Biology Chapter 16-17

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

35S Hershey and Chase used radioactive sulfur to label the phage's proteins.

PART B - Calculating missing data You can use Chargaff's rules to predict the percentage of one or more bases in the DNA of a species if at least one value is known. What is the %T in wheat DNA?

Approximately 28%

A nitrogenous base is indicated by the letter _____.

C

Which of these is(are) pyrimidines?

C, D, and E Pyrimidines are single-ring structures

The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.

CUG. In RNA uracil replaces thymine.

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

DNA The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.

What did Rosalind Franklin's famous photo 51 show?

DNA is a helix. The "X" pattern of the X-ray crystallography image matched the shape that Crick predicted for a helix.

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. The composition of DNA was well established by the 1950s. Models showed different arrangements of the components and sometimes introduced additional ones (such as magnesium), but all contained sugars, phosphates, and bases.

Which of these is a difference between a DNA and an RNA molecule?

DNA is usually double-stranded, whereas RNA is usually single-stranded. With some exceptions, DNA is a double-stranded molecule and RNA is a single-stranded molecule. type of sugar DNA takes deoxyribose H RNA takes ribose OH

In the diagram below, the two blue strands represent _____.

DNA. DNA is a double helix.

After DNA replication is completed, _____.

Each new DNA double helix consist of one old DNA strand and one new DNA strand DNA replication is semiconservative.

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

Franklin Rosalind Franklin conducted these X-ray diffraction studies of DNA

Primary structure

Primary structure--the unique amino acid sequence of a polypeptide These levels of structure are shown below for hemoglobin, the oxygen-carrying protein found in red blood cells. (Note that a hemoglobin molecule is made up of two α subunits and two β subunits; these are polypeptides and should not be confused with the α helix and β pleated sheet.)

Secondary structure

Secondary structure--aspects of structure that result from hydrogen bonding between the backbone constituents of the polypeptide. (Examples: α helix, β pleated sheet)

The first step in the replication of DNA is catalyzed by _____.

helicase The first step of DNA replication is unwinding the DNA double helix.

RNA processing converts the RNA transcript into _____.

mRNA The editing of the RNA transcript produces mRNA.

Which of these nitrogenous bases is found in DNA but not in RNA?

thymine DNA contains thymine; RNA contains uracil. They both contain cytosine, adenine, and guanine.

Nucleic acids are assembled in the _____ direction.

5' to 3' New nucleotides are added to the 3' end of a growing polynucleotide.

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 Since the phage DNA entered the infected cell, it makes sense that DNA is the genetic material.

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?

translation Translation is the process by which information encoded in RNA is used to manufacture a polypeptide.

Which of the following clues would tell you if a cell is prokaryotic or eukaryotic?

whether or not the cell is compartmentalized by internal membranes All cells contain chromosomes, which carry genes in the form of DNA, and all cells have ribosomes, tiny complexes that make protein according to instructions from the genes. A rigid cell wall can be found surrounding the plasma membrane of prokaryotes as well as some eukaryotic cells. Within the cytoplasm of a eukaryotic cell, however, are a variety of membrane-bound organelles of specialized form and function, structures that are absent in almost all prokaryotic cells.

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

1' ... 5' The nitrogenous base is attached to the sugar's 1' carbon and the phosphate group is attached to the sugar's 5' carbon.

Place the events in the transcription of a gene in their proper order from left (first event) to right (last event).

1. RNA polymerase binds promoter. 2. RNA polymerase transcribes gene. 3.RNA polymerase reaches terminator. 4. RNA polymerase exits gene, RNA is released. Transcription begins when a molecule of RNA polymerase binds to a promoter. Transcription continues through the gene, producing the RNA. Once RNA polymerase reaches the terminator, the RNA is released, and RNA polymerase falls off the DNA.

Given a DNA molecule with the sequence of bases 5'-ATTGCA-3', what would be the sequence of the complementary strand? (It will be helpful to draw the DNA molecule when answering the question.)

3'-TAACGT-5' Complementary strands of DNA run in opposite 5′ → 3′ directions from each other, an arrangement that is referred to as antiparallel. Wherever one strand of a DNA molecule has an A, the partner strand has a T, and a G in one strand is always paired with a C in the complementary strand. Adenine (A) pairs with uracil (U) instead of thymine (T) in RNA, as thymine (T) is not present in RNA.

Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms?

5 bases. In the most general case of x bases and y bases per codon, the total number of possible codons is equal to x^y. In the case of the hypothetical Martian life-forms, is the minimum codon length needed to specify 17 amino acids is 5 (2^5=32), with some redundancy (meaning that more than one codon could code for the same amino acid). For life on Earth, x=4 and y=3, this the number of codons 4^3, or 64. Because there are only 20 amino acids, there is a lot of redundancy in the code (there are several codons for each amino acid).

same is Adenine, Guanine, and Cytosine while DNA has Thymine and RNA has Uracil

5' to 3'. Covalent bond from 3' to 5' RNA is a single chain while DNA has two held by Hydrogen bond

The direction of synthesis of an RNA transcript is _____.

5' —> 3'. Nucleotides are added to the 3' end of RNA

Given a template strand of 3'-ATGCTTGGACA-5' and a partially-made complementary strand containing only 5'-TAC-3', what would be the sequence of the new strand of DNA (including the 5'-TAC-3') if the only additional nucleotides available to DNA polymerase were those containing the bases G, A, and C?

5'-TACGAACC-3' DNA polymerase will continue to add nucleotides onto the growing strand as long as it has nucleotides with the bases required to complement the template strand. If it is missing one kind of base, it will stop at that point on the strand.

In the accompanying image, a nucleotide is indicated by the letter _____.

B is indicating a single nucleotide.

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 made up of protein and nucleic acid. Genes are located on chromosomes. Chromosomes are found in the nucleus. When Watson and Crick began working on their model, scientists knew that genes were found on chromosomes in the nucleus and that chromosomes were composed of proteins and nucleic acid. Watson and Crick were two of the few to focus on the nucleic acid, DNA, instead of proteins.

What catalyzes DNA synthesis?

DNA polymerase This enzyme catalyzes DNA synthesis.

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 Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled either in short 5' to 3' segments, which are later joined together by ligase, or be assembled continuously.

What is the role of DNA polymerase during DNA synthesis?

DNA polymerase is the enzyme that catalyzes the addition of a nucleotide onto the 3' end of a growing DNA strand. DNA polymerase is the enzyme complex responsible for synthesizing a new strand of DNA, using an existing strand as a template. DNA polymerase is the enzyme complex responsible for synthesizing a new strand of DNA, using an existing strand as a template.

1. The new DNA strand that grows continuously in the 5' to 3' direction is called the leading strand. 2. Okazaki fragmentsare the short sections of DNA that are synthesized on the lagging strand of the replicating DNA. 3. During DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is called a replication fork. 4. The enzyme that can replicate DNA is called DNA polymerase. 5. After replication is complete, the new DNAs, called daughter DNA, are identical to each other.

DNA replication is a central process in biochemistry and must be done with the highest precision. If a mistake is made in the replication of DNA, the error will propagate into future generations. An error that occurs during replication is called a mutation.

Which of the following terms associated with transcription describe regions of nucleic acid?

Gene, promotor, terminator The gene itself, the promoter, and the terminator are all DNA deoxyribonucleic acid sequences. The RNA (ribonucleic acid) that is produced is another. The RNA polymerase enzyme that performs transcription is a protein and therefore not a nucleic acid.

The two strands of a DNA double helix are held together by _____ that form between pairs of nitrogenous bases.

Hydrogen bond. If you had trouble with this question, review the following material: DNA molecules have two polynucleotides, or "strands", that wind around an imaginary axis, forming a double helix. The sugar-phosphate backbones are on the outside of the helix, and the nitrogenous bases are paired in the interior of the helix. The two strands of DNA are held together by hydrogen bonds between the paired bases.

During ______, the cell grows and replicates both its organelles and its chromosomes

Interphase Interphase can be divided into three phases: G1 phase, S phase, and G2 phase. During all three phases of interphase, a cell grows by producing proteins and cytoplasmic organelles. Duplication of the chromosomes, crucial for eventual division of the cell, occurs entirely during the S phase of interphase. Cell division occurs during M phase, which can be divided into two stages: mitosis and cytokinesis.

During translation, nucleotide base triplets (codons) in mRNA are read in sequence in the 5' → 3' direction along the mRNA. Amino acids are specified by the string of codons. What amino acid sequence does the following mRNA nucleotide sequence specify? 5′−AUGGCAAGAAAA−3′

Met-Ala-Arg-Lys An amino acid sequence is determined by strings of three-letter codons on the mRNA, each of which codes for a specific amino acid or a stop signal. The mRNA is translated in a 5' → 3' direction.

start/methionine AUG stop codon UAA UAG UGA\ amino acid AAA AUC CAC GCA ACU UGC

Nearly every mRNA gene that codes for a protein begins with the start codon, AUG, and thus begins with a methionine. Nearly every protein-coding sequence ends with one of the three stop codons (UAA, UAG, and UGA), which do not code for amino acids but signal the end of translation.

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

Nitrogenous base, phosphate groups, and sugars. DNA is composed of a sequence of subunits, each containing a phosphate group, a deocyribose sugar, and one of the four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C).

Quaternary structure

Quaternary structure--the aggregation of multiple polypeptide subunits to form a functional protein

In the diagram below, the gray unit represents _____.

RNA polymerase untwists a portion of the DNA double helix.

The synthesis of a new strand begins with the synthesis of a(n) _____.

RNA primer complementary to a preexisting DNA strand The synthesis of a DNA strand begins with the formation of an RNA primer.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing RNA processing edits the RNA transcript that has been assembled along a DNA template.

Which of the following diagrams most clearly shows the details of the bonds between nitrogenous bases of complementary nucleotide pairs?

Structural diagram While the complementary nature of the interactions between the base pairs is demonstrated in all four diagrams, only the structural diagram shows the molecular details--the specific number and location of hydrogen bonds that form between complementary base pairs.

Tertiary structure

Tertiary structure--the overall shape of a polypeptide, resulting from interactions between the side chains (R groups) of amino acids. (Examples: hydrophobic interactions, van der Waals interactions, disulfide bridges, hydrogen bonds, and ionic bonds)

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. Targets of Group 1 can be used more than once.

The DNA double helix is constructed from two strands of DNA, each with a sugar-phosphate backbone and nitrogenous bases that form hydrogen bonds, holding the two strands together. Each DNA strand has two unique ends. The 3' end has a hydroxyl (-OH) group on the deoxyribose sugar, whereas the 5' end has a phosphate group. In the double helix, the two strands are antiparallel, that is, they run in opposite directions such that the 3' end of one strand is adjacent to the 5' end of the other strand.

Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

The bonds or interactions that hold together adjacent nucleotides in the sugar-phosphate backbone of DNA are Covalent bonds. The bonds or interactions that hold together complementary bases from opposite strands of DNA are hydrogen bonds. The bonds or interactions between stacked nucleotide units that help hold the DNA molecule together are van der Waals interactions. Adjacent nucleotides in the sugar-phosphate backbone are held together by the strongest type of chemical bond--covalent bonds--shown by a solid line. Complementary bases from opposite strands are held together by stable, but weaker hydrogen bonds, shown as dotted lines. Van der Waals interactions--an even weaker type of interaction--play a role in holding the DNA molecule together.

The insertion or deletion of a nucleotide pair is a type of point mutation.

The insertion or deletion of a single nucleotide pair may cause a frameshift mutation, as in the cystic fibrosis 1660delG allele. Frameshift mutations can result in extensive missense. The large-scale changes in protein primary structure typically result in the production of a nonfunctional protein. The insertion or deletion of three nucleotide pairs does not cause a frameshift mutation. This is the type of mutation responsible for the cystic fibrosis [delta]F508 allele, the most common allele seen in cystic fibrosis patients. As you saw, the [delta]F508 allele is missing a single phenylalanine amino acid. This relatively modest change in protein primary structure unfortunately results in the production of a misfolded protein that is degraded in the endoplasmic reticulum and never makes it to the plasma membrane. The normal allele for this gene codes for the CFTR protein. CFTR transports chloride ions between certain cells and the extracellular fluid. People who inherit two recessive alleles (with mutations) have an extremely high concentration of extracellular chloride, which causes the mucus that coats certain cells to be thicker than usual. The mucus builds up in various organs, including the pancreas, lungs, and digestive tract. Effects include chronic bronchitis, recurrent bacterial infections, and poor absorption of nutrients from the intestines.

Addition of a nucleotide onto a DNA strand is an endergonic reaction. What provides the energy to drive the reaction?

The release of pyrophosphate from the incoming nucleotide, and then hydrolysis of the pyrophosphate to inorganic phosphate. Each deoxyribonucleotide enters the reaction as a triphosphate, and hydrolysis of the phosphates releases the free energy needed for the nucleotide to bind to the growing strand.

How is translation initiated? See Concept 17.4 (Page)

The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation. ALL OF THE ABOVE

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? See Concept 16.1 (Page)

The traits were heritable The fact that offspring of transformed bacteria also showed the pathogenic trait meant that the transforming agent had to be involved with the genetic material.

Suppose that the triplet of nucleotides indicated in bold (AGC) spans two codons, that is, CTA and GCC. If the triplet AGC were deleted from this DNA coding sequence, what effect would it have on the resulting protein? 5'-ATGCTAGCCTATCGTAAC-3'

The two flanking codons would be altered, but the rest of the amino acid sequence would be the same because there would be no frameshift. When a deletion of a set of three nucleotides that is out of frame to the reading frame of codons occurs, it only affects the codons flanking it. Once the ribosome reads past that point, the rest of the codons are in frame because a full triplet was deleted at one time.

Which one of the following is true of tRNAs? See Concept 17.4 (Page)

There are four types of tRNA .tRNAs carry special sequences known as codons. Each tRNA binds a particular codon. tRNAs are double-stranded. NONE OF THE LISTED ANSWERS The correct response is not listed in the choices. The tRNA transfers an amino acid to the growing polypeptide chain. It is a molecule involved in translation of mRNA.

True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.

There are no tRNAs complementary to the three stop codons; termination occurs when release factors recognize the stop codon in the A-site and catalyze the release of the polypeptide from the tRNA in the P-site.

Mutations

There are two categories of point mutations: A nucleotide-pair substitution is the replacement of one nucleotide and its partner with a different pair of nucleotides. A nucleotide-pair insertion or deletion is the addition or loss of a nucleotide pair. Nucleotide-pair substitutions can result in silent, missense, or nonsense mutations. A silent mutation does not change the amino acid sequence of a polypeptide. A missense mutation causes one amino acid to be substituted for another, which can have a range of effects. A nonsense mutation results in the production of a premature "stop" signal and will cause translation to be terminated early. Nonsense mutations frequently result in the production of nonfunctional proteins. Sickle-cell disease results from a single missense mutation in the DNA that codes for the β-globin subunit of hemoglobin. In fact, the missense mutation you identified above, which changes a glutamic acid to a valine, is the mutation that causes sickle-cell disease. (However, remember that each person has two copies of this gene; it is only when both copies carry the missense mutation that sickle cell disease is severe. Heterozygotes, who carry one sickle-cell allele and one normal allele, only experience symptoms under low-oxygen conditions.) The figure below shows how a single amino acid substitution affects the higher-level structure of the hemoglobin protein and ultimately causes red blood cells to become sickle-shaped.

Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?

Topoisomerase This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template

RNA plays important roles in many cellular processes, particularly those associated with protein synthesis: transcription, RNA processing, and translation.

Transcription/RNA processing: snRNA, pre-mRNA Translation: rRNA, tRNA, mRNA Not used in protein: RNA primers In eukaryotes, pre-mRNA is produced by the direct transcription of the DNA sequence of a gene into a sequence of RNA nucleotides. Before this RNA transcript can be used as a template for protein synthesis, it is processed by modification of both the 5' and 3' ends. In addition, introns are removed from the pre-mRNA by splicing process that is catalyzed by snRNAs (small nuclear RNAs) complexed with proteins. The product of RNA processing, mRNA (messenger RNA), exits the nucleus. Outside the nucleus, the mRNA serves as a template for protein synthesis on the ribosomes, which consist of catalytic rRNA (ribosomal RNA) molecules bound to ribosomal proteins. During translation, tRNA (transfer RNA) molecules macth a sequence of three nucleotides in the mRNA to a specific amino acid, which is added to the growing polypeptide chain. RNA primers are not used in protein synthesis. RNA primers are only needed to initiate a new strand of DNA during DNA replication.

2 step process. transcription mrna serves as temporary info carrier to carry outside the nucleus. Translation occurs inside a ribosome--a large complex of protein and ribosomal RNA or rRNA. Two subunits of the ribosome associate with the mRNA. Ribosome translates the code of nucleotides in the mRNA into the sequence of amino acids in a protein.Although many other protein factors also have roles in this process, the main players in translation are the mRNA molecule, the two subunits of a ribosome, and a pool of molecules called transfer RNAs or tRNAs. Each tRNA is attached to a specific amino acid and is therefore called an aminoacyl tRNA.

Translation occurs in three stages: initiation, elongation, and termination. Initiation stage begins when an mRNA molecule and the small subunit of the ribosome associate. In Eukaryotes, the small subunit binds to a chemical group on the mRNA called the 5' cap that then slides to the first AUG sequence, which is the start codon in the mRNA. An aminoacyl tRNA binds to the AUG triplet. This tRNA contains a complenentary triplet-the anticodon-that forms hydrogen bonds with the bases in the start codon.The large ribosomal subunit then joins the complex, completing the initiation stage of translation. Elongation stage: the ribosome builds the protein during the elongation stage. An aminoacyl tRNA occupies the middle position, called the P site (for peptidyl). The tRNA at the P site holds the growing polypeptide chain. A site holds new aminoacyl tRNAs that enter the ribosome. The E site (for exit) the ribosome ejects the used tRNA, which no longer holds an amino acid. Elongation begins when a new amino acid tRNA enters the A site where the cycle continues. The large ribosomal subunit catalyzes a reaction in which the two adjacent amino acids form a covalent bond called a peptide bond. At the same time, in the P site, the bond between the tRNA and its amino acid breaks. Translocation: the ribosome slides one codon down the mRNA, in the 5' to 3' direction. Termination: In the genetic code, three triplets, including the UAA codon, function as stop codons and trigger the end of protein synthesis. In the cell, there is no tRNA that has an anticodon complementary to a stop codon. Instead, proteins called release factors enter the A site, recognize the stop codons, and catalyze a reaction in which the polypeptide is cleaved from the adjacent tRNA. The mRNA and the two ribosomal subunits dissociate. Each component is now free for another round of protein synthesis.

True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.

True When the 3' end of one DNA strand points in the same direction as the 5' end of the other DNA strand, the strands are said to be antiparallel.

Use the codon table to determine which mRNA triplets code for the amino acid cysteine, Cys.

UGU, UGC. There are only two mRNA triplets that code for the amino acid Cys: UGU and UGC.

PART D - Evaluating a hypothesis If Chargaff's equivalence rule is valid, then hypothetically we could extrapolate this to the combined genomes of all species on Earth (as if there were one huge Earth genome). In other words, the total amount of A in every genome on Earth should equal the total amount of T in every genome on Earth. Likewise, the total amount of G in every genome on Earth should equal the total amount of C in every genome on Earth. Calculate the average percentage for each base in your completed table. Do Chargaff's equivalence rules still hold true when you consider those six species together?

Yes, the average for A approximately equals the average for T, and the average for G approximately equals the average for C. The averages from the table support Chargaff's A = T and G = C equivalence relationships.

What does a mutagen cause? See Concept 17.5 (Page)

a change in sequence of DNA. Mutations are changes in the genetic material of the cell.

A hydroxyl is present at the 3' end of the growing DNA strand. What is at the 5' end?

a phosphate group The 5' phosphate is an important player in the reaction that joins the next deoxyribonucleotide onto the growing strand.

As a result of its involvement in a chemical reaction, an enzyme

is unchanged by the reactants or products. An enzyme is a macromolecule that acts as a catalyst, a chemical agent that speeds up a reaction without being consumed or changed by the earlier reaction. An enzyme catalyzes a reaction by lowering the Ea barrier, enabling the reactant molecules to absorb enough energy to reach the transition state. Enzymes emerge from the reaction in their original form, having neither donated nor received matter or energy from the reactants.

Which nucleic acid is translated to make a protein?

mRNA is the message that is translated to make a protein. tRNAs carry amino acids to the growing polypeptide chain on the ribosome so it cannot be the correct answer.

What process repairs damage to a preexisting double helix? See Concept 16.2 (Page)

nucleotide excision repair In nucleotide excision repair, a section of DNA containing the damage is removed, and the gap is then filled in and completed by DNA polymerase and DNA ligase.

What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called? See Concept 16.2 (Page)

telomeres Telomeres consist of many copies of a short DNA sequence that is bound by specific proteins.

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

template An old DNA strand is used as a template for the synthesis of a complementary new strand.

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 This is referred to as specific base pairing.

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?

transcription Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA.

Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?

A substitution missense affects only one codon, but a frameshift missense affects all codons downstream of the frameshift. Many genetic diseases are caused by missense mutations.

Polypeptides are assembled from _____.

Amino acids Proteins are composed of amino acid monomers

During mitosis, centromeres separate and chromatids become individual chromosomes during which phase?

Anaphase During prophase and prometaphase, the duplicated chromosomes become condensed. During metaphase, the duplicated chromosomes are all aligned at the metaphase plate, a plane that is equidistant between the spindle's two poles. Anaphase is the phase where the two sister chromatids of each pair separate and each chromatid becomes an independent chromosome. This is followed by telophase, during which two daughter nuclei form in the cell, the nucleoli reappear, and the chromosomes become less condensed.

Duplication of chromosomes occurs during S phase of the cell cycle. Duplication requires the separation of complementary DNA strands to allow for DNA replication. Which of the following statements best explains how weak hydrogen bonds function better in this situation than stronger bonds would?

Complementary DNA strands are separated or "unzipped" for the replication process. Weak hydrogen bonds between complementary strands are easily disrupted during DNA replication because they are not high-energy chemical bonds. Hydrogen bonds connect complementary bases from opposite strands of the DNA molecule. Hydrogen bonds are relatively weak, low-energy interactions that allow complementary DNA strands to "unzip" during S phase replication.

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

DNA can change. Errors in copying can result in changes in the DNA sequence that could be inherited by future generations. DNA stores genetic information in the sequence of its bases. DNA can be replicated by making complementary copies of each strand. The structure of DNA suggested that the order of bases contains information. Because A is always paired with T and G with C, the order of bases on one strand determines the order on the other strand. Thus, if a DNA molecule were unwound, each strand could be copied into a complementary strand, producing an exact replica of the original molecule.

The enzyme that can replicate DNA is called _____.

DNA polymerase. (DNA replication is a central process in biochemistry and must be done with the highest precision. If a mistake is made in the replication of DNA, the error will propagate into future generations. An error that occurs during replication is called a mutation.)

Which of the following shows the flow of genetic information?

DNA to RNA to protein DNA directs RNA synthesis and, through RNA, controls protein synthesis; this entire process is called gene expression. The sites of protein synthesis are cellular structures called ribosomes.

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

Hershey and Chase Hershey and Chase did a series of classic experiments demonstrating that DNA is the genetic material of the T2 phage.

Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?

It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one. When the sequence of bases in a gene is changed by a single nucleotide-pair substitution, it can have different effects on the product depending on where it is and whether or not the mutated codon codes for the same amino acid as the original codon.

Where does RNA polymerase begin transcribing a gene into mRNA? See Concept 17.2 (Page)

It starts after a certain nucleotide sequence called a promoter. In both eukaryotes and prokaryotes, RNA polymerase binds to the gene's promoter and begins transcription at a nucleotide known as the start point, although in eukaryotes the binding of RNA polymerase to the promoter requires transcription factors.

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. Different scientists took different approaches to understanding the structure of DNA, based upon their training and the tools available. In the end, the problem was solved using all these different approaches.

Before a molecule of mRNA can be translated into a protein on the ribosome, the mRNA must first be transcribed from a sequence of DNA. What amino acid sequence does the following DNA nucleotide sequence specify? 3′−TACAGAACGGTA−5′3′−TACAGAACGGTA−5′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-His-Lys-Gly).

Met-Ser-Cys-His Before mRNA can be translated into an amino acid sequence, the mRNA must first be synthesized from DNA through transcription. Base pairing in mRNA synthesis follows slightly different rules than in DNA synthesis: uracil (U) replaces thymine (T) in pairing with adenine (A). The codons specified by the mRNA are then translated into a string of amino acids.

The letter A indicates a _____.

Phosphate group Phosphate groups contain phosphorus..

Which of the following enzymes creates a primer for DNA polymerase?

Primase This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.

Which of the following statements about DNA synthesis is true?

Primers are short sequences that allow the initiation of DNA synthesis When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.

Which of the following statements about Okazaki fragments in E. coli is true?

They are formed on the lagging strand of DNA. DNA synthesis always proceeds in the 5' to 3' direction. While DNA is synthesized continuously on the leading strand, Okazaki fragments are formed on the lagging strand because DNA synthesis always proceeds in the 5' to 3' direction.

Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced? Enter the sequence of bases as capital letters with no spaces and no punctuation. Begin with the first base added to the growing RNA strand, and end with the last base added

UGAGCC There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence.The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand.The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction.In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.

What enzyme catalyzes the attachment of an amino acid to tRNA?

aminoacyl-tRNA synthetase This enzyme matches a particular tRNA with a particular amino acid.

During RNA processing a(n) _____ is added to the 5' end of the RNA.

modified guanine nucleotide During RNA processing a(n) _____ is added to the 5' end of the RNA.

This is an image of a _____.

phage This is a T2 phage, a type of phage that infects E. coli.

What materials does DNA polymerase require in order to synthesize a complete strand of DNA? Select all that apply.

single-stranded DNA template, 3'-OH end of the new DNA strand, all four deoxyribonucleotides triphosphates (containing A, C, T, or G) In order for DNA polymerase to synthesize a complete new strand of DNA, it requires a template to determine the order of bases on the new strand, a 3'-OH end to add more nucleotides onto, and the full set of four kinds of nucleotides (A,C,T,G) if they are needed to complement the template strand.

You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.

sugar with two, and not three, oxygen atoms DNA nucleotides are composed of deoxyribose sugars, whereas RNA nucleotides are composed of ribose sugars.

In the diagram below, the green unit represents _____

the promoter The promoter is the region of DNA at which the process of transcription begins.

Which of the following sequences shows a frameshift mutation compared to the wild-type mRNA sequence?

wild-type 5'-AUGCAUACAUUGGAGUGA-3' mutant 5'-AUGCAUACAUCUGGAGUGA-3' In order for an insertion or deletion to cause a frameshift mutation, it must cause the reading frame of each triplet of bases after it to be shifted by one or two places.

Which of these is a tRNA?

B

Which of these correctly illustrates the pairing of DNA and RNA nucleotides?

GTTACG CAAUGC In RNA, uracil takes the place of thymine.

This is an image of a(n) _____.

Nucleotide Nucleotides are composed of a pentose sugar, a nitrogenous base, and a phosphate group.

Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?

Phosphate groups The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis.

Which of the following processes is an example of a post-translational modification?

Phosphorylation. Enzymes can phosphorylate proteins to alter their activity.

Various types of chemical bonds or interactions maintain the three-dimensional (3D) structure of large biological molecules like DNA. Not all types of bonds or interactions are shown in all diagrams. The types of bonds or interactions shown depend on the emphasis of the particular diagram. Which of the following diagrams most clearly shows the overall 3D shape and atomic composition of DNA?

Space-filling model The space-filling model shows each atom making up the two strands, and reveals the helical shape and the double-stranded structure of the DNA molecule.

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. Chargaff's observation was an important clue to the A-T and G-C pairings that Watson and Crick eventually proposed.

Your body contains tens of thousands of different proteins, each with a specific structure and function. The unique three-dimensional shape of each of these diverse proteins is based on several superimposed levels of structure. Which of the following is an accurate statement about proteins?

The primary structure of a protein is the order of amino acids in a polypeptide, as coded for by the DNA of a gene. If you had trouble with this question, review the following material: The primary structure of a protein is its sequence of amino acids, which dictates secondary and tertiary structure. Secondary structure, such as α helices or β pleated sheets, is the result of hydrogen bonds between the repeating constituents of the polypeptide backbone. Tertiary structure is the overall shape of a polypeptide resulting from interactions between the side chains (R groups) of the various amino acids, and quaternary structure is the overall protein structure that results from the aggregation of two or more polypeptide chains into one functional macromolecule.

A nonsense mutation causes an early Stop codon to occur. A missense mutation causes a wild-type amino acid to be replaced by a different amino acid. A silent mutation does not change the wild-type amino acid sequence.

These are the three possible outcomes of small-scale substitutions in genes.

Part A-Analyzing the data Tables like the one shown here are useful for organizing sets of data representing a common set of values (in this case, percentages of A, G, C, and T) for a number of different samples (in this case, species). Does the distribution of bases in sea urchin DNA and salmon DNA follow Chargaff's rules?

Yes, because the %A approximately equals the %T and the %G approximately equals the %C in both species.

During RNA processing a(n) _____ is added to the 3' end of the RNA.

a long string of adenine nucleotides A poly-A tail is added to the 3' end of the RNA.

The action of helicase creates _____.

replication forks and replication bubbles A replication fork is the transition region between paired and unpaired DNA strands.

Where does translation take place?

ribosome. Translation, or protein synthesis, occurs at the ribosome.

Spliceosomes are composed of _____.

small RNAs and proteins

A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain. See Concept 17.1 (Page)

three...amino acid Three nucleotide bases make up a codon and specify which amino acid comes next in the sequence.