Khan Academy Practice Questions

The lagging strand of a DNA molecule undergoing replication reads 3'-CGCATGTAGCGA-5'. What is the code of the DNA that is the template for the complementary leading strand of this segment? 5'-CGCATGTAGCGA-3' 3'-GCGTACATCGCT-5' 3'-CGCATGTAGCGA-5' 5'-GCGTACATCGCT-3'

3'-CGCATGTAGCGA-5'

In a cross of AaBb x AaBb, what fraction of the offspring can be expected to express one of the two dominant alleles, but not both? 9/16 3/8 1/2 3/16

3/8

Suppose the brown allele for eye color (B) is completely dominant over the blue allele for eye color (b). If two brown-eyed parents produce a child that is blue-eyed, what is the probability that at least one out of the next two children they produce will also have blue eyes? 44% 12.5% 50% 25%

44% The probability of having zero children with blue eyes is ¾*¾=9/16. 9/16 ≈ 56%. This is the probability of having zero children with blue eyes. The probability of having at least one child with blue eyes is the opposite (or complement) of this: 100% - 56% = 44% Scratchpad

Deacetylation of histones has which of the following effects? -Coiling of the histone structure, allowing it to be accessed by transcriptional machinery -Coiling of the histone structure, preventing it from being accessed by transcriptional machinery -Uncoiling of histone structure, preventing it from being accessed by transcriptional machinery -Uncoiling of histone structure, allowing it to be accessed by transcriptional machinery

-Coiling of the histone structure, preventing it from being accessed by transcriptional machinery

Which of the following is NOT a function of the 5' terminus of mRNA? -Protects the mRNA from degradation -Regulates nuclear export of mRNA -Promotes ribosomal binding for translation -Promotes polyadenylation of the 3' terminus

-Promotes polyadenylation of the 3' terminus

The active site model (also called the lock and key model) of enzyme-substrate binding differs from the induced fit model in which of the following ways? -The induced fit model holds that the shape of the active site is permanently altered by substrate binding -The induced fit model holds that enzyme-substrate binding does not take place at the enzyme's active site -The induced fit model holds that the shape of the substrate is irrelevant to enzyme-substrate binding -The induced fit model holds that the shape of the active site is altered during the course of substrate binding

-The induced fit model holds that the shape of the active site is altered during the course of substrate binding

A non-conservative mutation is one in which: -The new amino acid has different biochemical properties than the original -A frameshift has occurred, causing production of a new amino acid -A large segment of DNA is deleted -No effect results in the protein

-The new amino acid has different biochemical properties than the original

In a bacteria possessing the lac operon, which of the following occurs when glucose is low and lactose is abundant? -Beta-galactosidase acetylases the operon -Lactose permease cleaves lactose to glucose and galactose -Lactose metabolism is increased by lactose binding to the operon -Transport of lactose into the cell is enhanced

-Transport of lactose into the cell is enhanced

In pea plants, the allele for tall stalks (T) is dominant over the allele for short stalks (t). Suppose a cross between a tall pea plant and a short pea plant produces 43 tall offspring and 47 short offspring. If one of the tall offspring is crossed with one of the short offspring, what ratio of genotypes would be most likely in their offspring? 1 TT : 2 Tt : 1 tt All Tt 3 Tt : 1 tt 1 Tt : 1 tt

1 Tt : 1 tt

In labrador retrievers, the allele for black coat color (B) is dominant to the allele for brown coat color (b). However, if a lab has two copies of the recessive allele for a pigment-depositing gene (e), it can only have yellow coat color. In a cross of two doubly heterozygous black labs (BbEe x BbEe), what fraction of the next generation would one expect to be yellow? 1/8 1/4 1/16 3/16

1/4

The X-linked recessive trait of color-blindness is present in 5% of males. If a mother who is a carrier and father who is unaffected plan to have 2 children, what is the probability the children will both be male and color-blind? 50% <1% 25% 6.25%

6.25% There is a 50/50 chance each child will be male. The probability of having 2 males is .5 * .5 = .25 = 25%. Each male receives only 1 X-chromosome and it must come from the mother since the Y chromosome can only come from the father. Since the mother is a carrier, there is a 50/50 chance she will pass on the gene for color-blindness to each male child and a 25% chance she will pass it on to both. Combining the last two hints, we know there is a 25% chance of having two sons and a 25% chance of two sons being colorblind. To find the probability of both these events happening we multiply them together: 25% * 25% = ¼ * ¼ = 1/16 = 6.25%.

Electrophoretic separation of leucine from a protein sample would be least effective at which of the following pH values? 1.4 7.4 2.4 0.4

7.4 Leucine has an aliphatic side chain (carbon-carbon straight chain) at physiological pH, leucine exists as a zwitterion electrophoretic separation of leucine from a protein sample would be least effective at pH 7.4

What is an operon? -A protein that binds to an RNA segment and blocks the attachment of DNA polymerase, halting transcription -A reversibly-bound protein that enhances the transcription of a particular segment of RNA -A protein around which DNA is coiled until it is transcribed; also the chief protein component of chromatin -A unit of DNA containing a cluster of genes under control of a promoter and a repressor

A unit of DNA containing a cluster of genes under control of a promoter and a repressor

Which of the following has a net negative charge at physiological ph (7.4)? A) Glutamic Acid B) Histadine C) Asparagine D) Lysine

A) Glutamic Acid acids have a negative charge at physiological pH

S-Adenosyl methionine (SAM) is a molecule utilized in various metabolic pathways to transfer methyl groups from SAM to an acceptor. What is the proper designation of the complex of SAM and its enzyme together? A) Holoenzyme B) Prosthetic group C) Cofactor D) Coenzyme

A) Holoenzyme - SAM would be like acetyl-CoA which is a coenzyme - coenzyme is a type of cofactor - cofactor + enzyme = holoenzyme

Certain bacteria synthesize toxic proteins which are responsible for many of the problems they cause in humans. If you were to develop a drug designed to inhibit bacterial protein synthesis without interfering with normal human protein synthesis, what might be a logical target for the drug? A) Ribosomes B) Golgi apparatus C) RNA D) DNA

A) Ribosomes bacteria don't have a golgi drug targeting RNA/DNA would have undesired effects on human nucleic acids humans & bacteria use different types of ribosomes

Under which of the following conditions would one expect ATP hydrolysis to be non-spontaneous? A very basic environment (high concentration of proton acceptors) A temperature slightly below 37 C. ATP concentrations very far below equilibrium concentration, and ADP concentrations very far above equilibrium concentration No enzymes available to lower activation energy

ATP concentrations very far below equilibrium concentration, and ADP concentrations very far above equilibrium concentration Hint ATP hydrolysis is always spontaneous under standard conditions. It may or may not be spontaneous under conditions that deviate from those defined as standard. All chemical reactions, regardless of what conditions they occur in, will seek to establish equilibrium concentrations of products and reactants.

In sickle-cell disease, a glutamate →valine substitution results in formation of HbS molecules, which: Aggregate abnormally and cannot adequately carry O2 Have abnormally high-affinity binding for O2 Stabilize the wall of the red blood cell against oxidative damage Cause experience high levels of repulsion between neighboring HbS molecules

Aggregate abnormally and cannot adequately carry O2

Local conditions can affect the specificity of an enzyme for its substrate, and thus the enzymes catalytic ability: which of the following alterations would most likely not affect an enzyme in this manner? A) Increased temperature B) Increased substrate concentration C) Increased concentration of H+ D) Increased concentration of OH-

B) Increased substrate concentration - the specificity of an enzyme for its substrate is partially governed by the shape of the enzyme active site. - an enzyme active site is stabilized by non-covalent intramolecular interactions - non-covalent intramolecular interactions are affected by heat & pH, amongst other things - alterations in substrate concentration would not affect the specificity of an enzyme for its substrate

Which of the following properties of a protein is least likely to be affected by changes in pH? A) Tertiary structure B) Primary structure C) Net charge D) Secondary structure

B) Primary Structure Changes in pH will not alter amino acid sequence or break peptide bonds. However charges will change which can affect higher order structures

A polypeptide with a net positive charge at physiological pH most like likely contains amino acid with what R group? A) Aromatic B) Basic C) Aliphatic D) Acidic

Basic

In what direction is DNA synthesized when catalyzed by either DNA polymerase or reverse transcriptase? -Both DNA polymerase and reverse transcriptase catalyze the synthesis of DNA in the 5' to 3' direction -DNA polymerase catalyzes the synthesis of DNA in the 5'→3' direction, while reverse transcriptase catalyzes the synthesis of DNA in the 3'→5' direction -Both DNA polymerase and reverse transcriptase catalyze the synthesis of DNA in the 3' to 5' direction -DNA polymerase catalyzes the synthesis of DNA in the 3'→5' direction, while reverse transcriptase catalyzes the synthesis of DNA in the 5'→3' direction

Both DNA polymerase and reverse transcriptase catalyze the synthesis of DNA in the 5' to 3' direction

The unique cyclic structure of which of the following amino acids plays a central role in the formation of alpha helices and beta sheets? A) Valine B) Serine C) Proline D) Methionine

C) Proline Plays a central role in the FORMATION of alpha helices & beta sheets. While the unique structure can also disrupt both alpha helices and beta sheets, its ability to make sharp turns facilitates the FORMATION of both structures, with proline commonly being found at the beginning of alpha helices or at the turns in beta sheets.

A new drug is developed which selectively cleaves covalent bonds between 2 sulfur atoms of non-adjacent amino acids in a polypeptide chain. Which level of protein structure in affected molecules would be most directly affected by the drug? A) Primary structure B) Quaternary structure C) Tertiary structure D) Secondary structure

C) tertiary structure

Glucose is oxidized to what molecule during cellular respiration? Water Carbon dioxide ATP Oxygen

Carbon dioxide

What is the rate limiting step in the production of energy from free fatty acids? Degradation of acetyl-CoA to enter the Krebs cycle Dehydrogenation of fatty acyl-CoA Carnitine acyl-transferase activity β-oxidation within the mitochondrial matrix

Carnitine acyl-transferase activity Hint The utilization of fatty acids is a coordinated balance of synthesis and oxidation, which is tightly regulated. When carbohydrate sources of energy are readily available (glucose), the metabolism of acetyl-CoA yields malonyl-CoA. In great abundance, malonyl-CoA induces the synthesis of fatty acids. In addition to its contribution to fatty acid synthesis, malonyl-CoA also inhibits fatty acid oxidation at a key regulatory point. Malonyl-CoA inhibits carnitine acyl-transferase I on the outer mitochondrial membrane. The carnitine-mediated entry of fatty acids into the mitochondria (carnitine shuttle) is the the limiting step in β-oxidation.

A gene for corn has two alleles, one for yellow kernels and one for white kernels. Cross pollination of yellow corn and white corn results in ears of corn that have an approximately even mix of yellow and white kernels. Which term best describes the relationship between the two alleles? Genetic recombination Incomplete dominance Chimerism Codominance

Codominance

Molecule 'X' is an enzyme inhibitor that reversibly binds to an enzyme at a site that is distinct from its active site. Molecule 'X' must NOT be what type of inhibitor? Mixed inhibitor Uncompetitive inhibitor Competitive inhibitor Noncompetitive inhibitor

Competitive inhibitor

Molecule 'X' is an enzyme inhibitor that reversibly binds to an enzyme at a site that is distinct from its active site. Molecule 'X' must NOT be what type of inhibitor? Uncompetitive inhibitor Competitive inhibitor Mixed inhibitor Noncompetitive inhibitor

Competitive inhibitor

The effect of allolactose is: -Dissociation of RNA polymerase from DNA, terminating transcription of genes regulated by the lac operon -Conformational change in the repressor protein, inducing the lac operon -Repression of the lac operon when glucose is present -Enhancement of binding of RNA polymerase to DNA, increasing gene transcription

Conformational change in the repressor protein, inducing the lac operon Allolactose is not involved in the relationship of RNA polymerase and DNA. Nor does allolactose deactivate the lac operon when glucose is present.

What is the benefit of anti-oxidant compounds? Reverse existing mutations resulting from reactive oxygen species Diminish direct damage of O2 on red blood cells Catalyze production of free-radicals in the cell Counteract the actions of damaging reactive oxygen species

Counteract the actions of damaging reactive oxygen species

What constitutes the phosphodiester bonds in DNA? Covalently linked nucleotides Hydrogen bonds between complementary strands Covalently linked amino acids Hydrogen bonds between nucleosides

Covalently linked nucleotides

A nonsense mutation is one that: Changes an amino acid from one to another Creates a premature stop codon Deletes segments of RNA Adds an additional codon to an RNA transcript

Creates a premature stop codon

Hydrogen bonding between separate subunits of DNA polymerase is an example of which of the following? A) 1 degree structure B) 2 degree structure C) 3 degree structure D) 4 degree structure

D) 4 degree structure Primary, secondary and tertiary structure have to do with individual polypeptides 4th degree structures are interactions between separate subunits -- 4 degree structure refers to the global 3-D arrangements found in multi-subunit proteins.

What relative change in protein concentrations would be the most direct result of a disease which halts the function of the rough endoplasmic reticulum? A) Increased concentrations of intracellular proteins B) Decreased concentrations of intracellular proteins C) Increased concentrations of extracellular proteins D) Decreased concentrations of extracellular proteins

D) Decreased concentrations of extracellular proteins ribosomes are either free floating in cytoplasm or bound to the RER Proteins translated freely in the cytoplasm tend to remain within the cell as cytoplasmic proteins Proteins translated on the RER are further modified as they enter the ER, bud from it through a vesicle, move progressively through Golgi to plasma membrane Ribosomes on RER synthesize membrane & secretory proteins.

Intercalation of ethidium bromide into DNA results in: Deformation of the DNA molecule Displacement of RNA polymerase Constitutive expression of oncogenes Missense mutations

Deformation of the DNA molecule Ethidium bromide does not cause missense mutations. Ethidium bromide does not interact with RNA polymerase.

Based on their compositional differences, different lipoproteins serve very different biological roles; what physical quality of lipoproteins most likely determines their function? Volume Shape pH Density

Density Lipoproteins are the spherical carrier molecular assemblies in which lipids are transported throughout the body. Examples include HDL, LDL, and chylomicrons. The functional properties of lipoproteins are largely determined by which apolipoproteins they express, as apolipoproteins are important signalling molecules for receptor-mediated recognition. Apolipoproteins are simply lipoproteins unbound to lipids. Different apolipoproteins will bind lipids in a different fashion, resulting in a difference in the ratio of lipid content to protein content. A high lipid content relative to a low protein content would be much less dense than a lipoprotein with a high protein content.

From where are the nine essential amino acids utilized by humans derived? De novo synthesis only Both exogenous and endogenous sources None of the above Dietary protein only

Dietary protein only

The antibiotic doxycycline is known to bind and inhibit a particular ribosomal subunit to inhibit bacterial proliferation. How might this affect the 80S ribosome in human cells versus the 70S subunit in prokaryotes and why? -Doxycycline would inhibit human ribosome function by binding the 30S subunit, because both humans and prokaryotes share the 30S subunit -Doxycycline would not affect human ribosomes, because human ribosomes are made up of 30S and 50S subunits while prokaryotic ribosomes are made up of 30S and 40S subunits -Doxycycline would not affect human ribosomes, because human ribosomes are made up of 60S and 40S subunits while prokaryotic ribosomes are made up of 50S and 30S subunits -Doxycycline would inhibit human ribosome function by binding the 40S subunit, because both humans and prokaryotes share the 40S subunit

Doxycycline would not affect human ribosomes, because human ribosomes are made up of 60S and 40S subunits while prokaryotic ribosomes are made up of 50S and 30S subunits

Cellular respiration involves the flow of electrons from one chemical species to another: which of the following best describes this process? Electrons from glucose are ultimately transferred to carbon dioxide Electrons from glucose are ultimately transferred to oxygen Electrons from oxygen are ultimately transferred to water Electrons from oxygen are ultimately transferred to glucose

Electrons from glucose are ultimately transferred to oxygen

What is the basic order of events in the digestion and mobilization of dietary fats? Emulsified by bile→ degradation by lipases→ absorption and conversion into triacylglycerols→ incorporation into chylomicrons Degradation by lipases→ absorption and conversion into triacylglycerols→incorporation into chylomicrons→ emulsified by bile Degradation by lipases→ emulsified by bile→ incorporation into chylomicrons→ absorption and conversion into triacylglycerols Emulsified by bile→ incorporation into chylomicrons→ absorption and conversion into triacylglycerols→ degradation by lipases

Emulsified by bile→ degradation by lipases→ absorption and conversion into triacylglycerols→ incorporation into chylomicrons

Nitric oxide (NO) is an important cardiovascular signaling molecule. It has also been implicated in DNA mutations in bacteria and in human cells, though these mutations are not always associated with cancer formation. Therefore, NO would be an example of an: Exogenous carcinogen Exogenous mutagen Endogenous carcinogen Endogenous mutagen

Endogenous mutagen NO is produced by the body, and therefore is an endogenous compound. Not all mutagens are carcinogens, and NO has not been consistently shown to be a carcinogen.

Pyrimidine dimers resulting from UV light damage to DNA are removed from sequences via the action of what class of enzymes? Polymerases Ligases Helicases Endonucleases

Endonucleases Helicases 'unzip' DNA helices. Polymerases synthesize nucleic acids, for example DNA polymerase catalyzes the synthesis of DNA. Ligases join two separate nucleic acid strands by the formation of a phosphodiester bond. Endonucleases cleave specific sequences of DNA, such as pyrimidine dimers resulting from UV light damage to DNA.

What is the role of an activator? Binds to an operon and transcribes RNA Displaces a repressor protein from an operon, allowing RNA polymerase to proceed in transcription Enhances interaction between RNA polymerase and the promoter Causes conformational changes in the DNA, bringing promoter regions into proximity with enhancer regions

Enhances interaction between RNA polymerase and the promoter An activator does not interact with repressor proteins. Nor does the activator perform the actual act of transcription. The activator's role is to enhance the interaction between the promoter region and RNA polymerase, usually by binding a promoter-proximal element.

A point mutation within what functional division of a DNA sequence would be most likely to ultimately result in the production of proteins which differ from the non-mutated form by only a single amino acid? Centromeres Exons Introns Telomere

Exons

Which association between complementary bases would require the most energy to break (has the highest bond dissociation energy)? Please choose from one of the following options. A:U G:C All are equal A:T

G:C

Micro RNA (miRNA) primarily aids in transcriptional and post-transcriptional regulation by which method? -Gene silencing through translational repression or target degradation -Cleavage of telomeres from 5' termini -RNA editing via deamination of specific DNA sequences -Gene amplification through binding directly to critical DNA promoter regions

Gene silencing through translational repression or target degradation Recall that microRNA does bind directly to mRNA, however it does not bind to promoter regions. miRNA has no role in RNA editing or cleavage of telomeres. The role of miRNA is to cause repression or degradation of the target through mRNA binding.

A deficiency of oxaloacetate would most likely increase the catabolism of what potential energy source? Glucogenic amino acids Acetyl-CoA Acetoacetyl-CoA Ketogenic amino acids

Glucogenic amino acids Hints Oxaloacetate (OAA) is an important intermediate in the citric acid cycle and in gluconeogenesis. OAA is principally formed from either malate or pyruvate. Ketogenic amino acids, as well as fatty acids, are principally metabolized to form acetyl-CoA. Glucogenic amino acids enter the citric acid cycle at multiple points, with the common theme of ultimately producing glucose. Many glucogenic amino acids are catabolized to pyruvate, or directly to form OAA. A deficiency of oxaloacetate would most likely increase the catabolism of glucogenic amino acids.

An individual presenting with a mysterious disease affecting his connective tissues is found to have numerous defects in multiple regulatory proteins. If these proteins are characterized by highly abnormal patterns of glycosylation, to what structure might the patient's disease most likely be attributed? Mitochondria Golgi apparatus Lysosome Ribosome

Golgi apparatus Mitochondria are the site of cellular respiration, and are essentially 'power plants' of the cell. Lysosomes are pretty much just cellular trash cans (and recycling centers). The ribosome is the site of translation of mRNA into protein. However it is not a site of glycosylation. This patient may have a disorder which is affecting the function of their golgi apparatus.

Approximately how many molecules of ATP can be produced from the oxidation of a 20 carbon fatty acid, including those produced in the Krebs cycle? 107 129 136 100

Hint Start simple-- a 20 carbon FA will yield 10 molecules of acetyl-CoA (20 carbons available, two carbons per acetyl-CoA). Recall that for each acetyl-CoA, the Krebs cycle produces 10 molecules of ATP. Remember that the process of oxidizing fatty acids to form molecules of acetyl-CoA also generates energy. Each pass of β-oxidation generates one molecule of NADH and one molecule of FADH_2 To produce 10 acetyl-CoA, this fatty acid will require 9 passes of oxidation. 2.5 ATP can be generated per NADH, and 1.5 ATP per FADH_2 2.5x9= 22.5; 1.5x9= 13.5; 13.5+22.5+100 = 136 Approximately 136 molecules of ATP can be produced from the oxidation of a 20 carbon fatty acid, including those produced in the Krebs cycle.

A gene, TALL, has recently been discovered that helps control the height that people will reach and results in taller than average height. Which of the following statements about this gene's heritability are true? If TALL has 25% penetrance, it must be autosomal recessive If TALL has 50% penetrance, then only half the population has the TALL gene If TALL has variable expressivity, everyone with the TALL gene will be tall If TALL has constant expressivity, every cell in the body will express the TALL protein

If TALL has variable expressivity, everyone with the TALL gene will be tall If TALL has variable expressivity, everyone with the TALL gene will be tall

Suppose a white-furred rabbit breeds with a black-furred rabbit and all of their offspring have a phenotype of gray fur. What does the gene for fur color in rabbits appear to be an example of? Complete dominance Codominance Mosaicism Incomplete dominance

Incomplete dominance

Assuming all other reaction conditions remain constant and that the reaction is allowed to proceed to equilibrium, how would the reaction S⇋P be affected by the addition of an enzyme catalyst? Both increased reaction rate and increased formation of product Increased total product formed Neither increased reaction rate or increased formation of product Increased reaction rate

Increased reaction rate

A proto-oncogene can be converted to an oncogene by all of the following EXCEPT: Increased repressor binding Chromosomal rearrangement Gene deletions Gene amplification

Increased repressor binding A proto-oncogene can become oncogenic by deletions in the gene, or by chromosomal rearrangements. Any increase in protein expression can contribute to oncogenicity, and this can be caused by gene amplification. Increased repressor binding is unlikely to cause oncogenic conversion, as this will result in decreased protein generation

Local conditions can affect the specificity of an enzyme for its substrate, and thus the enzymes catalytic ability: which of the following alterations would most likely not affect an enzyme in this manner? Increased concentration of H+ Increased temperature Increased concentration of OH− Increased substrate concentration

Increased substrate concentration The specificity of an enzyme for its substrate is partially governed by the shape of the enzyme active site. An enzyme active site is stabilized by non-covalent intramolecular interactions. Non-covalent intramolecular interactions are affected by heat and pH, amongst other things. Alterations in substrate concentration would not affect the specificity of an enzyme for its substrate.

Phosphoglucomutase, which catalyses the formation of glucose-6-phosphate from glucose-1-phosphate, is best classified as which of the following enzyme type? Kinase Oxidoreductase Isomerase Lyase

Isomerase---glucose-6-phosphate is an isomer of glucose-1-phosphate.

At what point during normal DNA replication is genetic material lost from the telomeres? -Attachment of DNA polymerase to the leading strand -Joining of adjacent Okazaki fragments -Enzymatic action of telomerase -"Unzipping" by DNA helicase

Joining of adjacent Okazaki fragments Telomeres are the 'caps' at either end of a chromatid, which protects the DNA from deterioration. It has been theorized that telomere length is inversely correlated with the aging process (shorter telomeres = aging). The shortening of telomeres is due to the 'end replication problem'. This problem arises from the fact that DNA polymerase synthesizes DNA only in the 5' to 3' direction. One strand (the leading strand) is read without interruption, but the lagging strand must be synthesized in a discontinuous fashion. Okazaki fragments are pieces of newly synthesized DNA along the lagging DNA strand, separated by RNA primers. The final RNA primer at the terminal end of the new strand cannot be converted to DNA by DNA polymerase and joined to the strand by DNA ligase, because there is nowhere for these enzymes to bind. As such, this last primer is degraded, and thus each successive DNA copy is slightly shorter than the last.

What are the major products of amino acid catabolism? Ketone bodies and tetrahydrofolate Glucose and tetrahydrofolate Tetrahydrofolate and glycogen Ketone bodies and glucose

Ketone bodies and glucose Hints There are two main pathways by which amino acids are metabolized. The two groups are defined by the end products of the amino acids degraded. One group is degraded to acetoacetyl-CoA and/or acetyl-CoA. The other is degraded to pyruvate, α-ketoglutarate, succinyl-CoA, fumarate and/or oxaloacetate. The amino acids contributing to each of these pathways are called ketogenic or glucogenic, respectively.

The amino acids in hemoglobin (or any protein) uniformly have which of the following configurations? A) D B) L C) S D) R

L Configurations (either relative or absolute) refers to the stereochemical configuration around the chiral carbon. Due the differences in the priority of different side chains, not all amino acids have the same "Absolute Configuration" which refers to the R/S naming convention. Some amino acids are R, some are S. However, all amino acids have the same "Relative Configuration" which refers to the D/L naming convention. All biologically produced AA's are in the L configuration.

Which of the following enzyme types catalyzes the formation of a single bond between two substrates through the elimination of H2O Isomerase Hydrolase Ligase Oxidoreductase

Ligase

What chemical properties describe a free fatty acid molecule capable of producing the most energy when used as a fuel source, relative to other free fatty acids? Longer hydrocarbon tail with a lesser number of unsaturated bonds Shorter hydrocarbon tail with a greater number of unsaturated bonds Shorter hydrocarbon tail with a lesser number of unsaturated bonds Longer hydrocarbon tail with a greater number of unsaturated bonds

Longer hydrocarbon tail with a lesser number of unsaturated bonds

What is the functional relationship between codons and amino acids? -Many different codons may code for the same amino acid -Codons and amino acids randomly associate around a particular tRNA -A single codon may code for many different amino acids -A given amino acid is only coded for by a single codon

Many different codons may code for the same amino acid

A silent mutation is highly unlikely to affect protein because: -The silent mutation does not cause a frameshift -Multiple codons can code for the same amino acid -The silent mutation substitutes the same type of amino acid -The dominant allele can compensate for the silent mutation

Multiple codons can code for the same amino acid

Which type of mutation results in the sickle-cell disease phenotype? Conservative mutation Non-conservative missense mutation Frameshift mutation Codon deletion

Non-conservative missense mutation A conservative mutation might result in conservation of the hemoglobin protein's function, therefore this is not the correct choice. A codon deletion could potentially result in a change in the protein, however that is not the mutation causing sickle cell disease. The glutamate→ valine substitution is a non-conservative missense mutation.

Electrophoretic separation at pH 6 of a sample of polypeptide 1 (mw 100) polypeptide 2 (mw 200) and polypeptide 3 (mw 400) would result in which of the following? (Note: the isoelectric point of each polypeptide occurs at pH 6) A) Polypeptide 2 would move the farthest B) None of the polypeptides would move C) Polypeptide 3 would move the farthest D) Polypeptide 1 would move the farthest

None of the polypeptides would move Isoelectric point for a polypeptide is the pH at which the molecule does not have a net charge. Separation happens depends on the presences of a negative charge

All hydrophobic amino acids (valine, leucine, isoleucine, etc.) share which of the following properties? Polar uncharged R groups Basic R groups Nonpolar uncharged R groups Acidic R groups

Nonpolar uncharged R groups

With respect to the binding of regulatory compounds, what properties define an enzyme as being allosteric? Reversible, covalent binding of regulatory compounds Irreversible, noncovalent binding of regulatory compounds Reversible, noncovalent binding of regulatory compounds Irreversible, covalent binding of regulatory compounds

Reversible, noncovalent binding of regulatory compounds

Given that ∆G'° for the reaction S⇋P is negative in the direction of S→P, reaction equilibrium favors the formation of which substance? The reaction proceeds equally in both directions S The reaction does not proceed in either direction P

P

Enzymes undergo a decrease in catalytic efficiency in the presence of excess temperature, but can regain this efficiency once temperature returns to normal: this suggests that increased temperature does not disrupt which of the following aspects of enzyme structure? Van der Waal's forces Hydrophobic interactions Peptide bonds Hydrogen bonds

Peptide bonds Enzymes are strings of amino acids joined by peptide bonds. Heat disrupts non-covalent interactions between amino acids in the enzyme, resulting in the denaturation of enzyme structure. Increased temperature does not disrupt peptide bonds.

Suppose that in barley plants, the allele for tall stalks is dominant over short stalks and the allele for wide leaves is dominant over thin leaves. What would be the best way to determine the genotype of a barley plant with a tall stalk and wide leaves? Perform a testcross with a barley plant that has a tall stalk and wide leaves Perform a testcross with a barley plant that has a short stalk and thin leaves Perform a testcross with a known heterozygous barley plant Perform a testcross with a barley plant that has a tall stalk and thin leaves

Perform a testcross with a barley plant that has a short stalk and thin leaves

Please review Chromosomal Inheritance questions on Khan

Please review Chromosomal Inheritance questions on Khan

With respect to the binding of regulatory compounds, what properties define an enzyme as being allosteric? Irreversible, covalent binding of regulatory compounds Irreversible, noncovalent binding of regulatory compounds Reversible, noncovalent binding of regulatory compounds Reversible, covalent binding of regulatory compounds

Reversible, noncovalent binding of regulatory compounds

A researcher was doing test crosses on mice, but forgot which mice he had bred together. When the litter was born, every mouse had black eyes, and half had brown fur. What was the genotype of the parent mice? R = red fur; r = brown fur B = black eyes; b = brown eyes RrBB x Rrbb rrBb x RRBB RrBb x rrBB RrBb x RrBb

RrBb x rrBB

If the enzyme-catalyzed reaction E + S ⇋ ES ⇋ E + P is proceeding at or near the V_{max} ​max ​​ start subscript, m, a, x, end subscript of E, what can be deduced about the relative concentrations of S and ES? S is abundant, [ES] is vanishingly low S is abundant, [ES] is at its highest point [S] is vanishingly low, [ES] is vanishingly low [S] is vanishingly low, [ES] is at its highest point

S is abundant, [ES] is at its highest point At vmax, the reaction is proceeding at a rate which is equal to the physiologic rate at which the enzyme can function. At Vmax the enzyme is fully saturated, and no more free enzyme is available to bind the substrate and catalyze the reaction. If all of the enzyme, E, is bound and operating, it must all exist in the ES state. In order to maintain Vmax there must be sufficient substrate for the enzyme to bind, so [S] must be high enough to sustain this saturated state.

Methylation of CpG islands is essential to which process(es)? -Enhancing cell differentiation into different organ systems with distinct functions -Reversible inactivation of genes as cells terminally differentiate -Stable silencing of DNA as cells terminally differentiate -Enhancing oncogenic potential of rapidly-differentiating cells

Stable silencing of DNA as cells terminally differentiate CpG methylation diminishes the oncogenic potential of cells. CpG island methylation does not have a role in the differentiation of cells. However, once cells are done differentiating, their DNA needs to be turned off, or silenced. CpG methylation permanently, or stably, silences the DNA of cells that have completed the process of differentiation.

What does it mean to say that ATP hydrolysis is a spontaneous chemical reaction? That the reaction does not require an input of energy to proceed That the products of the reaction have lower free energy than the reactants That the products of the reaction have higher free energy than the reactants That the reaction requires an input of energy to proceed

That the products of the reaction have lower free energy than the reactants

Enzymes catalyze biochemical reactions by altering which of the following quantities associated with the reaction? The enthalpy of formation ΔH The change in Gibb's free energy Δ The activation energy Ea The equilibrium constant K​eq ​​

The activation energy Ea

Where within the eukaryotic cell might a drug which exclusively binds to tRNA binding sites exert its effects? The nucleus The mitochondrial inner membrane The lysosome The cytosol

The cytosol

In order to analyze the catalytic effect of two different enzymes on the same chemical reaction, it is best to compare which of the following quantities? -The difference between transition state energies -The differences in free energy between the reactants and products -The differences in entropy between the reactants and products -The differences in enthalpy between the reactants and products

The difference between transition state energies Denaturation of an enzyme will alter the kinetics of a reaction that it catalyzes. The kinetics of a reaction can be characterized by a rate-constant. Denaturation of E is most likely to affect the rate-constant associated with X.

How does the free energy (G) of a system containing one mole of ADP compare to the free energy of a system containing one mole of AMP under standard physiological conditions? The free energy of the ADP system is negative and less than the free energy of the AMP system, which is also negative The free energy of the ADP system is positive and greater than the free energy of the AMP system, which is also positive The free energy of the AMP system is positive and greater than the free energy of the ADP system, which is also positive The free energy of the ADP system is positive; the free energy of the AMP system is negative

The free energy of the ADP system is positive and greater than the free energy of the AMP system, which is also positive. Hint The free energy of a system can never be negative. Remember, free energy (G) is not the same as free energy change (∆G). ADP contains one more phosphoanhydride bond than AMP.

If two genes experience independent assortment, which assumption is most likely true? -The expression of one gene does not affect the expression of the other. -Crossing over between the genes does not occur. -They are located in close proximity on the same chromosome. -The genes are located on different chromosomes or are far apart on the same chromosome.

The genes are located on different chromosomes or are far apart on the same chromosome. expression and assortment are different

ATP hydrolysis under standard biochemical conditions has ∆G < 0, implying which of the following about the reaction under these conditions? The hydrolysis reaction is spontaneous The hydrolysis reaction is exothermic The hydrolysis reaction decreases entropy Cleavage of the phosphoanhydride bond that occurs during hydrolysis does not require the input of energy

The hydrolysis reaction is spontaneous Hint Cleaving a covalent bond always requires an input of energy. Exergonic reactions are not necessarily exothermic: entropy matters as well. As a rule of thumb, if a reaction has more products than reactants, entropy is usually positive.

A cross between two pea plants with genotypes PpLl and PpLl results in an F1 generation that is 25% PPLL, 50% PpLl, and 25% ppll. Which reason most likely explains why other possible genotypes are not present? The genes underwent independent assortment The loci of the genes are close together. The loci of the genes are on different chromosomes. Crossing over occurred between chromosomes.

The loci of the genes are close together

Which of the following best predicts the result of raising the pH of an equilibrium mixture for the exergonic reaction of ATP hydrolysis The reaction is pushed to the left, and the entropy of the system increases The reaction is pushed to the right, and the entropy of the system decreases The reaction is pushed to the left, and the entropy of the system decreases The reaction is pushed to the right, and the entropy of the system increases

The reaction is pushed to the right, and the entropy of the system increases Hint Le Châtelier's principle implies that if you remove a product from a reaction at equilibrium, more product will be produced until equilibrium is reestablished. Raising the pH of a mixture increases the amount of proton-accepting hydroxide molecules. As a rule of thumb, if a reaction has more products than reactants, the entropy of a system has usually increased.

The induced fit model of enzyme binding states that which of the following molecules alters the enzyme active site to more closely match the shape of the substrate? An allosteric effector A cofactor The substrate A coenzyme

The substrate A substrate for an enzyme is the reactant of the reaction that the enzyme catalyzes. An enzyme and a substrate must come into close physical proximity for binding to occur, and such proximity can introduce physical forces that alter the shape of the enzyme. The induced fit model of enzyme binding states that the substrate itself alters the enzyme active site.

What is the function of the spliceosome? -To condense DNA into small, manageable units -To cleave introns from RNA and ligate the cut ends -To cleave telomeres prior to transcription -To cause conformational changes in DNA that are amenable to splicing

To cleave introns from RNA and ligate the cut ends

How do the majority of fatty acids enter the outer membrane of the mitochondria? Transferase facilitated entry of free fatty acids Free diffusion of carnitine bound fatty acids Transferase facilitated entry of carnitine bound fatty acids Free diffusion of hydrophobic free fatty acids

Transferase facilitated entry of carnitine bound fatty acids Hint Even though they are predominantly hydrophobic, most dietary fatty acids are too large for free diffusion across membranes, which presents a kinetic barrier to their transport. Although a high FFA concentration outside of a cell may establish a gradient such that their transport into the cell is energetically favorable, the energy required for the movement of large molecules is substantial. Coupling the transfer of large molecules to energetically favorable reactions allows this barrier to be overcome. Three reactions allow for FA entry into the mitochondria, in a process known as the carnitine shuttle. First, acyl-CoA synthetase links coenzyme A with the fatty acid, made favorable by the hydrolysis of two bond in ATP (to make AMP). Second, fatty acid acyl-CoA is attached to carnitine via carnitine acyltransferase I, and the acyl-carnitine enters the outer membrane. The majority of fatty acids enter the outer membrane of the mitochondria via transferase facilitated entry of carnitine bound fatty acids.

What of the following provides the best evidence that DNA is the genetic material? Biomolecular composition of chromosomes Mechanism of semi-conservative DNA replication Transformation using heat-inactivated bacteria Presence of DNA in all cells

Transformation using heat-inactivated bacteria

What dietary source of energy contains the most energy per gram (kcal/g)? Proteins Triglycerides Cellulose Disaccharides

Triglycerides

In the ABO blood group system in humans, if a person of type-B blood has children with a person of type-AB blood, what blood types could their children have? Type-B and type-AB Type-AB, type-A, type-B, and type-O Type-AB, type-A, and type-B Type-A and type-B

Type-AB, type-A, and type-B

Which of the following is true of large-scale deletions? -Less likely to be fatal than nucleotide-level mutations -Usually involve changes to DNA as well as to epigenetic mechanisms -Enhance silencing of important oncogenes due to altered methylation -More likely to result in frameshift mutations than small deletions

Usually involve changes to DNA as well as to epigenetic mechanisms Large-scale deletions are more likely to be fatal than small-scale deletions, since more genetic material is absent. Such large deletions could potentially reduce, not enhance, the methylation of important oncogenes. In addition to deleting important genetic material, large deletions are likely to affect some of the epigenetic mechanisms associated with genes, and not just the genes themselves.

Which of the following molecules cannot be classified as an enzymatic cofactor? Heme Mg2+ Flavin adenine dinucleotide (FAD) Valine

Valine A cofactor is a nonorganic molecule whose presence is necessary for the proper function of an enzyme. Valine is an organic molecule, namely an amino acid.

Oxygen is reduced to what molecule during cellular respiration? Water Carbon dioxide ATP Glucose

Water

A compound consists of approximately 72g carbon and 6g hydrogen. What is the empirical formula? a) C6H6 b) CHO c) CH d) C6H12

c) CH, correct. The empirical formula is the smallest whole-number ratio of the elements making up a molecule.

The alpha helix is an example of which of the following structural properties of proteins? tertiary structure secondary structure quaternary structure primary structure

secondary structure

The active site of an enzyme E, which catalyzes a reaction X, is partially denatured: which of the following quantities associated with X is most likely to be affected by the partial denaturation of E compared to the native form of E? the heat of reaction ΔH the boltzmann constant kB the equilibrium constant K​eq ​​the rate-constant k

​​the rate-constant k

How would the addition of a catalyst to the reaction S⇋P affect the difference between the free energies of S and P in their ground states (∆G'°)? The change in ∆G'° cannot be predicted without more information ∆G'° would become less negative ∆G'° would not change ∆G'° would become more negative

∆G'° would not change