1.What are STRs (short tandem repeats) and how are they used for DNA profiling?
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Question
1.What are STRs (short tandem repeats) and how are they used for DNA profiling? What is the difference between a coding and non-coding region of DNA?
2.Watson and Crick discovered the structure of DNA. When they were developing the model, it had to be compatible with the known roles of the genetic material in the cell. What are the 4 roles that the DNA must be able to do, in order to be the genetic material of the cell?
3.What are the 4 basic chemical components of DNA? How does Chargoff’s ratio explain the relationship between these components?
4.The structure of DNA is a double helix, meaning it is made up of two strands. What is the orientation of these strands? What part of the DNA molecule is the “genetic code” in other words what part of the DNA codes for proteins?
5.Describe how a change in DNA sequence could result in a changed sequence of amino acids in a protein.
6.What is a regulatory region in DNA and how can it control gene expression?
7.What is a transgenic organism?
Explanation / Answer
1. STR are the short sequences of DNA, normally of length 2-5 base pair that are repeated many times in a head-tail manner. They are widely used today for human identity testing applications including forensic DNA analysis. Human genome contains thousands upon thousands of STR markers, only a small core set of loci have been selected for use in forensic DNA and human identity testing. Commercial kits are available to generate DNA profiles containing these core STR loci. By using PCR techniques, they are used for DNA profiling.
Coding region of DNA refers to the region which codes for mRNA which is then used for transcription and translation. These are in a definite pattern like A-U, C-G for RNA. Non coding region refers to the region that does not code for mRNA.
2. Four roles of DNA are;
i) It must be able to replicate itself.
ii) it must be able to control the living processes.
ii) capable of variation to facilitate adaptations.
iv) control development and reproduction.
3. Four important base of DNA, purine-adenine(A) and guanine(g)
pyrimidines- cytosine(C) anmd thymidine(T)
According to Chargaff rule, purine and pyrimidine base pairs are in equal amounts. i.e. A+G= T+C.
4.DNA strand orientation is by convention 5' 3'. This means for a given gene, the gene orientation relative to the 5' 3' DNA strand. The genetic code consist of three letters words(triplet or codon). These codes are called genetic codes and proteins are synthesised from them. Out of these code one is 'start code' from which amino acid chain form and one is 'stop signal' from where termination take place.
5. A change in sequence of amino acid may cause mutations because a different protein can be synthesised out of it which leads to mutation. eg, mRNA codes UUC for the amino acid phenylalanine and its complementary sequence is AAG in DNA. A single nucleotide change in DNA can change the mRNA codon, which can change the amino acid coded for, which can change the stucture of the protein. So, if G was changed to T, then the mRNA codon would no longer be UUC but UUA instead, resulting in the amino acid leucine instead of phenylalanine. This change in an amino acid can change the folding of the protein and thus can alter its structure.
6. Activators and repressors, regulate gene expression in DNA.
7. Transgenic orgainsm is a genetically modified organism whose genetic material has been altered using genetic engineering techniques.They are generally used to produce improved organism as in case of fruits to improve the yield and quality of the product.
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