LC CH 11
Some epigenetic effects are caused by differences in DNA _____ during development.
methylation Methylation is a process by which methyl groups are added to the DNA molecule, which can change the activity of a DNA segment without changing the sequence.
A student discovers a small amount of DNA in a test tube but doesn't know its origin. She finds that it has no associated histone proteins and is circular. This DNA is most likely from which genome? A mitochondrial DNA B plant nuclear DNA C human sex chromosomes D eukaryotic nuclear DNA
mitochondrial DNA Mitochondrial DNA has no associated histones and is circular.
Many petite mutants in yeast grow slowly, are deficient in aerobic respiration, and exhibit cytoplasmic inheritance. These mutations usually involve defects in genes located on
mitochondrial DNA. Mitochondrial petite mutants often have large deletions in mtDNA or, in some cases, are missing mtDNA entirely.
What would you expect to see in regions of DNA that are sensitive to digestion by DNase I in terms of acetylation?
more acetylation Acetylation causes the histones to hold the DNA less tightly, making it more susceptible to DNase I.
Which statement best describes chromatin associated with actively transcribed genes as compared to chromatin associated with genes which are not being actively transcribed?
more relaxed and more acetylated Acetylation of histone tails causes the histones to loosen their grip on DNA so that the genetic information is more accessible to the transcriptional machinery.
The antibiotics tetracycline and erythromycin inhibit protein synthesis in eubacteria but have no effect on protein synthesis encoded by nuclear genes. Cycloheximide inhibits protein synthesis encoded by nuclear genes but has no effect on eubacterial protein synthesis. Which antibiotic will most likely inhibit protein synthesis in mitochondria? A tetracycline and erythromycin B tetracycline C cycloheximide D erythromycin
tetracycline and erythromycin The same antibiotics that inhibit protein synthesis in eubacteria generally inhibit mitochondrial protein synthesis.
Which of these descriptions of the arrangement of DNA in eukaryotic cells is most accurate?
tightly packed and dynamic DNA must be tightly packed to fit within a cell, but the packing must be reduced sometimes to allow for access to the genetic information contained within the DNA.
Chromosomal puffs on polytene chromosomes in Drosophila indicate areas of active
transcription. The correlation between the occurrence of transcription and the relaxation of chromatin at a puff site indicates that chromatin structure undergoes dynamic change associated with gene activity.
When double-stranded DNA is heated, the hydrogen bonds holding it together are broken. What structure of DNA does this result in?
two single-stranded DNA molecules With enough heat, the two DNA strands separate completely in a process called denaturation or melting.
Which of the eukaryotic DNA sequences would likely be in a gene family together? Choose the most complete answer. (1) 5' ATCGTAAGCTA 3' (2) 5' GCTCCCCA 3' (3) 5' ATCGTATCGTA 3' (4) 5' ATTTTTTTGGGGG 3' (5) 5' ACCGTAAGGTT 3'
1, 3, 5 Genes within unique-sequence DNA are present in several similar, but not identical, copies and are collectively referred to as a gene family.
How many copies of the H2B histone would be found in chromatin containing 50 nucleosomes?
100 The nucleosome is a core particle consisting of DNA wrapped about two times around an octamer of eight histone proteins (two copies of H2B).
A diploid human cell contains approximately 6.4 billion base pairs of DNA. How many histones are present in such a cell? Assume that the linker DNA encompasses 40 base pairs. A 288 million B 32 million C 288 billion D 200
288 million Each nucleosome contains two of each of the four types of histones, and a nucleosome plus one molecule of histone H1 constitute the chromatosome.
A diploid human cell contains approximately 6.4 billion base pairs of DNA. How many histones are present in such a cell? Assume that the linker DNA encompasses 40 base pairs.
288 million Each nucleosome contains two of each of the four types of histones, and a nucleosome plus one molecule of histone H1 constitute the chromatosome.(6.4x40)+(8x4)= 288 million????
Each sequence is one strand of a double-stranded molecule. Which DNA molecule would have the highest melting temperature? A 5′-AAAAAAAAAAAA-3′ B 5′-ATATAATTGCAT-3′ C 5′-GCAGGATCCGCG-3′ D 5′-ATGCGGCCAATA-3′
5′-GCAGGATCCGCG-3′ This molecule consists almost entirely of GC base pairs and would have the highest melting temperature.
Which statement about telomeres is NOT correct? A Telomere sequences usually are the same length on different chromosomes and in different cells within the body. B Telomeres usually consist of short sequences repeated hundreds to thousands of times. C Telomeres serve as end caps that stabilize chromosomes. D Telomeres allow for the replication of the ends of chromosomes.
Telomere sequences usually are the same length on different chromosomes and in different cells within the body. The length of telomeres varies greatly from chromosome to chromosome and between different cells of the body.
Which statement about telomeres is NOT correct? A Telomeres serve as end caps that stabilize chromosomes. B Telomeres usually consist of short sequences repeated hundreds to thousands of times. C Telomere sequences usually are the same length on different chromosomes and in different cells within the body. D Telomeres allow for the replication of the ends of chromosomes.
Telomere sequences usually are the same length on different chromosomes and in different cells within the body. The length of telomeres varies greatly from chromosome to chromosome and between different cells of the body.
Which of these is NOT a key feature of a centromere? A Most of the centromere is made up of heterochromatin. B The centromere is located at the ends of a chromosome. C Most centromeres are defined by epigenetic modifications. D There are no specific sequences that are found in all centromeres.
The centromere is located at the ends of a chromosome. The centromere is located in the middle of a chromosome.
Which statement about chromatin organization is NOT true? A Chromatin consists primarily of DNA and histone proteins. B Heterochromatin is more highly condensed than euchromatin. B The default (normal) condition of all chromatin is to be transcriptionally active. D Actively transcribed genes are found primarily in euchromatin.
The default (normal) condition of all chromatin is to be transcriptionally active. At any one time, only a small fraction of the genome is transcribed, and most genes are sequestered from the transcription machinery within tight coils and loops of chromatin.
Leber's hereditary optic neuropathy (LHON) is a disease caused by a mutation in mitochondrial DNA that usually produces acute loss of vision, resulting in complete blindness in young adulthood. Bill has a severe case of LHON. His mother, however, has only a mild case of the disease. What is the most likely explanation for the fact that Bill is severely affected but his mother is only mildly affected? A Bill's mother is heteroplasmic for the LHON mutation. B LHON exhibits incomplete dominance. C LHON is an X-linked disorder that more severely affects males. D LHON is a recessive disorder.
Bill's mother is heteroplasmic for the LHON mutation. The different severities of the disease in Bill and his mother are most likely due to the fact that Bill's mother is heteroplasmic for the LHON mutation and, by chance, Bill received a larger number of mutant mitochondria than his mother.
All of these repeated sequences can be found in telomeres EXCEPT A TTGGGG. B TTAGGG. C CCGGGG. D TTAGGC.
CCGGGG. Telomeres take the form 5'−(A or T)mGn−3', where m ranges from one to four and n is two or more.
Which variant histone protein takes the place of the usual histone in nucleosomes of centromeres of most eukaryotes?
CenH3
Which of these is generally NOT true about epigenetic effects? A Epigenetic effects are more easily reversed than genetic changes. (Methylation and other chemical changes of DNA and chromatin are easily reversed by particular cellular enzymes.) B Epigenetic effects are often influenced by environmental factors.(The environment can influence the activity of enzymes responsible for chemical modifications of DNA and chromatin that bring about epigenetic effects.) C Epigenetic effects are rare and do not affect very many traits. D Epigenetic effects often involve changes in methylation of DNA bases.
Epigenetic effects are rare and do not affect very many traits. Scientists have discovered a wide variety of epigenetic effects in a large number of organisms.
Which of these is generally NOT true about epigenetic effects? A Epigenetic effects often involve changes in methylation of DNA bases. B Epigenetic effects are rare and do not affect very many traits. C Epigenetic effects are more easily reversed than genetic changes. D Epigenetic effects are often influenced by environmental factors.
Epigenetic effects are rare and do not affect very many traits. Scientists have discovered a wide variety of epigenetic effects in a large number of organisms.
What happens to a chromosome that loses its centromere?
It will not segregate into the nucleus in mitosis and is usually lost. A chromosome lacking a centromere fails to connect to a spindle microtubule and is usually lost because it fails to move into the nucleus of a daughter cell during mitosis.
What happens to a chromosome that loses its centromere? A It will not segregate into the nucleus in mitosis and is usually lost. B It attaches to a spindle microtubule and moves to the spindle pole. C Special proteins bind to this chromosome, protecting it from degradation. D The chromosome will shorten each time the cell divides.
It will not segregate into the nucleus in mitosis and is usually lost. A chromosome lacking a centromere fails to connect to a spindle microtubule and is usually lost because it fails to move into the nucleus of a daughter cell during mitosis.
Which statement about chromatin organization is NOT true? A Heterochromatin is more highly condensed than euchromatin. B Actively transcribed genes are found primarily in euchromatin. C Chromatin consists primarily of DNA and histone proteins. D The default (normal) condition of all chromatin is to be transcriptionally active.
The default (normal) condition of all chromatin is to be transcriptionally active. At any one time, only a small fraction of the genome is transcribed, and most genes are sequestered from the transcription machinery within tight coils and loops of chromatin.
A protein encoded by chloroplast DNA that is considered to be the most abundant protein on Earth is
RuBisCO. RuBisCO makes up about 50% of the protein found in green plants and is considered the most abundant protein on Earth.
What would the telomeres look like in a cell that produces defective shelterin protein? A The telomeres of different chromosomes would be stuck together. B They would be in a t-loop. C The G-rich unpaired strand would not have protein bound to it. D The telomeres would be repaired as a double-strand break.
The telomeres would be repaired as a double-strand break. Shelterin is a multiprotein complex that binds to telomeres and protects the ends of the DNA from being inadvertently repaired as a double- stranded break in the DNA.
Which statement about C-values is TRUE? A Organisms with very high C-values do not have very many highly repeated DNA sequences. B Humans have a higher C-value than salamanders. C Typically, bacteria have a higher C-value than eukaryotes. D There is not a strong correlation between C-value and organismal complexity among eukaryotes.
There is not a strong correlation between C-value and organismal complexity among eukaryotes. Most of the variation in C-value among eukaryotes is due to vast differences in the amount of highly repetitive DNA sequences that do not seem to contribute to structural complexity.
Which of these is NOT a characteristic of DNA sequences at the telomeres? A They are located at the center of a chromosome. B One strand consists of guanine and adenine (or thymine) nucleotides. C They consist of repeated sequences. D One strand protrudes beyond the other, creating some single-stranded DNA at the end.
They are located at the center of a chromosome. Telomeres are located at the ends of a chromosome.
Which of these statements about highly repetitive DNA sequences is incorrect? A They tend to be present in hundreds of thousands to millions of copies that repeat and cluster in certain regions of the chromosomes. B They are rarely transcribed into RNA molecules. C They are sometimes referred to as satellite DNA due to the behavior during centrifugation. D They tend to contain protein coding sequences in tandem repeats.
They tend to contain protein coding sequences in tandem repeats. Protein coding sequences are found in unique-sequence DNA.
Neutralizing their positive charges would have which effect on the histone proteins?
They would bind less tightly to DNA. The positive charge of histones is attracted to the negatively charged DNA, so a reduction in the positive charge will weaken the bond between them.
A geneticist isolates mitochondrial DNA from a human, a yeast, and a plant. She places each DNA in a separate test tube, but the labels fall off the tubes and she doesn't know which tube contains which DNA. She analyzes one tube and finds that the DNA in it has about 17,000 bp, contains no introns, and has little noncoding DNA between the genes. This tube most likely contains mitochondrial DNA from A a human. B yeast. (Yeast mitochondrial DNA has noncoding DNA.) C plant. D Cannot tell with the available information.
a human. Human mitochondrial DNA consists of about 17,000 bp, has no introns, and has little noncoding DNA between the genes.
If two strands of DNA from two different sources hybridized at almost all bases, what could you infer about the level of complementarity between the two strands?
a large amount of complementarity A large amount of complementarity can be inferred when the DNA from two sources hybridized at almost all bases.
One explanation for the decrease in oxidative phosphorylation with age is that
damage to mitochondrial DNA increases with age. Because mtDNA is physically close to the enzymes taking part in oxidative phosphorylation, mtDNA may be more prone to oxidative damage due to oxygen radicals.
The symptoms of many human genetic diseases caused by defects in mitochondrial DNA first appear in middle age and increase in severity with age. Which hypothesis explains this late onset and progressive worsening of mitochondrial diseases?
decline in oxidative phosphorylation with aging Oxidative phosphorylation normally declines with age, and if it falls below a critical threshold, tissues do not make enough ATP to sustain vital functions and disease symptoms appear.
Which characteristic helps to generate extensive size variation in the mitochondrial DNA of plants? A absence of termination codons B introns C direct repeats D telomeres and centromeres
direct repeats Crossing over between these repeats can generate multiple circular chromosomes of different sizes.
The extent of _____ can be used to measure the similarity of nucleic acids from two different sources. A hybridization B degradation C melting D denaturation
hybridization The extent of hybridization between DNA from two species can be used to measure the similarity of their nucleic acid sequences and to assess their evolutionary relationship.
In most bacteria, chromosomal DNA A is distributed diffusely and evenly throughout the bacterial cell. B is attached to and wound tightly around histone proteins. C is complexed to several proteins that help to compact it. D exists as a relaxed, open circle.
is complexed to several proteins that help to compact it. The bacterial genome is too large to fit within the cells without extensive packing, which is accomplished by nonhistone proteins.
Would you expect a chromosome that has a large amount of repeated DNA sequences to have a high or low density of genes? A high; the repeated sequences each encode a protein, so there would be many copies of that gene/protein present B low; repeated DNA sequences do not typically encode genes, so there would be a low density of genes in the chromosome relative to the repetitive DNA sequences C low; repeated DNA sequences have no function, so there would be no genes present in the chromosome D high; since there is a high difficulty of repeated DNA, the chromosome itself would be very large and have a high density of genes
low; repeated DNA sequences do not typically encode genes, so there would be a low density of genes in the chromosome relative to the repetitive DNA sequences Typically the DNA that codes for proteins is considered unique-sequence DNA, which is not repeated.
Which statement best describes chromatin associated with actively transcribed genes as compared to chromatin associated with genes which are not being actively transcribed? A more relaxed and more acetylated B more compacted and less acetylated (Highly compacted DNA is less accessible to the transcriptional machinery.) C more compacted and more acetylated D more relaxed and less acetylated (Active chromatin is more relaxed due in part to being more highly acetylated.)
more relaxed and more acetylated Acetylation of histone tails causes the histones to loosen their grip on DNA so that the genetic information is more accessible to the transcriptional machinery.
Poky mutation A exhibits biparental inheritance, whereas poky mutation B exhibits maternal inheritance. These results suggest that A mutation A is in mitochondrial DNA and mutation B is in nuclear DNA. B mutation A is in nuclear DNA and mutation B is in mitochondrial DNA. C mutation A is autosomal and mutation B is X-linked. D mutation A is in mitochondrial DNA and mutation B is in chloroplast DNA.
mutation A is in nuclear DNA and mutation B is in mitochondrial DNA. Mutation A is in nuclear DNA and therefore exhibits biparental inheritance; mutation B is in mitochondrial DNA and therefore exhibits maternal inheritance.
Most DNA is _____ supercoiled, which eases the separation of the two strands during replication and transcription.
negatively Under rotated molecules exhibit negative supercoiling.
A DNA molecule 300 base pairs long has 20 complete rotations. This means that the DNA molecule is
negatively supercoiled. Under rotated molecules exhibit negative supercoiling.
A stretch of 100 base pairs of DNA contains 15 complete rotations. This DNA molecule is A negatively supercoiled. (This DNA molecule has more rotations per 100 bp than relaxed DNA. UNDERROTATED) B positively supercoiled. C denatured. (Denatured means that the double helix is disrupted and the two strands have separated from each other.) D relaxed. (100 bp of DNA would assume about 10 complete turns)
positively supercoiled. This DNA molecule has more rotations per 100 bp than relaxed DNA. OVERROTATED
A cell is heteroplasmic for a mitochondrial DNA mutation. After several cell divisions, some of the resulting progeny cells are heteroplasmic, some are homoplasmic for the mutation, and some are homoplasmic for wild-type mtDNA. Which process is responsible for this variation among cells in their mtDNA? A meiosis B mitosis C replicative segregation D Both mitosis and meiosis
replicative segregation Replicative segregation results in random separation of mitochondrial DNA, which leads to some cells with the mutation, some cells without the mutation, and some cells with both the mutation and wild-type DNA.
What is the purpose of a telomere?
stabilizes the end of a chromosome Telomeres serve as caps that stabilize the chromosome and also provide a means of replicating the ends of a chromosome.
What is the purpose of a telomere? A acts as a site of attachment for spindle fibers in a chromosome B stabilizes the end of a chromosome Cguides the chromosome through meiosis D joins two or more chromosomes together
stabilizes the end of a chromosome Telomeres serve as caps that stabilize the chromosome and also provide a means of replicating the ends of a chromosome.
When DNA is overwound or underwound compared to its relaxed state, it is said to be
supercoiled. One type of DNA tertiary structure is supercoiling, which takes place when the DNA helix is subjected to strain by being overwound or underwound.
The _____ structure of the genetic material refers to the folding that allows it to be packed into the confined space of a cell.
tertiary The tertiary structure of DNA is the higher-order folding that allows DNA to be packed into the confined space of a cell.
