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Questions and Answers
What is the reason the DNA helix maintains a uniform distance between its strands?
The pitch of the DNA helix is approximately 2.2 nm.
False
What is the role of histones in eukaryotic DNA packaging?
Histones help package negatively charged DNA by binding to it due to their positive charge.
In prokaryotes, the region where DNA is held together with proteins is called the ______.
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Match the following DNA packaging structures with their descriptions:
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Which of the following statements about base pairing in DNA is true?
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Genetic information in retroviruses flows from DNA to RNA and then to Protein.
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How many base pairs are typically found in a single turn of the DNA helix?
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The length of DNA in a typical mammalian cell is approximately ______ meters.
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What is the primary structure of a nucleosome?
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Study Notes
Human Genome Project (HGP)
- 50% of discovered genes have unknown functions.
- Less than 2% of the human genome is protein-coding.
- Repeated DNA sequences constitute a significant portion of the genome.
- Chromosome I contains the highest number of genes (2,968) while Y chromosome has the lowest (231).
- Around 1.4 million single nucleotide polymorphism (SNP) sites exist across the genome.
Applications of Human Genome Project
- Identifies defective genes for early treatment opportunities.
- Determines genes linked to susceptibility for certain diseases for preventive measures.
- Predicts proteins and potential diseases/disabilities associated with specific genes, facilitating the development of targeted drugs.
DNA Fingerprinting
- Compares DNA from various sources to identify genetic similarities and differences.
- Utilizes satellite DNA or repetitive DNA sequences which do not code for proteins.
- High degree of polymorphism in these sequences forms the basis of DNA fingerprinting.
- Genetic variations (polymorphisms) result from mutations.
Satellite DNA
- During centrifugation, DNA separates into two peaks: a major peak (bulk DNA) and a minor peak (satellite DNA).
- Types of satellite DNA include mini-satellite and micro-satellite.
- Classification criteria involve base composition (A:T rich vs. G:C rich), sequence length, and number of repetitive units.
Variable Number Tandem Repeats (VNTR)
- VNTR is a DNA probe labeled with a molecular marker, such as a radioactive isotope.
- It is a class of satellite DNA, specifically mini-satellite.
- VNTR sizes range from 0.1 to 20 kb, producing individual-specific autoradiogram patterns after hybridization.
Process of DNA Fingerprinting
- Introduced by Alec Jeffreys using VNTRs due to their high polymorphism.
- The HGP aimed to map and understand the complete human genome, starting in 1990 and completing in April 2003.
- Coordinated by the National Institutes of Health (NIH) and U.S. Department of Energy, with international collaboration.
- Included sequencing genomes of model organisms like mice and yeast for research purposes.
Goals of HGP
- Identify around 20,000 to 25,000 human genes.
- Determine the sequence of all 3 billion chemical base pairs in human DNA.
- Store genomic information in databases and improve data analysis tools.
- Transfer relevant technologies to various sectors and address ethical, legal, and social issues (ELSI) arising from genomic research.
Methodology of HGP
- Used Expressed Sequence Tags (ESTs) to identify genes expressed as RNA.
- Full sequencing of both coding and non-coding regions was conducted, followed by assigning functional annotations.
- Bacteria and yeast served as common hosts for sequencing employing bacterial artificial chromosomes (BAC) and yeast artificial chromosomes (YAC).
Features/Outcomes of Human Genome
- The human genome contains approximately 3,164.7 million nucleotide bases.
- Average gene size is about 3,000 bases, with dystrophin being the largest known gene at 2.4 million bases.
- Estimated total gene count is around 30,000, with 99.8% nucleotide sequences conserved across individuals.
- DNA base pairing follows the rule: guanine pairs with cytosine and vice versa, forming uniform helical structures at a distance of 0.34 nm between base pairs.
Central Dogma of Molecular Biology
- Proposed by Francis Crick, describing the flow of genetic information from DNA to RNA to protein.
- Some retroviruses reverse this flow, moving from RNA to DNA.
DNA Packaging
- Length of DNA in mammalian cells is approximately 2.2 meters, exceeding typical nuclear dimensions.
DNA Packaging in Prokaryotes
- Prokaryotic cells lack a defined nucleus and have DNA organized in a nucleoid region held together by proteins.
DNA Packaging in Eukaryotes
- Negatively charged DNA is associated with positively charged histone proteins, which are rich in basic amino acids.
- Histones exist in five isoforms (H1, H2A, H2B, H3, H4) forming histone octamers, around which DNA wraps to create nucleosomes.
- Nucleosomes resemble a 'beads-on-string' structure when observed under an electron microscope, containing approximately 200 base pairs of DNA.
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Description
Explore the key findings and implications of the Human Genome Project. This quiz covers interesting facts about gene functions, protein coding, and genetic variations that emerged from the research. Test your knowledge on the significance of SNPs and gene identification in medical advancements.
