Cell Bio Chapter 5 and 8 HW

Which of the following is considered a housekeeping protein?

RNA polymerase

Which structure is normally on the 5' end of a DNA strand

phosphate group On the 5' carbon of the pentose sugar (deoxyribose), a phosphate group is attached. The hydroxyl group of the sugar molecule is positioned on the 3' carbon, while the nitrogenous base is positioned on the 1' carbon. The differing chemical groups on the sugar molecules that compose DNA, together with the nature of the phosphodiester bond that links nucleotide monomers into a DNA polymer, result in the 5'-to-3' polarity that is used to describe DNA.

What type of bond connects base pairs?

hydrogen A DNA molecule is composed of two polynucleotide chains (DNA strands) held together by hydrogen bonds between the paired bases. Each strand of a DNA double helix contains a sequence of nucleotides that is exactly complementary (due to hydrogen-bonding) to the nucleotide sequence of its partner strand. The sugar-phosphate backbone of each strand is composed of a phosphodiester bond between individual nucleotides.

A housekeeping gene is a gene whose cellular function is

important for processes found in all cell types.

The technique whereby human chromosomes are stained and identified is called a

karyotype Scientists can stain chromosomes from a human tissue sample in order to identify all the chromosomes. Identification is done from the staining pattern or by using chromosome sequence-specific fluorescent dyes and can be helpful in identifying abnormalities in the size, number, or sequence rearrangement of chromosomes.

Although all of the steps involved in expressing a gene can in principle be regulated, what is the most important stage of control for most genes?

transcription initiation

Which form of control directly influences which mRNAs are selected by ribosomes for the synthesis of proteins?

translational control

A cell can change the expression of its genes in response to external signals.

true

In eukaryotes, where do transcription regulators bind?

upstream, downstream, or within the genes they control

Which of the labels in the following figure shows a nucleosome core particle?

B Approximately 147 bp DNA is wrapped around a core of eight histone proteins to form a "nucleosome core particle." This is the basic unit of chromatin. The nucleosome is the core particle plus the ~200 bp of linker DNA between core particles.

Which of the following describes the Lac operon in E. coli when lactose, but not glucose, is present in the culture medium?

CAP, but not the Lac repressor, is bound to the Lac operon's regulatory DNA, and the Lac operon is expressed.

Which of the statements below is supported by the Avery, McCarty, and MacLeod experiment and the data in the figure above?

DNA from one strain of bacteria can alter the phenotype of another strain if that DNA is taken up by the other strain. The Avery, McCarty, and MacLeod experiment and the data in the figure demonstrate that DNA from one strain of bacteria can alter the phenotype of another strain if that DNA is taken up by the other strain. The researchers prepared an extract from the disease-causing S strain of pneumococci and showed that the "transforming principle" that would permanently change the harmless R strain pneumococci into the pathogenic S strain is DNA. This was the first conclusive evidence that DNA could serve as the genetic material.

Another step in PCR requires small single-stranded DNA primers to anneal to a target sequence on denatured DNA. Two primers are used. Ideally these primers will have similar melting temperatures. The melting temperature is defined as the temperature at which 50% of the DNA is in the single-stranded form. Which of the following primers will have the highest melting temperature?

G G G G A A A T T T C C C C Since G-C base pairs contain an extra hydrogen bond, it takes more heat energy to separate them. Thus primers with greater G-C content have a higher melting temperature. There are software programs, such as Primer-BLAST, that aid in designing PCR primers to amplify a given DNA sequence. The structure of DNA, with covalent phosphodiester bonds linking adjacent nucleotides within a single strand and hydrogen bonds (three for G-C base pairs and two for A-T base pair) linking complementary base pairs and thereby holding the two single strands into a double helix, explains both parts of this question.

The results of the Hershey and Chase experiment in this image are consistent with the results from the Avery, McCarty, and MacLeod experiments, which determined that DNA was the "transforming principle" that changed nonpathogenic bacteria into pathogenic bacteria.

Hershey and Chase showed definitively that genes are made of DNA. Radioactively labeled viruses were allowed to infect E. coli, and the mixture was then disrupted by brief pulsing in a Waring blender, followed by centrifugation to separate the infected bacteria from the empty viral heads. When the researchers measured the radioactivity, they found that much of the 32P-labeled DNA had entered the bacterial cells, while the vast majority of the 35S-labeled proteins remained in solution with the spent viral particles. Furthermore, the radioactively labeled DNA also made its way into subsequent generations of virus particles, confirming that DNA is the heritable, genetic material.

Which statement is true about the association of histone proteins and DNA?

Histone proteins have a high proportion of positively charged amino acids, which bind tightly to the negatively charged DNA backbone. Histone proteins have a high proportion of positively charged amino acids, which bind tightly to the negatively charged DNA backbone. Because the entire DNA backbone is negatively charged, the electrostatic interaction between histones and DNA can occur throughout the length of the DNA molecule, regardless of the nucleotide sequence. It is important to note that the lysine and arginine residues that interact with the DNA backbone are distant from those in the histone tails that undergo modification to regulate chromatin form.

The DNA in eukaryotic chromosomes is folded into a compact form by interactions with which of the following?

Histones The DNA in eukaryotic chromosomes is folded into a compact form by interactions with histone proteins. Histones are responsible for the first and most fundamental level of chromatin packing: the formation of the nucleosome. Even at interphase, when chromatin is in a relatively relaxed form, the packing of DNA around histones shortens the DNA molecule to about one-third its original length. During mitosis, chromatin packs even further, first forming a chromatin fiber that then folds into loops, eventually resulting in the highly condensed mitotic chromosome, which is approximately 10,000 times shorter than the original DNA strand.

In bacterial cells, the tryptophan operon encodes the genes needed to synthesize tryptophan. What happens when the concentration of tryptophan inside a cell is high?

It activates the tryptophan repressor, which shuts down expression of the tryptophan operon.

Which of the following is a function of the protein component of chromosomes?

It packages the DNA strands. Chromosomes are made up of protein and DNA. The DNA carries the genetic information, and the protein component helps store the long DNA molecules in the cell, in addition to controlling access to the DNA molecules.

Why are individual DNA strands considered polar?

One end terminates in a hydroxyl group, while the other terminates in a phosphate Individual DNA strands are considered polar because one end terminates in a hydroxyl group, and the other in a phosphate. The end with the free hydroxyl group (which is attached to the 3' carbon position of the sugar) is called the 3' end, while the end bearing the phosphate group (which is attached via the 5' hydroxyl group of the sugar) is called the 5' end. Polarity is established by the phosphodiester bonds that link individual nucleotides to each other to form the DNA polymer, as shown in the figure below.

In the late 1920s, bacteriologist Fred Griffith was studying Streptococcus pneumoniae. This bacterium comes in two forms: one that is highly infectious (called the "S strain" because it forms colonies that appear smooth when grown on a nutrient plate in the lab) and one that is relatively harmless (called the "R strain" because its colonies appear rough). When injected into mice, the S strain is lethal, whereas the R strain causes no ill effect. Griffith confirmed that when the S strain is killed by heating, it is no longer infectious. But he then discovered that if he injected mice with both the heat-killed S strain pneumococci and the live, harmless R strain bacteria, the animals died of pneumonia. Furthermore, their blood was swarming with live, S strain bacteria that, when grown in culture, remained infectious and lethal.Based on these results, what could Griffith conclude?

Some substance in the infectious S strain can change the harmless R strain into the more lethal form. Griffith's results opened the door to experiments that would demonstrate that DNA is the genetic material. But his work did not, on its own, provide information about the identity of the substance that carries hereditary information. Based on his results, Griffith could conclude that some substance in the infectious S strain could change the harmless R strain into the more lethal form. The Griffith experiments were performed in the early 1900s, well before the Watson and Crick publication, along with a series of other publications including those by Avery, McCarty, and MacLeod and by Hershey and Chase, all of which led to the acceptance that DNA was the hereditary biomolecule.

Some applications in biology, such as polymerase chain reaction (PCR), require melting the DNA double helix into single strands of DNA. This can be accomplished by heating the DNA. As DNA is heated, why does the double helix structure denature into single strands of DNA but not into individual nucleotides? In other words, why do the single strands remain intact even though the double helix does not?

The double helix is held together with hydrogen bonds, while the single strands are linked by phosphodiester bonds. Within each strand of DNA, adjacent nucleotides are connected via covalent phosphodiester bonds. In contrast, relatively weaker hydrogen bonds between complementary base pairs hold the two strands of the double helix together. These structural differences support the function of DNA. DNA must be able to unwind into single strands during DNA replication and transcription, and it is important that each strand remains intact to serve as a template for new DNA strand synthesis or RNA production.

Which of the following statements is not true about the differences between liver cells and kidney cells in the same organism?

They contain different genes.

How do chromatin-remodeling complexes work?

They use the energy from ATP hydrolysis to alter the arrangement of nucleosomes, rendering certain regions of the DNA more accessible to other proteins. Chromatin-remodeling complexes are multi-subunit protein machines that utilize ATP to reposition DNA along the histone. Using the figure below, you can visualize the action of the chromatin-remodeling complex as moving a string (the DNA) over a spool (the histone). In this figure, the blue bands on the DNA have been included to help show the movement of the DNA over the histone "spool" and in the process, certain regions of the DNA have now become more accessible while others are more sequestered away.

Intense exercise can change gene expression.

True

Once heterochromatin has been established, it will often spread until it encounters which of the following?

a barrier DNA sequence The form of chromatin in which a stretch of an interphase chromosome finds itself largely depends on the modification of histone tails. When heterochromatin-specific proteins bind to a chromosome, they tend to also modify the tails of neighboring nucleosomes, causing the spread of heterochromatin. This spread continues until the remodeling proteins reach a DNA sequence that acts as a barrier. Barrier sequences can function by having a different histone modification that favors the euchromatin conformation. For example, a common barrier DNA sequence modification is the addition of an acetyl group to lysine 9 on histone H3, which blocks the heterochromatin-inducing modification of methylation on that same lysine residue of histone H3.

Which chemical group is at the 3' end of a DNA strand?

a hydroxyl group A hydroxyl group is located at the 3' end of a DNA strand. The phosphate group on a nucleotide is attached to the 5' carbon of the pentose sugar and reacts with the 3' hydroxyl group to form the phosphodiester bond that links individual nucleotides into a DNA polymer, as shown in the figure below. Because of the nature of the phosphodiester bond, DNA strands have a distinct polarity, with one end harboring a free hydroxyl group (the 3' end) and the other harboring a free phosphate group (the 5' end).

Transplanting the nucleus of an epithelial cell into an egg cell lacking genetic information leads to the formation of

a normally developing embryo.

What is an operon?

a set of genes transcribed as a single mRNA from a single promoter

The tails of the core histone proteins can be chemically modified by the covalent addition of what type of chemical group?

acetyl, methyl and phosphate The tails of the core histone proteins can be chemically modified by the covalent addition of methyl, acetyl, or phosphate groups. Each modification alters the physiology of the histone by modulating the packing of the chromatin fiber. Acetylation of histone tails, for instance, can reduce the affinity of the tails for adjacent nucleosomes, thereby promoting the euchromatin form. Alternatively, methylation of histone tails has the opposite effect and promotes condensation into heterochromatin.

Which option correctly describes the two strands of DNA in a double helix?

antiparallel in orientation The two strands of DNA are considered to be antiparallel in orientation. This means that one strand runs 5' to 3' against the 3'-to-5' orientation of the other strand, as shown in the figure below. In double-stranded DNA, base-pairing is such that A always pairs with T, and G always pairs with C, hence the term "complementary base-pairing." Base pairs are held together via hydrogen-bonding, which allows for both a stable double-stranded structure and the ability to separate the strands to allow for DNA replication and transcription

Which region is most likely to contain the highest density of genes?

b-euchromatin Heterochromatin tends to be relatively gene poor, whereas euchromatin is relatively gene rich. This is due to the gene expression machinery requiring access to the DNA in chromatin for transcription.

If lactose and glucose are both available to a bacterial cell, which carbon source(s) will be used?

glucose

Which of the following represents the specialized DNA sequence that attaches to microtubules and allows duplicated eukaryotic chromosomes to be separated during M phase?

centromere The specialized DNA sequence that allows duplicated eukaryotic chromosomes to be separated during M phase is a centromere. During this stage of the cell cycle, the DNA coils up, adopting a more compact structure and ultimately forming highly compacted, or condensed, mitotic chromosomes. Once the chromosomes have condensed by histones, the centromere allows the mitotic spindle to attach to each duplicated chromosome in a way that directs one copy of each chromosome to be segregated to each of the two daughter cells. The telomeres mark the ends (tips) of each chromosome, and these structures contain repeated nucleotide sequences that are required for the ends of chromosomes to be fully replicated. They also serve as a protective cap that keeps the chromosome tips from being mistaken by the cell as broken DNA in need of repair. Nucleosomes are the basic units of eukaryotic chromosome structure and are composed of histone proteins. Nucleosomes convert the DNA molecules in an interphase nucleus into a chromatin fiber that is approximately one-third the length of the initial DNA. As this histone association with DNA increases, the chromosome becomes much more visible in the microscope.

What is the term that describes the complex of DNA and proteins that makes up a eukaryotic chromosome?

chromatin The complex of DNA and proteins that makes up a eukaryotic chromosome is called chromatin. Chromatin functions to condense the long, linear DNA into a more compact form. The fundamental unit of chromatin is the nucleosome, which is composed of the DNA molecule wrapped tightly around histone proteins. Nucleosomes appear like "beads on a string" and can be further condensed into more compact arrangements.

When are chromosomes in their most compacted form?

during mitosis During mitosis, the chromatin structure that packages chromosomes gets even more compacted than usual. This is to compress the chromosomes into discrete bodies that are easier to separate and organize.

Different cell types that respond to the same hormone usually turn on the same sets of genes.

false

Once a cell has become specialized to produce the set of proteins that are responsible for its distinctive properties, its gene expression patterns remain fixed.

false

The karyotype below was obtained from a human cell. Based on the chromosome spread, what cell type could have been used?

female human liver cell With the exception of the gametes (sperm and eggs) and highly specialized cells that lack DNA entirely (such as mature red blood cells), human cells each contain two copies of every chromosome, one inherited from the mother and one from the father. The maternal and paternal versions of each chromosome are called homologous chromosomes (homologs). The only nonhomologous chromosome pairs in humans are the sex chromosomes in males, who inherit an X chromosome from the mother and a Y chromosome from the father. Females contain two X chromosomes, one inherited from each parent.

At any given time, a typical differentiated human cell will express how many of its approximately 19,000 protein-coding genes?

from 5000 to 15,000

Using powerful new sequencing technologies, investigators can now catalog every RNA molecule made by a cell and determine at what quantities these RNAs are present. In an experiment, researchers measured the relative quantities of two different mRNAs—one transcribed from gene A, the other from gene B—in two different cell types. Gene B is expressed in both the liver and the brain whereas gene A is expressed in the brain but not in the liver. Which most likely encodes a housekeeping protein?

gene b only

The type of bond that holds together neighboring subunits in a single strand of DNA is a

phosphodiester bond. DNA is a long polymer of nucleotides held together by phosphodiester bonds. This forms a single strand of DNA. The two strands of DNA are held together by hydrogen bonds between the nucleotide bases.

Prokaryotes have chromosomes that are circular in structure. Which of the following would such chromosomes lack?

telomeres Prokaryotes have chromosomes that are circular in structure, so these chromosomes would lack telomeres, which are a feature of linear chromosomes. While prokaryotes and eukaryotes exhibit differences in the structure of their chromosomes, the structure of the DNA itself is largely the same between these two groups of organisms.

In eukaryotes, multiple genes can be expressed simultaneously by

the binding of a specific transcriptional regulator to several genes.

Which of the following statements most accurately describes the expression of the repressor protein of the tryptophan operon

the gene for the tryptophan repressor is expressed constitutively.he gene for the tryptophan repressor is expressed constitutively.he gene for the tryptophan repressor is expressed constitutively.

Which is not an example of epigenetic inheritance?

the inheritance of a single point mutation in a gene

In the early part of the twentieth century, scientists thought that proteins were the most likely carriers of genetic information. What characteristic of proteins led scientists to this belief?

their chemical diversity In the early part of the twentieth century, scientists thought that proteins were the most likely carriers of genetic information because proteins are so chemically diverse. Proteins, which are built from a set of 20 different amino acids, were thought to have the chemical diversity necessary to encode the information needed to build cells. DNA, which is built from a set of only four nucleotides, seemed too chemically simple for the task. Proteins are very abundant within cells, vary in size from quite small to quite big, and fold into well-defined, three-dimensional structures, but it is their chemical complexity that caused scientists to speculate that proteins were involved in the genetic code.

"Although my nucleotide partner in double-stranded DNA is nearly twice my size, we are remarkably well matched. Of course, when the heat is on, we tend to go our separate ways easily because we are only connected by two hydrogen bonds. Who am I?"

thymine Single-ring pyrimidine bases (cytosine, thymine) always pair with a larger, double-ringed purine base (guanine, adenine) in a specific manner, as shown in the figure below. Notable from this figure is the fact that G-C base pairs form three hydrogen bonds, whereas A-T base pairs only form two. Applying heat to a double-stranded DNA molecule will result in its separation into single strands, sometimes referred to as "melting." Because of the difference in the number of hydrogen bonds, A-T base pairs will separate before G-C base pairs. Uracil, which is a base found in RNA but not DNA, is complementary to adenine and, in effect, replaces thymine in RNA molecules.

"I'm a nitrogen-containing base, just like the other nitrogenous bases. However, they don't let me into their exclusive 'DNA base club.' Who am I?"

uracil Uracil is the nitrogenous base that is only found attached to ribose sugars and not attached to deoxyribose sugars. Thus, the uracil nucleotide is part of RNA but not DNA. Adenine, thymine, guanine, and cytosine are regularly found within DNA. Adenine, guanine, and cytosine are also regularly found within RNA, along with uracil.

The transcription initiation site of a eukaryotic gene is found at which location?

where RNA synthesis begins