AP EXAM REVIEW

nonsense mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

messenger RNA (mRNA)

A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.

transcription factor

A regulatory protein that binds to DNA and affects transcription of specific genes.

alternative RNA splicing

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

Coding strand

Nontemplate strand of DNA, which has the same sequence as the mRNA except it has thymine (T) instead of uracil (U).

frameshift mutation

A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.

Deletion

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.

insertion

A mutation involving the addition of one or more nucleotide pairs to a gene.

translation

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of 'language' from nucleotides to amino acids.

ribozyme

An RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing.

Codon

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

mutagen

A chemical or physical agent that interacts with DNA and causes a mutation.

RNA processing

Modification of RNA transcripts, including splicing out of introns, joining together of exons, and alteration of the 5' and 3' ends.

transcription initiation complex

The completed assembly of transcription factors and RNA polymerase bound to a promoter.

missense mutation

A base-pair substitution that results in a codon that codes for a different amino acid.

Mutation

A change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus.

TATA box

A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.

wobble

Flexibility in the base-pairing rules in which the nucleotide at the 5' end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3' end) of a codon.

primary transcript

An initial RNA transcript; also called pre-mRNA when transcribed from a protein-coding gene.

Nucleotide pair substitution

A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides.

transfer RNA (tRNA)

An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA.

terminator

In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

point mutation

A change in a gene at a single nucleotide pair.

ribosomal RNA (rRNA)

The most abundant type of RNA, which together with proteins makes up ribosomes.

transcription unit

A region of DNA that is transcribed into an RNA molecule.

spliceosome

A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.

signal-recognition particle (SRP)

A protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.

aminoacyl-tRNA synthetase

An enzyme that joins each amino acid to the appropriate tRNA.

exon

A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed.

domain

An independently folding part of a protein.

polyribosome (polysome)

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

RNA polymerase

An enzyme that links ribonucleotides into a growing RNA chain during transcription.

template strand

The DNA strand that provides the pattern, or template, for ordering the sequence of nucleotides in an RNA transcript.

promoter

A specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

Gene editing

Altering genes in a specific, predictable way.

CRISPR-Cas-9-system

A technique for editing genes in living cells, involving a bacterial protein called Cas9 associated with a guide RNA complementary to a gene sequence of interest.

Ribosome

A complex of RNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus.

P site

One of a ribosome's three binding sites for tRNA during translation. This site holds the tRNA carrying the growing polypeptide chain.

triplet code

A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.

gene expression

The process by which DNA directs the synthesis of proteins or, in some cases, just RNAs.

Silent mutation

A nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.

poly-A tail

A sequence of 50 to 250 adenine nucleotides added onto the 3' end of a pre-mRNA molecule.

Start point

In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.

Transcription

The synthesis of RNA using a DNA template.

E site

One of a ribosome's three binding sites for tRNA during translation. This site is the place where discharged tRNAs leave the ribosome.

5' cap

A modified form of guanine nucleotide added onto the nucleotide at the 5' end of a pre-mRNA molecule.

signal peptide

A sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell.

intron

A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed.

anticodon

A nucleotide triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.

RNA splicing

After synthesis of a eukaryotic primary RNA transcript, the removal of portions (introns) of the transcript that will not be included in the mRNA.

reading frame

On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

A. It causes specific double-strand DNA breaks that result in blunt ends on both strands.
B. It adds numerous GC pairs, which resist hydrolysis and maintain chromosome integrity.
C. It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
D. It adds a single 5' cap structure that resists degradation by nucleases

C

What are telomeres?

A. The ends of linear chromosomes.
B. The structures that hold two sister chromatids together.
C. The sites of origin of DNA replication
D. Enzymes that elongate the DNA strand during replication

A

The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?

A. DNA is the genetic material.
B. DNA is a polymer consisting of four monomers: adenine, thymine, guanine, and cytosine.
C. Bacterial replication is fundamentally different from eukaryotic replication. The key should not be way longer than the distractors.
D. DNA polymerase is an enzyme that synthesizes leading and lagging strands during replication only in one direction.

D

In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

A. helicase, DNA polymerase, DNA ligase
B. nuclease, DNA polymerase, RNA primase
C. nuclease, DNA polymerase, DNA ligase
D. DNA ligase, nuclease, helicase

C

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?

A. C6
B. the 5' phosphate
C. The 3' OH
D. a nitrogen from the nitrogen-containing base

C

Which of the following lists represents the order of increasingly higher levels of organization of chromatin?

A. nucleosome, looped domain, 30-nm chromatin fiber
B. nucleosome, 30-nm chromatin fiber, looped domain
C. looped domain, 30-nm chromatin fiber, nucleosome
D. 30-nm chromatin fiber, nucleosome, looped domain

B

If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?

A. Amplification of other genes would compensate for the lack of histones
B. Spindle fibers would not form during prophase
C. The cell's DNA could not be packed into its nucleus
D. There would be an increase in the amount of DNA produced during replication

C

Hershey and Chase used a DNA-based virus for their work. How might the results have been different if they had used an RNA virus?

A. With an RNA virus, the protein shell would have been radioactive in both samples.
B. With an RNA virus, radioactive protein would have been in the final pellet.
C. With an RNA virus, neither sample would have had a radioactive pellet
D. With an RNA virus, radioactive RNA would have been in the final pellet

D

After the first replication was observed in their experiments testing the nature of DNA replication, Meselson and Stahl could be confident of which of the following conclusions?

A. Replication is semi-conservative
B. Replication is not conservative
C. Replication is neither dispersive nor conservative
D. Replication is not dispersive

B

DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed during DNA replication?

A. ATP
B. RNA primers
C. Ribozymes
D. DNA polymerase

D

Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication

A. The lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together
B. The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.
C. The leading strand is synthesized at twice the rate of the lagging strand
D. The leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end.

B

Which of the following characteristics would you expect of a eukaryotic organism that lacks the enzyme telomerase?

A. An inability to repair thymine dimers
B. A reduction in chromosome length in gametes
C. An inability to produce Okazaki fragments
D. A high probability of somatic cells becoming cancerous

B

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?

A. The single-strand binding proteins were malfunctioning during DNA replication
B. The proofreading mechanism of DNA polymerase was not working properly
C. The DNA polymerase was unable to add bases to the 3' end of the growing nucleic acid chain
D. There were one or more base pair mismatches in the RNA primer

B

In a healthy eukaryotic cell, the rate of DNA repair is typically equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?

A. DNA replication will proceed more quickly
B. DNA replication will continue by a new mechanism
C. The cell can be transformed into a cancerous cell
D. RNA may be used instead of DNA as inheritance material

C

AT a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:
3' CCTAGGCtGCAATCC 5'
An RNA primer is formed starting at the lowercase T of the template. Which of the following represents the primer sequence?

A. 5' ACGTTAGG 3'
B. 5' GCCUAGG 3'
C. 5' GCCTAGG 3'
D. 5' ACGUUAGG 3'

D

In his transformation experiments, what phenomenon did Griffith observe?

A. Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
B. Mice infected with a pathogenic strain of bacteria can spread the infection to other mice
C. Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into pathogenic form
D. Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains

C

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

A. DNA contains nitrogen, whereas protein does not
B. DNA contains purines, whereas protein includes pyrimidines
C. DNA contains phosphorus, whereas protein does not
D. DNA contains sulfur, whereas protein does not

C

Which of the following statements accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

A. Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not
B. Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many
C. Prokaryotic chromosomes have histones, whereas eukaryotic chromosomes do not
D. The rate of elongation during DNA replication is slower in prokaryotes than in eukaryotes

B

Which of the following molecular characteristics cause histones to bind tightly to DNA?

A. Both histones and DNA are strongly hydrophobic
B. Histones are positively charged, and DNA is negatively charged
C. Histones are negatively charged, and DNA is positively charged
D. HIstones are covalently linked to DNA

B

Which of the following effects might be caused by reduced or very little active telomerase activity?

A. Cells maintain normal functioning.
B. Cells age and begin to lose function
C. Cells may become cancerous
D. Telomere lengthens in germ cells.

B

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight, and mutations to the DNA are in their skin cells are left uncorrected. Why are the mutations not corrected in individuals with this disorder?

A. The disorder causes mitosis to stop during metaphase
B. The disorder causes cells to be unable to repair thymine dimers.
C. The disorder makes cells unable to replicate DNA
D. The disorder makes cells unable to form chromosomes.

B

Which of the following statements accurately describes one characteristic of histones?

A. The carboxyl end of each histone extends outward from the nucleosome and is called a "histone tail."
B. Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.
C. Histones are found in mammals, but not in other animals or in plants or fungi.
D. Each nucleosome consists of two molecules of histone H1.

B

A heat killed, phosphorescent (light-emitting) strain of bacteria is mixed with a living, non-phosphorescent strain. Further observations of the mixture show that some of the living cells are now phosphorescent. Which of the following observations would provide the best evidence that the ability to phosphoresce is a heritable trait?

A. Phosphorescence in descendants of the living cells
B. Especially bright phosphorescence in the living strain
C. Evidence that DNA was passed from the heat-killed strain to the living strain
D. Evidence that protein passed from the heat-killed strain to the living strain

A

Which of the following statements correctly describes the difference between ATP and the nucleotides used during DNA synthesis?

A. The nucleotides have the sugar deoxyribose; ATP has the sugar ribose
B. ATP is found only in human cells; the nucleotides are found in all animal and plant cells
C. ATP is found only in human cells; the nucleotides are found in all animal and plant cells.
D. The nucleotides have two phosphate groups; ATP has three phosphate groups.

A

In DNA replication in E. coli, the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following results would you expect?

A. Replication would only occur on the lagging strand.
B. Replication would not be affected as the enzyme primase in involved with RNA synthesis
C. Replication would only occur on the leading strand.
D. Replication would not occur on either the leading or lagging strand

D

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?

A. 16%
B. 8%
C. 22%
D. 72 %

C

Who performed classic experiments that supported the semiconservative model of DNA replication?

A. Franklin and Wilkins
B. Hershey and Chase
C. Meselson and Stahl
D. Watson and Crick

C

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated form the bacteria, the DNA separates into two classes. One class of labeled DNA includes ver large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). Which two classes of DNA do these different samples present?

A. lagging strands and Okazaki fragments
B. Leading strands and RNA primers
C. Okazaki fragments and RNA primers
D. leading strands and Okazaki fragments

D

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

A. DNA in both daughter cells would be radioactive
B. One of the daughter cells, but not the other, would have radioactive DNA.
C. All four bases of the DNA would be radioactive.
D. Neither of the two daughter cells would be radioactive

A

Which of the following statements accurately describes the structure of a eukaryotic chromosome?

A. It is a single linear molecule of double-stranded DNA plus proteins.
B. It is constructed as a series of nucleosomes wrapped around two DNA molecules
C. It is composed of a single strand of DNA.
D. It has different numbers of genes in different cell types of an organism

A

Which of the following types of molecules help to hold the DNA strands apart while they are replicated?

A. primase
B. DNA polymerase
C. Ligase
D. single-strand DNA binding proteins

D

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine. What is the significance of the structural arrangement?

A. It allows variable width of the double helix.
B. It determines the type of protein produced.
C. It determines the tertiary structure of a DNA molecule
D. It permits complementary base pairing.

D

Which of the following structural characteristics is most critical for the association between histones and DNA?

A. Histones are highly conserved (that is, histones are very similar in every eukaryote).
B. Histones are small proteins.
C. There are at least five different histone proteins in every eukaryote.
D. Histones are positively charged.

D

Which of the following statements describes the process of transformation in bacteria?

A. A strand of DNA is created from an RNA molecule.
B. External DNA is taken into a cell, becoming part of the cell's genome.
C. A strand of RNA is created from a DNA molecule
D. Bacterial cells are infected by a phage DNA molecule.

B

In DNA replication, the resulting daughter molecules contain one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

A. RNA synthesis is conservative.
B. DNA replication is semiconservative.
C. DNA replication is not conservative
D. DNA replication is conservative.

B

In DNA replication, the resulting daughter molecules contain on strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

A. RNA synthesis is conservative.
B. DNA replication is semiconservative
C. DNA replication is not conservative
D. DNA replication is conservative

B

Which of the following statements correctly describes the difference between the leading and lagging strand in DNA replication?

A. The leading strand is synthesized continuously in the 5' -> 3' direction, while the lagging strand is synthesized discontinuously in the 5' -> 3' direction
B. The leading strand requires an RNA primer, whereas the lagging strand does not.
C. The leading strand is synthesized in the 3' -> 5' direction in a discontinuous fashion while the lagging strand is synthesized in the 5' -> direction in a continuous fashion
D. There are different DNA polymerases involved in elongation of the leading strand and the lagging strand

D

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?

A. The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
B. Base pairings create unequal spacing between the two DNA strands.
C. One strand contains only purines and the other contains only pyrimidines
D. The double helix structure of DNA creates nonparallel strands

A

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?

A. Telomerase eliminates telomere shortening and retards aging.
B. Telomerase shortens telomeres, which delays cellular aging.
C. Telomerase would have no effect on cellular aging
D. Telomerase will speed up the rate of cell proliferation

A

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?

A. No replication fork will be formed
B. Replication will require a DNA template from another source.
C. Additional proofreading will occur
D. Replication will occur via RNA polymerase alone.

A

Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?

A. Oswald Avery, Maclyn McCarty, and Collin MacLeod
B. Matthew Meselson and Franklin Stahl
C. Erwin Chargaff
D. Alfred Hershey and Martha Chase

C

It became apparent to Watson and Crick after completion of their model that the DNA molecules could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

A. Complementary pairing of bases
B. side groups of nitrogenous bases
C. Sequence of bases
D. Phosphate-sugar backbones

C

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

A. It unwinds the parental double helix
B. It stabilizes the unwound parental DNA
C. It synthesizes RNA nucleotides to make a primer.
D. It joins Okazaki fragments together

D

Semiconservative replication involves a template. What is the template?

A. an RNA molecule
B. DNA polymerase
C. one strand of the DNA molecule
D. single-stranded binding proteins

C

In E. coli what is the function of DNA polymerase III?

A. to unwind the DNA helix during replication
B. to degrade damaged DNA molecules
C. to add nucleotides to the 3' end of a growing DNA strand
D. to seal together the broken ends of DNA strands

C

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned each nucleotide has only one phosphate and two to five nitrogen atoms, Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

A. Radioactive nitrogen has a half-life of 100,00 years, and the material would be too dangerous for too long.
B. There is no radioactive isotope of nitrogen
C. Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
D. Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

D

Which of the following statements correctly describes the structure of chromatin?

A. Heterochromatin is composed of DNA< whereas euchromatin is made of DNA and RNA
B. Both heterochromatin and euchromatin are found in the cytoplasm
C. Euchromatin is not transcribed, whereas heterochromatin is transcribed
D. Heterochromatin is highly condensed, whereas euchromatin is less compact

D

Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?

A. the activity of telomerase enzyme
B. DNA polymerase that cannot replicate the leading strand template to its 5' end
C. gaps left at the 3' end of the lagging strand because of the need for a primer
D. gaps left at the 5' end of the lagging strand template

D

Elements

The fundamental substances that make up all matter, consisting of atoms of the same atomic number.