturing ways mainly reduces electrostatic interactions :
- A.
B-mercaptoethanol
- B.
Detergents by SDS
- C.
High or low PH
- D.
Urea or guanidine
Correct Answer
C. High or low pHExplanation
High or low pH can denature proteins by disrupting electrostatic interactions. At extreme pH values, the charged amino acid residues in proteins can become protonated or deprotonated, leading to a change in the net charge of the protein. This change in charge disrupts the electrostatic interactions between amino acid residues, causing the protein to unfold and denature. Therefore, high or low pH can effectively reduce electrostatic interactions in proteins.Rate this question:
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- 9.
When one oxygen molecule is binding of myoglobin, it becomes easier for next oxygen to bind , binding first oxygen facilities second and so on ..
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
This statement is false because myoglobin is a single oxygen-binding protein and does not exhibit cooperative binding like hemoglobin. Each myoglobin molecule can only bind to one oxygen molecule at a time and does not facilitate the binding of additional oxygen molecules.Rate this question:
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- 10.
Which of the following is correct :
- A.
Hb F has no affinity to O2.
- B.
There is a His amino acid in position 143 in gamma chain in Hb F.
- C.
BPG can bind to Hb F.
- D.
There is a substitution between His and Ser amino acid in gamma chain in Hb F.
Correct Answer
D. There is a substitution between His and Ser amino acid in gamma chain in Hb F.Explanation
Hemoglobin F (Hb F) is the fetal hemoglobin found in developing fetuses and newborns. The correct statement is that there is a substitution between histidine (His) and serine (Ser) amino acids in the gamma chain of Hb F. This substitution occurs at position 143 in the gamma chain. The structure of hemoglobin F differs from adult hemoglobin (Hb A), and this substitution is one of the structural differences contributing to its higher oxygen affinity compared to Hb A. The higher oxygen affinity of Hb F is crucial for efficient oxygen transport from the mother to the developing fetus during pregnancy.Rate this question:
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- 11.
The _______ is the single shape a protein adopts under physiological conditions.
- A.
 minimal configuration
- B.
Native conformation
- C.
Primary structure
- D.
Most stable enantiomer
Correct Answer
B. Native conformationExplanation
The native conformation refers to the specific shape or structure that a protein adopts under normal physiological conditions. This conformation is crucial for the protein's proper functioning and stability. It is determined by the protein's primary structure (sequence of amino acids) and is considered the most stable and functional form of the protein. The minimal configuration and most stable enantiomer are not directly related to the protein's shape, while the primary structure only provides the foundation for the protein's folding into its native conformation.Rate this question:
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- 12.
Which statement is false about a globular proteins that performs its biological function as a single independent polypeptide chain?
- A.
Its tertiary structure is likely stabilized by the interactions of amino acid side chains in non-neighboring regions of the polypeptide chain
- B.
It could contain α-helices that are stabilized my hydrogen bonding.
- C.
It likely has extensive quaternary structure to maintain its globular shape.
- D.
Non-covalent forces are the primary source of stability for the secondary and tertiary structure.
Correct Answer
C. It likely has extensive quaternary structure to maintain its globular shape.Explanation
Globular proteins that perform their biological function as a single independent polypeptide chain do not typically have extensive quaternary structure. Quaternary structure refers to the arrangement of multiple protein subunits to form a functional protein complex. In this case, since the protein functions as a single polypeptide chain, it does not require multiple subunits to maintain its globular shape. Instead, its tertiary structure is likely stabilized by the interactions of amino acid side chains in non-neighboring regions of the polypeptide chain. Additionally, it could contain alpha-helices that are stabilized by hydrogen bonding, and non-covalent forces are the primary source of stability for the secondary and tertiary structure.Rate this question:
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- 13.
What does it mean to say a protein is oligomeric?
- A.
In vivo it establishes an equilibrium between two or more active conformations
- B.
It has more than fifty amino acids.
- C.
The active protein involves the association of two or more polypeptide chains
- D.
The proteins has multiple α-helices.
Correct Answer
C. The active protein involves the association of two or more polypeptide chainsExplanation
A protein is considered oligomeric when it involves the association of two or more polypeptide chains. This means that the protein is made up of multiple subunits, each consisting of one or more polypeptide chains. These subunits come together to form a functional protein complex. The oligomeric nature of the protein allows for increased stability, regulation, and diversity of function.Rate this question:
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- 14.
Conditions in the tissues which enhance the delivery of oxygen by hemoglobin are the presence of
- A.
Carbon dioxide.
- B.
2,3 BPG
- C.
Protons.
- D.
All of the above.
- E.
A and B above
Correct Answer
D. All of the above.Explanation
The presence of carbon dioxide, 2,3 BPG, and protons in the tissues enhances the delivery of oxygen by hemoglobin. Carbon dioxide helps to lower the pH of the blood, which promotes the release of oxygen from hemoglobin. 2,3 BPG binds to hemoglobin and reduces its affinity for oxygen, allowing for easier oxygen release. Protons also lower the pH and promote oxygen release. Therefore, all of these conditions work together to enhance the delivery of oxygen by hemoglobin.Rate this question:
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- 15.
A hyperbolic binding curve differs from a sigmoidal binding curve in that the hyperbolic curve
- A.
Has a single equilibrium constant for oxygen binding
- B.
binds more oxygen after the initial proteins first bind oxygen
- C.
Shows cooperativity.
- D.
Binds up to four molecules of oxygen
- E.
All of the above
Correct Answer
A. Has a single equilibrium constant for oxygen bindingExplanation
A hyperbolic binding curve differs from a sigmoidal binding curve in that the hyperbolic curve has a single equilibrium constant for oxygen binding. This means that the binding of oxygen to the protein follows a simple and direct relationship, where the binding affinity does not change as more oxygen molecules bind. In contrast, a sigmoidal binding curve indicates cooperativity, where the binding affinity increases as more oxygen molecules bind to the protein. The fact that the hyperbolic curve does not show cooperativity and binds up to four molecules of oxygen further supports the explanation that it has a single equilibrium constant for oxygen binding.Rate this question:
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