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Mutagens can even affect the chromosomes. The chromosomal changes can be either involving their structure or their number. The numerical changes are referred to as ‘ploidy’. It can be detected as ‘aneupoidy’ and ‘polyploidy’. The structural abnormalities include ‘deletions’, ‘duplications’, ‘inversions’, and ‘translocations’. These changes in the structure and the number of the chromosome are […]
Chemical Mutagens Mutations can be caused by chemicals such as: Base analogues Compounds that resemble the four bases of nucleic acids are called base analogues for example, 5-bromouracil and 2-amino purine. These base analogues can be incorporated into DNA. They lead to transition mutations (purine to purine) as a consequence of altered base pairing in […]
‘Mutation’ refers to heritable changes in the base sequence of the DNA. The most common types of change are a substitution, an addition or a deletion of one or more bases. A physical or chemical agent that causes or increases the frequency of mutation is called a ‘mutagen’. The process of producing a mutation is […]
Endogenous DNA Damages There are five main types of damage to DNA due to endogenous cellular processes (Figure 8.2). These include: Spontaneous damages can include the loss of a base, deamination, sugar ring puckering and tautomeric shifts. Figure 8.2 Types of DNA damages When compared to the nuclear DNA, the mitochondrial DNA is more […]
Inside a cell, there is a complex interplay of molecular events of which DNA repair occupies a significant importance. If proteins or RNA molecules are damaged, they can be immediately replaced using the information encoded in the DNA. However, if a DNA is damaged, it is irreplaceable and repairing the damages of the DNA, therefore, […]
At the Level of Post-transcriptional Modification In eukaryotes, much of the gene regulation takes place during the mRNA processing. Approximately 75 per cent of pre-mRNAs are degraded within the nucleus. This selective degradation acts as the control point of gene regulation. Alternative splicing of pre-mRNA permits the synthesis of different versions of a protein. Alternative […]
Regulatory proteins contain domains not only for DNA binding but also for protein–protein interactions with RNA polymerase, other regulatory proteins or with other subunits of the same regulatory proteins. For examples, they include many eukaryotic transcription factors that function as gene activators. Some important examples of protein–protein interaction domains include the leucine zipper and the […]
Regulatory proteins generally bind to specific DNA sequences. Their affinity for these target sequences is approximately 104–106 times higher than their affinity for many other DNA sequences. Most regulatory proteins have discrete DNA-binding domains containing substructures that interact closely and specifically with the DNA. Figure 7.13 Gene regulation by miRNAs Within the regulatory proteins, the […]
Various molecular mechanisms operate to control gene expression at the level of transcription. cis-Acting Regulatory Sequences: Promoters and Enhancers These are the sequences that control the transcription of adjacent genes. Genes transcribed by RNA polymerase II have core promoter elements including the TATA box and Inr sequences. These cis-acting sequences serve as the binding sites of […]
Chromosomal regions that are activated for transcription are marked by a variety of structural changes. The packaging of eukaryotic DNA into chromatin limits its availability as a template for transcription. Thus, modifying chromatin structure plays a key role in controlling the gene expression in eukaryotes. The transcription of eukaryotic gene is strongly repressed when it is […]