AP Biology Unit 3 Chapter 13

On a scale of 0 to 6, where 6 is the most trustworthy, how would you rate this site? (Note that all responses will be marked as "correct" at this point.)

5-6 very trustworthy

True or false? The Taq enzyme is a type of DNA polymerase that allows researchers to separate the DNA strands during the annealing step of the PCR cycle without destroying the polymerase.

False

Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA?

Franklin

Who demonstrated that DNA is the genetic material of the T2 phage?

Hershey and Chase

True or false? Comparison of the sequences of the same gene across species can give some insight into the existence of a common ancestor with that gene.

True

Archaeologists unearthed a human skull with a small dried fragment of the scalp still attached. They extracted a tiny amount of DNA from the scalp tissue. How could they obtain sufficient DNA for an analysis of the ancient human's genes?

Use the polymerase chain reaction.

What information can not be obtained from the sequence of a gene?

Whether the gene is methylated.

The letter A indicates _____.

a DNA double helix

In recombinant DNA experiments, what is used to cut pieces of DNA and what joins the resulting fragments to form recombinant DNA?

a restriction enzyme ... DNA ligase

The DNA double helix is composed of two strands of DNA; each strand is a polymer of DNA nucleotides. Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases. The structure and orientation of the two strands are important to understanding DNA replication. Drag the labels to their appropriate locations on the diagram below. Pink labels can be used more than once.

a. 5' end b. hydrogen bond c. 3' end d. deoxyribose sugar e. nitrogenous base f. phosphate group g. 3' end h. 5' end

Drag the labels to their appropriate locations in the diagram to describe the name or function of each structure. Use pink labels for the pink targets and blue labels for the blue targets.

a. Breaks hydrogen bonds, unwinding DNA double helix b. synthesizes RNA primers on leading and lagging strands c. replaces RNA primers with DNA nucleotide d. catalyzes phosphodiester bond formation, joining DNA fragments. e. lagging strand f. leading strand g. relaxes supercoiled DNA h. coats single-stranded DNA i. synthesizes DNA 5' to 3' on leading and lagging strands

After DNA replication is completed, _____.

each new DNA double helix consists of one old DNA strand and one new DNA strand

Rank the primers in the order they were produced. If two primers were produced at the same time, overlap them.

earliest h and a b and g c and f d and e latest

Which of the following functions in the regulation of gene expression?

euchromatin

After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

labeled DNA ... DNA

The DNA double helix is composed of two strands of DNA; each strand is a polymer of DNA nucleotides. Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases. The structure and orientation of the two strands are important to understanding DNA replication. Drag the labels to their appropriate locations on the diagram below. Pink labels can be used more than once.

leading strand -made continuously -only one primer needed -daughter strand elongates toward replication fork lagging strand -daughter strand elongates away from replication fork -multiple primers needed -made in segments both strands -synthesized 5' to 3'

Gel electrophoresis separates DNA fragments on the basis of what characteristic?

length

Short segments of newly synthesized DNA are joined into a continuous strand by _____.

ligase

What is this an image of?

loops

In gel electrophoresis DNA molecules migrate from _____ to _____ ends of the gel.

negative ... positive

In nucleotide excision repair, damaged DNA is excised by what enzyme(s)?

nuclease

What process repairs damage to a preexisting double helix?

nucleotide excision repair

This is an image of a _____.

phage

What seems to be the main purpose of the blog post?

to convince the public that genetic engineering is not the solution to citrus greening

Early, flawed DNA models proposed by Watson and Crick and by Linus Pauling correctly described which property of DNA?

DNA is composed of sugars, phosphates, and bases.

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?

DNA polymerase can assemble DNA only in the 5' to 3' direction

During which step in the PCR cycle are nucleotides used?

Extension

The sticky end of the DNA restriction fragment shown here will pair with a DNA restriction fragment with the sticky end _____.

-ACGT

In the 1950s, when Watson and Crick were working on their model of DNA, which concepts were well accepted by the scientific community?

-Chromosomes are found in the nucleus. -Chromosomes are made up of protein and nucleic acid. -Genes are located on chromosomes.

Check each of the true statements about the proteins involved in cutting and pasting DNA. More than one statement may be true. Check all that apply.

-DNA ligase pastes together segments of DNA with matching sticky ends. -A restriction enzyme cuts DNA while DNA ligase pastes DNA. -A particular restriction enzyme only cuts DNA at one very specific DNA sequence.

What did the structure of DNA's double helix suggest about DNA's properties? Select all that apply.

-DNA stores genetic information in the sequence of its bases. -DNA can be replicated by making complementary copies of each strand. -DNA can change. Errors in copying can result in changes in the DNA sequence that could be inherited by future generations.

What steps could help refine the researchers' experiment to modify only the two target genes? Select all that apply

-Screen the rest of the mouse genome to be sure the 20-bp targets do not appear elsewhere in the genome. -Engineer a version of Cas9 that demonstrates higher fidelity to the target sequence.

What are the chemical components of a DNA molecule? Select all that apply.

-sugars -nitrogenous bases -phosphate groups

To create a molecule of recombinant DNA, which of the following is cut with a restriction enzyme?

-target DNA -starting DNA

The following figure shows the general steps that occur when a researcher uses the CRISPR-Cas9 system to modify a protein-encoding gene in a eukaryotic cell with the goal of modifying the protein product. Drag the descriptions of the steps to their appropriate locations on the figure.

1. Create plasmid expression vectors with genes encoding Cas9 and sgRNA. 2. Introduce the vectors into a eukaryotic cell. 3. The gene expression machinery of the cell produces the Cas9 protein and the sgRNA. 4. The Cas9 protien, guided by sgRNA, binds to its target sequence in the cell's DNA. 5. The Cas9 protien cleaves the target sequence. 6. During the process of DNA break repair, the target sequence may be modified. 7. The modified DNA sequence is transcribed into RNA. 8. the RNA is translated into a modified protien.

The following scenarios require application of CRISPR-Cas9 technology. Identify which technologies are the best fit for each research scenario.

1. Researchers want to make an endonuclease that binds to target DNA, but does not cut the DNA. This will allow them to target specific areas of the genome for other modifications without making cuts. dCas9 2. Researchers are studying a proposed oncogene in mice. They want to examine what happens when the gene is overexpressed. dCas9 and activation domain 3. Researchers are studying a proposed tumor suppressor gene in fruit flies. They want to examine what happens when the gene has lower than normal expression, without inactivating the gene entirely. dCas9 and repression domain 4. Researchers are studying the three-dimensional organization of genomic structure. They want to visualize the location of specific genomic loci within a living cell. dCas9 and fluorescent protein 5. Researchers identify some previously uncharacterized genes that might play a role in diabetes. They want to make mouse mutants with null mutations in those genes and study what symptoms arise as a result. Cas9 and NHEJ 6. Researchers are studying an allele associated with a longer life span in humans, which varies from the normal variant by six base pairs. In order to study this allele in the laboratory, they want to modify the mouse homologue to have the same 6 base pair variation. Cas9 and HDR

Assign a numerical score for each category. Then add up the total score. (The highest possible score is 6; the lowest is 0.) In what range does this source fall?

2 to 4

Drag the labels to their appropriate locations in the flowchart below, indicating the sequence of events in the production of fragment B. (Note that pol I stands for DNA polymerase I, and pol III stands for DNA polymerase III.)

2. pol III moves 5' to 3', adding DNA nucleotides to primer B 3. pol I binds to 5' end of primer A 4. pol I replaces primer A with DNA 5. DNA ligase links fragments A and B

How many DNA molecules would there be after four rounds of PCR if the initial reaction mixture contained two molecules?

32

Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

35S

Where would RNA polymerase attach?

A

What is the polymerase chain reaction (PCR)?

A method to amplify a fragment of DNA.

During which step in the PCR cycle do primers form bonds with a single-stranded template?

Annealing.

What did Rosalind Franklin's famous photo 51 show?

DNA is a helix

The radioactive isotope 32P labels the T2 phage's _____.

DNA

What are chromosomes made of?

DNA and proteins

Which of these DNA molecules is the shortest?

E (The shorter the DNA molecule, the farther it moves.)

DNA replication is said to be semiconservative. What does this mean?

Each new double helix consists of one old and one new strand.

Which one of the following statements is correct?

If a restriction enzyme is combined with a piece of DNA that contains its restriction site, the result will be restriction fragments.

Which of the following is true of DNA during interphase?

It exists as chromatin and is less condensed than mitotic chromosomes.

What is the function of helicase in DNA replication?

It untwists the double helix and separates the two DNA strands.

In the early 1950s, many researchers were racing to describe the structure of DNA using different approaches. Which of the following statements is true?

Jim Watson and Francis Crick built theoretical models, incorporating current knowledge about chemical bonding and X-ray data.

Complete the following sorting exercise to be sure you understand how the two break repair mechanisms are similar and different. Sort each item to the appropriate bin.

NHEJ Repair only: -More error-prone; likely to cause indels and frameshift mutations -Simply involves ligation of broken DNA fragments -Often results in nonfunctional (null) mutants HDR Repair only -Better for making complex substitutions -Uses an undamaged homologous chromosome as a template -Increases in frequency after single-strand breaks Both NHEJ and HDR Repair -Occurs after a DNA break (including breaks made by Cas9)

What do you find when you click these two links?

One links to another page on the CFS web site, and one links to a paper in a peer-reviewed journal.

Is the information provided by these sites consistent with what you found on the CFS web site?

Other sites discuss both the risks and benefits associated with GMOs.

In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?

Radioactively labeled phosphorus was present inside the infected bacteria.

What is the affiliation of the writer?

She is on staff at the Center for Food Safety (CFS).

Erwin Chargaff observed that the proportions of adenine (A) and thymine (T) bases were always equal, as were the proportion of guanine (G) and cytosine (C). Chargaff's observation suggests which of the following statements?

The data suggest that A would always pair with T and G would always pair with C in a DNA molecule.

Griffith's experiments with S. pneumoniae were significant because they showed that traits could be transferred from one organism to another. What else did he find that was significant?

The transferred traits were heritable.

Drag the correct labels to the appropriate locations in the diagram to show the composition of the daughter DNA molecules after one and two cycles of DNA replication. In the labels, the original parental DNA is blue and the DNA synthesized during replication is red.

first cycle: red and blue double helix second cycle: red and blue, red, red and blue, red helix

The letter C indicates _____.

histones

The unpaired nucleotides produced by the action of restriction enzymes are referred to as _____.

sticky ends

Which of the following is an example of "recombinant DNA technology"?

introducing a human gene into a bacterial plasmid

The action of helicase creates _____.

replication forks and replication bubbles

What is this an image of?

supercoils

What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?

telomeres

An old DNA strand is used as a _____ for the assembly of a new DNA strand.

template

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine