Molecular Basis Of Inheritance-Concept
Molecular Basis Of Inheritance
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Nucleosome model
1. Woodcock stated that chromatin appears as a chromatin beads.
2. These beads like structure were referred to as nucleosome.
3. This nucleosome is composed of DNA and histone proteins.
4. The central core is made up core histones H2A, H2B, H3, and H4.
5. Core particles are attached by linker DNA.
6. Linker DNA is 80 bp long.
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Clover -leaf model of t-RNA
1. The structure of RNA was explained by cloverleaf in the cloverleaf model.
2. It helps in providing the anticodon to the m-RNA template.
3. They have several loops like aminoacyl binding loop, anticodon loop and ribosomal binding loop which act as a functional binding site.
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Enzymes required for DNA replication
1. DNA Polymerase – Elongates a new DNA strand at a replication fork. Adds nucleotides one by one to the new and growing DNA strand.
2. DNA ligase – Joins sugar-phosphates of Okazaki fragments. Okazaki fragments are found on the lagging strand.
3. Primase – Starts an RNA chain from scratch that will eventually be replaced by DNA nucleotides (remember nucleotides come from DNA polymerase).
4. Helicase – Untwists the double helix at replication forks to make two parental strands available as template strands.
5. Topoisomerase – Relieves strain of ahead of the replication fork due to untwisting of the double helix.
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Characteristics of genetic code
1. Triplet code
2. Start signal
3. Stop signal
4. Universal code
5. Nonambiguous codons
6. Related codons
7. Commaless
8. Polarity
9. Degeneracy of code
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Wobble hypothesis
1. Wobble hypothesis explains the phenomena of multiple codons coding for the code for a single amino acid.
2. According to this theory the base in the first position of the anticodon on tRNA is an abnormal base which is able to pair with single type of nitrogenous bases in the third position of codon on m-RNA.
3. Our main wobble base pairs are guanine-uracil (G-U), hypoxanthine-uracil (I-U), hypoxanthine-adenine (I-A), and hypoxanthine-cytosine (I-C).
4. It does not follow the Watson and crick base pair rule.
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Reverse transcription
1. Reverse transcription is the synthesis of DNA from an RNA template.
2. A class of RNA viruses, called retroviruses, are characterized by the presence of an RNA-dependent DNA polymerase (reverse transcriptase).
3. For example, the virus that causes AIDS, is a retrovirus.
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Application of human genome project
1. Disorders:
More than 1200 genes are responsible for common human cardiovascular diseases, endocrine diseases (like diabetes), neurological disorders (like Alzheimers disease), cancers and many more.
2. Cancers:
Efforts are in progress to determine genes that will change cancerous cells to normal.
3. Health Care:
It will indicate prospects for a healthier living, designer drugs, genetically modified diets and finally our genetic identity.
4. Interactions:
It will be possible to study how various genes and proteins work together in an interconnected network.
5. Study of Tissues.
All the genes or transcripts in a particular tissue, organ or tumour can be analysed to know the cause of effect produced in it.
6. Non-human Organisms:
Information about natural capabilities of nonhuman organisms can be used in meeting challenges in health care, agriculture, energy production and environmental remediation. For this a number of model organisms have been sequenced, e.g., bacteria, yeast Coenorhabditis elegans (free living non-pathogenic nematode), Droso- phila (fruitfully), Rice, Arabidopsis etc.
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Mechanism of protein synthesis
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Lac operon
