DAT Question of the Day

Correct Answer: D. DNA polymerases require a primer base-paired to the template and with a free 3′-end.

DNA polymerase can add dNTPs (deoxynucleoside triphosphates) only to a pre-existing oligonucleotide chain that is annealed to the template DNA. The enzyme adds dNTPs on a free 3′-OH- group. Primers in replication are RNA based. These primers are then cut out via endonuclease activity and replaced with DNA nucleotides. Finally, DNA ligase fuses the gap between the fragments of DNA.

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Correct Answer: C. prevents glucose from leaking through the plasma membrane.

Glycolysis takes place in the cytosol. It is a characteristic of eukaryotic and prokaryotic cells. The first reaction of glycolysis is irreversible since it requires an energy investment. Glucose-6-phosphate cannot pass back through the plasma membrane.

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Correct Answer: C. a homozygous red haired cow

In genetics, a test cross is used to determine the genotype of an organism that expresses the dominant phenotype. The black cow could be BB or Bb for the black hair color. If you were to mate the cow with a homozygous black cow BB, all of the offspring would be black haired and this would not help the farmer determine the genotype of the original black cow. Likewise using a heterozygous black cow (Bb), could result in all black offspring, since there is only a 25% chance of getting a red haired cow if the original cow was heterozygous (Bb). A white cow nor an albino cow are not mentioned in the original question and would not be relevant in determining the genotype of the black cow. A test cross, uses a homozygous recessive individual, since this genotype is easily physically identified. If the 50% of the offspring are black and 50% are red, then the black cow was heterozygous (Bb). If all black offspring result, then the black cow was homozygous dominant (BB).

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Correct Answer: C. a nonsense mutation

A silent mutation often occurs in the wobble site of the codon on the mRNA strand. For most codons, if the third base pair is changed, the correct amino acid can still be made. A missense mutation results in the addition of an incorrect amino acid, but can still lead to a functional protein. Nonsense mutations result in a polypeptide chain that is shorter and is non-functional. For nonsense mutations, an insertion or deletion of a nucleotide base creates a premature stop codon (UGA, UAG, or UAA), terminating translation before the polypeptide can be completed. Transfer mutation is not an accurate term in biology.

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Correct Answer: A. Two squirrel populations separated by a river

In allopatric speciation, two species result due to the geographical barrier between the two species. Two birds living in different parts of the tree may result in two separate species over time, if the birds have different mating rituals or mating seasons. This would not be due to a geographical barrier and would be an example of sympatric speciation. Lion prides could still reproduce with one another especially since they inhabit the same area and climate. Insects with the same mating call would interbreed and this would not result in two different species over time. Similarly, two groups of dogs with different fur color should still be able to reproduce. However, two squirrel populations separated by a river may evolve into two different species over time, as the squirrels may be inhabiting different environments and are separated by the body of water.

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Correct Answer: A. radial

Spiral cleavage results in daughter cells after cell division, being located at an angle in relationship to each other. This is common in protostomes. Whereas radial cleavage results in the daughter cells after cell division being stacked on top of each other. Radial cleavage is seen in deuterostomes.

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Correct Answer: A. veins have valves

Veins carry blood to the heart, recollecting it from the body. Conversely, arteries carry blood away from the heart to the body. To prevent backflow and to promote the movement against gravity, veins have valves whereas arteries do not. Arteries also have very thick, muscular walls that enable pumping from the heart to the body. Veins are thinner in comparison and are not considered to have to “pump” blood or be under high pressure.

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Correct Answer: D. Sarcoplasmic reticulum

Calcium ions are essential for muscle contraction to occur. Without the release of calcium, the myosin head would be unable to bind to the actin at the binding sites. It is the calcium that binds and removes troponin from the myosin binding sites on the actin. This is done when the axon terminal nearest a muscle fiber releases acetylcholine, a neurotransmitter, which then causes the sarcoplasmic reticulum to release calcium into the muscle cell to allow for muscle contraction. The endoplasmic reticulum is responsible for protein modification following translation on a ribosome.

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Correct Answer: D. acrosome

The head of the sperm contains the acrosome, which has specialized enzymes that when released, help the sperm to penetrate and fertilize the egg. A plasmid is a small bacterium that can be used in recombinant DNA formation. The capsid is the protein coat that encapsulates a virus’ genetic material. The flagella are important for motility of the sperm but do not contain any enzymes.

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Correct Answer: C. Estrogen

Follicle stimulating hormone causes the follicle in the ovary to begin to divide to complete meiosis II. The growing follicle that will eventually release the egg during ovulation secretes estrogen. The estrogen then spurs the secretion of luteinizing hormone by the anterior pituitary gland, causing the follicle to rupture and release the egg. It is the estrogen and progesterone that is responsible for readying the endometrium for implantation should fertilization occur.

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