Biochem 1 review

A researcher is able to denature a protein by adding it to a solution with low pH. Which of the following bonds is not broken in this solution? A. Peptide B. Ionic C. Hydrogen D. Disulfide

A Adding the protein to a solution with low pH will denature the protein's quaternary and tertiary structures. Disulfide, hydrogen, and ionic bonds are all utilized in the tertiary structure of proteins, and will denature at low pH. Only peptide bonds, which exist at the level of primary structure are unaffected by low pH.

What is the correct amino acid sequence for this polypeptide? (See image) A. S-E-K-F-V-G-C B. C-G-V-P-K-D-S C. S-D-K-P-V-G-C D. C-G-V-F-K-E-S

A Amino acid sequences are written starting from the N-terminus and ending with the C-terminus. The amino acid at the N-terminus of this polypeptide is Serine (S), and the second amino acid is Glutamate (E). This eliminates all other answer choices.

Which of the following best defines/describes characteristics of an operon in E.coli, a prokaryotic cell? I. Genetic regulatory system II. Contains a cluster of genes which share a promoter III. Transcribed as multiple large mRNA molecules A. I and II only B. II and III only C. I, II, and III D. I only

A An operon is defined as a genetic regulatory system that contains a cluster of genes with the same promoter, which transcribes a single mRNA molecule.

Coenzyme Q is an important intermediate in the electron transport chain of the mitochondria. Currently, the substance is available to take as an over-the-counter supplement. What might someone taking the drug want to do around the time they take it? A. consume a meal that contains fat B. consume a meal that contains protein C. consume a meal that contains carbohydrates D. consume water

A Coenzyme Q must be lipid-soluble, as it is embedded in the mitochondrial inner membrane and must move around in it in order to transport electrons. Therefore, it would be best to consume the supplement with lipids (fat).

Researchers determine the rate of the uncatalyzed reversible reaction, A → B (see image), to be 0.0001 M/s. Enzyme AB is known to catalyze this reaction in vivo. If the researchers add Enzyme AB to a solution consisting of reactant A, which of the following will change? I. Ea II. ΔG III. Reaction rate A. I and III only B. I, II, and III C. I only D. II and III only

A Enzymes catalyze, or increase, the rate of reactions by lowering the Ea, or activation energy, necessary for them to proceed. They do not change the ΔG, or free energy change, of a reaction.

Gaucher disease is a metabolic disorder caused by mutations in the gene coding for the glucocerebrosidase enzyme. Symptoms of the disease include hypoglycemia and an accumulation of fat in internal organs. What kind of reaction does glucocerebrosidase likely catalyze? A. conversion of glycosphingolipids to glucose B. conversion of glucose to polypeptides C. conversion of polypeptides to glucose D. conversion of glucose to glycosphingolipids

A Glucocerebrosidase catalyzes the conversion of glycosphingolipids to glucose. For those with Gaucher disease who have a deficiency of this enzyme, glycosphingolipids (a kind of fat) build up and are unable to be converted to glucose. Without the glucose from this reaction, individuals with Gaucher disease suffer from hypoglycemia, or low blood glucose.

Red blood cells have proteins embedded on their surface where carbohydrate groups are attached. The differences in these surface carbohydrates are responsible for the recognition of different blood types (A, B, AB, O). What type of post-translational modification occurs to create these structures? A. Glycosylation B. Phosphorylation C. Lipidation D. Acetylation

A Glycosylation protein modification occurs when a sugar molecule is added to a protein. Glycoproteins, such as those that indicate blood type, are often involved in cell-to-cell communication and binding. Acetylation introduces an acetyl group to an organic compound. Lipidation is when a lipid is added to a protein. Phosphorylation is the addition of a phosphate group.

In 1952, Martha Chase and Alfred Hershey conducted an experiment to confirm that DNA was the genetic material. They added radioactive elements to a plate of bacteria before introducing bacteriophages. Which of the following elements did they add and why? A. Radioactive sulfur to label proteins and radioactive phosphorus to label DNA B. Radioactive phosphorus to label proteins and radioactive sulfur to label DNA C. Radioactive nitrogen to label proteins and radioactive phosphorus to label DNA D. Radioactive phosphorus to label proteins and radioactive nitrogen to label DNA

A In the Hershey Chase experiment, sulfur was used to label proteins since the amino acids methionine and cysteine contain this element. Sulfur would not label DNA since DNA is only composed of carbon, hydrogen, oxygen, phosphorus, and nitrogen. Nitrogen could not be used as a label to distinguish between DNA and proteins because both contain nitrogen.

In the neonatal intensive care unit, a nurse draws a newborn baby's blood and discovers that he is type A. What are the possible blood types of the baby's parents? I. Type A and type B II. Type A and type AB III. Type AB and type B A. I, II, and III B. I and II only C. II only D. I only

A Individuals with the type A phenotype can either have AA or AO as their genotype. Statement I is possible because the baby could get an A allele from the type A parent and an O allele from the type B parent if their genotype is BO. II is possible because the baby could get an A allele from the type A parent and an A allele from the type AB parent. III is possible because the baby could get an A allele from the type AB parent and an O allele from the type B parent if their genotype is BO.

In humans, having freckles is dominant to not having freckles and curly hair is dominant to straight hair. A homozygous freckled, straight-haired man mates with a homozygous freckle-less, curly-haired woman. What are the potential phenotypes of this set of offspring? A. freckles and curly hair B. freckles and curly hair, freckle-less and curly hair C. freckle-less and curly hair D. freckles and straight hair, freckle-less and straight hair

A Mating FFCC with ffcc will give FfCc as the first offspring's genotype.

A biochemist conducts an experiment to measure the enzymatic activity of peptidyl transferase. A cellular calorimeter is used to measure the energy released during formation of a bond between which of the following two atoms? A. carbon and nitrogen B. carbon and oxygen C. carbon and carbon D. nitrogen and oxygen

A Peptidyl transferase catalyzes the formation of peptide bonds during translation. Recall that a peptide bond forms between the carbon of a carboxylic acid part of one amino acid and the nitrogen of an amine group of another amino acid.

The Strecker synthesis is often conducted to produce racemic mixtures of methionine. Which of the following is not a starting component for the Strecker synthesis? A. Grignard Reagent B. Aldehyde or ketone C. Ammonia D. Potassium cyanide

A Remember that The Strecker Synthesis is a preparation of α-aminonitriles, which are versatile intermediates for the synthesis of amino acids via hydrolysis of the nitrile. Ammonia is used as the precursor for the amino group. Potassium cyanide is the precursor for the carboxylic acid group, An aldehyde or ketone serves as a scaffold for the amino and carboxylic acid groups. The Grignard reagent is the only thing listed not needed for a strecker synthesis reaction.

A researcher uses Sanger sequencing to sequence a gene coding for a human blood-clotting protein. The gene is 1,000 base pairs long, but after Edman degradation, the researcher finds the protein to only be 100 amino acids long. Which of the following best explains the discrepancy between the number of base pairs and the number of amino acids? A. Intron sequences are removed from mRNA before mRNA is translated. B. Multiple bases code for each amino acid. C. RNA splicing removes exon sequences from pre-mRNA. D. Wobble base pairing results in the discrepancy.

A Splicing is a post-transcriptional modification that involves removing intron sequences and ligating the remaining exons. Exons are the coding regions/sequences and are crucial for the continuation of translation after mRNA leaves the nucleus. Intron sequences are present in the gene, but will not be translated to amino acids, as they are removed before translation. Although each amino acid is coded for by 3 bases, there are 100 amino acids, rather than the 333 that would be expected to correspond with the 1,000 bases in the gene.

Renin is an enzyme produced by the kidneys which functions to regulate the renin-angiotensin-aldosterone hormonal system and maintain blood pressure. A renin experiment includes recording substrate (angiotensin) concentration and the resulting rate of the reaction at various time periods. The results are displayed below. Which of the following best describes what is taking place when the rate of the reaction is half of Vmax? A. Half of the active sites on renin are filled with angiotensin. B. All of the active sites on renin are filled with angiotensin. C. None of the active sites on renin are filled with angiotensin. D. Half of the active sites on angiotensin are filled with renin.

A The Km represents the concentration of substrate needed for the enzyme to reach half of its maximum velocity. When an enzyme reaches Vmax this means that all the active sites are filled with substrate. Therefore, at half of Vmax, half of the active sites are filled with substrate.

In mushrooms, the allele for black color exhibits incomplete dominance with that of white color. A true-breeding black mushroom mates with a true-breeding white mushroom and has offspring. Two of its offspring breed and have 100 offspring of their own. How many will be black in color? A. 25 B. 100 C. 50 D. 75

A The first set of offspring each received one black allele and one white allele from their true-breeding parents, meaning that the genotype of each is BW. They are gray, because the black and white alleles exhibit incomplete dominance and gray is the mixture of those 2 colors. Crossing two BW genotypes results in 25% BB (black), 50% BW (gray), and 25% WW (white).

Tryptophan is an amino acid essential to polypeptide synthesis within the cell. Prokaryotes contain the repressible "trp" operon, capable of regulating free intracellular tryptophan levels. Which of the following systems best characterizes that of the trp operon? A. Negative feedback; as tryptophan levels increase, tryptophan synthesis is repressed. B. Positive feedback; as tryptophan levels increase, tryptophan synthesis is induced. C. Positive feedback; as tryptophan levels increase, tryptophan synthesis is repressed. D. Negative feedback; as tryptophan levels increase, tryptophan synthesis is induced.

A The trp operon is a repressible system of gene expression in prokaryotes. A repressible system allows for constant transcription of a gene when unrepressed. When tryptophan is present in the cell, it acts as a corepressor, which can bind to the repressor, allowing the repressor to bind to the operator in order to block further transcription, thus repressing tryptophan synthesis. This can be described as a negative feedback system because the output of the system (tryptophan, which acts as a corepressor) is used to inhibit the system itself.

A researcher investigates one mechanism of protein folding and solvation layer formation. The protein studied is rich in phenylalanine and leucine amino acids. When the protein is submerged in an aqueous solution, the water molecules in the solvation layer cannot form hydrogen bonds with the protein's side chain. What will most likely result from the occurrence of this phenomenon? A. Nearby water molecules will rearrange themselves in order to maximize hydrogen bonding. B. The water molecules rearrange and do not hydrogen bond with the protein's side chain. C. Water molecules will form multiple solvation layers around the protein. D. Nearby water molecules will rearrange themselves in order to minimize hydrogen bonding.

A This phenomenon occurs because phenylalanine and leucine are both hydrophobic amino acids, and will therefore orient themselves towards the interior of the protein to avoid contact with water. At the same time, water molecules surrounding the protein will orient themselves to maximize contact with hydrophobic residues in order to maximize hydrogen bonding.

Suppose free adenosine in a eukaryotic cell was given a fluorescent tag. Where in the cell would fluoresce immediately after transcription? A. Nucleus B. Cytoplasm C. Cell Membrane D. Ribosome

A Transcription produces a strand of pre-mRNA. In order for this mRNA to be used in the cell (usually as a protein), the pre-mRNA must be processed into mature mRNA. In eukaryotes, this processing occurs in the nucleus of a cell. The 5' cap, poly-adenosine tail, and splicing are all necessary for a strand of mRNA to be able to leave the nucleus and be used by the cell. If the cell's free adenosine is given a fluorescent tag, fluorescence will occur in the nucleus after transcription, as the adenosine will be used in the addition of the poly-adenosine tail to the pre-mRNA.

In a petri dish, a biochemistry professor labels the alpha, beta, and gamma phosphates of ATP molecules with blue, red, and purple residues, respectively. He then introduces a serine kinase as well as serine. After waiting a few minutes and extracting the serines from the dish, what color should he expect them to be? A. purple B. blue C. red D. colorless

A When ATP is hydrolyzed, it tends to lose its third phosphate group, the gamma phosphate. It is the most unstable of the three and its bond to ADP is most easily broken

The repressor protein on the lac operon is constitutively expressed. When glucose is readily available to the cell, which of the following statements is true? A. Repressor protein binds to the lac operator. B. Repressor protein binds to the lac promoter. C. RNA polymerase binds to the lac operator. D. RNA polymerase binds to the lac promoter.

A When glucose is readily available to the cell, there is no need to transcribe proteins for lactose metabolism, so the transcription of the lac operon is repressed. This occurs because a repressor protein binds to the operator, which blocks RNA polymerase from transcribing the genes involved in lactose metabolism.

A medical student has developed a technology that allows him to control the number of nucleotide bases inserted into a rabbit's DNA. If he wants to introduce a mutation that causes a frameshift mutation, what number of bases could he choose to insert? I. 45 II. 50 III. 43 A. II and III only B. I, II, and III C. I only D. II only

A When insertion or deletion mutations occur in multiples of three nucleotides, it does not result in a frameshift mutation. The reading frame is not disrupted when 45 nucleotides are added because each codon is three nucleotides long, and this would add exactly 15 codons. Alternatively, adding 43 or 50 nucleotides would result in a frameshift mutation, seeing as the number of nucleotides added is not divisible by three.

Phenylketonuria (PKU) is an autosomal recessive disorder caused by mutations in the gene for phenylalanine hydroxylase, located on chromosome 12. This results in the inability to metabolize phenylalanine, the buildup of which leads to intellectual disability, delayed development, skin rashes, and several other symptoms. Which of the following best describes the expression of PKU? A. Penetrance B. Pleiotropism C. Linked gene D. Epistasis

B Pleiotropy describes when one gene influences multiple, seemingly unrelated traits. Phenylketonuria is a classic example because it involves one gene but can have several different phenotypic effects.

Duchenne Muscular Dystrophy is a disease characterized by progressive muscle weakness that is inherited in an X-linked recessive pattern. If the percentage of men who have the disease is represented by m, what is the percentage of females who have the disease? A. 2m² B. m² C. m D. 2m

B A male will always have the disease if he inherits one allele, because he only has one X chromosome. This means that m represents both the percentage of men who have the disease as well as the prevalence of the allele. For a female to have the disease, she must have two copies of the allele, since she has two X chromosomes. Recall that to find the probability of two random events occurring, the individual probabilities must be multiplied together. Multiplying m by m leads to the answer m². m x m = m²

A man has a rare mutation that decreases his levels of ATP throughout the day. Assuming otherwise normal physiology, how should this affect his ion concentrations on either side of his cell's phospholipid membranes? A. Sodium will build up outside the cell while potassium will build up inside the cytoplasm. B. Potassium will build up outside the cell while sodium will build up in the cytoplasm. C. Sodium and potassium will build up in the cytoplasm. D. Sodium and potassium will build up outside the cell.

B ATP is used to power the sodium-potassium pump, which is used to transport potassium to the inside of the cell and sodium to the outside of the cell. Without ATP, the man would not have fully functional sodium-potassium pumps, meaning potassium would not be able to enter the cell as much and sodium would not be able to exit the cell as much, leading to their respective build-ups outside and inside the cell.

A scientist dips a sample of liver DNA in Chemical Agent A, which causes a transversion mutation of all adenine bases to cytosine bases. She dips another sample of the same liver DNA into Chemical Agent B, which causes a transversion mutation of all thymine bases to guanine bases. After dipping the samples, which should she expect to have a higher molecular weight and why? A. The sample dipped in Chemical Agent A, because there are now more purines than pyrimidines. B. The sample dipped in Chemical Agent B, because there are now more purines than pyrimidines. C. The sample dipped in Chemical Agent A, because there are now more pyrimidines than purines. D. The sample dipped in Chemical Agent B, because there are now more pyrimidines than purines.

B Adenine and guanine are purines, while cytosine, thymine, and uracil are pyrimidines. Purines contain two carbon-nitrogen rings while pyrimidines contain one, which causes purines to have a higher molecular weight, due to the extra atoms.

Thyroxine (T4) is a peptide hormone released primarily by thyroid follicular cells. Thyroxine release is limited to thyroid follicular cells because these cells contain: A. the promoter of the set of genes that codes for thyroxine B. transcription factors for thyroxine expression C. the operator of the set of genes that codes for thyroxine D. the gene that codes for thyroxine

B All cells in the human body contain the same DNA, which includes genes, operators, and promoters. Differences in the transcription of these genes are what give different cells different functions. Transcription factors are proteins that bind to different sites on DNA to regulate transcription. A unique set of transcription factors regulates transcription in such a way that allows thyroid follicular cells to be the only cells that can express thyroxine.

A researcher adds 100M of the peptidase trypsin to a polypeptide mixture. The reaction is allowed to proceed for 5 minutes. What concentration of enzyme will remain at the end of the reaction? A. 50M B. 100M C. 25M D. 20M

B Enzymes are reusable and do not get used up in the reaction. The enzyme binds to its substrate, catalyzes the reaction, and is released unchanged. Therefore, the concentration will stay the same

A naturalist society has been studying a population of giraffes on a savanna. Which of the following is not an example of evolution in this population? A. Giraffes without spots existed 100 years ago, but no longer do, because so many were easily hunted by lions on the savanna. B. Giraffes with a behavioral trait to seek out low-hanging leaves have a greater chance of feeding. C. Male giraffes with blue tongues are more attractive to female giraffes, most of which choose to mate with blue-tongued males and bring blue-tongued giraffe calves into the next generation. D. There is a higher percentage of giraffes with long legs in 2020 than there was in 1920.

B Evolution describes any change to heritable traits within populations across generations. In the answer choice that does not describe evolution, some giraffes may have an evolutionary advantage, but there is no mention of a change to the inherited characteristics of the successive generation. The answer choices that do describe evolution all have some mention of changes in traits existing in the giraffe population across generations or periods of time.

Centimorgans are considered the unit of genetic linkage. If there is a distance of 5 centimorgans between the gene for eye color and the gene for hair color, what does this mean? A. The genes are 5x as likely to be inherited together than a pair of genes that is separated by 1 centimorgan. B. 5% of the time, these genes will be recombinant. C. They are more likely to recombine than another pair of genes that are 10 centimorgans apart. D. 95% of the time, these genes will separate

B If a pair of genes are separated by 1 centimorgan, that means that 1% of the time that meiosis happens, the genes will recombine, or separate through crossing over. In the case of the hair and eye color genes which are separated by 5 centimorgans, 5% of the time, they will recombine, or separate. The genes are 5x as likely to separate (not get inherited together) than a pair of genes separated by 1 centimorgan. A pair of genes that are 10 centimorgans apart are more likely to recombine than eye and hair color, since 10% is greater than 5%.

In a species of fish, blue color is dominant to green color and fins are dominant to no fins. A homozygous blue, finless fish mates with a homozygous green, finned fish. One member of the F1 generation is mated with a homozygous recessive individual. The offspring of this cross is 436 blue, finless fish, 464 green, finned fish, 49 blue, finned fish, and 51 green, finless fish. Which of the offspring are recombinant? A. the blue, finned fish B. the blue, finned fish and the green, finless fish C. the blue, finless fish and the green, finned fish D. the green, finless fish

B Mating BBff with bbFF will give an F1 progeny with the genotype BbFf. The F1 fish with the genotype BbFf will produce Bf and bF gametes, while a homozygous recessive (bbff) fish will only produce the gamete bf. Thus, assuming no crossing over, we can expect to see half of their offspring with the genotype Bbff (blue, finless) and the other half with the genotype bbFf (green, finned). Any offspring who do not express one of those two genotypes can be assumed to be recombinant.

In cellular respiration, glucose is oxidized by a series of dehydrogenases with cofactors NADH and FADH2. Which of the following reactions would provide the substrate that is eventually reduced by electrons carried by NADH and FADH2 if said reaction takes place inside the cell? A. cellular respiration B. photosynthesis C. glycolysis D. gluconeogenesis

B Oxygen is the final electron acceptor in cellular respiration, meaning it accepts electrons that are stripped from glucose and other substrates. Photosynthesis is the only of the above reactions that produces oxygen. In this way, the two reactions of cellular respiration and photosynthesis are coupled in plants.

Researchers have identified a certain prion that causes the human protein abc to misfold by affecting α-helices. When a cell is infected by this particular prion, what most likely happens to protein abc at the molecular level? A. More α-helices form than normal, binding to other α-helices and causing the proteins to aggregate. B. β-sheets replace normal α-helices, binding to other β-sheets and causing the proteins to aggregate. C. α-helices replace normal β-sheets, binding to other α-helices and causing the proteins to aggregate. D. Fewer α-helices form than normal, preventing the proteins from assuming their tertiary structure and causing them to aggregate.

B Prions are infectious agents that cause the proteins of a host cell to misfold and aggregate. One well-known mechanism by which prions cause proteins to aggregate is by replacing normal α-helices with β-sheets, which have an increased likelihood of binding to one another. The β-sheets of these misfolded proteins then bind to the β-sheets of other proteins, leading to protein aggregation. In this example, although the prion could potentially cause protein aggregation by increasing or decreasing the number of α-helices, it is more likely that β-sheets replace the α-helices. This has a higher likelihood of leading to protein aggregation.

Blood and DNA are extracted from mice after undergoing a 24 hour fasting period. DNA is added to vials with varying concentrations of siRNA. Which of the following observations would most likely be seen in the vial containing the highest concentration of siRNA? A. decreased rates of RNA splicing B. increased rates of mRNA degradation C. decreased rates of mRNA degradation D. increased rates of RNA splicing

B Small interfering RNA (siRNA) attaches to and degrades mRNA molecules. Therefore, if the concentration of siRNA is high, we would expect to see an increase in mRNA degradation. Note that degradation is different from splicing, which is the functional role of snRNA, not siRNA.

The majority of college campuses in the United States elected to use polymerase chain reaction (PCR) to test students for COVID-19 upon their return to campus. If a single sample of mucus is cycled three times through PCR, what will be the total number of copies of DNA? A. 2 B. 8 C. 4 D. 16

B The formula 2^n (n being the number of cycles of PCR) can be used to find the number of copies of DNA present. Each sample was cycled three times, so n = 3 and 2^3 = 8.

A researcher studies an isolated enzyme reaction as part of the development of a drug to inhibit said enzyme. How can the researcher manipulate the experiment to increase the reaction's Vmax? A. Increase the product concentration B. Increase the enzyme concentration C. Increase the inhibitor concentration D. Increase the substrate concentration

B The only way to change the maximum velocity of a reaction is by adding more enzyme. Increasing substrate concentration does not effect Vmax, as enzymes are already saturated with substrate at Vmax. Adding product or inhibitor would respectively not affect or decrease Vmax

A researcher performs an experiment in the enzyme kinetics lab. There is an unknown enzyme inhibitor Z and a beaker containing enzyme X and substrate Y. When the inhibitor is added, the enzyme is able to bind the substrate but the reaction does not produce any product. Enzyme inhibitor Z is most likely what type of inhibitor? A. Mixed inhibitor B. Uncompetitive inhibitor C. Noncompetitive inhibitor D. Competitive inhibitor

B Uncompetitive inhibitors bind to the enzyme-substrate complex, which prevents the enzyme from turning substrate into product.

High levels of cyclin-dependent kinase activity have been implicated in tumorigenesis. Which of the following amino acids' R groups would likely remain unchanged in the presence of a kinase? A. S B. W C. T D. Y

B W (Tryptophan) is the only one of the choices that does not include a hydroxyl (-OH) group. A kinase adds on a phosphate group to a molecule by removing a hydrogen and creating a bond between the Oxygen of the hydroxyl group and the phosphate of the phosphate group (O-P).

Complementary DNA (cDNA) is useful as a biotechnology for the expression of specific proteins in cells that do not typically express those proteins. Why does cDNA exclude non-coding DNA? A. CDNA contains promoters and other regulatory sequences. B. CDNA is generated by reverse transcription of transcribed RNA. C. The process of creating cDNA selects for exons. D. CDNA does not include introns.

B cDNA is generated from mRNA that has been transcribed from DNA. Because mRNA is transcribed from coding DNA, the generated cDNA will only contain coding DNA.

A biochemistry student is studying the effects of a deleterious mutation in the gene coding for ATP synthase in a mouse. What should she not expect to see as a direct result of introducing the mutation to a mouse's genome and studying the mouse's cells? A. Hydrogen ions will build up outside the mitochondrial membrane. B. Free phosphate will build up inside the cell. C. Oxygen will build up inside the mitochondrial membrane. D. ADP will build up, as it will not be converted to ATP.

C ATP synthase catalyzes the reaction between ADP and phosphate groups to form ATP. Without the enzyme, both of the reactants will build up inside the cell. To fuel this reaction, ATP synthase allows protons to travel down their electrochemical gradient (from outside to inside the mitochondrial membrane). Without it, protons will build up outside the cell. Cytochrome C Oxidase, rather than ATP synthase, is the enzyme that catalyzes the conversion of protons and oxygen to water. Therefore, the ATP synthase mutation will not directly affect oxygen use.

Given that a protein is composed of nonpolar amino acids and displays typical patterns of protonation/deprotonation for neutral amino acids, which of the following amino acids is this protein most likely composed of? A. Glycine, Histidine, Leucine B. Alanine, Proline, Lysine C. Glycine, Isoleucine, Proline D. Aspartic acid, Glutamic acid

C Glycine, Leucine, Isoleucine, and Proline are all nonpolar amino acids. Histidine, aspartic acid, glutamic acid, and lysine are all polar amino acids. Protein X is composed of non-polar amino acids.

Researchers have been able to plot an energy graph for the reversible reaction A → B (see image). Which of the following statements is false when comparing A → B to the reverse reaction, B → A? A. They have the same transition state energy. B. They have the same |ΔG|. C. They have the same Ea. D. A → B is exergonic, while B → A is endergonic.

C Although the graph shows the reaction of A → B, we can still use the energy graph to determine characteristics of the reverse reaction, B → A. First, we can see that A → B is an exergonic reaction since the product, B, is at a lower energy level than the reactant, A. This means that the reverse reaction, B → A, will be endergonic. We can also see that the energy difference between the A and B is the same no matter what direction the reaction is headed. Therefore, the ΔG of the two reactions will be equal and opposite in magnitude. Both reactions utilize the same pathway as well, meaning that they must reach the same transition state in order for the reaction to be completed. The key difference between these two reactions is Ea. Since both reactions utilize the same transition state but use a different product and reactant, B → A requires much more activation energy than A → B.

Ser108 and Gln114 are residues in the same α-helix of an antibody. A hydrogen bond: A. will form between the amino group of Gln114 and the carbonyl of Ser108. B. will form between the R groups of Ser108 and Gln114. C. will not form between these two residues. D. will form between the amino group of Ser108 and the carbonyl of Gln114.

C Amino acids in α-helices form hydrogen bonds with the amino acid 4 residues ahead of them. The amino group of one residue forms a hydrogen bond with the carbonyl of another residue. In this problem, Ser108 and Gln114 are more than 4 residues apart. They will not form a hydrogen bond.

The Centers for Disease Control (CDC) defines UV radiation as a form of non-ionizing radiation that is emitted by the sun and artificial sources, such as tanning beds. Overexposure may present risks including sunburn, premature aging, and skin cancer. If a woman develops skin cancer after years of using tanning beds, what type of mutation has likely caused this and why? A. Induced mutation, because radiation can cause errors in the replication of DNA. B. Spontaneous mutation, because radiation has caused errors in the replication of DNA. C. Induced mutation, because it has been induced by a mutagen. D. Spontaneous mutation, because it has been induced by a mutagen.

C An induced mutation arises due to the influence of environmental agents called mutagens, such as UV radiation. A spontaneous mutation is an unpredictable change in DNA caused by an error in replication.

In lactic acid fermentation, the enzyme lactate dehydrogenase transfers electrons from a molecule of NADH to pyruvate, creating lactic acid and a molecule of NAD⁺. What kind of enzyme is lactate dehydrogenase? A. Hydrolase B. Ligase C. Oxidoreductase D. Isomerase

C An oxidoreductase enzyme catalyzes a redox reaction, which involves a transfer of electrons between two molecules. Lactate dehydrogenase is an enzyme that catalyzes the transfer of electrons from NADH to pyruvate, making it an oxidoreductase.

When insulin binds to membrane receptors of liver and adipose cells, the GLUT4 transporter fuses with the plasma membrane, allowing glucose to enter the cells. In this example: A. insulin acts as an enzyme that stimulates GLUT4, a non-enzymatic protein. B. both insulin and GLUT4 act as enzymes that catalyze glucose uptake. C. neither insulin nor GLUT4 act as enzymes. D. GLUT4 acts as an enzyme that is stimulated by insulin, a non-enzymatic protein.

C Both insulin and GLUT4 are non-enzymatic proteins, meaning they do not perform catalysis. Insulin is a protein hormone that signals for glucose transporters such as GLUT4 to fuse with the cell membrane. GLUT4 simply acts as a channel for glucose to pass from the extracellular environment into the cell. Neither insulin nor GLUT4 are described as catalyzing any reaction, which is the function of enzymes.

2,4-Dinitrophenol, also known as the "yellow slimming pill" is often sold over the internet for weight loss. It works by uncoupling the electron transport chain, or disrupting oxidative phosphorylation. Which of the following mechanisms is the most likely way by which the drug causes weight loss? A. decreased glycolysis B. increased glycogenesis C. decreased fatty acid synthesis D. increased protein synthesis

C By disrupting oxidative phosphorylation, the drug must decrease the production of ATP. Fatty acid synthesis requires an input of ATP, so an individual taking 2,4-Dinitrophenol will synthesize less fat, and thus lose weight. Glycolysis is triggered by low ATP, so the drug will actually increase its rate. Protein synthesis and glycogenesis require ATP, so a decrease in ATP synthesis would not increase the rate of either process.

Nicotinamide adenine dinucleotide and flavin adenine dinucleotide are considered the electron carriers of cellular respiration. Which of the following best describes these carrier molecules? A. prosthetic groups B. enzymes C. coenzymes D. vitamins

C Coenzymes are organic (carbon-containing) molecules that assist enzymes in catalysis. NADH and FADH₂ do so by picking up electrons produced during the reduction of glucose and transferring them to protein complexes in the electron transport chain.

The magnesium ion is an important cofactor in DNA polymerase binding to and replicating DNA. This is an example of: A. covalent catalysis. B. lock-and-key catalysis. C. electrostatic catalysis. D. acid-base catalysis.

C During electrostatic catalysis, enzymes bind/stabilize molecules using electrostatic charge. For example, DNA is a very negatively charged molecule due to the phosphate groups found in its phosphodiester bonds. DNA polymerase uses the positively charged Magnesium ion to bind to DNA and allow for DNA replication.

The active site of cytosolic phosphoenolpyruvate carboxykinase 1 (PCK1) contains the residue Ser90. What kind of intermolecular interaction is least likely to occur between Ser90 and PCK1's substrates? A. Hydrogen bond B. Electrostatic C. Phosphodiester bond D. Dipole-dipole

C Enzyme active sites bind substrates reversibly via a variety of noncovalent interactions. A phosphodiester bond is a covalent bond, and is therefore least likely to occur in the active site of Enzyme X.

A scientist shines plane polarized light through various amino acids. Which amino acid will not show optical activity? A. R B. E C. G D. T

C Glycine (G, Gly) is the only amino acid that does not rotate the plane of plane-polarized light because glycine is an achiral compound, making it optically inactive.

A single cell is observed to be undergoing mitosis underneath a microscope. Loose chromatin condenses into compact chromosomes which then replicate. Which of the following best describes the content of the cell at this point? A. 46 autosomes and 1 pair of of sex chromosomes B. 46 autosomes and 2 pairs of sex chromosomes C. 22 pairs of autosomes and 1 pair of sex chromosomes D. 23 pairs of autosomes and 1 pair of sex chromosomes

C Human beings have 23 pairs of chromosomes: 22 autosomes and 1 pair of sex chromosomes, for a total of 46 chromosomes.

An ecologist wishes to introduce greater genetic variation to a population of monkeys. Which of the following events would allow for this? I. two strand single crossover II. two strand double crossover III. three strand double crossover A. I, II, and III B. I only C. I and III only D. I and II only

C In a two strand single crossover, chromatids from two different chromosomes exchange genetic material, resulting in more types of gametes and therefore, potentially more types of individuals. In a three strand double crossover, chromatids from two different homologous chromosomes exchange genetic material once, and then one homolog swaps once (between two of its own chromatids). This similarly introduces more types of gametes. In a two strand double crossover, chromatids from two different homologous chromosomes exchange genetic material, but then swap back at the same place, resulting in the original chromosomes. This does not result in increased genetic variation because no "net" crossing over has occurred.

In cellular respiration, glucose is oxidized through a series of steps and pathways. In which of the following pathways is NADH not produced? I. Electron transport chain II. Citric acid cycle III. Pyruvate decarboxylation A. III only B. I, II, and III C. I only D. I and II only

C In the electron transport chain, NADH transfers its electrons to membrane proteins, becoming NAD+. Therefore, in the electron transport chain, NADH is used, not produced.

MRNA from a cancer cell and mRNA from a healthy cell are analyzed using a microarray. Which of the following would indicate that a certain mRNA sequence is expressed at higher levels in the cancer cell? A. The same rate of denaturation and annealing in the cancer cell's DNA as the mRNA. B. The same palindromic sequence in the cancer cell's DNA as in the mRNA. C. The color of the cancer cell's fluorescent tag on that mRNA's well. D. A farther distance traveled from cathode to anode.

C Microarrays contain specific mRNA sequences in individual wells. In hybridization, an organism's mRNA is given a fluorescent tag and allowed to bind to mRNA sequences in the wells. If enough of an organism's mRNA binds a specific mRNA sequence, the well containing that sequence will fluoresce with the color that was originally attached to that organism's DNA. The process of hybridization with microarrays does not involve anodes/cathodes, palindromic sequences, or denaturation/annealing.

Vitamin B deficiencies can manifest in a variety of symptoms, including fatigue, depression, headaches, and inflammation. Vitamin B₃ (niacin) is a precursor for ____ and vitamin B₅ is a precursor for _____ inside the body. A. CoA; FAD B. CoA; NAD C. NAD; CoA D. NAD; FAD

C NAD is an electron carrier that is essential for glycolysis. Coenzyme A is also an essential biochemical molecule that carries carbon molecules to the TCA cycle during aerobic respiration. Vitamin B₃ (niacin) is a precursor for NAD and vitamin B₅ is a precursor for CoA inside the body.

Cyanide poisoning is often lethal because of the poison's ability to halt ATP production. Cyanide binds to the allosteric site of the enzyme cytochrome oxidase, where it decreases the Vmax of the enzyme without affecting its binding affinity. What kind of inhibitor is cyanide? A. Mixed B. Uncompetitive C. Noncompetitive D. Competitive

C Noncompetitive inhibitors often bind to allosteric sites of enzymes. These inhibitors, like cyanide, decrease the Vmax (and subsequently Kcat) of enzymes, thereby decreasing the turnover rate of enzymes. Because they can bind to the enzyme or the enzyme-substrate complex equally, they do not have an overall effect on an enzyme's Km.

A cell biologist uses a microscopic calorimeter to measure free energy changes of different processes inside the cell. What should he expect the change in free energy to look like for the process of protein synthesis? A. negative, because it is an anabolic reaction B. negative, because it is a catabolic reaction C. positive, because it is an anabolic reaction D. positive, because it is a catabolic reaction

C Protein synthesis is the process of linking several amino acids together to create a protein polymer. This process is considered anabolic because simple substances are joined to create a complex substance. Anabolic reactions are endothermic, meaning they require energy. Therefore, the change in free energy should be positive for this anabolic reaction.

During DNA synthesis, DNA polymerase proofreads newly synthesized nucleotides. Part of this process involves excising incorrect bases and replacing them with correct ones. DNA polymerase detects instability in the strand via which of the following? A. high A-T content B. unstable phosphodiester bonds C. unstable hydrogen bonds D. high G-C content

C Recall that bases from the 2 different strands pair to each other via hydrogen bonds. When incorrect base pairing is present, the hydrogen bonds are unstable. This instability is recognized as the DNA passes through the proofreading section of DNA polymerase.

Shayla decides to treat herself after the MCAT by eating a pasta dinner from her favorite Italian restaurant. After she eats, her body enters a postprandial state. Which cells in her body will be releasing hormones during this time? A. Pancreatic alpha cells will be releasing glucagon. B. Pancreatic beta cells will be releasing insulin while alpha cells will be releasing glucagon. C. Pancreatic beta cells will be releasing insulin. D. Neither alpha nor beta cells will be releasing hormones.

C The body enters a postprandial state after consuming nutrients. Especially after a pasta dinner (which is high in carbohydrates), Shayla's blood glucose will increase. To respond to this, beta cells from the pancreas will release insulin to allow cells to intake glucose. Alpha cells, alternatively produce glucagon in response to low blood sugar

A researcher wishes to introduce a mutation to an enzyme that utilizes Threonine to bind reactants in its active site. Which of the following amino acids would replace threonine in such a way to inhibit the activity of the enzyme? A. Tyrosine B. Serine C. Tryptophan D. Aspartate

C The distinguishing characteristic of Threonine is the -OH group on its side chain. Therefore, in order to inhibit this enzyme's active site, the researcher must replace Threonine with an amino acid that lacks a similar -OH group. Serine and Tyrosine both contain alcohols in their R groups, giving them similar bonding capabilities to Threonine. Aspartate is too similar to Threonine due to the carboxylic acid in its R group. Tryptophan is the best answer because it does not have an -OH group in its side chain.

In sea anemones, the allele for red color is dominant to that for pink color. A true-breeding red sea anemone mates with a true-breeding pink anemone and has offspring. Two of its offspring breed and have 100 offspring of their own. How many will be red in color? A. 25 B. 100 C. 75 D. 50

C The first set of offspring each received one red allele and one pink allele from their true-breeding parents, meaning that the genotype of each is Rr. Crossing two Rr genotypes results in 25% RR, 50% Rr, and 25% rr. Since both RR and the Rr individuals are red in phenotype, 75% of the 100 offspring will be red.

A pharmaceutical company develops an antibiotic targeted towards a bacterial strain resistant to the majority of broad spectrum antibiotics. The scientist should target which of the following cellular structures in order to kill the bacterium without harming human eukaryotic cells? A. Mitochondria B. DNA C. Ribosomes D. Endoplasmic Reticulum

C The prokaryotic and eukaryotic ribosomes differ in subunits and size, meaning that an antibiotic could be created to target one and not the other. Additionally, membrane-bound organelles (mitochondria, nucleus, and endoplasmic reticulum) are not present in prokaryotic cells.

Angiotensin converting enzyme (ACE) is the enzyme that converts angiotensin 1 to angiotensin 2 in the kidney. Which of the following is true regarding the enzymatic activity of ACE? A. ACE lowers the standard free energy change of the reaction. B. ACE increases the standard free energy change of the reaction. C. ACE lowers the free activation energy needed for the reaction to proceed. D. ACE increases the free activation energy needed for the reaction to proceed.

C The question specifies that ACE is an enzyme. Enzymes speed up reactions by lowering the activation energy needed for the reaction to proceed. Enzymes never affect the free energy change of a reaction.

5 nmol of hydrochloric acid is directed via pipette at the first exon of a gene, but also reaches nearby structures. Which of the following structures is least likely to be affected by the hydrochloric acid? A. Transcription start site B. Upstream promoter C. Enhancer D. TATA box

C This question tests knowledge of the location of various components of eukaryotic genes. While the transcription start site, TATA box, and upstream promoter are all located upstream of the first exon of a gene, the enhancer is located farther upstream than the rest of the genetic components. Therefore, if hydrochloric acid (which denatures DNA) were to be directed at the first exon in a genetic sequence, the enhancer of that gene would be least likely to be affected, based on its relative location.

A certain protein is 8 amino acids in length. How many different amino acid sequences are possible for this protein? A. 160 B. 1.15 ⋅ 10¹⁸ C. 2.56 ⋅ 10¹⁰ D. 1,600

C To determine the total number of amino acid sequences that are possible for this protein, we must take the number of naturally occurring amino acids (20) and raise it by the number of amino acids in this sequence (8). 20⁸ = 20 × 20 × 20 × 20 × 20 × 20 × 20 × 20 = 400 × 400 × 400 × 400 = 160,000 × 160,000 = 25,600,000,000 = 2.56 ⋅ 10¹⁰ possible sequences

Using unknown enzyme inhibitor G, a researcher designs an experiment involving various concentrations of the inhibitor. The same concentration of substrate is added to three beakers. The unknown enzyme inhibitor concentrations are listed below. A lineweaver-burk plot is automatically generated for each beaker reaction. Beaker 1: 0M enzyme inhibitor G Beaker 2: 7M enzyme inhibitor G Beaker 3: 25M enzyme inhibitor G Based on the lineweaver-burk plot, what is the most likely type of inhibition that is occurring via the unknown enzyme inhibitor G? A. Noncompetitive inhibition B. Mixed inhibition C. Uncompetitive inhibition D. Competitive inhibition

C Uncompetitive inhibitors lower both the Vmax and the Km. This translates to a constant slope on the lineweaver-burk plot with more inhibitor added, since the slope is defined by Km/Vmax. This also translates to an increase in the y intercept with more inhibitor added, as the y intercept is defined as 1/Vmax.

A biotechnology company is tasked with lengthening a segment of DNA as much as possible without altering the reading frame. How many thymine bases should he add to the segment? A. 124 B. 327 C. 642 D. 782

C Whenever an insertion or deletion of three (or a multiple of three) bases takes place, there is not a shift in the reading frame, which would affect all succeeding codons. This is because the reading frame divides the sequence of nucleotides into a set of non-overlapping, consecutive triplets. 642 is the greatest multiple of three out of the answer choices.

During a decarboxylation reaction, electrons are transferred to allow for the removal of a carboxyl group. What kind of catalysis could an enzyme perform to increase the rate of this reaction? A. Proximity-orientation catalysis B. Electrostatic catalysis C. Acid-base catalysis D. Covalent catalysis

D A covalent catalysis would help this reaction go faster because the enzyme can act as an electron carrier (electron sink) by covalently binding to its target molecule, thus helping with the transfer of electrons.

ATP synthase is a two-subunit protein embedded in the inner mitochondrial membrane. It catalyzes the formation of a P-O bond, converting ADP to ATP. What kind of enzyme is ATP synthase? A. Oxidoreductase B. Transferase C. Hydrolase D. Ligase

D A ligase is an enzyme that can catalyze the linkage of two molecules by way of forming a new bond. This is what ATP synthase does in forming ATP. Oxidoreductases catalyze redox reactions, those that involve a transfer of electrons. Hydrolases catalyze the cleavage of covalent bonds using water. Transferases catalyze the transfer of various functional groups from one compound to another.

Above is the redox reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase. In this reaction, which species is oxidized and which is reduced? A. 1,3 bisphosphoglycerate is oxidized while glyceraldehyde 3-phosphate is reduced. B. NAD⁺ is oxidized while glyceraldehyde 3-phosphate is reduced. C. 1,3 bisphosphoglycerate is oxidized while NADH is reduced. D. Glyceraldehyde 3-phosphate is oxidized while NAD⁺ is reduced.

D A species is oxidized when it loses electrons while it is reduced when it gains electrons. We can see that in this reaction, NAD⁺ becomes NADH, meaning it must have picked up a negative charge from electrons. Therefore, it has been reduced. In redox reactions, reduction is paired with oxidation (if one species gains electrons, the other must lose them). Glyceraldehyde 3-phosphate is coupled with NAD⁺'s reduction, so we know that it was oxidized

What is the ΔG° of the reaction B → A? (See image) A. -35 kJ B. -55 kJ C. 55 kJ D. 35 kJ

D Although the graph shows the reaction of A → B, we can still use the energy graph to determine the ΔG° of the reverse reaction, B → A: ΔG° = G(products) - G(reactants) ΔG° = G(A) - G(B) ΔG° = 45 kJ - 10 kJ ΔG° = 35 kJ Another way to solve this problem is to simply take the ΔG° of reaction A → B and reverse the +/- sign. For example, ΔG°(A → B) = -35 kJ, while ΔG°(B → A) = 35 kJ.

One class of anticancer drugs works by interrupting DNA replication in cancer cells. Specifically, these drugs inhibit cancer cells from relieving structural stress in DNA, thereby inhibiting replication. Which of the following enzymes does this class of drugs inhibit? A. Helicase B. Polymerase C. Ligase D. Topoisomerase

D As DNA is unwound by helicase and replicated by polymerase, a replication bubble ( an unwound and open region of DNA) forms and gets larger. DNA on the sides of the replication bubble maintains the same # of twits, but gets condensed due to the replication bubble besides it. This results in supercoiling (the over-winding of a double helix) which introduces structural stress. Topoisomerase relieves supercoil-induced stress by breaking DNA at the sides of the replication bubble and later rejoining it. Topoisomerase inhibitors area a class of anti-cancer drug that inhibit topoisomerase, thus taking away a cell's ability to relieve structural stress in the double helix that is created during replication.

Cyclic adenosine monophosphate (cAMP) is an intracellular second messenger used in a wide variety of cellular pathways. Which of the following sites on the lac operon is most likely to contain a binding site for cAMP? A. TATA box B. operator C. promoter D. catabolite activator protein

D At low glucose concentrations, the concentration of cAMP increases. cAMP binds to and activates the catabolite activator protein (CAP). CAP binds the lac operon at the CAP site and activate transcription of genes involved in lactose metabolism.

A farmer hires a genetic engineering company in order to improve his produce yield. The company would like to find out which of his crops exhibit codominance. Which of the following is not an example of codominance among his crops? A. A cross between a homozygous spiked seed and a homozygous fluffy seed producing spiked, fluffy seeds. B. A cross between a homozygous white corn and a homozygous black corn producing spotted corn. C. A cross between pesticide-resistant grass and insecticide-resistant grass producing grass that is resistant to pesticides and insecticides. D. A cross between a homozygous long watermelon and a homozygous round watermelon producing oval watermelons.

D Codominance is when neither allele is dominant over the other, and both are expressed. An oval watermelon is rather an example of incomplete dominance, which involves an intermediate trait between the two true-breeding parents, the long and round watermelons. A heterozygote, containing the long trait and the round trait exhibits an oval trait, or a mix of round and long.

Enzyme PCA9 uses the His residue in its active site to perform acid-base catalysis on substrates at physiological pH (7.35-7.45). At pH = 6, Enzyme PCA9 will most likely: A. continue performing acid-base catalysis. B. switch to performing covalent catalysis. C. switch to performing electrostatic catalysis. D. be unable to perform acid-base catalysis.

D Enzyme PCA9 normally operates at physiological pH (7.35 - 7.45). When exposed to pH conditions outside of their normal range, enzymes denature and lose their ability to catalyze reactions. Therefore, at pH = 6, we can expect that Enzyme PCA9 will denature and no longer perform catalysis of any kind.

Enzyme X catalyzes the transformation of Substance A into Substance B, during which heat is released. Which of the following is not correct regarding this reaction? A. This reaction is exothermic. B. Enzyme X lowers the Ea of this reaction. C. The concentration of Enzyme X is not affected by this reaction. D. Enzyme X makes this reaction more thermodynamically favorable.

D Enzymes catalyze reactions by lowering the activation energy (Ea) required to make a reaction proceed. They make the reaction more kinetically favorable, not more or less thermodynamically favorable. In other words, they do not change the ΔG of the reaction, which is a thermodynamic property. Enzyme concentration is also not affected during a reaction. We can tell that the transformation of Substance A to Substance B is an exothermic reaction because it produces heat.

Sample 1 of neuron DNA is treated with a laser that causes a mispairing mutation, turning all G-C pairs into A-C pairs. Sample 2 of the same DNA is treated with a laser that causes a different mispairing mutation, turning all A-T pairs into G-T pairs. Which sample will denature first when placed in an oven with rising temperature? A. Sample 2 because there are more G-T pairs. B. Sample 2 because there are no more A-T pairs. C. Sample 1 because there are more A-C pairs. D. Sample 1 because there are no more G-C pairs.

D G-C base pairs have 3 hydrogen bonds, while A-T pairs have two. Therefore, DNA with a higher number of G-C base pairs will be more stable and will have a higher melting temperature. Alternatively, having less G-C pairs in a DNA strand would result in a lower melting temperature.

Histone acetyltransferase (HAT) inhibitors are compounds used to restrict the increased catalytic activity of HATs associated with Alzheimer's disease, diabetes, and cancer. Which of the following best describes a section of eukaryotic DNA after treatment with a HAT inhibitor? A. Heterochromatin, with increased transcription. B. Euchromatin, with decreased transcription. C. Euchromatin, with increased transcription. D. Heterochromatin, with decreased transcription.

D HAT is an enzyme that adds acetyl groups to histones which uncoils DNA, allowing it to be more accessible to transcriptional machinery for the expression of genes. This results in euchromatin, a less dense and transcriptionally active form of DNA. A HAT inhibitor would decrease the effects of HAT, which would result in the transcriptionally inactive heterochromatin.

A student studies energy use in cells on a petri dish. She pipettes 1mL of hydrochloric acid into the dish and measures the concentrations of products and reactants of the reaction ATP + H₂O → ADP + Pi + H⁺. How should she expect this reaction to change after pipetting? A. The equation will shift to the left due to an increase in reactants. B. The equation will shift to the right due to an increase in products. C. The equation will shift to the right due to an increase in reactants. D. The equation will shift to the left due to an increase in products.

D Hydrochloric acid is strongly acidic with a pH of around 1. This means that adding it to the petri dish will increase the concentration of protons, which are a product in this reaction. According to Le Chatelier's Principle, increasing the concentration of products will shift this equation to the left in order to reach equilibrium.

When Gregor Mendel formulated the law of segregation, mitosis and meiosis had not yet been discovered. Which of the following statements accurately describes how this law applies to meiosis? A. In Metaphase II, chromosomes align at the equatorial plate. B. Cytokinesis I results in two non-identical daughter cells. C. In Metaphase I, homologous chromosomes align at the equatorial plate to ensure genetic diversity. D. In Anaphase I, homologous chromosomes are pulled apart towards opposite poles.

D In Anaphase 1, homologous chromosomes separate, resulting in haploid gametes that each contain only one copy of a gene. In other words, the alleles have separated. Metaphase I and II, on the other hand, demonstrate the law of independent assortment of alleles because the chromosomes line up in random positions along the equatorial plate. Cytokinesis is simply the stage during which the cytoplasm divides.

A factory worker for a biotechnology company loads syringes with manufactured insulin. He accidentally injects his thigh with a syringe. In regard to glycogenolysis, glycogenesis, and lipogenesis, how will his body respond to the injection? A. decrease glycogenolysis, increase glycogenesis, decrease lipogenesis B. increase glycogenolysis, decrease glycogenesis, increase lipogenesis C. increase glycogenolysis, decrease glycogenesis, decrease lipogenesis D. decrease glycogenolysis, increase glycogenesis, increase lipogenesis

D Insulin is released by the body after ingesting nutrients and triggers anabolic reactions so that the body can build larger macromolecules from smaller nutrients. Glycogenesis is the process of building glycogen stores from glucose while lipogenesis is the process of forming fat polymers. Both of these are anabolic reactions triggered by insulin. Glycogenolysis is the process of breaking down glycogen to release glucose, which is triggered by glucagon rather than insulin.

A chemist is conducting a series of bond-breaking experiments with a molecule of adenosine triphosphate. The breaking of which bond will allow him to measure the greatest change in free energy? A. the bond between the alpha and beta phosphates B. the bond between the alpha phosphate and ribose sugar C. the bond between the gamma and alpha phosphates D. the bond between the gamma and beta phosphates

D Phosphate bonds are high energy because the three negative phosphate groups repel each other, meaning that a lot of energy will be released when they are broken. The highest energy bond between the phosphates is the gamma bond, which is between the second and third phosphates. Because it contains the most energy, it is unstable and will release the most energy upon breaking.

Researchers run real-time polymerase chain reactions in eukaryotic cells to determine the degradation rate of mRNA after it leaves the nucleus. Which of the following mRNA molecules will be degraded the fastest? A. 5'- ACGCAUCGUGAAAAAAAA-3' B. 5'- ACGUAUCGUUGAAAAA-3' C. 5'- ACGUAUCCGUAAAAAAAA-3' D. 5'- ACGUAUCGUCGAAGAAAA-3'

D Poly-adenosine tails are a post-transcriptional modification added to mRNA to protect it against rapid degradation by enzymes outside of the nucleus. The longer the poly-adenosine tail, the longer the mRNA molecule will be able to survive in the cytoplasm. Therefore, the mRNA strand with the shortest poly-adenosine tail will be degraded the fastest.

A researcher is studying the enzyme pepsin, which breaks down proteins to smaller peptides in the stomach. The researcher designs a synthetic pepsin for individuals with trouble digesting proteins using endogenous pepsin. Which of the following could be increased to increase the catalytic efficiency of pepsin? I. Increase Km II. Increase Kcat III. Increase Vo A. I Only B. I, II, and III C. I and II Only D. II Only

D Remember that the equation for enzymatic catalytic efficiency is: catalytic efficiency = Kcat / Km Therefore, in order to increase the catalytic efficiency of an enzyme like pepsin, we could either increase its Kcat or decrease its Km. It is also helpful to remember that Kcat = Vmax / [E].

Guanyl transferase is the enzyme responsible for addition of the 5' cap during the conversion of pre-mRNA to mature mRNA. Which of the following functions would be altered after the addition of guanyl transferase inhibitors to a cell's cytoplasm? I. mRNA-ribosome binding II. Nuclear export III. RNA splicing A. I, II, & III B. I C. II & III D. I & II

D The 5' cap functions to promote ribosome binding, regulate nuclear export and protect the molecule from degradation by endonucleases. The 5' cap is not involved in RNA splicing.

After sequencing the genome of a diseased fruit fly, researchers discover a nonsense mutation in the gene coding for guanyl transferase, the enzyme responsible for addition of the 5' cap to pre-mRNA. The presence of this mutation will most likely result in which of the following? A. Absence of 3' poly-A tail B. Translation of mRNA C. mRNA exiting the nucleus via nuclear pores D. Degradation of mRNA in the cytoplasm

D The 5' cap functions to protect the mRNA molecule from degradation in the cytoplasm. Without the 5' cap, the mRNA molecule will be degraded in the cytoplasm by endonucleases. Thus, protein synthesis will not occur.

In infants, a significant portion of body weight is composed of brown fat. Brown fat contains thermogenin, which is an extra protein in the inner mitochondrial membrane. Thermogenin produces heat by allowing the facilitated transport of protons across the membrane. In brown fat cells, how does this affect ATP synthesis? A. no change to ATP synthesis B. increases ATP synthesis C. stops ATP synthesis D. decreases ATP synthesis

D Thermogenin produces heat by allowing protons to flow down their concentration gradient through facilitated transport. This dissipates the concentration gradient which is normally harnessed by ATP synthase to produce ATP.

Upon analysis via Edman degradation, researchers determine the weight of a particular type of histone to be 15 kDa. What is the mass of one nucleosome composed of this type of histone, not accounting for the mass of nucleic acids? A. 60 kDa B. 30 kDa C. 90 kDa D. 120 kDa

D This question requires you to recall that a nucleosome is a structural unit composed of a length of DNA coiled around 8 histones. 8 x 15 kDa = 120 kDa.

In one species of sexually reproducing bacteria, green color is dominant to blue color and presence of flagella is dominant to absence of flagella. A microbiologist conducts a dihybrid cross of two bacteria, both green and with flagella. How many of their 16 offspring should the microbiologist expect to be green and without a flagellum? A. 9 B. 8 C. 1 D. 3

D When conducting a dihybrid cross, one should expect the offspring to show phenotypes in a 9:3:3:1 ratio. 9 will possess both dominant traits, 3 will possess one dominant and one recessive trait, 3 will possess the other dominant and the other recessive trait, and 1 will possess both recessive traits. Given this, we can expect green bacteria with no flagella to make up 3/16 of the offspring.

A researcher spills a mutagen that causes nucleotide base insertions and deletions to DNA on the samples he is studying. He sequences the affected strands to see which ones now have altered reading frames. Which of the following has not undergone a frameshift mutation to the given template strand? 5'-TGCCTTAGC-3' A. 5'-TGCCTCCTAGC-3' B. 5'-TGCTGCCCTTAGC-3' C. 5'-TGCCTTATGCCCGC-3' D. 5'-TGCTGCCTTAGC-3'

D When insertion or deletion mutations occur in multiples of three nucleotides, it does not result in a frameshift mutation. The reading frame is not disrupted because each codon is three nucleotides long. In the correct answer, three nucleotides were added to the sequence (TGC). In the incorrect answers, two, four, and five nucleotides were added.

A patient with a consistent blood glucose level greater than 300 mg/dL is determined to be in diabetic ketoacidosis (DKA). DKA patients typically have a pH below 7.4. Which of the following amino acids would not be protonated when pH falls below 6.25? A. Arginine (pI=10.76) B. Proline (pI=6.30) C. Lysine (pI=9.47) D. Glutamic acid (pI=3.08)

D When pH is less than the pI of an amino acid, the solution is more acidic than the amino acid, and the amino acid becomes protonated. Because glutamic acid is the only answer choice with a pI lower than the pH of 6.25 specified in the question stem, it will not be protonated.

Vacuum ultraviolet circular dichroism is an experimental technique used to identify β-turns in polypeptide chains. Which of the following correctly describes the location and content of β-turns? A. found on the surface of proteins, and consist of amino acids with nonpolar R groups. B. found on the interior of proteins, and consist of amino acids with polar R groups. C. found on the interior of proteins, and consist of amino acids with nonpolar R groups. D. found on the surface of proteins, and consist of amino acids with polar R groups.

D β-turns are sharp turns in the amino acid sequence that allow proteins to maintain a compact structure. They are normally located on the surface of proteins. Since most proteins exist in polar solutions such as water, the amino acids that make up the β-turn are usually polar to interact with the surrounding solution.