Jumping Gene, Epigenetics

Jumping Gene, Epigenetics


Transposons (jumping Gene)

  • A transposable element (TE or transposon) is a DNA sequence that can change its position within a genome, sometimes creating or reversing mutations and altering the cell’s genetic identity and genome size.
  • DNA sequences that move to new positions within the genome
  • Discovered by Barbara McClintock
  • Movement is mediated by transposase, an enzyme encoded by the Tn itself.
  • replicative transposition frequently involves an RNA intermediate, in which case the Tn is called a retrotransposon.
  • Their trans-position is thought to be the basis for some rare cases of  hemophilia A and Duchenne muscular dystrophy.
  • DNA Sequence move from one segment to another through an RNA Intermediate
  • DNA segment is converted to RNA, RNA moves to another location, where it is reversely transcribed to a DNA

Epigenetics

  • It is the study of heritable changes in gene expression (active versus inactive genes) that do not involve changes to the underlying DNA sequence.
  • A change in phenotype without a change in genotype, which in turn affects how cells read the genes.
  • Epigenetic change is a regular and natural occurrence but can also be influenced by several factors including age, the environment/lifestyle, and disease state.
  • Epigenetic modifications can manifest as commonly as the manner in which cells terminally differentiate to end up as skin cells, liver cells, brain cells, etc. Or, epigenetic change can have more damaging effects that can result in diseases like cancer.
  • Three systems including DNA methylationhistone modification and non-coding RNA (ncRNA)-associated gene silencing are currently considered to initiate and sustain epigenetic change.
  • CpG islands are the common sites of methylation-demethylation so Hence methylation-demethylations plays an important role in regulation of gene expression
  • CpG islands of promoters are typically unmethylated, it favors transcription.

Biochemical functions of Epigenetic Modification:

  1.  Regulation of tissue specific gene expression.
  2.  X chromosome inactivation (Facultative Heterochro-matin) one of the two X-chromosomes in every cell of a female
  3. Genomic imprinting:
  1. Gene inactivation on selected chromosomal regions of autosomes is called Genomic Imprinting. This is the cause of preferential expression of one of the parental allele.
  2. Imprinting occurs in the ovum or the sperm, before fertilization.

4. Aging Process

Epigenetic Changes Causing Pathological Alteration

  1. Fragile X syndrome: Promoter site Hypermethylation causing FMR-1 gene silencing.
  2. Cancer: DNA methylation and histone modifications dictate which genes are expressed,
  3. DNA methylation is considered as a defence mechanism that minimise the expression of retroviral incorporated sequences.

Exam Important

  • Movement is mediated by transposase, an enzyme encoded by the Tn itself.
  • replicative transposition frequently involves an RNA intermediate, in which case the Tn is called a retrotransposon.
  • Their trans-position is thought to be the basis for some rare cases of  hemophilia A and Duchenne muscular dystrophy.
  • DNA Sequence move from one segment to another through an RNA Intermediate

Epigenetics

  • It is the study of heritable changes in gene expression (active versus inactive genes) that do not involve changes to the underlying DNA sequence.
  • A change in phenotype without a change in genotype, which in turn affects how cells read the genes.
  • CpG islands are the common sites of methylation-demethylation so Hence methylation-demethylations plays an important role in regulation of gene expression
  • CpG islands of promoters are typically unmethylated, it favors transcription.

Cancer: DNA methylation and histone modifications dictate which genes are expressed,

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