Biochemistry - GRE
Card 0 of 500
Which of the following nucleotides is present in RNA, but not DNA?
Which of the following nucleotides is present in RNA, but not DNA?
Uracil is one of the nucleotide bases that composes RNA. It is replaced by thymine in DNA.
Uracil, thymine, and cytosine are pyrimidine residues, capable of bonding and pairing with the purines adenine and guanine via hydrogen bonding. During DNA replication, thymine matches with adenine. During transcription, uracil matches with adenine.
Uracil is one of the nucleotide bases that composes RNA. It is replaced by thymine in DNA.
Uracil, thymine, and cytosine are pyrimidine residues, capable of bonding and pairing with the purines adenine and guanine via hydrogen bonding. During DNA replication, thymine matches with adenine. During transcription, uracil matches with adenine.
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Which of the following amino acids is NOT necessary for purine synthesis?
Which of the following amino acids is NOT necessary for purine synthesis?
Purines are defined by their two-ring structure. A six-member ring with two amine groups and a five-member ring with two amino groups join to form each purine molecule. Addition substituents on the rings (often ketones or other amines) determine purine identity.
Glycine, aspartate, and glutamine are necessary for purine synthesis, along with phosphoribosyl pyrophosphate (PRPP). Glycine is incorporated into the final purine product structure, while glutamine is converted to glutamate and aspartate is converted to fumarate. The final purine product is used to make useful molecules, such as adenine and guanine for nucleotide synthesis.
Purines are defined by their two-ring structure. A six-member ring with two amine groups and a five-member ring with two amino groups join to form each purine molecule. Addition substituents on the rings (often ketones or other amines) determine purine identity.
Glycine, aspartate, and glutamine are necessary for purine synthesis, along with phosphoribosyl pyrophosphate (PRPP). Glycine is incorporated into the final purine product structure, while glutamine is converted to glutamate and aspartate is converted to fumarate. The final purine product is used to make useful molecules, such as adenine and guanine for nucleotide synthesis.
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Which of the following processes allows DNA mismatch repair enzymes to distinguish between old and new DNA strands?
Which of the following processes allows DNA mismatch repair enzymes to distinguish between old and new DNA strands?
Template strand cytosine and adenine are methylated in DNA replication, which allows DNA mismatch repair enzymes to distinguish between old and new DNA strands.
In contrast, histone acetylation relaxes DNA coiling and allows for the DNA to be transcribed.
You can remember that methylation makes DNA mute, and acetylation makes DNA active.
Template strand cytosine and adenine are methylated in DNA replication, which allows DNA mismatch repair enzymes to distinguish between old and new DNA strands.
In contrast, histone acetylation relaxes DNA coiling and allows for the DNA to be transcribed.
You can remember that methylation makes DNA mute, and acetylation makes DNA active.
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In DNA, which of the following nucleotides forms hydrogen bonds with guanine?
In DNA, which of the following nucleotides forms hydrogen bonds with guanine?
Nucleotides (DNA monomers) and ribonucleotides (RNA monomers) are formed from a pentose sugar, phosphate group, and nitrogenous base. Each nitrogenous base has a complement that allows it to form hydrogen bonds to the template strand. This allows for the proper sequence of genetic code in DNA replication and RNA transcription.
Purine residues will always pair with pyrimidine residues. The purines are adenine and guanine. The pyrimidines are cytosine and thymine in DNA, and cytosine and uracil in RNA. Adenine will match with thymine or uracil, forming two hydrogen bonds, while cytosine will match with guanine to form three hydrogen bonds.
Nucleotides (DNA monomers) and ribonucleotides (RNA monomers) are formed from a pentose sugar, phosphate group, and nitrogenous base. Each nitrogenous base has a complement that allows it to form hydrogen bonds to the template strand. This allows for the proper sequence of genetic code in DNA replication and RNA transcription.
Purine residues will always pair with pyrimidine residues. The purines are adenine and guanine. The pyrimidines are cytosine and thymine in DNA, and cytosine and uracil in RNA. Adenine will match with thymine or uracil, forming two hydrogen bonds, while cytosine will match with guanine to form three hydrogen bonds.
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Which molecule transfers electrons from photosystem II to photosystem I?
Which molecule transfers electrons from photosystem II to photosystem I?
Photosystems I and II are each capable of conducting electrons, with photosystem II handing off electrons to photosystem I. This is accomplished by the electron carrier molecule plastocyanin.
Photosystems I and II are each capable of conducting electrons, with photosystem II handing off electrons to photosystem I. This is accomplished by the electron carrier molecule plastocyanin.
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Which product is made in photosystem I?
Which product is made in photosystem I?
Photosystems I and II are responsible for the light-dependent reactions of photosynthesis. These two photosystems work in tandem to create ATP and NADPH products. ATP is created in photosystem II, while NADPH is created in photosystem I.
Photosystems I and II are responsible for the light-dependent reactions of photosynthesis. These two photosystems work in tandem to create ATP and NADPH products. ATP is created in photosystem II, while NADPH is created in photosystem I.
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What fuels ATP synthase to make ATP from ADP + Pi in the light reaction of photosynthesis?
What fuels ATP synthase to make ATP from ADP + Pi in the light reaction of photosynthesis?
Excitation of photosystem II splits water in the thylakoid space into hydrogen and oxygen. The hydrogen then passes through ATP synthase to move down its concentration gradient and into the stroma. Excitation of photosystem I passes electrons to NADP+ reductase to convert NADP+ to NADPH. Regeneration of NADPH is necessary for the Calvin cycle.
Excitation of photosystem II splits water in the thylakoid space into hydrogen and oxygen. The hydrogen then passes through ATP synthase to move down its concentration gradient and into the stroma. Excitation of photosystem I passes electrons to NADP+ reductase to convert NADP+ to NADPH. Regeneration of NADPH is necessary for the Calvin cycle.
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During the photosynthetic light reactions, which of the following molecules acts as the electron acceptor?
During the photosynthetic light reactions, which of the following molecules acts as the electron acceptor?
Electrons excited in photosystem I are accepted by 
, thus converting 
to 
. 
is the reduced form of 
and while 
acts as an electron acceptor in certain reactions, the light reactions utilize 
which has an extra phosphate. 
and 
are not used to accept electrons in this context.
Electrons excited in photosystem I are accepted by
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Which of the following is an example of allosteric regulation of enzymes?
Which of the following is an example of allosteric regulation of enzymes?
The difference between the binding of cAMP and phosphorylation is that the latter is a covalent modification. Covalent modifications are a different way to regulate proteins, and do not fall under the category of allosteric regulation. Allosteric regulation only occurs outside of the active site, often simply called an allosteric site. The non-covalent binding of cAMP to a region of an enzyme outside of the active site thus qualifies as allosteric regulation.
The difference between the binding of cAMP and phosphorylation is that the latter is a covalent modification. Covalent modifications are a different way to regulate proteins, and do not fall under the category of allosteric regulation. Allosteric regulation only occurs outside of the active site, often simply called an allosteric site. The non-covalent binding of cAMP to a region of an enzyme outside of the active site thus qualifies as allosteric regulation.
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Which of the following is not a redox reaction?
Which of the following is not a redox reaction?
All of the given choices represent oxidation-reduction reactions that are important in cellular metabolism. Oxidation-reduction reactions involve the changing of oxidation states (commonly through the transfer of electrons). In the first reaction NAD+ is reduced. The second reaction shows the polymerization of two molecules of glucose via a condensation (dehydration synthesis) reaction. In the third reaction glucose is oxidized.
NADH and are important electron carriers that bring electrons to the electron transport chain and are formed during glycolysis and the Krebs cycle via reduction. The final choice represents the overall oxidation-reduction reaction that occurs for one molecule of glucose.
All of the given choices represent oxidation-reduction reactions that are important in cellular metabolism. Oxidation-reduction reactions involve the changing of oxidation states (commonly through the transfer of electrons). In the first reaction NAD+ is reduced. The second reaction shows the polymerization of two molecules of glucose via a condensation (dehydration synthesis) reaction. In the third reaction glucose is oxidized.
NADH and are important electron carriers that bring electrons to the electron transport chain and are formed during glycolysis and the Krebs cycle via reduction. The final choice represents the overall oxidation-reduction reaction that occurs for one molecule of glucose.
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Consider the following reaction:
Which atom is oxidized in the reaction?
Consider the following reaction:
Which atom is oxidized in the reaction?
Oxidation is the process of losing electrons, or acquiring a more positive charge. We can determine which atom has lost electrons by comparing the oxidation number of the atom as a reactant and as a product. Aluminum is in elemental form as a reactant, so it has an oxidation number of 0. As a product, it is bonded with oxygen, giving each aluminum an oxidation number of +3. Since it has a more positive charge, the aluminum has been oxidized.
Oxidation is the process of losing electrons, or acquiring a more positive charge. We can determine which atom has lost electrons by comparing the oxidation number of the atom as a reactant and as a product. Aluminum is in elemental form as a reactant, so it has an oxidation number of 0. As a product, it is bonded with oxygen, giving each aluminum an oxidation number of +3. Since it has a more positive charge, the aluminum has been oxidized.
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Which mnemonic would be most useful for remembering what happens during an oxidation-reduction reaction?
Which mnemonic would be most useful for remembering what happens during an oxidation-reduction reaction?
LEO says GER is a mnemonic for Loss of Electrons is Oxidation, Gain of Electrons is Reduction. An oxidation-reduction reaction is a chemical interaction in which one substance is oxidized and loses electrons, and thus is increased in positive valance, while another substance gains an equal number of electrons and is reduced, thus decreasing in positive valance. This is called a redox system or reaction. Along with LEO says GER, another popular mnemonic for this system is "OIL RIG," which stands for Oxidation is Loss, Reduction is Gain (in reference to electrons).
BARF is a mnemonic for Break (a bond) Absorb (energy), Release (energy) Form (a bond). This is used to remember whether energy is required or released when chemical bonds are broken and formed. OCEAN describes the big five personality traits: openness, conscientiousness, extraversion, agreeableness, and neuroticism. PASS stands for pull, aim, squeeze, and sweep—how to use a fire extinguisher. ROME is a mnemonic for Respiratory Opposite, Metabolic Equal. The values for the respiratory form of acid-base balance are opposite; if pH is high, carbon dioxide will be low and vice versa. For the metabolic form, the values are equal. If pH is high, carbonic acid will be high. If pH is low, carbonic acid will be low.
LEO says GER is a mnemonic for Loss of Electrons is Oxidation, Gain of Electrons is Reduction. An oxidation-reduction reaction is a chemical interaction in which one substance is oxidized and loses electrons, and thus is increased in positive valance, while another substance gains an equal number of electrons and is reduced, thus decreasing in positive valance. This is called a redox system or reaction. Along with LEO says GER, another popular mnemonic for this system is "OIL RIG," which stands for Oxidation is Loss, Reduction is Gain (in reference to electrons).
BARF is a mnemonic for Break (a bond) Absorb (energy), Release (energy) Form (a bond). This is used to remember whether energy is required or released when chemical bonds are broken and formed. OCEAN describes the big five personality traits: openness, conscientiousness, extraversion, agreeableness, and neuroticism. PASS stands for pull, aim, squeeze, and sweep—how to use a fire extinguisher. ROME is a mnemonic for Respiratory Opposite, Metabolic Equal. The values for the respiratory form of acid-base balance are opposite; if pH is high, carbon dioxide will be low and vice versa. For the metabolic form, the values are equal. If pH is high, carbonic acid will be high. If pH is low, carbonic acid will be low.
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Reduction of a compound results in a                      of electrons, thus rendering the compound's charge to be more                     .
Reduction of a compound results in a                      of electrons, thus rendering the compound's charge to be more                     .
The process of reduction causes a gain of electrons. Because electrons are negatively charged, any compound that becomes reduced will be more negative than it was prior to the reaction.
The process of reduction causes a gain of electrons. Because electrons are negatively charged, any compound that becomes reduced will be more negative than it was prior to the reaction.
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A researcher is studying the rate of an enzyme-catalyzed reaction by placing increasing amounts of substrate into a solution containing the enzyme. After a certain concentration, the rate of the reaction plateaus and does not go any higher. What has happened?
A researcher is studying the rate of an enzyme-catalyzed reaction by placing increasing amounts of substrate into a solution containing the enzyme. After a certain concentration, the rate of the reaction plateaus and does not go any higher. What has happened?
If the reaction rate has plateaued, this indicates that the enzyme has reached saturation. At this point, every active site on every molecule of enzyme is actively catalyzing the reaction as quickly as it can. The only way to change the reaction rate, at this point, would be to increase the concentration of the enzyme in the solution. Further increasing substrate concentration will have no effect.
We know that the enzyme has not become denatured because the reaction is still occurring. The rate of the reaction is constant during the plateau, and does not drop to zero.
If the reaction rate has plateaued, this indicates that the enzyme has reached saturation. At this point, every active site on every molecule of enzyme is actively catalyzing the reaction as quickly as it can. The only way to change the reaction rate, at this point, would be to increase the concentration of the enzyme in the solution. Further increasing substrate concentration will have no effect.
We know that the enzyme has not become denatured because the reaction is still occurring. The rate of the reaction is constant during the plateau, and does not drop to zero.
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In a Lineweaver-Burk plot, what quantity determines the y-intercept?
In a Lineweaver-Burk plot, what quantity determines the y-intercept?
A Lineweaver-Burk plot is a way to graphically represent enzyme kinetics. It is convenient because several portions of the graph readily display important information, such as rate constants. The y-intercept in particular is useful because it represents the reciprocal of the maximum velocity. The x-intercept describes the negative reciprocal of the Michaelis constant. The slope is the quotient of the Michaelis constant over the maximum velocity.
A Lineweaver-Burk plot is a way to graphically represent enzyme kinetics. It is convenient because several portions of the graph readily display important information, such as rate constants. The y-intercept in particular is useful because it represents the reciprocal of the maximum velocity. The x-intercept describes the negative reciprocal of the Michaelis constant. The slope is the quotient of the Michaelis constant over the maximum velocity.
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What information is contained in a Lineweaver-Burk plot that is not present in a standard Michaelis-Menten plot?
What information is contained in a Lineweaver-Burk plot that is not present in a standard Michaelis-Menten plot?
The two plots contain the same information. A Michaelis-Menten plot shows the relationship between initial reaction rate concentration of substrate (
versus 
). A Lineweaver-Burk plot shows the relationship between the inverses of these same two variables, however, it is much easier to visualize important data on a Lineweaver-Burk plot. The x-intercept, the y-intercept, and the slope all contain points of interest. A downside of the Lineweaver-Burk plot, however, is that it is more susceptible to inaccuracy if there is some flaw in the accumulated data.
The two plots contain the same information. A Michaelis-Menten plot shows the relationship between initial reaction rate concentration of substrate (
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Which of the following changes will alter 
of an enzyme-catalyzed reaction?
Which of the following changes will alter
The only option that will alter the 
is to add a non-competitive inhibitor. The addition of this inhibitor will affect the amount of free enzyme available to catalyze the reaction, and thus lower the 
by reducing the effective enzyme concentration.
Addition of a competitive inhibitor will alter the 
, but not the 
. Increasing the substrate concentration will have no effect once saturation has been reached.
The only option that will alter the
Addition of a competitive inhibitor will alter the
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A catalyst is an enzyme that promotes a reaction. In terms of free energy, what does a catalyst change about the reaction to promote the reaction proceeding?
A catalyst is an enzyme that promotes a reaction. In terms of free energy, what does a catalyst change about the reaction to promote the reaction proceeding?
During a reaction, the reactants must pass through high-energy transition states before they evolve into the products. The catalyst reduces the free energy of this transition state, thus making it 'easier' for the reactant to undergo the chemical reaction since the activation energy has been lowered.
During a reaction, the reactants must pass through high-energy transition states before they evolve into the products. The catalyst reduces the free energy of this transition state, thus making it 'easier' for the reactant to undergo the chemical reaction since the activation energy has been lowered.
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Which of the following properties is NOT a feature of the genetic code?
Which of the following properties is NOT a feature of the genetic code?
The genetic code refers to the sequence of DNA that codes for genes and proteins in the body. The genetic code is composed of three-nucleotide codons, each used to recruit an amino acid during translation and protein synthesis. Each codon codes for one and only one amino acid, making the code unambiguous; however, some amino acids have more than one codon that can be used to recruit them. This feature of the genetic code is known as degeneracy. Finally, the genetic code is universal. All living organisms use the same genetic material (DNA) in their cells and produce proteins through transcription and translation. Though the processes may change slightly between organisms, the general genetic code is universal to all cells.
The genetic code is not overlapping, meaning that the code is linear. Transcription of DNA has a fixed starting point and proceeds in a linear fashion, as does translation of mRNA. There is no overlapping or reverse reading of the genetic code.
The genetic code refers to the sequence of DNA that codes for genes and proteins in the body. The genetic code is composed of three-nucleotide codons, each used to recruit an amino acid during translation and protein synthesis. Each codon codes for one and only one amino acid, making the code unambiguous; however, some amino acids have more than one codon that can be used to recruit them. This feature of the genetic code is known as degeneracy. Finally, the genetic code is universal. All living organisms use the same genetic material (DNA) in their cells and produce proteins through transcription and translation. Though the processes may change slightly between organisms, the general genetic code is universal to all cells.
The genetic code is not overlapping, meaning that the code is linear. Transcription of DNA has a fixed starting point and proceeds in a linear fashion, as does translation of mRNA. There is no overlapping or reverse reading of the genetic code.
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For amino acids, the phi (
) angle refers to the bond between                      and the alpha carbon while the psi (
) angle refers to the bond between the alpha carbon and                     .
For amino acids, the phi (
These bonds are specifically referring to the invariable portions of the amino acid and, thus, do not involve the R group (functional group).
This is more of a definition-based answer. The phi angle refers to the bond between the amine nitrogen and the alpha carbon, while the psi angle refers to the bond between the alpha carbon and the carbonyl carbon of the carboxylic acid. These bonds play important roles in determining possible protein structures.
These bonds are specifically referring to the invariable portions of the amino acid and, thus, do not involve the R group (functional group).
This is more of a definition-based answer. The phi angle refers to the bond between the amine nitrogen and the alpha carbon, while the psi angle refers to the bond between the alpha carbon and the carbonyl carbon of the carboxylic acid. These bonds play important roles in determining possible protein structures.
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