Organic Chemistry, Biochemistry, and Metabolism - MCAT Biological and Biochemical Foundations of Living Systems
Card 1 of 2928
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
Because hemoglobin can act as a buffer in blood, it helps keep the pH constant. Which of the following portions of an amino acid can change with pH change?
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
Because hemoglobin can act as a buffer in blood, it helps keep the pH constant. Which of the following portions of an amino acid can change with pH change?
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All three portions can change with pH. The amino end can take on an extra proton to become positively charged, the carboxy end can lose a proton and take on a negative charge, and the side chain can do either depending on its structure. An amino acid with both a positively charged amino end and a negatively charged carboxy end is called a zwitterion.
All three portions can change with pH. The amino end can take on an extra proton to become positively charged, the carboxy end can lose a proton and take on a negative charge, and the side chain can do either depending on its structure. An amino acid with both a positively charged amino end and a negatively charged carboxy end is called a zwitterion.
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Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma.
Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts.
She sets up the following experiment:
As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.
After conducting the experiment described in the passage, the scientist attempts to determine the overall three dimensional shape of the protein toxin secreted by the cryptosporidium oocysts. What is the scientist investigating?
Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma.
Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts.
She sets up the following experiment:
As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.
After conducting the experiment described in the passage, the scientist attempts to determine the overall three dimensional shape of the protein toxin secreted by the cryptosporidium oocysts. What is the scientist investigating?
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The tertiary structure of a polypeptide chain is defined as the overall shape. It is determined by the primary structure, or sequence of amino acids, and the secondary structures in the polypeptide, which are usually composed of beta-sheet or alpha-helix conformations.
The tertiary structure of a polypeptide chain is defined as the overall shape. It is determined by the primary structure, or sequence of amino acids, and the secondary structures in the polypeptide, which are usually composed of beta-sheet or alpha-helix conformations.
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Which level of protein structure is stabilized primarily by hydrogen bonding?
Which level of protein structure is stabilized primarily by hydrogen bonding?
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Secondary structure is observed when the primary sequence of amino acids conforms into either alpha-helices and/or beta-pleated sheets. These conformations of the polypeptide chain are stabilized by hydrogen bonding alone.
Primary structure is determined by peptide bonds. Tertiary structure is determined by disulfide bonds and hydrophobic interactions. Quaternary structure is determined by interactions between multiple subunits.
Secondary structure is observed when the primary sequence of amino acids conforms into either alpha-helices and/or beta-pleated sheets. These conformations of the polypeptide chain are stabilized by hydrogen bonding alone.
Primary structure is determined by peptide bonds. Tertiary structure is determined by disulfide bonds and hydrophobic interactions. Quaternary structure is determined by interactions between multiple subunits.
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Collagen, the most abundant protein in the body, is an example of what type of protein?
Collagen, the most abundant protein in the body, is an example of what type of protein?
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Collagen is a structural protein that adds significant strength and resilience to the skin, tendons, and ligaments. Structural proteins, including collagen, also fall under the category of fibrous proteins. Globular proteins, in contrast, usually act as enzymes in the body or transport channels in the membrane.
Peripheral proteins are a type of globular protein found adjacent to the membrane, while integral proteins are transmembrane globular proteins.
Collagen is a structural protein that adds significant strength and resilience to the skin, tendons, and ligaments. Structural proteins, including collagen, also fall under the category of fibrous proteins. Globular proteins, in contrast, usually act as enzymes in the body or transport channels in the membrane.
Peripheral proteins are a type of globular protein found adjacent to the membrane, while integral proteins are transmembrane globular proteins.
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Amino acids are joined together to form polypeptides. Each amino acid is attached to another by a peptide bond.
What functional group is created when amino acids are joined together?
Amino acids are joined together to form polypeptides. Each amino acid is attached to another by a peptide bond.
What functional group is created when amino acids are joined together?
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Polypeptide formation involves the C-terminus of one amino acid attaching to the N-terminus of another. This polymerization results in a dipeptide with the byproduct of one water molecule. The newfound combination results in a carbonyl being attached to a nitrogen. This functional group is called an amide.
Polypeptide formation involves the C-terminus of one amino acid attaching to the N-terminus of another. This polymerization results in a dipeptide with the byproduct of one water molecule. The newfound combination results in a carbonyl being attached to a nitrogen. This functional group is called an amide.
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In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Which of the following is the LEAST important force that promotes protein folding?
In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Which of the following is the LEAST important force that promotes protein folding?
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Metallic bonding adheres to the "nuclei in a sea of electrons" model that explains the malleability, conductivity, and ductility of metals. Though some proteins (like hemoglobin) rely on a metallic compound, metallic interactions do not dictate the majority of protein folding interactions.
Proteins have a non-metal backbone, and are more dependent on dipole, hydrogen, covalent, and van der Waals forces to dictate their conformation.
Metallic bonding adheres to the "nuclei in a sea of electrons" model that explains the malleability, conductivity, and ductility of metals. Though some proteins (like hemoglobin) rely on a metallic compound, metallic interactions do not dictate the majority of protein folding interactions.
Proteins have a non-metal backbone, and are more dependent on dipole, hydrogen, covalent, and van der Waals forces to dictate their conformation.
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In the crusade to create a vaccine for Poliomyelitis, Jonas Salk and Albert Sabin created two separate vaccines that proved to be successful in preventing Polio onset.
The Salk vaccine, which is given by standard injection, contained virus particles inactivated by an organic solvent. This method has the advantage of inactivating each of the three Polio strains with no bias.
Albert Sabin's vaccine, given by oral inoculation via sugar water, contained live virus particles that had been genetically attenuated. With this method, each of the three Polio strains acquired separate mutations that made them unable to infect the human host cells. Strain 2 in particular contained one single nucleotide polymorphism in the internal ribosomal entry site (IRES) that prevented successful viral replication.
The organic solvent used to inactivate the Poliovirus in the Salk vaccine significantly alters the viral capsid. For the purposes of this question, let us assume that the capsid proteins are bound together by multiple di-sulfide bonds. Given this information, which of the solvents listed below would be most effective in disrupting the Poliovirus capsid?
In the crusade to create a vaccine for Poliomyelitis, Jonas Salk and Albert Sabin created two separate vaccines that proved to be successful in preventing Polio onset.
The Salk vaccine, which is given by standard injection, contained virus particles inactivated by an organic solvent. This method has the advantage of inactivating each of the three Polio strains with no bias.
Albert Sabin's vaccine, given by oral inoculation via sugar water, contained live virus particles that had been genetically attenuated. With this method, each of the three Polio strains acquired separate mutations that made them unable to infect the human host cells. Strain 2 in particular contained one single nucleotide polymorphism in the internal ribosomal entry site (IRES) that prevented successful viral replication.
The organic solvent used to inactivate the Poliovirus in the Salk vaccine significantly alters the viral capsid. For the purposes of this question, let us assume that the capsid proteins are bound together by multiple di-sulfide bonds. Given this information, which of the solvents listed below would be most effective in disrupting the Poliovirus capsid?
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The answer is 2-mercaptoethanol because it contains strong reducing groups that are capable of reducing the di-sulfide bonds.
Dimethyl sulfoxide (DMSO), methanol, and ethanol do not contain reducing groups capable of breaking di-sulfide bonds, if at all.
The answer is 2-mercaptoethanol because it contains strong reducing groups that are capable of reducing the di-sulfide bonds.
Dimethyl sulfoxide (DMSO), methanol, and ethanol do not contain reducing groups capable of breaking di-sulfide bonds, if at all.
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An enzyme that cleaves disulfide bridges would most disrupt a protein containing which amino acid sequence?
An enzyme that cleaves disulfide bridges would most disrupt a protein containing which amino acid sequence?
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Disulfide bridges are made between two cysteine amino acids. An enzyme that cleaves disulfide bonds would disrupt a protein containing the most cysteine residues; therefore, Tyr–Cys–Cys–Thr–Val–Leu is the correct answer.
Disulfide bridges are made between two cysteine amino acids. An enzyme that cleaves disulfide bonds would disrupt a protein containing the most cysteine residues; therefore, Tyr–Cys–Cys–Thr–Val–Leu is the correct answer.
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Proteins can have a maximum of four levels of structure: primary, secondary, tertiary, and quaternary. Although the proteins can spontaneously fold to a functional conformation, there are a variety of denaturing agents that can be used to disrupt the folding strategies of proteins. Mercaptoethanol is an example of a protein denaturing agent; its mechanism for dismantling proteins is to disrupt the disulfide bonds found in the protein. When urea is introduced to a protein, the hydrogen bonds holding the protein together are disrupted. Heat can also be considered a denaturing agent, which has the potential to disrupt all intermolecular interactions in a protein.
Which of the following levels of structure in a protein would not be disrupted by the introduction of mercaptoethanol?
Proteins can have a maximum of four levels of structure: primary, secondary, tertiary, and quaternary. Although the proteins can spontaneously fold to a functional conformation, there are a variety of denaturing agents that can be used to disrupt the folding strategies of proteins. Mercaptoethanol is an example of a protein denaturing agent; its mechanism for dismantling proteins is to disrupt the disulfide bonds found in the protein. When urea is introduced to a protein, the hydrogen bonds holding the protein together are disrupted. Heat can also be considered a denaturing agent, which has the potential to disrupt all intermolecular interactions in a protein.
Which of the following levels of structure in a protein would not be disrupted by the introduction of mercaptoethanol?
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When discussing the secondary structure of a protein, you can assume that the only forces that are relevant are the hydrogen bonds between the carbonyl oxygen of one amino acid, and the hydrogen on the amino group of another. Because hydrogen bonds are the only intermolecular interaction involved in secondary structure, mercaptoethanol would not affect the secondary structure.
Disulfide bonds are generally integral to defining the tertiary structure of a protein; thus, mercaptoethanol would affect the tertiary structure (and subsequent quaternary structure) of a protein.
When discussing the secondary structure of a protein, you can assume that the only forces that are relevant are the hydrogen bonds between the carbonyl oxygen of one amino acid, and the hydrogen on the amino group of another. Because hydrogen bonds are the only intermolecular interaction involved in secondary structure, mercaptoethanol would not affect the secondary structure.
Disulfide bonds are generally integral to defining the tertiary structure of a protein; thus, mercaptoethanol would affect the tertiary structure (and subsequent quaternary structure) of a protein.
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Proteins can have a maximum of four levels of structure: primary, secondary, tertiary, and quaternary. Although the proteins can spontaneously fold to a functional conformation, there are a variety of denaturing agents that can be used to disrupt the folding strategies of proteins. Mercaptoethanol is an example of a protein denaturing agent; its mechanism for dismantling proteins is to disrupt the disulfide bonds found in the protein. When urea is introduced to a protein, the hydrogen bonds holding the protein together are disrupted. Heat can also be considered a denaturing agent, which has the potential to disrupt all intermolecular interactions in a protein.
Which of the following levels of structure would not be affected by urea?
Proteins can have a maximum of four levels of structure: primary, secondary, tertiary, and quaternary. Although the proteins can spontaneously fold to a functional conformation, there are a variety of denaturing agents that can be used to disrupt the folding strategies of proteins. Mercaptoethanol is an example of a protein denaturing agent; its mechanism for dismantling proteins is to disrupt the disulfide bonds found in the protein. When urea is introduced to a protein, the hydrogen bonds holding the protein together are disrupted. Heat can also be considered a denaturing agent, which has the potential to disrupt all intermolecular interactions in a protein.
Which of the following levels of structure would not be affected by urea?
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Urea is used to denature proteins by interrupting hydrogen bonds. Hydrogen bonds are found in all levels beyond the primary structure, so all of the above levels will be affected by an introduction of urea.
Hydrogen bonds are particularly important to defining secondary structure, as it is these forces that create alpha-helices and beta-pleated sheets. Without proper secondary structure, tertiary and quaternary development will also be disrupted.
Urea is used to denature proteins by interrupting hydrogen bonds. Hydrogen bonds are found in all levels beyond the primary structure, so all of the above levels will be affected by an introduction of urea.
Hydrogen bonds are particularly important to defining secondary structure, as it is these forces that create alpha-helices and beta-pleated sheets. Without proper secondary structure, tertiary and quaternary development will also be disrupted.
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Which of these choices correctly pairs the level of protein structure with an example of that level of structure?
Which of these choices correctly pairs the level of protein structure with an example of that level of structure?
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There are four distinct levels of protein structure: primary, secondary, tertiary, and quaternary. Primary structure refers to the actual sequence of amino acids, like Ala-Met-Gly-Trp, which are held together by peptide bonds. Secondary structure, which includes alpha-helices and beta-pleated sheets, is the local three-dimensional shape created by hydrogen bonding. Tertiary structure is the overall shape of the protein subunit, caused by more distant interactions. Disulfide bonds (bonds between the sulfur atoms of two cysteine amino acids) are an example of tertiary structure. Finally, quaternary structure involves interactions between the peptide subunits of a larger protein complex.
There are four distinct levels of protein structure: primary, secondary, tertiary, and quaternary. Primary structure refers to the actual sequence of amino acids, like Ala-Met-Gly-Trp, which are held together by peptide bonds. Secondary structure, which includes alpha-helices and beta-pleated sheets, is the local three-dimensional shape created by hydrogen bonding. Tertiary structure is the overall shape of the protein subunit, caused by more distant interactions. Disulfide bonds (bonds between the sulfur atoms of two cysteine amino acids) are an example of tertiary structure. Finally, quaternary structure involves interactions between the peptide subunits of a larger protein complex.
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Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.
One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.
Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.
The polypeptides that make up the heavy and light chains of antibodies are most likely connected by covalent bridges involving atoms of which element?
Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.
One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.
Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.
The polypeptides that make up the heavy and light chains of antibodies are most likely connected by covalent bridges involving atoms of which element?
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Covalent bridges can be found in organic molecules, linking one region of the molecule to another. These bridges are almost invariably disulfide linkages, in which two sulfur atoms form a covalent linkage that provides a great deal of stability between peptide chains. Disulfide bridges are commonly involved in protein tertiary structure and other organic structural linkages, such as the joining of the heavy and light chains in antibodies.
Covalent bridges can be found in organic molecules, linking one region of the molecule to another. These bridges are almost invariably disulfide linkages, in which two sulfur atoms form a covalent linkage that provides a great deal of stability between peptide chains. Disulfide bridges are commonly involved in protein tertiary structure and other organic structural linkages, such as the joining of the heavy and light chains in antibodies.
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Which of the following is an example of the secondary structure of a protein?
Which of the following is an example of the secondary structure of a protein?
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By definition, the secondary structure of a protein is the hydrogen bonding between the amine and carbonyl groups in the amino acid chain. This usually occurs in the form of alpha-helices or beta-pleated sheets.
The linear sequence of the amino acids formed by peptide bonds is the primary protein structure. Interactions of R groups determines the tertiary structure. These interactions can be in the form of disulfide bonds, hydrogen bonding, or hydrophobic interactions.
By definition, the secondary structure of a protein is the hydrogen bonding between the amine and carbonyl groups in the amino acid chain. This usually occurs in the form of alpha-helices or beta-pleated sheets.
The linear sequence of the amino acids formed by peptide bonds is the primary protein structure. Interactions of R groups determines the tertiary structure. These interactions can be in the form of disulfide bonds, hydrogen bonding, or hydrophobic interactions.
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Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.
One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.
Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.
Antibodies are made of proteins, which form one of the broad classes of biological macromolecules. A glycoprotein is different from other kinds of proteins principally because .
Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.
One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.
Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.
Antibodies are made of proteins, which form one of the broad classes of biological macromolecules. A glycoprotein is different from other kinds of proteins principally because .
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The prefix "glyco-" indicates that some substrate has had a carbohydrate moiety added to its structure. Glycolipids are thus lipids bound to saccharide units, and glycoproteins are proteins bound to saccharide units.
The prefix "glyco-" indicates that some substrate has had a carbohydrate moiety added to its structure. Glycolipids are thus lipids bound to saccharide units, and glycoproteins are proteins bound to saccharide units.
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Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).
RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.
One of the main roles of RAN is to bind to nuclear import and export receptors and carry them into or out of the nucleus. Given that import and export receptors are proteins, what can we say about the cooperativity displayed by RAN when it comes to binding to import and export proteins?
Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).
RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.
One of the main roles of RAN is to bind to nuclear import and export receptors and carry them into or out of the nucleus. Given that import and export receptors are proteins, what can we say about the cooperativity displayed by RAN when it comes to binding to import and export proteins?
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Binding cooperativity occurs when binding of one substrate increases or decreases the affinity for the other substrates. For cooperativity to work, the protein in question must have multiple subunits, therefore being at least a dimer. RAN is a monomer, and therefore cannot show any cooperativity.
Binding cooperativity occurs when binding of one substrate increases or decreases the affinity for the other substrates. For cooperativity to work, the protein in question must have multiple subunits, therefore being at least a dimer. RAN is a monomer, and therefore cannot show any cooperativity.
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Which of the following is NOT a class of enzyme?
Which of the following is NOT a class of enzyme?
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The correct answer is pyrimidine complex. A pyrimidine refers to a type of nucleotide base. Enzymes commonly have the suffix -ase at the end of their name.
The correct answer is pyrimidine complex. A pyrimidine refers to a type of nucleotide base. Enzymes commonly have the suffix -ase at the end of their name.
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Which of the following functional groups would most likely act as an acid?
Which of the following functional groups would most likely act as an acid?
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Carboxyl groups, or carboxylic acids, are good acids due to the resonance between the two oxygen atoms, allowing for greater stability of the conjugate base upon removal of a proton. Acetals and aldehydes can act as weak acids, but carboxyl groups will be deprotonated first.
Carboxyl groups, or carboxylic acids, are good acids due to the resonance between the two oxygen atoms, allowing for greater stability of the conjugate base upon removal of a proton. Acetals and aldehydes can act as weak acids, but carboxyl groups will be deprotonated first.
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A molecule has three chiral centers. How many stereoisomers of this compound will have different boiling points compared to the original molecule?
A molecule has three chiral centers. How many stereoisomers of this compound will have different boiling points compared to the original molecule?
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The first step is to determine how many stereoisomers there are for this molecule. Since the number of stereoisomers is dependent on the number of chiral carbons, we can solve according to the equation 
, where 
is the number of chiral centers. Since there are three chiral centers, we determine that there are eight stereoisomers for this molecule. Keep in mind that this number includes the original molecule.
Next, we need to compare the different stereoisomers to the original molecule. The original molecule will have one enantiomer and six diastereomers. Remember that enantiomers have the same physical properties, so we will not include this isomer in the final answer. Diastereomers, on the other hand, have different physical properties compared to the original molecule. As a result, six stereoisomers will have different boiling points compared to the original molecule.
The first step is to determine how many stereoisomers there are for this molecule. Since the number of stereoisomers is dependent on the number of chiral carbons, we can solve according to the equation
Next, we need to compare the different stereoisomers to the original molecule. The original molecule will have one enantiomer and six diastereomers. Remember that enantiomers have the same physical properties, so we will not include this isomer in the final answer. Diastereomers, on the other hand, have different physical properties compared to the original molecule. As a result, six stereoisomers will have different boiling points compared to the original molecule.
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Which of the following steps of free radical chlorination does not produce a free radical as a product?
Which of the following steps of free radical chlorination does not produce a free radical as a product?
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The three steps of a free radical chlorination reaction are, in order, initiation, propagation, and termination.
Free radicals are produced in the initiation and propagation steps. The termination steps combine any two free radicals formed in the reaction to produce a compound that has no unpaired electrons (free radicals).
The three steps of a free radical chlorination reaction are, in order, initiation, propagation, and termination.
Free radicals are produced in the initiation and propagation steps. The termination steps combine any two free radicals formed in the reaction to produce a compound that has no unpaired electrons (free radicals).
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Which of the following amino acids is basic?
Which of the following amino acids is basic?
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On the MCAT you must be able to recognize the following as basic amino acids: lysine, arginine, and histidine. Important acidic amino acids include aspartic acid (aspartate) and glutamic acid (glutamate). Important nonpolar amino acids include: methionine, alanine, isoleucine, proline, phenylalanine, tryptophan, valine, and leucine.
On the MCAT you must be able to recognize the following as basic amino acids: lysine, arginine, and histidine. Important acidic amino acids include aspartic acid (aspartate) and glutamic acid (glutamate). Important nonpolar amino acids include: methionine, alanine, isoleucine, proline, phenylalanine, tryptophan, valine, and leucine.
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