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Answered on 07 Apr Learn Unit 2-Genetics and Evolution
Nazia Khanum
Separating repetitive or satellite DNA from bulk genomic DNA is a crucial step in various genetic experiments, especially those involving sequencing, mapping, or analyzing specific regions of the genome. Here are some common methods used for this purpose:
Density Gradient Centrifugation: This method separates DNA fragments based on their buoyant density in a density gradient solution, such as cesium chloride (CsCl) or sucrose. Since repetitive DNA tends to have a different density compared to unique genomic DNA, centrifugation can be used to separate these fractions.
Hybridization: Hybridization techniques can be employed to selectively isolate repetitive DNA sequences. This involves using specific probes that hybridize only to the repetitive DNA sequences of interest. The hybridized fragments can then be separated from the rest of the genomic DNA.
Fluorescence-activated cell sorting (FACS): FACS can be used to physically separate DNA molecules based on their fluorescence properties. Fluorescently labeled probes specific to repetitive DNA sequences can be used to tag and sort out the repetitive DNA fragments from the genomic DNA pool.
Restriction Enzyme Digestion: Some repetitive DNA sequences are associated with specific DNA methylation patterns or are located within regions of DNA that are resistant to digestion by certain restriction enzymes. By carefully selecting the appropriate enzymes, it is possible to selectively digest and remove bulk genomic DNA while leaving the repetitive DNA intact.
Size Selection: Repetitive DNA sequences often differ in size from unique genomic DNA fragments. Gel electrophoresis can be used to separate DNA fragments based on their size, allowing researchers to isolate specific size ranges that are enriched for repetitive DNA.
PCR-based Enrichment: Techniques such as polymerase chain reaction (PCR) can be used to selectively amplify repetitive DNA sequences using primers designed to target these regions. This can lead to the enrichment of repetitive DNA fragments in the final PCR product, which can then be further analyzed or purified.
Next-Generation Sequencing (NGS) Strategies: In some cases, NGS library preparation protocols incorporate steps specifically designed to reduce the representation of repetitive DNA sequences in the sequencing libraries. This may involve methods such as size selection, enzymatic digestion, or hybrid capture to selectively enrich for unique genomic regions.
Each of these methods has its advantages and limitations, and the choice of technique depends on factors such as the specific experimental goals, the type of repetitive DNA being studied, and the available resources and expertise.
Answered on 07 Apr Learn Unit 2-Genetics and Evolution
Nazia Khanum
During protein synthesis, codons play a crucial role in determining which amino acids are added to the growing polypeptide chain. The codon AUG serves two important roles:
Start Codon: AUG serves as the start codon for protein synthesis in most organisms. It signals the initiation of translation and the assembly of the ribosome-mRNA complex. The initiation process begins when the small ribosomal subunit binds to the mRNA at the AUG start codon, and then the initiator tRNA carrying the amino acid methionine binds to this codon. This marks the beginning of translation, with subsequent amino acids being added to the growing polypeptide chain.
Methionine: In addition to signaling the start of translation, AUG codes for the amino acid methionine. However, in many cases, this methionine is removed later from the mature protein after translation is completed.
On the other hand, UGA serves as a stop codon during protein synthesis. Stop codons signal the termination of translation and the release of the newly synthesized polypeptide chain from the ribosome. When the ribosome encounters a UGA codon, a release factor binds to the ribosome, causing the hydrolysis of the bond between the completed polypeptide chain and the tRNA molecule, leading to the release of the protein.
Answered on 07 Apr Learn Unit 2-Genetics and Evolution
Nazia Khanum
Genetic maps played a crucial role in the Human Genome Project (HGP) by providing a framework for organizing and understanding the vast amount of genetic information being generated. Here are some key contributions of genetic maps to the HGP:
Mapping of Genes: Genetic maps allowed researchers to locate and map genes along chromosomes. By identifying the relative positions of genes, researchers could infer their functions and relationships, aiding in the understanding of genetic disorders and diseases.
Linkage Analysis: Genetic maps facilitated linkage analysis, which is the study of how genes are inherited together. By examining the co-segregation of genetic markers with disease traits in families, researchers could identify regions of chromosomes likely to contain disease-causing genes. This helped in the identification of genes associated with various genetic disorders and diseases.
Physical Mapping: Genetic maps provided a foundation for constructing physical maps of chromosomes. Physical maps show the actual physical distances between genetic markers along chromosomes, helping to determine the overall structure and organization of the genome.
Sequence Assembly: Genetic maps were used in conjunction with DNA sequencing data to assemble the human genome sequence. By integrating genetic map information with sequence data, researchers could order and orient DNA sequences along chromosomes, leading to the assembly of contiguous stretches of the genome.
Comparative Genomics: Genetic maps facilitated comparative genomics studies by providing a reference framework for comparing the genomes of different species. By aligning genetic maps of humans with those of other organisms, researchers could identify conserved regions, study evolutionary relationships, and gain insights into the function and evolution of genes.
Overall, genetic maps provided a crucial foundation for the Human Genome Project, enabling researchers to systematically study and understand the structure, function, and organization of the human genome.
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Answered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
Two ways in which Single Nucleotide Polymorphisms (SNPs) identified in the human genome can bring revolutionary changes in biological and medical sciences are:
Personalized Medicine: SNPs can serve as genetic markers for predisposition to certain diseases or responses to medications. Understanding an individual's SNP profile can enable personalized treatment plans tailored to their genetic makeup, potentially leading to more effective and targeted therapies.
Disease Risk Assessment: SNPs associated with specific diseases can be used for early detection, risk assessment, and preventive measures. By analyzing SNP patterns in populations, researchers can identify genetic factors contributing to diseases and develop strategies for disease prevention and intervention.
Answered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
Answered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
Take Class 12 Tuition from the Best Tutors
Answered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
In E.coli growing in a culture medium where lactose is present as a source of sugar, the lac operon operates as follows: Lactose serves as an inducer, binding to the lac repressor protein and causing it to undergo a conformational change. This change prevents the repressor from binding to the operator region, allowing RNA polymerase to bind to the promoter and initiate transcription of the lac operon genes.
read lessAnswered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
Peptide bond formation occurs in the peptidyl transferase center of the large ribosomal subunit during translation. The amino acid-tRNA in the A site of the ribosome forms a peptide bond with the growing polypeptide chain attached to the tRNA in the P site, resulting in the transfer of the polypeptide chain to the amino acid in the A site.
read lessAnswered on 06 Apr Learn Unit 2-Genetics and Evolution
Sadika
Charging of tRNA with the appropriate amino acid is necessary during the translation process to ensure accuracy in protein synthesis. Each tRNA molecule is specific to a particular amino acid, and the charging process, catalyzed by aminoacyl-tRNA synthetases, ensures that the correct amino acid is attached to the appropriate tRNA molecule, ready to be incorporated into the growing polypeptide chain during translation.
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Lesson Posted on 28/05/2020 Learn Principles of Inheritance and Variation
What is a Polymerase Chain Reaction (PCR)?
Alka Srivastava
• I am doing my PhD in Botany from CSIR-National Botanical Research Institute. • I have completed my...
It is a revolutionary method developed by Kary Mullis in the 1980s, used to synthesize a new strand of DNA complementary to the offered template strand.
Components of PCR:
1. DNA template- the DNA strand that contains the target sequence which has to be multiplied.
2. DNA Polymerase enzyme- a type of enzyme that synthesizes new strands of DNA complementary to the target sequence. The first and most commonly used of these enzymes is Taq DNA polymerase (from Thermus aquaticus), whereas PfuDNA polymerase (from Pyrococcus furiosus) is used widely because of its higher fidelity when copying DNA.
3. Primers- a short sequence of nucleotides that provides an initiation point for DNA synthesis.
4. dNTPs(deoxynucleotides triphosphates)- single units of the bases A, T, G, and C, which are essentially "building blocks" for new DNA strands.
Steps in PCR:
1. Denaturation (96°): Heat the reaction strongly to separate, or denature, the DNA strands. This provides a single-stranded template for the next step.
2. Annealing (55°C-65°C): Cool the reaction so the primers can bind to their complementary sequences on the single-stranded template DNA.
3. The extension (72°): Raise the reaction temperatures so Taq polymerase extends the primers, synthesizing new strands of DNA.
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