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Questions and Answers
The genome of bacteria typically consists of multiple linear chromosomes.
The genome of bacteria typically consists of multiple linear chromosomes.
False
Eukaryotes contain nuclear and mitochondrial genomes.
Eukaryotes contain nuclear and mitochondrial genomes.
True
Protein-encoding genes make up the majority of bacterial DNA.
Protein-encoding genes make up the majority of bacterial DNA.
True
The nucleoid in bacteria is surrounded by a membrane.
The nucleoid in bacteria is surrounded by a membrane.
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The main role of nontranscribed DNA segments is only to code for proteins.
The main role of nontranscribed DNA segments is only to code for proteins.
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Unique sequences in the human genome make up roughly 41% of the total genome.
Unique sequences in the human genome make up roughly 41% of the total genome.
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The bacterial chromosome is compacted approximately 1000-fold to fit within the cell.
The bacterial chromosome is compacted approximately 1000-fold to fit within the cell.
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Moderately repetitive sequences are found tens of thousands to millions of times in the genome.
Moderately repetitive sequences are found tens of thousands to millions of times in the genome.
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Each bacterial chromosome contains millions of base pairs.
Each bacterial chromosome contains millions of base pairs.
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Microdomains in bacterial chromosomes are typically 1000 bp in length.
Microdomains in bacterial chromosomes are typically 1000 bp in length.
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Highly repetitive sequences, such as the Alu family, can be found clustered together in tandem arrays.
Highly repetitive sequences, such as the Alu family, can be found clustered together in tandem arrays.
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Transposons are a type of DNA segment that can only remain at their original genomic location.
Transposons are a type of DNA segment that can only remain at their original genomic location.
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The function of highly repetitive DNA is well understood among closely related species.
The function of highly repetitive DNA is well understood among closely related species.
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Transposable elements can only replicate through the process of transposition.
Transposable elements can only replicate through the process of transposition.
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Reverse transcriptase is used to convert RNA into double-stranded DNA.
Reverse transcriptase is used to convert RNA into double-stranded DNA.
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All species contain transposable elements in their genomes.
All species contain transposable elements in their genomes.
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The P elements are transposons found only in M strains of Drosophila.
The P elements are transposons found only in M strains of Drosophila.
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Transposons in E. coli can exist in at least five copies.
Transposons in E. coli can exist in at least five copies.
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Alu is a type of transposable element found in the human genome.
Alu is a type of transposable element found in the human genome.
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Tn10 is a retrotransposon that carries antibiotic resistance.
Tn10 is a retrotransposon that carries antibiotic resistance.
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Transposable elements (TEs) were first discovered by Barbara McClintock in the mid-1960s.
Transposable elements (TEs) were first discovered by Barbara McClintock in the mid-1960s.
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Ac/Ds transposable elements are only found in animal species.
Ac/Ds transposable elements are only found in animal species.
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Retrotransposons encode reverse transcriptase and integrase.
Retrotransposons encode reverse transcriptase and integrase.
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Simple transposons can move via a 'copy and paste' mechanism.
Simple transposons can move via a 'copy and paste' mechanism.
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Non-autonomous transposable elements cannot provide the necessary functions for their own transposition.
Non-autonomous transposable elements cannot provide the necessary functions for their own transposition.
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LTR retrotransposons are similar to viruses and can produce viral particles.
LTR retrotransposons are similar to viruses and can produce viral particles.
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All transposable elements are the same in structure and function across different species.
All transposable elements are the same in structure and function across different species.
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Transposase is crucial for the reinsertion of transposable elements at new locations in the DNA.
Transposase is crucial for the reinsertion of transposable elements at new locations in the DNA.
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The Ds element in corn is considered an autonomous transposable element.
The Ds element in corn is considered an autonomous transposable element.
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The coli chromosome has 800 to 1000 microdomains.
The coli chromosome has 800 to 1000 microdomains.
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Nucleoid-associated proteins (NAPs) can bend DNA but do not act as bridges between DNA regions.
Nucleoid-associated proteins (NAPs) can bend DNA but do not act as bridges between DNA regions.
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Negative supercoiling in bacteria helps in the compaction of the chromosome.
Negative supercoiling in bacteria helps in the compaction of the chromosome.
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DNA gyrase is a protein that relaxes negative supercoils in bacterial DNA.
DNA gyrase is a protein that relaxes negative supercoils in bacterial DNA.
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Eukaryotic chromosomes are typically circular and found in the cytoplasm.
Eukaryotic chromosomes are typically circular and found in the cytoplasm.
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Telomeres prevent translocations and are important for maintaining chromosome length.
Telomeres prevent translocations and are important for maintaining chromosome length.
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Repetitive DNA sequences can contribute to variations in genome size without adding extra genes.
Repetitive DNA sequences can contribute to variations in genome size without adding extra genes.
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In more complex eukaryotes like mammals, genes tend to be short and have few introns.
In more complex eukaryotes like mammals, genes tend to be short and have few introns.
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Quinolones are a class of drugs that inhibit bacterial topoisomerases without affecting eukaryotic topoisomerases.
Quinolones are a class of drugs that inhibit bacterial topoisomerases without affecting eukaryotic topoisomerases.
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Each set of eukaryotic chromosomes can consist of a single linear chromosome.
Each set of eukaryotic chromosomes can consist of a single linear chromosome.
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Transposons consist solely of genes that provide an advantage to the host.
Transposons consist solely of genes that provide an advantage to the host.
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The human genome comprises approximately 45% transposable elements.
The human genome comprises approximately 45% transposable elements.
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Drosophila crosses introducing P elements into strains without them can lead to hybrid dysgenesis.
Drosophila crosses introducing P elements into strains without them can lead to hybrid dysgenesis.
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Transposable elements do not influence gene expression.
Transposable elements do not influence gene expression.
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The corn genome contains a higher percentage of transposable elements than the frog genome.
The corn genome contains a higher percentage of transposable elements than the frog genome.
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Transposons can carry antibiotic-resistance genes in bacteria.
Transposons can carry antibiotic-resistance genes in bacteria.
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The absence of transposase-encoding genes in nonautonomous transposons does not affect their ability to transpose.
The absence of transposase-encoding genes in nonautonomous transposons does not affect their ability to transpose.
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Chromosomal abnormalities can arise from unregulated transposition of transposons.
Chromosomal abnormalities can arise from unregulated transposition of transposons.
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Insertion of exons into the coding sequence of a gene by transposable elements is called exon shuffling.
Insertion of exons into the coding sequence of a gene by transposable elements is called exon shuffling.
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Bacteria such as Escherichia coli show a high percentage of transposable elements in their genome.
Bacteria such as Escherichia coli show a high percentage of transposable elements in their genome.
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Study Notes
DNA: The Genetic Material
- DNA is the genetic material that stores information to produce an organism
- DNA molecules store information through base sequences
- DNA sequences are essential for synthesis of RNA and cellular proteins
- DNA sequences facilitate chromosome replication and proper segregation
- DNA is compacted to fit within the cell
Bacterial Chromosomes
- Bacterial chromosomes are typically circular
- Their length varies, for instance, Escherichia coli has ~4.6 million base pairs and Haemophilus influenzae has ~1.8 million base pairs
- A typical bacterial chromosome has thousands of genes, primarily protein-encoding genes
- Non-coding DNA segments between genes are called intergenic regions
- Repetitive sequences in bacterial chromosomes can affect DNA folding, gene regulation and recombination
- Origin of replication is the initiation site for DNA replication
Bacterial Chromosome Structure
- The bacterial chromosome is located within the nucleoid region of the cell, not surrounded by a membrane
- The DNA is in direct contact with the cytoplasm
Compaction
- Bacterial chromosomal DNA is compacted about 1000-fold to fit within the cell
- The chromosome has a central core with emanating microdomains
- Microdomains form macrodomains
- Nucleoid-associated proteins (NAPs) form micro and macro domains
- NAPs can bend DNA or serve as bridges between DNA regions
DNA Supercoiling
- Supercoiling is the coiling of a coil, a manifestation of structural strain
- Twisting or unwinding DNA can induce supercoiling, which can be positive or negative, referring to helical twisting forces
- The linking number (S) describes the relationship between twist (T) and writhe (W) in a DNA molecule (S = T + W).
- Overwinding leads to positive supercoiling
- Underwinding leads to negative supercoiling
Formation of Supercoils
- Separation of DNA strands during cellular processes (replication/transcription) reduces twist, which creates tension causing supercoiling
- Enzymes like topoisomerases relieve the stress thereby reducing the linking number
Supercoiling Enzymes as Drug Targets
- The ability of gyrase to introduce negative supercoils into DNA is essential for bacterial survival
- Quinolones and Coumarins are two classes of drugs that target bacterial topoisomerases. A quinolone example is ciprofloxacin
- These are used for treating bacterial infections. They don't target human topoisomerases
Eukaryotic Chromosomes
- Eukaryotic cells contain one or more sets of chromosomes
- Composed of several linear chromosomes
- These are located within the nucleus
- Eukaryotic chromosomes are much longer than bacterial chromosomes, ranging from tens of millions to hundreds of millions of base pairs in length
Organization of Eukaryotic Chromosomes
- Contain a long linear DNA molecule
- Multiple origins of replication per chromosome
- Contain a centromere, a constricted region crucial for chromosome segregation during mitosis and meiosis
- Contain kinetochore proteins linking the centromere with spindle apparatus
- Contain telomeres at chromosome ends to prevent translocations and maintain chromosome length
Eukaryotic Genes
- Genes are located between telomeric and centromeric regions along the chromosome
- Simple eukaryotes have relatively small genes with little non-coding intervening sequences
- More complex eukaryotes have longer genes and non-coding (intron) sequences ranging from less than 100 to more than 10,000 base pairs
Sizes of Eukaryotic Genomes
- Genome sizes vary greatly in eukaryotes; size variation is not necessarily related to complexity (like in salamanders)
- Variation in size is often due to repetitive sequences (non-coding regions)
Sequence Complexity
- Sequence complexity describes the frequency of base sequences in genomes
- Types of sequences include unique/non-repetitive, moderately repetitive and highly repetitive DNA
Transposable Elements (TEs):
-
TEs are segments of DNA that can move within the genome. They are called "jumping genes"
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There are Simple and Retro- transposons
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Simple transposons move via a "cut-and-paste" mechanism. They have flanking direct repeats, inverted repeats, and a transposase gene
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Retrotransposons use RNA intermediates. They have long terminal repeats (LTRs) and encode reverse transcriptase and integrase.
-
TEs can contribute to genome size variation, mutations, and chromosome rearrangements. They can also affect gene expression and potentially drive evolution.
Transposition
- Transposition is the movement of TEs within a genome
- Transposition can occur during replication
- Resulting in the increase of TE copies in the genome
Reverse Transcriptase
- Reverse transcriptase is an enzyme that is involved in retrotransposition; it uses an RNA intermediate to create a DNA copy
Transposable Elements Influence on Mutation and Evolution
- Transposable elements are common in genomes
- They can rapidly enter and proliferate in the genome
- They influence mutation and evolution in various ways including generating new genes or altering existing ones
Control of Supercoiling
- DNA gyrase (topoisomerase II) creates negative supercoils using energy from ATP.
- DNA Topoisomerase I relaxes negative supercoils by breaking one strand and rotating the DNA.
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Description
Explore the fundamentals of DNA as the genetic material and learn about the structure and significance of bacterial chromosomes. This quiz covers topics such as base sequences, gene encoding, and DNA replication in bacteria. Test your knowledge on these essential biological concepts.
