Prokaryotic & Eukaryotic Genomes

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Questions and Answers

Which of the following statements accurately describes the genome of eukaryotic cells?

  • Eukaryotic genomes are devoid of repetitive sequences.
  • Eukaryotic genomes share the same gene density as prokaryotic genomes.
  • Eukaryotic genomes feature a significant portion of non-transcribed DNA. (correct)
  • Eukaryotic genomes consist solely of coding sequences that are directly proportional to complexity.

How does the density of genes typically vary when comparing yeast, Drosophila, and human genomes?

  • _Drosophila_ genomes have the highest gene density among the three.
  • Human genomes have a higher gene density than yeast or _Drosophila_ genomes.
  • Yeast genomes exhibit a higher gene density than _Drosophila_ or human genomes. (correct)
  • All three genomes have approximately the same gene density.

Which of the following is a characteristic of the distribution of genes within eukaryotic genomes?

  • Genes are clustered exclusively in telomeric regions for efficient replication.
  • The distribution of genes appears random, although certain regions may be gene-poor or gene-free. (correct)
  • Genes are uniformly distributed across all chromosomes.
  • Gene distribution is strictly determined by the size of the chromosome.

Introns and regulatory elements make up what percentage of the eukaryotic genome?

<p>24% (A)</p> Signup and view all the answers

What is the approximate percentage of the human genome that does not code for proteins?

<p>98% (A)</p> Signup and view all the answers

Which of the following best describes the function of pseudogenes in the genome?

<p>They are non-functional copies of genes that have accumulated mutations. (C)</p> Signup and view all the answers

How do LINEs (Long Interspersed Nuclear Elements) contribute to the human genome?

<p>They make up approximately 20% of the genome and can replicate autonomously. (D)</p> Signup and view all the answers

Why are SINEs (Short Interspersed Nuclear Elements) significant in the context of the human genome?

<p>They are the most abundant mobile elements and are implicated in several human hereditary diseases and cancers. (D)</p> Signup and view all the answers

What is the suggested cause for the unusual sequences found in satellite DNA?

<p>They result from errors during DNA replication, due to polymerase slippage. (B)</p> Signup and view all the answers

How is the mitochondrial genome similar to that of a bacteria?

<p>It resembles a small bacterial genome in structure. (B)</p> Signup and view all the answers

What is a key difference between how the UGA codon is interpreted in the nuclear genetic code versus in mammalian mitochondria?

<p>In the nuclear code, UGA signals STOP, but in mammalian mitochondria, it codes for Tryptophan. (A)</p> Signup and view all the answers

Which of the following best describes the function of DNA polymerase?

<p>It synthesizes new DNA strands by adding nucleotides to a template strand. (D)</p> Signup and view all the answers

Why is bacterial DNA replication described as bidirectional?

<p>Because replication proceeds in two directions from the origin of replication. (D)</p> Signup and view all the answers

What is the significance of the semi-conservative nature of DNA replication?

<p>It means that each new DNA molecule contains one original and one newly synthesized strand. (C)</p> Signup and view all the answers

Which of the following characteristics is associated with genomes of viruses?

<p>Can be composed of DNA or RNA, single-stranded or double-stranded. (D)</p> Signup and view all the answers

Which of the following is true regarding viruses with single-stranded RNA (-) genomes?

<p>They need to be complemented into RNA(+) before being translated. (B)</p> Signup and view all the answers

Which is a major difference between prokaryotic and eukaryotic genomes?

<p>Prokaryotic genomes are more compact and primarily contain functional DNA, in contrast to the larger, more complex eukaryotic genomes with non-coding regions. (B)</p> Signup and view all the answers

What is the typical size range of DNA viral genomes?

<p>1.5 to 250 kilobases (kb) (C)</p> Signup and view all the answers

Which statement best describes extra-nuclear genomes?

<p>They are similar to prokaryotic genomes. (B)</p> Signup and view all the answers

Which of the following elements are required for transcription?

<p>Eléments régulateurs (promoteurs etc.). (A)</p> Signup and view all the answers

What distinguishes a processed pseudogene from a conventional pseudogene?

<p>A processed pseudogene lacks introns and/or a promoter, while a conventional pseudogene has become non-functional due to mutations. (A)</p> Signup and view all the answers

Which statement best describes SINE?

<p>They insert mobile elements. (C)</p> Signup and view all the answers

Which statement best describes the location of telomeric squences?

<p>They are located in terminal regions of DNA. (C)</p> Signup and view all the answers

Which statement best describes why protection is important?

<p>Protection. (D)</p> Signup and view all the answers

Which of the following is true of bacterial replication?

<p>Unité de réplication; réplicon. (A)</p> Signup and view all the answers

What is the error rate of DNA replication in E.coli?

<p>One error per 10^9 nucleotide. (C)</p> Signup and view all the answers

What is the speed of replication in E.coli?

<p>1000 nucléotides/seconde. (B)</p> Signup and view all the answers

Which of the following is a characteristic of extranuclear genomes?

<p>DNA replication begins from the origin of replication (ori C). (C)</p> Signup and view all the answers

Flashcards

Viral Genomes

Viral genomes can be DNA or RNA, single or double stranded, linear or circular and are classified using the Baltimore classification.

DNA Virus

A virus with a double-stranded DNA genome. Examples include Phage lambda, herpes simplex virus.

Monocatenary (+) RNA Virus

A virus with a single-stranded RNA genome that directly codes for proteins. Examples include TMV and hepatitis A.

Monocatenary (-) RNA Virus

A virus with a single-stranded RNA genome that needs to be complemented before coding proteins. Examples include the Ebola virus.

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Bicatenary RNA Virus

A virus with a double-stranded RNA genome; an example is Rotavirus.

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Retrovirus

A virus that uses reverse transcriptase to convert its RNA genome into DNA, which can then integrate into the host cell's genome. An example is HIV.

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Eukaryotic genomes

Eukaryotic genomes contain genes and intergenic sequences, including non-coding sequences (introns).

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Non-Coding DNA

Non-coding DNA, making up 98% of the human genome, includes introns, regulatory elements, non-coding RNA, telomeres, pseudogenes, and transposons.

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Pseudogenes

Non-functional copies of genes or gene fragments found in the genome.

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Repeated Transposable Sequences

Non-coding sequences found throughout the genome, including LINEs, SINEs and LTR elements.

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LINEs

Long Interspersed Nuclear Elements are highly abundant, autonomous sequences capable of replication and insertion.

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SINEs

Short Interspersed Nuclear Elements, such as Alu sequences, are non-autonomous and depend on other elements for transposition.

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Satellite DNA

Satellite DNA are repetitive sequences at centromeres

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Telomeric Sequences

The ends of chromosomes with repeated sequences like (TTTGGG)n

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Extranuclear Genomes

Extranuclear genomes are similar to small bacteria, not self-sufficient and found in chloroplasts and mitochondria.

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DNA Replication

The process where each strand of DNA serves as a template for synthesizing a new strand, resulting in a semi-conservative mode of replication.

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Semi-Conservative Replication

Each new DNA molecule consists of one original and one newly synthesized strand.

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Replicon

A unit of replication in prokaryotes, often circular.

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Theta Replication

Theta replication starts from on origin and proceeds bidirectionally.

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ADN Polymerases

Synthesis of new DNA is performed by the ADN polymerase enzymes.

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Study Notes

Organization of Prokaryotic and Eukaryotic Genomes

  • Chapter focuses on bacterial, viral, eukaryotic, and extranuclear genomes like chloroplasts and mitochondria.

Viral Genomes

  • Viruses exhibit diverse sizes, ranging from parvovirus at 20nm to ebolavirus at 80x970nm
  • Classified based on genome type using the Baltimore classification
  • Baltimore classification includes Groups I-VII, encompassing double/single-stranded DNA and RNA viruses

DNA Viruses

  • Examples: Phage lambda, Hepatitis B virus (5 kilobases), Herpes virus (100 kilobases)
  • Size: ranges from 1.5 to 250 x 10^3 kb; can reach 1.2 x 10^5 kb in mimivirus
  • Molecular structure: Double-stranded (Phages lambda, varicella, herpes simplex); or Single-stranded (Parvovirus)

RNA Viruses

  • Single (+) Strand: Directly codes for proteins (e.g., TMV, polio, hepatitis A, rubella)
  • Single (-) Strand: Requires complementation into RNA(+) strand to code proteins (e.g., rabies, measles, influenza, ebola)
  • Double Strand: Rotavirus associated with diarrhea
  • Retroviruses: Contain RNA strand that is reverse transcribed into DNA by reverse transcriptase, potentially integrating into the host cell's genome (e.g., HIV).

Eukaryotic Genomes

  • Prokaryotes: Entire DNA proportion is functional and correlates with complexity and base number
  • Eukaryotes: Possess significant non-transcribed genomic regions.
  • Gene density vary in species; Yeast:479, Drosophila:76, Human:11(genes per Mb)
  • Introns per gene average: Yeast (0.04), Drosophila (3), and Humans (9)
  • Percentage of genome occupied by repetitive sequences: Yeast (3.4%), Drosophila (12%), Human (44%)

Genomic Features

  • Genomes contains genes and intergenic sequences.
  • Genes contain non-coding sequences called introns
  • Gene distribution seems random, but genes can cluster for coordinated expression regulation
  • Some chromosomal regions are gene-poor (e.g., centromeres), while others are gene-void (e.g., telomeres).

Non-Coding DNA

  • Makes up 98% of the human genome.
  • Components include:
  • Introns.
  • Regulatory elements (promoters, etc.).
  • Non-coding, but functional RNA molecules.
  • Telomeres
  • Pseudogenes, transposons (transposable elements)
  • Only approximately 40% of the genome's genes are transcribed at any given time in a cell.

Pseudogenes

  • Non-functional copies of genes, truncated genes, and gene fragments
  • Conventional pseudogenes: Non-functional due to mutations.
  • "Processed" pseudogenes: Lack introns and/or promoters, rendering them non-functional.

Transposable Elements

  • Non-coding sequences repeated throughout the genome.
  • LINEs (Long Interspersed Nuclear Elements): 5000-6000 bp.
  • SINEs (Short Interspersed Nuclear Elements): 200-300 bp.
  • LTR (Long Terminal Repeat) types, and "tandem" repeated sequences
  • Relics of viral sequences are present in eukaryotic genomes, mutated to the point of being unable to produce viral particles but can still replicate and transpose.

LINEs

  • Present in hundreds of thousands of copies, constituting 20% of the genome
  • Active LINE sequences can replicate autonomously and insert at other genomic sites.

SINEs

  • Ex: Alu sequences
  • Restriction site for endonuclease Alu I
  • Most abundant mobile elements in human genome are arranged approx. every 6000 bp
  • Involved in several hereditary human diseases, including cancers

Satellite DNA

  • Located in centromeres
  • Short tandemly repeated DNA sequences (Ex: GAGAGAGAGA...; TATTTATTTATTTATTTATT...)
  • Caused by faulty replication

Telomeric Sequences

  • Found at chromosome ends; TTAGGG repeats
  • Possible roles: evolution, chromosome functionality, protection, gene regulation
  • Gene regulation mechanisms: RNA secondary structure, on/off switches, expression rates, transcription factor binding sites.

Extranuclear Genomes

  • Mitochondria and chloroplasts

Mitochondrial Genome

  • Resembles a small bacterium's genome, not self-sufficient, requires import of compounds from the cell
  • Nuclear genome: 3200 Mb with approx. 30,000 genes
  • Mitochondrial genome: circular double-stranded DNA of 16.6 kb and 37 genes
  • Genetic code variations: RNA codon interpretations differ between nuclear and mitochondrial genomes; mitochondrial genomes have unique codon interpretations in mammals, Drosophila, and yeasts

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