Proteins - GRE Subject Test: Biology
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How do enzymes speed up reactions?
How do enzymes speed up reactions?
Enzymes speed up reactions by lowering the energy required to begin the reaction (the activation energy). They do not have any direct effect on the change in free energy, nor do they provide extra energy to the system. Enzymes also cannot alter the substrate concentration. Catalytic action will never be able to influence the equilibrium constant or equilibrium concentrations of a reaction.
Enzymes speed up reactions by lowering the energy required to begin the reaction (the activation energy). They do not have any direct effect on the change in free energy, nor do they provide extra energy to the system. Enzymes also cannot alter the substrate concentration. Catalytic action will never be able to influence the equilibrium constant or equilibrium concentrations of a reaction.
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Which of the following is not typical of an enzyme?
Which of the following is not typical of an enzyme?
Enzymes are used to increase the rate of a reaction. This is accomplished by lowering the activation energy required for substrates to react, often by altering the transition state. Enzymes do not, however, increase the amount of products formed; they simply help the equilibrium be reached more quickly. In other words, enzymes change the rate of a reaction, but not the equilibrium.
Enzymes are used to increase the rate of a reaction. This is accomplished by lowering the activation energy required for substrates to react, often by altering the transition state. Enzymes do not, however, increase the amount of products formed; they simply help the equilibrium be reached more quickly. In other words, enzymes change the rate of a reaction, but not the equilibrium.
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Which of the following will not result from enzymatic activity in a cell?
Which of the following will not result from enzymatic activity in a cell?
Although it may seem counterintuitive, both the forward and reverse reaction rates are sped up by an enzyme. Without this happening, more product would be created by the enzyme than normal, and enzymes DO NOT increase the amount of products created in a system. Enzymes also do not affect the enthalpy of a reaction, so making a reaction more exothermic is not an acceptable answer.
Although it may seem counterintuitive, both the forward and reverse reaction rates are sped up by an enzyme. Without this happening, more product would be created by the enzyme than normal, and enzymes DO NOT increase the amount of products created in a system. Enzymes also do not affect the enthalpy of a reaction, so making a reaction more exothermic is not an acceptable answer.
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What is the group of proteins needed for cell synthesis in bacteria called?
What is the group of proteins needed for cell synthesis in bacteria called?
The replisome is coded for by essential genes passed between bacteria. Without these proteins, a bacterial cell cannot form more cells. "-some" stands for a collection of proteins that function together, and "repli-" for replication. The TATA box is a DNA sequence involved in the indication of the start of a gene, chromosomes are collected strands of genetic material, the spliceosome removes introns from pre-mRNA, but this, along with all post translational modification, only occurs in eukaryotes. The cytosome is the part of the cell that is specialized for phagocytosis.
The replisome is coded for by essential genes passed between bacteria. Without these proteins, a bacterial cell cannot form more cells. "-some" stands for a collection of proteins that function together, and "repli-" for replication. The TATA box is a DNA sequence involved in the indication of the start of a gene, chromosomes are collected strands of genetic material, the spliceosome removes introns from pre-mRNA, but this, along with all post translational modification, only occurs in eukaryotes. The cytosome is the part of the cell that is specialized for phagocytosis.
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After an unknown compound is added to an enzyme-mediated reaction mixture, the enzyme rate is reduced but 
remains constant. Which of the following best explains this situation?
After an unknown compound is added to an enzyme-mediated reaction mixture, the enzyme rate is reduced but
The Michaelis-Menten constant 
is temperature and pH dependent. It is the substrate concentration at which the rate is half of 
. Noncompetitive inhibitors alter the shape of an enzyme, slowing down the reaction rate without affecting 
. Competitive inhibitor bind to enzyme active sites, increasing the 
.
The Michaelis-Menten constant
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The Gila monster, H. suspectum, produces a neurotoxic venom containing helothermine, which causes lethargy and partial paralysis of the limbs. Considering that this toxin partially inhibits voluntary muscle contraction, which of the following is the most likely mechanism?
The Gila monster, H. suspectum, produces a neurotoxic venom containing helothermine, which causes lethargy and partial paralysis of the limbs. Considering that this toxin partially inhibits voluntary muscle contraction, which of the following is the most likely mechanism?
Helothermine is a peptide toxin that inhibits calcium channels in the cerebellar granule cells. The cerebellum is the part of the brain that controls voluntary muscle movements such as those in the limbs, and the toxin must be inhibiting very specifically to cause those two symptoms and not total paralysis or other problems.
Helothermine is a peptide toxin that inhibits calcium channels in the cerebellar granule cells. The cerebellum is the part of the brain that controls voluntary muscle movements such as those in the limbs, and the toxin must be inhibiting very specifically to cause those two symptoms and not total paralysis or other problems.
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Proteins have many functions. Which of the following can be functions of proteins?
I. Enzymes
II. Transcriptional regulators
III. Structural proteins
IV. Hormones
Proteins have many functions. Which of the following can be functions of proteins?
I. Enzymes
II. Transcriptional regulators
III. Structural proteins
IV. Hormones
Proteins serve all of these functions and many more. Most enzymes are proteins, which help to catalyze spontaneous reactions. Ribozymes can also serve this function but are instead made out of RNA. Proteins can act as transcriptional regulators which can turn on or off gene transcription. Structural proteins, such as actin, can help to maintain the shape of a cell. Other small proteins, such as insulin, can act as hormones which can diffuse throughout the body relaying important messages.
Proteins serve all of these functions and many more. Most enzymes are proteins, which help to catalyze spontaneous reactions. Ribozymes can also serve this function but are instead made out of RNA. Proteins can act as transcriptional regulators which can turn on or off gene transcription. Structural proteins, such as actin, can help to maintain the shape of a cell. Other small proteins, such as insulin, can act as hormones which can diffuse throughout the body relaying important messages.
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Enzymes come in many shapes and sizes and serve various functions. Which of the following are characteristics of enzymes?
I. Allow non-spontaneous reactions to occur
II. Bring substrates together in the proper orientation for catalysis
III. Reduce the activation energy of the reaction
IV. Reduce the free energy change of reaction
Enzymes come in many shapes and sizes and serve various functions. Which of the following are characteristics of enzymes?
I. Allow non-spontaneous reactions to occur
II. Bring substrates together in the proper orientation for catalysis
III. Reduce the activation energy of the reaction
IV. Reduce the free energy change of reaction
Enzymes are capable of many things but they are not able to help facilitate non-spontaneous reactions. An enzyme can however help spontaneous reactions occur much faster. Enzymes help catalyze reactions by orienting substrates in the necessary positions for reaction. Without enzymes, substrates would have to bump into each other with the exact necessary orientation and energy, which is very rare. Enzymes are capable of lowering the activation energy of a reaction but have no effect on the overall free energy change of a reaction; recall the distinction between kinetics and thermodynamics.
Enzymes are capable of many things but they are not able to help facilitate non-spontaneous reactions. An enzyme can however help spontaneous reactions occur much faster. Enzymes help catalyze reactions by orienting substrates in the necessary positions for reaction. Without enzymes, substrates would have to bump into each other with the exact necessary orientation and energy, which is very rare. Enzymes are capable of lowering the activation energy of a reaction but have no effect on the overall free energy change of a reaction; recall the distinction between kinetics and thermodynamics.
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Which of the following are true about enzyme inhibition?
I. Enzymes can be inhibited by end-products of that enzymatic pathway
II. Competitive inhibitors can lower an enzymes 
III. Non-competitive inhibitors inhibit enzyme action by binding to a site other than the active site
IV. Non-competitive inhibitors can lower an enzymes 
Which of the following are true about enzyme inhibition?
I. Enzymes can be inhibited by end-products of that enzymatic pathway
II. Competitive inhibitors can lower an enzymes
III. Non-competitive inhibitors inhibit enzyme action by binding to a site other than the active site
IV. Non-competitive inhibitors can lower an enzymes
Enzymes can be inhibited by end products of an enzymatic pathway. This is illustrated in the case of ATP acting as an inhibitor of enzymes found within the pathway for ATP production. This prevents the overabundance of a certain end-product. Competitive inhibitors do not lower an enzymes 
. Maximal velocity can still be achieved in the presence of a competitive inhibitor, but it requires a higher concentration of substrate to do so. Non-competitive inhibitors can lower an enzymes . This is because non-competitive inhibitors bind to sites other than the active site, known as allosteric binding sites.
Enzymes can be inhibited by end products of an enzymatic pathway. This is illustrated in the case of ATP acting as an inhibitor of enzymes found within the pathway for ATP production. This prevents the overabundance of a certain end-product. Competitive inhibitors do not lower an enzymes
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Which of the following statements about the general roles and properties of biological enzymes is not true?
Which of the following statements about the general roles and properties of biological enzymes is not true?
Enzymes are not consumed or used up during a reaction, rather they simply increase the rate of reaction by making it "easier" for the reaction to occur, i.e. lowering the activation energy. Equilibrium is not altered by the presence of an enzyme. There are examples of catalytic RNA molecules (ribosomes) and therefore biological catalysts are not always proteins.
Enzymes are not consumed or used up during a reaction, rather they simply increase the rate of reaction by making it "easier" for the reaction to occur, i.e. lowering the activation energy. Equilibrium is not altered by the presence of an enzyme. There are examples of catalytic RNA molecules (ribosomes) and therefore biological catalysts are not always proteins.
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The activity of certain enzymes can be modulated via effector binding to __________ sites; regulation at these sites often results in a conformational changes that alters the activity level of the enzyme either positively or negatively without the effector binding to the active site.
The activity of certain enzymes can be modulated via effector binding to __________ sites; regulation at these sites often results in a conformational changes that alters the activity level of the enzyme either positively or negatively without the effector binding to the active site.
The definition of allosteric enzyme regulation is that a cofactor or molecule binds and interacts with a site on the enzyme other than the active site. This often changes something about the shape of the enzyme which changes something about its interaction with its substrate, thus modulating how active the enzyme is.
The definition of allosteric enzyme regulation is that a cofactor or molecule binds and interacts with a site on the enzyme other than the active site. This often changes something about the shape of the enzyme which changes something about its interaction with its substrate, thus modulating how active the enzyme is.
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I. Cytochrome c oxidase, an important enzyme in the electron transport chain, uses copper ions as cofactors.
II. Cofactors are always metal ions, such as iron and copper.
III. An enzyme will have a binding site specific for one type of cofactor.
IV. Some cofactors can be formed from vitamins C, B12, and K, and these cofactors then serve to facilitate electron transport in many biological processes.
I. Cytochrome c oxidase, an important enzyme in the electron transport chain, uses copper ions as cofactors.
II. Cofactors are always metal ions, such as iron and copper.
III. An enzyme will have a binding site specific for one type of cofactor.
IV. Some cofactors can be formed from vitamins C, B12, and K, and these cofactors then serve to facilitate electron transport in many biological processes.
Cofactors are not always metal ions, nor are enzymes limited to interactions with a single cofactor. Cofactors can be metal ions, but they can also be organic molecules, and an enzyme may be able to bind and be altered by many of them. The other two statements are true.
Cofactors are not always metal ions, nor are enzymes limited to interactions with a single cofactor. Cofactors can be metal ions, but they can also be organic molecules, and an enzyme may be able to bind and be altered by many of them. The other two statements are true.
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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?
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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Hemoglobin is a protein that consists of four subunits: two copies of the 
and two copies of the 
subunit. How many individual polypeptide chains are present in a fully folded molecule of hemoglobin?
Hemoglobin is a protein that consists of four subunits: two copies of the
This question is primarily asking the difference between quaternary protein structure and lower levels of folding. In quaternary protein structure two or more folded polypeptide chains interact with one another to form a functional protein. In the case of hemoglobin, we are told that there are four subunits, indicating that there are four polypeptide chains. It does not matter that there are two copies of each subunit; they are each their own polypeptide chain. Subunits are folded independently first, then joined into quaternary structure by non-covalent intermolecular forces.
This question is primarily asking the difference between quaternary protein structure and lower levels of folding. In quaternary protein structure two or more folded polypeptide chains interact with one another to form a functional protein. In the case of hemoglobin, we are told that there are four subunits, indicating that there are four polypeptide chains. It does not matter that there are two copies of each subunit; they are each their own polypeptide chain. Subunits are folded independently first, then joined into quaternary structure by non-covalent intermolecular forces.
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What is the name of the bond that links amino acids together in protein primary structure?
What is the name of the bond that links amino acids together in protein primary structure?
Amino acids are covalently linked to one another by peptide bonds. The carboxylic acid portion of an amino acid connects to the amino terminus of the other amino acid, producing water as a byproduct. Peptide linkages are formed in the ribosome complex and result in the primary structure of the protein, Later, hydrogen bonding between amino acids plays a key role in secondary and tertiary protein structure.
Glycosidic bonds link adjacent monosaccharides in a carbohydrate polymer. Phosphodiester bonds are catalyzed by DNA ligase and are used to join nucleotides together to build nucleic acid chains.
Amino acids are covalently linked to one another by peptide bonds. The carboxylic acid portion of an amino acid connects to the amino terminus of the other amino acid, producing water as a byproduct. Peptide linkages are formed in the ribosome complex and result in the primary structure of the protein, Later, hydrogen bonding between amino acids plays a key role in secondary and tertiary protein structure.
Glycosidic bonds link adjacent monosaccharides in a carbohydrate polymer. Phosphodiester bonds are catalyzed by DNA ligase and are used to join nucleotides together to build nucleic acid chains.
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What level of protein structure is determined only by hydrogen bonds?
What level of protein structure is determined only by hydrogen bonds?
Secondary protein structure is exclusively dependent on hydrogen bonding.
Primary protein structure is established by the sequence of amino acid residues, joined by covalent peptide bonds at the ribosome. Once the primary structure is established, secondary structure arises as a result of hydrogen bonding between the backbones of the amino acids (not the functional groups). Secondary structures take the forms of alpha-helices or beta-pleated sheets, both of which can exist within a single molecule. Tertiary structure forms from hydrogen bonding between functional groups, hydrophobic interactions, and disulfide linkages. Quaternary structure can involve hydrogen bonding and other intermolecular forces and is present only when multiple polypeptides come together to form a single protein complex.
Secondary protein structure is exclusively dependent on hydrogen bonding.
Primary protein structure is established by the sequence of amino acid residues, joined by covalent peptide bonds at the ribosome. Once the primary structure is established, secondary structure arises as a result of hydrogen bonding between the backbones of the amino acids (not the functional groups). Secondary structures take the forms of alpha-helices or beta-pleated sheets, both of which can exist within a single molecule. Tertiary structure forms from hydrogen bonding between functional groups, hydrophobic interactions, and disulfide linkages. Quaternary structure can involve hydrogen bonding and other intermolecular forces and is present only when multiple polypeptides come together to form a single protein complex.
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An amino acid monomer at neutral pH will be found in what form?
An amino acid monomer at neutral pH will be found in what form?
At neutral pH an amino acid monomer will be found in the zwitterionic form in which there is a positive charge on the amino group and a negative charge on the carboxyl group. At very low an/or very high pH (less than 2 or greater than 12) there can be an overall negative or positive charge found on the amino acid, depending on the R-group.
At neutral pH an amino acid monomer will be found in the zwitterionic form in which there is a positive charge on the amino group and a negative charge on the carboxyl group. At very low an/or very high pH (less than 2 or greater than 12) there can be an overall negative or positive charge found on the amino acid, depending on the R-group.
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The linear sequence of amino acids in a protein determines its __________ structure.
The linear sequence of amino acids in a protein determines its __________ structure.
The linear sequence of amino acids within a protein makes up the primary structure. Protein secondary structure is defined by the localized three-dimensional structure of of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha-helices and beta-pleated sheets are examples of secondary structures. Protein tertiary structure is defined by the longer range interactions between amino acids within a single polypeptide chain. These interactions include ionic bonds, disulfide bridges, hydrogen bonds, and hydrophobic interactions. Protein quaternary structure is defined by the interactions between polypeptide chains. This often occurs in the formation of dimers and higher multimers.
The linear sequence of amino acids within a protein makes up the primary structure. Protein secondary structure is defined by the localized three-dimensional structure of of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha-helices and beta-pleated sheets are examples of secondary structures. Protein tertiary structure is defined by the longer range interactions between amino acids within a single polypeptide chain. These interactions include ionic bonds, disulfide bridges, hydrogen bonds, and hydrophobic interactions. Protein quaternary structure is defined by the interactions between polypeptide chains. This often occurs in the formation of dimers and higher multimers.
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Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein __________ structure.
Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein __________ structure.
Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein tertiary structure when they occur within a single polypeptide chain. However, if these interactions were to occur between separate polypeptide chains then they would be defining the quaternary structure of the protein. The linear sequence of amino acids within a protein makes up the primary structure. Protein secondary structure is defined by the localized three-dimensional structure of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha helices and Beta pleated sheets are examples of secondary structures.
Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein tertiary structure when they occur within a single polypeptide chain. However, if these interactions were to occur between separate polypeptide chains then they would be defining the quaternary structure of the protein. The linear sequence of amino acids within a protein makes up the primary structure. Protein secondary structure is defined by the localized three-dimensional structure of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha helices and Beta pleated sheets are examples of secondary structures.
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When presented with its ligand, glutamate, a metabotropic glutamate receptor (mGluR) can do any of the following except __________.
When presented with its ligand, glutamate, a metabotropic glutamate receptor (mGluR) can do any of the following except __________.
The key here is knowing that metabotropic receptors are NOT ion channels. They exert their effects through downstream signaling cascades. Ions cannot travel through a metabotropic receptor.
All other answers are potential outcomes of activating an mGluR.
The key here is knowing that metabotropic receptors are NOT ion channels. They exert their effects through downstream signaling cascades. Ions cannot travel through a metabotropic receptor.
All other answers are potential outcomes of activating an mGluR.
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