Chapter 7

Order the events that occur in one cycle of the polymerase chain reaction (PCR).

1) The reaction mixture is heated to 94 degrees C. 2) The double stranded DNA is denatured to form single stranded DNA 3) The temperature of the reaction mixture is lowered to allow the primers to anneal to the DNA template. The reaction mixture is heated to 72 degrees C. Taq polymerase extends the primer.

Label the indicated components of the DNA double helix.

1) major groove 2) minor groove 3) hydrogen bonds 4) sugar-phosphate backbone See Answer Image: https://i.imgur.com/YQ25VR2.jpg

Consider the information in the table. See Table: https://i.imgur.com/Mv0td6o.jpg Select the image that represents the structure of B‑form DNA.

B-Form DNA is the most commonly known DNA structure. A-Form DNA base-pairs are less centered. Z-Form DNA zig-zags. See Answer Image: https://i.imgur.com/VjJMm5Z.jpg

Identify whether the nucleotides shown contain a purine or pyrimidine base.

Left: Purine Middle: Pyrimidine Right: Pyrimidine See Answer Image: https://i.imgur.com/9lHjMB9.jpg

The diagram depicts the general structure of DNA, with a single nucleotide circled. Label the diagram with the names of the three components of a nucleotide.

Left: phosphate group Bottom Right: deoxyribose Top Right: nitrogenous base The Phosphate Group and the Nitrogenous Base are joined by Deoxyribose See Answer Image: https://i.imgur.com/7B61ET6.jpg

The diagram depicts the molecular structure of DNA. Label the diagram with the names of the three components of a nucleotide.

Left: phosphate group Middle: deoxyribose Right: nitrogenous base See Answer Image: https://i.imgur.com/l1rKFws.jpg

The diagram depicts the molecular structure of DNA. Label the diagram with the names of the components of the nucleic acid.

Left: sugar-phosphate backbone Middle: hydrogen bond Bottom Right: purine base Top Right: pyrimidine base See Answer Image: https://i.imgur.com/HlIS6vy.jpg

Arrange the features of eukaryotic chromosome packaging in order from the smallest unit to the largest unit.

Smallest Unit base pair nucleosome 30nm fiber chromosome genome Largest Unit See Answer Image: https://i.imgur.com/ArotZGm.jpg

DNA has unique properties that allow it to accurately retain genetic information, even after multiple rounds of replication. One aspect of DNA that allows it to accurately store genetic information is the base pairing from Chargaff's first rule of the four nucleotide bases. If the A content of a DNA molecule is 22%, what are the percentages of the remaining bases?

T = 22% G = 28% C = 28% See Answer Image: https://i.imgur.com/2Nl3owm.jpg

Label the components on the diagram of DNA structure by using all four of the provided terms.

Top Left: Chromosome Bottom Left: Chromatin Top Right: DNA Molecule Bottom Right: Protein See Answer Image: https://i.imgur.com/VQ5geZP.jpg

How many STRs are typically used to create a profile in forensic investigations?

☐ 25 ☐ 10 ☐ 2 ☐ 5 ☑ 15

If you start with one copy of a DNA fragment, how many rounds of PCR will it take to end up with a total of 32 copies?

☐ 31 ☐ 8 ☐ 16 ☑ 5 ☐ 4

The _____ chromosomes in a human cell from inside the cheek are found in the _____ .

☐ 46; cytoplasm ☐ 23; nucleus ☑ 46; nucleus ☐ 22; nucleus ☐ 24; cytoplasm

Which STR will have migrated farthest through an electrophoresis gel?

☐ AGCT repeated seven times ☐ GAAG repeated seven times ☐ GAAG repeated three times ☐ AGCT repeated five times ☑ GAAG repeated twice

If the sequence of one strand of DNA is AGTCTAGC, what is the sequence of the complementary strand?

☐ CGATCTGA ☑ TCAGATCG ☐ AGTCTAGC ☐ GCTAGACT ☐ GTCGACGC

Why is DNA replication called "semiconservative"?

☐ DNA is replicated, the process following strict base-pairing rules where A pairs with T and C pairs with G. ☐ DNA is replicated, each copy having one strand of DNA and one strand of RNA containing uracil. ☐ DNA is replicated, with one copy composed of the original molecule and one copy newly synthesized. ☐ DNA is replicated, the process always proceeding in a 5' to 3' direction and driven by polymerase molecules. ☑ DNA is replicated, each copy having one strand of the original molecule and one newly synthesized strand.

How is DNA stored in eukaryotic cells? Select the TWO answers that are correct.

☐ DNA is stored as multiple double-stranded molecules formed into chromosomes. ☐ DNA is stored as chromosomes consisting of a single DNA molecule and no protein molecules. ☑ DNA is a linear molecule wrapped around proteins and condensed into chromosomes. ☑ DNA is sequestered in the nucleus apart from the metabolic activity of the cytoplasm. ☐ DNA is a circular molecule that is free-floating in the cytoplasm of the cell.

Why can the same short tandem repeat region vary in length between the two copies of a chromosome of an individual?

☐ Differences signal polymerase to bind to the correct strand. ☐ DNA replication is an imperfect process. ☐ STR regions are modified during transcription. ☑ Each chromosome is inherited from a different parent. ☐ Variation prevents the propagation of copy errors.

Select the statement that best describes the function of heating and cooling in PCR.

☐ Heating facilitates strand denaturation, and cooling facilitates strand elongation. ☐ Heating facilitates primer attachment, and cooling facilitates strand elongation. ☑ Heating facilitates strand denaturation, and cooling facilitates primer attachment. ☐ Heating facilitates strand elongation, and cooling facilitates strand denaturation. ☐ Heating facilitates strand elongation, and cooling facilitates primer attachment.

You are investigating a crime. The DNA profile database has no perfect matches to the DNA collected at the crime scene. However, one profile in the database has at least one band in common with the crime scene DNA at every STR site. Which conclusion is most likely to be true?

☐ No logical conclusion can be drawn from these results. ☐ No close family relationship exists between the DNA collected at the crime scene and the DNA in the database. ☑ A parent-child relationship exists between the DNA collected at the crime scene and the DNA in the database. ☐ A high probability exists that the DNA in the database and the DNA collected at the crime scene are from the same person. ☐ A sibling relationship exists between the DNA collected at the crime scene and the DNA in the database.

Human red blood cells are enucleated (i.e., they do not have nuclei). Is it possible to isolate DNA from red blood cells? Why or why not?

☐ No, because human cells do not have nuclei. ☑ No, because the genomic DNA is found only in nucleated cells. ☐ Yes, because the genomic DNA is found only in enucleated cells. ☐ Yes, because genomic DNA is found in all cells. ☐ Yes, because genomic DNA can be isolated from other cellular locations.

Which statement about PCR is true?

☐ PCR does not generate a complementary DNA strand. ☐ PCR does not require nucleotides. ☐ Primers are not necessary for PCR. ☑ DNA polymerase is the enzyme that copies DNA in PCR. ☐ PCR can only replicate a few strands of DNA, and cannot replicate specific regions.

What is the polymerase chain reaction (PCR)?

☐ PCR selects variations of genes within DNA, called alleles, to increase the fitness of organisms by artificial selection. ☐ PCR determines the base pairs in a DNA sequence using temperature cycling, primers, fluorescent dye labels, and polymerase enzymes. ☑ PCR produces many copies of a DNA sequence from a small sample using temperature cycling, primers, free nucleotides, and polymerase enzymes. ☐ PCR modifies DNA within organisms, often species of agricultural importance, to increase the occurrence of desirable traits. ☐ PCR amplifies DNA within an organism to increase the expression of that DNA for the purpose of studying its effects.

What is the purpose of careful primer design before PCR?

☐ Primers are the nucleotides that are used in a PCR reaction to form DNA strands. ☐ Primers are used to separate the original DNA strand to give polymerase a place to start replication. ☐ Primers are enzymes that speed up the rate of a PCR reaction. ☑ Primers indicate the section of DNA that will be amplified and mark where DNA polymerase begins replication. ☐ Primers allow for complementary nucleotides to be added to the new strand of DNA.

From the STRs used in a forensic investigation, which STRs on which chromosomes would be particularly useful in determining whether crime scene evidence was left by a female or a male?

☐ STRs on chromosome 10 ☐ STRs on any chromosome would provide the necessary information. ☐ STRs on the X chromosome ☑ STRs on the Y chromosome ☐ STRs on chromosome 21

Identify the key structural features of a DNA molecule.

☐ Strong ionic bonds and hydrophobic interaction hold DNA together. ☑ The backbone of DNA is made of a sugar and a phosphate molecule. ☑ DNA bases are always paired purine with pyrimidine. ☐ DNA contains the nucleotide bases adenine, thymine, guanine, cytosine, and uracil. ☐ DNA is most often found as a left-handed helix, commonly referred to as A‑DNA. ☑ DNA strands are antiparallel and include a 5′5′ end and a 3′3′ end.

The given chromosomes are derived from a diploid cell. See Graphic: https://i.imgur.com/6kjaC8K.jpg Which set of terms describes the chromosomes labeled A and B?

☐ The chromosomes labeled A are non-sister chromatids and the chromosomes labeled B are nonhomologous chromosomes. ☐ The chromosomes labeled A are sister chromatids and the chromosomes labeled B are homologous chromosomes. ☐ The chromosomes labeled A are sister chromatids and the chromosomes labeled B are nonhomologous chromosomes. ☑ The chromosomes labeled A are non-sister chromatids and the chromosomes labeled B are homologous chromosomes.

In 1953, Francis Crick declared, "We have discovered the secret of life!" after solving the structure of DNA with his colleague James Watson. How did Watson and Crick use the width of DNA to determine the nucleotide pairing in DNA?

☐ The width of DNA is responsible for the 5' to 3' polarity of the DNA molecule. ☐ The width of the DNA molecule is too thick when a pyrimidine paired with another pyrimidine. ☑ The width is explained by a purine base pairing with a pyrimidine base. ☐ The width of the major and minor grooves is only created by purine-purine stacking.

The entire sequence of DNA in a cell used for DNA profiling is called the

☐ X chromosome. ☑ genome. ☐ Y chromosome. ☐ nucleus. ☐ chromosome.

Select the best description of a short tandem repeat.

☐ a nucleotide sequence of at least three bases that is discontinuously repeated in a DNA strand ☐ a nucleotide sequence of at least three bases that is continuously repeated in a DNA strand ☑ a nucleotide sequence of at least two bases that is continuously repeated in a DNA strand ☐ a nucleotide sequence of at least two bases that is continuously repeated at least 30 times in a DNA strand ☐ a nucleotide sequence of at least two bases that is discontinuously repeated in a DNA strand

What is short tandem repeat (STR) analysis?

☐ a technique that amplifies a small sample of DNA to a much larger quantity through replication ☐ a method that identifies the sequence of nucleotides in a given strand of DNA ☐ an analysis that assesses variation by comparing regions of DNA cut by restriction enzymes ☑ a procedure that compares the lengths of short, repeated DNA regions across samples

Which description best describes the function of chromosomes?

☐ allow genes from both parents to combine during fertilization ☐ hold the strands of the DNA double helix together ☐ provide genetic variation that is acted upon by natural selection ☑ enable more efficient packing and transport of genetic material in mitosis

What factor does gel electrophoresis use to separate DNA molecules?

☐ concentration of G-C pairs in the DNA molecules ☐ amount of positive charge on the DNA molecules ☑ length of individual DNA molecules ☐ concentration of A-T pairs in the DNA molecules ☐ concentration of protein in the DNA molecules

When copying a DNA sequence during PCR, the two original strands of the DNA molecule are separated by _____ ; then the enzyme _____ "reads" each template strand and adds _____ to make a new strand.

☐ cooling; DNA polymerase; any nucleotides ☐ forensics; DNA polymerase; complementary nucleotides ☐ DNA polymerase; primase; any nucleotides ☐ heat; primase; complementary nucleotides ☑ heat; DNA polymerase; complementary nucleotides

What intermolecular force is responsible for holding the two strands of a DNA double helix together?

☐ ionic bond ☐ phosphodiester bond ☐ covalent bond ☑ hydrogen bond

Which enzyme pairs corresponding nucleotides to a preexisting DNA chain in order to synthesize a new strand of DNA?

☐ ligase ☐ primase ☑ DNA polymerase ☐ helicase

Gel electrophoresis separates DNA for profiling based on the

☐ number of PCR products. ☐ number of chromosomes. ☑ size (length). ☐ shape of the double helix. ☐ gender of the individual.

You are studying the DNA profile of an individual, and you are looking at the results for a chromosome with just one STR site. How many bands will you see?

☐ one ☐ three ☑ either one or two ☐ one, two, or three ☐ two

Which of these describes a genome?

☐ the genetic material found in a cell's nucleus ☐ the protein‑coding genes in a cell or organism ☐ the haploid chromosomes in an egg cell ☐ the diploid chromosomes in a cell or organism ☑ the collection of genetic material in a cell or organism

How does the structure of DNA encode genetic information?

☐ the length of the DNA molecule ☑ the sequence of bases ☐ the sequence of amino acids ☐ the structure of the bases

Which phrase represents genetic variation between individuals?

☐ the number of chromosomes in the nucleus ☐ whether or not G pairs with C or T ☐ the number of chromosomes received from each parent none of these ☑ the number of STRs in their genomes

What naturally occurring process does PCR mimic in a test tube?

☐ transcription ☐ genomics ☑ DNA replication ☐ DNA condensation ☐ polymerization

What is the function of DNA?

☐ transfers genetic information from the nucleus to the cytoplasm ☐ activates enzymes from inactive states under specific conditions ☑ stores chemically coded, heritable information in an organism ☐ serves as a barrier to the environment in the cell membrane ☐ lowers the activation energy of important chemical reactions

Which person would have DNA that is least similar to yours?

☐ your identical twin ☑ your mother's brother ☐ your nonidentical twin ☐ your mother ☐ your older sibling

Select the statements that best describe how nucleotides pair with one another in a DNA molecule. Select the TWO answers that are correct.

☑ Adenine pairs with thymine, and guanine pairs with cytosine. ☐ Nucleotides pair with each other, joining two strands of DNA by covalent bonding. ☑ Nucleotides pair with each other, joining two strands of DNA by hydrogen bonding. ☐ Adenine pairs with guanine, and thymine pairs with cytosine. ☐ Nucleotides pair with each other to form the backbone of a single DNA strand.

In a human DNA sample, you detect DNA that is specifically from the X chromosome. Why are you unable to definitively determine the sex of that person (male or female) from the presence of the X chromosome?

☑ Both males and females have an X chromosome, and you would have to check for the presence of a Y chromosome. ☐ X chromosomes do not determine gender so you would have to have additional DNA analysis. ☐ Both males and females have an X chromosome so you would also have to evaluate the autosomes to determine sex. ☐ Males and females have different types of X chromosomes, so you would have to know which specific X chromosome was detected.

A DNA molecule consists of two polynucleotide strands that form a double helix. The strands are held together by hydrogen bonds between the nitrogen‑containing bases. One strand is complementary to the other strand, which means that a base on one strand is paired with a base on the opposite strand. The nucleotide bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). Choose the DNA sequence complementary to GACT.

☑ CTGA ☐ TCAG ☐ GACT ☐ AGTC

Why does DNA travel toward the positive electrode during gel electrophoresis?

☑ DNA is negatively charged, and opposite charges attract. ☐ DNA is neutral, but it associates with negatively charged RNA. ☐ DNA is positively charged, and like charges attract. ☐ DNA is neutral, but it associates with negatively charged proteins. ☐ DNA is neutral, but it associates with positively charged proteins.

Select the statements that correctly describe how a new DNA molecule reflects the original DNA molecule from which it was copied. Select the TWO answers that are correct.

☑ Each new DNA molecule contains an original strand and a newly synthesized strand. ☐ The two DNA molecules are exact opposites of each other according to base pairs. ☐ The nitrogenous bases in the new DNA molecule are A, T, G, and C, but the original molecule contains A, U, G, and C. ☑ Base pairing rules duplicate the base pairs of the original molecule in the new molecule. ☐ DNA replication proceeds in a 5' to 3' direction in the new DNA molecule and in the opposite direction in the original.

How are DNA fragments separated using gel electrophoresis?

☑ Smaller DNA fragments move through the gel more quickly than larger‑fragments. ☐ Negatively charged DNA fragments move through the gel more quickly. ☐ Smaller DNA fragments bind more strongly to the gel than do larger DNA fragments. ☐ DNA fragments complementary to probes in the gel travel more slowly through the matrix.

What are the structures in a cell that group genes together, are composed of chromatin (DNA and protein), and become visible under a light microscope during mitosis?

☑ chromosomes ☐ centromeres ☐ nucleic acids ☐ centrioles

An individual's STR may differ from the same STR of another individual by the

☑ number of times a particular sequence is repeated. ☐ specific chromosomal location of the STR. ☐ number of coding regions. ☐ order of nucleotides. ☐ specific bases present.

Select the parts that make up the backbone of the DNA molecule. Select the TWO answers that are correct.

☑ phosphate ☐ nucleoside ☐ glycine ☑ sugar ☐ nitrogenous base